rewinding a 120vdc dakota wind generator

[ted]

(blank)

[Norm]

 More information might help...does it have a data plate, field coils, how many segments on the commutator, 2 brushes?  etc.

   Like they ask at the parts store.....Make, Model and Serial number?.

                  ( :>) Norm.

[DCJake]

Ted,

are you going to re-wind it yourself? Or you looking for someone to do it? I know someone who has rewound the Jacobs.

Kevin

[ted]

Hi, Kevin:

I am considering all options, including trying to rewind it myself, with some detailed instructions.  I am located in the far east (RI), and they want $6500 to rewind and balance at the generator shop.  It seems a shame to go to a different type of generator, since this thing has withstood hurricanes, and all the other New England weather, or to bring in the powerline (this is about 1/3 the cost of that).  If I can find someone to rewind it, are there any improvements to this 100 year old design, like modern magnets, etc that can be made to improve performance?

Thanks for your response,

Ted

[wdyasq]

Ted,

You might get someone like "Zubbly" to rewind your machine.  In a previous life, he did motor and generator rewinding.  He could also evaluate the possibility of changing to Neo magnets.

HTH,

Ron

[DCJake]

Ted,

I know of a motor shop in Wisconsin that will re-wind that for you, he's has alot of experience with the Jacobs. About 9 months ago his rate for a 40V long case was $800 with the current cost of copper. Not really any improvements can be made. The high voltage generators can not be rewound for low voltage (24-48) because of the field coils. How do you plan on incorporating the 120V generator?

Kevin

[ted]

Hi, Kevin:

I don't know what you mean by "incorporating".  It has been on a 100' tower here(the top sections of the 2 WTIC transmission towers) for 25 years as part of a wind/solar system charging old telcells off the grid.

Please give me a number or address for your friend in Wisconsin.  He certainly sounds worth looking into.

Thanks,

Ted

[DCJake]

Ted,

I'm sorry I wasn't clear asking you how you going to incorporate the gen. I was wondering if you had a 110-120V inverter, they are not so common these days. Sounds like you have an inverter with that high of dc voltage input.

Give me a couple days to find his info. I know I have it somewhere.

Another thing, I've been told that the Dakotas used very inexpensive solder, not high temp solder. It was not uncommon for the coil leads to become unsoldered, which might be the cause of your short. Maybe check that out before you ship 500lbs across a few states.

Kevin

[ted]

Hi, Ron:

I would be interested in talking to Zubbly about the rewinding and the magnets if you can provide a contact, or get him to write me here.  Thanks for the comeback.

Ted

[ted]

Hi, Kevin:

Regarding the inverter, I've been down the whole line with inverters for the past 20 years.  I still have one of the 200# anchors sitting in the basement.  I was lucky enough to find Chad Lampkin about 6 or 8 years ago, and he built me a 120vdc inverter from a Heart 12v, that has been great.

I will check on the soldering as you suggest,, but I could use a little direction.  Are you talking about the field coils and where they are soldered, or something else?  Physically, in the generator, where would I look for these connections?  Also, when I get it back from the generator shop, I will be scraping between the bars on the commutator to make sure I haven't created a short with a dirty commutator.

Ted

[DCJake]

Ted,

how do you know it's shorted? What test have you done?

There could be grease from the bearing and carbon from the brushes on the back of the commutator? Dirt carbon/grease between the commutator bars? Or the solder problem? Is there any solder splatters on the inside of the case? Can you smell burnt insulation? Your field coils are open?

A way to check to see if the windings are shorted to the rotor is take an extension cord, cut the hot wire, plug a light into it, place one end of the cut hot wire on the commutator and the other on the shaft, plug it in. If the light bulb lights up, you are shorted. PLEASE BE CAREFUL WITH TEST.

Per Michael Hacklemans book. A good tool to clean/scrape between the commutator bars is to cut a hacksaw blade to a point and grind down the sides of the teeth. It should fit between the bars nicely.

Kevin

[ghurd]

There is an outfit in Michigan that rebuilds them.  Maybe Michigan Wind?

G-

[ted]

Kevin:

I didn't do any tests.  It wasn't putting out, and I also had problems with the top swivel bearing, so I took it down, and sent it to the generator shop, who told me it is shorted.  I did not try to clean up the commutator before I sent it, so I will do that when I get it back.  Would a continuity check between the commutator and the shaft do the same as the light bulb test?  They also said I had bearing problems inside the generator, so I will also check to see if the armature is contacting a field winding.  Is the check for open field coils continuity between field positive and negative?  A friend also told me that the only continuity you should find between the commutator bars is between bars opposite each other across the commutator, so I will be checking for that as well.

Thanks for the help.  If you think of anything else, please post it.

Ted

[DCJake]

 Ted,

yes, between the negative/positive on the field.

The motor bearings are easy to change, same bearing front and back 88508's.

Another simple test would be to hook it up to a 12V battery and make it a generator.

What kind of problems is the top bearing (Timken 395-S) giving you?

E-mail me @ akwindandsun@msn.com

Kevin

[Victor]

every commutator bar will show continuity with every other bar in a working generator.

[Flux]

Ted

The only really satisfactory way to test the armature is with a dc drop test. It's not that difficult and I think you will be able to do it.

Clamp a pair of leads to the commutator more or less diametrically opposite, you can trap the wires under blocks of wood or something to insulate the clamp.

Connect these leads to a 12v battery with a low resistance in series to limit the current to a safe value ( may not be needed with 110v armature but either check the current or use a couple of ohms to be safe )

Use a millivoltmeter to measure the volt drop between each pair of com bars, keep moving along one pair at a time from one of the battery connections to the other.

An analog meter is much quicker and more convenient but a digital will do.

The volts between bars should be more or less similar. A shorted coil will give a low or zero reading. A drastically high reading will indicate an open circuit.

You may get funny readings near the supply wires so confine your tests to the middle group of bars between supply points. Then move your supply points round 90 degrees and do the remaining bars.  Most likely you will get a different voltage once you change the supply points, that doesn't matter just look for similar readings in the new group.

Also look out for a ring of solder as mentioned above. If the commutator has been cleaned you will have lost the evidence but if it has not been touched look for burn marking on pairs of bars this is  a sure sign of thrown solder to the bars. An open circuit is much more common than a short.

A shorted coil will most likely be darkened or black from circulating current before it finally gave up.

Check field continuity as suggested and you can also connect your battery to the field and measure the volt drop across each coil to make sure one is not shorted out.

Finally as suggested it should run as a motor from a battery, smoothly and with no sparking. Sparking and a reluctance to start will again indicate a winding fault, usually thrown solder.

Unfortunately some faults will result in it motoring but still not generating.

Sorry this is a bit long winded but I think it is well worth doing some more tests as it may be a repairable fault.

Also clean between com bars as suggested. If for any reason the comm has been skimmed in a lathe, shorts often occur and careful undercutting and clearing of burrs is necessary.

Hope this helps to prove things one way or the other.

Flux

[ted]

Flux:

Thanks for the response.  Today when I picked up the generator from the shop, I found out why they want so much money to rewind the armature, which they say has 4 low spots on it.  They say that they have to replace the commutator, which will cost $3000.  There is nothing visibly wrong with this commutator, but they don't do rewinds without changing the commutator.  Do you have any thoughts on that?  They also said that they broke a field connecting wire, which may have been broken before they disassembled the generator.  I will try to test the armature as you say.

Ted

[Flux]

Ted

They are covering themselves, but the chances of a commutator fault are very low especially at that low voltage. If the winding tests ok it will eliminate the commutator. If it shows as a shorted winding you will not know if the short is in the coil or the commutator until you dis-connect the leads.

If all tests ok I would suggest you get the commutator skimmed by someone who knows what they are doing and undercut it and re-test to make sure there are no burrs causing shorts.

If you have to take it to a general engineering firm with no electrical experience, make sure they use a sharp tool with a fine point and only take very light cuts. Don't go deeper than is needed to clean up the low bars.

Even if you have to get it wound most places will test the commutator and re -use it.

Good luck.

Flux

[ted]

Flux:

I felt they were covering themselves, too.  I finally found the electric motor shop that did the field ten years ago (they had been bought out, and changed names) and they have it now.  I will let you know when they get back to me with some answers.

Ted