Outage: Car battery

[Scoob]

I built a custom 140 ah that can do over a constant 1000amps draw . That and a good inverter you can power a lot of things on your tank .

A 140 ah battery cannot draw 1000 ah

 

[Jamie814]

A 140 ah battery cannot draw 1000 ah

I think there is some misinformation and confusion in this thread......

 

[BeanAnimal]

A 140 ah battery cannot draw 1000 ah

140 Amp Hours @ 1000 Amps...

Not 1000 Amp Hours.

So ~7 minutes of power all considered (voltage sag and Peukert losses) if the current draw was 1000 Amps from a battery stack that held 140 Amp Hours of capacity.


Read it like "My tank holds 140 Gallons of water and my pump is a 1000 gallon per hour pump. So at full blast it will drain my tank in 8.4 minutes, but due to friction losses, more like 7 minutes".


That said, if you don't know exactly what you are doing, you have no business building high capacity or high current battery arrays. Wet, SLA, Lithium, etc. All have specific design criteria. Don't be deceived by "Well it is only 12V DC each". You are dealing with high capacity and high currents and mixed series/parallel arrays pose significant safety issues if not properly fused and maintained.

Shorted cells due to improper charging or discharge or simple manufaturing imbalance can lead to catastrophic failure (thermal runaway) of the stack. DIYing with Lithium cells is especially asking for trouble if you don't have the experience and knowledge to match discharge rates. Just tossing an import "smart" charger on a DIY stack is asking for a fire.

 

[Scoob]

Well a 140 ah battery isn't going to pull 1000 amps

 

[Scoob]

A 140 ah battery cannot draw 1000 ah

 

[BeanAnimal]

Well a 140 ah battery isn't going to pull 1000 amps

Respectfully, I think you are in over your head here.

Your basic car battery provides between 400 and 900 cold cranking amps (CCA), depending in size -- meaning it can deliver that many amps continuously for 30 seconds at 0 degrees Fahrenheit before dropping below 7.2 volts. It can provide even more current at room temperature. Marine batteries and other types can provide even higher CCA. But let's not get caught up on CCA, it is just a current/time rating. The current itself is the point. That same 900 CCA battery may be able to deliver far higher current for even short time, say 1200 to 1500 Amps at peak discharge, even more at direct short.

We can get into the math of various array topologies, but the bottom line is that 1000 A sustained from a 140 aH battery array is not unreasonable at all.

 

[Scoob]

Respectfully, I think you are in over your head here.

Your basic car battery provides between 400 and 900 cold cranking amps, depending in size -- meaning it can deliver that many amps continuously for 30 seconds at 0 degrees Fahrenheit before dropping below 7.2 volts. It can provide even more current at room temperature.

We can get into the math of various array topologies, but the bottom line is that 1000A from a 140aH battery array is not unreasonable at all.

Yeah I used to work on cars still do. Actually building one at the moment.

I also have big solar array with 2 off these https://signaturesolar.com/eg4-ll-s...enclosed-rack-with-door-wheels-busbar-covers/ so 12 batteries.

Let's get into the math. All I was saying it won't pull 1000 amps. I know it goes higher. I could see maybe 500 amps . That's my opinion.

That's all I was getting at

 

[BeanAnimal]

Let's get into the math. All I was saying it won't pull 1000 amps. I know it goes higher. I could see maybe 500 amps . That's my opinion.

That's all I was getting at

If you are talking about a specific setup not being capable of 1000A, then sure. A quick look at your setup shows that you have 12 batteries in parallel. Each is rated at 100A continuous. They are capable of far more, but the BMS sets that continuous limit.

Even with each battery capped at 100A by the BMS, the 12 units provide 1200A continuous. The actual derated 500A (or whatever you cited) continuous limit is set by the external overcurrent protection, busbar and wiring constraints, and the inverter’s limits and not the cells or the basic topology. The design goal here is long run time, not high current.

So back to the statement that we are talking about: "140ah at 1000a" is not unreasonable if that is what he built to. I am not here to argue if it is a reasonable specification to build to. That part is opinion.

From a factual standpoint, I would not want to be anywhere near a 48V 1000A capable high capacity array built by a DIYer. Overcurrent protection, cell balance, busbar design, fault current consideration, and proper interrupt ratings are critical. At 48 VDC and 1000 A, arc management becomes a problem and ‘good enough’ guesses are dangerous. Shorting a 12 V, 1000 A car battery to the frame is one thing and usually a brief wrench melting event. A partial short at 1000 A driven by a bank of 12 or more 48 V batteries is another, and it could easily persist for minutes, generating enormous amounts of heat.

What math exactly do you want to get into?

 

[Scoob]

From a factual standpoint, I would not want to be anywhere near a 48V 1000A capable high capacity array built by a DIYer. Overcurrent protection, cell balance, busbar design, fault current consideration, and proper interrupt ratings are critical. At 48 VDC and 1000 A, arc management becomes a problem and ‘good enough’ guesses are dangerous. Shorting a 12 V, 1000 A car battery to the frame is one thing and usually a brief wrench melting event. A partial short at 1000 A driven by a bank of 12 or more 48 V batteries is another, and it could easily persist for minutes, generating enormous amounts of heat.


Our solar is setup solid. Not a good enough guess. I'm done here.

Have a lovely day !!!

 

[BeanAnimal]

Our solar is setup solid. Not a good enough guess. I'm done here.

Have a lovely day !!!

I think you missed the point.

The comment was about DIY battery arrays, not off-the-shelf engineered modules (your battery cabinets and batteries and BMS).

1. You stated your own setup is limited to about 500A.
2. Your battery system isn’t “DIY.” You bought modular components with integrated BMS, busbars, wiring, and overcurrent protection.

This exchange started because:

A:
You misread the claim “140 Ah that can do 1000A” and responded “A 140 Ah battery cannot draw 1000 Ah.”
I corrected that. It’s 140 Ah at 1000A. That is possible.

B:
You then said “Well a 140 Ah battery isn’t going to pull 1000 amps.”
I showed that it can, depending on design.

C:
You shifted to “All I was saying is it won’t pull 1000 amps… that’s my opinion,” basing that on your system, not the one being discussed.

So I pointed out that even your system is capable of 1200A continuous at the battery level, but is likely limited downstream to ~500A by design. A 1000A continuous system is absolutely feasible if built for that purpose.

My point stands: a DIY high current array is not something I would want to be near. The “I’m done” response is just walking away from an argument you lost with the first post and doubled down on twice.