A 36volt fan motor would be a find. You might consider a 24v fan with a power resistor to drop the extra voltage. A Zener diode would also work, as the current should be small enough to manage the power dissipation.
Grainger makes a number of products for servicing commutator bars. By re-surfacing the copper, the brushes will be less prone to wear as arcing is reduced. Search www.grainger.com for "commutator bar cleaner" for a look at the variety of sizes and grades. Most motor houses sell them locally as well. Use a medium grade to flatten out peaks and valleys, then finish with a fine grade to leave a smooth surface. If the bars are still nice and flat, just a fine grade stone will polish them to near new. Motor shops will typically turn off a few thousandths if the surface is really bad.
As brushes wear, the spring pressure lessons, permitting increased brush wear rates and additional com bar heating. You might consider a fresh set of brushes now, saving the worn set as a reserve. If you use the 50% set first, the commutator bars might be trashed by the time you reach the end. Putting in a set of freshies now will only extend the motor's life, and the used ones won't go bad. Better to have three sets at 50% and a decent set of com bars, than two new sets of brushes and a dead motor. Additionally, when you clean up the com bar surface, a new set of brushes will seat properly, where as a worn set will carve the bars back to their former profile to some extent.
Be Well,
Arby
From: Myles Twete <matwete@comcast.net>
To: electricboats@yahoogroups.com
Sent: Sun, June 20, 2010 11:00:15 AM
Subject: [Electric Boats] ETEK brush life findings
It's been about 7 years now since I installed a B&S Etek motor on my outboard.
Until yesterday, I had never taken the brush assembly off to check brush wear.
Looking at the 8 brushes, the following was noted:
· Brush length was reduced about 50%, about ½" left of the original approx. 1"
· Brush length varied among the 8 brushes—or so it appeared. The reality is that the routing of the brush wire to 2 or 3 of these brushes makes them spring out about 1/16" less than the others. This will result in these brushes (and circuits) being the first to stop allowing current to flow.
· Brush dust was everywhere in the brush housing. Not caked in, but more than I'd expected. Greater forced air flow thru the motor would be advisable. I use a 48v Papst 6" muffin fan running on 36v, located above the brush housing and pulling the brush dust up thru the motor, the brush housing, the fan and then out. The strategy is right, but it probably would be good to increase the flow rate to get more of this brush dust out.
Now, I'd estimate that this boat has averaged 30 outings per year, with a run time of 2 hours per outing and spinning at an average of 1600RPM. So in 7 years, the motor has operated about 420hours and turned something like 11-million revolutions.
Assuming the same usage rate going forward, this brush assembly will last at least 5 more years, giving about 12-years on a set.
I have 2 spare brush assemblies…the question is, will the boat, the motor and I live long enough to use all 3 of these brush sets?
Does anyone have a source for replacement brushes themselves for the ETEK motor?
If I had a good source for brushes, I'd offer my spare brush housings for sale.
-Myles
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