Inverter Reality Check

[Dieseldonkey]

If the van has a small 750w microwave or a similar wattage kettle running just for 2 minutes or so at a time, but powered from a leisure battery and inverter, is a short duration high load viable without damaging a leisure battery?

 

[Loz]

A 750w kettle will probably take just over 8 minutes to boil so even that will not drain a battery, its how many times you do that and run your microwave before recharging is the issue.

 

[Dieseldonkey]

Thanks @Loz. So it's the state of charge remaining in the battery that affects it's condition and service life, rather than the sudden high demand for current, over a few minutes?

 

[mmi]

A short play with numbers because I like numbers .

From a battery 750 W = 12 Volts x 63 Amps, add some margin for inefficiency of inverter, lets say 15%. It would mean the current draw from battery would be about 72 Amps. If having a battery with capacity of 72 Ah (AmpHours) the battery would be drained in an hour.

If I understood your question your concern was if the current above would damage your battery in the long run. Definitely not – a 72 Ah battery has no problems with that. It is well within “specified working range”. Even to drain the battery in one go.

The warm up power because of battery’s internal resistance at 72 Amps is about 30 Watts. So the warming of battery is hardly even measurable considering the mass.

Just a note that thanks to battery’s internal resistance you will notice voltage drop of about 0.5 Volts at the battery.

So when to worry – if having more than five kettles on at same time .

As you said, the enemy of battery is deep discharge, if left in that state for weeks.

 

[Pauly]

I have exactly this setup, low wattage kettle running a 1000w quality pure sine inverter and works fine but we only use it on the odd occasion when out and about
Can make 3 cups at a time and takes 6-7 minutes to boil but happy with it and very handy after a long day out and about before a long my drive home

 

[J8usx]

Which inverter do you have please Pauly?

 

[Pauly]

I have a sterling pro power pure sine
Pro Power SB Pure Sine Wave Inverters

 

[DaveyB]

Running a Sterling 1600W pure sine wave inverter myself. Also have a 1000W kettle.

 

[Dieseldonkey]

Thanks for sharing your knowledge chaps.
@mmi. Liking your numbers very much.
@Pauly. Will add one of those inverters to the shopping list.

So a pie and bovril is about 0.1kWh worth