battery charging

Post by **jamesc76** » 03 Oct 2007, 15:56

i've got hold of a compact 3 stage (bulk charge, absorption charge, and float) charger thats kicks out 8a now i have spoken to the manufac. and they said its really designed for gell absorbed batterys but will charge a wet lead acid style battery but might get a bit warm, the charger has a fitted in fan so they say it would be ok
But i was wondering what charge a 90amp hour battery could take??

Plus do you think i could run stuff in the van thats 12v whilst its charging say when on a campsite etc???

Post by **jamesc76** » 04 Oct 2007, 06:59

anyone???

Post by **toomanytoys** » 04 Oct 2007, 07:40

Mmm..
If its for gel batteries, then it must be voltage limited.. a Gel battery will keep pulling the voltage up on an ordinary charger easily seeing 16v, so gel ones should never be left on charge with a standard battery charger..

Should be ok to use a the "gel" charger on a normal battery.. (the manufacturer didnt say you shouldnt so thats ok then.)

I wouldnt try and run the charger to power your 12v things.. even a cool box takes 5-6 amps..

the 90a battery ought to be keeping up with most stuff in anycase.. what are you using?
Put the charger on (to charge the battery) when you are not using 12v...

Post by **jamesc76** » 04 Oct 2007, 08:12

thats was my main idea charge when not in use just wondered if you could! Tho i would wire it up onto the battery which would still be connected to everything thats plugged into it !

Post by **toomanytoys** » 04 Oct 2007, 09:05

Would have thought its only going to be a problem if parked up for more than a couple of days... you shouldnt have much running off 12v when parked up.. lights, radio, heater... not much else..

Post by **irish.david** » 04 Oct 2007, 10:51

It'll be fine for charging your batteries and for running 12v stuff on hookup. The reason why battery chargers have a current rating on them is because that is the maximum current they can output in any given situation.

The 3 stages of a 3 stage charges are:

Bulk - This means that the charger is outputing maximum current while trying to bring the battery voltage up to a predetermined level (normally around 14v). This is when the charger is working hardest as it's trying to drag the voltage level of a battery with a low charge up to 14v by "filling it up" with current. A voltmeter across the battery will show a slowly rising voltage and charger will be kicking out 8A.

Absorption - The battery has reached the predetermined voltage level and now the current going to the battery gradually decreases from 8A to another predeteremined current (normally between 0.5A to 1A). The voltage on the battery is now stable at around 14v and the charger will start to cool down as the current drops off. When the charger reaches the low current limit it switches to float charge.

Float - The voltage out of the charger drops to around 13.5v to enable the battery to stay charged but without stressing it or boiling off the electrolyte.

You can see what stage you're at using a voltmeter and measuring the voltage across the battery terminals.

When you're on hookup, if you start running 12v things like coolboxes etc, the charger will sense the current increase and drop into either absorption or bulk mode, depending on the current demand. You can plug something in that draws way more than 8A (as long as your wiring can take it) and the charger will supply the "first 8A" with your batteries supplying the rest. This would be ok for a short while but if you left it plugged in for ages you'll drain your battery. That being said, if you plugged in something that used 10A (eg a 1200W device) you'd be taking 2A from your batteries. If they were fully charged you could leave it plugged in for a month before they were flat.

With an 8A charger you can safely plug in devices up to about 800W without your battery draining (or getting charged much).

Hope this helps.

Dave

Post by **jamesc76** » 04 Oct 2007, 15:14

wow what a brill write up there david cheers very much!!! the final bit about using 12v stuff whilst charging is what i thought would happen, the charger has led's on it that shows what stage its in plus says if the fan is off then its a clear sign thats its in float mode ?

cheers again

james