Technical inverter question

[peter21]

Hi all,

I am trying to work out optimum size for an inverter for our motorhome.

We would like to run electric bike battery chargers from the inverter and plugging my battery charger into a power meter , on the 240 V mains, shows that it is using 90 W and drawing a current of .72 A.

Does this mean that an inverter running off 12V would draw about 14 A? The charger delivers its charge at 40 V and 1.8 A., according to the plate on the charger.

What size of inverter would cut the mustard?

I have looked at other threads on this issue but cannot find an answer to my specific question.

Thanks in advance.

 

[Lenny HB]

Yes your figures are right you get away with a 150 watt inverter but startup current can be quite high on switch mode power supplies on startup especially if they have not been used for a while. I would go for a 300 watt pure sine wave inverter.

 

[Richard n Ann]

240 V mains, shows that it is using 90 W and drawing a current of .72 A.

At 90w the current should be 0.375A

Or if the charger is taking 0.72A the wattage is 172.8w

They don't match up

 

[Robert Clark]

I’d be concerned about battery size too
Our 2 electric bikes pull about 20A and need about 4 hours to charge from flat

 

[peter21]

At 90w the current should be 0.375A

Or if the charger is taking 0.72A the wattage is 172.8w

They don't match up

Hi, Thank you, you are right. I rechecked and I think that the problem was that the meter doesn’t record power and current simultaneously;
the charger must have dropped the charge current as the battery voltage came up, between my readings.

Today it reads .35 amps and 78 watts.

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