100ah Battery Voltage Question

[maddogrc]

i'm yet to leave the fridge running for more then 5 hours so far...

i plan to probably leave the fridge running for 15 hours max before doing a day of driving, say 4 to 5 hours of driving, when camping/4wding. well the car will be running during 4wding so its still getting a charge...

i honestly dont know the charge rate of the car...

i plan to eventually get a proper charger (multistage like the ctek) and then do a full slow charge after every trip to keep it looked after and maintained.

1 hour a day is probably MINIMUM i drive however.

i'm guessing its time to invest in a deep cycle battery then ay tony? you say that i'm probably using 46Ah for 23 hours of use (approx 50% being cycling), then i actually think getting a deep cycle would be a good choice.

is it worth getting a 100Ah battery? if 50% discharge of a deep cycle is a safe point then a 100Ah probably works out better in the end if i'm doing 46Ah a day approx.

 

[maddogrc]

actually, forget that last post...

in your personal opinion, what is the best and easiest way (also hopefully affordable) to make it so that i can leave my fridge running every day? (higher setting during the day, put it down to lower settings at night).

by the sounds of it a 100Ah deep cycle would be the go since 50% is a safe discharge point of a deep cycle, and i'd be only using 46Ah MAX per day.

the car would be driven at least 1 hour a day MINIMUM up to 5 hours (with a few say 10-30min stops).

EDITTTTTTTTTTTTTTT:

just did some more reading and it seems like a 120Ah AGM might be the way to go.

faster charging which is beneficial since i only do a few hours of driving each day, with the fridge on all the time.

 

[Old.Tony]

The AGM is a good battery and doesn't suffer from over-voltage like gel batteries can - your alternator is capable of high voltages, and the regulator keeps it down, but they vary from 14.4 to 14.7V and gel batteries can't tolerate over 14.4V.

They're not cheap batteries but they'll give you a good service life if they're kept well.

The trick is to keep the battery as charged-up as you can manage. If you're investing in a good multistage charger, then you could tack another $80-100 on top and use it via an inverter to charge the battery constantly (and supply 240V to the fridge while the battery is being charged).

Assuming minimal outlay ... If you're driving for 5 hours a day, that battery is going to get a decent charge off the alternator. Don't worry about counting the fridge power consumption while driving ... so it's19 hours of operation, 50% duty cycle = 9.5 hours @ 4A per hour = 38Ah used each day. You would charge at higher than the 7A, that figure was a "optimal" charge rate - so your battery ought to do well.

Just make sure you use really good cable from the engine compartment and don't use a chassis earth - pull both positive and negative lines all the way back, drop a 30A thermal breaker right near the battery and run that through a relay that only comes on when the ignition is on.

 

[maddogrc]

in your last sentence, do you mean that for any accessory i hook up such as the fridge to run both + and - leads back to the aux battery??? if yes then i already do that. if no then where do i earth the aux battery to???

also your statement about the charger... you imply i should purchase say a Ctek or similar, connect it up to an inverter in the car, and then drive around with the inverter and charger always on so that the battery is ALWAYS charging and kept topped up???

but yeah, one of the other forum members here found a good battery shop and they're flogging off 120Ah AGM batteries for $264, and thats a hard price to beat!

cheers for all the info tony, hopefully my setup will go well with the new AGM.

 

[Old.Tony]

Yes to all of it.

Earthing to the chassis becomes a weak point in the electrical chain and it might give out on you when you least expect it. Wiring up as you have done is the way to go.

The idea of starter battery -> fuse -> relay -> cable to tub -> inverter -> charger -> aux battery is one that I am using myself, it not only charges the aux battery better, but it runs the fridge on 240V while the battery is being charged so the battery charger doesn't get confused.

When you are charging a battery, the charger looks at the voltage going in and adjusts itself according to that. If a load is placed on the battery, that voltage will drop, the charger will see that drop and may think the battery needs even more charging, so instead of sitting in absorption mode (nearly full) the charger may swing into boost mode, which isn't good for the battery.

Using an isolation mechanism and charging off your starter battery (and therefore your alternator) directly is fine, just remember to fuse both sides of the cable right near the batteries.

 

[maddogrc]

my setup which as shown in the redarc manual is...

start battery - cable - 80A fuse - cable - isolator - cable - 80A fuse - cable - aux battery (all cabling is pretty decent sized, could of done 0 gauge, but as i dont plan to use the batteries in dual cranking mode i thought my 2 gauge wiring was adequate.

got the aux battery grounded to chassis earth, and i made sure to grind the paint off the chassis first, also for the isolators earth i made sure to grind off the paint on the firewall where i mounted it.

do you think that just having it as a basic setup where its simply charged off the alternator is GOOD enough, with me giving the battery a good slow 'conditioning' charge say once to twice a month to keep it 'regular'?

 

[Old.Tony]

It sounds okay, the only way to really tell is to try it out. It can always be changed! When you're home for a few days, whack the battery on a charger and when it's full, disconnect everything for about 6 hours and measure the voltage. If it's around 12.6-12.8V, it's all good.

 

[KraftyPg]

Pretty much the same set up has been working for myself and my old man in different cars for the last 15 years in 8 different cars.

The only differences are I only have one fuse of about 50Amp between the isolator and the second battery and it's self resetting and I only ever bother whacking it on a 240V charge about once every 12 months unless I know I've run the battery down.

I only ever use the inverter when I'm out on the farm or not close to a 240V supply and we need drills or saws etc and in 15 years we've only ever had one battery and one Piranha isolator system fail.

 

[dunkmuddie]

if ur after a AGM try fullriver on ebay mine 120ah only cost $335 and its great done a few good long trips away with no problems

 

[maddogrc]

theres a place here in perth doing 120Ah AGM batts for $264

definitely a bargain, and hopefully alright quality...