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Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301
Posted: 01:07pm 01 Oct 2021
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Hi to all members. It has been yonks' since I have posted, (bad health) but I'm hoping this forum is the place to ask about Fisher & Pykels because of the vast experience members have had with them.(even though they have mostly moved on from them) If a F&P was wired as a single phase generator, would the maximum output still be around 2 to 3 amps? Kind regards to everyone, Rastussee Rastus graduate advise generously
Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458
Posted: 07:30am 02 Oct 2021
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Not sure why you would want to wire it as single phase. It would be better to leave it as a 3 phase generator and then rectify it if you want DC output. Three phase rectifiers are pretty cheap. If you want an AC output then it is a different matter. If you were trying to get AC output it would not be at 50 hz, unless it was being turned very slowly. From memory they have lots of pole pieces. So the synchronous speed would be very slow. If haven't had much to do with them for a while but my memory says that they were 12 poles at least. That would give a synchronous speed of 500 rpm. More information on what you want to do would help. Pete
Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301
Posted: 07:45am 02 Oct 2021
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Hi Godoh, thank you for replying. Yes, I'm considering AC output, trying to make do with repurposing. I'll look into how many poles the F&P have, unless someone can tell me directly. Are you suggesting the output will be 1/3-2/3 of total possible power? Kind regards Rastus Edited 2021-10-02 19:03 by Rastussee Rastus graduate advise generously
Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301
Posted: 05:41pm 02 Oct 2021
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I'm shooting from the hip buy thinking out loud and hope it doesn't annoy people. If I rewired a F&P with 18 poles 2 phase, would the rotor be compatible with this set up and would the output be better than 2-3amps? Unfortunately I've forgotten more than I remember about F&P's as generators and at my age time is running out to search for information that others have at their finger tips. Kind regards Ronsee Rastus graduate advise generously
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:04pm 02 Oct 2021
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Output is limited to how much current each individual coil can handle before it gets destructively hot. If you are using only one of the three phases, total output current will be limited to one third of what might otherwise be available.
The three sets of windings cannot all be rewired into a single phase. Its like a three cylinder piston engine where the pistons all go up and down at different times.
Connecting different phases in series will cause the voltages to cancel out, so that will not achieve anything useful. There is no simple solution to this I am afraid Cheers, Tony.
Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458
Posted: 07:37am 03 Oct 2021
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The problem you will have to overcome with rewiring the machine is that you still need to produce a sinewave. If you try rewiring it for two phases you will end up with ( at best) two sinewaves that are 120 degrees or 240 degrees apart. You also end up with a wasted set of pole pieces. You would probably be better using three transformers or a three phase transformer to send the AC to where you want it then rectifying it there. If you tried to rewind it with only one phase and used every pole piece the waveform would be all wrong. Pete
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 08:27am 03 Oct 2021
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Suggesting from Pure Ignorance.....
I have played around a lot with 3 Phase motors as generators. The three phase output is connected to Capacitors to get a Single phase AC output which is considerably more than the output of a single phase. The caps effectively delay/ Align the phase outputs so they all line up into one. I'm sure that is technical heresy but the way I understand it and essential the end result.
3 phase motors can also be run from single phase supply with the addition of appropriate caps.
I don't know if this works the same with a Permanent magnet motor hence my Ignorance but because of said Ignorance I can't see why not Other than one needs the caps to energise the windings and the other does not.
I await to be educated by those with better knowledge.... Or a suggestion how this could be done to help the OP. There are some documents online with graphs on choosing the right caps for different size/ speed/ and voltage motors. I have found there is a fair tolerance thought. Higher Uf gives more power at lower engine speed but Voltage overshoots quickly and lower cap's mean higher speed/ frequency but more stability.
Out of Curiosity, why the need for the AC output? What are you looking to power?
Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301
Posted: 10:57am 03 Oct 2021
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Hi Warpspeed, thank you for developing the conversation and explanation. I was suggesting to have every second pole having 9 pairs for each of the 2 phases but don't no if the stator would work on that arrangement. If so 370rpm might work for 50hz-60hz?
Hi Godoh, yes I was thinking of using only one of the 2 phases. I looked at 3phase to single phase transformers but could only find one, others are advertised as "converters". ("I don't know much about them") However I have used 12V to 240V inverters to run appliances
Hi Davo99, I have read the "Capacitor post" on this site, they increased amperage output but I don't think the application was to retain AC current but not a 100% sure of that.
I am contemplating making a motorized generator 230-240V 50-60Hz without having to use an inverter meaning the current goes from AC to DC then AC. It is probably "the impossible dream but I thought I would ask. I hope admin doesn't mind me posting here because most of the F&P plus power experts use this Forum. If they want me to post in "other" I would need a lot of help to repost. Kind regards Ron Edited 2021-10-03 20:59 by Rastussee Rastus graduate advise generously
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:57pm 03 Oct 2021
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Three phase to single phase cannot be done directly. But three 120 degree phases to two 90 degree phases is possible with a Scott-T transformer, sometimes called the Scott Tee connection.
Its a lot of trouble to go to, and it does not spread the load equally across the three phases anyway, so is not really of much help for what you are trying to do.Cheers, Tony.
Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458
Posted: 09:44pm 03 Oct 2021
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If you are just going to make a generator then why not make one with a DC motor driving an Alternator. That would be much easier.
There are Single phase to Three phase converters about but they are basically an inverter and you are trying to get away from those. Using a generator is less efficient than using an inverter. The windage and friction losses plus the copper losses in a motor generator will add up, you may only end up with 60% efficiency. Where as a good inverter will be around 95% efficient.
If you are making a generator then why not use a three phase motor to drive it if you want to stick with an AC motor. The only thing that will be hard is keeping the frequency stable to the motor to maintain your output frequency. From what I remember the F&P motors that I played with were only around 300 watts so it may be a fruitless exercise, better achieved in other ways. have fun Pete
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 11:44pm 03 Oct 2021
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As suggested, the better option would be to use a 3 Phase Motor. All you would need to do would be add some caps to get a single phase output. Look up "C2C". it's very simple and easy to set up.
Any generator like this without an inverter is going to be very unstable in frequency and voltage and is really a balancing act with the load. If you want to run lights or a resistive element as constant loads, Great. If you want to switch different loads in and out like run a fridge with other things so the power demands may very, they are terrible and basicly useless.
I have run 3 phase motors through a 3 phase rectifier ( or a bunch of single phase units) and into a solar inverter to get a single phase output. OK if you are connectimg to mains, horrible if trying to run stand alone due to the inverters need for accuracy in output and most of all frequency.
I am building 2 Generators atm. A proper 3 Phase 10 KW unit for stand alone operation and a 12 Kw 3 Phase IMAG which will be for backfeeding the mains. This can be directly coupled and run as a motor until over driven by the engine at which point it pushed power back and is Frequency locked so no issues there. Also much more efficient than with the C2C method.
Finding generator heads here in oz is stupidly Difficult especially 2 bearing models that can be Pulley driven off an engine as against being direct coupled to one which means they are generally 3000Rpm 2 pole screamers and need the correct Taper on the crank shaft of the engine. I looked at importing some 2 bearing units from Chynaah but the freight is ridiculous like anything else that can't be sent in a post pack and no one seems to do them here I can find.
Seems to be so much in the way of simple and basic machinery we can't get here even though it's all over the rest of the world.
Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301
Posted: 02:44am 04 Oct 2021
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Hi Warpspeed, Godoh and Davo99, thanks for the explanations. I had my suspicions but now convinced that it would not provide the results I am after. I am also satisfied with the alternative suggestions that I will follow up. Kind regards Rastus Edited 2021-10-04 20:37 by Rastussee Rastus graduate advise generously
Rastus Guru Joined: 29/10/2010 Location: AustraliaPosts: 301
Posted: 10:40am 04 Oct 2021
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Hi Davo99, are your gen projects on the forum? Also what 3 phase motor will produce 15 amps per leg. Any help will be appreciated! Kind regards Rastussee Rastus graduate advise generously
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:19pm 04 Oct 2021
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While its possible to run a three phase motor as a self excited alternator, its only practical for one very specific application, charging a battery from an internal combustion engine.
The windings need to be resonated with capacitors, and the engine must be run at a fixed rpm to coincide with the resonant frequency. The ac output can be rectified and applied to a battery. The battery regulates the output voltage, preventing any wild excursions of voltage with small changes of rpm or load.
There is no way to control the charging current, the whole thing needs to be shut down when the battery voltage rises to a maximum.
Without the battery, you might easily see several hundred volts which can easily blow up any load. As you increase the load, the voltage rapidly falls. At some point the machine will fail to self excite and output will drop to zero. The whole thing is very hairy, almost impossible to control, and impractical. It will however, work quite well charging a battery provided the whole thing is set up to run at a useful specific rpm and voltage.Cheers, Tony.
Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458
Posted: 11:03pm 04 Oct 2021
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Hi Warp, there are other applications for three phase induction generators. Years ago Rainbow Power company built induction turbines with pelton wheels for micro hydro applications. The generator outputs around 380 volts AC from memory. That takes care of long runs from the turbine to the control box. The control box has a regulator that drops the 380 volts to 12 volt or 24 volt Dc to charge batteries, their controller also includes a dump load that the controller switches to when the battery is charged. Nice little units, only around 300 watts but over a 24 hour period they are very useful for small stand alone power systems. F&P motors work well for hydro turbines when the windings are reconfigured, but need quite a bit of head to overcome the cogging caused by the permanent magnets. Pete
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:06am 05 Oct 2021
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Yes its possible, with the voltage reduced to feed INTO A BATTERY, and then use a dump load when the battery is full.
But if you just want some general purpose ac to drive say some 230v lighting, its not going to work.
The problem is, you fire up your wind/hydro/engine and the rpm rises, at some speed the thing suddenly hits resonance and you instantly go from zero to 340 volts ac for example at no load. It will not start up under load. Must be disconnected from any load to enable the resonant energy to first build up.
Assuming your bulbs don't blow you switch in some load, the voltage falls to 290v. A little bit more load 200v, more load still 90v, more load, the voltage suddenly collapses to zero with the generator still running at normal speed.
Unless you judge the load to exactly match the power that is available, the voltage will either be destructively high, or collapse completely. Its fun to try out, but bloody useless as a general source of usable power.
There are plenty of u-tube videos showing some hero demonstrating how a huge 10Hp three phase induction motor can light a single 100 watt bulb. Or similar. What they do not show you is how a 60 watt bulb will instantly blow from over voltage, and two 100 watt bulbs connected, glow only dull orange.Cheers, Tony.
Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458
Posted: 04:08am 05 Oct 2021
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Yep, I can't see any sense in trying to run 230 volt loads from an induction generator. It is hard enough getting a normal regulated alternator to do that job. I prefer to leave generators for emergency battery charging and welding. The rest of the time an inverter and battery works great. The last time I helped someone with a hydro turbine and induction generator they had something like 350 metres of three phase flexible cord winding its way through the forest to his shed. Hopefully no one finds it with a spade, that could be quite an interesting experience. Sometimes it is best to offer suggestions, like hire a ditch witch and bury it, then just forget the experience and walk away. Cheers Pete
phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135
Posted: 07:34am 05 Oct 2021
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Without a battery system induction generators can only be used to supliment an existing AC supply. The driving motor govenor is set to about 4% above synchronous speed to achieve full output. For stability it is best if the induction generator supplies less than 50% of the total load. Frequency and voltage are determined by the primary generator. Phil
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 07:45am 05 Oct 2021
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Maybe some pictures I did recently of the layouts with the engine and motor but nothing too helpful.
Also what 3 phase motor will produce 15 amps per leg.
A pretty bloody big one!!
Depends what you are trying to do, stand alone or Grid Coupled.
My 12 Kw 3 phase is rated at 21A per leg As a MOTOR. As a stand alone I think it would be pushing it to get that as a generator. Might scrape it in but might not. Grid coupled, should be plenty of headway.
That motor weighs 170Kg so it's not light. The engine I am driving it with is another 125KG but that is not enough to drive it to full output. Off the top of my head, you would probably want something around 15 Hp, Maybe a bit more to get that out of the 3 phase as a stand alone genny. For grid coupled the efficiency is the same as when used as a motor.
When used stand alone, you have to balance speed and torque with you engine. I have found to get max power out of a 3 Phase you often have to spin it quite quickly which inevitably means the frequency is off. also tends to push the voltage high. There is a catch 22 there. To keep the voltage down you lower the connected capacitance. Lower the connected capacitance and the output becones more touchy and harder to energise the Field on startup which means you often have to rev the crap out of the motor to bring the field up unless you want to flash the windings every time which can be entertaining if you try flashing them with a 12 V battery when the thing is already singing along at 250V + TIP: Use thin wire so it just blows off easily like a ready made fuse.
If you are running an IMAG grid connected, the efficiency is better and so is the output control. Once the motor is Grid locked, driving it faster is very limited but the harder you drive it torque wise the greater the AMPERAGE output. The voltage rise will be very small and certainly not going to run away.
If you had a specific load you wanted to offset, then you could run the grid Connected IMAG and then hit your load and use the IMAG to compensate the power being used so your power meters were not spinning off the wall. It the only spiny type power meters you could push power back to the grid and get credits... Pretty much exactly the same as a solar inverter does.
Grid Connected gives all the benefits or a regular generator with the low cost of a ( used) 3 phase motor.
What are you wanting 15A per leg for? Certainly not going to get that out of a F&P motor!!
Even if you had a grid connected IMAG that only did 10 Per phase, that's a 2.4KWh saving off your power bill. Another application where this may be useful is High load situations. My shed is really underwired for the distance for the house. Fine for small loads but when I run the Compressor, plasma and welder with one or the other even on stand by Or the compressor Kicks in when I have one going, The voltage drop can cause problems. Because I have 3KW of solar on the roof connected to that circuit, the overall power at that point is always good to the point where I get the opposite problem being Voltage rise. Using one of the heavier loads pulls it back down and I can run to the capacity of the wire without problem.
A Grid connected IMAG could do the same thing. Even a small 4 KW 3 Phase could provide plenty of power in such a setup.
Again, as standalone, these are only good for FIXED resistance loads. Water heater, bar or oil heater, Incandescent lighting etc. Anything that is frequency dependent or loads that may switch on and off are NOT going to be suitable for an IMAG. That said, if say you had a 12 A load and you switched a 1A load and voltage wasn't terribly critical, you would probably be OK.
There is NO on the fly regulation with these. You set the output by Engine speed and caps connected. I usually shoot over voltage a bit and dump the load and get ready to increase engine speed some more. You could also switch capacitors in and out to do fie tuning. I have also seen where people connect a Cap to the load. That means that each load has it's own balanced capacitance so it's load is compensated when it is in circuit. That could help with loads being switched in and out but I still would only be doing dumb and insensitive loads like Resistance.
For grid Connected, there are NO caps, just a direct connection like a motor and the Motor phase locking with the grid will take care of all the regulation.
Let me know what sort of load you have in mind and I can give you a heads up it it would be worth while or not and if so some suggestions how to set an IMAG up . I believe these can be very effective and Cheap for the RIGHT application but for many, are useless.
Very much a matter of horses for courses.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 11:19am 05 Oct 2021
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I have not tried this. As a 3 phase is typicaly 240/ 2XX v per leg and rectifying it add 30%? voltage increase are you saying that the caps could allow the motor to run UNDER nameplate voltage or would the battery have to be 220V at least?
With the normally suggested capacitance on an IMAG, it's VERY easy to over shoot to 600V or more. Done it many times and surprised I haven't blown the 400V caps I use. Lucky it was only for a second or 3 but still.
Yes, this is what I have in mind. If it's possible to run the IMAG under nameplate Voltage, it must take a LOT of capacitance to do that.
I would agree is somewhat hairy but rather than impossible to control I'd say has fairly tight balancing requirements. I would also agree and Disagree with being Impractical. If you wanted to run lights that were all turned on and all turned off and no variation or run say a water heater that again ran it's course and then dropped out, No difficulty with those once set up with caps and fixed throttle on the engine.
It's really no different to driving a Vehicle. Along the flat it requires so much throttle to do a certain speed and as long as the road remains flat and the throttle position set, the speed will remain the same. Come to a Hill and it will require more throttle or the speed will drop and if the vehicle is heavy enough, may stall.
As long as the road is the same, wether flat or a constant hill so the throttle input does not need to change, then the IMAGS work in a similar fashion and quite well. Like roads being never the same gradient, usually electrical loads are not constant either which makes IMAGs LIMITED ( quite a bit) in their application however if there is a fixed load they can by applied to like a truck crossing the Nullabor, then in that niche they can be quite workable.
It will however, work quite well charging a battery provided the whole thing is set up to run at a useful specific rpm and voltage.
In this case the battery is a (relatively) constant/fixed load.
General purpose AC, No, they are Crap and relatively useless. To drive some FIXED lighting, would most certainly work and I have a setup in the shed right now I can demonstrate that. Once the engine speed is set to a given value of capacitance and the load remains relatively fixed, the thing will run all day quite happily. I ran a test couple of months back. 4 Kw engine, 4Kw 3 phase. I started off with a couple of 150W lights and then plugged in an adjustable temp heat gun. By slowly ramping up the engine speed and the heat gun, I had it all running quite happily and left it like that for about 20 Min. Was quite stable.
Absolutely. Once the IMAG energises, the voltage will run away at the blink of an eye and drop nearly as quick as well. When unloaded it's almost impossible to dial in a fixed and sustained Voltage although can be done close enough. With a load the voltage is more stable but if the load is low, say 300W on a 4 KW motor, it's VERY easy to push the thing 50V higher with a very slight increase in engine RPM.
Quite a few time I have gone though trouble shooting wondering why the thing won't energise before I realise I left the load switched in. It is possible To energise with a load if you rev the engine hard and flash the windings and its slow to come up and then you have to be ready for the over shoot. Not recommended.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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