| Author |
Message |
steve souza (Stevebnut) (24.91.90.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 06, 2002 - 4:47 pm: | |
Hi all
My question is this-- I hooked up an inverter today(3000watt/6500 surge)
when i threw the switch my air conditioner would hum but the compressor would not start.
I have four 1000 amp truck batteries and the bus 300 amp alternator so 12 volt shortage is not the problem.
The meter on the inverter did not reach full wattage during the draw for the ac so i am not drawing more watts than it puts out.
the inverter is a modified sine wave. could this be my problem?
my battery cables do not get warm nor does the inverter fan kick on.
everything else seems to run on the inverter.
any ideas?
thanks Steve Souza |
Tom Caffrey (Pvcces) (64.114.233.155)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 06, 2002 - 10:45 pm: | |
Hi Steve, it would be a good idea to check the voltage at two places when running your test again.
Check the DC voltage at the input to the inverter. Check the AC voltage at the input to the AC. Both of these tests should be done with a digital meter that is capable of averaging the modified sine wave.
If the voltage at the input to the inverter falls to anything below 12 volts, even a little bit, then its output could be too low to start the compressor.
If the input to the AC falls below 115 volts AC, then there may not be enough voltage to start the compressor.
Modified sine wave is not as effective at starting motors and running them, so if the voltage falls even a bit, motors are harder to start and they are noisier.
The voltage on sine wave can fall quite a bit and still start the compressor.
In some cases, it may be possible to change a starting cepacitor on the compressor and improve it enough to start reliably.
One thing to watch out for on inverters; they are real fussy about good connections and good batteries if you want them to do their best.
I believe those batteries you have cannot be 1000 amp hour rated; 8D batteries are only 220 amp hours. Could you be looking at the cold cranking amps?
If you are, that is a horse of another color. For what it's worth, our 2 KW inverter will not start our Dometic 13,500 btu AC, either. Our inverter just reports an electronic overload on our Link 2000 and shuts off.
Part of the problem to be solved if you run your AC on your inverter while going down the road is that there is going to be at least 10% of the power that the AC uses turned into heat inside the inverter.
I realize that the ratings are supposed to be continuous, but if the temperature should rise far enough in really hot weather even with the fan running, the inverter will turn off and have to be reset.
Good ventilation so that the inverter can stay cool will be needed if you don't want the AC quitting when you need it the most.
Tom Caffrey PD4106-2576 |
j maxwell (66.42.92.21)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 1:08 pm: | |
sounds like u may have a Trace DR series. They are not suitable for heavy induction loading. Not enough stages of inversion, causing too much lag between the amperage and voltage of the output, sort of like an out of phase condition with multi-phase power. The cheaper mod sign wave electonic inverters have the same problem. Even if u do manage to get one that will start the compressor, you will experience severe loss of efficiency in the inverter as well as unacceptably low voltage to the compressor, and they will evetually trip off after a period of time from overheating. The Trace U series is a little better, with about a 20% effeciency loss on induction loading. The real solution is a sine wave inverter and that involves more dollars. |
steve souza (Stevebnut) (24.91.90.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 6:09 pm: | |
thanks all--I was afraid my galaxy inverter at 450 was too cheap.
Oh well --i guess you get what you pay for.
Steve |
Henry Draper (12.82.133.47)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 6:16 pm: | |
Hi Steve,
Your post got my curiosity going, so I went out and tried to start my air conditioner using only my inverter and battery bank.
It fired up, no problem.
My inverter is a Heart Marine 30--modified sine wave. The air conditioner is a Coleman.
For what it's worth.
Henry |
Ross Carlisle (Ross) (216.107.197.16)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 07, 2002 - 9:59 pm: | |
When I did my research on inverters vs. generators, I found that to get an inverter that would reliably run just one AC was going to take about $4000 between the inverter, 24V battery bank, battery isolators and equalizers. And this setup would only work with the bus pumping huge amounts of amperage back into the battery banks.
For $5000 I could get an 8KW diesel genset that would run all of the AC's any time, plus everything else on the bus...Parked or running down the road.
I went with the genset. My thoughts on this are that if the inverter can not run at least 2 AC's plus my other 120V loads while under way, it is useless to me.
Ross |
jmaxwell (66.42.92.13)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 1:06 am: | |
Ross: After having gone the inverter, battery bank, isolator route and a gas gen I tend to agree with your economic reasoning. I'm starting a new coach and it will have a diesel gen set, well isolated, cooled, and vented that will handle my entire A/C load. I will also install a good inverter, but I intend to rely more heavily on a good and adequate generator this time around. I'm even going to transfer the solar system over to the new coach just so I can continue to demonstrate to everyone how useless solar power is. |
FAST FRED (63.215.224.253)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 5:35 am: | |
How will you be regulating the loads , so when you only need a single air cond you will still have the big gen set loaded ?
With only a slight load , a diesel doesn't even last as long as a gas gen set, and rebuilds are a pain to HAVE to do.
FAST FRED |
Peter Broadribb (Madbrit) (216.67.212.54)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 6:11 am: | |
Fred,
if you want to power 3 a/c units, how can you load any genset up when they are not in use. Surely the amount that these units are used is rarely relative to their capacity. RVs don't have a constant load like in an emergency power supply or a mobile medical unit has. They are a thing of convenience. It is all a trade off somewhere.
I use mine to supply enough power for my needs, so please explain how I can power those 3 a/c and still run the genset during cooler times when all I want to use is the TV, a coffee maker, microwave and charge the batteries. Even if I have an inverter for those smaller loads, I will still need to run the genset to charge up the batteries.
I plan to "excerise" the unit from time to time when at home.
The gas Onans which were installed in nearly all older RVs are still going strong despite total abuse from unknowing owners and invariably little load. I am still sticking to my 12.5kw diesel and going to love it.
Peter. |
FAST FRED (63.208.83.38)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 8:18 am: | |
You have answered your own question , you will have to put up with a shortened service life on the diesel gen set.
The gas can handle light loads much better, so they live long and prosper , even with severe abuse.
It DOES make the cost per hour of air cond time much higher as the fuel "saved" with a diesel is lost to the shortened service life.
BUT if only 3 air cond at once can let you be comfortable , thats life.
FAST FRED |
Peter Broadribb (Madbrit) (170.215.37.70)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 12:42 pm: | |
Fred,
the 3 a/c was just a "for instance", but you see my point. I was just trying to make an example of a situation that most RVs have. There is the summer a/c requirements and then there is the winter low draw periods and no genset arrangement will cover both. I know that the life span of the diesel will be shortened, but how long a span will that be? Probably longer than I will ever own the bus.
Gas is not viable as it means another fuel, propane is not good for me as I don't want the neccessary larger chassis mount tank, I am using 2 large cylinders for easier fill-ups. And yes, I am using propane for as much as I can, even though I am still tempted to use a house fridge, possibly a small under counter unit and a seperate similar freezer. Anyone go that route? Anyone have actual battery use figures on using house fridges and not all this theory stuff as the comsumption ratings may not always be truthful.
Peter. |
johnwood (206.252.250.185)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 2:59 pm: | |
Perhaps the ideal setup is an inverter that will run but not start both a/c units and a genset that will supply enough amperage to fully charge the bateries through the inverter. (I am speaking of a Trace SW series with transfer and charging ability here) and a fair, but not huge size battery bank.
Reasoning goes that the inverter is "smart" enough to use a smaller genset to its fullest capability to balance usage between running loads and providing battery charging automatically. Even autostarts the genset when needed. This way the genset would run at close to full load the majority of the time and give economy of operation as well as long life for the diesel.
What do ya think of this idea? |
Scott Whitney (24.205.235.106)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 3:16 pm: | |
I've run my DuoTherm roof A/C from my Heart Marine 30. Seems to work fine, although I have not tested it for hour after hour yet. (ran it for about a half hour while underway) When I was testing and setting up the inverter, I was able to start the A/C from using just one battery. Of course, I did not run it very long as that is a good way to discharge a battery in no time. But the point is - it worked, even on a small one-battery bank. I think the inverter is the key item.
Scott |
Henry R. Bergman, Jr. (Henryofcj) (63.224.197.10)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 3:17 pm: | |
Wow, lots of good answers. Now my 2 cents worth. Are your cables from the batteries TO the invertor large enough? Bigger is better.
Used to have a neat article from an old Home Power magazine that did an excellent job figuring out proper DC cable size. Can't find it.
If the distance from the providing batts to the invertor is of any significant length, go to larger cable diameter. This may help. Thanks. |
Henry Draper (146.129.147.36)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 5:26 pm: | |
Henryofcj (great name!) makes an excellent point.
The problem could be the cables. I happen to know that both Scott and I, both of whom had no problem running the air conditioner with our Marine 30s, have 0000 wire going from batteries to the inverter.
Henry (ofEdmonds!) |
Jojo Colina (Du1jec) (68.8.172.117)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 8:47 pm: | |
Now for my $.02. I run a Coleman 13500 btu while under way all the time with a Trace DR3624 fed by 20 12v/100AH AGM batteries in a series/parallel configuration with cross ties for 24 volt output charged by the bus alternator controlled by an Ample Power SAR v3 voltage regulator. I have run the AC for approx 6.5 hours once while parked just to see how long it would be before the over discharge protection on the DR3624 kicked in. Of course all interconnect is with 4/0 welding cable with terminals both crimped and soldered. |
Ross Carlisle (Ross) (216.107.195.149)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 9:13 pm: | |
Fred...
As noted in another post, no genset can be loaded perfectly all of the time. I expect to be running 2 AC's if I'm running AC. The third will come on if it's real hot. I added the third at the last minute. I figured it's better to have it and not need it than to need it and not have it. I could have gone with a bigger genset, but I thought that 8KW would provide all the power I need and would not be under loaded most of the time. Yes...There will be times that the genset will run just to run the microwave...But most of the time it will be loaded properly.
After reading all the posts, I still see no point in spending megabucks on an inverter that is not capable of providing all of the buses power requirements. I may put a lower end inverter on the microwave and TV/Sat reciever, but the heavy loads like AC's will run from the genset.
Ross |
Tom Caffrey (Pvcces) (64.114.233.202)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 08, 2002 - 10:29 pm: | |
While FAST FRED's concern about running a lightly loaded generator seems legitimate, I think the problem was much worse with two stroke engines. They would overcool on a light load.
Another way to minimize this problem is to choose a genset that can develope enough power without having very much displacement. Light loading problems are more related to size of the engine rather than it's rated horsepower.
If an engine can keep its chambers and oil hot, then condensates in the crankcase shouldn't be much of a problem.
Tom Caffrey PD4106-2576 |
FAST FRED (63.208.82.85)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 5:07 am: | |
Its not to my taste in engineering but Volvo used to install an exhaust valve that would close down in light loads.
This would make the engine work that much harder and keep the rings seated.
So you pay for the light loads with fuel , instead of Volvo parts.
The need for a TEC in monthly camping could perhaps be better done with a good sized DC gen set that would be throttable , a big batt and inverter set .
If the DC set could run 2 air cond , "straight thru " the inverters, the rest of the time the batts could hold the small stuff between charges.
How to cook is beyond me , as 120V is very slow for real meals.
FAST FRED |
Don KS/TX (64.24.4.125)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 6:48 am: | |
Sometimes if we repeat something often enough, we start to believe it. Does anyone have any REAL statistics on effects of genset loading, diesel or otherwise? WRICO never mentions this when you speak to them about it. I just bought a new Onan Marquis 6.5KW LP for a concession trailer, and it has absolutely no cautions about light loading, and in fact is built to encourage and accomodate just that, with a three year guarantee! I have never seen any figures from any manufacturer suggesting this, and have friends with huge generators that have never seen 80 percent load in their bus and don't even own enough stuff to load them 80%. They seem to be running just as well now as they did 10 years ago, no overhauls or problems. Over the road diesels with 500 hp or so rarely see an 80 % load either unless cruising far beyond the legal limits. Old wives tale or facts? |
Doug (65.161.188.9)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 9:57 am: | |
All
Read my post on another thread about generators and loading vs size.
My experience - and this is actual experience - not a wives tale or a theory - is that diesel is not good for a sometimes used gen set. Don KS/TX made a choice with the LP powered Ohno, and I suspect his will run a long time with the proper care. LP fired gen sets are good at that. The fuel costs more but the maintenance is less.
The issue of lightly loaded gen sets is more directed toward diesel and it's cost vs operating length before overhaul (AKA MTBOH or MTBF) vs a gasoline (or propane) gen set. diesel likes to be worked harder and has a varity of problems from running underloaded (running too cool and overfueling or cylinder washdown). This is particular in the Detroit 2 cycle diesel engines (they were originally designed in the 1930s I believe and while refined since then, are still an old but reliable design), but occurs in others also.
It is possible to maintain a diesel gen set in such a way that the device will outlast a gas or LP gen set, but few people that I know will spend that kind of money or time. Diesel is a great thing, but it also requires careful maintenance to obtain long life!
You will find that few manufacturers will tell you about underloading a generator. Onan didn't when I bought a dozen diesel fueled standby generators (20 to 60KW size) and one 40KW propane generator. The only one that was trouble free was the propane gen set. The diesels were constantly breaking down, not starting, had fuel problems, and 2 siezed up on me! We started changing them out when I left that place several years ago.
So much for my experience. Anyone had an opposite experience? I'm all ears. |
Jojo Colina (Du1jec) (68.8.172.117)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 11:55 am: | |
Maybe this thread should be renamed Diesel Gensets, Pros and Cons. It seems to have strayed from its original topic. Maybe Ian could start a new thread with the proper title and move messages to it. |
Ross Carlisle (Ross) (216.107.195.82)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 1:09 pm: | |
"WRICO never mentions this when you speak to them about it. "
When I saked Dick Wright about this, he said that underloading was more of an issue on the older gensets. He said that it is not as critical with the newer diesels engines.
Ross |
steve souza (Stevebnut) (24.91.90.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 7:01 pm: | |
well now that i have all my genset questions answered i won't have to ask them later LOL
My cables going to the galaxy inverter are less than 30 inches and they do not get warm so i believe the cables (2-2/0 for pos and 2- 2/0 for neg) are sufficient
still perplexed?>"><?
oh well-back to the drawing board
thanks for the input, i really enjoy all the replies.
Stevebnut |
Jojo Colina (Du1jec) (209.75.20.72)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 7:59 pm: | |
Steve,
It is probably your inverter. Like I said in my previous post, my Trace DR3624 which is 3600 watt powers my Coleman 13500 BTU AC just fine.
Jojo |
Ross Carlisle (Ross) (216.107.197.151)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 8:11 pm: | |
"when i threw the switch my air conditioner would hum but the compressor would not start."
You probably have aready run the unit in question from shore power, but just in case....
Yetserday I hooked up the third AC and it did exactly what yours is doing. Turns out the unit is bad. We think it has a bad compressor. Dometic is replacing it.
Ross |
steve souza (Stevebnut) (24.91.90.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 09, 2002 - 8:58 pm: | |
Jojo-- yes i am in denial, the inverter is new but it is a cheap one so i will probably check the voltage under load to see if it is putting out enough volts.
Ross-- my air conditioner is a new one and works excellent on shore power(cools my 35 foot bus on low coool in 90 plus degrees and humid) i live on the coast of mass in new bedford.
thanks---Stevebnut |
Tom Caffrey (Pvcces) (64.114.232.195)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 10, 2002 - 12:37 am: | |
When I made my last post on this thread, I said that I didn't think that keeping the oil and chambers hot would be much of a problem with the newer four stroke engines.
I forgot to mention that I believed that would be true of water cooled engines, not air cooled ones which don't have any control over their cooling.
Sorry about not mentioning that.
Tom Caffrey PD4106-2576 |
Dwight (67.213.8.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 14, 2002 - 4:24 pm: | |
Question is ???
Maintain a 10 or 20 battery bank system w/inverter or a generator ??
My experience with batteries in a motorhome has been 2 to 3 year life ?????
you are going to have to have the gen. anyway, so ?? help me here, I do not see the batteries and inverter thing for the A/C units ????? |