Problem with contactors wired in parallel

[hmmmnz]

No much of an update, I've gone through all the wiring again. Everything is going to and from where it's supposed to, I've meggered everything to earth, all good.
Im still waiting on MTU changing out the starter motors and solenoids. (they won't just give to me to fit, so I'll just have to wait)
I've plenty of other testing to do. And currently the power car starts and runs, so I can carry on (good detective work figuring out its a train) its a class 43 hst.

I've checked the wiring against other trains, and it's the same.

It pretty much leaves me with the solenoid /starter motor being the problem. As to what that problem is. ...

I'll keep you posted, they are supposed to be changing them out tonight

 

[Lucien Nunes]

I'm not sure how we actually got to reasoning that the starter(s) are faulty without actually checking their performance, or has that actually been done? I'm not that familiar with rail traction applications and I'm sure the OP is, but for a large diesel, given the lack of constant motor power, this start doesn't sound too far off the mark that I would immediately suspect them. I would certainly want to see current readings that are significantly too high before splashing out on new ones.

Last (for now ) could it be that one motor is not engaging the flywheel so the other is doing all the work?

The main contactors don't operate until both the solenoid contacts are closed, which indicates the starters are both engaged. A disengaged series connected starter would be massively overspeeding, I think you would know about it.

The cranking current/starter motors current waveform is an analogue of the variation on torque required to undertake suck-squeeze-bang-blow of the diesel cycle in each cylinder

It's a 16-cyl, so the torque ripple at the crankshaft is pretty low, and much higher in frequency than the contactor impulsing.

One test that I didn't mention, that I would have done in the absence of a fast enough meter or scope to follow the coil voltage accurately, would have been to get a filament lamp - a string of 24V lamps if necessary - and watched it that way. Then, the same at the battery terminals on the panel, and at the starters etc. The filament lamp has multiple uses as a troubleshooting tool, especially as a series limiter for SMPSUs and DUTs that might go into runaway or short during test.

 

[hmmmnz]

I'm not sure how we actually got to reasoning that the starter(s) are faulty without actually checking their performance, or has that actually been done? I'm not that familiar with rail traction applications and I'm sure the OP is, but for a large diesel, given the lack of constant motor power, this start doesn't sound too far off the mark that I would immediately suspect them. I would certainly want to see current readings that are significantly too high before splashing out on new ones.

basically ive ruled out everything i can at my end, so starters and solenoids is the next thing in line, it may not be the most scientific or technical way of going about it, but hey ho. there it is.

i dont know if you noticed the resistor bank on the drawing in series with the starter motors i presume that would do the same as a string of lights, im not sure where you are going with switch mode power supplys or why i might need to limit them, (i guess i missed something in the previous posts)

any way, ill let you lot know, if im still paddling up ---- creak after the starter motors have been changed, if it does sort it ill see if i can get them and pull them apart to see what have failed or possibly caused the problem.

 

[Lucien Nunes]

im not sure where you are going with switch mode power supplys or why i might need to limit them

Nowt to do with your job, just singing the praises of the humble filament lamp as a multi-purpose troubleshooter and problem solver. In your predicament I might have hooked up a suitable lamp across the coils to get a clear, reliable and fairly responsive visual indication of the depth of the fluctuations in the feed to the contactor coils. A 100W 230V gasfilled GLS has the same order of time constant as a DMM bargraph but it's immune to noise, true RMS over any waveform and any frequency from dc to MHz, and leaves your DMM free to take another measurement while watching the lamp out of the corner of an eye.

 

[marconi]

HST trainset capacities - https://www.railforums.co.uk/threads/hst-trainset-capacities.73196/

Two starter motors at £3000 each (see#29) = £6000

FGW long distance HST (2+8); 375 standard class, 112 or 118 first class.

Say average standard class ticket is £50 and first class £100. Assume 70% and 60% occupancy so a single one way trip for an HS125 produces revenue of circa:

(375 x 50 x 0.7) + (118 x 100 x 0.6) = 13125 + 7080 = £20205

 

[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.