Current rating for 12v plug on 300W in-car inverter

Question

I have an in-car inverter which is rated 300W. This is the only labeling:

I need to source a 12V cigarette socket plug to connect to the input.

I have found the following one which is labled: Carpoint Universal plug 6-24v max 8amp

Assuming I have a 12V car power supply, would the 300W rating on the inverter, suggest that this plug would have an insufficient current rating:

P = IV
  = 8 * 12
  = 96 Watts

Or should I be calculating based on the 230V output device connected:

I = P/V
  = 300/230
  = 1.3 Amp

Of course, with the latter calculation I'm unsure if this applies exactly to the inverter's input.

Your first calculation ie with 12V is the way to go, but try 300/12... — Solar Mike, Jun 24 '20 at 08:10

score 2 · Accepted Answer · answered Jun 24 '20 at 08:10

Power at the input is the same as power at the output minus inefficiencies or losses. In your case your inverter will take 300/12 Amps or about 30 Amps allowing for losses.

The cigar lighter is totally inadequate for this the inverter should be hardwired straight to the battery with a suitable fuse in the wiring near to the battery.

score 1 · Answer 2 · answered Jun 24 '20 at 08:13

That inverter will draw 300W / 12V = 25A at full load (assumed maximum).

So that plug is not sufficient. You will need wires sized for 30A, go higher if necessary and a suitable fuse.

I would connect direct to the battery so as not to overload the car's existing electrical wiring.

score 0 · Answer 3 · answered Jun 24 '20 at 08:10

0

The connector knows nothing about your inverter. It only knows about the current through the contacts so it's 8 A at 12 V is the limit.

answered Jun 24 '20 at 08:10

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score 0 · Answer 4 · answered Jun 26 '20 at 05:30

The 8A is the current rating for the plug (based on gauge of wires/connections, maximum heat, any fuses inside), so 12V * 8A.

You are not only limited by the plug but also by the wiring harness, for which the current is limited by a fuse, usually in the fuse box.

This is for a vehicle? Do you know the max current that can be supplied?

If you plan to use less than 300W you could use your actual rating instead. These inverters are efficient enough to scale down almost proportionately.

So for 300W you'll need to supply 25A, but for 100W you'll only need 8.3A.

Not all your "12 V auxiliary power outlets" in the car can supply enough power, even for a cigarette lighter.

You'll need a wire gauge of 12AWG for 20A up to perhaps 15ft (if you need precise values I can look that up) Not only is voltage drop a concern, but also heat generated in the wire.

Current rating for 12v plug on 300W in-car inverter

4 Answers4