battery connections

zozomike · September 2012

Hello experts! Where can I find a good connection diagram for 12 each 6 volt ( cr225s) in a 24 volt system? Mine do not seem to be charging equally and I wonder If my configuration is the best. Yes I have equalized,
Thanks in advance
Michael

Cariboocoot · September 2012

Re: battery connections

Six parallel strings of two in series.
There's you problem: the chances of all six strings sharing current equally is about 'nil'.

You can see the different methods at this Smart Gauge site: http://www.smartgauge.co.uk/batt_con.html
Method #1 is always the wrong way to do it.
Method #2 works best when limited to two parallel strings.
Method #3 is the only choice for three parallel strings or more.
Method #4 really only works with four parallel strings.

In your case you substitute two 6 Volt batteries in series for each single battery shown.

But really you should go to higher Amp hour batteries and reduce the number of parallel strings.

westbranch · September 2012

Re: battery connections

Marc ah hem,,, "12 each 6 volt ( cr225s) in a 24 volt system" sounds like 4 - 6 volt cells X 3 strings = 12??

Cariboocoot · September 2012

Re: battery connections

westbranch wrote: »

Marc ah hem,,, "12 each 6 volt ( cr225s) in a 24 volt system" sounds like 4 - 6 volt cells X 3 strings = 12??

Right, right. So only three strings. Much better than six, but still possible problems.

(I'm restructuring the porch roof. Sure hope I'm not making that kind of math error there.

)

waynefromnscanada · September 2012

Re: battery connections

I've been using the #3 that Carriboocoot mentioned, on my six L-16 batteries in my 12 volt system.The only way to go with 3 strings. Works awesome and by the way, my batteries are now over 10 years old and still good to go!

inetdog · September 2012

Re: battery connections

Cariboocoot wrote: »

Right, right. So only three strings. Much better than six, but still possible problems.

(I'm restructuring the porch roof. Sure hope I'm not making that kind of math error there. )

Seen on a passing sweatshirt:

1. Measure twice
2. Cut once
3. &)($#^!
4. Buy more material
5. Repeat steps 1-4

BB. · September 2012

Re: battery connections

It is debugging time...

Here is a "list" and the order I would do them in. I highly suggest getting a DC current clamp meter (like this one or better) + DMM.

If flooded cell, check electrolyte levels (above plates, at least--not too full or you will have a mess). Charge again if added water.
Measure and log the specific gravity of each cell.
With a rested bank (a few hours of no load/charging) check the battery (or cell--if you can) voltages. Look for high/low voltage across cell/battery.
Turn on a heavy load and let run for a few minutes. Log voltages
Use DC Current Clamp to measure current in each battery string (and log).
Use a DMM set to 2.00 or 0.200 (200mV) full scale and look for excessive voltage drop across each connection/length of cable.
Turn of loads and start heavy charging. Log beginning voltages.
Log current through each string.

Now look at the above logs and find any differences. If most connections/wires have near zero volt drops and you see one with "high" voltage drop--check for dirty/loose/corrosion connections (or corrosion inside wire insulation).

Looks at the battery/cell voltages. A high voltage during charging can be an "open" or sulfated cell. Similarly, a low voltage during discharging can indicate open/sulfated cells.

You have been equalizing--Are the cells close together in specific gravity (around 0.015 to 0.030 maximum difference from high to low cells)? Are you charging/equalizing until SG stops rising (checking every 30-60 minutes)?

What is your solar array/charge controller's typical maximum charging current? What is the voltage/AH rating of your battery bank? Are you running around 5% to 13% of rated current (of 20 Hour AH capacity) as a charging current?

-Bill

zozomike · September 2012

Re: battery connections

BB. wrote: »

It is debugging time...

Thanks guys, it is debugging time, and I reckon I am the bug! Yes I will follow your suggestions.
Here is what I did a few years ago, (as configured diagram) not sure why I did it this way but was probably without adult supervision, and I actually added the last string almost a year after the original setup. Seems like I just need to make this change? (as revised diagram)
Michael
Attachment not found.

Cariboocoot · September 2012

Re: battery connections

Better, but still less than perfect.

Key here is to make sure that the wires between batteries are equal length and wires between battery strings are equal length.

Another hint: if you draw your diagrams with all the battery polarities the same way it's easier to understand, even though you have to have diagonal connecting wires.

BB. · September 2012

Re: battery connections

You have competing requirements here...

Marc is suggesting to rotate the batteries to minimize wire length (voltage drop). Short/heavy cables are ideal--along with equal current paths between each battery string.

The "problem" with short/low resistance wiring paths is that any differences between batteries (age, temperature, dirty/loose connections, etc.) will tend to "steer" the current more (i.e., a colder battery with slightly dirty connections will get less current that a warmer battery with "good" low resistance connections).

The other issue to review--Connections from the Inverter and Charge controllers should be short and heavy too.

The inverter takes lots of current and simply needs short/heavy wires for low voltage drop. For a 12 volt system, you probably want a maximum of ~0.5 volt drop, 1.0 volt for a 24 volt, and 2.0 volt drop max for a 48 volt battery system.

For charge controllers, you want short heavy wires so the the voltage drop in the wiring does not interfere with the accuracy of the voltage as read by the charge controller... Roughly, my suggestion is around 0.05 to 0.10 volts maximum drop for a 12 volt system and ~0.1-0.2 volt max for 24 volt, and 0.2 to 0.4 volt drop maximum for a 48 volt battery bank.

You can use a generic voltage drop calculator to play around with distances and wire gauges to see what "works best" for you.

-Bill

zozomike · September 2012

Re: battery connections

BB. wrote: »

You have competing requirements here...

Thanks so much guys, well here is a simplified diagram. The battery connects are all 02 x 14" even though NAWS invoice called them 02 x 12" and the string connects are all 02x 27" and currently the inverter connects are 02 x 5'. Since this is a vertical rack with each string on a separate shelf, I will have to go to 6' positive cables for the inverter and MX80. When I do that will I need to change the negative inverter and controller cables to be of equal length as the positive? Any issues with this plan? I am hoping to get another year from the batts as I want to add more pv next year ( currently 1980w Solar worlds) and would like to do all at one time of course. Attachment not found.
Michael
Attachment not found.

Cariboocoot · September 2012

Re: battery connections

The only wires that need to be equal length are those involved with parallel current paths. The negative and positive wires from the battery bank to the inverter and/or charge controller do not have to be equal length.

zozomike · September 2012

Re: battery connections

Cariboocoot wrote: »

The only wires that need to be equal length are those involved with parallel current paths. The negative and positive wires from the battery bank to the inverter and/or charge controller do not have to be equal length.

Thanks for your help. Iv'e ordered a DC clamp on meter, ( needed an excuse I guess) and the extra length cables I need to reconfigure the batteries. After I get things rearrainged I will run through the tests you outlined.
Michael

battery connections

Comments

Categories