electrical question AC from inverter and induction cooktop.

[Robin]

Portable induction cooktops are on sale here at under $100 and I know some boats have them, but run them on shorepower 120VAC or with a generator. We don't have a generator, except for a 1KW portable Honda but do have a 3KW Magnum modified sinewave inverter/ charger and if needs be we can run the engine with it's 150A alternator charging. So questions:-

Will a a portable induction cooktop run on the inverter?
How many Dc amps would a typical induction cooktop take, I haven't found any published AC watt consumption figures?

Would such a cooktop trigger the inverter to come on, I think it needs to 'see' a certain AC minimum load before it cuts in and no shorepower is seen as available?

I have a mind blank over such AC power, OK with AC from the shore setup, Ok with Dc from the batteries, but put the two together and I'm left scratching my head in despair!

Secondary question too please, we have some on board AC table lamps fitted with 120VAC 15w energy saver bulbs supposedly equivalent light output to 60W incandescents, how many DC amps would these take via an inverter, a friend said less than the usual cabin 12VDC fluorescents is that correct?

TIA

 

[Piers]

Hi Robin,

First, Volts x Amps = Watts is a great little formula to use to answer some of your qns. To check the required supply for the hob, just see what KW the cooking rings on the hob requires and use the formula to check supply v demand.

Second, our induction hob is very Hz sensitive. The supply has to be 50hz (we are in the UK but yours would be 60Hz) +/- 1Hz or it won't work. I'd recommend checking the tolerance of your proposed purchase to see if it can mate with your supplies.

All the best.

 

[john_morris_uk]

Some interesting questions. Power is amps x (rms) volts whether it's AC or DC but there are a couple of complications. Portable induction hobs can be up to 2kw so ignoring any power used by the control circuitry at 115 volts AC that's just under 17.4 amps. If your invertor was 100% efficient and your batteries held up at around 13.8 volts on load then the invertor would draw just under 150 amps.

The trouble is that the invertor isn't 100% efficient. Firstly most invertors have a 'standby current draw'. This might only be a few thousandths of an amp or it could be half an amp or even 2 amps. Then it also loses a bit of power (as heat) in the process of converting 13.8 volts to 115 or 230 volts AC. The good news is that invertors can achieve efficiencies of 98% or so. The bad news is that modified square wave invertors can mean less efficiency of devices being powered. In fact some things won't work at all...

The 150 amp alternator wound appear on paper to be 'just' capable of keeping up with the demand of a 2kw induction hob powered by your invertor but again, it isn't quite as simple as that. It's 150 amp rating will only be achieved under the most perfect if conditions. As soon as it warms up etc it will be derated.

My conclusion is you need to get a high current ammeter and try the system out. It might work ok but you might have to keep the charging going a little to catch up any deficiencies of charge accrued while you are using the hob. This also assumes that the hob doesn't object to being run by your invertor!

Regarding the small lamps, the invertor becomes very inefficient at very low current draws so your local man of knowledge is almost certainly wrong. Although 15 watts should only pull just over an amp each at 13.8 volts via the invertor, the invertor will be taking 0.5 amps of more just to run its internal circuits. If your fluorescent lights are 8 watt ones then they will definitely take less current. 12 watt and 18 watt fluorescent lights (the other common powers in use) will still almost certainly take less due to the inefficiencies already mentioned. The auto standby is often adjustable but it's there to avoid current drain when the invertor isn't being used.

I hope I've explained it all reasonably clearly. I'm on my phone so it's hard to read back the whole text.

 

[savageseadog]

The obvious answer would be a 12V or 24V induction hob, if such a thing exists

 

[rosssavage]

Have to be 12vac or you end up with a huge electromagnet!!

 

[Robin]

I think I will just stick to gas (propane) cooking and just occasional short use of the 950W microwave via the inverter or AC shorepower or the Honda portable gennie which at 1KW can run one of the two on board sir conditioners to cool either the main cabin or the sleeping cabin down.

Thanks to all for the replies and have a happy New Year Y'all!

 

[david_bagshaw]

Try a microwave on your inverter, if that works then the induction hob might. Induction hobs are very fussy as to voltage and frequency.

 

[Robin]

The microwave works but I have no idea what wattage the induction cooktops are that are on sale, it didn't say on the box that is on show in the store nor on the seller's website.