12v 100amp Generator

[Biggles]

I'm thinking of making a diesel powered12v say 100amp generator, then using a PSW inverter to get 240v.

 

Firstly am I barking up the wrong tree?

 

And assuming there is some mileage in it how big an inverter would a 100amp alternator power?

 

 

[magnetman]

i've got a similar project on the go. kubota z482 diesel engine with a large pulley (like the one timleech made for you) and a 155a renault watercooled alternator.

 

i'm going to use it for charging but in theory 100a as you suggest would run about 1kw psw inverter. if you had a decent bank of batteries you could probably draw a higher peak load for short periods.

I wouldn't build an ac genny like that though...

[nb Innisfree]

When our 100 amp 24v alternator is flat out it just keeps up with our 3kva Victron running a 2kw Bosch w/m with heater and wash cycle running.

[Timleech]

How about putting a Travelpower unit onto a small diesel engine?

 

Tim

[blackrose]

Can you really build a generator that's as reliable and quiet as one you can buy?

[Biggles]

How about putting a Travelpower unit onto a small diesel engine?

 

Tim

 

The TP stuff tends to be pretty expensive. But can't see why not.

 

How many HP would you need for 100amp alterntor

Regards kris

 

Not sure really hadn't thought it through, but there area few 5hp single cylinder engines which I think would be up to the job pullied right to give the right alternator RPM at the engine maximum torque.

[nb Innisfree]

How many HP would you need for 100amp alterntor

Regards kris

About 2.5 bhp I would think, 3 to be on the safe side.(for 12v) Edited May 24, 2013 by nb Innisfree

[mattlad]

Can you really build a generator that's as reliable and quiet as one you can buy?

Probably not. But if you can build it you can fix it.

[Tony Brooks]

Not sure where Innisfree got his data but its the alternator efficiency that is in doubt. He may well be correct but a swift calculation assuming a 30% efficiency (and it might be 50%) at an output voltage of close to 14 volts gives just over 5 hp.

[nb Innisfree]

Not sure where Innisfree got his data but its the alternator efficiency that is in doubt. He may well be correct but a swift calculation assuming a 30% efficiency (and it might be 50%) at an output voltage of close to 14 volts gives just over 5 hp.

I'm quoting from memory from my alternator graph so it may be a bit fuzzy, I seem to recall 6 or 7 bhp for 100 amps @24 volt. Don't have the graph with me so stand to be corrected on that.

[Timleech]

The TP stuff tends to be pretty expensive. But can't see why not.

 

Yes it is, but you would be going straight to 240V instead of round the houses.

For that matter, why not just have a direct coupled 240V alternator, if that's all you are wanting from it?

Presume the engine can be fixed speed?

Much cheaper than other options.

 

Tim

[Biggles]

Yes it is, but you would be going straight to 240V instead of round the houses.

For that matter, why not just have a direct coupled 240V alternator, if that's all you are wanting from it?

Presume the engine can be fixed speed?

Much cheaper than other options.

 

Tim

 

 

I already have a 240v 6.5Kw 3000rpm 2 pole genny but the output is crap, as it seems are most 3000rpm generators. It upsets too many items on the boat, especially switch mode power supplies. It was fine in the days when gennys were simply required to run simple things like motors, lights, heaters but modern electronics are a lot more fussy about the quality of the sign wave produced. This is why a 1500rpm 4 pole genny is better and more expensive and requires more power to drive.

 

I would happily continue with the current genny if it could be made clean somehow.

[onionbargee]

How many HP would you need for 100amp alterntor

Regards kris

5 hp approx.

 

 

don't forget the alternator's fan, (or water pump) is a pulling a heavy load too.

 

A cut and paste from Zena.com

• What modifications will have to be made to your stock electrical system (charging indicator, means of starting/exciting your new high current replacement alternator, fusing, oversize wiring, type of voltage regulator, etc.)?
  • Have you selected an appropriate voltage regulator for the type of batteries in use and the high current alternator which is ultimately selected?
  • Will it be necessary to monitor and control battery temperature when charging?
  • Will it be necessary to monitor and control alternator temperature when charging?
  • Have you replaced stock wiring with large enough cable to insure safe operation.

 

 

.Is your engine large enough?For example, if you are driving your alternator with a diesel engine, and assuming adequate flywheel mass and a 3:1 engine drive pulley to alternator pulley ratio, a high efficiency, high current, 12V alternator will require about 1 hp per 30 amps of output power + about 1-2 hp for engine operating/muffling loads -- when operating at its maximum rated output current.Therefore, for a 150 Amp alternator, operating at full output, the expected diesel engine load would be about 7-8 hp.If using a gasoline engine instead of a diesel, with a slightly lower 2 to 2.5:1 drive ratio, figure on a requirement of about 1 hp per 15 amps of output power + about 1-3 hp for engine operating/muffling loads -- i.e., 11-14 hp for a 150A alternator. Is your charging system large enough to provide a proper load for your engine when being used only for charging at an appropriate engine operating speed?For example, if you are driving your charging system with a diesel engine you want the system to provide enough load so that the engine will be operating within its normal operating parameters (average alternator load when charging between 20-80% of engine's rated output power at the speed chosen for charging). Operating with too small of a load, for extended periods, can contribute to greatly accelerated engine wear. ALSO, operating at too low of an engine speed (regardless of load effects) can be bad for your engine -- carbon deposit buildup, poor cooling, lack of proper lubrication. We recommend that the minimum engine speed used for high amp charging be kept well above the point at which full engine oil pressure is produced and/or above the point at which full cooling system function is realized.

 

 

 

 

 

Edited May 25, 2013 by onionbargee

[magnetman]

there is a forum called microcogen which discusess all this they do lots of combined heat and power anorakism

[nb Innisfree]

Looking at a Kipor 2600, it has a 4.4 bhp engine and has a rated output of 2.3kva + a max of 2.6kva. On that basis100 amp @12v (1.2 kw) will need approx 2.3 bhp, so 3 bhp should do it whether it's petrol or diesel, after all bhp is bhp regardless of fuel.

[Biggles]

Microgen is indeed a mine of information.

 

This thread in particular

 

http://www.microcogen.info/index.php?topic=2228.0

[magnetman]

Looking at a Kipor 2600, it has a 4.4 bhp engine and has a rated output of 2.3kva + a max of 2.6kva. On that basis100 amp @12v (1.2 kw) will need approx 2.3 bhp, so 3 bhp should do it whether it's petrol or diesel, after all bhp is bhp regardless of fuel.

that will be taking as much as it can from the engine and is probably direct drive so it wouldn't be technically the same as the op I don't think.

 

eta and where do I get a quiet (ie,watercooled) 3bhp diesel engine (small one) ?

 

kubota oc95 is small but it is half oil cooled half air cooled so not that quiet

Edited May 25, 2013 by magnetman

[onionbargee]

Petter AB1W or AC1W ? Cheap as chips engines.

Edited May 25, 2013 by onionbargee

[nb Innisfree]

that will be taking as much as it can from the engine and is probably direct drive so it wouldn't be technically the same as the op I don't think.

 

eta and where do I get a quiet (ie,watercooled) 3bhp diesel engine (small one) ?

 

kubota oc95 is small but it is half oil cooled half air cooled so not that quiet

I don't think one exists, anyway I was only answering a poster's query regards power needed. I think you will have to use a bigger engine at lower revs and suitably geared.