Thread: Second battery question....

I run an optima yellow top for my aux battery an red top for my starter. I only have a 35ah because my bracket is pretty small and cbf changing. Obviously bigger is better as yo are able to run more off for a longer time without recharging. I bought both my batteries from battery Mart in NSW I think for 350 a pop with free postage. So far no issues apart from I don't drive enough to keep my fridge on 24/7. If your only gonna be using every now and then the optima boasts significant shelf life (keeping charge) over other batteries. Have a look at the optima site and compare for yourself. Hope I've been a little bit of help.

I have a td5 and although it's different, obviously there's some similarities. Mine is mounted in the back bin and is a 150ah battery from a mob in Perth, $350 or thereabouts, delivered to me in Adelaide. Mine will run my 60L fridge for a few days in the parked car over summer without running out of power. It won't keep it going for a week, but I can't see me ever needing that. I only leave my car Unused for at most 2-3 days and that's only a couple of times a year at that. I keep a whole lot of water in it and also beers and flavored milk when I need to. There's plenty of info on here about amp- hours and all the deal to.

Sent from my iPhone using Forum Runner

Originally Posted by Barney2803

Mine is mounted in the back bin

I wish I had a back bin . Does anyone have any suggestions of where I can mount a bigger battery in a d2 with rear seats. I plan on getting a drawer system and platinum slide so maybe something with that somehow?

Mate,

As I understand it a fridge pulling 3A from a 45Ah battery will run for 15 hours 45/3=15. This means it would run comfortably overnight. Check the draw of the fridge on the manufacturers specs and pre-cool it off the mains at home with your six pack of babysham already in it. make sure any fat Scotsmen stealing your chocolate close the lid properly.

Get the biggest Ah you can as taking the V8 for a spin to recharge the battery will cost you more after about 50km!

Good luck buddy.

Just a quick thought don't drain your battery dead

If you wanting to prolong the life of it keep the amperage to No less than 30% of battery AH

booya on the throne

There is a thread on here somewhere that gives all the good guts on what AH really means.

My recollection of it was that a 100 AH battery will only give you 50 hours at 1 amp of drain and then it would be considered a flat battery. Again from memory a batt is flat at 10.5 v?

I run an ARB 49ltr from a 100AH and with the fridge set to shut off when batt v is 11.3
I get at least 48 hours from the fridge set at 2 deg, they are super efficient. Love it.

The Ah rating is based on a specific discharge rate which is usually give as something like C/10 or C/20. C is the capacity in Ah, and the number is the time in hours, so given a capacity of 66Ah for a yellow top optima we can calculate the current draw at which the battery was rated: 66Ah/20h= 3.3amps.

Battery capacity varies with load, so a load higher than 3.3 amps will reduce the effective capacity.

The load specification of a fridge is given under a specific set of conditions. The ARB 47lt is rated at 0.87amps per hour when set to 3ºC with an ambient temp of 26ºC-31ºC. The fridge will actually draw more than the above figure when it is running but because the compressor will cycle the hourly consumption is relatively low.

Assuming you never discharge below 33% a 66Ah battery has a usable capacity of 44Ah.

Once you have your load figure you can determine the approximate run time from the battery.

Battery capacity (Ah) / (load in amps) = Time in hours

44/0.87 = 50.56 hours.

If you set the fridge to a cooler temperature or run it in hotter conditions the current draw will increase, and your run time will decrease.

Waeco give specs for nominal load rating of the fridge, and run time per hour rather than amps per hour. The CF-50 is rated at a nominal current of 7.0 amps and will run 15% of the time with an internal temp of 5ºC and an ambient temp of 32ºC. By multiplying the nominal current by the run time you can determine the amps per hour used - 7 x 0.15 = 1.05 amps per hour.

The Waeco example shows that while fridge ratings show low average amp
per hour current draw, the reality is that they run at close to their nominal current rating for short periods of time. This means the fridge is loading the battery at higher discharge rate than the specified capacity rating for short periods and will reduce the rated capacity of the battery.

The figures are 100% as there is a correction factor based on the battery design, but this isn't usually published and the calculations without are close enough for estimation purposes.


cheers
Paul

A battery is like a tank full of water with a tap and hose connected. If you turn on the tap the water comes out of the hose a certain rate. This is the same as the amps when you turn on something electrical. Amps are a flow rate. The total volume of water in the tank is equivalent to the Ah or AmpHours of the battery. Another similarity is that the water comes out of a tank at a certain pressure; this is equivalent to the voltage. As you take water out of the tank and the water level drops, the pressure drops, too, to the point when the tank is nearly empty, the water comes out at a dribble and isn't really usable. Also, the faster the water comes out, the lower the pressure of the water flow. Similarly for the battery; when fully charged it might have 13.8 volts but as you use up the electricity the voltage of the battery drops. The voltage will also be lower the faster you draw down the current.

The two main differences between a battery to a water tank is that firstly, the capacity of the battery in Ah, which is the amount of current you can extract, depends on the rate you take it out (in amps) and the ambient temperature. Secondly, whilst you can empty and refill a water tank as many times as you like, a battery has only a certain number of recharging cycles and that number depends on a number of factors including how much you take out of the battery. Thus if you flatten a battery, you can significantly reduce the number of recharge cycles, and hence the life, of the battery.