Another motor question!

[dickm]

(Really aimed directly at Bob 9Fingers, but it's possible others may be interested/have suggestions.)
Was using my Elu flipover saw a couple of days ago, running beautifully and cutting like a dream. Tried to use it yesterday, and it didn't seem to get up to speed as fast as usual, and was totally lacking in power - could easily be stalled on 2" softwood. I'd had a similar problem (discussed at length with Bob) with my Lurem Universal, and that somehow sorted itself out, so wondered if it was actually a problem with our mains supply, as we are out in the sticks. But it was only affecting the flipover. Tried again today, and same problem. Takes several seconds to spin up to full speed, or possibly a bit less than full speed, and can be stalled easily.
There is nothing physical rubbing on the saw, everything spins freely by hand (WITH THE POWER DISCONNECTED ).
My immediate thought is the start capacitor, but do they "half fail"? Sort of assumed they were either live or dead, never sickly. It's a HUGE starting cap (about 2" diameter, 7" long) though only labelled 100mF/250V. And it appears only to be a start cap, not start plus run.
Thoughts??

 

[9fingers]

I'm not familiar with this machine but most ELU stuff I have seen use brush motors?
However assuming this is an induction motor as you suggest then a failed starting capacitor would not give the symptoms you state.

Once up to speed, the capacitor would be switched out and the motor would run at full power.
More normally, a failed start capacitor would mean the motor never reaches synchronous speed and the fuse will blow (or let the magic smoke out).

Do you have a model number/manual

Bob

 

[9fingers]

Is this a TGS173? Looking at the online parts diagrams, the lack of any centrifugal switching suggests that this may be a capacitor run motor and indeed a failure of the capacitor (or its associated winding) would give a massive power drop. Spare ones are still available from the usual elu/B&D/DW suppliers such as http://tinyurl.com/4y8gux7

Bob

 

[dickm]

Is this a TGS173? Looking at the online parts diagrams, the lack of any centrifugal switching suggests that this may be a capacitor run motor and indeed a failure of the capacitor (or its associated winding) would give a massive power drop. Spare ones are still available from the usual elu/B&D/DW suppliers such as http://tinyurl.com/4y8gux7

Bob

Thanks, Bob - just what I needed (but possibly didn't want!) to hear...

Yes, it is the TGS173. Might be tempted to try replacing the cap with one of similar rating that I'm pretty sure is lurking around somewhere.

When you say "associated winding", I'm guessing this is not easily replaceable?

 

[Stoday]

Make sure you use capacitors rated for motor running, these are polyester film capacitors. Motor start capacitors are often much cheaper electrolytic capacitors, which are OK for starting, but won't stand up to continuous operation.

The size you need should total 100μF — 100 microFarad or thereabouts. You can make this up by adding smaller capacitors. For example, Maplin sell 440V 30μF motor run capacitors for £8.49. You could use three of these connected in parallel. The 440V is the maximum voltage, not the operating voltage, so the higher the better, even though you use it at 230V.

 

[9fingers]

Is this a TGS173? Looking at the online parts diagrams, the lack of any centrifugal switching suggests that this may be a capacitor run motor and indeed a failure of the capacitor (or its associated winding) would give a massive power drop. Spare ones are still available from the usual elu/B&D/DW suppliers such as http://tinyurl.com/4y8gux7

Bob

Thanks, Bob - just what I needed (but possibly didn't want!) to hear...

Yes, it is the TGS173. Might be tempted to try replacing the cap with one of similar rating that I'm pretty sure is lurking around somewhere.

When you say "associated winding", I'm guessing this is not easily replaceable?

The OEM spare part capacitor seems remarkably well priced at £16 especially when compared to a new motor or stator at around the £250 mark :shock: Which is how the 'associated winding' is replaced.

I absolutely agree with Stoady- your experiments must use continuously rated AC capacitors even for a quick test.

HTH

Bob

 

[dickm]

Thanks guys. Unfortunately the spare motor start cap I had was only 25mF (how do you type mu/micro?). So in a bit of a quandary - 3 off 30mF from Maplin would be more than the full price of the right one just to test it. On the other hand, even the £16 Miles tools want for the "proper" one might be wasted unless it's definitely the cap that's gone. Though as it's a 110V saw, it might be possible to at least test it with lower rating caps? (Guess that's why the existing cap is only 250v rating)
Will at least take it off and measure its capacitance, which might tell me something?
Ah, decisions, decisions!

 

[9fingers]

Ah! 110v model - that does rather explain the low working voltage of the capacitor.

Go on Dick, Splash out it's only 3 pints or a bottle of scotch for a new one!

Bob

 

[dickm]

Go on Dick, Splash out it's only 3 pints or a bottle of scotch for a new one!

That's one and a half bottles of Bells at our village shop!
(Only drink the single malts when someone else is paying )

 

[dickm]

Well, weird or what??

Took off the cover plate over the electrical connections, and tested the cap on a Fluke multimeter. 102mF, which sounded OK, so started checking the spiders' web of connections. Checked the DC resistance of all possible combinations, and there was nothing obviously anomalous. All the wires go via a block of connectors each of which has spades on one end and screw-in ones on the other. The only thing that looked even slightly dubious was one wire end that was a bit corroded, so cleaned that up with sandpaper.
Checked it without the blade connected, and it seemed to get up to full speed, so put the blade on and tested it with a piece of softwood. Went through that like the proverbial butterknife.

So what the h*** :?: :?: :?:

 

[wyldpuss]

One of life's liitle mysteries there Dick. Somethings you can explain, others you just accept.

Roy.