Gel battery charging

[Wh05apk]

After a but of general advice please.

We have a 246ah gel battery, so should last us days off grid, what voltage/state of charge should I allow it to drop to? After a couple of days from full it gets down to about 70% at this time of year with minimal solar boost, once below about 85% though the inverter keeps cutting out at 11,8v when running my wife's hair dryer (pulling about 35a)
I assume the inverter us cutting out due to the demand, as voltage soon recovers, but what is a safe level to allow the battery to drop to, for long battery life?

 

[Raul]

For long life you should never see it below 12v. Ideally 12,2v.
As a idea, you got max a 125ah from full charge to play with.

 

[Wh05apk]

For long life you should never see it below 12v. Ideally 12,2v.
As a idea, you got max a 125ah from full charge to play with.

So safe to go down to about 50%?

 

[bigtwin]

The 50% guidance is for wet batteries; With gel you can go down to 20%.

How/where is your inverter connected? Is it far from your battery?

Ian

 

[Wh05apk]

I thought it could go much lower, but never needed to so far.

The inverter is about 2inches above the battery, I assume a short cable run, factory fitted 1800w. But if battery below about 80% vintage drops to below 11.8v which is when it is set to cut out.

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[SandraL]

I guess the question is do you have a 246ah battery.
Perhaps worthwhile to fully charge battery and then do a test discharge against a known load to find out if battery has deteriorated.

 

[Theonlysue]

They take longer to charge than wets.
I do wonder how long she has hairdryer on for?
Yiu seem to be using a lot of power in a couple of days, else its not recharging fully?

 

[Wh05apk]

The hairdryer cuts out after about 30 seconds, even at about 80%.

When fully charged. We use about 15%overnight, but there is a very high drain if about 0.6a with everything turned off (dealer claims this is normal, but seems excessive)

 

[Richard n Ann]

The hairdryer cuts out after about 30 seconds, even at about 80%.

When fully charged. We use about 15%overnight, but there is a very high drain if about 0.6a with everything turned off (dealer claims this is normal, but seems excessive)

Our drain is 0.2 amps with nothing on except the main switch. I would find out what is using your 0.6 amps and disconnect it/them if possible.

As for discharging, you should always discharge as little as possible, and the battery will have a longer life but gels tolerate discharge better.

Also gels aren't as good at delivering high amperage because the gel doesn't disperse the heat as well, wonder if that's why the voltage is dropping with the hairdryer on ? Lenny HB will know. Are the cables nice and thick to the inverter?

 

[Richard n Ann]

Thinking further, maybe the inverter cut out is set too high. It's normal for battery terminal voltage to drop under high load.. Our car battery drops to 9v during cranking but it's not flat of course ?

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[autorouter]

The current of 35A is well below the the recommended limit of C/5 (246/35 = 0.14 = C/7), so this setup should work better than you are saying. It would be worth measuring the voltage at the battery terminals when the hairdryer is running. You can tell from that if the voltage drop along the cables is OK, or maybe there's a bad connection somewhere dropping the voltage at the inverter terminals.

 

[Lenny HB]

Apart from the inverter tripping out at a fairly high underload voltage it sounds like your system is working OK.

The 0.6A drain is on the high side but not unusual, mine is about 0.4A and with the panel off about 0.15A, if your van has an LCD display panel it will be higher.

Gels are safe to take down to 80%DOD and still have a good life.
e.g. A good quality Flooded Cell like the Varta LDF range at 50% DOD its rated at 200 cycles, an Exide Gel at 50% DOD is 850 cycles and at 80% DOD it's 500 cycles.
Offload voltage for 75% discharge is 12.0v.

Gels are not keen on high currents being taken out of them it is recommended for an 80 a/h battery to keep the current draw to 20 amps however a bit more than this for short periods won't do any harm, 30 amps doesn't appear to be a problem, you just can't hammer them like Flooded Cells.

I have 3 x78a/h Gel batteries (234a/h) just on solar charging, 1000w inverter mounted next to the batteries with less than 1/2 m of 16mm sq cable to it.

I've just been out to my van and run a test for you.
Batteries sitting at 13.01v and 99.5%.
I switched the inverter on and fired up an 800w kettle, it took 80 amps for the first 10 secs then settled to 78 amps. Battery voltage stabilised at 11.82v.

11.8v cut off on the inverter sounds too high to me, mine is set to 10.5v, bear in mind we are talking about on load voltages which will be much lower than the offload voltage we measure the state of charge by.

What size cables is your inverter wired with?
1800w inverter I expect to see at least 25mm sq cables.

With regard to your 0.6A standing current, have you got a proper isolating switch in line with the 12v power cable to the inverter as an inverter if left connected will be in standby mode drawing anything up to 0.2A.

Your power usage sounds OK at around 36a/h per day, I would be using 35 - 40 a/h a day at this time of year and if it's cold a fair bit more.
You don't say how much solar you have, I have 300 w with a Votronic MPPT regulator. At this time of year on a bright sunny day I would be lucky to get 10a/h back into the batteries, any cloud or rain will wipe out any solar input.

 

[Off da Grid]

What’s the wattage of the hair drier, my wife’s home one is very powerful so we’ve got a travel one about 900 watts for the van when on low amp hookup.
Some invertors pull a lot of current even when switched off, some people put a switch in the 12v line to totally isolate it when not needed, that might help

 

[Lenny HB]

What’s the wattage of the hair drier, my wife’s home one is very powerful so we’ve got a travel one about 900 watts for the van when on low amp hookup.

He said it takes 35A so probably 400W.

Some invertors pull a lot of current even when switched off, some people put a switch in the 12v line to totally isolate it when not needed, that might help

I just said that.

 

[Wh05apk]

Thanks Lenny, we have 450w of solar so similar figures to yours, I have dropped the inverter cut off to 11.5 and seems to work ok, just seems to have been set up too cautiously.

The inverter has a remote switch in the panel, which is normally left off, switching off directly at the unit makes no difference to the draw on the panel.

As you say seems normal now, but still concerned at the 0.6a draw, over 24 hours that is about 15ah, so would take a 100ah battery to 50% in 3 days! Glad we have a big battery and plenty of solar, even if little use this time of year.

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[Lenny HB]

The inverter has a remote switch in the panel, which is normally left off, switching off directly at the unit makes no difference to the draw on the panel.

The switch on the unit will still only be a soft off, best to fit one of these.

As you say seems normal now, but still concerned at the 0.6a draw, over 24 hours that is about 15ah, so would take a 100ah battery to 50% in 3 days! Glad we have a big battery and plenty of solar, even if little use this time of year.

How much is the draw if you turn the control panel off?

 

[Richard n Ann]

How much is the draw if you turn the control panel off?

Ours is 1ma ?? any less and the multimeter wouldn't measure it ?

 

[Lenny HB]

Ours is 1ma ?? any less and the multimeter wouldn't measure it ?

I take it your panel is hard not software switched to the distribution unit then.

 

[Wh05apk]

The switch on the unit will still only be a soft off, best to fit one of these.


How much is the draw if you turn the control panel off?

Don't know but assume minimal , as if switched off there is negligible drop overnight.

 

[Richard n Ann]

I take it your panel is hard not software switched to the distribution unit then.

Yes no faffing about with screens and software, it must be the last of the good ones (2014) ?

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