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Old 11-22-2016, 04:07 PM   #1
coosa
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Default Battery Pack Questions - Slightly OT

This is a little OT, but I know that there are lots of smart guys here who can answer my questions, so maybe I can get away with asking here.

In addition to a couple of EZGO 36 volt carts, I have a remote cabin that's off the grid and runs off a combo of batteries that are charged by solar panels and a small generator. The generator primarily runs the ac in the summer and also charges the Black Beauty cart that stays there all the time. I have been powering the cabin with 4 of the 12 volt marine batteries. I use 12 volts for all lights, most of them LED, and have an inverter to run the tv and sat box. The batteries are getting old, so I'm gonna replace them with a 36 volt golf cart pack. I've also bought a larger inverter - 1500 watts - and plan to add a small coffee pot and microwave and run them with the inverter. I briefly used a golf cart pack before, but I pulled them out and put them in a cart and put the 12 volts back into use. I've been running the cabin with the batteries and solar panels for 10 years now, so I know the answer to most issues that come up, but I have a few questions regarding wiring in the new battery pack.

1) I will take the 6 six volt batteries and wire them in series in pairs to essentially make them into 3 12 volt batteries. Then I'll wire those 12 volt batteries parallel and hook the wires for everything to the last 2 batteries. I am thinking that I need to use a 4 gauge cable to hook the + and - of the last 2 batteries so that they don't overheat when running something heavy on the inverter. But I think it should be ok to use regular size 12 wire on the rest of the connections. I'm using size 12 wire for all connections now, but I do have a smaller inverter. Is this correct, or do you guys think I need 4 gauge cables for every connection?

2) I need to add a permanent battery charger that I can run off the generator to recharge the batteries occasionally when the sun can't keep up with our usage. I was thinking of a 30 amp marine charger that has 3 banks at 10 amps and 12 volts each. Then I can hook up each pair of batteries separately and charge them faster than anything I have available now. I have been able to get by with just solar power so far, but a microwave is gonna pull a lot of power. Is there any real advantage to using this type of charger vs just hooking a single 12 volt charger into the pack? Is there a better alternative than what I have in mind?

3) I learned on here not to pull 12 volts out of a 36 volt pack for accessories because it pulls down 2 of the batteries at a different rate than the others. But in a setup like this, does it make any difference? Right now, I have everything hooked to just one of the 12 volt batteries, but they seem to all pull down equally. Am I correct on this that it doesn't hurt anything to power everything from the last 2 batteries?

4) And last, I have a set of Trojan 105s that are 2 years old and already broken in well. I followed Scotty's directions and this cart feels stronger now that it did when the batteries were new. Would I be better off to pull the batteries from this cart and install them at the cabin, and then install the new battery pack into the cart and break them in properly? I am thinking I would be better off to do it this way than to just put the new batteries into the cabin. Usage there is pretty random, and I don't see an easy way to break them in.

I know there are sites for solar homes, but these are all questions related to the kind of battery packs that you guys work with all the time. Thanks for any help!
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Old 11-22-2016, 04:38 PM   #2
cgtech
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Default Re: Battery Pack Questions - Slightly OT

12g wire is grossly under size, your inverter will draw 125a from a 12v battery at full load Pull your positive & negative from opposite ends like this (brackets = batteries) __[]=[]=[] ¬ . All 3 batteries will have their positives tied together, and their negatives tied together. I'll draw a picture in a few. This battery configuration makes 6x 6v batteries into a large 12v battery.
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Old 11-22-2016, 05:58 PM   #3
coosa
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Default Re: Battery Pack Questions - Slightly OT

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12g wire is grossly under size, your inverter will draw 125a from a 12v battery at full load Pull your positive & negative from opposite ends like this (brackets = batteries) __[]=[]=[] ¬ . All 3 batteries will have their positives tied together, and their negatives tied together. I'll draw a picture in a few. This battery configuration makes 6x 6v batteries into a large 12v battery.
Thanks, that's the kind of info I was looking for. I was gonna wire them exactly as you have drawn, except I was gonna pull the power from the set of batteries at one end instead of + on one and - on the other end. I can understand that if I do that I will be pulling power from the whole pack at once.

I don't doubt your advice at all; I've seen your excellent posts for years. But could you help me understand why that is better? The way I was gonna do it will pull power from only the last pair of batteries when the inverter has a heavy load, but won't the pack then equalize soon after its finished running? Is doing it that way shortening the life of the batteries?

If I hook it the way you have drawn it I will need to buy a longer cable for the - side. The inverter came with 3 gauge cables that are only 3' long and it wouldn't reach the other end. But I guess I'll need to buy a whole roll of cable to use cables on all connections.

Thanks again for the help.
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Old 11-22-2016, 06:32 PM   #4
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Default Re: Battery Pack Questions - Slightly OT

The best reason is the resistance of the cables. The way you were planning puts the farther set away most isolated from the load by the resistance of the cables. Not sure if it's a huge deal, but I know how I would do it.
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Old 11-23-2016, 05:49 AM   #5
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Default Re: Battery Pack Questions - Slightly OT

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The best reason is the resistance of the cables. The way you were planning puts the farther set away most isolated from the load by the resistance of the cables. Not sure if it's a huge deal, but I know how I would do it.
The way cgtech recommended is the way solar energy system designers set up battery banks. It evens out minor voltage drops better, allowing batteries to remain balanced the best. If you drive your loads from one end, the batteries on that end get worked slightly more and go bad faster than those at the other end.

On my own solar power system, I have 3/0 main cables running the length of the wall that my batteries are on and each set of 48V are wired into those 3/0 mains. I'm now using sets of 8 - 435 Amp/Hr L16H (6V each) batteries in series.
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Old 11-23-2016, 12:09 PM   #6
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Default Re: Battery Pack Questions - Slightly OT

Overkill is underrated, so use the thickest cables that are possible and practical to connect the batteries in series/parallel and connecting them to the inverter.

The batteries are stationary, so flexibility isn't an issue. In fact, solid copper bus bars could be used.

Personally, I would install the new batteries in your cart and break them in before using them in your solar power application.
You'll need all the AH storage capacity you can get from them to run a coffee pot or microwave via an inverter.

A T-105 is a 6V-225AH battery and two in series yields a 12V-225AH battery.
Three of those series pair connected in parallel yields a 12V-675AH battery.

That is roughly 8100 Watt-Hours of energy stored, however that is at the 20 hour discharge rate which is only an amp flow of 11.25A and you will be drawing over ten times that number of amps, so Peukert's Law comes into play and with 125A being drawn, the effective storage capacity is only about 950wH and not all of that is usable since you won't be completely discharging the battery.

Then there is the efficiencies of the inverter and the appliances to take into consideration. My guess is that you might get about half an hour run time when the inverter is operating at its rated power. Of course, this is a worst case scenario since you probably won't be running the inverter at its rated power very much.
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Old 11-24-2016, 01:13 AM   #7
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Default Re: Battery Pack Questions - Slightly OT

Thanks for all the great info. You guys may have convinced me to just run the wires for the microwave straight to the generator and just crank the thing whenever I need it. The coffee pot is one of those little 4 cup ones with no timer and it will only be used for brewing. I'll cut it off once it makes. The microwave is a small 600 watt output with mechanical dials, but it says it runs on 8 amps, so I guess that's around 960 watts input. I seldom do any serious cooking at the camp, the microwave is just to warm up stuff already cooked. I run it 3 minutes a day when I use it.

I know that I've gotten by all these years with 12 volt batteries wired wrong with too small wire simply because I never pull a very heavy load from it. The TV uses 40 watts and the led lights don't use much at all. Trying to run a microwave is taking it to a new level and I at least knew I needed some advice on how to do it right. I have been keeping the microwave under the shed and sitting it on a bucket when I used it, so moving it to the kitchen counter is kinda like adding indoor plumbing. :)

Thanks again for all the help.
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Old 11-24-2016, 01:58 AM   #8
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Default Re: Battery Pack Questions - Slightly OT

Whoa, don't let us slow you down on going solar. All you need is some cables! Do it, 3 minutes of microwave is no reason to scrap the idea
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Old 11-24-2016, 02:14 AM   #9
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Default Re: Battery Pack Questions - Slightly OT

Quote:
Originally Posted by coosa View Post
Thanks for all the great info. You guys may have convinced me to just run the wires for the microwave straight to the generator and just crank the thing whenever I need it. The coffee pot is one of those little 4 cup ones with no timer and it will only be used for brewing. I'll cut it off once it makes. The microwave is a small 600 watt output with mechanical dials, but it says it runs on 8 amps, so I guess that's around 960 watts input. I seldom do any serious cooking at the camp, the microwave is just to warm up stuff already cooked. I run it 3 minutes a day when I use it.

I know that I've gotten by all these years with 12 volt batteries wired wrong with too small wire simply because I never pull a very heavy load from it. The TV uses 40 watts and the led lights don't use much at all. Trying to run a microwave is taking it to a new level and I at least knew I needed some advice on how to do it right. I have been keeping the microwave under the shed and sitting it on a bucket when I used it, so moving it to the kitchen counter is kinda like adding indoor plumbing. :)

Thanks again for all the help.
My primary inverter is an Outback GVFX 3648, grid-tied 3.6KW 48V. The only reason I used the 3/0 wire is because I already had coils of it that I had salvaged from a TV station transmitter building that was being demolished. 0 or 1/0 was the recommended guage in my case. I run my house, including a convection oven and a 1 KW microwave oven, full-sized fridge, and a sub-zero upright freezer. Microwave ovens, especially the smaller ones, are not a significant load because the number of minutes of actual use are extremely low as compared to other more common loads that require power all day. In order to minimize output power consumption and damage to appliances, I suggest that you use a true sinewave inverter.

You should be able to power your microwave from your batteries, just upgrade the wiring between them. 2 AWG wire should be adequate to carry the loads without too much voltage drop.

I also have an off-grid cabin with an 800 watt inverter that has no utility power nearby. A 25 year old 110W solar array has been running it for years and now it has only a single 12V, 100 A/H gel cell that a buddy of mine gave to me 2 years ago. He had retired it from his solar power system a few years ago and it tested as still good. I run a modern 700 watt microwave oven once in a while on that one. The main usage is to run one LED light in each room, the bedroom, kitchen, bathroom, and living room. I can turn on all 4 LED lights and the inverter does not come out of idle mode unless I turn on the ceiling fan or use the microwave.

As previously mentioned, if you want to upgrade your batteries, use the ones from your golf cart. Since they are already broke in, they are ready for use. Put the new batteries in your golf cart and break them in.
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Old 11-24-2016, 09:29 AM   #10
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Default Re: Battery Pack Questions - Slightly OT

CGtech - thanks for the encouragement. It's actually been a solar cabin for 10 years, but it's underpowered with only 75 watts. The cabin has just evolved over the years. My dad and I built it in 1979; it was 16x24' with one main room and 2 tiny bedrooms. It had a wood heater, a Coleman stove and a Coleman lamp. That was it. I got tired of it being so dark so I wired it up with 2 50 watt 12 volt lights and carried a trolling motor battery every time I went. I'd leave it hooked up until the lights went out, and then we'd hook up dad's battery. Kinda hard on the batteries and they had to be hauled home to be charged, but it worked.

My dad passed away in 2000 so the cabin was left up to me. I didn't charge anything for a while, but eventually other family and friends started going more and I added another bedroom and a bathroom in 2006. I built it during deer season and made the hunters work part of their visit. It ain't the highest quality work. :)

The cabin is about 50 yards from a 4 acre pond, so I built a pumphouse by the pond and put in a 12 volt pump with one battery and one solar panel and it supplies the cabin water. My wife refuses to take a shower in it, but everyone loves having the RV style commode.

I also added lights in every room, a generator, a window AC unit and a 27" TV with a sat receiver. My daughter and her family go often now and the women want it more like home. The microwave inside is mainly to make them happy.

Bob, I'm sure I could learn a lot from you. Your home system is far more advanced than my cabin can ever be. I do have to consider the costs, so my new inverter is a $150 Northern Tool special. It's modified sine wave. If it burns up the microwave I haven't lost much.

What do you think of the idea of a 3 bank marine charger as a backup for the solar panels? Is there something better just for that? I've read a good bit on different sites dedicated to home solar, but they are all focused on big systems for full time use. My cabin gets used for a couple days and then sits unused for a week or 2. The charge controller rarely shuts off, so my batteries reach 100% only a few times in the summer. But it works, and we have lights and a TV.

Thanks for all the help!
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