# which inverter?

#### auntiebessie

##### Free Member
need to charge two 36v lithium e.bike batteries when of grid, any advice on what power and type of inverter I should buy please?

#### JeanLuc

You need to start by checking the data plate on the charger that came with the batteries. It should include the wattage demanded by the unit.
For example: Input 100-240V ∼ 50-60Hz XX Watts YY Amps

It is the XX figure that you need in order to size the inverter - normally specified in Watts output. If XX W is not shown, but YY A is, then XX times 230 will give you the Watts figure.

OP

#### auntiebessie

##### Free Member
Thanks for the advice. Did you mean amps times 230, also should I times the input or output figure by 230?

#### Wildman

##### Free Member
muiltiply the amps by the voltage. to get the wattage required to run the charger The inverter should preferably be double that to prevent overheating. Let us know the lithium battery details and those of the charger we can then give some idea of how much it will take out of your 12v battery to ensure you have sufficient leisure battery capacity to cope with it.

#### jockaneezer

Don’t know how to link to another thread here on my tablet, but Forestboy started a thread on this on Wednesday in the Technical section, should explain everything you need to know.

#### JeanLuc

Thanks for the advice. Did you mean amps times 230, also should I times the input or output figure by 230?
Yes, INPUT amps x 230Volts = Watts used by the charger.
You can probably get away with a Modified, or Quasi-sine wave inverter for the battery charger, but if you want the best option that would allow you to run more sensitive things from it too, go for a Pure sine-wave model (much more expensive).

I don't know haw much you know about this, so apologies if it seems patronising, but having calculated the watts needed by the charger (as above), divide that number by 12 (volts) to get the current drawn by the inverter from the batteries. E.g. a 500W load on an inverter will draw 500/12= 42 amps from the leisure batteries. In fact it will be a bit more than this as no inverter is 100% efficient so the draw in this case could be up to 50 amps for an 85% efficient inverter. If you have one 100 Ah battery, you should not run the inverter with this load for more than one hour as it would take 50 amp-hours (Ah) from the battery, or 50% of it's capacity - the accepted safe discharge limit.

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