questions regarding inverter and amps

[leewaytoo]

Hi,
I have 32 fortune batteries configured in 2p4s X four for 800ah's...12v. Overkill 120a BMS X four.
My inverter is 4000w- 8000w surge.
question is.............. are the amps drawn evenly from the batteries for the inverter when I use the 1250w microwave?
thank in advance for your replies.
r

 

[Bob B]

Probably not .... but you can mitigate that by making sure you wire the positive to one end of the pack and the negative to the other.

 

[Bob142]

If you wire the battery bank properly, yes.

See page 19 of Victron's Wiring Unlimited. The Posts, Halfway, and Busbars methods will give you equal current draw from each battery.

Wiring Unlimited

Wiring Unlimited is a great resource that covers many many common topics and questions relevant to DIYers. It is a free E-book from Victron Written by Margreet Leeftink. Check it out! Download

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This FAQ post will show you the math:

Battery FAQ

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[leewaytoo]

If you wire the battery bank properly, yes.

See page 19 of Victron's Wiring Unlimited. The Posts, Halfway, and Busbars methods will give you equal current draw from each battery.

Wiring Unlimited

Wiring Unlimited is a great resource that covers many many common topics and questions relevant to DIYers. It is a free E-book from Victron Written by Margreet Leeftink. Check it out! Download

diysolarforum.com

This FAQ post will show you the math:

Battery FAQ

If you have a battery question and it's not a "beginner" question please try one of the battery boards. Batteries play an important role in solar PV systems providing power while the sun is down or during peak demand hours with excess grid charges. During the day solar energy is converted by...

diysolarforum.com

thank you for the links................I forgot to state that the 4 2p4s banks are all connected to the same 1000a bus bars, with equal length cables.
So. it would seem from the reading of page 19 that I should be good. I use the android app for overkill bms to monitor and log the Ah's used for each bank. there is a difference, although not much.

tks again.

 

[Steve_S]

1250W ÷ 12V = 104.16A uncorrected for inneficiency, 120.44A corrected for 15%.
A battery pack, whether it is 1P4S or 2P4S will still behave the same with regards to load/charge handling which is limited by the BMS to 120A out & 60A in MAX per pack (and that is to limit, not suggested) FET Based BMS' should ALWAYS be derated by 20% for safety & longevity.

4 Equal packs should divide the load/charge by four, so that 120A draw will be 30A per pack in parallel.
Packs in Parallel will stay close to each other but individual pack voltages will float up/down during operation which is normal, as long as it is not excessive. IF all of a sudden one pack goes out of "sync" that is an indicator that something is wrong. It is quite normal to see some fluctuation / variation though, and seeing 1/2V difference is fine, more than that start looking at connections and links.
--** provided **-- the battery packs are identical in capacity & config. If using different AH packs things vary more at Hi/Lo ends of the voltage curve.

You stated that you have 4 packs 2P4S with 800AH. but not cell size.
Normal LFP specs are 1C Discharge & 0.5C Charge C-Rates. so for a 100AH cell based pack, that is 100A Discharge for 1 hour and 50A charge rate for 2 hours.

The general unwritten rule is to not exceed 250A draw from a battery bank (excluding surge handling).
This translates as 12V=3,000W, 24V=6,000W, 48V=12,000W

 

[leewaytoo]

1250W ÷ 12V = 104.16A uncorrected for inneficiency, 120.44A corrected for 15%.
A battery pack, whether it is 1P4S or 2P4S will still behave the same with regards to load/charge handling which is limited by the BMS to 120A out & 60A in MAX per pack (and that is to limit, not suggested) FET Based BMS' should ALWAYS be derated by 20% for safety & longevity.

4 Equal packs should divide the load/charge by four, so that 120A draw will be 30A per pack in parallel.
Packs in Parallel will stay close to each other but individual pack voltages will float up/down during operation which is normal, as long as it is not excessive. IF all of a sudden one pack goes out of "sync" that is an indicator that something is wrong. It is quite normal to see some fluctuation / variation though, and seeing 1/2V difference is fine, more than that start looking at connections and links.
--** provided **-- the battery packs are identical in capacity & config. If using different AH packs things vary more at Hi/Lo ends of the voltage curve.

You stated that you have 4 packs 2P4S with 800AH. but not cell size.
Normal LFP specs are 1C Discharge & 0.5C Charge C-Rates. so for a 100AH cell based pack, that is 100A Discharge for 1 hour and 50A charge rate for 2 hours.

The general unwritten rule is to not exceed 250A draw from a battery bank (excluding surge handling).
This translates as 12V=3,000W, 24V=6,000W, 48V=12,000W

yes they are fortune 100ah 2p4s configured into 4 "packs" for 12v. I wish the batteries would discharge equally. they do not. Although the app is not exactly exact.... it changes parameters on it's own sometimes.
thanks for your reply
r

 

[MisterSandals]

yes they are fortune 100ah 2p4s configured into 4 "packs" for 12v.

It sounds like you've wired them properly. But do you happen to have a pic? Sometimes (actually quite often) a few hundred pairs of eyes can spot something afoot (like at the Circle K).

Did you do any cell testing and matching before assembling your packs?
Did you top balance your cells?
How do the individual cells in the misbehaving batteries look? One or two pairs high/low or all? Does their voltages in the BMS app correspond to measuring voltages at the cells?

Just looking for clues...

 

[leewaytoo]

It sounds like you've wired them properly. But do you happen to have a pic? Sometimes (actually quite often) a few hundred pairs of eyes can spot something afoot (like at the Circle K).

Did you do any cell testing and matching before assembling your packs?
Did you top balance your cells?
How do the individual cells in the misbehaving batteries look? One or two pairs high/low or all? Does their voltages in the BMS app correspond to measuring voltages at the cells?

Just looking for clues...

I am not able to check the suggestions that you gave at this time... I need to use the batteries at this time due to the heat here, plus 110 yesterday and the day before..... I hope to be able to do so soon. tks for the directions.....
r