Required voltage for this large saw (German three phase schematic)

[jim hardy]

The photo of the burnt winding has what looks like a piece of metal sticking out at the fault location. This could well be the base cause of failure, perhaps a leftover from a previous rebuild. A rewind is due in any case.

at 300% several wires are burnt away

I am wondering if it was my setup that caused it or if it was already on its way out the door.

i don't think your hookup caused that. You would have heard arcing and smelt smoke.

 

[Asymptotic]

Those fuse ratings seem reasonable when you take into account the in-rush currents of the transformer and of the contactors/relays. Time Delay fuses at closer to rated current are an option but are seldom seen in practice

This second sentence, and what follows regarding primary inrush and relay coil-induced inrushes seen by the secondary are all valid points, but the originally specified T2A fuses on both primary and secondary still strikes me as overkill (provided the 'T' signifies a time lag fuse).

Table 2 and 3 from a Littelfuse white paper on transformer fusing.
https://m.littelfuse.com/~/media/el...elfuse-transformer-protection-white-paper.pdf

An additional complication is the BOM doesn't specify fuse voltage. Have to assume it is 500V because a 250V rated fuse wouldn't be acceptable when the primary is wired for higher voltages.

 

[Asymptotic]

When I put this Weg 21 motor on it and started it up, it was producing 240 on all three legs at a little over idle, no 12 v boost required. I ran it for just long enough to get a reading, shut it down and checked the temp of the motor and caps, all were cool, then I fastened the Caps together and grounded them. It was the last time it produced more than 9v ac and that was with a 12v boost to the Caps otherwise it would only put out 3-4 volts.

I'd be interested how this critter was wired. What with the 24 uF/360V (oil-filled?) capacitors, mention of a "12 v boost", and motor belted to a gas engine it appears an attempt to re-purpose a 3 phase induction motor to perform as a generator. I don't have hands-on experience with these rigs, but from what I've read they're temperamental beasts.

 

[Kurtisinger]

Hi Asymptotic.. honestly, I don't have any experience with them either but as far as I can tell it's not much different than an three phase automotive alternator. Except of coarse, one is built for low voltage and high amperage and the other built for high voltage and low amperage. Both can be excited by DC to produce AC. So far I think the reason people find them to be temperamental is because they try to draw large amperage from them, trying to start motors etc. I am presently looking for large hp 3 phase motors because I see lots of industrial 3 phase equipment around for free or dirt cheap that I would like to have and use instead of investing in more expensive single phase equipment that have a shorter life cycle.

As far as those 360v 24 uf Caps go. I'm using them because I have more of them than other sizes. I was planning to put a bank of them on each leg to see if it would stabilize current draws. I have read many articles on how to size Caps and so far all that I've accomplished is further confusion as people say all kinds of stuff. Presently, I am incapable of doing the math to figure out exactly what they should be, plus my knowledge of AC is minimal as you already know. I am learning lots in this forum though, thanks to you guys... : )

 

[jim hardy]

I'd be interested how this critter was wired. What with the 24 uF/360V (oil-filled?) capacitors, mention of a "12 v boost", and motor belted to a gas engine it appears an attempt to re-purpose a 3 phase induction motor to perform as a generator. I don't have hands-on experience with these rigs, but from what I've read they're temperamental beasts.

i too was curious

look up "Induction Generator"

it differs from an automotive alternator in that there's no external current going to the rotating part.
So it has to be 'excited' from the stator side
and that requires AC current to the stator in order to make a rotating magnetic field for the rotor conductors to 'cut' .
The usual implementation is to let it draw its magnetizing current from the grid.
though with enough external capacitance the motor can make its own exciting current

and at first that's what i thought @Kurtisinger was up to.

But i can't quite make out how he wired his capacitors.

 

[Kurtisinger]

i too was curious

look up "Induction Generator"

it differs from an automotive alternator in that there's no external current going to the rotating part.
So it has to be 'excited' from the stator side
and that requires AC current to the stator in order to make a rotating magnetic field for the rotor conductors to 'cut' .
The usual implementation is to let it draw its magnetizing current from the grid.
though with enough external capacitance the motor can make its own exciting current

and at first that's what i thought @Kurtisinger was up to.

But i can't quite make out how he wired his capacitors.View attachment 239884

What I meant is that they are both 3 phase.

Keep in mind that this is an experimental and very temporary setup. I do have a piece of welding cable and a spike for ground but the ground here is frozen solid right now.

 

[jim hardy]

dont worry about ground for now.

I see the capacitors effectively not connected on one side
but tied together on the other

so all they do is tie together those two black and one white wires that go someplace else.
With one side floating they're electrically "not there".If this is just a plaything
you might be able to figure out which of those burnt up wires goes with which
splice them by soldering into each a splice of similar sized copper wire between the loose ends
than soak the whole area with varnish or high temperature paint.

I've had good luck with woodworker's polyurethane varnish
and with engine enamel from the auto parts store.

It's cheap, takes an hour or two to prepare and solder the burnt wires
and works for me about half the time.

If there's insulation failed back inside the stator where you can't see it you'll have to rewind

but I've fixed appliance motors, a drill press motor and an automobile starter that way.

Good Luck

and have fun !

old jim

 

[Kurtisinger]

dont worry about ground for now.

I see the capacitors effectively not connected on one side
but tied together on the other

View attachment 239892

so all they do is tie together those two black and one white wires that go someplace else.
With one side floating they're electrically "not there".If this is just a plaything
you might be able to figure out which of those burnt up wires goes with which
splice them by soldering into each a splice of similar sized copper wire between the loose ends
than soak the whole area with varnish or high temperature paint.

I've had good luck with woodworker's polyurethane varnish
and with engine enamel from the auto parts store.

It's cheap, takes an hour or two to prepare and solder the burnt wires
and works for me about half the time.

If there's insulation failed back inside the stator where you can't see it you'll have to rewind

but I've fixed appliance motors, a drill press motor and an automobile starter that way.

Good Luck

and have fun !

old jim

Sorry old Jim.. T1, T2 & T3 from the motor each go to a Cap. The other black wires go to a clip for the +12vdc to excite the windings. Some people say you need it and some people don't say anything about it. Interesting how the Weg 21 was putting out 240 without it. Especially considering the shape of it.

Yes it is a play/educational thing so I will try to patch it for fun, thank you.. So far all the photos of equipment that I have posted to this thread have come out of the junk pile and didn't cost me anything except for the belt and one pulley, about $30 worth. So if I blow something up it really doesn't matter. My main goal is education but I do try to use a little money every time I get some, to invest in tools as I have lots of space and I love to build stuff. Also one of my properties doesn't have grid service so it won't hurt my feelings to have brushless Gensets.

I am kind of wondering if it would be possible to dump the rectifier from an alternator and run it parallel with a three phase induction motor and engage it only for the amperage to start motors.

Here is my next victim. This one is a three wire.

 

[Asymptotic]

Sorry old Jim.. T1, T2 & T3 from the motor each go to a Cap. The other black wires go to a clip for the +12vdc to excite the windings. Some people say you need it and some people don't say anything about it. Interesting how the Weg 21 was putting out 240 without it. Especially considering the shape of it.

It's impossible this rig ever put out 240V as currently wired. Look more closely at the mark-up @jim hardy did in post #37.

These capacitors have (2) 1/4" push-on tabs on each capacitor connection pad. None of the wires are connected on one side of the cap, each of the motor 'T' leads are connected to the other side, and the black wires buttspliced together to the 'exciter' alligator clip lead are all connected to the motor 'T' leads on the same capacitor pads.

Trace it out.
Aren't the motor leads shorted together?
How should capacitors be connected to the 'generator' motor?

The Delta motor in post #38 isn't a good choice for what you are trying to do.

• It is a 2 pole (3450 RPM at 60 Hz) versus the previous 4 pole (1730 RPM at 60 Hz) motor. You'll need to spin it at least twice as fast.
  
• It is a 200V motor.
• The saw motor you want to drive is 3.0 KW, the previous 'generator' motor was rated 5 HP/3.73 KW (just barely enough), but this Delta is only rated 3 HP (2.24 KW). Chances are it'll bog down and stop generating the moment saw blade touches wood.

 

[Kurtisinger]

It's impossible this rig ever put out 240V as currently wired. Look more closely at the mark-up @jim hardy did in post #37.

These capacitors have (2) 1/4" push-on tabs on each capacitor connection pad. None of the wires are connected on one side of the cap, each of the motor 'T' leads are connected to the other side, and the black wires buttspliced together to the 'exciter' alligator clip lead are all connected to the motor 'T' leads on the same capacitor pads.

Trace it out.
Aren't the motor leads shorted together?
How should capacitors be connected to the 'generator' motor?

The Delta motor in post #38 isn't a good choice for what you are trying to do.

• It is a 2 pole (3450 RPM at 60 Hz) versus the previous 4 pole (1730 RPM at 60 Hz) motor. You'll need to spin it at least twice as fast.
  
• It is a 200V motor.
• The saw motor you want to drive is 3.0 KW, the previous 'generator' motor was rated 5 HP/3.73 KW (just barely enough), but this Delta is only rated 3 HP (2.24 KW). Chances are it'll bog down and stop generating the moment saw blade touches wood.

Shorted out? So is that why the weg21 burned out? Should each side of a winding go to one side of a capacitor?

I wasn't actually planning to try and boot the saw with the Delta motor. Been looking for an 8 to 10 hp motor to be powered by the 14 hp Kohler engine. Going to try running some smaller motors like the Delta before actually plugging it into the saw.

I have seen so many different article that say different things. Some say a motor has to be twice the size as the motor that will be run. I've seen up to six times the size is required. Some say that caps are needed, some don't say anything about it. Some think there are only six terminal three phase motors, some only mention nine terminal motors. So far I haven't found any articles that explain things thoroughly.

Thanks Asymptotic.

 

[Asymptotic]

Shorted out? So is that why the weg21 burned out? Should each side of a winding go to one side of a capacitor?

I wasn't actually planning to try and boot the saw with the Delta motor. Been looking for an 8 to 10 hp motor to be powered by the 14 hp Kohler engine. Going to try running some smaller motors like the Delta before actually plugging it into the saw.

I have seen so many different article that say different things. Some say a motor has to be twice the size as the motor that will be run. I've seen up to six times the size is required. Some say that caps are needed, some don't say anything about it. Some think there are only six terminal three phase motors, some only mention nine terminal motors. So far I haven't found any articles that explain things thoroughly.

Thanks Asymptotic.

Don't know why the motor winding burned out. Was thinking the motor had been wired differently during the period when it was observed generating voltage because I can't see how it could have with the three leads tied together.

Some say a motor has to be twice the size as the motor that will be run. I've seen up to six times the size is required. Some say that caps are needed, some don't say anything about it.

Making an induction generator out of a scrap motor appears to be in the same league as "the Professor stranded on Gilligan's Island" inventions. From what I've read, it can work, but with a long string of caveats.

• The more severe the load service, the more oversized the generating motor must be. A saw is probably considered light to moderate service while an air conditioning compressor would be considered severe.
  
• If residual magnetism in the motor steel can provide enough reactive power to supply no-load magnetization current then the "generator" will develop terminal voltage once the rotor is turning above synchronous speed. This happy condition is by no means guaranteed, and very iffy when it does occur, because the generator must supply both real and reactive power. If the load ever draws enough current that it cuts too deeply into this necessary magnetization current, generator output will collapse.
  
• A properly sized, delta-connected capacitor bank connected across the generator leads is added to reliably supply reactive power.
  
• If the generator motor doesn't have enough residual magnetism to get the process started, it is necessary to goose it by temporarily applying a DC source across a pair of leads after the generator shaft is turning above sync speed.

https://en.wikipedia.org/wiki/Induction_generator