House Battery issues...

[dreadlocks]

yeah, Golf Cart.. they have huge cells with thick plates, you'll end up with more capacity, they often survive mistakes like you made a several times (just ignoring em for a few months), whereas AGM only takes once.

In a bank one bad battery will turn all the rest bad too unless you catch it immediately, I highly doubt you'll be able to do anything to recover acceptable performance out of what your left with now.

 

[Joe917]

Golf cart batteries are the best bang for the buck, however they do not do well delivering high amps, ie. for a microwave or induction cooker.
A microwave run at "50% power" runs at 100% power for 50% time. My understanding was induction is the same.
We are using 4 Rolls Surrette 6volt GC batteries, I was told by their tech to keep max charge and discharge to 90 amps.(not enough for a microwave.)


.

 

[dreadlocks]

90A @ 24v is enough for 2100W output, thats far more than enough for even a big microwave... My lil dorm microwave runs off a 1000W inverter, and I never seen a microwave that didnt work on a 15A 120VAC circuit (1800W)

 

[Joe917]

90A @ 24v is enough for 2100W output, thats far more than enough for even a big microwave... My lil dorm microwave runs off a 1000W inverter, and I never seen a microwave that didnt work on a 15A 120VAC circuit (1800W)

1000 watt microwave draws more than 1000 watts, as much as 1500 watts. divide by 12 volts even 11.5 because of the current and you are looking at 130 amps.
the 90 amps recommendation from Rolls refers to two strings 45 amps each.

 

[dreadlocks]

but OP is running 24v with a 24v inverter, thats half the amps.. so 65A at 24v.. he'll never see 12v let alone 11.5v

 

[Joe917]

If he is running a 24 volt system then he will have one string of 4 gc batts and his max draw should be 45 amps. 1500 watts by 23 volts is 65 amps again too much for the batteries.
45 amps per string. 12 volts 2 strings 90 amps, 24 volts one string 45 amps.

 

[dreadlocks]

S6 GC2 | Rolls Battery

www.rollsbattery.com

Maximum Charge Current (String) = 40A

You can discharge at rates much greater than that, they have 547 Cranking Amps, 684 Marine Cranking Amps, with ratings and outputs up to 84A on the very spec sheets.. Golf Carts pull a lot more than 40A.. a bit of googling around shows most in the 300-500A range.. but according to "their tech" an 8 battery 48v golf cart cant use more than 45 amps.. what use are they in golf carts then? Trying to claim you cant discharge a battery at a rate greater you charge it is nonsense.

 

[gait]

Ok electrical gurus...
I'm having low voltage issues with my battery bank.

1. 4 x 100amp AGM in series/ parallel to deliver 24v
2. About 4-5 years old

3 . Never discharged under 50% and more likely 60% most times
4.Problem free until this trip...HOWEVER, I did leave them unattended after 2018 trip for about 4-5 months. They finished the trip fully charged. The battery monitor showed good levels of charge but I think it had a glitch from lack of cycling and wasn't reading correctly.

1. Inverter has indicated low voltage alarm twice. Once on this trip (today) and once on a short trip a couple of months ago. After the short trip I bought battery charge up and reset battery meter.
2. Yesterday, batteries went to FLOAT (first time since realising problem a while back) but this morning had low voltage alarm. Battery % at around 65% capacity.
3. The induction cooker we run from the inverter normally draws about 30 amps on the appropriate setting. It was pulling 53 at the lower voltage!

I'm struggling to understand how batteries at 65% can show low voltage and why I wouldn't be able to use more of the remaining capacity without having low voltage issues.

Thanks for any feedback. Neil

someone mentioned Peukert earlier. When a big current is drawn from a lead acid battery the voltage droops. As batteries age they have less capacity and the voltage droops more. Also, the inverter tries to supply the power required by the induction cooker. As the battery voltage droops the inverter needs more amps to maintain the watts (volts x amps) to the cooker. The increased amps causes the battery voltage to droop further - and so on until the inverter (or alarm) says "low volts" and shuts down. The battery voltage then recovers over a few minutes to the at rest volts.

The capacity isn't lost. Its just not available at the amps you require. Less amps (and thus less voltage droop), like a couple of lights, will be lit by the 65% battery for a long time.

AGMs are better than wet cells in this usage as the internal resistance is lower, the Peukert factor is lower, there is less voltage droop for the same amps at same state of charge.

I'm guessing your batteries are no longer up to the task of powering the induction cooker for as long as they used to. Just in case though check the cables between battery and inverter (too small is large voltage drop which increases with amps) and check for hot spots (also voltage drop).

A contributor to shorter life is discharge / charge at high rates. In simple terms chemistry isn't instant and takes time to catch up. Push too hard and the results aren't as intended. I notice you don't use the induction cooker on full.

While I'm here. Nothing bad (chemically or physically) happens when the batteries are discharged below 50%. Just cycles are consumed to shorten life. In simple terms, one discharge to 50% is worth two discharges to 75%. A bit more complicated but the capacity below 50% is usable, just a matter of economics - whether to pay for excess capacity or replace smaller battery more frequently. In your case you need the big lead acid to provide the power without too much voltage droop.

My starter batteries (2 x NS70) provide lots of amps (CCA) but the voltage gets well below 11V fairly rapidly. The starter motor is designed for that, the amps fall as the volts fall and equilibrium is reached. The induction cooker is "constant power", which is very different to the starter motor. Having said that its lower amps than the starter.

I hope this helps and doesn't tell you stuff you already know.

 

[WhereisFranklin]

someone mentioned Peukert earlier. When a big current is drawn from a lead acid battery the voltage droops. As batteries age they have less capacity and the voltage droops more. Also, the inverter tries to supply the power required by the induction cooker. As the battery voltage droops the inverter needs more amps to maintain the watts (volts x amps) to the cooker. The increased amps causes the battery voltage to droop further - and so on until the inverter (or alarm) says "low volts" and shuts down. The battery voltage then recovers over a few minutes to the at rest volts.

The capacity isn't lost. Its just not available at the amps you require. Less amps (and thus less voltage droop), like a couple of lights, will be lit by the 65% battery for a long time.

AGMs are better than wet cells in this usage as the internal resistance is lower, the Peukert factor is lower, there is less voltage droop for the same amps at same state of charge.

I'm guessing your batteries are no longer up to the task of powering the induction cooker for as long as they used to. Just in case though check the cables between battery and inverter (too small is large voltage drop which increases with amps) and check for hot spots (also voltage drop).

A contributor to shorter life is discharge / charge at high rates. In simple terms chemistry isn't instant and takes time to catch up. Push too hard and the results aren't as intended. I notice you don't use the induction cooker on full.

While I'm here. Nothing bad (chemically or physically) happens when the batteries are discharged below 50%. Just cycles are consumed to shorten life. In simple terms, one discharge to 50% is worth two discharges to 75%. A bit more complicated but the capacity below 50% is usable, just a matter of economics - whether to pay for excess capacity or replace smaller battery more frequently. In your case you need the big lead acid to provide the power without too much voltage droop.

My starter batteries (2 x NS70) provide lots of amps (CCA) but the voltage gets well below 11V fairly rapidly. The starter motor is designed for that, the amps fall as the volts fall and equilibrium is reached. The induction cooker is "constant power", which is very different to the starter motor. Having said that its lower amps than the starter.

I hope this helps and doesn't tell you stuff you already know.

Thanks Gait. Your explanation is very clear.

I suspect a loss of capacity due to age which probably leads to greater voltage droop. The 50% limit was based on longevity mainly, along with the capacity to be able to recharge that 50% under typical conditions on a daily basis.

I over spec'd the cabling when installing so pretty sure it would be ok but a good suggestion and I'll look up my notes to double check the ratings.