# Brush Advance - when, how much, and what to expect?



## major (Apr 4, 2008)

Stunt Driver said:


> Using forklift motor, and running 72v system. Done 3-5 degrees of advancement, but cant' understand - did the current go up at 2-3 kRPMs?


Hi Stunt,

Yeah, I suspect the current increased at a load equal to that prior to advance. Advancing brush position has the effect of field weakening, meaning more current at a given torque, but higher RPM at that point.



> What to expect, and how to do tuning here?


Trial and error  The sole reason to advance brushes is to improve commutation, reduce arcing. It only changes motor efficiency slightly and depending on the load, can raise it or lower efficiency, just as field weakening does. If you don't have commutation problems, leave it alone. If you have excessive arcing, advance it just enough to get rid of the streamers. Small pinpoint sparks are acceptable. 



> Meaning how to understand result of advancement by driving and observing speed, voltage, rmp and Amps?


Easy, observe the commutator. 

Regards,

major


----------



## alvin (Jul 26, 2008)

HI Major
Can you hear arcing? 
Thanks
Alvin


----------



## major (Apr 4, 2008)

alvin said:


> HI Major
> Can you hear arcing?
> Thanks
> Alvin


Not from here 

It is possible that arcing would be audible. If it is, it is likely doing some damage. I'm half deaf anyway. Too many concerts in my youth. But in general I would not count on sound alone unless you first verify it with a visual.

Ask Tesseract. He has been up close to arcing motors recently. Hey Tess, can you hear me?

Regards,

major


----------



## alvin (Jul 26, 2008)

I don't hear anything on mine. You know I saw a web site somewhere that said you could tell if it was advanced by the relationship between the brushes and field bolts. I think mine are advanced I don't 
know how much. I think I am going to pull my motor today and replace
the rear bearings. They are not screaming but when backing out of 
the garage thats is the only noise I can hear. I'll check the wear on my 
clutchless coupler also.
Alvin


----------



## Tesseract (Sep 27, 2008)

major said:


> ...
> Ask Tesseract. He has been up close to arcing motors recently. Hey Tess, can you hear me?


Oh yeah, you can hear it once the streamers start wrapping around from brush to brush and zorching is imminent. Zorching itself makes a big boom.


----------



## Duncan (Dec 8, 2008)

Major,

Can I do the arc test with a high voltage and no load using a controller to prevent overspeed?

Otherwise I would have to do the tests in the vehicle

Thanks


----------



## major (Apr 4, 2008)

Duncan said:


> Major,
> 
> Can I do the arc test with a high voltage and no load using a controller to prevent overspeed?
> 
> ...


Duncan,

You need the high current, high voltage and high RPM to really tell. So it is on the vehicle or on a dynamometer. One of those video cameras can help, or a brave friend 

major


----------



## Stunt Driver (May 14, 2009)

Thanks all, I guess it will take long time to try and measure. I am mostly worried of range and top speed - i'll try to measure both a few times, and then change advancement. Not very precise measurement, but at least something.


----------



## paker (Jun 20, 2008)

Stunt Driver said:


> Thanks all, I guess it will take long time to try and measure. I am mostly worried of range and top speed - i'll try to measure both a few times, and then change advancement. Not very precise measurement, but at least something.


From my experience rewinding slot car motors if you advance the motor timing, say from 1 degree to 11 degrees, you increase rpm and decrease torque. When you decrease torque it takes more amps to move the same amount of weight than at 1 degree timing.


----------



## Stunt Driver (May 14, 2009)

What i'm not clear with - will this decrease range? Higher RPMs means higher speed at the same gear, which should bring more range. But in city driving with stop and go style - more energy will be wasted that range gained.

So why advance timing at all?


----------



## major (Apr 4, 2008)

Stunt Driver said:


> So why advance timing at all?


Hey Stu,

Read post #2.


> The sole reason to advance brushes is to improve commutation, reduce arcing.


Regards,

major


----------



## Forklift Guy (Apr 20, 2009)

You might want to look up " Shifting of the neutral plain in a dc series wound motor". It will explain the effects of voltage and amperage in regards to self inductance in the armature.

Forklift Guy.


----------



## major (Apr 4, 2008)

Forklift Guy said:


> You might want to look up " Shifting of the neutral _plain_ in a dc series wound motor". It will explain the effects of voltage and amperage in regards to self inductance in the armature.
> 
> Forklift Guy.


Hi FL Guy,

I didn't find much on a google search, even when I spelled it plane. Perhaps you can provide links to the better references you have found.

Appreciated,

major


----------

