| Author |
Message |
Mike Tornesello (206.170.33.81)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 10:02 pm: | |
My ac system is all hooked up and I'm about to set up my DC panel. I realized that I don't have the same basic knowledge about fusing for DC as I do for AC. AC goes by wire size, the way I understand it. 15A for 14 ga wire, 20A for 12ga wire and on up generally speaking. Can anyone clue me in on basics for 12v and 24v DC? I need some rules of thumb. Thanks, Mike |
johnwood (206.252.250.153)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 11:18 pm: | |
check out www.backwoodselectric.com they have a great tutorial and discussion about DC living. |
FAST FRED (63.215.226.236)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 5:31 am: | |
There are two things to protect , the wiring and the load.
If you use a good sized wire on a good sized load , most any protection device works .
But if you have a nice circuit that handles a few loads , a circuit breaker or fuse that keeps the wire from catching fire , will not keep the user , radio ,tv ,typical small load from smoking.
Thats why there is a small fuse in your car radio , to protect the device , not the car wiring.
An inline fuse can be added to items that draw little juice , if there not factory installed.
Fusing DC for Major wiring (200 to 400A) and requires a very $special fuse if the power source is thousands of amps , loke a big batt bank.
Then its time for a "class T " fuse and holder , as stopping what could be hundreds of or thousands of amps is much harder.
FAST FRED |
Jim Ashworth (Jimnh) (172.150.198.65)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 9:22 am: | |
Mike- To keep it simple, amps is amps, no matter what the voltage. Same rules apply for protecting the wiring whether with ac or dc current. Fast Fred has good advice to protect devices with smaller fuses. It would be a good idea to oversize the wire on dc circuits because of voltage drop. You can check this out by running a 12v lamp through 50 ft of wire and have another going through only a couple of ft of wire. Put them side by side and note the difference in brilliance. If the wire is sized properly for the load, there will be no difference. I have noticed that a half dozen 20w halogen lights on 25 ft of 12ga wire will be dimmer than the same on 10 ft of the same wire. Number 10 wire is a pain to work with compared to 14ga, but for longer runs, it may be worth it.
Jim |
Mike T (206.170.3.201)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 9:47 am: | |
All of the wiring I've run so far is 12 ga. It is all under 25 ft. with only one exception for a single light. I ran a separate circuit for almost everything, so I only have two lights on a circuit usually. I'm thinking I'll use 15A or 20A fuses on those and calculate the other items such as fantastic fans to see if the draw is more or less than the lights keeping the amps below 20 and the wattage as my guide for excessive voltage drop. Does that make sense? I'm still at a stage where I could run a #10 wire if necessary. Would it make any sense to follow the AC rules and use a 30A fuse for the 10ga wire?
Johnwood, I found www.backwoodssolar.com. Is that what you meant? Thanks to all. Mike |
johnwood (206.252.250.68)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 12:44 pm: | |
Steve Willey's site? Yeah. Guess working from memory is a bit precarious when you get older, eh? Used to live on next ridge over from Steve. Interesting fellow. Made it into Forbes Magazine a few years back. Knows his stuff as he has been living and selling it since the mid 70's. Used to get paid to do conservation speeches by schools and such. |
FAST FRED (63.208.87.65)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 3:22 pm: | |
For the most comfortable inside lights , get a copy of a Granger cat. and look at the "12V "bulbs list.
You will find bulbs fron 12.6 to over 14 V as "12v".
When sitting on just batts the lowest voltage "12V" bulb will be brightest , and easiest to read by.
The list could be avilable elsewhere ,
and sorry I don't own Grangers.
FAST FRED |
Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 5:21 pm: | |
Hello Mike;
Do not mean to rain upon your parade, but have you considered leaving the low voltage bus systems alone and running EVERYTHING for the "house" side thru a sine wave invertor?
When I built my cabin (armstrong tools too!) all the wiring was standard to code 120 VAC stuff. (except of course the rooftop PV panels and battery cables)
Actually saved enough $money$ to nearly pay for the old Trace (old now--new then) invertor to power everything the cabin had on 120 VAC. I am finding out an average bus equals a BIG AE (alternate energy) home.
True you will have to use upgraded stuff like proper wiring in your mobile bus which vibrates. But, you should still save lots of money by ignoring any low voltage, high amperage circuits. Thanks. Henry |
Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 6:21 pm: | |
Opps!! Forget to say (I hate getting old!!) that the big energy hoggs would NOT be wired thru the sine wave invertor, like the roof top AC units and the like.
These would only run thru the gen set or thru shore power. This would require a smaller invertor, thus $cheaper$. Thanks. Henry |
Mike T (207.214.217.161)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 12:25 am: | |
Henry, I actually do have inverted power and it is running a large amount of stuff. Most of it is optional stuff but not all. I installed a new 24 volt battery bank that is dedicated just to that. I have 12 volt batteries and chargers that came with the shell I bought so I decided to keep them on the idea that I would not need to load the 24v bank with lighting and small things like that so maybe I could use the inverters for some of the big loads. (including an electric fridge). The 12 volt batteries are not going to be very expensive like the inverter 24v bank and I will probably abuse them more and not worry about it. Also, the amount of loss of efficiency for the inverted system makes me want to use it less if possible when 12v is there to be had with more efficiency. The calculations for battery bank sizing shows that, I think. I've been reading your posts about your project and see that you are excited about the all electric idea. I am driven by redundance. I have at least two of everything in my conversion and multiple sources of energy, and believe me, my friends have a ball making fun of me. I have fun though. Whatever drives your bus or floats your boat. Right?! Mike |
Scott Whitney (66.214.200.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 2:36 am: | |
I am in the process of setting up my DC system. Here is what I have so far:
1) 300A fuse btwn the 12v battery bank and the 3Kw inverter.
2) 100A fuse btwn inverter input and the DC load center
3) 6Ga. cable going from 100A fuse to 3 ATC fuse blocks (front, middle & rear of bus)
4) Each fuse block has automotive blade fuses for individual loads. (5A-30A depending on device) All loads on a separate circuits.
However, I have not yet installed any DC lighting so I don't know how many 12v lights I'll put on an individual circuit. But all circuits are using 10Ga wire, so I should be able to add more loads later without fear of overloading the wiring.
Scott |
FAST FRED (63.208.87.246)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 5:29 am: | |
Some folks have found that the loss of 10% thru the inverter is about equal to the voltage loss from much DC wiring.
AND gadgets for 120V are far cheaper , $15. for an AC blender VS well over $100 the DC model.
Depending on the leignth of circuits an AC circuit can be an advantage.
The other alternative to lower line loss , not used often , but cheap , is what is called a Ring circuit , where the DC comes out of the protection (cb or fuse), and then goes around the circuits in a ring , rather than a dead end.
Works where there are loads of lights or other really spread out items.
FAST FRED |
Mike T (206.170.3.35)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 8:55 am: | |
Fred, does the other end of the ring connect back
to the protection? Mike
Scott, you got me thinking. That system sounds smart. Thanks. |
Peter Broadribb (Madbrit) (170.215.38.21)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 1:20 pm: | |
Mike,
yes it does. It balances out the flow of the power better as the appliance draws from the shortest and easiest route to get the power it needs. So you can run out on one side of the bus and back on the other and the lights on each side will be as bright as each other. It also saves on all the branches running from the main run down the bus as you can often take the run right to each outlet or light.
I was surprised by Fred using the term "ring". When I moved to the USA from England, I built our home and asked about a "ring main". I was told that was the English term for a "Home Run" in the USA. I suppose it is just another East coast meeting West coast thing...... LOL.
Peter. |
Scott Whitney (66.214.200.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 1:47 pm: | |
BTW, www.waytekwire.com is a great source for inexpensive DC components. Fuse blocks, fuses, circuit breakers, wire, switches etc. Someone on MAK's board turned me on to them. I ordered all my stuff and was very pleased with the company. 50ft roll of 6ga. cable for about $25 bucks, fuse blocks for about $12 bucks etc. . .
Scott |
Henry R. Bergman, Jr. (Henryofcj) (63.164.175.133)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 4:34 pm: | |
Yea, the big weakness on planning to run most everything thru only one invertor is obviously, what happens when you eventually blow up or lose the invertor?
Oh no!! Oh well, back to the drawing board. Two invertors? One on line and another as a backup? Not very $smart$!! Am I having fun yet?? Henry |
Mike T (206.170.33.113)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 7:15 pm: | |
Henry, I ran two inverters in series for 220v. You're right, not very $smart$ but I'm into the whole inverter thing as much as you are. My whole system is on them. I haven't even turned them on yet. Maybe this weekend.
Thanks everyone for all of the input. I never can express how grateful I am to this board. Mike |
Tom Caffrey (Pvcces) (64.114.233.254)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 11, 2002 - 11:08 pm: | |
Scott, I was puzzled by items numbered (2) and (3) in your earlier post. Does the 100 amp fuse come off the inverter side of the 300 amp fuse?
If it does, it looks to me like it would squeeze the 300 amp fuse capacity, because 3 KW at 12 volts would work out to be something like 275 amps, when you make allowance for the 10% loss in the inverter. If there was any serious surge, you would run way over the fuse rating without any other loads.
The 6 guage wire fed by the 100 amp fuse looked too small for the fuse. If I recall right, 2 guage is rated something like 95 amps. Even if there are 3 6 guage wires, each going to a different panel, the fuse wouldn't protect you if a short occured.
Maybe I am reading something into your post that you didn't mean. If I have got it right, you might want to take a closer look at some of those ratings.
It looks like you've got quite a system going, there. For what it's worth, we were lucky enough to get transit fluorescents in our coach. We like a lot of light and they are sure easy on batteries.
Good Luck.
Tom Caffrey PD4106-2576 |
Scott Whitney (66.214.200.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 12, 2002 - 2:27 am: | |
Hi Tom,
Here is a link to my wiring diagram. It is easier to see than explain in bullet points:
http://www.dustyfoot.com/Floorplan.html
The 300A fuse probably is squeezed close to capacity. In some places in the inverter documentation, it called for a 300A fuse. In other places it called for a 350A fuse. But I could not find a 350A, so I bought a 300A instead. I have not blown it yet. If I do, it will be a $40 mistake as the fuses are quite expensive. I am guessing it will be very rare that I will draw that much except for an occasional surge. It starts the A/C no problem.
The 100A fuse for all my other DC loads may be oversized. I am certainly open to suggestions on this one. This fuse was cheap. I admit, I bought the 100A fuse sort of as a best guess what the max of all my non-inverter DC loads might be. I could probably drop this fuse down to 50A? DC loads, other than the inverter, will be things like: water pump, lighting, computer, satellite dish, music system etc. No one item will be a heavy draw. Lowering the 100A fuse to 50A would probably be better for the 6Ga. cable?
Scott |
Tom Caffrey (Pvcces) (64.114.233.182)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 12, 2002 - 11:16 pm: | |
Hi Scott, it looks like you ought to unhook that 6 guage wire at the inverter and change your 100 amp fuse to a 60 amp one. Then, when you reconnect the 6 guage, it should be connected ahead of the big fuse coming off your house battery.
That would give you as much as you could get in inverter protection and capacity as possible. The 60 amp fuse needs to be before any 6 guage wire if you want all of your 6 guage protected.
It looks as though your genny out to put out 53 amps, so if you used the jumper in the junction box between the generator and the female 50 amp plug that connects L1 and L2 together, you could run both ACs off the generator.
That will only work if your generator windings are connected to put out 120 volts only, not 240.
I know what you mean about finding the right fuse. I got lucky and found some listings in a search on Google. I think I used T-1 fuse for keywords.
Isn't that big wire for the inverter and the shunt a bear to work with? I spent a lot of time on ours.
Good luck and happy bussin!
Tom Caffrey PD4106-2576 |
Mike T (206.170.3.111)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 13, 2002 - 9:33 am: | |
I'm worried I left something out now. What's a shunt? My inverter wiring diagram didn't call for that. I've seen them in the parts catalogs and I thought it was needed for ammeter installation. Mike |
Scott Whitney (66.214.200.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 13, 2002 - 12:45 pm: | |
Hi Tom,
Thanks for the info. You are right, my 6 ga. should probably originate from the battery and not the inverter input. Not sure why I got started thinking along these lines. Guess I fugured once the four-ought was run, all loads should come from that. But it would make more sense to locate the second fuse as close to the bat bank as possible and run fresh 6ga. for all the other loads. . . I am going change it over, as it is easy to do now.
Yes, my genny is two legs of 120VAC and should be able to run both airs at the same time. (although I have not purchased my rear air yet)
The smaller size fuses (100 and lower) I found at Waytek for only a few bucks each. So picking up a 60A and tossing the 100A is no big deal. The expensive 300A fuse is a slow blow and should handle any surges on the inverter. (knock on wood)
Hi Mike,
The shunt is for ammeter use. It can handle very high loads, in my case 500A, and creates a very small but very accurate voltage drop across it. An ammeter then measures this small voltage drop and can calculate the current flowing thru it. You can get dual shunts so that two separate banks can be monitored or single shunts for only a single bank.
If you use a Link 1000, 2000 or 2000R (I am sure there are other models too) it can control a Heart inverter AND display current. I find this very handy to know exactly how much of a charge the batteries are taking. Also, you can walk around the bus and turn different devices on and off and watch exactly how much current they draw. Gives a 'real' world' measurement of power use. The Link will also use this and other data to calculate approx. how long you can run any given load before the batteries are considered dishcharged.
The shunt goes into the neg. side of the cabling. Could be installed at a later time, but working with that 0000 is a bear sometimes. Might want to put a shunt in now if you can. You can always wire up the ammeter (or other controller) later, but the cabling is a bit less forgiving.
Scott |
Mike T (206.170.3.57)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 13, 2002 - 3:25 pm: | |
Scott,
sounds like the shunt is cut into the negative line (not parallel to it) and the ammeter is parallel across the shunt. Do I have that right?
Does it matter what the distance from the battery is? Thanks a million, Mike |
johnwood (206.252.250.128)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 13, 2002 - 4:05 pm: | |
Correct; Shunt in series and the meter in parallel with the shunt. |
Richard Bowyer (Drivingmisslazy) (66.190.119.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 13, 2002 - 5:01 pm: | |
Scott, I believe the meter is really a voltmeter, calibrated in amps. It is important to get the right meter. Also, I believe the shunt can go in either the positive or negative leg.
Richard |
Scott Whitney (66.214.200.214)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 14, 2002 - 12:50 am: | |
Yes, that is correct. The shunt goes in series with the negative battery cable. True, the meter is actually a voltmeter that is calculating current. It measures two voltages, one on the battery side of the shunt and another on the load side of the shunt. It subtracts the two and obtains the voltage drop across the shunt. Since the resistance of the shunt is very low, but a known constant, the meter calculates current based on the voltage drop using on Ohm's law. So basically it is two voltmeters and a calculator that give a reading in amps like an ammeter.
The shunt is rated for a specific resitance and max current. You need to match the meter to the shunt, although, I believe there are a couple of standards. Or just buy both from a Heart/Trace dealer and you know it will work as designed.
I suppose, in theory, the shunt could go in either pos or neg, but the Link 2000R manual places it on the neg side. This works fine cause the catastrophe fuse is on the pos side so each 0000 cable has one break in it before the inverter/load connection. Can't see how it would really matter, though, as long as the meter could be calibrated to either pos or neg values.
BTW, if you look at my elec diagram, I include the wires that measure the voltage drop across the shunt using the wire color codes recommended in the Heart manual.
Scott |
Merlin Moon (Mrmerlin) (65.24.96.77)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 22, 2002 - 12:45 am: | |
Scott --
Looked at your wiring diagram and now I have a question. You are driving down the highway running air conditioner #1 which appears to operate through the inverter. The engine 300 amp alternator is replenishing the batteries ... no problem. No need to start genset in this case. NOW ... you stop the engine and forget to kill air conditioner #1. Does it continue to suck power from the batteries or is there a fail-safe to prevent this? The reason I'm so interested is, I had planned on rigging one air conditioner to operate while motoring along, but could not figure out how I could keep myself from accidentally draining the batteries. Ignition kill circuit that shuts off the a/c? In that case I'd have to figure out how to activate the a/c when I needed it to run from shore (or genset) power. There must be a way, but I'm electrically challenged. |
Scott Whitney (66.82.32.1)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 22, 2002 - 2:35 pm: | |
Hi Merlin,
Yes, it would definitely kill the batteries if I forgot to turn the A/C off or start the genset or plug in. For me personally, I am very aware of my power consumption and am continually checking battery voltage etc. So I doubt I'd forget for very long that the A/C was running if I were on battery power. Not to mention, I am tying my engine batteries and my house batteries manually thru a big switch - so if I forgot to isolate them after shutting the engine off, I'd kill everything. But my personal preference is for simple (as possible) circuits with manual control instead of complex cicuits with too many things happening automatically.
But a failsafe method could probably be rigged up with some clever wiring. Not sure how you would do it though . . . set up a relay powering the A/C that was only energized IF the alternator were charging OR IF the genset were running OR IF shore power was present. Might be a bit complex, though.
Scott |