Generator voltage drop


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Old 06-06-16, 11:37 PM
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Generator voltage drop

I'm new to this posting threads thing so forgive my ignorance please but I'm in a fix. We have an old Almand permanent magnet 4.8 kw slow speed generator with a 2 cyl. Lister air cooled diesel engine. We use it about 3 months out of the year 24/7 running a 1 & 1/2 h.p. submersible pump. Last year it spit out the bearings on the back end of the generator and from the smell of things, fried the windings. I took it to a shop (4 hrs. away) and they machined in a new bearing cup and re-wound it. 6 weeks ago I set it up for a test run. It would start the pump but in a few minutes it would kick the reset on the pump control box. Had a well guy come out and checked the pump & wiring and although the pump was pulling higher amps (worn pump maybe) it was within range and ran fine using a different generator. I took the generator back to the repair shop. They bumped up the hertz to 62 and said it works. I brought it back on site but still the same problem. The generator running with no load shows on my Radio Shack voltmeter 230v. I tried the generator on a 5 h.p. motor running a hydraulic pump and it would start & run it (showing 213 v. on my voltmeter) but would drop to 90 v. as soon as I touched a hydraulic lever. There is no rpm gauge on the engine but it would lug down and smoke but I expected that knowing that 5 hp motor is too much for a 4.8 KW generator. (The generator running with no load shows on my Radio Shack voltmeter 230v.) I pulled the pump out of the well (big job pulling 300 ft. of 2 in. pipe) and built a test barrel and took the generator and pump to the repair shop and told them to fix it so it all worked! They called me Friday evening and said they give up, come get it and never bring it back. I contacted Almond (they don't make generators any more) and talked to a guy that had been with them 35 yrs. and he was kind enough to dig out a service manual (for a different generator but basically the same) and it troubleshoots that it may have partially lost magnetism with the fix being, send back to factory to be re-magnetized (which they DON'T do anymore!). I've been on the computer and phone all day trying to find a repair shop and when I mention re-magnetizing, they ALL say duh? but eagerly try to sell me a new generator.
Any ideas? I need help. I know NOTHING about the internal workings of a generator. This is a sweet machine. Only uses 7 gal. of diesel per 24 hrs.
 
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Old 06-07-16, 12:22 AM
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I know nothing about generators too but I did find an article on re-magnetizing the motor on the generator here How to Remagnetize an Electric Generator | eHow . They have three articles on generators that I could find doing a quick search but the first article is what you are looking for. Basically you use an electric drill a steel rod and a battery powered drill to fix your generator. Whether this will work or not is debatable but I have used ehow before and most if not all of their advice is not bad.

If it doesn't work then it is time for a new generator. I would get as high a voltage of battery powered drill as possible to try this. It isn't very specific in the instructions but that just makes sense to me. Welcome to the forum.
 
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Old 06-07-16, 12:59 PM
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This process is also called "flashing" the generator or "flashing the exciter". Try some google searches on that term. There are a number of instructional web sites that show how to do it in a bootleg DIY way with batteries and drill motors if you don't have access to a motor shop that can do it.

It seems like a reasonable fix given how long the generator has sat unused. The residual magnetism can decrease when a generator sits unused for a lengthy time. If you do get it running again, make sure to run it about an hour every month with some dummy load connected.
 
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Old 06-08-16, 01:14 PM
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Richard and Ben, did you guys miss this little bit of information in the beginning?

We have an old Almand permanent magnet 4.8 kw slow speed generator with a 2 cyl. Lister air cooled diesel engine.
If this indeed a permanent magnet generator then there are no electromagnet (field) coils to "flash". If the permanent magnets have lost their magnetism then the ONLY thing to do is to have the magnets removed and re-magnetized.
 
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Old 06-08-16, 01:50 PM
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Good catch Furd....................
 
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Old 06-08-16, 10:12 PM
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Thanks for all the input guys. I DID go online and googled "flashing" and "re-magnetizing" generators and found everything from the drill thing to hooking it up to the power supply of another generator to D.C. jumping fields or whatever but the further I looked, the more confused I got. But Furd touched on what was a big question I had in my mind. Will those tricks work on a PERMANENT MAGNET generator? I take it that it won't. So, HOW does somebody re-magnetize the magnets?
 
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Old 06-08-16, 11:35 PM
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Probably won't help but I found this: Body
 
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Old 06-09-16, 01:35 AM
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I've never seen a permanent magnet generator beyond one used on a bicycle for the head lamp. Back in the olden days when cars had a "generator" rather than an "alternator" we used to "polarize" the field by connecting the battery to the field coils momentarily.

There is a 120 kw steam-driven exciter generator in the hysterical () museum where I used to volunteer. It had sat for more than 20 years without running, maybe a whole lot more than that and when we tried to get it to generate some power to light a few bulbs it did nothing. I "flashed" it from a 120 volt rectifier I had installed on the in-plant telephone system and when disconnecting I drew an arc at least three inches long. I don't know how many amperes were flowing but the silly thing did work after that.

Ron, I wish I had some good news for you because that old beast must have been a real sight when running. Unfortunately, I just don't know what to tell you.
 
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Old 06-09-16, 01:47 AM
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I "flashed" it from a 120 volt rectifier I had installed on the in-plant telephone system and when disconnecting I drew an arc at least three inches long. I don't know how many amperes were flowing but the silly thing did work after that.
Furd, I wonder if you could do this with a DC welder? Wrap a few turns of insulated wire around the magnets, Connect welder ground to one end of the coil and a steel plate to the other and then weld a bead on the steel plate.
 
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Old 06-09-16, 03:06 PM
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Good thinking, Ray, but I don't think it will work in practice. Remember that you need to have opposite polarity on the magnets across from each other and that this being a slow speed generator there are lots of magnets. Ron didn't state what the speed of the unit was but I know those old Lister engines didn't turn very fast. 1200 rpm would require a six-pole (magnets) generator and I suspect this unit was more like 900 RPM (eight poles) or possibly as slow as 720 RPM which would be a ten-pole generator.
 
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Old 06-09-16, 04:04 PM
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Well it was three in the morning when I came up with that idea.
 
 

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