gel battery voltage

[native pepper]

Bought a 12ah x 12v gel battery the other day for a small project and when got it home discovered it was at 12.7v, so charged it up over night. On the battery it states it doesn't need charging as it is full. After sitting for few hours the next day, the battery had dropped to 13.1v recharged it and the same thing happened. Contacted the supplier and was told 12.7v was a fully charged gel battery and looking at some battery sites some say the same thing.

Maybe I've been playing with lifepo4 to long, but thought a fully charged lead acid battery was 13.8v, not 12.7v. Have they changed the goal posts, is this some new technology, or have batteries always been fully charged at 12.7v. All my life, 13.8v has been what have used for lead acid and gel is lead acid. Checked the voltage of the 360amp gel just put back into the bus and they are sitting at 13.9v, on solar before the sun came up.

[T1 Terry]

!2.8v is fully charged for a lead acid battery, anything after that is surface charge. some batteries use very aggressive specific gravity levels designed for cold climates and at room temp here the voltage could be as high as 13.1v or more. !3.8v is the float charge required to finish fully charging a lead acid battery, 13.6v is required to keep it fully charged but not boil off any electrolyte.
Be very careful charging and discharging Gel batteries, they have a very low current acceptance and discharge voltage to avoid hydrogen and oxygen bubbles forming at the plate surface. These will never be reabsorbed into the gel and will cause sulphation on the plates where the bubbles sit seriously reducing the batteries useability

T1 Terry

[native pepper]

Thanks, that makes sense, sent if back because it wouldn't hold the charge at 12.7v either. Yet my 360ah gel pack, sits at 13.6-14v every time I check it.

[native pepper]

Have another question, ran into a bloke yesterday who has a 24v truck, but uses a 12v crane/winch on it and 12v accessories, like fridge and fuel transfer pump. He runs it by connecting to just one of the batteries to get 12v and asked him how long he'd been doing that and he said a year or so, because it was cheaper to use 12v things than 24v and didn't seem to have any effect on the batteries as he only uses the 12v when the engine is running.

As I'm installing a new fuel pumping system, which will run on 12v, I'm putting in a 12v battery charged from a 24v-12v converter which is an expensive exercise. Would setting it up as the truckie has, have an adverse effect on the 24v batteries and charge system.

[BruceS]

I did exactly that for 3 years on my 24V truck.
The 2 batteries will NOT equalize and eventually you'll have 10v in one and ATTEMPTING to reach 14v in the other one to get the 24v. (nominal)
I overcome it by swapping the 12v feed from battery to battery EVERY weekend. I also had two volt gauges on the dash showing volts from each battery.
The most important thing is to be VERY sure the earth wire doesn't short to chassis when on the high side battery!!! Cassette players, radios & CB's do not like 24V!!!
Only do it if the load is really light. I guess you could use a 2pole/3 position changeover switch too? Just keep swapping the feeding battery.

[native pepper]

Thanks. that sounds reasonable Bruce, thought that may be the case, but relied upon my late friend for all the electrical technicalities for decades and now am on my own and constantly running into the need for understanding, when in the past didn't need to. Will stick with using a 12v supply for my fuel system driven from a 12v battery powered from the 60amp 24-12v converter on the bus. Sent back a 12v x 12amp gel battery which wouldn't hold a 12.7v charge and am waiting for an AGM deep cycle 9amp battery to arrive, which will be much better suited to the job of driving a small 2.5amp fuel pump when on the road and it's half the price of the gel.

The bloke with the truck had what looked like a permanent connection to just one battery, when I run into him again, will point out what you've said and see if it rings a bell for him. Thanks again.

[bob r]

I did as Bruce said used the 12v side and swapped battery's each weekend, had two radios phone and Engel plus fan's.

Bob

[native pepper]

I'd probably forget to change the battery over, so would like a separate supply. The power from the battery will come through the auxiliary gel pack, which us going back in. the girls want a bigger hot water supply, so am installing another 80lt tank to satisfy them. Go a cheap battery switch and got the new battery today, will install it into it's little box tomorrow and put it in the bus between showers and sleet.

The 12 gel will be charged by the 24v alternator through a 24v AG deep cycle battery, into a 60amp 24v to 12v converter. Or grid connect 40amp battery charger, each section has battery protection switching, isolation switches between each battery including the new one. This way one thing going wrong doesn't effect the operation of others and I like backups when mobile, lots of them if possible.

[bob r]

I had no problem forgetting to change battery's,if I didn't clean the terminals regularly they would disappear.

Bob

[T1 Terry]

Have another question, ran into a bloke yesterday who has a 24v truck, but uses a 12v crane/winch on it and 12v accessories, like fridge and fuel transfer pump. He runs it by connecting to just one of the batteries to get 12v and asked him how long he'd been doing that and he said a year or so, because it was cheaper to use 12v things than 24v and didn't seem to have any effect on the batteries as he only uses the 12v when the engine is running.

As I'm installing a new fuel pumping system, which will run on 12v, I'm putting in a 12v battery charged from a 24v-12v converter which is an expensive exercise. Would setting it up as the truckie has, have an adverse effect on the 24v batteries and charge system.

On the Volvo low loader the power lift ramps used a 12v hydraulic pump, the truck was 24v and an auto lec had fitted a 24 to 12 DC to DC between the main 24v and the 12v half of the battery. A never ending pain in the rectum as the high current would destroy what ever connectors were used, stuck in the middle of now where one day it decided it didn't want to lift the ramps, I put the 12v cable across to the 24v terminal and every thing went well after that. No more groaning pump, no more hard starts, no more melted battery terminals. The balancer system remained as I couldn't see any reason to take it off and the truck received a flash 12v stereo as a bonus

T1 Terry