Inverter for 4 Ring Induction Domestic Hob?

[Lodesman]

Dashew switched to induction - you might post a comment here with your question(s): SetSail » Blog Archive » Efficient Electric Cooking Part 1

[deckofficer]

If your planning on cooking via inverter and lead acid batteries, I agree with the above posts. Induction is a great way to cook with gen set or shore power, but due to peukert effect and voltage sag of lead acid batteries, I don't think it will fly. If you had a LiFePO4 battery bank and 48 volt inverter you would be good to go.

[smac999]

if you're trying to get 5000 w for (a 4 element stove, no idea what a ring or hob is...), run the gen for 10 mins while cooking...


an inverter that big just for that would be silly

[brightontrader]

Thanks to all posters, lots of views.

I have already installed the whirlpool 4 ring cooker top, so committed.

The previous cooker ran on one ring only on inverter, my thinking is that with this system I can run 2, total load 3.8kw, and still have other items such as PC, fridge etc running concurrently.

Having an induction at home for 2 years I know how I use it: On induction you only use full power rarely as its so powerful you burn the bottom if not just water in pan, then simmer at around .6 power setting...I have a relatively low power electric kettle for tea/coffee...

So 2 x rings = 3.8x.6 =2.28kw plus some more on start up...The 4 rings would only be used on SP, ie: most of the time when the wife is on board messing up the galley.

Reality is you do not necessarily use a cooker for long periods if you have a microwave/combi oven (I have), fry some fish, veggies on another ring, (full english breakfast takes 10 mins to fry up) how long is that? 25 mins max...Bread making is in oven, same for stews (man food at sea).

As I have posted, when actually passage making have 30amps coming from Prop alternator continually under sail, 50amps from engine if motoring. If at anchor then the issues come into play, then I do have a generator albeit only 6.5kw.

How much loss does a 5000w 24v mastervolt do. Its supposed to be 91% efficient. What does this really mean? And is there a lot of power used when idle?

Anyway, have put a bid in now on ebay, if I win it will mean a cheap expensive 5kw quality inverter. If I lose will get hold of 3.5 or 4kw one to run 2 rings. I have a source of very heavy duty deep cycle batteries made for US Army tanks, hoping to get 2 shortly as a gift, seconds, ie rejects due to scratches apparently.Boat is presently under batteried anyway.

Really I should have gone back to gas but boat I have bought has never had gas and fitting it is problematic....

This yacht, a steel dutch built one off, 46' on deck, 40' waterline, has the space for more batteries and large inverter, its not a racing boat, its a go anywhere cruiser. I bought it for a good price (I think) and am prepared to spend some on it getting it right and going for new approach equipment is a risk but also I have spent 6 yrs cruising off grid before (15 yrs ago) so do know how I use stuff. I also spent most time when not actually passage making in marinas even in places like Phuket, going out into Pangna bay with guests for a week at most off grid. In Europe, the Med, its hard to even find anchorages as most good ones have been developed into marinas anyway (Spain)!!!!

Wonderful thing about this is can flog mistake purchases on ebay, am changing out 10 yr old Lowrance radar and chartplotter for Raymarine kit and new autohelm already, will ebay off old kit soon. Its winter here, the boat is in a marina presently, will try unhooking shorepower for a while and try systems for a couple of days, see how it goes.

[transmitterdan]

Efficiency of inverters is measured from input terminal to output terminal. You can never achieve that in a boat unless all your cables are zero length. I see too many inverter installations where the DC wires are too small and/or long thus efficiency is significantly reduced. If you do the math and use wire big enough to not significantly reduce efficiency you might be able to achieve 85% efficiency. But you may be surprised how big the wire has to be. At 5000W and 24V the RMS battery current is about 250A. The wire size will be huge (12mm minimum and preferably 15mm) for even a 1M length. And it would be even larger for longer runs. Most inverters will not accept large enough wire so creative installation is required.

[brightontrader]

Dan, very good point, thanks.

May have to go to much smaller inverter from comments on here, like a 2.5kw to 3kw and if I win ebay auction 5kw use for small hydro am installing on a weir or re sell it,,,,,,auction is in 4 hours, have put in a minimum bid..oh dear..

I also remember reading that inverters run best on near full load and if over specified waste a lot..

[jwing]

Originally Posted by sea-bee

Our house is off grid, with about 2000w solar and 400AHr LiFePO4 batteries. On these hot summer days we have excess power, and use a single induction hotplate for quick cooking off the inverter. Draws about 100 amps.

Chris

Chris, check your numbers. My 1800W induction hob draws less than 15 amps at full power.

I only use full power to quickly boil water; when I say "quickly", only other induction hob users know what I'm talking about. After the water reaches boiling, the power is lowered to 10% or 20% to maintain a simmer. I never cook anything at higher than 30%.

Brightontrader, I'm sure you are aware that any one of the coils on your hob cannot draw the full 7.2 kW and even with two coils active at 100%, you will probably not draw 7.2kW. Different manufacturers have different ways of distributing the power. You mentioned you don't have the distribution information on your unit; you might find it here:
The Induction Site: Whirlpool Induction Hobs

Meanwhile, to get to your inverter question, think about how you will really use the hob while asea. I doubt you will ever use all four zones simultaneously. Let's say you would use a small one at 100% and a large one at 30%. Then, put a pan of water on each and fire them up accordingly. Use a multimeter to measure your actual current draw. That will help you accurately size your inverter.

Good induction electrical requirement primer here: Induction Cooking: Kitchen Electricity 101

[transmitterdan]

Jwing,

Chris is talking about battery amp draw when he mentions 100A. You have to be careful when discussing amps to know whether it is the AC side or the DC side. As a general rule of thumb in 24V systems the DC current is 6 times higher than the AC. So your 15 amps AC becomes 90A DC. For 12V systems the DC current is 12 times more than AC.

[atoll]

Originally Posted by transmitterdan

Jwing,

Chris is talking about battery amp draw when he mentions 100A. You have to be careful when discussing amps to know whether it is the AC side or the DC side. As a general rule of thumb in 24V systems the DC current is 6 times higher than the AC. So your 15 amps AC becomes 90A DC. For 12V systems the DC current is 12 times more than AC.

I think his cooker is 240 volts ac,not 110volts ac,so the draw would be;

24vdc-240vac=10x

12vdc-240vac=20x

[K_V_B]

Is it single phase 240V? Most larger induction cookers sold in Europe are actually set up for 3 phase 400V. You would then need three inverters in parallel. However it would solve the problem of getting enough power.

You probably need an inverter with power assist. You won't often run your hob at full power. But when you do your generator will be used to provide most of the power, and the inverter only needs to add the balance. A Victron Multiplus for example.

[brightontrader]

Jwing, very useful links....both of them. I do have the 1st Whirlpool cookertop, albeit a different layout (and only paid $377 new not $1000+) prices have obviously come down a lot since that was written.

I see that I could get by with my current inverter (Victron 1.5) for the one ring (1.4kw) which is exactly what I had before (ceramic) with the complicated power management system. Now have ditched that and am already better off as it worked intermittently.

The 30amp wiring to ring main was already in place as the ceramic on all 4 rings on full used 7kw, will take my chances on on 7.4kw on 30amp circuit (240V) as cannot think will ever use all 4 on full blast. (may print a neat sign to warn as much and put by cooker!) 2nd link from Jwing told me needed 30amp for 7.2 but also said that could probably get away with it if appliance used 7.4 as will never use all 4 on full power...so sorted...(At least on SP, if there is a fire can simply step ashore and call the insurance company

So, very pleased posted questions as replies have given me answers I needed, very quickly and now know that the induction change out from ceramic is worthwhile and do able, with maybe a slightly bigger (3kw) inverter with a overload cutout switch. Will give me 2 rings off grid on batteries and all 4 on SP obviously,.maybe 4 on genny...

now does anybody want to buy a 5kw Mastervolt Dakar Pure sine.....going very cheap//$1185

[brightontrader]

KVB, you are writing concurrently with me.

Its a domestic Whirlpool, single phase....I had 3 phase in my factories, haven't thought of 3 phase on boat, I don't think marinas would supply it apart from to superyacht berths maybe.

Mine is a superyacht, to me anyway..

[transmitterdan]

Originally Posted by atoll

I think his cooker is 240 volts ac,not 110volts ac,so the draw would be;

24vdc-240vac=10x

12vdc-240vac=20x

Atoll,

You are probably right about the 240V (hob should have given it away). But since the inversion process is not 100% efficient I like to plan for about 20% more current to make up for inefficiencies in inverter and wire. So DC current would be 12X (24V) and 24X (12V) as a better rule of thumb for 240V inverter systems. Thanks for correcting my mistake.

[jwing]

Originally Posted by transmitterdan

Jwing,

Chris is talking about battery amp draw when he mentions 100A. You have to be careful when discussing amps to know whether it is the AC side or the DC side. As a general rule of thumb in 24V systems the DC current is 6 times higher than the AC. So your 15 amps AC becomes 90A DC. For 12V systems the DC current is 12 times more than AC.

Thanks for the clarification!

[ryon]

I could go on with my list of reservations, but it seems to be working for you and that's what's important. You make a point about pure sine wave inverters, and those shouldn't be necessary in this application at all. A dirty square wave or whatever should work just as well.