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windowexperts asked

Which AH rating do I use when connected in Series?

I have 4, 6v deep cycle, 200 ah batteries in series/parallel. Since they are 6v each, I realize that I have a total of 400 ah collectively. That means that I have 200 usable ah before needing to recharge.

When configuring the Vicktron 712 Battery Monitor, would I use the 400ah setting?

I am just making sure that I should not be using 800ah as my setting since they are 6v batteries connected in Series.


battery capacity
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solgato avatar image solgato commented ·

It’s the Capacity spec @ 20h you want to input when setting up the 712 and not Reserve Capacity, so make sure the 200ah is the Capacity spec and not the Reserve Capacity Spec.

Capacities/Amps remain the same when wired in series with Voltage doubling, and the opposite when wired parallel, so then you have 2x6V@200 series=200 @ 12V plus another 2x6V@200 in series=200 @ 12V. The two banks in parallel then combine for a total of 400 @ 12V.

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Mark avatar image Mark ♦♦ solgato commented ·

The advice in the 1st line is incorrect.

Reserve capacity is a time rating, indicating how long a battery can power a constant 25A load for. A load of 25A is used for this test/metric, regardless of the battery size, which may be quite high for smaller batteries. The reserve capacity time rating is not entered into a BMV.

With regards to the BMV, you need to enter the batteries energy capacity at the constant 20h discharge rate. The constant discharge current (over the 20 hours) will vary depending on the particular battery capacity. The battery capacity is calculated from the constant current x 20h to provide the total battery capacity rating (in Ah). This is the most common metric provided with batteries designed for cyclic use.

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solgato avatar image solgato Mark ♦♦ commented ·

Sorry, my bad. I fixed the info. I meant to say @20Hr but that stupid RC rating @25A came out instead!

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Mark avatar image Mark ♦♦ solgato commented ·

I thought that it was most probably just a typo - no problem.

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zuzullo avatar image zuzullo Mark ♦♦ commented ·

Hi guys, Is this a value that is normally written on the battery?

I have a few ones one mine but cant relate to your guidelines :/

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solgato avatar image solgato zuzullo commented ·

From that sticker the capacity appears to be 80ah. As you can see they also provide 350Wh @20h which is the kind of confusing info I talked about in a previous post about battery specs and setting up the BMV-712. The consumer battery market uses all kinds of specs that can cause confusion, so if one is concerned about using the correct info, I suggest using the internet to find specs on a particular battery instead of using the sticker.

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zuzullo avatar image zuzullo solgato commented ·

Thank you as well for your input Solgato :)

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Mark avatar image Mark ♦♦ zuzullo commented ·

I'm not very familiar with any unique ratings on marine batteries, but the info on your battery is quite weird for me...

It is common & OK to provide a battery capacity rating in kWh or Wh (instead of Ah) & this is simply obtained by multiplying the Ah rating by the voltage. So in this case 80Ah x ~12v = 960Wh or 0.96kWh.

This is a lot higher than 350Wh as stated on your battery - so I have no idea what usage/test scenario the 350Wh relates to...

If the battery is about the size of a big 4WD deep cycle battery (which is what it looks like to me) then roughly speaking it should be about 65 to 80Ah @20h discharge rate.

I also tried to quickly look up a data sheet for your battery, I did find one but not one in English. Regardless it is not much help & did not provide the more detailed information/clarification I expected.

If it were me, I would logically assume the 80Ah to be the 20h discharge capacity rating and proceed with that.

You could also try to contact the manufacturer directly to request a proper detailed data sheet &/or clarification.

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zuzullo avatar image zuzullo Mark ♦♦ commented ·

Hi Mark, thank you. The answer from the battery manufactor was "C20 is 80Ah". So the value to insert on the BMV is 80.

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2 Answers
Mark avatar image
Mark answered ·

If you have 4x 6v 200Ah batteries wired in series/parallel configuration, the final battery bank will be 12v 400Ah. The BMV simply treats the battery bank as one large single battery.

Accordingly you should enter 400Ah into the BMV setup, regardless of the fact that you will not discharge the batteries to below 50% SOC.

You can then set the 'discharge floor' on the BMV to 50% and the 'time to go' calculation will consider this discharge level in that calculation.

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boekel avatar image
boekel answered ·
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