Problem with contactors wired in parallel

[Lucien Nunes]

Caution, rather Fermi...

Probability that starters are actually OK = 25%
Cost of Fluke Scopemeter £1250
All-in cost of calling OP to site £100/hour
Time taken to set up scopemeter and take readings at coils, starter resistor bank (to indicate current) etc. 15 mins.
Time of typical train journey=90 mins

(6k-1250-15/60*100)*0.25*90/15=£28350 + all variable operating costs (slightly<£20205) saved in the duration of one journey, i.e. further testing before replacing starters is more cost-effective than running the train.

The big plus, though, is that the OP gets a free Scopemeter

 

[DPG]

One of the best threads for a while this one.

Apart from the one about the answers to exam questions obviously.

 

[hmmmnz]

Well she's running properly again. The starters got changed, started with A bank solenoid and starter
And sure enough it ran perfectly.
They decided to change B bank one as well. As they were both changed 3 months ago.
Hopefully I'll find out what the failure point of the solenoid/starter was.


There was no way in hell they were going to buy me a scopemeter, the railway would rather replace 20k worth of components "just in case" than have an absolute that a given problem was the problem.


Many thanks for all the input, and ideas and some pretty awesome spec finding.

Much appreciated.

I'll keep you posted if I get any info from MTU regarding their starters (also the railway doesn't have to pay for them, now they have been the failure point)

 

[marconi]

Hmmmnz - your initial hunch, after careful elimination of other possibilities, was right. Well done Sir. Good engineers, of which there are many Scotsmen, have this sense of what is probably wrong. In your case the starters are very stressed, frequently - electrically and mechanically - which is not good fro reliability.



M

PS: Lucien Nunes, if you ask him nicely, will write you a business case for a scope meter albeit one that does not use his last dubious Fermi estimate ;-)

A Markov chain analysis using expected cost outcome after a some Monte-Carlo runs would be more persuasive.

 

[hmmmnz]

Lol. I'm sure there are lots of great Scottish engineers... I'm not one of them... Being a kiwi ?
But sometimes you just have to rule out everything you can with the tools available to you and swap out the rest.
Its certainly been the weirdest electrical problem I've come across, and I'm still not sure what exactly went wrong. I hope I get some more info from MTU.

 

[dmxtothemax]

it can only be one of two things,
1 - coils not receiving correct power, / so a volt meter should findthat one out !
Or
2 - the contactor has developed a fault / In which case I would also replace them both.

 

[hmmmnz]

it can only be one of two things,
1 - coils not receiving correct power, / so a volt meter should findthat one out !
Or
2 - the contactor has developed a fault / In which case I would also replace them both.

Lol. A few months too late, and it was neither the contactor or a voltage drop.

If you go back through the thread you'll see the videos.