DC Motor brushes replacement

Yes!

Change them all.

Hey, I faced that problem once! I maintained the motors and generators for a fleet of aircraft and their associated ground handling equipment for a few years. Most of the maintenance was good old common sense.

Brushes are cheap. Labour to pull the generator or motor out and get it into your shop is expensive. If you have to pull the brushes to check them anyway, why would you NOT replace them all? They will still need to be run in, whether one is changed or all are changed, and that means time on the bench.

I only ever had one brush fail when all the rest were good, and that was because it had an internal crack in it. I just replaced that brush because all the rest only had about 300 hours on them. Barely run in! But generally, we just changed them all when we had the chance.

The danger in replacing only one brush when the rest are worn (even though still serviceable) is that the overworked technician who is in your job "next year", will only pop one or two brushes out to decide if the motor is good for this maintenance cycle, and if he pulls the relatively new one, he might think the rest are nice and long as well. An error which could lead to failure and serious problems down the road.

Thanks TVP45,Mr. Truman Brain,Yousef (for details) but:

If our company has a strict plan to check ALL brushes every 250 runing hours,then can we replace only defected one?

if No? why?

Hello,

I had assumed you had a fairly low power motor here, under 10 hp for example. If that is so, the brushes are cheap compared to the labor required to replace them.

You must also ask why a brush failed. My experience has been mainly contamination and occasionally a lead or spring break. In any event, if one is bad, there is an increased chance the others are.

You want even wear and pressure.

But, the most critical item is this: most dc motors are seen in industrial and commercial settings where downtime, particularly at 3 am on a Sunday morning, is incredibly expensive. The Japanese quality gurus have a word that I always forget but basically means everybody should strive to continually reduce defects and improve processes.

Finally, watch the Indianapolis 500 race. When a driver comes in with one bad tire, do they change just that one?

The only time you would change only one brush is if there was something seriously wrong with it. There is no reason why the performance of the generator would suffer by having one brush longer than the others.

There are several reasons why a generator would miss its next scheduled inspection. This is the human element at work! IF it was MY airplane, and IF I was flying in it, and IF I was really cheap or IF suitable replacement brushes were hard to get, and IF the brushes are easy to check but hard to replace, I might replace them one at a time as they needed it, but I think that would be false economy. The paperwork burden of logging every single brush would contribute to potential skimping on proper maintenance.

Good practice would demand that you change them all even if only one brush was defective. The only exception would be if a brush crumbled during its run in. Which is one of the reasons you DO a run in, after all! Such crumbling would clearly indicate that there was some manufacturing defect that did not affect the others. But if it wore more than 10% or so, I would change them all. And of course, when in doubt, check the manual, you don't want to void a warranty to save a couple bucks worth of carbon!

I would change them all, and quarantine the defective brush, and its mates pending investigation. But thats just me.

Nice to read your replies,but I still think that if we have strict rules for checking and the brushs holder' springs are good. changing one brush is enough.

I will wait for more convincing reasons.

Thanks

The practice in the case of the early Tri-ang Railways XT60 and X04 motors, now largely superseded by the 'Ringfield' and its successors and its 5-pole replacements the MW005 and the Airfix 1001, is to change both brushes. They are as 'cheap as chips', and the performance of the locomotive will go up considerably if the commutator slots are picked out with a device such as a cocktail stick (canned motors are a much more difficult option, and with the Portescap series (1219, 1616, 1624 and 16C1) one would do better to leave the things alone). While one is at it, clean the commutator surface with a tissue or a cotton bud soaked in methylated spirits, and clean both the treads of the wheels and the phosphor-bronze pick-up strips. If a meths-carrying 'track cleaning car' (R344?) is not available, then from time to time it is worth cleaning the rails as well. For steel rail use nothing stronger than a rag and methylated spirits. For nickel-silver rail one of those composite rubber-and-abrasive rail polishing blocks works rather better. To go further, an electronic track cleaner is a worthwhile investment that will work with feedback controllers though the jury is out as to whether they can be used on those new-fangled DCC systems.

Every model railway needs maintenance!