Voltage drop from wire connecting 12 batteries in series 2V vs 6V

[JocelynQC]

HI, my question is similar to "Voltage drop from wire connecting batteries in series" but different.
I presently have 12 x 6V battery (400 amp/hr) for my off grids install. 3 banks of 24v.
I have to change them, I was looking at replacing with only 1 Bank, of 12 x 2V battery at 1200 Apm/hr, To simplify maintenance (less cells) and imbalance (parallel banks)
My question is: What would be the the voltage drop due to the interconnects? What amperage do I use to make my calculus?
Example, if I draw 10 amps at 120 (which is usual for me, its a house not a cabin), its 50 amps at 24V, do I use 50 amps to compute the voltage drop (in %) or 2V (my individual battery)? (Battery interconnect would be around 12 inches)

Tks for any help

Jocelyn Hould

 

[barry]

do I use 50 amps to compute the voltage drop (in %) or 2V

Your question doesn't make any sense. You're equating current and voltage. Maybe you need to restate your question.

 

[JocelynQC]

you are quite right
correction:
How many amps do I use to compute the voltage drop: 24 (the total voltage of the serie, which gives 50 amps), 2 (my battery voltage, which gives 600),or else?

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oops, what do I have today? Sorry my correction was still confus(ed)(ing)

How many amps do I use to compute the voltage drop due to the battery interconnects of the described system when there is a load of 10 amps at 120V on the inverter:
- 50 amps (amperage of the load at 24V)
- 600 amps (amperage of the load at 2V)
- Else?

Tks

 

[ads-ee]

Your wire losses are directly related to Ohm's law, if you draw 50A then a 2AWG cables that have less than 0.2 mOhm/ft will only drop 10 mV (0.0002Ohms * 50A with 1 ft cables). It's the reason autos usually use 2AWG cables for the starter motor as it can easily draw upwards of 100A to way over 200A if the engine is really cold (they also have much longer cables connecting everything so more ohms of cable loss).

If you are using something smaller than 4AWG with 50A your likely going to have issues with overheating of the cables (with potential melted insulation and eventual shorts/fires).

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Also using 12 2V batteries in series to get your 24V is likely to be less efficient as all batteries have internal resistance and placing them in series means you are adding up the battery resistances. I would say having multiple banks of 12Vx2 for 24V would be better. The 24V would have far less source resistance with that configuration.

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10 amps at 120V on the inverter:
- 50 amps (amperage of the load at 24V)
- 600 amps (amperage of the load at 2V)
- Else?

Tks

You are still confused....

You don't have 600 A on each 2V battery in series, that would be 1200 VA from each battery since the current is the same for all the batteries in series. I kind of doubt you need 14.4KW from your batteries as you are only producing 1200 W from the inverter.

Due to losses you will also see more than 50A from 24V, not an expert in this area but I would at least add at least 10-15% to that amperage to account for the inverter and other losses, you don't end up with melted wires and fires.

With 12 2V batteries in series you will have 50A through each battery. The original design has 3 banks of 4x6V so each battery only has to supply 50/3 = 16.7A. Your design is going to have lots of battery heating issues and will have short battery life span.

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You might also consider using 3 banks of 2x12V for half the number of batteries.