Author Topic: Brushed Servo Motor (Read 3644 times)

arbela47000 · « **on:** September 28, 2008, 08:06:17 PM »

I see brushless and brushed motors for sale. Is there anything wrong with brushed servo motors for wind generators?

micro mechanix · « **Reply #1 on:** September 28, 2008, 05:41:41 PM »

Brushes wear down, armature contacts corrode, the need for cooling air flow thru the windings increases the rate of wear. They just don't have the long service life desired.

of course if you have a FREE salvaged brushed dc motor then the price when it comes time to replace it is not so high. If the brushes are easily found then you can extend the life from months to a few years.

scottsAI · « **Reply #2 on:** September 28, 2008, 05:42:39 PM »

Arbela47000,

Brushes ware out.

Automotive alternator has brushes. Good for near 100,000 miles (OK 70k:). Most think this would make a good generator. Only last a few months if low winds maybe longer.

Quick study will show the mileage a wind turbine goes in a year is in excess of 1 Million miles equivalent a year! Current loading effects brush life, higher current = shorter life.

Have fun,

Scott.

harley1782000 · « **Reply #3 on:** September 28, 2008, 05:52:53 PM »

Wait a sec, I bought my truck brand new in 1999 with 19 miles on it, it now has 167,590.3 mile on it. Same Alternator. Never been changed yet.

Jim

arbela47000 · « **Reply #4 on:** September 28, 2008, 06:57:37 PM »

Good explanation, micro mechanix and Scott. Thank you for clarifying that point.

scottsAI · « **Reply #5 on:** September 28, 2008, 08:16:03 PM »

Harley1782000,

I would count my blessings.

Not have a car alternator last beyond 70k.

Some lasted less than 30k. POS.

Also adds to confusion why some wind turbines last longer than others!

Have fun,

Scott.

zap · « **Reply #6 on:** September 29, 2008, 10:29:24 AM »

Scott maybe you've just had a bunch of bum steers.

Rabbit diesel, 140K miles, original alternator
Rabbit, 72K miles when purchased, I put another 52K miles on it, original alternator
Ford F150, 60K miles when purchased, I put another 130K miles on it, original alternator.
diesel Buick, 149K miles when purchased, I put another 45K miles on it, original alternator.
GMC cube van, 75K miles on alternator when purchased, I put another 55K miles on the same alternator.
Dodge 250, 37K miles when purchased, I've put 101K miles on it and the original alternator is still going although it might be getting weak.

With the exception of the GMC and the Dodge, all were bought new or from family members so I knew the alternators were original. I knew the GMC's history from service records and I knew the Dodge's record from talking to the previous owner.

Those are just some of mine. My Dad put 265K on his 1979 diesel Rabbit with the original alternator.

mikeyny · « **Reply #7 on:** September 29, 2008, 10:58:00 AM »

92 mitsubitshi fuso 4 cyl diesle. 360,000 miles. original alternator with vacume pump on backside charging 2 750 cranking amp batteries. Also original clutch. go figure.

Mike

Slingshot · « **Reply #8 on:** September 29, 2008, 12:11:15 PM »

Quick study will show the mileage a wind turbine goes in a year is in excess of 1 Million miles equivalent a year! Current loading effects brush life, higher current = shorter life.

Have fun,

Scott.

Scott,

How did you come up with the "over a million miles a year" number? I don't calculate very close to that.

Ungrounded Lightning Rod · « **Reply #9 on:** September 29, 2008, 03:15:25 PM »

And my Eagle Talon's alternator lasted a tad over 100,000. So "your mileage may vary".

However it doesn't really apply to servo motors. Alternator brushes ride slip rings: Nice and smooth, with even voltage across them. DC servo motor / generator brushes ride a commutator: Something like a cheese grater, and they're constantly bridging and jumping to/from segments with different voltages and interrupting currents as they're thrown to the next winding segment.

ghurd · « **Reply #10 on:** September 29, 2008, 03:18:45 PM »

A million miles is a lot. 100K miles is not much when related to a windmill.

I wouldn't change alts every month or 2.

The bearings are not so great for the type of load.

Scott,

What they said...

My Toyotas because that's what I can recall.

New Tacoma, 96, 175K now and still fine.

Camry 96, 225K(?) now, used, though I believe it is the factory unit, still fine.

A 99 4-runner, 125K and still fine.

A 92 truck (pre-Tacoma?), 250K before I lost track of it.

An 89 Camry, used, 190K?, though I believe it was the factory unit sent into the rust crusher.

A few VW Rabbit/Golf diesels, near ~200K?, then traded them in

No recollection of changing an alt.

Then again,

An 86~89 Ford Tempo?, there were 2 kinds of alt.

"Nissan" alt? Something not "Ford". Anyway, it was not Ford.

Burned up the alt on a regular basis. 25K? Sometimes 5K? Sometimes 1K?

I could change it in 15 minutes, in the dark raining parking lot of Red Lobster, hood up to hood down. Kept the box, recpiet, and tools in the car. PepBoys shared the parking lot.

Aftermarket alt's specified the battery must be fully charged or the warrenty was void.

wdyasq · « **Reply #11 on:** September 29, 2008, 08:00:11 PM »

Izusu NPR - over 500k miles (480k when odometer checked out and figure I drove another 80k) when #2 wrist-pin let loose and actually broke the cam ... as evidenced by piece of cam on alternator mount. Removed alternator and put on another NPR .....

Other Alternators have lasted 75k - 250k ... I usually will replace bearings when other high mileage maintainence requires vehicle to be down long enough to go to alternator shop and be 'checked out' (there is a good local alterantor/starter guy).

8766hrs is a 'year' at 50mph is 435,330 miles. Make sure you have a good seat if you drive that much a year.

Ron

arbela47000 · « **Reply #12 on:** September 29, 2008, 08:03:53 PM »

Probably something like: Typical cranks/year (two per day=730), time spent running alternator on each crank (2 seconds), average mileage per year (15,000 miles)

730 * 2 = 1460 seconds (24 minutes, 20 seconds) every 15,000 miles

Let 1460 seconds equal X.

There are 21,600 sets of X in a year. If the turbine only spins half the time, that's 10,800. So, if X also represents 15,000 miles, then:

10,800 * 15,000 = 162,000,000 miles

Looks like "over a million miles a year" to me with plenty of wiggle room for calculation and assumption errors. Someone please correct me if I'm wrong.

If you just consider the rotary distance traveled by the brushes in a year, that is likely far less than the number I came up with, so that may be where some of the misunderstanding comes in.

Also, my last Camry alternator kicked it after 30,000 miles. This one has been in for about 50,000, so "results may vary," as someone else said.

scottsAI · « **Reply #13 on:** September 29, 2008, 08:58:14 PM »

Slingshot,

OK, hope you like it.

Assumptions Vehicle

Average vehicle is driven 12,500 miles/year.

Average tire is 24 inches diameter x 3.141592654 = 75.39822368 in. circumference.

63,360 inches / mile or 840.338 tire rotations per mile.

Equals 10,504,226 rotations per year!

Assumptions Wind Turbine

typical vehicle generator is around 1kw so picked a 7 foot wind turbine.

Target Blades with TSR 6 to 7 what I see most often.

Wind speed to have a good wind generator is cited at 12mph average wind speed.

288.1 RPM with TSR 6 at 12mph winds.

Vehicle alternator will not output at this speed so a speedup is required.

Using this as reference:

http://web.media.mit.edu/~nathan/nepal/ghatta/alternator.html

Lots of field current required below 2100 rpm.

Will use 8:1 speed up, Alternator targeted 2304 RPM

x 365 x 60 = 525,600 minutes a year.
,211,402,880 rotations per year.

Ratio of wind to vehicle is 115:1 well in excess of a million miles equivalent. (needed 80:1)

How's that? Please Check my math, last time came to just under 1 million!

Have fun,

Scott.

Jerry · « **Reply #14 on:** September 29, 2008, 11:06:05 PM »

Another thing to concider. The brushes in a car alt are not carrying the charge current.

The brushes on the smooth slip rings are supplying a small amount of current to the rotor coil. Most lickly never over 4 amps.

The stator is wired directly to the 3 phase brige rectifier. This is the part that handels the high current in a car alt.

JK TAS Jerry

chubbytrucker01 · « **Reply #15 on:** September 30, 2008, 11:00:14 AM »

In my big truck I have gone through 5 alternators in 935,000 miles. Factory original delco 33si lasted 300,000. Replaced it with a delco 33si it lasted 300,000 miles. Replaced it again with a leece neville 140amp and got 300,000 out of it. This was when I started using it to charge deep cycle batteries as well as my starting batteries. Replaced it with another leece neville that was rebuilt. It lasted about 50,000 miles. The rectifier went up in smoke. It wasn't replaced in the rebuild. I am now running a leece neville 160amp and no problems yet. I don't know what happened to the first two alternators because this was about the time I started reading about diy electricity and didn't understand about how an alternator worked. The delco 33si alternators are what the mechanics call a gray ghost. It is rather large in size, it is brushless. It's rotor coil is attached to the case so it doesn't spin. It has a rotor made of soft metal that spins around the rotor coil and excites the stator windings. It's major drawback I have been told is it's small rectifier. The leece neville are are just conventional alternators scaled up a little to produce more power. The first two of these that fried didn't have anything to do with the brushes. The rectifiers smoked in both of these. I have a ford bronco that has eaten 2 alternators since I bought it and the rectifier burned up in both of them. Which I was told by my local starter alternator guy that is the common failure for them. When you cycle stuff harder than it was designed to do it won't hold up.

Slingshot · « **Reply #16 on:** October 06, 2008, 08:46:48 AM »

Scott,

It appears you are comparing alternator rotations in wind to tire rotations in a car.

Because the discusson was on the topic of alternator-brush life, I think we should compare how many times the ALTERNATOR would rotate in the car vs in the wind.

Please comment on my example:

AUTOMOBILE

Cars (with tachs) I have owned seem to have gearing that puts me around 2000 RPM at 60 MPH. This equates to 2000 engine revolutions per mile.

Ratio of engine pulley diameter to alternator pulley diameter looks to be about 3:1 or more. Conservatively, this equates to 6000 alternator revolutions per mile.

1 million auto miles = 6 billion (6,000,000,000) alternator revolutions.

WIND TURBINE

There are 525,600 minutes in a 365-day year.

In order to complete 6 billion revolutions in one year, the turbine speed would have to average 11,415.53 RPM.

I can't imagine any turbine averaging over 11,000 RPM all year long. I expect it's more like 300 or 400 RPM average, so I think it would actually take more like 30 years for a wind-turbine alternator to accumulate the automotive equivalent of a million miles' usage.

scottsAI · « **Reply #17 on:** October 06, 2008, 11:06:19 PM »

Slingshot,

I would say good job!

Realized missing pulley ratio after posted, hoping someone noticed, that means your thinking! Great.

Passenger car RPM might be lower at 60MPH. Yet, higher for trucks and off road vehicles.

One car 750RPM at 55MPH. They had to use over drive to get decent millage. IRock Z.

Pulley ratio sounds good.

Let's use your numbers.

The wear mechanism of a brush assembly is based on the surface type, rings vs commutator, RPM to a degree and Mostly Current. Any of these in excess can dominate the wear.

To get output at 700RPM will require excessive field current causing more wear that at some higher RPM with less field current.

Vehicles target 2,000 RPM and up for output so that is what I used.

Wind turbine at 300-400 is not going to work, requires speedup! Or strong magnets.

My understanding average wind speeds are over 24 hours.

If your targeting cut in at 6 MPH with average winds of 12, RPM will be doubled. (assuming not in stall).

Lets suggest 1400 RPM is required at cut in? And 2000 RPM at 12 MPH stalled or it would be 2800.

So will you accept on the average 2000 RPM? 24/7. (using speedup)

Based on this it will take 11,415 / 2000 = 5.7 years to hit a million miles.

1 Million miles is 10 times rated life of a vehicle. (and alternator)

The wind turbine using a vehicle alternator will exceed its live in 0.57 years.

Discussions above state automotive alternators last 30k to 300k miles.

Expect failure in couple months to few months past a year!

Better? And thanks.

Have fun,

Scott.

Slingshot · « **Reply #18 on:** October 08, 2008, 11:50:57 AM »

Bottom line, though, is a million vehicle miles equals 6 billion alternator revolutions, unless we disagree greatly on engine speed (see final paragraph).

The assumptions you make about average wind speed determine how long it takes for a wind turbine to turn that many times. I don't think that 2000 RPM in average wind is close to typical, though.

For years, Southwest Windpower marketed a unit called the "Windseeker" that used a modified Delco alternator and tilt-back furling. It turned about 300-400 RPM in charging winds.

I have personally owned a 1970's Wincharger turbine, which used a brush-type alternator purpose-built for wind application. It even had an automotive-type external voltage regulator that controlled the field current. It was about a 200- to 300-rpm unit in charging winds.

These are typical examples of auto-type alternator designs used in wind turbines. So, I have to stand by my math and call it over 30 years for these turbines to accumulate a million auto-equivalent miles of alternator rotation.

If you feel typical auto engine speeds are really in the 750-rpm range at 60 mph, then you'd cut my estimate to 11 or 12 years, but I think a little checking will show that 2000 rpm is more typical. Actually, I've never seen any passenger car that did 60 at 750 rpm ... that's a little below idle spec for most. I will admit that 1200-1300 is right for some V8s with overdrive, but that's not the global average over many types.

scottsAI · « **Reply #19 on:** October 08, 2008, 10:11:37 PM »

OK Slingshot,

Nobody I know has built a wind turbine using an automotive alternator lasting beyond a year. Does not say it cant happen.

Most alternators are rated around 700w to 1.5kw for passenger to 2.5Kw for trucks. No idea what a semi uses. Delco states their alternators are 60% efficient at 80% load, above and below that is less. 50%?

With the Wincharger example I did not realize you were talking about a 200 w peak turbine. OK, it should last much longer.

Based on this discussion I will restate: (Thank you)

A wind turbine during its life exceeds 1 Millions car miles equivalent.

Now you going to design a wind turbine with a generator designed for 100K miles and expect to get more than a million from it? Does not work for me.

Efficiency is a big issue, why go to the trouble to build a wind turbine and get half the power out? Not saving much money if any? (unless free parts) I understand modifications can improve the alternators life and efficiency, but that is another story. The total cost of a wind turbine in time and money is not dominated by the cost of the generator. What I see here is people spend hours for months and about $2,000 to build a 10' 1kw wind turbine with tower and controller (that is on the low end). To save $100 by using an automotive alternator just does not work for me.

Have fun,

Scott.

Slingshot · « **Reply #20 on:** October 09, 2008, 11:59:25 AM »

Scott,

We are definitely in agreement on your last statement! I don't advocate using them either. The original discussion related to brush wear, not general appropriateness of the unit.

***********************

Now you going to design a wind turbine with a generator designed for 100K miles and expect to get more than a million from it? Does not work for me.

Efficiency is a big issue, why go to the trouble to build a wind turbine and get half the power out? Not saving much money if any? (unless free parts) I understand modifications can improve the alternators life and efficiency, but that is another story. The total cost of a wind turbine in time and money is not dominated by the cost of the generator. What I see here is people spend hours for months and about $2,000 to build a 10' 1kw wind turbine with tower and controller (that is on the low end). To save $100 by using an automotive alternator just does not work for me.

Have fun,

Scott.

taylorp035 · « **Reply #21 on:** August 05, 2009, 09:27:00 PM »

My old bmw 740il had 166,000 miles on it's original alternator and it was WATER COOLED!

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Author Topic: Brushed Servo Motor (Read 3644 times)