Burning up the brushes

[flowers9]

New to the hobby, What are some of the reason I'm burning the brushes out of the motor. The motor is a 820BB. running on 24 volts (2) 3cell Lipo's. The boat is a home built 33" by 11" with all equipment is 6 1/2 pounds. speed +/- 25. After each 10 min. run checked the motor temp it was never over 115. after about 15 runs over in a 2 week period the motor would fail and the brushes were shot.

[Jeepers]

I am gonna say to much voltage.

[ED66677]

nope! 24 cell max!
did you first break it in? or just run with this setup out of the box? this may cause the brush to wear out very quickely at high amp!
but something worries me (may some expert confirm) but such a setup hull/motor under 24 volts should go faster (I might be wrong) but what prop are you running? what's you battery capacity and what's your run time?... just to figure out how many amp this setup drain!
did you watercoold it? can and brushes?

[Fluid]

While there are many possible reasons, some 800/820-series motors have a long history of premature failure in boats. I've personally seen two go down after minimal, not abusive use. It seems that some motors just can't handle extended running at high apm draws - high compared to what they were designed for that is. Most are just cordless tool motors that were never intended to run for ten minutes at 50 amps....or even five minutes at 25 amps.

Without knowing what the boat type is or other details like how much capacity was used in ten minutes it is impossible to positively diagnose your problem. But I suspect the problem may just be a poor motor....


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[flowers9]

#1 I didn't break in the motor, didn't know I had to. Ran it right out of the box
#2 Running the 820 on a outboard drive with stock 45m surface prop
#3 Speed is an Est. may be running faster?
#4 Batterys are 3 cell 4200 mah
#5 both can and brushes are water cooled
#6 Run time the last run was 12 min. all cells were at 4.175 at the start and 3.825 at the end and the temp. was 96.5
#7 boat is a scrath built tunnel, plans were from 1970.

#8 How do you break in a brush motor?

[ED66677]

so you're running at 21 amp average, probably 25-30 constant witch is not bad for this motor! I'm pretty sure it can handle more! prop seems to be appropriate considering the amp draw.

Break in: I use an old computer power supply and connect the motor to the 5volt output and let it run for 30minutes to 1 hour, be carefull to break it in the same direction you will use it, the aim is to have the brushes shaped to the collector so that the contact between represent the largest surface as possible, if you dont break in a brushed motor, high amp will generate arcs because contact area is not a surface but peaks, arcs concentrate on peaks, arcs will melt brushes and collector in peaks areas and generate holes!
I've ran 600 race under 9 NiMh cells at 30+amp (3 time the nominal) and did not melt any brushes, I did performed a 30 minutes break in first!

[Fluid]

The answer may be in the use - in an outboard where it can be constantly exposed to water. Your 820 would wear away the brushes quickly when wet. I had this problem with brushed 05 motors many times. It just depends on the composition of your brushes. Over three hours running wet under load is a lot different than running the motor in water without a load during breakin. I'm reasonably sure that this is the problem.

You do not have to break in brushes to get good motor life and power, it is just a little better with a beak-in. Remember that the tools the motor was designed for do not get a water break-in and they last a long time.


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[ED66677]

good point Fluid!
if wet under load brushes may not last longer than a single run! it did happened to one of my 600 during a test in a pond where it was running reverse (miswired) while hatch was opened, in 5 second one brush was soldered to the collector and just went away!

[flowers9]

Thanks for all the info, not breaking in the motor was most likely my major problem. rookie lesson well learned. One more question? On setting up the surface running prop How much of the blade is above the water line? Thanks again

[Fluid]

While it depends on the boat, on most surface drive default setups the prop centerline is about even with the keels of the sponsons. It can be moved up or down 1/4" to fine-tune the setup.


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