Thread: 12V caravan battery charging

Understood you might consider replacing the S240-12 with a multistage battery charger which has options for calcium and/ or wet cell. The one I have boosts the calcium battery charge to close to 16V for a short time...
When I was contemplating a deep cell batterypack (for a CPAP machine) I was advised not to connect AGM and Gell batteries in parallel simply for the reason that they have different charge profiles... in that they charge/discharge at different rates depending on the load. So your batteries may be ok just charging at different rates. ...?

yea,, the van came with the gel in it,,
was just too hard to throw away a 12 month old battery when we added the second(then 6 months later the third---),,

Originally Posted by Pedro_The_Swift

310watts solar (11amps)
310AH of batt storage (1 x gel, 2 x AGM)

When i woke this morning the Batt V was 12.2. Yesterday was totally cloudy. Today has been 95% sunny and the batts reach 12.9( no batt use during the day except water pump) but after 4 hours (night time) use of just the telly(3.5a max) the bats now reads 12.36.

still there?

two questions,
I have a Meanwell S-240-12
already installed, (and access to 240v) but I am not at all sure how long I can leave it running,,,

This battery drain cant be normal,, can it?

can I sneak a third question in?
any easy way to check a gel batt?
it is the First battery in the bank so
heavily wired

I hope that all makes sense,,

I just had to quote your post so I could refer to it.

310w is 25.83amps. 310w divided by 12v = 25.83. Ohms law. unless your solar panel is a higher voltage.

If you have 310 AH batteries, it'll take just a bit longer than 12 hrs at full sun light. 310amp/hr / 25.83 = 12. I say a bit longer as you'll lose a little bit in heat, that's just how things work.

Now to work out how long you can run things, you need to know how much current they draw. It doesn't matter if you know the watts or amp/hr as you can use Ohms law to work it out. Just divide the watts by 12v to get the amp/hr.

Voltage is a real bad way of looking at the level of you batteries. Most batteries are floated at 13.8v but as soon as you apply load, they drop quickly to 12.?v. Now while it might have dropped 1v from 13.8v to 12.8v in less than 5 minutes (usually much faster) it's not going to keep dropping at that rate.

Most AGM batteries are good down to 10.5v. The spec sheet should be able to tell you how much the capacity will drop with how many full cycles from full charge to full flat. The more frequently you go from more extreme charged to flat the shorted the life. AGM aren't that sensitive though. I have what I consider a cheap, 22AH Power Sonic battery that they estimate it will still provide 60% capacity at 300 full discharges.


This will give you an idea. The first page gives an idea of how long the battery will last at X amp draw.

http://www.power-sonic.com/images/po.../PDC-12200.pdf

I run an Engel fridge that draws 2.7amp/hr when the compressor is running but the compressor doesn't run all the time. I have tested it and get over 12hrs from my little $62, 22ah battery but then it's as low as it's recommended to go at 10.5v. Immediately as the controller cuts power to the fridge the voltage jumps back to 11.2v as the load is removed. It's not charged, it's just how batteries behave. 12hrs is enough to get me most of the way through the night then it starts charging as soon as the sun comes up. I'm in Darwin so we don't get many cloudy days in the dry.

Now at full sun my solar panel only puts out 5amp/Hr but as the fridge only draws 1.8amp/hr (average) then my battery is being charged at 3.2amp/hr (5amp - 1.8amp = 3.2amp) which mean my battery will be fully charged in a little over 6.8hrs (a little more to compensate for heat loss). Also I move camp each day and during this time the battery is being charged from the Disco alternator.

Now a little more. Batteries have limits to the rate they are charged. They have sweet spots and too slow can be just as bad as too fast as the battery doesn't get stirred up enough when they are charges too slow. Too fast is usually worse then too slow though. Then batteries won't just accept an unlimited charge. For example most modern car alternators will produce over 100amp/hr at least but batteries won't charge at this rate.

My little 22AH battery won't charge any faster than 6amp/hr when it's flat and then as it get closer to the supply voltage the charge rate falls.

Happy Days

Most multi meters will measure current up to 10amp. I use this though:
Radio Control Planes, Helicopters, Cars, Boats, FPV and Quadcopters - Hobbyking*
Just because I'm in to R/C and I have one but it's handy to know how much power things are using when you want to know how long batteries will run something for.

Happy Days.

Thanks everyone,,
This sudden usage spike is a NEW thing,,
We've been parked up in the van now for 2 months and this is the first time the Morningstar has gone to Amber,, it actually stayed at amber all day yesterday even when the batts read 12.9----,,

Its a big job to disconnect the batts, I'd like to know what I'm looking for- before I start,,,

Hi again Pedro and if it was sunny all day yesterday and your batteries did not get up to 13.5v to 14v, then there is something wrong.

You would have replaced at least 75-90Ah and that should have put the terminal voltage up around 13.5 at least.

What was your battery voltage this morning?

12.2

[QUOTE=joel0407;2165501]I just had to quote your post so I could refer to it.

"310w is 25.83amps. 310w divided by 12v = 25.83. Ohms law. unless your solar panel is a higher voltage."

Joel as I understand it the calculated output from a solar panel is based on it's open circuit potential. Usually around 17 plus volts, so 310 watts actually needs to be divided by at least 17 volts giving 310 divided by 17= around 18 amps. This information should be available on the back of any solar panel. Then allowing for heat and resistance, voltage drop etc. 15 amps is probably realistic and then there is shading and angles to consider so Pedro's 11 amps is conservative but not to far from the money if used for daily production calculations IMO.

And if you are totally reliant on solar generation (as we are when stationary) for fridge etc. a very conservative output/production estimate is a good thing IMHO.
We run two fridges plus lighting etc. and carry 320 watts and 275A/h storage and no issues so far.
But....... you still need sunny days! Which fortunately isn't a problem up here out west in the winter.

Cheer,
Paul.