Author Topic: A Little Advice (Read 7233 times)

Jaust · « **on:** November 15, 2014, 08:10:14 PM »

Hey all, New to this forum. Came from another that was no help at all. I have a cabin that I bought this summer and we're all off grid eventually I'm planning on looking into solar but for now I need to get some info on my battery setup. I have 12-6v batteries wired in series and parallel for 12v and 1420ah and a 2400w Xantrex inverter/charger. The info I'm getting is not only that this is too many in string but very dangerous. When I asked why I got the cold shoulder and no explanation. I'm thinking of rewiring to get either 24v or 48. Any advice would be greatly appreciated.

dnix71 · « **Reply #1 on:** November 15, 2014, 08:48:39 PM »

I don't know about dangerous, but it is very difficult [actually almost impossible] to properly charge and equalize a combination series/parallel string like that. A straight series string to make 72v nominal would be better assuming you know how to follow the NEC and have an inverter charger that can handle that voltage. More than 48v nominal (which is really 58v+ fully charged) means you need to follow code for legal/insurance/safety reasons.

The only sure way to equalize a parallel/series string is to have a separate charger for each 6v battery. Newer power packs with lithium cells have a battery management chip on each cell that isolates each cell during charging and prevents over/under charging. Nothing off the shelf exists for golf cart batteries.

The other down side to your arrangement is that at 12v you are pulling a lot of current. A 24v arrangement would make more sense if you have no other choice about it. A series of 4 six-volt batteries and three parallel strings of those would be better balanced, but still far from ideal.

Are you using 12v directly for anything?

hydrosun · « **Reply #2 on:** November 15, 2014, 10:19:30 PM »

When starting to design a system you want to plan ahead to see how the system will grow in thefuture. A good rule of thimbis to use the voltage that will keep the normal amperage under 100 amps. So over 1200 watts use 24 volts, over 2400 watts use 48 volts. Alot of systems have grown over the years and either changed voltage or use bigger wiring. My own system outgrew 12 volts and switched to 24 volts.
So if you are changeing the inverter to a higher voltage to limit the number of battery strings and you think your solar array will be bigger than 2400 watts you would want to go to a 48 volt system. That way you could use one Midnite solar controller to handle up to 5000 watts of solar panels.
Chris

Jaust · « **Reply #3 on:** November 16, 2014, 01:37:29 AM »

Dnix71 and hysrosun, thank you so much for the info. As I said, I've spent 3 days in another forum going back and forth with guys and being criticized for setting up a system like that and saying it's so dangerous they won't even give me advice on how to rectify it. The setup came in the cabin I bought. I totally get what you're saying dnix71 on the charging and that so I will look into wiring to 24 or 48v. And no I don't have any specific 12v but I'm really not knowledgable about electricity so I didn't know how that effects your everyday stuff like the TV, DVD player, lamps ,cell phone charger, etc... The appliances are all gas so that's no problem. when I get back from there next wrk ill have an exact list of specs for the battery ah, inverter size, wire size, etc. It's only a weekend cabin and we don't use any more than 3kwh a day c usually either a 2 or 3 day weekend at the most. I just unplug the cabin and charge the battery bank through the inverter/charger with a Honda 3000 generator. It goes through the 3 phases of charging into float mode after a couple hours of chargingevery couple weeks.

The other thing I would ask you both is if you had the battery and inverter setup I have, how would you change it for yourselves? What would you change without starting from scratch so I don't have to throw away 12 good batteries? If I have to start from scratch what kind of battery and inverter setup would you use in case you never used solar. Also thank you for not making me feel like an idiot for not being knowledgable on this subject.

joestue · « **Reply #4 on:** November 16, 2014, 05:06:05 AM »

it is not dangerous unless by safe you mean each battery is fused. and at 12 volts you can use regular automotive fuses, and its very difficult to shock yourself, so i don't know why anyone would think its dangerous.

it is also not difficult to setup the batteries correctly, but you should have a star connection of equal wire length for each string of two batteries.
like this, but with 6 volts and two batteries per string
http://forum.solar-electric.com/attachment.php?attachmentid=1652&stc=1&d=1299627623
or like this http://www.canalworld.net/forums/uploads/gallery_2174_346_3657.gif

Flux · « **Reply #5 on:** November 16, 2014, 11:58:19 AM »

If you have the kit, stick with it. Upgrade if you ever need to change the inverter.

Parallel strings are not a problem, series ones always are and unless you use equalisers for every series battery you will have to baby sit them, monitor them and equalise them somehow if they get out of step.

There is only one issue with lots of strings in parallel, the end connections to each string all need the same resistance so don't run link bars and connect at random. The correct way is as shown in the link from joestue with the star connections fanning out with all the leads the same length.

Fit a fuse sized for your inverter and not much bigger in the total supply lead. Fuses in each parallel string seem like a good idea and may be some use if you do something silly, but in normal life they will never blow even if one battery drops a couple of cells.

2400W is big for 12v but if they make an inverter that size you need 250A to power it so what is the danger.

Batteries are dangerous if you do something silly so treat them with respect but a parallel bank is no worse than a series one of the same capacity.

Flux

dnix71 · « **Reply #6 on:** November 16, 2014, 03:52:09 PM »

The reason I asked about using 12v directly is that 12v appliances are common. Since you have an unusual number of batteries, if you used 12v lighting and refrigeration you would not need an inverter. I run that way I real life. 12v compressor fridge, 12v led lights and 12v car charger to run my laptop. You say you have gas, so that takes care of cooking. I have piped in city gas and cook that way. Your hot water could easily be made with a gas fired spot heater.

You haven't said how you get water. An NSF rated 12v Sureflo water pump costs less than $100, but a 12v Dankoff well pump assembly would be closer to $700. 24v well pumps are more common because doubling the voltage cuts the wire size requirements a lot.

The other advantage to going direct 12v is that if your inverter goes out now, you have nothing. With 12v each appliance stands alone.

Jaust · « **Reply #7 on:** November 16, 2014, 05:08:41 PM »

I have no 12v except a couple lights in the kitchen that I run off a seperate 12v battery. I'm in a private park and the water is supplied. My stove, fridge, water heater and heater in the living room are all gas. I also have gas lights in every room.

Mary B · « **Reply #8 on:** November 16, 2014, 05:57:54 PM »

I have 16 6v batteries, 4 in series for 24 volts then 4 strings in parallel. Went to that from 12 volts to drop the need so extremely large copper wires. Every bank is fused on each end for safety with a 100 amp fuse. bus bars are solid copper and the fuses bolt onto the battery and onto the bus bar for super short leads. I feed the bus bars from opposite ends to balance out the current draw/charge.

madlabs · « **Reply #9 on:** November 16, 2014, 06:28:59 PM »

I had a bank of ten 6V batteries for years, wired for 12V with a 2500 watt inverter. Then I upgraded to 48V system and now have 16 batteries. They were all used so I don't mind the problems with such a big bank, and I equalize regularly.

When I buy new batteries I'll get just 8 bigger ones. 16 is too many for good balancing. But it all works and as long as you proeprly fuse, select wire guage etc, there is nothing dangerous.

Jonathan

Jaust · « **Reply #10 on:** November 17, 2014, 12:57:35 AM »

Thanks for the input all. Some great info and offgrid is new to me. I pretty much got ripped apart on another forum for even having a 12 setup, even though it came setup that way in the cabin I bought in July. I am thinking now of going at least to 24v with the batteries I have and then when it's time to replace them I'll look at maybe even going to 48. I would probably also look at investing in bigger batteries to have a smaller bank.

madlabs · « **Reply #11 on:** November 17, 2014, 01:27:09 PM »

I wouldn't change voltage until you have outgrown your inverter, or if it blows. When it does, I would consider jumping to 48V. That's what I did, I used whatever 12V stuff I could lay my hands on when I was just moving off grid. It was cheap and available. Once I got a good system going I started saving up and buying parts to upgrade as I could find good deals, and then finally did the change.

Not too much stuff is being made in 24V any more. Most things are going to 48V. For me, the savings in copper and such aren't worth it to go 24V, but they are for 48V. My .02.

JOnathan

Edit: Just to add, a 12V system is neither inherently dangerous or safe. Nor any other voltage. To be as safe as possible, all system, regardless of voltage, need to be designed right, built right, used right and the operator to know all this and take the proper precautions.

Bruce S · « **Reply #12 on:** November 17, 2014, 02:34:47 PM »

Welcome to the forum too .

We try NOT to make people feel like Idiots , we've all been there and had to learn too.
I can't really add anything to what others have said.
Except like FLUX said treat the batteries with respect and you'll be just fine.
1 thing you might want to do,,, check on ALL of the 12Vdc items you plan on having connected to the inverter, ADD the power-on or instantaneous power-on which is normally the max they are rated at, add them all up for Max current and see if that inverter charger is over sized ( not a bad thing really) but if it's running idle most of the time , then possibly you could go with a unit more correctly sized to your max load plus say 25% for growth.
IF however you want to use just the items you've already listed and not purchase extra "stuff" then you should be okay.
BTW:: How is everything being charged? I may have missed that part of the post.
Cheers
Bruce S

Jaust · « **Reply #13 on:** November 17, 2014, 07:27:05 PM »

Thanks again all for some great info. Madlabs, I felt the same way as far as safe or not. I figured dealing with batteries and electricity is dangerous either way if not treated with respect. The gentleman who I bought my cabin from did a great job as far as wiring size, connections, venting, etc.. And I make sure to keep the batteries in the best shape I can. They just made me feel like an idiot even though I've come to these forums to learn about my system and what's the best setup for my needs and have found the people in this forum not only to be knowledgable but willing to share that knowlege and I thank you all for that. And Bruce S, I have at Honda 3000 genny that came with the cabin that I charge the batteries with at this time.

SparWeb · « **Reply #14 on:** November 21, 2014, 02:36:28 PM »

Jaust,
Welcome to the forum.
As you can see, practical matters are what concern us, here. So far, we've kept the shouting to a minimum.
Great starter setup, too, by the way. Keep an eye on it like they say, and you won't need to upgrade for a while.

OperaHouse · « **Reply #15 on:** November 21, 2014, 05:12:51 PM »

I missed that too. Sounds like you are just using a generator to charge the battery. As you get into it more you will better understand what your needs are. There are alternatives to what people usually recommend. I have lights, refrigeration, hot water, ventilation and pumping from PV and only have a single car battery at my camp where I stay for 5 months. Don't feel I'm missing anything except I have to fire up the gen to do laundry. Might solve that next year.

Jaust · « **Reply #16 on:** November 21, 2014, 07:46:05 PM »

Thanks guys. Hopefully next year I'll be able to get the solar set up. We've only had the cabin since July so I am keeping an eye on the sun position so I can get the best placement. I'm just learning about the inverters and finding out about the power draw even when I'm not using anything in the cabin and was wondering at least during the summer would I be better off turning off the inverter during the day and saving that battery draw. All of my appliances are gas so the only time I'm using my lighting and TV and such is later at night after it gets dark because we spend most of the day outside on the creek.

thirteen · « **Reply #17 on:** November 21, 2014, 09:20:44 PM »

I will suggest that you keep a notebook record of your usage and any changes you may make. Length of genset running to charge stuff. Voltage record, water used in batteries, date of cleaning of the batteries. Little things like that help when you try to remember things a year after you changed something. A wall note pad would work or something like it. Ink pen on the wall writing used alot. A pair of safety glasses hanging on the entrance to where the batteries are my just save an eye . Just a simple idea. 13

SparWeb · « **Reply #18 on:** November 21, 2014, 10:15:35 PM »

My inverter (a Xantrex 4024) has a stand-by mode that I use often. It stops running when the load is less than (about) 20 watts and won't start again unless a 30 watt load is switched on. This saves a huge amount of battery life because leaving a 4024 turned ON draws 30 watts anyway. You just have to get used to the delay before the lights come on, because the inverer in standby only tests the line once every second.

If your inverter doesn't have a setting like that, you might be able to rig up an on/off switch anyway, it may have a connector for a "remote" or "standby" switch. See if you can download the manual for the unit (good luck with the current Schneider website though). If the user's manual is impossible to find, maybe a member or two here have a copy, so just ask. Xantrex inverters are pretty common with the RE crowd - not so much as they used to be though.

OperaHouse · « **Reply #19 on:** November 22, 2014, 09:19:52 AM »

There are remote fob transmitters on ebay. A good project would be having couple remotes around the house. That turns on the inverter. Five minutes after no current is drawn from inverter, it shuts off.

Jaust · « **Reply #20 on:** November 22, 2014, 10:32:24 AM »

Great advice guys. I like the idea of a remote in the cabin. I have a Xantrex and I do have the manual. I read it when I first got the cabin before I knew anything about inverters and I plan on reading it again when I'm up the for Thanksgiving weekend now that I know more about it. I have started a notebook to keep track of all my wattage useages, battery maintenance and such as I can barely remember what I had for dinner last night. I'm also looking at a monitor for the batteries to mount in the cabin because right now besides sticking my meter on them when I first arrive, I don't have any idea of how much draw down I'm putting on them over a 2 or 3 day weekend. I can only guess by doing some math and how long it takes the inverter/charger to go through the first 2 stages and into float mode. How do you all keep track? Or if you have solar also do you get your readings from your charge controller?

SparWeb · « **Reply #21 on:** November 22, 2014, 10:01:29 PM »

Nice to hear from someone who isn't afraid of a little math. Yes that will be enough to get you familiar with the needs and the current status of the battery bank.
If you can sort out the capacity of the batteries in Amp-hours, then you can also do some checking on the relative size ratios. By that I mean that you can compare the battery capacity "C" with the current drawn by the loads and the recharge delivered by the supplies.
Generally, an inverter that draws more than the "C" rate is probably overloading them, or a charger that puts less than "C/20" is undercharging them.
The next numbers to get used to are the voltages associated with various states of charge.
I'm attaching a handy article, one that helped set me off on the right foot.

birdhouse · « **Reply #22 on:** November 23, 2014, 05:21:27 PM »

Quote

How do you all keep track?

i don't really. i bought a cheap chinese back lite digital volt meter that is hooked to the bank. you can get a pretty good idea of state of charge by glancing at it. i leave it on all the time while i'm using my off grid place. you can learn quite a bit about your bank by watching the voltage change as various loads are added and removed.

+1 on running with your current set up. unless you want to spend a few thousand on a new inverter/charger just to be able to switch voltages. some fuses might be good to add.

adam

madlabs · « **Reply #23 on:** November 24, 2014, 02:07:03 PM »

You can get a battery bank tracker. They do drift off over time and then you reset it.

What I do is I have delveloped a feel for how fast my batteries charge. So if I turn on the genny and the volts stay low (13 volts or so) they are really hungry. If it jumps up to 13.8 or higher, they need some charge but aren't too hungry. If the volts pop up to 14.4 then they are 80-85% charged. Now, all of these numbers depend on the constant current of using your genny. So when on solar power, I take a look at the volts AND the incoming amps to see how the bank is doing.

And of course, I add in the factors of how much power did I use last night? Did the batteries get a full charge yesterday? What is the weather out look, etc.

It's intimidating at first, but if you frequently check your system and are observant you will quickly develop a feel.

Jonathan

Jaust · « **Reply #24 on:** November 24, 2014, 06:57:44 PM »

Good advice, Thanks Jon. I just picked up a kill-a-watt today so I can get an exact reading on my power usage. Then I'll get a better idea of my total Kwh usage per day and like you said you'll just get a better idea of what the batteries are doing.

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Author Topic: A Little Advice (Read 7233 times)