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Post by Deleted on Jul 4, 2020 17:58:51 GMT
Hi Chris
Thanks for the suggestion....it might be something to look at in the future...right now I'll take the quickest route...as said...time is a consideration...
Kind regards
Pete
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Post by silverfox on Jul 4, 2020 20:23:40 GMT
Peter
Maidenhead is north of the Thames!!!
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Post by Deleted on Jul 4, 2020 20:44:42 GMT
Peter Maidenhead is north of the Thames!!! who's in maidenhead? |
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Post by Deleted on Jul 5, 2020 9:37:02 GMT
I thought that I would try one of the old motors, stripped it down, cleaned and fitted new brushes... exactly the same result?
Of course, this tells me nothing, could still be either the motor or electronics... I was just taking a stab in the dark, a bit of desperation perhaps?. A wasted exercise really but at least I felt that I was doing something.
I was going to order a new motor tomorrow, now I'm not so sure?...lol
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Post by silverfox on Jul 5, 2020 10:12:40 GMT
Apologies Peter, put in wrong forum!!!
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Post by Deleted on Jul 6, 2020 9:50:55 GMT
just to update, I've bitten the bullet and ordered a new motor and speed controller.... this will get me running for now, I'll look into what the components on the board need changing to fix the old units later, guess I'll need to learn something new... I'm sure that they will cost just pennies but knowing nothing about such things and being up against the clock, I've taken the quickest route to get things back up and running. One question for anyone that may know about such things, I've read that a common failure on these is the SCR's which are soldered to the speed controller board and bolted to the heatsink. Now, these haven't failed this time around as no fuses blew but on my first control unit the fuse did blow and two of these SCR's show signs of burning, so this will be the first board that I take a look at. Here's a picture of the board that hasn't blown an SCR, there are 5 of them down the right hand side of the picture, the square blocks that sit upright and bolted to the heatsink. I have read that these can range between 4 and 6 in numbers, I don't know why they vary in number.  Can anyone identify these, the motor is 750W DC Pete |
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Post by jon38r80 on Jul 7, 2020 11:53:19 GMT
The part number will be engraved or printed on the face furthest from the heat sink usual. Th part doesnt usual depend on the motor size as the board is usualy tuned to the motor with a changeable resisitor.
If you are like me you will need a pretty strong magnifying glass to read the part number.
Have fun getting them desoldered.
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Post by Deleted on Jul 8, 2020 22:01:37 GMT
Hi guys..thanks for all the replies...to update this thread, I am now back up and running.
I changed the motor first as that was the easiest and was also what Warco and the manual suggested was the problem. When this had no effect I then replaced the KB speed controller, at last this had the desired effect. So I'm back up and running but still none the wiser as to which part had failed. Yes the SC was at fault but why? It worked fine in as far as it conttolled the motor, just not under load which according to the manual troubleshooter can only be the motor, which it wasm't. I can not see any sign of damage on the board itself. No burning smell nor signs of burning, the SCR'S( normal culprit) all look fine. I guess the good news is that I now have 3 working motors and a disasembled motor in stock. I also have the two damaged SC boards, the original board does show signs of burning around the SCR's so I will try to source replacements and hopefully repair the board. The one that just failed though is a different matter, I have no idea which component has failed to stop the motor when under load.
I tried one of the suggestions found on the ME forum to test the board with an electric light bulb. I did this and could dim/brighten the bulb but I also noted that the bulb was flickering which from what zo've read is a sign of board failure.
Does anyone know which part failing would cause this, can anyone give me an idea of where to look?
Looking at both boards which look in good condition I'd like very much to repair them and put aside for the future.
Any ideas chaps?
Pete
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960 
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Post by don9f on Jul 8, 2020 23:25:53 GMT
The last fleet of trains I worked on before retiring had “Propulsion Inverters” that were taking high voltage dc and producing a variable frequency three phase output to the traction motors. In essence these inverters were just much bigger versions of yours, with the predominant failure mode being with the devices known as IGBTs (equivalent to your SCRs). These could fail short or open circuit and had a finite lifespan....ie failure was inevitable and only after about 4 years in the service conditions they worked in!
There would hardly ever be any visible signs of failure, but the control system was “intelligent” and would lock the inverter out if any device exceeded a very short “window” of mismatched conditions....eg it was “on” when it should have been “off”, or vice versa.
This probably doesn’t help much, but just illustrates that failure of components, even high power ones, doesn’t necessarily result in burnt remains (but obviously yes it can)!
Your mention of the flickering lamp is interesting, but whether that’s due to a dodgy SCR, I don’t know. You’d probably have to desolder and remove them for testing....is it worth it? Don’t know how much these controllers cost.
Cheers Don
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Post by Deleted on Jul 9, 2020 8:09:45 GMT
Thanks for that Don, very useful...yes these SC's are also inverters too. As well as regulating the voltage to the motor they also convert AC to DC. The boards cost approx £100 and I believe the SCR's cost very little, a couple of £'s so worth fixing. I read on the ME forum of one chap who's fixed his board twice just from replacing the SCR's so worth a go. Not only will it save me money buy it will also give me some spares and so not much down time next time it fails....
Thanks for the info Don...
Pete
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Post by steamer5 on Jul 9, 2020 9:58:56 GMT
Hi Pete,
Interesting discussion!
I had my SX 4 stop working, worked fine before I went away for a week & wouldn't after!!
Anyway after much internet searching it sounded like its not an uncommon problem....go figure that! The discussion found that using the estop was the problem! It set a spike which fired something! So after waiting 3 months & forking out a bunch of $ I was up & running. It is possible to put a relay in to prevent this & I have one kindly supplied by Pete (Doubletop) the only issue is I'm not sure were to put it! No idea if your mill may suffer the same issue, so more for interest than anything else.
Cheers Kerrin
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Post by Deleted on Jul 9, 2020 10:30:00 GMT
Hi Kerrin I would guess that the relay would go in the motor wires, those between motor and board. I'm no expert though so this may be wrong...  Pete |
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jem
Elder Statesman
Posts: 1,064
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Post by jem on Jul 9, 2020 15:51:47 GMT
Now you have a good board, test your motors, so that next time you know that it is not the motor.
best wishes
Jem
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Post by Deleted on Jul 9, 2020 17:10:30 GMT
Hi Jem
The motors were working, just kept stalling... only way I can test them is to take them somewhere to get the windings tested. I think they are ok but will test one when i replace the SCR's, if I can't stall the motor on that board I know that the motors are working fine....I could end up with two spare motors and boards, should keep me going for a decade at least.
Pete
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