voltage of a fully charged lead acid battery

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voltage of a fully charged lead acid battery

Postby davilara on Mon Oct 22, 2018 10:32 am

I just bought a multi-meter to check my lead acid batteries and wonder if by opening the DC breaker to the Inverter I can make valid battery voltage readings without disconnecting the batteries from each other?

I regularly check specific gravity, by the same token I wonder if I can make valid SG readings without disconnecting the batteries from each other?
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Re: voltage of a fully charged lead acid battery

Postby JRHill on Mon Oct 22, 2018 11:02 am

As long as your SGs show the batteries are achieving a sufficient recharge and the dispersion of the readings is close, the voltage readings won't tell you much. But having the meter around will certainly be useful for other stuff.
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Re: voltage of a fully charged lead acid battery

Postby mikedowdell on Mon Oct 22, 2018 11:33 am

Opening the DC breaker will open the circuit so yes it will effectively disconnect the in series batteries from each other as there is no return path. Those batteries in parallel however will still have an effect on each other. You also want to wait for the batteries to settle after a charge, and without a load before making your voltage measurements, which can take hours. In general, 2.11 volts per cell is considered fully charged (aka 12.7 for 6 cells) however different batteries will have different readings and the voltage does not offer a complete picture by any means.
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Re: voltage of a fully charged lead acid battery

Postby davilara on Mon Oct 22, 2018 2:34 pm

Thank you both for your prompt reply.

I was looking also for where to measure the voltage as by looking at the template supplied by the battery manufacturer it seem like it shall be verified at the cells. The following YouTube video shows how it is done, so checking at the cells level is not unusual.

https://www.youtube.com/watch?v=_8qgZoovWHI

I enclosed as an attachment the prior measurements.

I have two battery banks each with eight (6V) batteries in series as shown in the attached image. I believe if the DC breaker is off then they are not in parallel. Any comments?

Any additional comments regarding the procedure as well as the interpretation will be welcomed.
Attachments
MA9 Solar System.jpg
Rolls-S550 Inspección Baterias 7.17.2018jpg_Page1.jpg
Last edited by davilara on Mon Oct 22, 2018 4:25 pm, edited 1 time in total.
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Re: voltage of a fully charged lead acid battery

Postby Mike Curran on Mon Oct 22, 2018 4:57 pm

davilara wrote:I was looking also for where to measure the voltage as by looking at the template supplied by the battery manufacturer it seem like it shall be verified at the cells. The following YouTube video shows how it is done, so checking at the cells level is not unusual.
I watched the YouTube video and I would be extremely leery of sticking metal probes down into each cell to get per-cell voltages. You can much more safely determine whether one or more cells is low by taking a reading across the entire 6 volt battery, after all if one cell is bad, you're going to replace the entire battery anyway. I don't see the advantage of taking per-cell readings unless you're a battery researcher or somesuch.
davilara wrote:I have two battery banks each with eight (6V) batteries in series as shown in the attached image. I believe if the DC breaker is off then they are not in parallel. Any comments?
Not necessarily. If your battery banks' positive terminals are tied together before the DC breaker, they will still be connected in parallel even with the breaker open. See attached sketch.
1540252567444-2145971469.jpg
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
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Re: voltage of a fully charged lead acid battery

Postby davilara on Mon Oct 22, 2018 5:44 pm

The recommendation to taking a reading across the entire 6 volt battery makes sense to me as the batteries will be tested while not being charged.

- If your battery banks' positive terminals are tied together before the DC breaker, they will still be connected in parallel even with the breaker open.

I understand the statement. It is exactly as suggested Outback wiring diagrams as follow. As you can see there are two DC Breakers but also looks like they are connected at the shunts.

Maybe disconnecting the poles at the ends of each battery bank will be good enough but if not necessary that would make it easier. This would be good to know.

The requirement to remove surface charge is something new to me, your comments will be welcomed.

https://www.batterystuff.com/kb/article ... ics.html#6
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Re: voltage of a fully charged lead acid battery

Postby Mike Curran on Tue Oct 23, 2018 8:52 am

If you're determined to take voltage readings, then all you need do is disconnect one positive lead from one of your two battery banks [along with opening the 2 (?) DC breakers]. All other connections can be left as is.

However, as JRHill says, specific gravity is the best way to judge the condition of your battery, NOT voltages. If you take SG's you need not be concerned about surface charge, whatever that is :smile: . Edit: I admit I have taken voltage readings but in conjunction with SG readings. I do not take them with the battery at rest OR disconnected from load, as I believe SG's will be essentially the same regardless.
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
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- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
- 12 Surrette/Rolls 2V x 1766Ah
- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

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Re: voltage of a fully charged lead acid battery

Postby davilara on Tue Oct 23, 2018 9:59 am

I do not take them with the battery at rest OR disconnected from load - love it. I use a refractometer to read SG, only one drop per cell is enough and works fine for me, easy and convenient.

As we joke at home - very much better!

Will take all your recommendations.

\:D/

Thanks.
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