quick battery question

[trains]

Hi chaps.

I have a standard N55 battery 460cca, which I used for my 2nd battery in my dual batt setup, and used it with a borrowed 3 way.
Have used it on the fridge for up to 5 hrs without charge when we went on some of the better walks when we did the center last year.

It s still going fine after all that abuse, my question is this.
How would it go running an engel, or evakool type fridge overnight?

I know that the 460 is cold cranking amps for heavy starting, and not a guide for amp hrs.
I have tried to search for this, but i must be doing something wrong as Ive waded thru alot of posts without this information im looking for.

Can someone either direct me to a post where this is covered, or could it be explained how to calculate amp hrs from a normal 12v battery.

I assume that in the evening, it would be without charge for 12 hrs, consuming say 2 amp hrs/ hr = 25ish amp hrs.

Cheers

Trains

[drivesafe]

Hi trains, someone else can correct me here but I think you will find the a battery with a designation of N55 usually means it’s the equivalent of a 55 A/H battery.

Check with the battery’s manufacturer’s web site and again, someone here might be able to clarify this but I have a bank of batteries that are Exide 200 A/H agriculture batteries and they all N200.

If this is the A/H of the battery then you should be able to get a fair idea of how long it will operate the fridge for and base your usable capacity of the battery at about 50% so you have about 27 A/H to work with.

Cheers

[trains]

I rang the supplier, and they said that it has 80min of reserve meaning that if the alt stops charging, it can continue to run for another 80 min without recharging.

I realise that all starter batteries have some form of reserve capacity, I just wanted to know your experiece of running fridge loads on a starter battery, and how long its taken to get down to 10.5v which seems to be average for their cut out.

Cheers

Trains

Ps they offered me a deep cycle 60ah for 175. But I dont think it will fit.


Edited to add.
taken from a battery site.
Reserve capacity is the time in minutes that a new, fully charged battery will deliver 25 amperes at 80 degrees farenheit and maintain a terminal voltage equal to, or greater than, 1.75 volts per cell.


So I assume that 25amps/1.3 (80mins) = 19 amps/ hr available total.
Therefor if 19 amps are available for 1 hr, and I use say 2 /hr
I have about 9 hrs of 2 amphrs use till it drops to the 1.75v/cell. which I assume is 10.5v, 6cells x 1.75.

Is this correct way of looking at it.

cheers

T

[drivesafe]

Hi again trains, if your N55 is fully charged when you start powering the fridge, then based on the info you have supplied you would ( theoretically ) get about 27 hours of operation by the time the battery got down to 10.5 and cut out ( if your fridge has an automatic cut-out ) but in reality you would get about 20 to maybe 23 hours operation before the cut-out activated because the load on the battery will actually lower the voltage, even though the battery has more capacity and the bigger the load the greater the voltage drop is going to be. So if you were to place a load of, as you posted above ( and these are very VERY rough comparisons ) 19 amps on your 55 amp battery you would be lucky to get an hours operation but a 2 amp load is going to take roughly 20 ours the flatten the battery, a 100% improvement in operating time But again, these are NOT the correct figures, just an example of what is likely to happen.

As I posted, go and check out the manufactures web site, some of them give load vs operating times.

But there is something else you should consider. If you continually take the battery down to 10.5 volts ( 100% discharged ), you are going to shorten it’s operating life.

If you can, and depending on the battery, try not to use more than 75 to 80% of the batteries capacity which is about 11.7 to 11.6 volts.

Cheers

[me3@neuralfibre.com]

80RC * 0.4 = a/h

Give you about 30AH

That's using all it's got - not good for it's life.

You fridge will use *approx* 40Ah per 24Hrs

Work it out from there.

Paul