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Author Topic: basic question - 3ph pma (5kw) to 240v ac, without batteries  (Read 2061 times)
julian
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« on: August 14, 2014, 07:10:42 PM »

Im sure this is a borderline foolish question, but the discussion here is largely more complex than im wanting.

Im just wanting to turn an engine driven PMA into a 240v generator.

It may be better to use a standard generator, but i have the PMA, so, if i can do it without too much bother / expense, then it would be preferable to use the kit i have.


Im not adverse to batteries, i just dont need them (system will be a grid back up, and minor outage on switch over is acceptable) and they would, i expect, add another layer of expense / complexity.


I would like the engine to track the load, which is possible on a standard generator, but, with PMAs and grid tied inverters, it is not (easily).

Again, i feel like i should be able to answer all this by reading here, but most threads seem to be about off grid / batteries, whilst i just want a cheap option to go from my PMA to a 240v socket.

Thank you.
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biff
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« Reply #1 on: August 14, 2014, 07:35:27 PM »

     Hi Julian,
               The idea is already out there. It is called an "Inverter Generator",  You would need a set of rectifyers, then a set of capacitors ,Then of course the inverter itself,one which could track the different loads through relays,etc,, The engines are usually 2 stroke petrol which can rev high and adjust very quickly to match the loads. It is quite advanced stuff and not really a beginners task at all.
                                                  Biff
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marcus
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« Reply #2 on: August 14, 2014, 10:13:38 PM »

I guess if I were doing it I would use a small car-type battery instead of a capacitor, and a battery based off-grid inverter. If the PMA is being driven at constant RPM then it should be generating a constant EMF you would only need a modest amount of engine speed control to compensate for load dependant voltage sag - raise the RPM if battery volts drops below charging voltage and drop them if it goes too high - the battery will stabilise the voltage over short durations  so the engine control wouldn't have to be superfast.

Well it'd work in theory - practice is a bit more fiddly.
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clockmanFR
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« Reply #3 on: August 15, 2014, 09:07:07 AM »

With PMA's its matching the load on the PMA to the engine that is rotating it for steady useable power.

I have a couple of spare 5kW PMG's (from defunk Chinky Wind Turbines) but matching them to a PTO from the back of a tractor to give a steady output at the correct voltage was near on impossible. As the voltage of these grid tie PMG's would rise and fall very quickly and the HZ and power are all over the place.

In real life the Grid stabilizes the Grid Tied PMG's. My working HP Turbines PMG's are controlled by close matching of the wind power, blade design and diameter, against the rectified output direct into my battery bank, and matched diversion dump loads. My battery bank is big enough to take all the power produced, and then it is inverted to give a smooth output that will run 220vac -240vac stuff without damaging it.

However saying all this, I recall seeing a couple of times, 20 years ago, On Site Arc Welders generator set up, that when the arc commenced the small engine would rev its head off and produce the juice. The time lag was about 1/2 a second and took a while to get used to. Never really got time to take one apart and see how the unit worked. 
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billi
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« Reply #4 on: August 15, 2014, 10:12:43 AM »

I guess if I were doing it I would use a small car-type battery instead of a capacitor, and a battery based off-grid inverter. If the PMA is being driven at constant RPM then it should be generating a constant EMF you would only need a modest amount of engine speed control to compensate for load dependant voltage sag - raise the RPM if battery volts drops below charging voltage and drop them if it goes too high - the battery will stabilise the voltage over short durations  so the engine control wouldn't have to be superfast.

Well it'd work in theory - practice is a bit more fiddly.

Me too ,  a decent taiwan 3.5 kw off grid inverter with 3000 watt   inbuilt MPPT charger upto 140 Voc (hope this would be enough)  costs about 1000 Euro   , then find a 48 volt battery  whistlie

And one has a backup system , where the engine does not need to run always (silent) and even can connect PV to the battery and produce el. units much cheaper than with fossil fuels
« Last Edit: August 15, 2014, 10:18:07 AM by billi » Logged

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julian
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« Reply #5 on: August 15, 2014, 03:19:44 PM »

Ok, well here is some background -

I have a lister CS and plenty of veg oil.
I have a 5kw pma
I have a 2.5kw SMA sunny/wind boy.

...most of it is in storage.

I live in a built up area, where i cant run the engine much anyhow (i purchased it for when i thought we were going somwhere else)

We are grid connected, but i thought i might set up the engine for use in power cuts (when the noise of a generator will probably be more tolerated)


It seems though that the sensible option would be to look out for a 240v alternator.
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« Reply #6 on: August 15, 2014, 04:39:13 PM »

I have a 240v altenator that I used when I started experimenting with the lister. From memory it is a 4.5kw markon and it did work some years ago. You are welcome to it if it will help you. I think you have the cs6 in which case it will only be good for a continual 2.5kw load. I will probably have the pulley I used as well. I have the starter motor that will start the cs to go with it if you want.
Let me know.
Dick
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