Auxillary battery sizes ?
Submitted: Monday, Mar 02, 2009 at 01:35
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Member - Daniel M (QLD)
Hi all
I have just installed a dual battery system primarily to run my Waeco cab50 fridge. Trouble I am having is that the battery doesn't seem to be holding its charge for very long. Originally had a second handy in so replaced it with a new one and had the same trouble. Next step is to put a bigger battery in. I am wondering if anyone would be able to tell me a good size to go for. Currently have an N50 and was assured it would do the job but am flat out keeping the fridge cold for 3 or 4 hours. any help would sure save me a lot of trial and error, not to mention my bank account!!!:)
cheers
Reply By: Member - John and Val W (ACT) - Monday, Mar 02, 2009 at 06:59
Monday, Mar 02, 2009 at 06:59
Daniel,
Depends on the current drawn by your gear, and how you charge your battery. You really need to have a way of measuring this. A cheap multimeter will do the job, but it MUST have a 10 amp range and you must be careful using it. (Above all don't connect directly across the battery when it is set up to measure amps. For safety (of the meter) always leave it set to the 20Volt range unless you need it for a particular current measurement then change the setting back immediately after). Jaycar, Dick Smith etc will have something suitable.
Check out our electricity blog,
Electricity for Camping for some useful numbers .
Basicly, if you are running a fridge, I'd aim for a battery of at least 100 amphour capacity, more if you want more than 2 days out of it without charging.
HTH
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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Follow Up By: Member - John and Val W (ACT) - Monday, Mar 02, 2009 at 07:10
Monday, Mar 02, 2009 at 07:10
Daniel,
A second thought - The fridge won't run if the available voltage is too low. You MUST use heavy cable from the battery to minimise voltage drop, and the shorter the better. Again, a multimeter will be very useful to measure the voltage at the battery, and if you can, at the fridge. The fridge may also have a settable low voltage cutout - you may get longer life from your battery if set to a lower cutout voltage.
Final thought. Don't discard your present new battery. Add another one in parallel to it. (i.e. connect the two positive terminals together, and the two negatives together. (not to the positives!!)
Cheers
John | J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
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Reply By: Crackles - Monday, Mar 02, 2009 at 07:17
Monday, Mar 02, 2009 at 07:17
Dan if you are having problems with 2 different batteries then there is a possibility the wiring to your fridge is undersized or the plugs are causing voltage drop.
I'd confirm the batteries state of charge (volts & hydrometer) to see if they are in fact flat when the fridge stops. If not then
test the volts at the battery & at the fridge while it's running to see if there is a large voltage drop.
How long do you need it to run as this ultimately will determain how large you'll need to go?
Cheers Craig............
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Reply By: oldtrack123 - Monday, Mar 02, 2009 at 17:52
Monday, Mar 02, 2009 at 17:52
Hi Daniel
Your fridge will draw around 4amps while actually running. the actual run time will be affected by:- ambient temp ,thermostat setting[ the colder you set it the longer it will run] & how warm & how much warm stuff you put into it.
You should be using a deep cycle battery for this sort of application , they are designed for this type of duty & a standard cranking battery is not.
Deep cycle batteries are rated in amphours of capacity & for long life should not be regular discharged below 50% of their capacity
A 100amp hr battery should only have 50 amphrs taken from it before recharging.
As I said if your fridge draws 4apms , it will use 4amphrs per hour of actual running time.A 100 amp hr battery will run it for 25hrs actual running time.
HOW LONG IT ACTUALLY RUNS FOR DEPENDS ON HOW YOU ARE USING IT
If being used as a fridge,not a freezer, this actual run time could be 8<12+hrs per day
AnswerID:
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Reply By: kcandco - Tuesday, Mar 03, 2009 at 09:42
Tuesday, Mar 03, 2009 at 09:42
Hi Daniel
what size wire have you used from fridge to battery (actual diameter of wire... not including insulation)?
how long is this wire?
what type of connections do you have?
what is the rc stated on battery?
I have a N70 starter battery and get 10 hrs runtime without starting car (about 42amphrs used) but I know this is not good for the battery and try to avoid it.
regards Kc
AnswerID:
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