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Three phase genset build.. Questions

Kurtis

Registered
Hi.. I am building a three phase genset so I can bench and use three phase equipment in a neighborhood that only has single phase. I am an old mechanic so I have a fairly good understanding of DC but only the basics for AC and three phase, so I have a few questions.

For a start, when I first put this together and started it, it was putting out 240v on all three lines. When I went back to try it again it wasn't generating current at all except some residule current. However, when I knock the belt off the engine the rpms go way up like the engine was working quite hard to turn the motor. I am spinning the motor the opposite direction it was set for but I didn't think that would matter until it was connected to another machine. The only thing that I changed between trials is that I grounded the capacitor bodies.

Also, I am beginning to think that I don't have a big enough motor to power the piece of equipment that I am trying to bench right now which is an Holz Her panel saw. The pdf for it was to big to post on Smokstak so it can be viewed at http://altpubad.com/Temp/EL2511029.pdf

Any help would be greatly appreciated.. Thanks
 

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Wayne 440

Registered
I claim no expertise, but have some comments

(1) I agree that your "generator" ( a 3.73 kW motor) is probably too small to power the 3kW saw motor.

(2) The drive ratio between your engine and the "generator" is also a problem, unless that engine makes a lot more power at low speeds than I think it does.
The desired speed for your "generator" is (I think) around 1870 RPM, my guess is your engine is turning only about 1000 RPM.

(3) You wrote "...The only thing that I changed between trials is that I grounded the capacitor bodies..." I suggest that you carefully reverse that change, since the voltage collapse happened immediately after.

Have you considered making a rotary phase converter instead?
 
Last edited:

DMeed

Subscriber
Last Subscription Date
07/12/2019
I'm trying to figure out how a 575V motor is creating 240V.

Is there a quick primer on using induction motors as generators?

Also how is a motor/generator that is rated 5.25 amps is going to supply power to a motor that takes 10 or 12 amps at 240V

I would second the rotary phase converter idea.
 

dalmatiangirl61

Subscriber
Last Subscription Date
07/10/2019
He said 240v per leg, which might be close to 575 between legs? I agree, find a different motor and build a rotary phase converter.
 

Radiomike

Registered
This is an induction generator, it depends on having some residual magnetism to start generating with the capacitors proving the leading VARs for excitation. It has to be run at super-synchronous speeds usually around 50 to 100 rpm above nominal synchronous. There is a good wiki article on estimating the required capacitance. https://en.wikipedia.org/wiki/Induction_generator#Excitation it also details the use of DC to start the self excitation process. The value of the capacitors determine the voltage. I note your blue motor has a rated voltage of

If you suspect the capacitors then check then with a "Megger" for ground faults and a series resistance and use three voltmeters to calculate the value of Xc. Note the capacitors have an internal 1Mohm internal resistor. , They should however test clear of ground.

Have you thought of a rotating phase convertor. A bank of capacitors and a pilot motor would be a lot simpler, unless you need an independent source. Another option is a variable speed (VSD) unit these have a 240volt single phase input and a 240V three phase output. https://www.ebay.ca/i/182935786653?chn=ps&mkevt=1&mkrid=706-89093-2056-0&mkcid=2&dispItem=1

https://www.amazon.com/Variable-Frequency-Inverter-Converter-Engraving/dp/B07CJXQWVT

I see your blue motor is rated at 575V and 5 amps but the red motor is 6.1 Amps at the highest voltage

Mike
 

pegasuspinto

Registered
Youtube is full of people who have sucessfully used VFD's to convert single phase to 3 phase. Many VFD's are even built for the purpose. And amazingly cheap.

I am a little confused what all the circuitry in your hole saw is trying to accomplish, but the VFD may well replace it, as the VFD can do soft start, speed control, and reversing functions internally.

If I recall correctly, trying to use an induction motor as a generator is a bit sketchy, as the field is unstable and may well collapse on a surge load. I think the compensation is to use a considerably larger motor then the load requires.
 

Radiomike

Registered
I assume your Panel saw is like this https://www.youtube.com/watch?v=4MAsVT693E4.

The schematic for the control looks complex but is mostly a series of interlocks to prevent mal and mis-operation and to maintain safety for the operator. There must be an English version available somewhere. Any induction generator will struggle to provide not only the motive power but the correct voltage for the auxilliary circuits, and what appears to be a single phase fan. Using an induction generator will give large voltage swings when the main motor is switched on and off. The control circuit and its transformer will not be happy being subjected to large over-voltages.

The duct tape covered wiring on the main motor is a source of some concern. Has someone been modifying the wiring and bypassing the safety interlocks?

One suggestion is a VFD for the main drive and a single phase supply to the control circuit and exhaust fan. Or a rotary phase convertor which can maintain a closer voltage.

From the schematic it looks possible to separate the single phase parts from the three phase parts.

Mike
 

Kurtis

Registered
Hi Wayne, thank you. I was thinking that I would have to adjust the pulleys somewhat. Trying to keep them as large as possible because of the distance between them. I put the platform together so I could easily switch motors up for testing. I put different caps on it today with no change, just 3-4 volts on each line. Could I, have blown the flashing of it by turning it the wrong direction?
 

Wayne 440

Registered
From a distance, my guess is that flashing it can't hurt the existing situation. From the referenced page - " To flash it momentarily connect a car battery across the generator output terminals while it is running full speed ‘with no load’. ONE second is more than enough time...".
 

Kurtis

Registered
I'm trying to figure out how a 575V motor is creating 240V.

Is there a quick primer on using induction motors as generators?

Also how is a motor/generator that is rated 5.25 amps is going to supply power to a motor that takes 10 or 12 amps at 240V

I would second the rotary phase converter idea.
Hi DMeed.. thank you. I realize now that I need a much bigger motor. I am wonder what a 14 hp engine could comfortably power. The present location of the saw has single phase but I don't have any grid services at my shop so three phase generators would be benificial. Especially since I see a lot of that kind of equipment laying around for the price of scrap metal. I am a bit confused by all the numbers listed on the saw motor as far as amps go. Somebody else mentioned that it was 6.1 amps. Can that motor be configured that many different ways?

This is an induction generator, it depends on having some residual magnetism to start generating with the capacitors proving the leading VARs for excitation. It has to be run at super-synchronous speeds usually around 50 to 100 rpm above nominal synchronous. There is a good wiki article on estimating the required capacitance. https://en.wikipedia.org/wiki/Induction_generator#Excitation it also details the use of DC to start the self excitation process. The value of the capacitors determine the voltage. I note your blue motor has a rated voltage of

If you suspect the capacitors then check then with a "Megger" for ground faults and a series resistance and use three voltmeters to calculate the value of Xc. Note the capacitors have an internal 1Mohm internal resistor. , They should however test clear of ground.

Have you thought of a rotating phase convertor. A bank of capacitors and a pilot motor would be a lot simpler, unless you need an independent source. Another option is a variable speed (VSD) unit these have a 240volt single phase input and a 240V three phase output. https://www.ebay.ca/i/182935786653?chn=ps&mkevt=1&mkrid=706-89093-2056-0&mkcid=2&dispItem=1

https://www.amazon.com/Variable-Frequency-Inverter-Converter-Engraving/dp/B07CJXQWVT

I see your blue motor is rated at 575V and 5 amps but the red motor is 6.1 Amps at the highest voltage

Mike
Thank you Radiomike. The wiki article was exactly what I needed to see. Especially this part: An induction machine can be started by charging the capacitors, with a DC source, while the generator is turning typically at or above generating speeds. Once the DC source is removed the capacitors will provide the magnetization current required to begin producing voltage.

An induction machine that has recently been operating may also spontaneously produce voltage and current due to residual magnetism left in the core.

I don't know how many articles that I have read that didn't say anything about that. All say the residue current will build up.

I assume your Panel saw is like this https://www.youtube.com/watch?v=4MAsVT693E4.

The schematic for the control looks complex but is mostly a series of interlocks to prevent mal and mis-operation and to maintain safety for the operator. There must be an English version available somewhere. Any induction generator will struggle to provide not only the motive power but the correct voltage for the auxilliary circuits, and what appears to be a single phase fan. Using an induction generator will give large voltage swings when the main motor is switched on and off. The control circuit and its transformer will not be happy being subjected to large over-voltages.

The duct tape covered wiring on the main motor is a source of some concern. Has someone been modifying the wiring and bypassing the safety interlocks?

One suggestion is a VFD for the main drive and a single phase supply to the control circuit and exhaust fan. Or a rotary phase convertor which can maintain a closer voltage.

From the schematic it looks possible to separate the single phase parts from the three phase parts.

Mike
Hi RadioMike.. Yes it is model 1265 built in 1992. From what I gather so far, the motor is three phase, the automated counter balance is two phase, and there is a small transformer in the electrical box that is single phase, which I assume runs the sensors. Lol, the duct tape actually serves no purpose, I should have taken it off so as to not confuse things further. Turns out that a pin dropped out of the saw which actuates a mechanism that locks the saw in place before it will start up. Appears somebody wasn't very observant and thought it was an electrical problem so they messed around with the wires.

I am wondering, if I put a bigger motor on and put and a bigger bank of caps on, if it would level out power surges.

This is an induction generator, it depends on having some residual magnetism to start generating with the capacitors proving the leading VARs for excitation. It has to be run at super-synchronous speeds usually around 50 to 100 rpm above nominal synchronous. There is a good wiki article on estimating the required capacitance. https://en.wikipedia.org/wiki/Induction_generator#Excitation it also details the use of DC to start the self excitation process. The value of the capacitors determine the voltage. I note your blue motor has a rated voltage of

If you suspect the capacitors then check then with a "Megger" for ground faults and a series resistance and use three voltmeters to calculate the value of Xc. Note the capacitors have an internal 1Mohm internal resistor. , They should however test clear of ground.

Have you thought of a rotating phase convertor. A bank of capacitors and a pilot motor would be a lot simpler, unless you need an independent source. Another option is a variable speed (VSD) unit these have a 240volt single phase input and a 240V three phase output. https://www.ebay.ca/i/182935786653?chn=ps&mkevt=1&mkrid=706-89093-2056-0&mkcid=2&dispItem=1

https://www.amazon.com/Variable-Frequency-Inverter-Converter-Engraving/dp/B07CJXQWVT

I see your blue motor is rated at 575V and 5 amps but the red motor is 6.1 Amps at the highest voltage

Mike
Sorry Mike, forgot to ask. Isn't it kind of dangerous jump starting a 240v system with a 12v battery?
 

Radiomike

Registered
The red motor, which is the saw motor, can be configured two ways "Y" or "Δ". The motor is desined for two frequencies 50 and 60 HZ, The name plate has 50//60Hz. and the connections given as Δ/Y So the four current ratings are first the 50Hz then a // and the 60HZ. Each of the two connections are in order so the currents are (50HZ Δ) (50HZ Y) // (60HZ Δ) (60HZ Y).

Although it is not clear from the schematic if running on 220 3phase or 440 3Phase you must need to change tappings on the control transformer.

The use of DC is to provide a brief amount of magnetic flux to start the self-excitation process. Without this flux, be it a flash or sufficient residual, nothing happens - no volts.

Your saw motor look to be in Y or higher voltage configuration. I would check and voltage tappings on the control transformer.

If you have a single phase supply it is an easy matter to power the control circuit only and function check the control circuit and logic. The contactors should energise and every thing should work except the main saw motor.

Mike
 

Kurtis

Registered
The red motor, which is the saw motor, can be configured two ways "Y" or "Δ". The motor is desined for two frequencies 50 and 60 HZ, The name plate has 50//60Hz. and the connections given as Δ/Y So the four current ratings are first the 50Hz then a // and the 60HZ. Each of the two connections are in order so the currents are (50HZ Δ) (50HZ Y) // (60HZ Δ) (60HZ Y).

Although it is not clear from the schematic if running on 220 3phase or 440 3Phase you must need to change tappings on the control transformer.

The use of DC is to provide a brief amount of magnetic flux to start the self-excitation process. Without this flux, be it a flash or sufficient residual, nothing happens - no volts.

Your saw motor look to be in Y or higher voltage configuration. I would check and voltage tappings on the control transformer.

If you have a single phase supply it is an easy matter to power the control circuit only and function check the control circuit and logic. The contactors should energise and every thing should work except the main saw motor.

Mike
Thank you Mike for all the info and help. That 575 doesn't have any continuity between W1 & W2. Don't know how I did that, unless it's an intermittent connect somewhere.
 

Radiomike

Registered
The motor connection, the correct way to connect the links, is shown in the schematic you referenced in your first posting. It looks to be in DELTA, lower voltage connection. The control transformer is marked for the two voltages, it seems to have links in and set for 240 Volt. So overall the motor and transformer seem to be set up for 240 Volt. If you decide to do some wire changes mark the wires with numbers as in the schematic and I always like to use crimps, Numbers are cheap https://www.ebay.com/itm/Cable-Wire...m41fbb061f6:g:AJ4AAOSwDXFcdBVT&frcectupt=true

Mike
 

Kurtis

Registered
The motor connection, the correct way to connect the links, is shown in the schematic you referenced in your first posting. It looks to be in DELTA, lower voltage connection. The control transformer is marked for the two voltages, it seems to have links in and set for 240 Volt. So overall the motor and transformer seem to be set up for 240 Volt. If you decide to do some wire changes mark the wires with numbers as in the schematic and I always like to use crimps, Numbers are cheap https://www.ebay.com/itm/Cable-Wire...m41fbb061f6:g:AJ4AAOSwDXFcdBVT&frcectupt=true

Mike
Thank you Mike.
 
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