Introduction: Repairing a Small DC Electric Motor

Picture of Repairing a Small DC Electric Motor

Can we fix it? You bet! cost your time. In reality it is a cheap low powered motor that sells for about £1 and not worth the effort  if you have more money than time but having gone to the trouble of salvaging it you may as well fix it and you never know when you might have to fix it because you need it, and the principles apply to other motors as well
 

Step 1: Clean It

Picture of Clean It

If it needs it clean it with scotchbrite and soap to remove any corrosion and goo it doesn't matter that it gets wet you're going to strip it completely and dry it thoroughly anyway. DO NOT leave the scotchbrite in the kitchen sink to be used later to clean pots and pans copper salts are toxic and the contacts/brushes may well be beryllium copper as it has spring qualities and others that are useful in this application BUT beryllium compounds are also toxic and cumulative poisons, so wash your hands after as well

Step 2: Take It Apart

Picture of Take It Apart

Place a small blunt blade between the drive gear and casing and leaver the gear off. Using a very small flat bladed screwdriver unbend the tabs securing the back to the case and pull it off. Push the drive shaft down on the table grip the armature and with draw it from the body of the motor it will kick sideways as it comes free.

Step 3: Clean and Examine

Picture of Clean and Examine

I used disposable paper tissues for most of my cleaning kitchen towel or cotton rag would work as well.
 Notice the green goo the colouration is due to copper salts and possibly beryllium salts both of which are toxic ( I am possibly over stating this but it is better that you know than don't)
Check the brushes are intact if not there replacing them is not impossible but is not covered by this instrucable set aside for further work.
wipe clean the commutator armature and shaft assembly use a solvent if required, I tend to use lighter fuel the liquid type not gas as my cleaning solvent of choice isoprop will probably do as well but avoid acetone/cellulose thiners or white spirit as these could damage cheap laquer on the windings. The bearing surfaces shoud be smooth and bright.The armature (large & in this case 3 lobed ridge section) should be free fron rust. The Comutator (short brass section on the left before the large black ring) this should be free of obviouse ridges smooth and have a clear gap between each segment. The small brass ring to the right of the armature is a thrust race this stops the armature comming into contact with the motor casing. There should be no visible broken wire or signs of burning on the windings and idealy the continuity of the windings should be tested with a multi meter or  a lamp/LED and battery ( a step I forgot until doing the write up I just glanced at it and decided all was fine)
Turn your attention to the case clean inside check there are no metal /rust fragments sticking to the field magnets and that the magnets are secure.Twist up a small taper and clean the bore of the front bearing in this case it appears to be a nice little oilite type bearing this could be a useable scavenge if the motor is unrepairable.
On larger motors say a car starter motor reconditioning is possible with patience files emery cloth  wire brushes and scotch brite on a motor this size your opptions are much more limited metal polish rag and a scraper made from a sewing needle are about your limits.
I have come across articles covering rewinding the armature of a motor from a CD drive to make a higher powered motor for a model plane so all things are possible but other than as an exercise in can I do this is it worth while?
 

Step 4: Repairs

Picture of Repairs

All motors will be different but on this one the brush carrier is a separate unit from the back plate located on a pin and in a slot in the back plate to remove it was simply a case of putting my thumb nail in the joint and pushing you may wish to use a small screwdriver or knife blade.
clean the back plate and brush carrier again I used lighter fluid and tisue paper.
Source your replacement cable I used a strand from an old ribbon cable, strip a short length of insulation and bend the stripped end at a right angle. Gentley prise the brush from the carrier and push the stripped wire down into the locater slot push the brush back on top of it, bend the wire round the bottom of the brush carrier and trim it off. I find small nail clippers make good wire cutters and can be used for stripping insulation as well onec they have been used in this manner they are useless as nail clippers. Whilst you have it appart  rewire the other brush to.

Step 5: Reassembling

Picture of Reassembling

apply a drop of light oil to the front bearing shaft grip the armature and commutator assembly by the commutator and reinsert into the case keep a firm grip on both as the field magnets will make it kick around. Apply a light smear of petroleum jelly(vasaline) to the commutator if the motor has carbon brushes do not grease the commutator.
Next Do Not use any more force than you would on a touch screen, place the rear bearing shaft at the top of the V formed by the brushes and push in until it touches the back of the case at this point the commutator should have just entered the brushes. align the shaft with the rear bearing bore and push together. Once the shaft can be seen in the bore and the back plate has engaged with the case slightly more force may be required. check the motor spins the apply power to test once you have confirmed the motor is working recrimp the tags holding the back plate on. They do not need to be over tight if the motor won't run after you have recrimped the tags gently losen them as you did when disassembling. I refitted the drive gear as well just so I didn't lose it it would probably be a good idea to secure the new cables with hot melt glue or epoxy resin as they are only a friction fit and will not stand being pulled very hard or at all.
 

Step 6: Other Motors 1

Picture of Other Motors 1

having recently rationalised my pile of salvage cd drives into useful parts I thought I'd open one of the small motors up to show the intervals of small brushed motors are similar. This one (there are actually photos of 2 different motors here one with attached wires one that was soldered to a pcb) operated the tray mechanism. The back plate was staked in (the case is pressed in enough to stop it coming off and moving) this took careful work with a pair of small side cutters to undo. I then inserted a small screwdriver into what is the cable port on the wired version and twisted to remove the back plate. This not only bent the back plate but also damaged the field magnets (which appear to be the flexible strip used on magnetic display boards) as I inserted the screwdriver beyond the case. The brushes in this case are just fine wires this meant the armature assembly has to be inserted into the back plate before the case on reassembling. their position checked and adjusted using a sewing needle. Once reassembled the back plate was pressed back in place using long nosed pliers and a safety pin as a spacer a small nut or a stack of washers would have done instead. This also straightend the back plate and the motor remains functional despite the damages caused in dismantling.

Step 7: Larger Motor

this step will be added next time I have cause to disassemble something bigger.

Comments

FredF62 (author)2017-06-03

Hello,

I have an electric golf buggy, which, after a period of rest (4 months) is completely dead.

The controller is capable of alerting when something is wrong; in this case the alarm is indicating that: "The motor? is disconnected or there is a motor problem". To investigate, I disconnected the motor (12v 200W 3000RPM) from the rest of the circuitry and applied the 12v current directly. It spun.

I then proceeded to test the rest of the component (controller and tiller). In order to eliminate "The motor is disconnected" alarm from the controller, I completed the circuitry with a small fan (5v -12v). I managed to faithfully reproduce all the fault alarms as well as the "All well" condition.

So, here I stand. Every single component appears to be working perfectly OK independently, but when assembled the buggy won't budge.

I would very much appreciate if you could give me some idea as to what to do next.

All the best and thankyou,

Fred

Unata (author)2016-12-02

Hi,

Around a year ago, I purchased an electric hand drill/ mini dreme along with accessories for cutting, drilling, polishing etc. This was purchased from an online Hongkong shop. This drill worked very well to begin with, but now I find that the motor runs haltingly. I dissembled the unit and found that the 18 V DC power is fed to a voltage stabilizing circuit and a small potentiometer for speed control. I tried oiling the motor, but the motor only runs haltingly. I did not find the clips on the rear of this motor, so I could not dissemble it. Can you please diagnose the problem and whether this can be repaired.

To give you a better idea, I am giving a video link to the faulty motor in operation.

https://youtu.be/xcwTVZWtN9o

Many Thanks,

Atanu

Stan1y (author)Unata2016-12-03

I can't remember when I last saw or even if I've seen a motor limp before, it seems to be behaving a bit like a stepper motor, I suspect the speed control board , can you disconnect the motor from the power supply and power it directly to confirm it is a motor fault not the speed controler

Unata (author)Stan1y2016-12-03

many thanks for your prompt response.

Yes friend, I also was getting the same opinion about the power input getting erratic. I shall dissemble the motor and feed it 12V DC from one of the eliminators. Hope that works. Also will see the output being given out by the speed control board.

The speed control board/ PCB has a small Pot, some resistors and a three legged regulator. Could it be that the bushes are loose and are only touching the commutator intermittantly?

I will take a photo and send you shortly.

RaymondC50 (author)2016-06-13

I have a Sony reel player that the motor seems freezing, move fan (attached to motor) and sometimes will start on its own, is there grease to fix problem ?

Stan1y (author)RaymondC502016-06-14

That sounds as if it isn't developing enough torque to overcome the initial friction. I'd start by making sure there is no fluff or hair wrapped around any of the shafts and pulleys in the drive train.

Then remember just because a little oil is a good thing a lot isn't always better, a drop or two is all you will need. I use 3 in 1 oil for lubricating small bearings, DO NOT get the graphited version. you want a light oil no thicker than vegetable cooking oil but DO NOT use vegetable oil as it will react with the old mineral oil lubricant and produce a gum. Similarly I am uncertain as to how a synthetic engine oil will react. Something sold as sewing machine oil will be suitable. Gun oil might be ok but its a long time since I had an air rifle so can't be certain. At a pinch I'd risk using baby oil as long as it is liquid paraffin based but it is a bit too thin.

I suspect or at least would hope that a motor in such a device would have proper carbon brushes that have worn to the point that they are no longer making proper contact replacing them will be fiddley, probably messy and require sourcing some brushes of about the right dimensions that can be cut or sanded to the right shape and profile for the armature. Hope this is of help.

RaymondC50 (author)Stan1y2016-06-14

Thank you, I have enjoyed this oversized cassette player, use FM transmitter into headphone jack and a couple FM radios on either side of my place , like awesome. Is hard to find parts. Is it same principal for turntables ?

Stan1y (author)RaymondC502016-06-15

I did have an exchange of emails with one of the other comments on here about a turntable. It had worn brushes it also had some form of centrifugal speed controller built into the motor I believe in the end he went with new motor and ESC to replace it

Stan1y (author)RaymondC502016-06-15

The only battery/ mains ( so definitely had a dc motor) turntable I ever took apart had a rubber wheel driven by the motor running on 2 different sized lips inside the turntable to give 45 or 33 rpm so keeping the original motor or replacing it with one of exactly the right spec would be essential to keep the speeds right but that was in the 50 to 90's. now electronic speed controllers are small and cheap. and this site gives you all the info you need to set it up to the right speed. pretty much any DC motor that will over come the drag of the stylus in the grooves should do it

http://www.vinylengine.com/strobe-discs.shtml

The two mains only turn tables I've taken apart both used belt drive, worn belts are a problem making new ones isn't so long as you can find a drive belt the right diameter or profile see

https://www.instructables.com/id/mini-bench-grinder...

I go into detail there on doing that

GusG3 (author)2015-07-24

I have a tiny 7mm motor that's wire has broken right before it goes into the motor. Would I be able to replace the lead?

raghavag (author)2015-05-25

I too have the motor but the copper brush is lost can i replace it with some thing else

jexter (author)2014-03-20

Nicely documented! Here's why I would do this, even though little motors that size a usually dirt cheap:

- You might spend days surfing the web looking for the right size/power/speed replacement, and then pay $5 shipping for a $1 motor.

- It might have an unusual mounting bracket that would be difficult/time-consuming to duplicate.

-It's a repair from an old battery operated toy, and you need to keep the original parts for it to retain it's value to collectors.

- This is Instructables, and this is the kind of stuff people here like to do!

Cheers!

Stan1y (author)jexter2014-03-22

I strongly suspect that the shaft armature comutator assembly could be swapped from one small motor to another with specialised mounts if the armature windings had been burnt out as the shaft lengths and diameters do seem to be pretty much the same on these small motors

perofri (author)Stan1y2015-03-13

Stan, I have another small motor with tiny parts that need replacement and don't know if I'm supposed to replace the part or the motor itself. Can we discuss?

Stan1y (author)perofri2015-03-14

I'm happy to help if I can, if you could post some images in the I made this section or add them to a comment it would help me help you and what power the motor is to.

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