| Author | Message | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 1 Registered: 8-2008 Posted From: 12.51.220.74 Rating: |
This thread was from several months back, when someone discovered that the CG he was at had ratty power on 1 leg, better of the other leg, and bought that lesson by sacrificing a microwave oven to the vengefuls gods Pele and Reddy Kilowatt. Responses covered checking the power, making an adapter, etc. One solution that everyone is missing is to set your rig up for 100% boondocking, with shore power only used to charge the house batteries. Batteries are excellent strain relievers -- especially when you are dealing with "divergent" power levels from the shore. If you get a QUALITY battery charger, it and the batteries will handle wide swings in voltage, while you in the coach will never even notice them. This means spending a little more for deep-cycle batteries (and losing a little space for a second set), and significantly more on a big inverter -- figure about $1000 in uprate costs -- but this will come back to you the first time you don't have to replace your electronics! In addition, you will have given your rig superior capabilities, useful whether spending the month on shore power, overnighting in the Wally World RV Center, or a weekend on that hilltop with the view (and nothing else). | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 427 Registered: 10-2006 Posted From: 208.100.193.42 Rating: N/A |
Any of the inverters with the "pass thru" ability that match and boost the line voltage are THE way to go , if you can afford the buck$. Toss in a good battery monitor Link or similar , learn to watch it and the batts will go 6 or 7 years. FF | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 429 Registered: 10-2006 Posted From: 208.100.193.42 Rating: |
E-Meter From SeattleEVA Jump to: navigation, search An E-meter measures the state of charge of batteries. In a nutshell, it measures the current flow into and out of the battery pack. The thing is that the effective capacity of a lead-acid battery is dependent on the rate at which it's discharged. A simplified example: A 100 Ah (amp-hour) battery can provide 1 amp for 100 hours, or 2 amps for 50 hours, or 5 amps for 20 hours. That's the theory. In actuality, the more current you draw, the lower the actual capacity you get out. So, you may get 1 amp for 100 hours, but 5 amps for only 19 hours, and instead of 50 amps for 2 hours, you'd only get 50 amps for 1 hour. This is known as the Peukert's Law. Anyhow, an e-meter not only measures the total amps that go into (charging) and out of (discharging) a battery, but takes into account the rate that it's used, and uses Peukert's empirical formula to calculate the effective charge, giving a more accurate indication of the battery's true state of charge (SOC). Short version: Battery Fuel Gauge. A commonly used E-Meter for electric vehicles it the Xantrex Link-10. http://www.xantrex.com/web/id/237/p/...product.aspThe Link 10 is a state-of-the-art battery bank monitor that uses sophisticated microprocesor technology to report all significant battery information. Xantrex also make the Link-20 and the XBM e-meters. * Build it yourself battery monitor for multi-battery packs http://home.earthlink.net/~evtkw/ Includes plans schematics and details - by Tim Wong * Gordon Stallings battery monitor with schematics http://genki.home.ionet.net/BattMon/BattMonArticle.html * PakTrakr http://www.paktrakr.com/index.html monitors individual batteries in packs of multiple batteries * Smart Gauge (UK) http://www.smartgauge.co.uk/ Great technical info on how battery monitors work. * http://www.rc-electronics-usa.com/am...y-monitor.html * http://www.micromediaplus.com/microlog_dmm-3_dmm-4.html * http://www.rotordesign.com/s10/cellmon/cellmon1.pdf schematic for battery low voltage threshold indicator With a bit of work , one can be built , but the combo of a good (Trace) inverter with a Link 10 or 20 will satisfy most boaters. FF | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 518 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
First off, Fred has outdone himself on this one!! The above post took a whole lot of time and effort to hunt up all that info and link it up! Secondly, lets think about the original suggestion, in a 40 foot bus with two 15,000 BTU roof airs, or three smaller ones. The way I read this post, the suggestion is to install a "QUALITY" battery charger on the incoming shore power, make DC out of it, then run that thru an inverter to run the A/C and the rest of the bus? (Its going to take two inverters to run two large or three small roof airs, AND the aforementioned microwave?) This proposed setup would require "twinned" inverters to provide that much power, a 120/240 bus panel, and a 50 amp shore service, (which would be necessary anyway with that much load.) What wasn't mentioned, was the fact that the "QUALITY" battery charger would have to put out over THREE HUNDRED AMPS of 12VDC, or 150 AMPS of 24 VDC! Then we have to buy the second inverter to run the rest of the load, right? Since we are talking about power quality here, I think I am safe to assume that the inverters won't be MSW? Bottom line of this is that there is no way a second 4KW pure sine wave inverter, and a 150/300 amp "QUALITY" battery charger can be bought for a thousand dollars, even if you buy the inverters without battery charging. Next thing not thought of, or mentioned 'til now is HEAT. Electrical flow produces 3412 BTU per kilowatt hour, so lets say we are putting 30 amps into the battery charger at 120 VAC, and we are getting 30 amps back out of the inverters, and we'll ignore the batteries. That's 25,566 BTU, so let's hope all three of these pieces are outside in well ventilated compartments! All this in the name of filtration? Sorry to be a grump, George | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 135 Registered: 1-2007 Posted From: 208.81.157.90  Rating: N/A |
George, while I agree that such devices give off a fair amount of heat and need ventilation, if all the power consumed is given off as heat, there would be no output to do useful work. 30 amps at 120VAC is worth about 12.3 BTU. If it was all dissipated in the charger (12.3 BTU) as heat, there would be none left to charge the batteries. If the inverter was dissipating another 12.3 BTU it would need to come from the batteries and would leave no output to power anything. Anywho, George is right, every time you convert from AC to DC or visa versa there are losses given off as heat and other ways. If you have enough AC or batteries, great. If not, you need to consider the losses. Don 4107 | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 519 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Don, I appreciate your input, and all I want to differ with is one word, and one letter! In the above situation, I used 30 amps for a number. 30 amps at 120 Volts is 3600 Watts. The electrical constant for resistance heat is 3.41 BTU per Watt. So, the flow of current thru the transformer and rectifier of the battery charger will produce 12.3 !K! BTU of heat while being changed from 120 VAC to 12 or 24 VDC. (K is the letter I want to differ with you on.) The only word to differ on is ALL. All the power is not lost, only what is turned into heat. So when you turn the 12/24 VDC back into 120 VAC, you produce another 12.3 K (as in thousand) BTU of heat. So, if we just put a K after each of your 12.3s, we're close to the 25.5 K BTU I am talking about. I suppose I should also have asked about the effect of ratty power on the electronics in the "QUALITY" charger also? Anyhoo, regards, and I hope I cleared it up? George | ||
| David Lower (Dave_l)
Registered Member Username: Dave_l Post Number: 42 Registered: 11-2007 Posted From: 69.196.133.195  Rating: N/A |
Hello, Is there any diference in useing 2, 6, or 12 volt batteries other than the number and weight of them required in makeing a battery bank. Dave L Thanks Fred for answering my question.:-) (Message edited by dave l on August 12, 2008) | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 136 Registered: 1-2007 Posted From: 208.81.157.90 Rating: N/A |
Yep George, that is what happens when I try two things at once like typing and thinking!! Left out the Ks. You are talking about "resistance heat" and that is not the type of devices we are discussing. If as you say "Electrical flow produces 3412 BTU per kilowatt hour" then every item that the current flows through would have to dissipate the total wattage as heat. Not just the transformer or diodes but the power cord, the outlet, the circuit breaker ect, every item in the circuit. Some power is lost as heat, but not the total input wattage. That is why chargers and inverters have a efficiency rating telling you how much current is consumed by the device. For instance, if your charger is 95% efficient then it is consuming 5% of the input power. No where near the full wattage or BTU content of the input current flow. If you have a way to produce 12.3K BTU of heat from a 30 Amp input and still have 30 Amps of current left to do some work you have solved the energy crisis for the world. Don 4107 | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 520 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Don, I think we are actually talking about the same thing, just looking at it a little differently! A 1500 Watt heater uses about 13 amps of 120 VAC to produce about 5200 BTU of heat. The magnetic field in the heater from the current flow is just ignored. Now we hook up a two horsepower motor (746 Watts per horsepower, 100% efficiency.) That's 1492 Watts consumed, which will generate about 5175 BTU, AND two horsepower. The motor will be ODP, TEAO, or TEFC, Open Drip-Proof, or Totally Enclosed Air Over, or Totally Enclosed Fan Cooled, because of the heat it generates. Just as you say, all of the components will develop heat, in relation to their resistance, or technically impedance as it is an AC circuit we're talking about? The primary winding in the battery charger WILL develop heat, WHILE it's inducing current in the secondary winding, which also develops heat. The same thing happens in the inverter, which will develop heat in the oscillator and the transformer windings. One more thought, an incandescent light bulb gives off light as well as heat. Still another, look back at all of the posts on cable size and voltage drop when using an inverter. All the loss in the cables and connections IS heat. As far as the output current being 95% of the input current in an efficient inverter, absolutely, but the inverter does have a BIG heat sink and a cooling fan, (so does the charger!) Lets look at Ohm's law for a minute, and you will agree that in modern English, Amps=Voltage/Resistance. So, if we have essentially no resistance, we would have huge current flow, right? The inductance in a transformer, plus the resistance of the windings controls the current flow, and produces heat. So, we both have a way to produce a horsepower, AND about 2500 BTU out of 746 Watts! Or some heat and some light. Regards, George | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 430 Registered: 10-2006 Posted From: 208.100.193.225 Rating: N/A |
Is there any diference in useing 2, 6, or 12 volt batteries other than the number and weight of them required in makeing a battery bank. Not really , the 2v will usually be the best , as there really deep cycle batts, and easier to lift. The problem with batts is they take a long time to get 100% full, that first 85% is quick, after that its slow. The other hassle is they will have far less capacity at a high discharge rate , so the discharge rate should be held down to 15% of the 20 hour rate. For a person with a gen set that means sizing the battset to live on the top 85% down to 50% , or only 35% of what you paid for. FF | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 618 Registered: 7-2006 Posted From: 66.217.103.185  Rating: |
Of course, when everything's running on cheap propane, and the only thing you might need electrical power for, is the AC units.... (Oh.... but what am I thinking?) | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 431 Registered: 10-2006 Posted From: 208.100.193.122 Rating: N/A |
only thing you might need electrical power for, is the AC units.... For someone with a closed stateroom the DC air cond might work OK for a quiet nights sleep. FF | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 521 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
The humor is improving!!!! | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 6 Registered: 8-2008 Posted From: 71.140.185.254 Rating: N/A |
Wow, talk about Pessimism A-Go-Go! Think about this. Your aircons can run on cheap, small, dirty inverters, one per unit. However, look at your coach. What do you have that's electronic? Microwave, computer, printer, TV, DVD recorder, stereo, GPS, satellite system, and the chargers / wall warts for your cell phone, laptop, digital camera . . .that's a lot of stuff to trust to shore power in a place where the guy next to you may have made extensive use of chewing gum wrappers in the latest repairs to his electrical system! But look again . . .most of that stuff doesn't run when the rest is running. You don't need one big inverter, you can run on multiple smaller (and cheaper) inverters, or even 12V adapters (go for the ones which are regulated). How many times have you passed by small inverters with $5 price tags at swap meets, yard sales, etc, because you don't know what you would do with them? Now you know! You need one good charger, but everything else can be broken out into separate subsystems. It just takes a little planning and consideration of what you're trying to do. Oh, maybe I should mention that this is what I've done a number of times when setting up remote radio and TV translators, only to stay on the air while watching some of the other stations melt into slag following nearby lightning strikes on lines. The strikes fry our chargers, but the rest of the station is okay. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1331 Registered: 12-2000 Posted From: 76.69.140.249  Rating: N/A |
Yup, I'm a fan for a bunch of individual small inverters, just as I'm a fan for the Trace 4024, a stock coach alternator and a good generator. REDUNDANCY. Ran a truck in Yellowknife in winter, one 150 watt inverter for the battery blankets around the truck batteries, another for the heat trace cable wrapped and insulated around the fuel filter, one larger 2000 watt Cobra for the microwave or television or electric cube heater if the heater/defroster gave up, Koolatron cooler was already 12 volt.... If something crapped, there was some back-up or choices for what to shed. If one big one craps under those conditions...no choices! Lots of ways to do stuff, Your way is right for you! happy coaching! buswarrior | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 433 Registered: 10-2006 Posted From: 208.100.193.47 Rating: N/A |
nearby lightning strikes on lines. Look up the BRICKWALL or other units that handle this problem. Not only lightning but an wonky "automatic" switch may feed your neighbors gen set juice to the campsite. FF | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 2076 Registered: 1-2001 Posted From: 75.108.85.14 Rating: N/A |
Here is the link to Brickwall: http://www.brickwall.com/ Richard | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 7 Registered: 8-2008 Posted From: 71.140.185.254 Rating: N/A |
Fred, what's the advantage of spending all of that money on a Brickwall for major spikes when you are still stuck with the ratty park power problem? The same money takes care of BOTH problems if you go with the constant-charge, constant-drain idea. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 522 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Keith, Before this goes any further, will you please explain to us what you consider "ratty park power to be?" Then please explain what the output wave form of a modified sine wave inverter looks like, and what the waveform a utility company provides is called. Then, please tell us, besides fire danger, what you think improper wiring methods in an adjoining bus in a park does to the bus next door. I don't get any pleasure out of being pessimistic, and if you read this entire thread, you will see that I have explained what I said in great detail, and with NO NEGATIVE COMMENTS. Since that was your first post, I would like to suggest to you that you be qualified, and able to explain your future posts. As your profile is blank, we don't even know where in the world you live, or what kind of bus you own, so please fill out the rest of it. After you reply, we can discuss power quality at great length, and I will gladly explain any electrical questions you have. There is a reason why I have asked of you what I have, and please don't take offense to it, just answer the questions please, or say you don't know, and several of the electricians on board will be glad to explain. George | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 328 Registered: 7-2006 Posted From: 75.209.193.237 Rating: N/A |
 RCB | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 9 Registered: 8-2008 Posted From: 71.140.185.254 Rating: N/A |
I'll give you the definition that was promoted by a former professor of mine: "If an increase or decrease in load is reflected in the operation or performance of any other module on the bus" [the power line, that is], "you have ratty power. In other words, if you notice it, it's ratty." He went on to describe ratty power as the equivalent of choking. You breathe all of your life. Unless your attention is drawn to it, you don't notice the quality of your breathing -- unless you choke. Of course, we were talking about aerospace hardware, but power is power. Isn't fire danger ENOUGH to be concerned about? Improper wiring in the bus next door can result in such things as below-90 drops in YOUR bus when their heater, aircon or microwave come on, or when they plug in. And no, I'm not an electrician, but I kinda figure that several decades doing aerospace, communications, broadcast and computer engineering oughta count for something . . . | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 10 Registered: 8-2008 Posted From: 71.140.185.254 Rating: N/A |
Oh, BTW, one thing that I learned in aerospace was that everything should do more than one thing. That's my objection to the Brickwall -- you spend money to do only one thing, while a constant-charge, constant-drain system does several things (transient swamping, redundant power, isolation of subsystems and increasing plugs-out power time). | ||
| Ray Drummond (Ray_d)
Registered Member Username: Ray_d Post Number: 46 Registered: 4-2006 Posted From: 68.123.110.10 Rating: N/A |
Keith, Constant-charge, constant-drain, could you exlpain. I like the everything doing more than one thing idea. Thanks, Ray D | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 12 Registered: 8-2008 Posted From: 71.140.185.254 Rating: N/A |
You are constantly charging the batteries (as needed) from shore power. You are constantly draining the batteries (as needed) for your onboard systems. The charger has a circuit breaker, and if there's a major spike, your batteries will swamp the transient during the fraction of a second before the breaker trips. Meanwhile, your systems just keep chugging along. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 435 Registered: 10-2006 Posted From: 208.100.193.211 Rating: |
"One thing that I learned in aerospace was that everything should do more than one thing." Very true with bushel baskets of OPM (other peoples money) and a huge restraint on both weight and size. Busses are BIG , so every item that is dual or tripple purpose means you LOOSE 2 or 3 things at a time instead of only one. A pass thru ($$$Quality) inverter will bring up the voltage aviliable for your use. So your air cond can run on 120v in that 100V crapola campground , and your battset only has to provide the juice to make up the power. Most shore chargers I have seen are limited to about 100A of DC , not a lot to live on. Or were you going to get a half dozen? FF | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 13 Registered: 8-2008 Posted From: 71.140.185.254 Rating: N/A |
The cool thing about a DC power bus is that you can put on multiple power sources. There are larger 12VDC sources available, or you can once again go redundant and hang several chargers on the system. Remember also that you're thinking about sustaining maximum load -- in truth, this is very rarely necessary. However, yes, I agree that putting the stuff that can run on ratty power should be given the ratty power when it's available. For a tangent that I'm NOT going off onto, let me mention that a lot of "120V" electronics actually run on an internal 12VDC or 24VDC bus . . .something that a person could take advantage of, with a little thought. Anyway, my whole point in starting this was to get people to think about their power systems, to realize that they have options other than the common ones, and that those options might be better. I'm going to be offline for a couple of days, see you all when I get back. Oh, BTW, the only time I didn't have to squeeze every penny in the budget was in my dreams . . . | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 438 Registered: 10-2006 Posted From: 208.100.193.119 Rating: N/A |
"120V" electronics actually run on an internal 12VDC or 24VDC bus . . Great , you get to buy a DC blender ($120)for your Margeritas , that burns out with the first low voltage ice chop , instead if a 120V ,, $15 K-mart unit (or $2,00 tag sale ) that lasts "forever". The usual burn out item for DC folks is the crappy Jabsco macerators (and others). An item that lasts for years in the 120V version, and is replaced 3 times a year by some if DC, boats and campers alike. FF | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 523 Registered: 8-2006 Posted From: 207.231.75.253 Rating: |
Keith, As I said before, I don't want to beat you up. I still mean it, but I feel I need to clarify the replies to your original post which read: "One solution everyone's missing...is to use a good charger and inverter..." That was your FIRST post on this board, and we're all bus nuts, not ignorant! So I suggest to you that you throw your next idea out as a question, eg: Hey bus nuts, what do you think of ____? "One solution that everyone's missing" IS pretty demeaning to everyone on this board. We're all quite polite, so you didn't get "flamed" once. Enough of that, now let me explain why none of us have done what you suggest. AC power has essentially 3 components, voltage, amperage, (current) and frequency. In North America, AC is 60 cycles per second, which is also known as HERTZ, abreviated Hz. Europe and Asia still use 50 Hz. MOST AC motors are synchronous, which means the speed they run at is controlled by the frequency. The formula for determining how fast an AC motor runs is: Hz X 120/ # of poles, which are "winding groups." Power is provided by utility companies as a sinusoidal (sine) wave, at 60 Hz. There is nothing that improper wiring methods can do to alter this frequency. Improper wiring methods in the next bus won't affect the load on the campgroud power either, the load is either there or it isn't. Unfortunately, your cheap inverters are not frequency controlled, and produce what is called either a modified sine wave, or a quasi-sine wave. It has been posted here many times that some electronics such as printers, will not run on Modified Sine Wave, MSW, because the output wave is so distorted that the timing circuit in the printer actually sees 90 Hz. As is correctly mentioned in the posts above, resistance (heating) appliances work well on MSW. Any deviation from pure sine wave produces excess heat in motors, AND THE MAGNETRON TUBES IN MICROWAVES, which is hard on them. The next thing to be considered is power factor, which is the lead or lag between the voltage wave, and the available current portion of the wave. In a mostly inductive circuit, transformers and motors, current will lag the voltage. In a capacitive circuit, current leads the voltage. You see banks of capacitors on utility poles because all of us using motors and transformers put too much inductive load on the utility company, which causes the power factor to go away from unity into a lagging condition, which produces much less effective power, and more heat. The utility company then has to put capacitors in their primary circuit to overcome all of the inductance we give them. I won't ask what the power factor is on a cheap inverter. Bottom line, the reason none of us have done what you suggest, is because of the very poor power quality of very cheap inverters, the fact that all of the appliances that will run on MSW inverters will run on low campground voltage, the fact that 30 amps of 120 VAC will have to be transformed into 300 amps of 12 VDC, and back into 120 VAC by several little MSW inverters, AND the "GOOD" charger's 120 VAC electronically controlled input is just as susceptable to damage as the appliances it is supposed to protect! Like it or not, this setup is also going to produce over 25,000 BTU of heat, which is over 2 tons of air conditioning. NOW, a Trace SW4024, and the other quality inverters by Xantrex, Heart, Outback, etc. all have bypass function for a reason, which is to allow use of campground, OR GENERATOR power, (which is clean) when available. All of those inverters have idling function, which means they consume about half a watt while on with no load, and will automatically switch between shore, gen, and battery. Cheap MSW inverters do not have this capability, so they invert all the time, and consume several watts unless turned off, also, their output frequency is influenced by the input voltage. I don't even want to think of the logistical nightmare of switching and properly grounding 5 or 6 small inverters, each serving one receptacle in a bus? I've deliberately left out harmonics and other stuff, as this is too long already, and nobody is going to read the second half. John MC9 makes a VERY important point in his comment about propane!! Think about an RV refrigerator, which will run on whichever source is available, and most of these will go to AC as the first source. If you're plugged in, that's fine. If you're not, the fridge is still going to see AC, and use the batteries and the inverter to produce heat, which is really inefficient, instead of propane. I think I've thought too hard for a Saturday morning, and its too early for a beer! Oops forgot, I don't drink, so what am I going to do now? I know, go soak my head! Regards, HTH, FWIW, George | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 2077 Registered: 1-2001 Posted From: 75.108.85.14 Rating: |
George, I have to take a small exception to this part of your excellent post. "MOST AC motors are synchronous" Most AC motors are really induction and they run at a speed determined by the frequency of the AC power, the number of poles, the input voltage, less the inherent slip in an induction motor. Therefore a four pole induction motor, with an input frequency of 60 hertz,will run at 1800 rpm minus the inherent slip. Generally around 50 rpm at full load for a full load rpm of 1750 rpm. The full load rpm is determined by the construction of the motor itself and could be as high as 1780 rpm and as low as 1710 rpm. A true synchronous motor actually locks to the input frequency. A four pole synchronous motor with an input of 60 hertz will run at exactly 1800 rpm. There is no inherent slip in this type of motor. Even with a voltage input reduction of possibly 30 or 40 percent it will stay locked into the 60 hertz input frequency, regardless of load, and will rotate at 1800 rpm. Conversely, the induction motor rpm will vary with not only load but also on input voltage variations. Another advantage of the synchronous motor is that by changing the exciter voltage it can present either a leading or lagging power factor to the utility power. With the proper excitation it will operate at unity or 1.0 power factor. Synchronous motors are significantly more expensive than the induction motor. In the equipment I used to manufacture I would sometimes over size the synchronous motor and then operate it at a relatively high leading power factor. To the utility company it appeared as a large capacitor bank and helped improve the facilitys power factor. Utility companys generally charge for a poor plant power factor. Generally below about 0.85 lagging. Many times we could improve the facility power factor enough to get above the penalty level and actually save the company from the penalty. This was a great selling factor since the unit I sold would actually pay for itself over a period of time. Richard (Message edited by drivingmisslazy on August 16, 2008) | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 524 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Richard, You are exactly right, and you've got my vote! It is interesting to note the trouble I am having with power quality in a plant in Richmond right now. A variable frequency drive displays an input power fault code, and locks out. Unfortunately, the drive is from another vendor, which we install on our machine, and it doesn't tell us what the fault is, it just quits. The good news is that PG&E came out Friday morning and put a recording voltmeter on all three legs, along with current coils, they are going to record until Tuesday afternoon, then take the meter back to the shop and download it. Suspicion is pointing to the Delta connected transformers, and a larger load than when the factory was originally built. I just wish the drive would tell us what the fault is to start with, even though it only happens once every day or two. Putting a bunch of capacitors across the lines works, but it sure wastes current. Does a watthour meter correct for poor power factor, or does it just look at current regardless of how far behind the voltage it is? If the answer is no, correcting the power factor in the plant without capacitors would be slick! Regards, George | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 2078 Registered: 1-2001 Posted From: 75.108.85.14 Rating: N/A |
Quote: "Putting a bunch of capacitors across the lines works, but it sure wastes current" end quote. Power factor correction capacitors do not waste current. That is why utility companies all install them to help improve the power factor thereby by reducing the current they are required to supply. Every facility that I have visited has a lagging (inductive) power factor. And in my facilities the utility company measured both KW and KVA. The KVA includes the actual KW used plus the amperage for the lagging power factor. It is my understanding that this may vary from utility to utility. Also where the penalty starts for poor power factor. Possibly anywhere from .09 to .80 lagging would be when they would start penalizing. For example, if a facility has a .07 lagging factor then the utility service must provide an additional 30% amperage to handle this power factor. One large example that I know of was Little-John Reuland electric in the Los Angles area. They had a very large motor and generator repair facility. In order to maintain the power factor at about 1.0 (unity)PF, they operated a three phase, 2400 volt, 1,000 hp synchronous motor 24/7. By varying the motor excitation they could adjust the power factor and maintain the facility power factor at or about 1.0. There is an insignificant amount of additional power (KW) utilized, but the amperage must be supplied which means larger transmission lines and distribution transformers. At least that is how I understand it. LOL Richard | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 525 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Richard, I am familiar with LJR, as that is where we take our Baldor motors for warranty work. I didn't really state it well when I said that capacitors waste current. The current that travels thru them IS gone, but it certainly does result in less total current consumed by them and all the nearby plants! Now we've really swamped the original poster, wait 'til he gets back and reads this! LOL, HTH, FWIW, and whew, Regards again, George | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 161 Registered: 12-2000 Posted From: 71.99.19.85 Rating: N/A |
Keith, I understand where you're coming from, having spent most of my working life in telephone central offices. There everything runs on -48V DC floated on huge batteries and very sophisticated chargers. The typical office runs around 2000 amps and the batteries are there both to filter the DC from the chargers and provide backup in case the AC power fails. I even considered a 48 volt system in my bus as I had access to surplus telco equipment. In the end, it just wasn't worth it. It would take a whole bay of batteries and the available inverters were just too physically large to be practical. BTTDB | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 21 Registered: 8-2008 Posted From: 71.198.253.223 Rating: N/A |
"Great , you get to buy a DC blender ($120)for your Margeritas , that burns out with the first low voltage ice chop , instead if a 120V ,, $15 K-mart unit (or $2,00 tag sale ) that lasts "forever". " I dunno Fred, but I don't think there's a lot of electronics in a blender. Your point about the 12V blender is well-placed, though. My point, however, was that electronic units usually have a high-voltage section (power supply) that steps the 120VAC down below 12VDC (5VDC used to be the standard, now some devices are 3VDC). Knowing this, you can bypass the AC supply and hook directly to the 12VDC power bus thought a voltage regulator ($1.99 or so). This is why the "wall wart" is so popular. | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 22 Registered: 8-2008 Posted From: 71.198.253.223 Rating: N/A |
"I don't even want to think of the logistical nightmare of switching and properly grounding 5 or 6 small inverters, each serving one receptacle in a bus?" Same here. But rethink this. One GOOD inverter for your computer and monitor. One GOOD inverter for your HDTV and audio system (unless they use wall warts, in which case you just need voltage regulation and filtration). Once the expensive stuff is done, you add a couple of CHEAP inverters for the bulk of your sockets -- because you have a lot more stuff plugged in than you are actually using at any given moment. Just because your total POSSIBLE load is 10kW doesn't mean you use more than 3kW at a time . . .so a 2000W unit serving, say, the left-side sockets, and another serving the right-side sockets, will handle all of your non-sensitive load, while still providing plenty of protection for microwave oven, lights, etc. Some of the best sources for top-quality inverters are wrecking yards which get the Killed-in-Action ambulances and fire trucks (especially if your area uses Mobile Intensive Care Units, with all of the instrumentation that they haul around). They don't get many of them, but you only need a couple! | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 23 Registered: 8-2008 Posted From: 71.198.253.223 Rating: N/A |
"Unfortunately, the drive is from another vendor, which we install on our machine, and it doesn't tell us what the fault is, it just quits." Maybe they were the guys who developed the early Macintosh, which was equally forthcoming as it crashed. | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 24 Registered: 8-2008 Posted From: 71.198.253.223 Rating: N/A |
Let's do the math: Most people in sticks and bricks are completely at the mercy of the line power. I have a strip from a power monitor that was plugged into the computer room at an ELECTRIC COMPANY that looks like an EKG. On the other side of the constant-charge, constant-drain system, it looks nice and clean. People in RVs and bus conversions have more options (genset and battery), but usually just hook up to the same power line that slags microwave ovens. In either case, the power is ratty -- often worse for us, because we have a more "divergent" set of loads on a common power line. So, we have to spend money to attenuate the problem. The question is where that money should go. I have had nothing but success over several decades of doing constant-charge constant-drain systems in radio and TV stations, ENG trucks, etc. After all, this is the basic power system in just about all motor vehicles today. By spending the money on superior isolation, you get superior isolation -- which is no doubt reassuring when the lights are out and you have no power at all! By spending the money on a constant-charge, constant-drain system, you can still be up and running when the power is out all around you. The unit price is comparable (the audio-quality Brickwall runs about $260 per 1650W, true-sine-wave, 100%-duty-cycle 1850W inverters start in the $290 range, less for refurbs). How much you spend on batteries will depend on how long you want to run with no shore power or genset, but you want a minimum of 500Ah worth of battery to swamp transients into. Is this perfect? No, of course not. But it's a system that works, is cost-effective, and opens more options for you at about the same expense. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 530 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Keith, In my reply to your original post, I went into great depth to explain why "all of you are missing..." the way to cure "ratty" campground power. I also asked you to at least post where in the world you live, and your bus model in your profile. As of this date, you have not. NOW, as to a direct reply to your post 2nd above, where you replied to my comment about the problems in PROPERLY grounding 5 or 6 small inverters. #1. What is a "wall wart?" #2. "Same here. But rethink this. One GOOD inverter for your computer and monitor, one GOOD inverter for your HDTV and audio system." "Once the expensive stuff is done, you add a couple of CHEAP inverters for the bulk of your sockets...will handle all of your non-sensitive load, while still providing plenty of protection for microwave..." The way I do math, "one GOOD inverter, plus one GOOD inverter, plus a couple of CHEAP inverters," is VERY close to the five or six I mentioned would cause logistical issues in proper grounding. A few posts down, you did mention "I am not an electrician." I just don't know how to say this to you, but EVERY ELECTRICAL DESIGN MANUAL, OR GENERATOR SIZING MANUAL SAYS TO DESIGIN FOR MAXIMUM POSSIBLE LOAD. I say this because I am a licensed electrical contractor. I made specific reference to the adverse effect of MODIFIED SINE WAVE CURRENT (as in cheap inverters) on magnetron tubes in microwaves, which you have ignored. Total number of posts has nothing to do with quality or accuracy, but your first post on this board did read "Something everyone is missing..." None of us are missing a 300 amp battery charger, (we already have house batteries,) and [wall warts?] and "CHEAP" inverters as a solution to campground power problems!!!!! Modified sine wave power, without frequency control, (as in cheap inverters,) is much more damaging than low voltage utility power. Improperly grounded buses, as in multiple cheap MSW inverters without ground/neutral switching is dangerous. In short, your original suggestion would require the purchase of a 300 AMP 12VDC battery charger, we already have house batteries, and several cheap inverters. Cheap inverters produce MSW, and do not idle. When boondocking, this will result in short house battery life between charges. Cheap inverters do not have ground/neutral switching, which will result in the bus frame connected to the campground neutral somewhere in this poorly though-out scheme. Like it or not, electricity produces 3.41BTU/Kilowatt hour, so your suggestion WILL PRODUCE over 25,000BTU of heat between the battery charger and the inverters. 12,000BTU=1Ton of A/C, and since the cheap inverters don't idle, you would end up with them inside so you could turn them off, and it would be hot in there. Bottom line? You would come out with worse power quality than you had before, and it is obvious that you have not done what you have suggested in a bus yet! AND, you ignore the fact that damage to [all of the electronics you worry about out] isn't avoided by doing this, the electronics in the high voltage side of the charger are STILL connected to your "ratty" campground power. Do us all a favor, post on what you are qualified, electricity is dangerous, leave out jargon, and reply directly to a post. I didn't think about it at first, but Niles and BW are right, this looks like another infomercial to me. I didn't think of this until now, and I admit it, right here in front of everyone, but on the idea of my first post on the logistical nightmare of grounding 5 or 6 cheap inverters, at one appliance per inverter, per Mr. Info. Sound and computer coaxial cables do have a ground sheath woven over the inner core, right? Two inverters with no connection between them other than 12V, (read no synchronization,) and the coax ground, (through the grounded antenna base, DVD player, etc.) sounds like a possible difference of potential to me of 240 VAC, which will definitely let the smoke out of something! (Don't let your wife touch the TV and the computer right after she has her hair done!) I give up, George Keith's post of 5:21 pm was made after I started, so I'm talking about his 3rd post above. Note he still doesn't answer any of the questions I raised before. G (Message edited by George Mc6 on August 23, 2008) | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1343 Registered: 12-2000 Posted From: 76.68.120.176 Rating: |
definitely a pattern emerging... oh dear... happy coaching! buswarrior | ||
| Jim Wilke (Jim Bob) (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 302 Registered: 2-2001 Posted From: 69.77.156.190 Rating: N/A |
George, wall warts are the little transformer power supplies that nearly everything uses today. Always plugged in, always using some power. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 537 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Well, Nice that somebody answered it for him!!! Properly called a plug-mounted transformer if you are an electrician. A surface-mounted thermostat if you are in the air conditioning business! Now we all see why I told him not to use jargon. Regards, George | ||
| Keith Wood (Ft6)
Registered Member Username: Ft6 Post Number: 34 Registered: 8-2008 Posted From: 71.198.253.223 Rating: N/A |
The bottom line: I've been doing this for decades, in numerous types of installation including broadcast radio and TV, emergency communications, and aerospace. It works. It has proven to be cost effective. George, you do NOT design for maximum load -- you design for DISTRIBUTED load. That's why there are a bunch of 15A breakers in the box, instead of one 600A breaker. The difference between what I'm talking about and what you are talking about is that you are starting with a single AC supply, from which all power buses feed, while I'm talking about separate supplies for different power buses. One big inverter is far more expensive than smaller inverters equal to the same total load. In addition, the one big inverter has to be clean enough for the most sensitive equipment, while with the separate inverters, you only have to buy top grade filtering sufficient for the sensitive equipment, and can use cheapie units for things which aren't as sensitive, such as blenders, aircons and lights. Sorry to have confused you over "wall wart." My current coach is a Buffalo. I've had several buses over the years. I've also owned half a dozen RVs of various size, as well as a herd of other rolling stock and more than one airplane. As far as where I am, sorry, that's information that I would rather not just hand over to anyone interested enough to enter my name in Google. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 544 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Keith, I have asked you several questions over the life of this thread, and you have essentially failed to respond. The beauty of this board is that all of us can read everything that has been posted, and form our own opinions. Although you say "I have been doing this for years in broadcast radio and TV...," you do not say that you are doing it in a bus, and it works well! Have you ever looked at the amount of air conditioning in one of your radio/tv transmitters? The reason your suggestion won't work, is expensive, and dangerous, is obvious to anyone electrically qualified, for the following: 1. To do what you suggest in your post immediately above, which involves running "blenders, aircons, etc..." would require a 300 AMP 12 VOLT BATTERY CHARGER, just to run the two inverters and two roof airs! Then you are going to need more amperage to run the rest of the bus. (That's not me, that's OHM's LAW!) 2. I have previously mentioned the "logistical nightmare of grounding 5 or 6 CHEAP inverters," and your reply is a matter of record. Now I want you to explain how your proposal would comply with sections 551.32, 551.46 (A)(2), 551.54 (A), (B), and (C) of the NATIONAL ELECTRICAL CODE? As information to you sir, these sections concern Recreational Vehicles. You will find this section starting on page 800 of the 2002 NEC Handbook. 3. I will say it again, MODIFIED SINE WAVE CURRENT IS HARD ON MAGNETRON TUBES IN MICROWAVE OVENS. 4. I think I handled this in #1, but how do you power all of your 15 amp breakers, if you don't have enough power to supply them? In your post immediately above, you say, and I quote: "George, you do NOT design for maximum load..." Well, section 551.20 Of the National Code tells how to design Combination Electrical Systems in RV's, and unfortunately your post differs considerably from the code's requirements! Specifically, for those without a code book handy, section 551.20 (B) says" The first 20 amperes of of load at 100 percent, plus The second 20 amperes of load at 50 percent, plus All load above 40 amperes at 25 percent..." 5. Ownership of "airplanes and a herd of other rolling stock" doesn't make you a qualified RV electrician. My phone number, e-mail, City, and State are in my profile, because I don't have anything to hide, also I offer breakdown help. Does Catch-22 apply here? (If you're not qualified, you don't know it?) Once again, I'm not a grump, I don't enjoy picking on people, you have not answered any of the questions I have asked. As I said politely before, this suggestion WON'T WORK, for several reasons. 1. It will require more than a 300 amp 12V battery charger. 2. It will generate more than 25,000 BTU of heat to run a 300 amp battery charger, and two MSW inverters just to run two roof air. 3. FOUR (or more) inverters, NONE OF WHICH are made to be twinned to provide 120/240VAC can't be properly (or safely) installed, according to the National Electric Code, as it pertains to RV's. One of us has put some thought into this infomercial, one of us hasn't. One of us is a licensed electrician, one of us isn't. Sorry, but I don't want to see any bus fires or electrocutions! The correct answer sometime ago would have been: Gee, I never thought of all of that! It's over George |
