12 volt battey bank

Gregb · August 2013

I have 10 100 watt 12 volt panels , EPsolar Tracer 4210 Mppt. Auto recognition 12/24 volts ,
the tracer will handle 500 watts at 12 volt and 1040 at 24 volts. Can I run 5 strings of two panels in series to the controller and will it still send the correct voltage to the 12 volt battery bank?

BB. · August 2013

Re: 12 volt battey bank

Welcome to the forum Greg.

With the MPPT charge controllers we usually talk about here on the forum (typically US designed), they are designed to limit their output current to rated load, and usually will back off on output current if they are running hot.

So, while there is no maximum input current limit for the solar array, there is a rough maximum cost effective solar array... For a 40 amp MPPT controller charging a 12 volt battery bank, I would have suggested:

40 amps * 14.5 volts battery charging * 1/0.77 panel+controller deratings = 753 Watt array "cost effective" maximum array.

In fact, many of these controller have been designed to be used as down "converters" -- You can have a 24 or 48 volt battery bank, and use the controller to charge a 12 volt battery bank (run 12 volt radios, etc.). Batteries, relatively, have very high output current available and the "US" MPPT controllers will work just fine.

Looking at the Manual for this controller (PDF--If I got the right one), specifically says that the controller will disconnect the solar array if there is too much current available from the array.

They very clearly say that the maximum solar array is 520 watts for this controller on a 12 volt battery bank. Working backwards:

520 Watts * 1/40 amps = 13 volts nominal battery charging voltage at maximum current (ignoring losses).

Anyway--I guess that you can run any combination of ~520 watt array from Vmp~17.5 volts to Vmp~66 volts or so for a 12 volt battery bank (I have not gone through the manual in detail--so I may be misreading some of the information).

The operational description does not make 100% sense (is the input limit based on current or power--I.e. if you run a 520 watt array at Vmp-array = 52 volts--That would be Imp-array of only 10 amps--So could you run the array at ~4x the wattage and not have any problems? -- I don't know.

-Bill

niel · August 2013

Re: 12 volt battey bank

the simple answer is no because the controller is limited to 500w at a 12v output and if you intend to use all of the inputted power. it would work even though the full power of all of the pvs would not be realized for the batteries. you would need 2 of those controllers to handle that much power and then there would be a configuration problem as you can't run 2 and a half strings of 2 in series.

Gregb · August 2013

Re: 12 volt battey bank

The panels have a imp 5.29 I will be adding 2 more 100 watt panels and one more 40 amp MPPT controller to make six stings of two. then have three strings of two wired to each controller.
my concern is feeding the controller with 24 volts and having a 12 volt battery bank. Thank you for your time helping me on this.

BB. · August 2013

Re: 12 volt battey bank

It "should" work fine--That is what MPPT controllers are used for (down converting Array voltage to Battery voltage efficiently).

But, you might have to buy the controller and see if it works. Unless somebody here has tried it already.

-Bill

Gregb · August 2013

Re: 12 volt battey bank

I will be adding two more 100 watt panels and a additional 40 amp Mppt controller then splitting the six strings of two ,three to each controller The IMP on each panel is 5.29 amps my only concern is bringing 24 volts from the panels to the controller . Will the controller feed the battery bank with 12 volts or 24 volts. Im using 10 Everstart 27 DC deep cycle Marine batteries wired for 12 volt.

BB. · August 2013

Re: 12 volt battey bank

That is what the controller is supposed to do (change 24 volts at 5 amps to 12 volts at 10 amps -- i.e., 120 watts in = 120 watts out).

You can do the testing anyway... As long as the Battery is not feed too much current (say over ~40% of its amp*hour capacity--example: 100 AH * 40% = 40 amps maximum) during testing--The battery will simply clamp the bus voltage to ~12.5 to 15.0 volts.

If you leave the controller pumping current into the battery bank--It will over charge the batteries and cause them to gas, and significant wear from over charging.

-Bill

WillBkool · August 2013

Re: 12 volt battey bank

I think that you will have trouble with 10 12v batteries in parallel. Could you go to a 24v system? Even then, you would have 5 parallel strings of batteries.

Gregb · August 2013

Re: 12 volt battey bank

The battery bank gives me 1090 ah@ 12 volts and I have a 5000 watt pure sine wave inverter that is 12 volt to 120 volt. A this point with what I have invested i don't want to change to a 24 volt bank. The only reason I want to run the panels a ta 24 volt set up in six strings of two, is to save on the wire size from the location off the panels to the charge controllers.

Gregb · August 2013

Re: 12 volt battey bank

So 10 109 amp hour batteries for a total off 1090 ah @ 40 % = 436 do I use the ah for the total bank or the ah for just one bat for the total charging amps?

Cariboocoot · August 2013

Re: 12 volt battey bank

Two things:

WillBKool is absolutely correct about ten parallel batteries. This is failure waiting to happen.

A 5kW 12 Volt inverter is a horrible idea. If you were to actually run it at that rate it would draw over 400 Amps, require parallel DC wiring, 'flatten' the batteries very quickly, and produce a lot of heat for the power rather than work. This is marketing at its worst: selling people on the idea that more Watts is automatically better. Odds are the brand is AIMS.

When calculating recharging current peak you use the total Amp hour capacity of the battery bank. So in this case it would be 1096 Amp hours * 0.1 = 109 Amps peak current. No single charge controller can handle that. At 80 Amps max it would work providing loads aren't too heavy and the DOD not too deep.

I'm going to suggest you re-evaluate the whole system, starting with the loads in Watt hours per day and peak Watts required. Frankly, this set-up has "bad idea" written all over it. This is the sort of thing I get called in to fix, throwing out practically everything while the owner complains that somebody (inevitably whoever sold it) told them it would work.

Just trying to save you headache and heartache.

Gregb · August 2013

Re: 12 volt battey bank

Thanks for getting back to me on this . I have no one to blame but me. I was looking for the most, for the best price.So with 12, 100 watt panels and 10, 109 ah batteries 2, 40 mp Mppt controllers what would do you.

Cariboocoot · August 2013

Re: 12 volt battey bank

Gregb wrote: »

Thanks for getting back to me on this . I have no one to blame but me. I was looking for the most, for the best price.So with 12, 100 watt panels and 10, 109 ah batteries 2, 40 mp Mppt controllers what would do you.

I'd go up to a 24 Volt system if at all possible. Here's why:

1). The current required to supply any given amount of Watts is basically cut in half, with a resulting increase in efficiency due to less conductor heating.

2). The ten batteries would be reconfigured as only five parallel strings of two. Not perfect, but still half the parallel connections. You would still want to use positive and negative bus bars, equal length wiring, and a battery post fuse on each string.

3). The panels are capable of being configured as six strings of two in series. Again you will want fuses or breakers on each panel string as there are more than two parallel connections.

4). The charge controllers can output 40 Amps at either 12 or 24 Volts. The difference being you'll have 548 Amp hours @ 24 Volts instead of 1096 @ 12 Volts. This is the same equivalent power, but less current is required in charging. You should be able to get 38 Amps @ 24 Volts from your 1200 Watt array. This would require only one 40 Amp charge controller. It would be a peak charge rate of about 7%; not ideal, but viable.

In considering this, you might want to drop one string of batteries if you can manage it. 436 Amp hours @ 24 Volts would be up to about 4.7 kW hours AC, which is quite a bit of power. My system runs approximately half that and supplies all needs but I would welcome doubling the battery bank and the 300 more Watts of solar you will have.

vtmaps · August 2013

Re: 12 volt battey bank

You have been warned that 10 parallel batteries is a bad idea.
To understand why read: http://forum.solar-electric.com/showthread.php?14674

--vtMaps

Gregb · August 2013

Re: 12 volt battey bank

Ok if i wire my battery bank into 5 parrallel strings of two i will still have a 12 volt bank. I don,t expect to use the full 5kw of the inverter but the cost was reasonable at the time . Being new to all this I can use all the help I can get. Thanks, where can I get the buss bars?

Cariboocoot · August 2013

Re: 12 volt battey bank

Gregb wrote: »

Ok if i wire my battery bank into 5 parrallel strings of two i will still have a 12 volt bank. I don,t expect to use the full 5kw of the inverter but the cost was reasonable at the time . Being new to all this I can use all the help I can get. Thanks, where can I get the buss bars?

If your batteries are 12 Volts and you put two in series you then have a 'string' that is 24 Volts.

Give this thread a read: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

Related thread but about panels on an MPPT type controller: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

Bus bars are often something you have to make, as they need to be specific to the particular installation. In this case they'd need enough space to accommodate five connections from batteries (large), one from the inverter (large), and one or two from the charge controller(s) (smaller).

In pre-made bus bars you might try a local marine supply store. Look for Blue Sea products. Something like this one: http://www.bluesea.com/products/2723/DualBus_Plus_150A_BusBar_-_5_16in-18_Stud_5_Gang

Blue Sea also makes battery post terminal fuse blocks.

kenputer · August 2013

Re: 12 volt battey bank

These MPPT controllers can take PV input of 150 volts , 2 strings of panels 1 controller 24 volt bank or 12 volt with 2 controllers.

waynefromnscanada · August 2013

Re: 12 volt battey bank

Gregb wrote: »

Ok if i wire my battery bank into 5 parrallel strings

NOT good idea at all! Anything over 3 parallel strings is bad news, becomes almost impossible to get the strings to properly share load and charge currents. Even 3 strings can be a serious problem, and the result is shortened battery life. Use bigger, but fewer batteries if at all possible - - or prepare for premature battery failure.

Blackcherry04 · August 2013

Re: 12 volt battey bank

Parallel Strings do not work, so says the people that do not have them. I have had them for 30 years and NEVER had the problems that are posted here. Good Luck to you. I have more than 50 customers that all have 4-6 in parallel I never see one bank that does not function correctly. I do like to number mine and shuffle them once a year and clean all the connections, thats battery maintenance.

niel · August 2013

Re: 12 volt battey bank

gregb,
don't forget that in going with a 24v battery bank that you would need a 24v inverter. i say why stop there and go to 48v on the battery bank and get a 48v inverter. they do cost more though, but it is better utilization of your batteries and pvs. you can resell the present 12v inverter in the for sale section or keep it just in case. of course you would need to either add two more batteries or subtract two batteries to utilize a 48v battery system as they would be in multiples of 4 12v batteries per string then.

waynefromnscanada · August 2013

Re: 12 volt battey bank

Blackcherry04 wrote: »

Parallel Strings do not work, so says the people that do not have them. .

True, I now have a series string, but that didn't happen until after the experience of a 3 string system. And yes, I was VERY careful to have equal length cables etc, the works. Mostly it was OK, but not totally, and now I'm much happier with the single string, no more worries about unbalanced current flows. But to each his or her own.

Cariboocoot · August 2013

Re: 12 volt battey bank

Noto Bene:

It is not a case where parallel battery strings absolutely do not work, causing the system to fail to function from Day One.

It is a case where the more parallel battery strings you have the more likely you are to develop problems with the system over time as resistance inevitably changes per string.

The higher the system Voltage the less the effect of these resistance differences.

Ten parallel batteries on a 12 Volt system is asking for trouble early on. It is best to keep the number of parallel batteries down to two here, as this Voltage will notice the effects most dramatically.

For a 24 Volt system it is reasonable to expect four parallel batteries will work fine over the expected lifespan providing they are installed properly to begin with and maintained.

For a 48 Volt system you could probably go with eight. But at that point you have introduced a lot of extra wires and connections and the hassle of dealing with same may not be worth it over the simpler method of just plain using larger batteries to begin with.

Gregb · August 2013

Re: 12 volt battey bank

How about if i run the batteries in 5 strings of two still running 12 volts into two large buss bars then tap into the bars in the center for the inverter?

Blackcherry04 · August 2013

Re: 12 volt battey bank

Rather than being in the weeds on the viability of Parallel vs Series, trying to run any Inverter above 1500 watts or so @ 12 V with continuous output will be a failure. The voltage sag alone would kill the system in a couple minutes. Short term, you can run a Microwave, toaster or a coffee maker, but any system with less than a full charge will struggle to handle it regardless of the cable size. 5000 Watt Inverter, the batteries might handle the surge for a few seconds. We have a rule on high current items, if it's more than a Minute, start the generator. The problem is the Batteries cannot release enough current fast enough, so you get the Dip and Recovery syndrome.

Cariboocoot · August 2013

Re: 12 volt battey bank

Gregb wrote: »

How about if i run the batteries in 5 strings of two still running 12 volts into two large buss bars then tap into the bars in the center for the inverter?

There's nothing to be gained by that.

When you put two 12 Volt batteries in series you get 24 Volts. The only way to get 12 Volts from them then (aside from using a converter) is to use one half or the other; you can't tap a bus bar with 24 Volts on it anywhere and get 12 Volts.

As Blackcherry says a 12 Volt inverter trying to supply high Wattage draws a lot of current, and that in turn will pull Voltage down. Remember my mentioning the problem with 5kW on 12 Volts? When you get up to only 2kW you're looking at over 167 Amps, and trying to sustain that requires a good size battery bank and really good wiring.

It is best to avoid 12 Volt systems unless there is a particular need for the 12 Volts as in a mobile application like an RV.

12 volt battey bank

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