My Sliprings

[mitcamp]

My first attempts were with copper connectors that you would connect 2 lengths of 1 1/2 inch together with. They got better as time went on, trying different brushs,holders and springs. I had a good working model for up to 200-300 watts. I am still servicing a 250 watt machine at a cottage, 90 miles from a hydro pole and the sliprings and brushes are still operational after 8 years. I clean them with emery cloth and put on some electrical grease each time I,m in the area,usually once or twice a year.

When I started building Hugh,s 8 foot 500 watt I used the same sliprings for about a month. They got black quickly and in a storm with the brake on, it actually caught on fire. The sliprings got so hot they melted the insulator that they were mounted on. The insulation burned ,along with the short wires to where they were connected to the #2 mainlead wires. I spent probably months trying different idea,s until I came up with what I,m using now. I have near 2 dozen 500-1000 watt machines around the countryside. I am using the same sliprings and brushes on my 18 foot diameter Dual Rotor,except I am running 2 brushes on each slipring and I have a spot to add the 3rd set of brushes if needed.



The neg wire comes out of the hole in the coupling under the bottom slipring. This is a new machine and you can see the tiny holes drilled on the bottom edge of the lower slipring.  This is where I attach the neg wire that goes to my batterys with a robust terminal and a healthy metal screw. This wire # 6 is only going 5 feet through the mast pipe, where I will connect it to #1 and then to the batterys. The metal screw must be short so it does not go through the high tempature insulated sleeve that lines the inside of the slipring. Outherwise it would short to generator ground. I bring the positive lead up the center of the mast pipe, out the top,  to the top slipring and connect it to the top lip of the same.

You  can see the red positive wire that attaches to the top brush and the black wire below that attaches to the lower brush. Of course these red and black wires are going to the rectifiers which are mounted within a foot away.

The sliprings are made at a local machine shop, the brushes are starter brushes and available at a local auto shop,and so the springs. I make my own mounts from angle iron and weld on mounting tabs for the brush holders.  I cut the brush holders out of 5/8 inch thick teflon sheet.

Someone asked if the cover on the generator was off a washing machine, well thats a no. I purchase all my magnet wire from a commercial winding firm and that sells me ends of rolls. In this case they buy thier wire in 100 lb buckets and I get whats left in the bucket. Some buckets Ive got, had 22 pounds in it. I went to school with the guy and he charges me 3.00 a pound. And I use the buckets to make a weatherproof shelter for my generators.

All my generators have yaw bearings. Check out my files for more pictures.    Mitcamp

[drdongle]

They look great! can you tell us about the insulating materal that the rings are mounted on?

[dinges]

Interesting reading!!

Not wanting to 'push' you, but the more pictures, explanations, details, etc. the better

E.g. of earlier, failed attempts or what didn't work.

I started a thread on the subject a couple of weeks ago:

http://www.fieldlines.com/story/2006/5/6/102016/2184

I love reading about those sliprings, it's the one area in homebuilt windmills that's still underdeveloped, IMHO. I know most people don't want to bother with it or feel there's no need for it. But I like to complicate matters

Question: how much pressure do you put on the brushes? I don't see any springs.

And how often do you have to service, if you have to service at all. I know you do some preventive maintenance & re-grease, but you think it's really necessary to do this? Me, I don't like climbing masts, you see...

Personally I think I would mount 2 or 3 brushes per slipring (4-6 in total). Sliprings are a case where more and bigger is better.

Peter.

[tecker]

I just happened to be ripping into a washer at the time and they looked similar but smaller on closer inspection. Don't mind me .That's poly board I think is it spring loaded? I 've got a couple of brushs sets for delco altermators I was thinking of giving them a try . But the poly ( or is that delrin)looks cool . The other option would be some castings with brass or stainles inserts . About how often do you forsee having to clean This  setup .  

[Epower]

Here is a site for you to check out on "carbon brush care and more". This will help in your design. (http://www.reliance.com/prodserv/motgen/c7090/} They state that you should never use emery cloth since the grit is conductive. Check "Mechanicl Intergrity and Setup" as noted on their site. When I worked in the electric motor industry many moons ago, we used a special stick material (white in color) to help breakin the new brushes along with lubricating the slipring at the same time. Check your local electric motor/generator rebuilder. Hope this info helps...Epower

[mitcamp]

Dr. D They are both machined,and the high temp teflon is pressed into the brass ring. I,ll try to find a better picture or I will lay it out in a exploded view layout and take a picture of it.I will ask the machinist to give me more details on the teflon material he uses. Best I can do

[mitcamp]

Dinges, Look at the last picture and you will see the springs. They look like a black thin clothespin and one end is drilled and a rivit is put into keep it in place. The springs are at the rear of the holder. There is a better picture in my files showing the springs. Don,t most of these generators need a little bolt tighening,oil or grease the tail pivot, clean and lube the sliprings while your there.

[Epower]

One other site to be checked out on "materials best suited for slip rings and commutators" ( http://64.90.169.235/megab2/costeff/tn45/sec10.htm )...Epower

[hvirtane]

I looked at your picture files. The last two pictures of the sliprings show also the springs really well.

Very good pictures and descriptions.

Thank you a lot for sharing the data.

- Hannu

[Flux]

Just a few general comments on a few points raised.

It's not emery that's conducting but silicon carbide ( carborundum here). No so much a problem with slip rings as commutators with voltage between bars.

For rotating machines use glass paper ( sand paper) unless you have proper brush seating stones as mentioned.

In this case conditions are different and removing oxide is far more important than any worry about conducting particles, so any form of "scratching" paper is probably ok.

In any normal rotating machine, oil or grease on the slip rings is a cause of trouble, it sets up a process that is virtually spark erosion.

Rotating machine slip rings develop a "skin" that offers good conduction and low friction and under normal conditions it is bad practice to remove this unless there is other troubles.

These rings will never form that "skin" but will form layers of corrosion that will eventually cause poor contact.

With the right grade of brushes this is a case where a film of lubricant may be beneficial to slow the corrosion and may not cause sparking problems. The brush pressure need to be higher than for rotating machines and not all brush types will tolerate lubricant.

If you can keep the weather out well enough then lubricant maybe more of a nuisance than a help.

Mounting the brushes on heavy brass arms may be an advantage to reduce heat build up and also help with electrical conduction to relieve the load on the "pig tails"

If you must use slip rings, then this is the way to do it.

[mitcamp]

"These rings will never form that "skin" but will form layers of corrosion that will eventually cause poor contact"

Flux,you are right about that. My early sliprings were of copper and even with the low amperage they took on a black glaze within a 2 month period. I asked an elderly starter,generator repairman and he advise me to change the brushes. I,m not really up on what brushes are made of,so I took his advise and behold, it certainly helped. I am using starter brushes now and I selected the ones with the heaviest pigtails I could find.

"If you can keep the weather out well enough then lubricant maybe more of a nuisance than a help."

 I pay special attention to getting a good cover over the sliprings. The cover as I said is the buckets the wire comes in and its almost bulletproof, and it covers the yaw bearing at the same time.

These brass sliprings are 3/8 in thick and there is no way they are going to wear out. Flux, are you suggesting that I would have better luck if I held back on the thin film of grease. I,m all ears

Flux, while I,m at it do I have enough rectifier on this machine. Normally this machine gives me 20 - 90 amps in 15 m.p.h wind. At furling speed 25 m.p.h it blacks out my 200 amp meter. I have a digital amp meter and an anolog amp meter on the negative cable, with a 200 amp shunt,so I believe I,m getting a accurate reading.  

[Flux]

For normal rotating machines, any form of lubricant is asking for trouble, it forms an insulating film and then a spark punches through and etches a hole, the result is very rapid destruction.

With these rings with no continuous rotation the brush pressure can squeeze the film out. If you keep the weather out and the corrosion forms slowly enough to be rubbed off as the machine yaws then you will have better contact without any lubricant.

There is no need for it as a lubricant, even the high copper content brushes the rings and brushes will last many years.

Brush grade does make a lot of difference, with dc machines the volt drop is typically 1 volt per brush and at 200A that means a lot of heat. AC brushes can generally have lower resistance as there is no problem with commutation that dc machines have to contend with.

This is a very special case where you need a very low brush drop and also something slightly abrasive to keep the rings clean. Your starter brushes are likely to be the best that is readily available, there are different grades of them but you will have virtually no choice, you are right to choose the heaviest ones you can find. Any low metal content brush will not tolerate any form of lubricant at all.

Your rectifier may be ok as it looks to have plenty of heat sink. That may take care of peaks up to 200A but you will need more bridges to maintain it for long. Try to make sure the metal bases of the bridges don't exceed 60 deg C, that will push the junction temperature well up inside. That most likely limits you to 40 deg C on the heat sink to allow for the temperature gradient on the mounting.

Short term failure of those bridges usually comes from excess junction temperature in the diodes. Long term failure often comes from the failure of the crimp connections to handle anything like 30A on a long term basis. The connection resistance deteriorates and the lugs get hot and cause failure.

Flux

[mitcamp]

I will leave the lube alone in that case. Nice to get a answer from someone who knows. I will add another 3 rectifiers to the machine some day there is no wind. Its up 100 feet and that thing pushes a feller all around the tower if there is the slightist breeze.I have to put a strobe up one of these days to.

By the way I recieved a 200 amp digital meter and a new 200 amp shunt in the mail today.  When I went to change the shunt,I noticed I had put a 50 amp in 2 weeks ago, certainly by accident as I have 50 and 100 amp shunts on hand. On close examination it looked like it got real hot, probably from one of the 200 + amp voyages its been on lately. It now has the proper shunt. My question is: Was I getting an acurate reading this past 2 weeks, the shunts all have 75 m/v written on them. Thanks for your input and what part of North America do you reside in, if you don,t mind.    Mitcamp

[Flux]

A 50A shunt will produce 75mV with 50 A flowing. 100A will produce 75mV with 100A.

If you had a 50A shunt in place of 100A your currents will be half of what you thought you had, assuming your meter is scaled to read directly from the 100A shunt.

75mV is the standard shunt drop for analogue meters and some digitals are scaled to use this also.  If you are using a digital mV meter you have to do sums and a 75mv shunt is not so convenient.

Your meter should have the information on shunt mV for fsd. Digital meters are ideal for precision measurements under steady conditions but are a pain for this sort of job.

Sorry I am in UK.

Flux

[dinges]

You say brushes are characterized by a voltage drop (say, 1V). At 200A that's indeed a lot of power, 200W... All the more reason for my idea of installing 2-3 brushes per slipring.

Correct me if I'm wrong, but I thought brushes/sliprings most important parameter is their (transition) resistance. In this case, R=U/I 1/200.005 ohm. 5 milli-ohm. Which is extremely good, IMO. Yet at 200A still 200W...

(with amp-plugs that are properly crimped, I usually have 5-6 milli-ohm of resistance...)

[drdongle]

Thanks.

Did you us a specal grade of brass or just what he had lying around?

[mitcamp]

Dr D I believe these are fairly hard and I,m only guessing. My machinist makes bushing for heavy equipment, although I will ask at my next visit. I guessed at the weight before, but today I weighed them, the weight is 2 pounds for each brass ring. They measure 2 inch high and 2 1/2 inchs across the top. The teflon bushing on the ring could be changed to accomadate a smaller pipe.  I am having another slipring model made at this time to accomadate the larger (over 1500 watt)machines so I can put up to 4 or 6 sets of brushes per ring.   Mitcamp

[Flux]

Peter

This will not directly apply to windmill slip rings with high metal content brushes but for normal dc machines using carbon brushes the volt drop is virtually constant.

If you add more brushes in parallel then the current density falls and the drop changes very little.

This will no doubt still apply to some extent with the copper/carbon brushes but the drop will be a lot lower. The main gain from more brushes is likely to be a reduction in temperature at each brush  rather than a reduction in volt drop, but the loss should come down to some extent with more brushes.

Flux

[mkseps]

My experience with slip rings involves working on military equipment using turrets, ie, tanks etc.  Many of these applications involved moving high currents to the turret functions.  From this, Peter is correct - use more brushes to carry the currents but it also helps in the case of a spark of one of the brushes.  It is unlikely that two brushes on the same ring would spark (not good)at the same time.  One other thing; most automobile starter brushes are designed for short time electrical service.   Many of the automobile stater brushes are copper impregnated. The brushes I was familiar with were silver impregnated which substantially lowered the brush electrical resistance but also improved lubricity.  Most brush manufacturers can supply such carbon/silver brushes both stock or custom.

Gene