Thread: Dual Batt and Inverter (second battery stuffed?)

too much current draw for the battery but I doubt it, its sounds like the battery is on the way out.

An inverter draws approx. 1/10th number of amps as its wattage output, ie a draw of 300W will load 30 amps. This is a rough guide based on inverter efficiency ratings, Your fridge is going to use only 3 to 6 amps. Some deep cycle batteries are not designed to run high discharge currents. So an inverter should be run within a battery's current rating. Personally I use a semi-deep cycle battery which does both starting and cycling.

I usually run with it draws about 1/8th of the watts your drawing from it in amps

look at the laptops plug pack and it will say XWatts (my toshibas draw anything from 60 -90 w

lets work on 80w to drive an 80w 240v load the battery needs to be able to supply 10Amps at 12V to the inverter terminals. To confirm that its NOT a case of 2 switchmode power supplies trying to eat each other grab a bedside lamp that has an incandescent bulb (the old school kill the planet by making a wire hot type) in it of the same rating as the plug pack you are trying to run.

IF the inverter shuts up with the same wattage bulb on it and the battery voltage plays nice then you have the funky wave dance happening between the inverter and the plug pack and it doesnt take long for something to go "foom" and then the smoke gets out.

IF it doesnt then its the battery..

BUT take hope if the inverter shuts up with the XXW light bulb in it you may be able to kill off the funky wave dance caused by the laptops inverter by the addition of a 10-25W light bulb as dummy load to buffer the wave form.

Originally Posted by bee utey

An inverter draws approx. 1/10th number of amps as its wattage output, ie a draw of 300W will load 30 amps. This is a rough guide based on inverter efficiency ratings, Your fridge is going to use only 3 to 6 amps. Some deep cycle batteries are not designed to run high discharge currents. So an inverter should be run within a battery's current rating. Personally I use a semi-deep cycle battery which does both starting and cycling.

thanks bee utey - does this mean I should be looking for a dual purpose battery, or just look for a DC Batt that can give 30A+?

thats almost never a bad plan thatway if you need to you can jumpstart off of your second battery if you kill the main or replace the main with the secondary.

My current favourite battery is a Besco N70EX Extreme, this battery is rated at 620 CCA and 80AH so it will run your fridge, start the engine, run the winch etc and fit instead of a standard battery. It is rated for 4WD service and has water filling caps. My last one just died after 8 years. A replacement was $160.

As it is described as a "semi-deep-cycle" I assume its cycle life is shorter than a specific deep cycle battery, but you need to ask yourself how many times you fully cycle it in a given year. If you spend your whole year on the road travelling a full deep cycle may be better. For casual use my choice suits me well.

Dont run a laptop off an inverter if you can avoid it...

Get a 12v to XX volt laptop power supply... Your laptop will much prefer it

Also more efficient with less losses

had same issue as Flagg. I was attempting to run a Bushman 12V fridge (3 amps max) from the a 12V 10 Amp outlet in the rear of my p38. OK when engine running but fridge would cycle but not start when engine shut off. Similarly, 150W inverter would squeal whether engine was running or not.

I ran a larger +ve feed and also a direct earth (6g B&S) from the main battery to a fuse box I installed behind the subwoofer unit...problem solved on both counts.