A 12v Car battery, connected to a 600watt 12v-240v Inverter, powering a 400watt halogen heater, how long run?

Question

I'm trying to see how long a mains (240v) Halogen Heater will run for from a Car battery (not connected to engine, just standalone). I want to use an Inverter connected to the car battery which will convert 12volts to 240volts to power the heater. The Inverter is rated at 600watts, and the Heater is 400watts, so how long will it run for before going flat? Anyone help do the maths/theory for me?

Answer 1

you forgot to include the power loss created by the inverter.
sorry jaktyee96

Answer 2

It depends on the type of battery you are going to use.

Car batteries are different to Caravan (or leisure) batteries, as car batteries are not designed to be used in the way you propose, but they do look the same.

A car batteries normal use is to store power, give lots of current for a short time to start a car engine with the starter motor, and then be recharged by the alternator soon afterwards. Car batteries do not like to be "deep discharged" and will soon fail if they are. You seldom take more than 10 - 20% of the available power out of a car battery in normal use

Leisure or Caravan batteries will provide power over much longer periods and can be discharged to around 80% of their total capacity without long term damage. If you are going to use this method get a Leisure battery and not a car battery.

If you have a typical 70 or 80 amp/hour leisure battery (car battery size!) then you can expect it to last for beween an hour to an hour an a half - depending on how efficient your inverter is and more importantly at what voltage it will shut itself down (it does this automatically to protect the battery). Make sure you use heavy duty cables from the battery to the inverter and keep these as short a possible - if you need to extend the cable do this with the mains output side. Remember that there will be 30 - 40 amps of current flowing in the battery wires so make sure you use thick enough cables and appropriate fuse to protect against short circuits etc.

Here's the maths:

400w = 33.33 amps @ 12volts (400/12)

Inverter efficiency can vary, so estimate 85% at a high load

33.33 / 0.85 = 39.21 amps.

Typical battery = 70 to 80 amp/hour

80 amp hour x maximum 80% discharge = 64 amp hours max

64 amp hours @ 39.21 amps = ~1.6 hour maximum

Good luck.

Answer 3

Here's what I got!

The inverter is stepping the voltage up from 12 to 240 which is a step-up up factor of 20. The heater you are using is 400w, so...

400w / 20 = 20Amps The inverter will draw 20Amps @ 12v from the car battery.

*Damn - I thought I had it right, transformers and things like that have always confused me! I've been looking at everyone elses answers for a few minutes and I understand it all now. 400w is 400w no matter what the voltage is so you would divide it by 12, the smallest voltage, the step up factor doesn't matter. Thanks everybody! Good job I looked back on this question.*

Answer 4

You'll be lucky to get an hour from a 60ah car battery. Use at least 6²mm cable as the inverter will be drawing at least 33 amps.

Randombus you have an error in your calculation!! should be 400/12 =33.33 amps!!

Peekatchoo, I am well aware of this, but was trying to keep the answer simple as it's not a viable project in any case!!

Answer 5

12v To 240v Inverter

Answer 6

It depends on the AMP Per Hour rating of the 12 volt battery
for eg.60amp ==I reckon 30 hours If battery is fully charged however the drop off curve could lessen the time considerably.
It might be 3 hours its along time since Ive done this sort of maths& Im, abit rusty.

Answer 7

With the losses inherent in the motor and the alternator, the battery will gradually go flat. Actually a motor itself puts some power back into the circuit, it uses a lot to start but them the amount of current drops considerable as it runs. I'm not sure what your question has to do with cars and transportation though.

Answer 8

what size wire makes a big difference in this application, I really cant see it working due to the amp draw from the heat strips will be strong for the battery combined with the inverter to step up to. good luck and let me know!