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Excessive sparking on CamVac motor

Halo Jones

Halo Jones

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Hi All,

One of the motors on my CamVac 386 has started sparking excessively. I've just checked the brushes and there is plenty of life left in them. All the sparks are coming from the armature that brushes make contact with. Any ideas?

Cheers,

H.
 
Brush length is not the only possible problem. The brushes need to be completely free to slide in the carriers and the spring pressure needs to be quite strong. Also the armature should spin freely and coast to a stop when you switch off.

The nature of the sparks can help diagnose the problem too. If there is a line of sparks in the direction of the armature axis just where the brush contacts the commutator then suspect the issues above.

If there is a ring of sparks starting to stretch out from one brush to the other around the curve of the commutator, then it is likely that the windings have a shorted turn and will need replacing.

Make sure all the filters are clear as there is not much margin in the design of these motors and they need max air flow to get the heat away. Overheating causes armatures to fail.

Good luck

Bob

Induction motors are the way to go. Brush motors are the spawn of the devil!
 
Hi Bob,

Thanks for your advice. I have had a chance to take another look at the offending motor. If I get the terms wrong for anything please forgive me!

So, I checked resistance across polar commutator bars and all pairs had equally low resistance (ie about 3 ohms). I then checked neighbouring bars and they all had really high resistance (ie did not register on my meter or in the M ohm range). I assume (hope!) that this means there are no obvious shorts in the armature.

I think I may have found the problem though.
Here is the motor in question:
camvac%20motor%201.jpg


I noticed a lot of play in the armature shaft. The shaft has a bearing on the end which is housed in the cage(?) shown. This "cage" also holds the brushes in place:
camvac%20motor%203.jpg


There was also a flat spring thing (right of the image) which sits on the end of the bearing and I assume helps prevent any lateral movement of the shaft. Another band of metal fell out which I can only assume was acting as a shim for the bearing as there is a mm difference between the diameter of the bearing and the housing in which it sits:
camvac%20motor%202.jpg


When I reassembled everything and tried it again I noticed that the shim was vibrating up and down, and occasionally hit the tops of commutator bars so maybe this is what was causing the shorts?

Do you think it would be worth getting a new bearing that fits the housing better the trying everything or am on a hiding to nothing?

Cheers,

H.
 
if it is just the spacer band moving couldn't you just araldite it in place?
 
I thought about making a thicker shim and inserting it but slightly scared this could also work loose at some point. At this stage I don't want to do anything irreversible so I would not be wanting to use any glues.
 
The loose bearing is almost certainly due to an oversized housing possibly due to wear, rather than an undersized bearing.
I'm guess this motor was not new to you?
I think a previous bearing has failed and worn the housing and has been bodged with a shim.
If the bearing feels rough then pop in a new one - only a couple of quid on ebay - they get a hard life at those sorts of speeds
If the shim needs to be thinker then by all means experiment until the gaps is filled but then use either epoxy or a loctite bearing retaining compound. The latter is an anaerobic adhesive which if needed can be broken by heating to 200C or so.

Get that sorted and see if the sparks go away.

hth

Bob
 
Well I managed to get everything shimmed and turning nicely, wired it all up and.....

only slightly better :( - sparks still arcing from each brush.

Unless anyone has any ideas it looks like I am saving pennies for a replacement motor. Luckily the camvac I have has two motors so it still somewhat useful - glass half full and all that!

This is an e-bay purchase that has worked perfectly for two years. And to be totally fair to CamVac I reckon that my machine is at least 20 years old. It is badged as Tyme and was probably sold with their lathes which went out of production some time in the 90s!

H.
 
My RP DX motor had the same symptom, not necessarily the same cause but worth mentioning which was that the spring on one of the bushes had somehow got sloppy and wouldn't hold the bush close enough. It sparked for a while and then conked out as the bush moved out of range. So checking all the assemblies around the bushes for tightness is always on my list now although you've had yours out so I'm guessing you've already done all that.
 
Hmm. All the springs seemed to be fine and they are sliding ok. One thing I did notice is that one brush is 2 or 3 mm shorter than the other one. Is that a sign of brush /spring problems?

I've been investigating and a pair of brushes is £23 whereas a new motor seems to be about £100 of the bay. I'm not sure I want to buy new brushes when it is the quarter of the price of a new motor and not guaranteed to fix it. It will just have to wait a little while. Three family birthdays and the summer hols coming up means money is diverted away from woodworking at the moment!

H.
 
Another thought just occurred to me - what is to stop me replacing the motor with a suitable Numatic motor? They seem to be exactly the same design, with the same suction capacity but half the price. The only things I would have to check was that the capacitor was the same and that diameter of the impeller housing was the same so the filter cage etc would fit. :eusa-think:
 
Brush motors do NOT use capacitors. They do not need any phase shift to start them. They even work on DC hence the class of motors being known as "universal" motors.
That little cylinder in a camvac is a suppressor which eventually fails and does nothing useful so when it lets the smoke out, just cut it out and don't bother to replace it.

If the numatic motor is the same form fit and function ( and sucks and blows in the right direction!) then it should be no problem to use instead.

Bob
 
That little cylinder in a camvac is a suppressor
Click to expand...

:eusa-doh:

Just when I think I am starting to get the hang of this motor malarkey I make a stupid conceptual mistake like that!

I just need to see if I can find some dimensions on the motors in the Numatics. Some web digging tonight methinks!
 
It's a bit tricky when juxtaposing knowledge of motors against Bob....there is nothing he doesn't know about them....including inverters :-)
 
Halo Jones":3nl7o310 said:
That little cylinder in a camvac is a suppressor
Click to expand...

:eusa-doh:

Just when I think I am starting to get the hang of this motor malarkey I make a stupid conceptual mistake like that!

I just need to see if I can find some dimensions on the motors in the Numatics. Some web digging tonight methinks!
Click to expand...


What is the typical price of a used numatic? Maybe buy one of those and either rob it for the motor or if it won't fit you have a cheap shop vac or sell it on for similar money, and then know you need to buy a genuine motor.

Bob
 
Try measuring the brushes then search ebay for 'carbon brushes'. You might find the same size for a few pounds...
 
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