24v or 230v Generator ?

[I Spartacus]

OK I have been reading all the threads regarding generators/gen-packs. I can see that there are only about three companies that do good diesel ones . These being either 3000rpm or 15000 rpm.

 

What I have noticed is that 1500rpm units are actually only running at about 40% of their rated power such as the Kubota Z602 max rpm of 3200. . I am fully aware that we are all tied to this as we require mains voltage at 50Hz or what ever it is. Running the engine faster will give us 60Hz.

 

It clearly states on the engine data sheets that the best and most efficient fuel efficiency and torque is at about 2400rpm making it more efficient.

 

If running at 1500rpm the engine will produce about 5 Kw of power but running at 2400 rpm it will produce just over 9 Kw. Yes there will be further losses from the generator as they are never 100% efficient..

 

So are we missing something ! Would it be better to directly generate 24v dc and put it into a larger inverter , I would still need an inverter anyway .I could still have the generator only producing 4kw at 1500rpm and if I require more I could run it at 2400 rpm and say get 7Kw.

 

I am sorry to say the company only make these PMG's in 24v or 48v and come in 5Kw or 7Kw at 24 v.

 

So what do you all think ? Would this be a better way, and are there any advantages. Mind you there would be a lot of amps flying around.

Edited May 28, 2016 by I Spartacus

[Murflynn]

OK I have been reading all the threads regarding generators/gen-packs. I can see that there are only about three companies that do good diesel ones . These being either 3000rpm or 15000 rpm.

 

the 15000rpm one won't last very long

[Giant]

This is basically what the newer petrol gennies do, they generate DC and then have a built-in inverter to supply the AC. So the output frequency is decoupled from the engine RPM, which can then be continuously adjusted to keep up with the the load.

 

Note that this is done with a pretty high DC voltage, I think they may be as much as 600V DC internally.

 

I haven't seen this in marine diesel gennies yet but maybe someone's doing it.

 

Running a 12V or 24V DC generator to a battery bank and then using a normal inverter achieves the same thing, but more cable losses at those voltages.

[I Spartacus]

the 15000rpm one won't last very long

Yes a slight slip of the hand Lol

 

This is basically what the newer petrol gennies do, they generate DC and then have a built-in inverter to supply the AC. So the output frequency is decoupled from the engine RPM, which can then be continuously adjusted to keep up with the the load.

 

Note that this is done with a pretty high DC voltage, I think they may be as much as 600V DC internally.

 

I haven't seen this in marine diesel gennies yet but maybe someone's doing it.

 

Running a 12V or 24V DC generator to a battery bank and then using a normal inverter achieves the same thing, but more cable losses at those voltages.

Yes the common practice has usually been to make it in AC and then rectify it back to DC and then convert it back again to Ac via inverter

it is more efficient doing it that way. My friend made one using a HV AC alternator, he rectified it back to Dc and put it into an inverter

just like the travelpack you can get on the boats today. it worked very well for him.

[magnetman]

Yes a slight slip of the hand Lol

 

 

Yes the common practice has usually been to make it in AC and then rectify it back to DC and then convert it back again to Ac via inverter

it is more efficient doing it that way. My friend made one using a HV AC alternator, he rectified it back to Dc and put it into an inverter

just like the travelpack you can get on the boats today. it worked very well for him.

The Dc concept is very interesting. If you have time the victron energy "Energy Unlimited" paper is worth reading.

 

It does include some advertising but also makes a very strong case for DC generation of power on smaller vessels which do not call for continuous generator operation like big yots do.

Download available here.

 

 

https://www.victronenergy.com/support-and-downloads/whitepapers

 

 

PS victron do sell big inverters.. And batteries but one does not have to use victron equipment !

Edited May 29, 2016 by magnetman

[magnetman]

This is basically what the newer petrol gennies do, they generate DC and then have a built-in inverter to supply the AC. So the output frequency is decoupled from the engine RPM, which can then be continuously adjusted to keep up with the the load.

 

Note that this is done with a pretty high DC voltage, I think they may be as much as 600V DC internally.

 

I haven't seen this in marine diesel gennies yet but maybe someone's doing it.

 

Running a 12V or 24V DC generator to a battery bank and then using a normal inverter achieves the same thing, but more cable losses at those voltages.

Fischer panda and Paguro do variable speed inverter marine diesel generators.

 

Not sure about other manufacturers.

[I Spartacus]

Fischer panda and Paguro do variable speed inverter marine diesel generators.

 

Not sure about other manufacturers.

Thanks magnetman yes I have been gathering all the information off their sites, also whisperpower do them as well.

The Panda one has an inverter so the PMG is a DC unit hence the smaller size and weight.

 

The Paguru 8500 unit is just over the top, 860l x 580w x 650t and the weight is 200kg simply just to large and heavy for a NB

I have been talking to my friend who is a diesel fitter, we have worked out that we can build one with a finished weight

of 100kg we would need to sort out the cooling system heat exchange etc and do some other alterations. The fitting of the

Axil flux pancake PMG is simple as it just bolts onto the flywheel and held in place by the engine bell housing mounting.

 

Using the Kubota z602 engine, and the special 24v 5 or 7 kw pmg would give you lots of surplice power if ever required

and very very good fuel consumption of about 350g of fuel per Kwh,, it looks very tempting but I would need to sort out a good inverter.

[cuthound]

On larger diesel gensets I have seen a gearbox used to allow them to run at higher rpm whilst deliveringb50 Hz but then you introduce more frictional losses, which affects fuel consumption.

 

I once saw a 2000kVA genset that started at 1800 rpm (60 Hz) and then once the load was introduced, dropped to 1500 rpm (50 Hz), but this was in an attempt to get better load acceptance on a highly turbochsrged engine.

[I Spartacus]

On larger diesel gensets I have seen a gearbox used to allow them to run at higher rpm whilst deliveringb50 Hz but then you introduce more frictional losses, which affects fuel consumption.

 

I once saw a 2000kVA genset that started at 1800 rpm (60 Hz) and then once the load was introduced, dropped to 1500 rpm (50 Hz), but this was in an attempt to get better load acceptance on a highly turbochsrged engine.

 

Yes those large gensets are nice, we had some large caterpillar generators rated at 4Mw each they were very nice, they were direct drive with diamond stators.we also had a 3.5 Mw Jenbbacher CHP that was total rubbish.

It was forever breaking down.

I have been looking at these small gensets, and it looks like some of these companies are going the DC route with the inverter. On another mater I was trying to calculate the cost per Kw for gas for cooking and heating the boat

I came up with a cost of about 30p per Kw it was only a quick estimate, does anyone actually know the the correct cost

for gas per Kw.

Edited May 30, 2016 by I Spartacus