Wednesday 18 September 2013

12DC Generator

I am sick and tired of my current 230v genset causing all sorts of problems with unstable voltage, poor quality sine wave and noise, (engine not electrical) although I suppose there is plenty of that too. My Victron doesn't like it and I have killed so many switch mode power supplies for mobile phones, iPads, even the power supplies in a Sky box, a DAB radio and a NiMH drill charger which actually caught fire didn't like it.

So why have I or indeed any boaters got a generator?  I think in most cases 99% + its to charge our batteries.  Of course we all have one bolted to the side of our main engine which by and large does an excellent job of charging the start battery for which it was designed for and a pretty fair to poor job of charging supplementary or house batteries via various methods of diverting surplus charge elsewhere.

When I did my alternator conversion the one thing I didn't expect to be as successful as it has proved was the ability to run my oven 2.2kw through the inverter and still be putting in as required depending on the SOC of the batteries up to 60amps of charge.  This set me thinking, why the hell am I making 230v to run my inverter charger to then charge the batteries at a maximum of 120amps when my new alternator on the main engine I have seen putting in over 180amps without conversion losses.  I have read somewhere that the Victron inverter on charge makes 800w of heat as well. Heat I really don't want. This I can well believe as I had to add additional fans to the inverter space under the stern steps in order to keep it cool enough to keep the charge rate up as it shuts down the charge rate according to the running temperature. 

So you might wonder where this is leading.  Well as I see it its simple. Use my current 500cc genset engine to spin a 12v alternator instead of running a 4000cc (4L) to do the same.  Big engines like this suffer from bore glazing running on tickover or low loads.  Google bore glazing its an interesting topic with many views generally eventually agreeing its not a good thing.

My initial research lead me to a 220amp automotive alternator

but this would need spinning at 5000+rpm so gearing would be required.  I had considered running a 3kw 230v alternator at 1500rpm (4 pole) but again this still had the electrical conversion losses but in preparation for this I managed to con my current genset into running at 1500rpm by removing a slow run cutout relay.  At 1500rpm its as quiet as a sewing machine.   But then I will need to have made for me a drive pulley set and this will have additional frictional losses and belt slip reducing the limited power the genset engine has.

So having bought the 220amp automotive unit 

220amp Automotive alternator

I did some more Googling  and found a slow speed 12v alternator from the USA. 

The Ecoair company  make probably exactly what I and every boat owner needs, and a 24v version also.

325amp Slow spin alternator

After exhaustive discussions with one of the directors I have purchased one of the 12v (14v) units with the option of becoming the UK / EU importer distributor.

So having stripped my current genset:-

Vetus genset with cocoon

The 230v armature still to be removed

Armature and coupling removed

Flywheel end of the engine

This seems to be a 6 hole fixing with 200mm PCD so I will need to look up the SAE of this fixing.

This is an ongoing project so I might start a separate blog on this conversion.  In the meantime if you want to follow it make sure to bookmark it of check back regularly 


  1. Hi Kev, first of all let me send my congratulations on creating a ‘fix’ for Sue and Vic on No Problem. They are good friends and it’s nice to see them back in action!
    I want to run a couple of things by you if I may.
    We are having a wide beam boat built by Lambon Boats and fitted out by Stuart of Barn Owl boats and I am having a bit of a crisis about the way I intend to generate my power.
    I have specified a Beta 75 engine and a GenSet 10, both in cocoons with 960Ahrs worth of 2 volt traction batteries. I remembered in our last conversation you mentioned that you had 2x500watt solar panels and I had the idea that, why don’t I have 6x500watt solar panels(the boat will have a 46ft 3ins cabin roof), a bigger alternator on my engine and dispense with the genset altogether. I have noted your comments on bore glazing, but, as we will be continuous cruisers, I am hoping the engine will only be used for propulsion.
    I have done no research on this yet, it’s just an idea, but I would value your opinion on whether you think it is feasible.
    Regards, George. 07909 902543

  2. Watching intently Kev. I've looked but haven't found a ribbed belt pully assy for my Yanmar yet. If I do this might be a viable option to carrying a honda generator.

  3. Hi Kev. Reading your blog with interest as we're having a widebeam built to live on and it's great to pick up ideas that might be able to be incorporated during the build rather than after. Early stages yet but my attempt at a blog is

  4. Hi Rick

    I had to get one made when I did the alternator modification. I wasn't able to find an off the shelf solution with a PK profile which is what's to be found on automotive alternators. Any good machine shop should be able to knock one up for you. The PK specification is available on the net.

    1. Hi have the same gen on a Portofino sunkker
      had the same problem and used a car alternator
      tested it at 2500 revs and delivered 13,8 volts
      works fine but now have problem with control panel

    2. Hi have the same gen on a Portofino sunkker
      had the same problem and used a car alternator
      tested it at 2500 revs and delivered 13,8 volts
      works fine but now have problem with control panel