Diesel Gen vs Inverter

[jpceir]

Lots of 'which diesel genny?' type questions on the forum.

Any advice/comments on using an inverter to supply AC (for a microwave) - at less than £.5k, rather than a £5k (approx) generator? Plus the cost/hassle of fitting the genny

 

[Anonymous]

The big problem is getting a big enough battery bank that is suitable for fast, deep discharge. For this you really need traction or semi-traction batteries. You also have to replace all that charge, of course. Once you enter the realm of cooking by dc you will need more that the occasional use of the main engine, wind and solar.

Unless, of course, you plan to only use it while under power at sea in which case it could make a great deal of sense since you will have 70A or so available from the alternator to take part of the load and replace the balance quite quickly.

 

[trouville]

Id like to know which microwave walms food evenly none cook food?do they? my land based one which runs on French nucliar power make one part very hot(an odd sort of heat) and other parts remain cold am i missing somthing? To use one aboard just get a 1kw honder silent gen. thats super small and dose 1000hours/liter?? more or less seems to go for ever, i fill mine once a year

 

[Talbot]

Get yourself a new microwave with a turntable. There is no excuse for one that cooks unevenly. I first used one cooking in a hotel in 1974 and have never had a problem with cooking appropriate food in it.

 

[dk]

I am fitting a 1500W inverter to run an 800W microwave. It will draw around 50A from my 360Ah DC bank, but will cook all I need in 6 minutes, thereby using just 5Ah of total current. 10 minutes would use 8.3Ah, so it is actually quite an energy effiecient means of cooking - and doesn't require the use of gas.

 

[jpceir]

I did the same calculation - which is why I've also ditched the gas.

I'm looking to install a 1500 Watt inverter - got a very good price at the boat show.

Given the inverter system actually works, why the huge interest (on this list) in generators? Are there significant advantages to the generator? In the longer term?

 

[Anonymous]

[ QUOTE ]
It will draw around 50A from my 360Ah DC bank, but will cook all I need in 6 minutes, thereby using just 5Ah of total current. 10 minutes would use 8.3Ah, so it is actually quite an energy effiecient means of cooking - and doesn't require the use of gas.

[/ QUOTE ]At this rate you are discharging your batteries at a 7 hour rate and you will be lucky to get 70% capacity - probably more like 65%, I think. So you are not using 5Ah, you are using 7.5Ah. To recharge the batteries, assume a charge efficiency of 85% and you will need to put back into the battery around 8.5Ah - far more than the 5Ah you are budgeting on. Don't forget the the volts on discharge will be around 12V (probably lower in your case) and the charging volts will be around 14V so there is a difference between the energy value of Ah discharge vs Ah on charge.

So, as for energy efficiency in the 'green' sense of the word, it is a diabolically inefficient way to heat a can of soup since you will also have a conversion efficiency from an internal combustion engine (or similar at the power station) of only 40% plus transmission losses... The greenest way to heat your soup would be charcoal, meths or electricity from home-made solar, wind or water flow.

Nevertheless, I am not casting stones - heating your soup in the microwave isn't a major environmental issue /forums/images/graemlins/smile.gif (Though heating your pies and pasties in a microwave would be a major gastronomic issue)

 

[rallyveteran]

Having spent 5 years circumnavigating, I can tell you that diesel generators had a very high failure rate on other yachts. Whether that was because they were badly designed or poorly maintained doesn't matter too much - a failure is a failure - especially if it is hard to fix. The problem was accentuated in those vessels with AC watermakers where the failure of the generator rapidly made a difference to quality of life.

As I didn't have room for a large low revving generator, I was advised by the boatbuilder to opt for a large battery bank, second alternator and inverter. These served me well.

Of course if you remain within easy reach of good shoreside support and parts distribution the balance of arguments may be different.

Rallyveteran

 

[jpceir]

Didn't mean to trigger a 'green' debate. My primary motivation is the cost (of inverter vs genny), and whether there were any long term operational issues with the inverter option.

The KISS principle suggests that the inverter is the better long term solution, with the assumption that the battery bank doesnt get trashed everytime we microwave a bit of fish for lunch<g>.

 

[mocruising]

I have a 1500 Watt inverter and a 800 K Watt microwave and a bank of 4 x 120 A/hr batteries on the domestic side. The system works well. The combination of 1500 inverter and 800 microwave seems quite common. As it happens the boat is also equipped with a 6 KW gen. set which we rarely use during our cruising at the moment based in the Med as we seem to spend most of our time in marinas. I expect to use the gen. set more as we go further a field and spend more time at anchor away from civilisation. Unless you are planning to do some long distance voyaging I should stick to the cheaper simpler option of the inverter you can always add a gen. set at a later date. I would not get rid of the gas have both.

 

[Anonymous]

[ QUOTE ]
The KISS principle suggests that the inverter is the better long term solution, with the assumption that the battery bank doesnt get trashed everytime we microwave a bit of fish for lunch<g>.

[/ QUOTE ]Batteries deteriorate when they are cycled. The faster and deeper the discharge, the more they deteriorate and it is irreversible. So, if you do use your batteries to supply your cooking fuel they will not last as long as they might otherwise have done. To put this in perspective, the curves Exide have published in a recent booklet, for flooded lead acid batteries, indicates a 50% reduction in Ah capacity after around 300 cycles of around 40% discharge (the lines on their graph are very wide, presumably because they don't have exact numbers).

At 50% reduction in capacity I would be thinking of replacing my batteries.

 

[boatmike]

I think I agree about cooking fish,veggies etc but some things will still be better in the gas oven like roasts (I like my food!)
I think you make a very good point that I should take my microwave with me this year though as it would cut down on gas used and I already have a 1500W inverter. High power for short bursts sounds OK and you certainly don't need a genny for that..... Hmmmm..... Might add a couple more solar panels........

 

[boatmike]

Which would cost far less than buying ,running and maintaining a gert big heavy generator now would it not?