Battery questions - please help!!!!!

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Battery questions - please help!!!!!

Postby michaelc » Wed Nov 22, 2006 4:18 pm

Hi everyone,

I’m a newbie to this forum so please bear with me. I’ve read quite a few old posts on the subject but can’t seem to find the answers to my questions.

I have a Camper Trailer with a 12 Volt 100 amp hour Deep Cycle Battery (J&J Batteries D70Z Deep Cycle Lead Acid). I want to run a 12 volt/240 volt portable fridge (yet to be bought), a couple of ARB flouro lights & a portable DVD player at times (and maybe some more stuff at a later stage).

Would the battery be able to cope with all of these devices being used at the one time (as required)? Or could some of the devices be damaged due to not getting enough power from the battery?

Does this battery provide 12 volts all the time, whether it has already had 6 amp hours or 60 drawn from it (assuming it was fully charged prior to use) or do the volts drop?

Is there some sort of gadget I can buy to measure how many amps are left in the battery, or do I have to try and keep track of that in my little brain?

If I was to charge the battery directly from a generator for a few hours each morning & night, is it possible to overcharge/damage the battery if I leave the generator going for too long? How can I tell when it is fully charged?

I have heaps more questions, but they might be answered depending on what I am told about the above questions.

Thanks for your help.

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Postby Ozzycamperboy » Wed Nov 22, 2006 11:43 pm

Okidoke, i shall struggle to answer it to the best of my ability, but dont do anything drastic till sumone else here has either backed me up, or shot me down :mrgreen: ... here goes;

100 amp hours means you can run something that draws one amp/hr for 100 hrs, easy enough, BUT you dont generally want to drain a battery past 1/2 full cause it shortens its life span. So this should give you 50Ah to play with. So what you need to find out is what all these little gadgets draw in amp hours.

For eg, my fridge draws4.5 Ah. So I should be able to run this fridge for 11.1 hrs before battery is half charged ( 50 divided by 4.5)

Fluro lights should draw bugger all, and I imagine the DVD player would be similar :idea: . Is it rechargeable or does it run straight off a car battery?? You should be able to find out how much juice they require on the back off the box or maybe on the bottom of the actuall DVD player, but it might be in 'watts'.. in which case wait for another reply cause I only just had Ah's explained to me :lol:

You shouldn't have any trouble running multiple gadgets at one time, just means the battery will drain quicker.

Gadget you can get to keep track of how much juice is left and/or being used is called a 'multi-meter'. Less than $30 i think for a not too shabby one.

And I can't see over-charging a deep-cylce being a problem, but stay tuned for a more definate answer :lol: . BTW, deep cycle battery's take longer to charge than a normal car battery, so 1-2 hrs might not be enough :idea: You can tell when it's charged with the multi meter doohickey, also, most battery chargers have alittle light on em that tell you when its charged :?
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Postby Kramer » Thu Nov 23, 2006 10:17 am

Micheal, an Idea to charge the battery would be to go and buy yourself a good 240V battery charger to run off the generator. The 12V output of those little generators are a little weird and not regulated well.

I think deep cycle batteries are a little bit more touchy than normal car batteries <- someone at battery world might be able to help, but don't buy anything from them as they are $$$ and a good battery charger has really good regulators in them and will not over charge the battery.

Ozzy was right on the amp hours, your fridge will draw the most then the DVD player but that is not used all the time maybe 1.5hrs a day. The 12V flouro's won;t draw much but I have found that those little 240V flouro's from supercheap to be heaps better in terms of how much they light up, you could run these while charging up the battery again.

A good thread on Downunder4x4 that might help is ... al+Battery
they are a great bunch of people there and can probably answer your question much better than me!

Also welcome to the forum :armsup I actually come from Bundy but now live in Gladstone. Good to see some more QLD forum members now to stop all those southerners from moving here hmmmmmmnn.... I might move the rabbit fence to the QLD border down south :grin:
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Postby elpaulos » Mon Nov 27, 2006 12:37 am

good answers above.Hope this helps.
Power in Watts is equal to V (voltage) multiplied by I (amps). So your 200W light pluged into a 240V (home plug) is drawing 0.8 amps.
Or a 200W light plugged into your 12V battery will draw 16 Amps.
The balance ( if you calculate) is taken up in resistance. All electronic curcuitry has resistance hence a final figure of 192.
The charging of batteries for a long period will end up what's called trickle charging. No dramas. Can't explain it properly so I won't, but I charged a 185AH marine batt 12V for a week and had no less loss/gain than charging for a few days. BTW the current pull on this batt was 26-27 Amps at any given time.
If it were me I'd charge multiple 6 or 12 v batteries. That way I'd be able to isolate different horses for different courses. Keep your big batt for the big league. And as I said hope this helps.
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Postby michaelc » Thu Nov 30, 2006 8:27 am

Thanks for your replies everyone. Looks like, to be on the safe side, I'm going to install a dual battery in my ute (allbeit a very small one due to the space limitations in the engine bay of an RA Rodeo). This way I can leave the fridge on in the truck whilst setting the trailer up and then also pull the dual battery out of the truck if the big one in the camper trailer ever fails me/goes flat.

I've just bought a big 85 litre Evakool frige/freezer - probably a bit of overkill in size & power usage (is only the wife, kid and me), but I'd hate to be thinking to myself down the track "I wish I had a bigger one (esky that is)".

Anyways, thanks for your help. Good to see there are so many great people out there willing to lend a hand.


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Postby Komodo » Thu Nov 30, 2006 10:30 am

Correct P = V*I.

Fluros are good but most fluros you guys are talkiung about are infact CCFL not fluros. Your best but more expencive option is actually LED strip lighting. these drawer less current. Ive found with my Waeco that the best thing to do is to treat it a little like it is still an esky. By that I mean I like to have chilled water so i fill a couple of 1.25 ltr "pump" water bottles and freeze them and stick them in the fridge before I leave. I also run the fridge on 240V mains for a day before I leave so that the cold start of the fridge doesnt drain my battery.

Dual battery isolators are good and RedArcs are about the best you can get and are fine for dissimilar batteries (ie AGM and Gel Cell with lead acid start battery) Remember differnt types of batteries have different float voltages.

As Kramer said the 12V output on those generators isnt very well regulated and a DC-DC regulator is actually a better and more efficient way of regulating this voltage than using a 240V charger as generators rely on a 3 pole alternator which is then stepped up to 240V DC then converted to AC using an invertor. Most of which are NOT pure sine wave. Many people will argue that modified sine ware of square wave inveters are fine and more efficient than pure sine wave inverters. True they are more efficient becuase they use switch mode PSUs and hit peak voltages of 240V but they are damaging to more equiptment than they are noted for. A pure sine wave 240 is infact closer to 315V from memory but root mean square comes in at the 240 - 250V mark.

Your fridge will draw around 5 Ah but this is only whilst the fridge is "on cycle" if you use the fridge like an esky and only open it when needded and keep it in the shade and cool then the on cycles are shorter and less frequent. DVD players especially portable ones draw about the 5 ah mark as well. IMO get a couple of 100AH AGM batteries chuck one in the camper and connect on to the battery system of the vehicle via an anderson plug and just saw them around when one is getting low. 50% is the lowest you want to drain your battery but 80% is actually better. Charge your battery using 240V step down charger as these will float your battery upto around 15.5V on charge and will let the batteries internal resistance drop it back to between 14.4 and 13.8 once off charge - THIS IS FULL CHARGE! 12V is not full charge. Batteries are a combination of cells. From memory cells vary between 1.1 and 1.5V generally in 12V batteries
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Postby Cruzin » Mon Dec 18, 2006 9:14 pm

All above have good answers to your question, but you may wish to look/post here also,

and also google "Collyn Rivers" he has a multitude of books and ifo on 12v systems for CTs
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Postby Kramer » Mon Dec 18, 2006 10:14 pm

Geez Cruzin your a wealth of info and from QLD nice to see you here :+
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