240v without genset

[roly_voya]

I am looking at fitting a 240v inverter system running off the main engin alternator to power an electric oven, kettle and breadmaker, anyone ever tried this.

I am looking at Studer XPC1642 (from ampair) or Victron combi inverter both giving 1600w cont' and 2Kw+ P30

The oven is a Panasonic Dimension4 drawing about 1500w peak for each of microwave, grill and fan oven functions

Alternator will probably be Bosh 90A 24v (2Kw useable output)

The limitations seem to be current draw from batteries which is around 80A. I want to keep this below the 5h battery rate to mimimise voltage drop of and be kind to the batteries which suggests a 400ah plus bank. I have room to fit this and assuming I run the engine while cooking night and mornig will mean a normal max discharge cycle of less than 25% so thinking of fitting good 'leisure' batteries rather than proper deep cycle jobs. As well as being lots cheaper the higher charge acceptance rate and thinner plates might lead to less problems getting up to full charge and shorter engine run times.

This idea came about because I don't want gas on board and spend long periods going to work (as a nurse) when the 'conveniences' become more like essentials when rushing for an early shift. Have been living in a marina for the last 12 months but want o have more freedom this season

If the whole lot goes pearshaped at sea I am fitting a taylors hob so will still be able to cook!

PS in Milfor Haven area and always interested in meeting other liveaboards

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[Ric]

This seems a massive expenditure and complication if your entire reason is to avoid gas. A well installed gas system is not dangerous and will save you huge money. I have my bottle in an outboard draining locker, and it is controlled by a fail-close solenoid valves on the neck of the bottle. To open it I press a button by the gas cooker. The solenoid closes automatically if gas is detected in the bilge, or if there is electrical failure. The system cost about E150. The cooker itself has a thermal valve, and I also have a hand valve directly upstream from the it, which I turn on only when I need.

240v on board is great - but surely not simply to avoid gas?? Sorry if this is irritating advice...

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[Anonymous]

Kinder so your batteries, cheaper and better would be an ac generator driven from your engine. I experienced this six years ago on a Broads hire boat and investigated at the time - a company specialised in supplying all the kit you need. On the one I used, you set the engine revs to around 2000 RPM to give around 50 Hz and even from no load to full load (there was a toaster, microwave and kettle) the frequency drop was small. Not surprising, really, since the throttle on a marine diesel is basically a speed regulator. I used to tweak the revs back up to 2000 when the load was high.

It worked very well indeed. I wish I could remember the name of the people who marketed the kit but I don't, so you'd be best researching the internet for yourself or hope that someone else here knows what I'm on about. If they don't you could try one of the two UK newsgroups - the one on inland waterways is very heavily into this sort of thing. I'm pretty sure that it will be cheaper than an inverter, extra batteries, heavy wiring and switchgear, and be lighter and less bulky.

Taking big lumps of energy out of any lead acid accumulator is to be avoided unless there is no practical alternative, in my experience.

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[Talbot]

240v on board a boat has its own hazards which must be recognised. There have been some nasty accidents with people being electrocuted on their boats even with professionally installed systems. Personnaly I would rather have gas (stands back and waits for comments on last sentence/forums/images/icons/smile.gif

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[Anonymous]

That's as maybe but the original poster asked how he or she could get 240V ac to run an electric oven, a kettle, and a breadmaker. I'm with them on all of those things; gas is slow to heat a kettle and knocks a big hole in your gas supply (which you have to carry on board in all weathers!), many small boats don't have room for a oven - you are stuck with a hob/grill which is a real pain cos you can't use cook-chill convenience foods - really useful for someone working odd hours, like a nurse. Lots of people who have got used to a breadmaker really like the result; you can cook your own recipe just as you like it. There isn't a gas option for those things. Lots of small boats don't have room for a decent diesel generator and you see people messing about with small petrol gensets on deck, or on the dockside - not ideal at all. I agree with the questionner 100% that what is needed is a source of 240V ac derived from the main engine. I just don't think that it should be via the 12V alternator, stored in a battery and then inverted and stepped up again, I think it ought to be generated by a 240Vac generator running off the main engine.

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[Ric]

There are several systems that do produce 240v direct from the main engine. It has a 240v ac alternator, which is then fed into a modulating box which converts it into a perfect 50hz sine wave. The systems are very expensive. If you have a volvo engine, you can get one from them for about £3500 approx (I'm converting from price I know in Euros). You can also get cheaper ones that will fit any engine, BUT you will have lots of installation costs as they are not so easy to bolt on. And as somebody else has pointed out, you have to be very careful with the installation as it can be a dangerous system.

They are a good option for 240v if you have a smallish engine. For bigger engines, better get a separate generator I think.

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[HaraldS]

I have such a system, though more to have a backup for hi-power AC if the generator fails, and also to make use of some extra power when I need to motor.
I don't cook electrically, but we have an electric kettle and if we have AC power anyway, like in marina, under engine or when the generator is running we use it in favor to gas. The other big AC users are: Watermaker, dive compressor, washing machine, microwave etc.

I have just upgraded to a bigger 3000W inverter and sold the 1500W continous power that I had before on ebay a week ago. Both are Victron and seem very good.

For testing I have run a 2750W heater for an hour from the batteries, which are supposed to be replaced this spring and they were happily supporting this torture.

You need to keep a couple things in mind though: The currents on the DC side are VERY high, even on my 24V system I was drawing 140 Amps, with 12V this is getting close to impossible.

You need very solid wireing on the DC side, any bad contact could turn into a fire hazard, and you need fat wires. I'm running 70mm2 from the battery bus to the inverter, for 2.5 meters length and still have about 8% loss on the cable when under full load. Remeber that the loss on the DC wires goes up square with power you draw. Under full load (2800W) I measured a loss of 7% in the inverter (93% efficient) and another 8% on the wires to the bus. So overall 85% and that still misses the cables from bus bar to the battery groups.

Didn't run the engine on that test, as it is still winterized, so didn't measure the drop from the alternator to the bus bar. In total, and with very good wireing I would still estimate around 80% efficiency from the engine alternator to the AC outlet. At 24V the alternator looses about 6% in the diodes and at least as much again in the winding and field.

In the end a lot of heat is generated in the DC part due to the low voltages and a 12V system would be twice as bad.

Another thing to worry about at loads like this is the health of the alternator itself. Originally I had a compact 90A 28V Alternator from Balmar fitted and it died, just during regular charging getting too hot. When I asked Balmar they said the spec is menat for short term and the alternator is too small for the 420Ah battery bank.

I fixed the Balmar and kept it as a spare, but fitted an AmpTec from Onboard Power, which has a bigger frame and gives 135A at 28V. This thing has been very reliable and troublefree, putting out enourmos power.

I the levels of power output that you are looking for you will also need at least twin pulleys and v-belts, to not have them slip.

This may sound discouraging, but if the system is well done and sized, it will certainly work very well.

The AC side is easier and straight forward, but I woud always recommend a sensitive ground fault breaker.



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[Anonymous]

I'm pretty certain that this kit was around £1000 including almost everything. It was just a fairly large 240V alternator, a small control box, various brackets, etc. I think. There was no attempt at automatic frequency control; the user just nudged the throttle to keep a designated RPM. Perfectly good enough for many loads, such as heaters, microwaves, etc. but nowhere near good enough for a telly, video or audio equipment. Those are pretty low power and are well suited to an inverter - or direct dc, of course. I would be considering one myself but for the fact that my main engine will be fairly big and I want two independent sources of electricity. I very nearly put one in my small boat and probably would have done in due course in preference to windgens and solar panels. The hire firm was a Blakes agent down by Lowestoft. If you thumb through the Blakes catalogue you'll probably find them offering microwave, etc. on board. They were a friendly crowd and I'm sure they'd tell you who supplied the kit.

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[roly_voya]

Re: 240v without genset - Thanks

Thanks to you all for considering this, some interesting stuff. I agree with the comments about 24v being essential to keep current draw in sensible proportions but also because if you take that sort of load of a battery there is a risk of crashing the nav gear. With 24v I can run the 12v stuff via a DC converter and backup battery gtiving stable 13.8v and enough for essential systems in emergencies. Comments about this being a lot of expense to aviod gas, well yes and no. I don't like the small gas cookers wich tend to burn cakes and pies at the back as the burner is to close to the shelf and the thermosats are not very good. I don't have room to fit something like the taylors gas cooker which is exellent but not shaped for traditional hulls with 4ft wide soles. Also lack of standardisation make getting bottle difficult even in Europe as eack country has different fittings. Finally I want to be self sufficient for up to 6 months, thats a lot of gas bottles. The solution is a taylors hob and fan oven/microwave. The breadmaker is unbeatable if you regularly make bread as it saves time and mess (ever tried scraping dow of the cabin walls after a frisky wave!) I can live with UHT milk but not without fresh bread.

As to mechanics the electrics are all new as the boat didn't have any when I got her so the system was desined with this srt of power in mind. Wiring run from batteries is about 18" ie direct through a bulkhead and will use high power starter cable direct (exept for fuse) to the inverter then to a bus bar for distribution. AC curcuits are protected by 30ma RCD and independant water ground. So far I ave everything but the alternator/inverter fitted and it has worked faultlessly on shure power for 6 months. The only problem was when I got a 'proffessional' electrition to check the system and do the final hookup (I was concerned about liability if a fault blew the dock supply) He connected the box upside down and fried the RCD - so much for professionals!!!!

Thanks for the point about alternators burning out, I thought all the Balmar units where American KKK hot rated for continuos output but ther does seem to be a problem with getting supplies to tell you the true cont' output rather than peak - will look into higher output units or current limiting output. This is important as the idea is to use run the engin morning and evening to cook, heat water and charge batteries in the same way that you would use a biult-in gen-set. The inverter will only be run off batteries for light loads or very short periods.

To answer the questions about cost, as this is a 'new built' I am looking at installing units rather than replacing existing stuff and when I costed between a 12v system plus small inverter and gas supply to a decent stove plus petrol genset it came to a similar amout as this system - the whole electrical instalation will have cost less than a diesel gen-set designed for a boat.

Finally the whole thing is desinged to work in layers so if the 24/240v fails the 12v system still works and if the whole lot goes I light the oil lamps, cook on the parafin hob and stream the walker log.

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[dk]

Re: 240v without genset - Thanks

Just one thing - if you fit a smart regulator with a temperature sensor to the alternator it will shut down (well, not actually reduce to zero, but severely reduce) the demand if the alternator overheats, cutting back in when it has cooled.

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[dk]

Roland

The only way to run this sort of gear is to have an AC generator, which I think is a little OTT for your size of boat. Seriously, each function of the cooker, at 1.5kW, will draw 150 amps minimum including voltage drop and internal inefficiencies. So, using the oven for an hour would use 150Ah of power alone. Now put the kettle on at the same time, that’ll likely draw the same, so that’s 300 amps you’ll be demanding at once from ther poor old batteries and inverter. So, a 2kW inverter will trip out every time you forget and put two things on at once! Just boiling a kettle, say, four times a day would use around 50Ah! To run this sort of set up would require, in my opinion, some 800Ah of battery power – minimum. That in turn would require a generator to recharge properly.

Inverters are battery killers – even a laptop will draw 8A from the batteries through an inverter. There is a place for them, if you must have AC, but the figures have to be calculated very accurately – especially when it comes to your charging facilities. I would recommend you choose a 1kW inverter and limit all AC devices to 1kW, 400Ah of deep cycle AGM battery power (forget leisure batteries – they’ll be knackered in a quarter of the time) and fit a 100A heavy-duty alternator with a temperature-controlled smart regulator.

If you must choose any electric cooking device make it a microwave and possibly a small kettle, and up the inverter to 2kW pure sinewave.

If you don’t like gas on board, why not use a diesel cooker – modern ones are really very good and don’t create condensation or smelly fumes.

Duncan


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