New 100 Ah battery only lasting 90 minutes on 300w discharge

[Tariq0101]

My newly bought 100 Ah battery should provide 1200 watt hour so it should last 4 hours on my consumption but only lasting 90 minutes, is the battery bad or I should try some more times?
I'm charging it at 10A charger and it only needs 2 hours to fully charge, does that mean it's capacity is only 20Ah?

My setup details:
Personal computer consumes 220 watt
LED screen consumes 40 watt

 

[snoobler]

Welcome to the forum.

22-25A is a pretty heavy load for a 100Ah battery. It will NOT last 4 hours. A 100Ah battery will deliver 5A for 20hr yielding 100Ah. Pull more than 5A, and you reduce the capacity. At over 4X the rated 5A current, you'll likely have about 3 hours available, so it's acting more like a 60-70Ah battery due to you pulling heavier loads than its 20hr rating allows.

This phenomenon is called Peukert's Law.

In order to not damage the battery, you should limit your discharge to 50% of that, so you really only have about 1.5 hours of power.

If your battery has a "RC" or Reserve Capacity rating, that's the number of minutes it can deliver a 25A current above 10.5V. You will find it's definitely less than 4 hours.

Such a heavy load will also cause the voltage to sag such than any voltage-based cut-off is triggering early.

Poor connections and/or thin wires may also contribute to voltage sag.

"10A charger" may not be properly charging your battery. It's important to charge to the voltages specified by your battery manufacturer. if you don't do this, you may find that your battery is consistently undercharged to as low as 80%.

Here's my speculation:

Insufficient charging, and heavy load possibly coupled with thin wires and/or lose connections is causing the voltage to sag excessively where the inverter is reaching the low voltage alarm or cut-off. Alarms and cut-offs are not always where they should be to ensure you get all of your capacity out of the battery. Even after shut-off, there is still a fair amount of capacity left, just not enough to maintain the voltage needed to support the load.

IMHO, given the load, battery size and 90 minutes of use, that's about where you want to be to ensure you don't cycle the battery too deeply and kill it before its time.

 

[MisterSandals]

bought 100 Ah battery

Battery type? LiFePO4? Lead Acid? Other?

Link to product?

 

[Tariq0101]

Battery type? LiFePO4? Lead Acid? Other?

Link to product?

Lead acid, locally made I don't think the brand is known elsewhere

 

[Tariq0101]

Welcome to the forum.

22-25A is a pretty heavy load for a 100Ah battery. It will NOT last 4 hours. A 100Ah battery will deliver 5A for 20hr yielding 100Ah. Pull more than 5A, and you reduce the capacity. At over 4X the rated 5A current, you'll likely have about 3 hours available, so it's acting more like a 60-70Ah battery due to you pulling heavier loads than its 20hr rating allows.

This phenomenon is called Peukert's Law.

In order to not damage the battery, you should limit your discharge to 50% of that, so you really only have about 1.5 hours of power.

If your battery has a "RC" or Reserve Capacity rating, that's the number of minutes it can deliver a 25A current above 10.5V. You will find it's definitely less than 4 hours.

Such a heavy load will also cause the voltage to sag such than any voltage-based cut-off is triggering early.

Poor connections and/or thin wires may also contribute to voltage sag.

"10A charger" may not be properly charging your battery. It's important to charge to the voltages specified by your battery manufacturer. if you don't do this, you may find that your battery is consistently undercharged to as low as 80%.

Here's my speculation:

Insufficient charging, and heavy load possibly coupled with thin wires and/or lose connections is causing the voltage to sag excessively where the inverter is reaching the low voltage alarm or cut-off. Alarms and cut-offs are not always where they should be to ensure you get all of your capacity out of the battery. Even after shut-off, there is still a fair amount of capacity left, just not enough to maintain the voltage needed to support the load.

IMHO, given the load, battery size and 90 minutes of use, that's about where you want to be to ensure you don't cycle the battery too deeply and kill it before its time.

Thanks for your elaborate response.
What you said is true when I connect a 12v LED bulb it lights normally after the inverter shuts down.
So in your opinion everything is fine, I should just get a bigger battery?

 

[MisterSandals]

Lead acid

In that case, you can typically only discharge 50% of your 100ah. Going below 12v drastically
shortens the life of a battery (as well as keeping it below 12v for extended periods).

So your 100ah lead acid battery has 50ah of usable power. Apply snoobler's math to that
corrected number.

 

[snoobler]

Thanks for your elaborate response.
What you said is true when I connect a 12v LED bulb it lights normally after the inverter shuts down.
So in your opinion everything is fine, I should just get a bigger battery?

There may be other issues. Worth assessing the issues mentioned below.

Insufficient charging, and heavy load possibly coupled with thin wires and/or lose connections is causing the voltage to sag excessively where the inverter is reaching the low voltage alarm or cut-off. Alarms and cut-offs are not always where they should be to ensure you get all of your capacity out of the battery. Even after shut-off, there is still a fair amount of capacity left, just not enough to maintain the voltage needed to support the load.

Once you've eliminated any potential issues, if you need more run time, you need more battery.

 

[snoobler]

Battery type? LiFePO4? Lead Acid? Other?

Link to product?

We are in the Lead Acid forum...

 

[MisterSandals]

We are in the Lead Acid forum...

doh!

But then I am surprised that you said this:

A 100Ah battery will deliver 5A for 20hr yielding 100Ah.

 

[rin67630]

Lead acid, locally made I don't think the brand is known elsewhere

With Lead-Acid you have only 60% really available. And that depends on the overall load you will put on the battery.
If you discharge the battery at C/4 then it would not last very long, 90 minutes is a bit short, but I am not surprised.
Besides that, battery capacity is frequently advertised very very over estimated.
You have got plenty of unserious vendors, especially amongst no names.

Also: what kind of lead-acid battery is it?
An automobile cranking battery?
A specialized solar deep cycle?

 

[rin67630]

I'm charging it at 10A charger and it only needs 2 hours to fully charge, does that mean it's capacity is only 20Ah?

That is not impossible. Unserious vendors are everywhere.
Can you give details on how you have been charging it?
From which low voltage to which high voltage? how long did you stay at maximum voltage?

 

[Tariq0101]

There may be other issues. Worth assessing the issues mentioned below.

Insufficient charging, and heavy load possibly coupled with thin wires and/or lose connections is causing the voltage to sag excessively where the inverter is reaching the low voltage alarm or cut-off. Alarms and cut-offs are not always where they should be to ensure you get all of your capacity out of the battery. Even after shut-off, there is still a fair amount of capacity left, just not enough to maintain the voltage needed to support the load.

Once you've eliminated any potential issues, if you need more run time, you need more battery.

I'll check all of that thanks.
One last question though, would that still be a "heavy load" on a 240Ah battery?

 

[Tariq0101]

With Lead-Acid you have only 60% really available. And that depends on the overall load you will put on the battery.
If you discharge the battery at C/4 then it would not last very long, 90 minutes is a bit short, but I am not surprised.
Besides that, battery capacity is frequently advertised very very over estimated.
You have got plenty of unserious vendors, especially amongst no names.

Also: what kind of lead-acid battery is it?
An automobile cranking battery?
A specialized solar deep cycle?

Deep cycle, a friend recommended the brand and said they're decent

 

[snoobler]

I'll check all of that thanks.
One last question though, would that still be a "heavy load" on a 240Ah battery?

Divide capacity by 20. That's the max current to obtain rated capacity. 240/20 = 12A - still about 1/2 of what you need.

22A * 20 = 440Ah battery to get the 20 hour rating. Again, you could only use 1/2 the capacity - so 10 hours.

 

[snoobler]

doh!

But then I am surprised that you said this:

Why? lead-acid batteries are rated based on their 20 hr capacity. Did I math wrong, and I just can't see it?

 

[MisterSandals]

A 100Ah battery will deliver 5A for 20hr yielding 100Ah.

To me, and i am not trying to play with words, it sounds like you are implying that the OP can expect to get 100ah out of his 100ah lead acid battery.

I know thats how battery makers rate things and was probably your intention.

This discussion has since covered usable amp hours so i am done with this.

 

[rin67630]

My setup details:
Personal computer consumes 220 watt
LED screen consumes 40 watt

The most efficient approach will be to work on that.
A decent desktop-style laptop my be cheaper than any high load battery and will cut your power by 3 at least.
Beside that, it has an own battery.

 

[rin67630]

Why? lead-acid batteries are rated based on their 20 hr capacity. Did I math wrong, and I just can't see it?

Solar deep cycle batteries are -according to German DIN- rated to 100h capacity.

 

[snoobler]

Solar deep cycle batteries are -according to German DIN- rated to 100h capacity.

Cheater cheater punkin eater.

 

[Tariq0101]

The most efficient approach will be to work on that.
A decent desktop-style laptop my be cheaper than any high load battery and will cut your power by 3 at least.
Beside that, it has an own battery.

I thought about that but electronics have become very expensive in my country because of inflation and I'm left with that PC so it's not an option