starting a dead DMU

Ken H · 26 May 2019

So there is a dead sprinter somewhere. batteries as flat as a pancake.

Can you bump start it with another unit? Can you jump start it via the couplers?
If you have a 2 car unit, and one carriage is dead, can you jump/bump start it with the power of the other carriage?

And what is the correct procedure for starting a dead unit?

I think the old pre sprinter DMU's could be bump started - am I right on that?

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Highlandspring · 26 May 2019

Ken H said:
So there is a dead sprinter somewhere. batteries as flat as a pancake.

Can you bump start it with another unit? Can you jump start it via the couplers?
If you have a 2 car unit, and one carriage is dead, can you jump/bump start it with the power of the other carriage?

You can jump start a second generation DMU from another unit with leads directly between the batteries. You can also use a boost pack.

Ken H said:
I think the old pre sprinter DMU's could be bump started - am I right on that?

The epicyclic gearbox and fluid flywheel doesn’t allow that. You can only bump start a direct mechanical drive.

Ken H · 26 May 2019

Highlandspring said:
You can jump start a second generation DMU from another unit with leads directly between the batteries. You can also use a boost pack.

The epicyclic gearbox and fluid flywheel doesn’t allow that. You can only bump start a direct mechanical drive.

So you need a fitter then, I assume. not a driver job?

Highlandspring · 26 May 2019

Ken H said:
So you need a fitter then, I assume. not a driver job?

Yes, fitter required.

physics34 · 26 May 2019

A few times the batteries have gone on the DMU berthed overnight at Oxted bay, a fitter has turned up with a battery pack.

dk1 · 26 May 2019

If a fitter was not provided then the unit would just attatch & be dragged by another. Portable tail lamp on the back or headlight if leading.

big all · 26 May 2019

Ken H said:
So there is a dead sprinter somewhere. batteries as flat as a pancake.

Can you bump start it with another unit? Can you jump start it via the couplers?
If you have a 2 car unit, and one carriage is dead, can you jump/bump start it with the power of the other carriage?

And what is the correct procedure for starting a dead unit?

I think the old pre sprinter DMU's could be bump started - am I right on that?

the alternator on the dead motor coach is turned by the drive shaft provided the drive shaft is not isolated and after say 5 mins running at above say 40mph you would have enough charge and power being generated by the alternator to start a cool but not cold engine
just make sure all but essential lights are off

MichaelAMW · 26 May 2019

big all said:
the alternator on the dead motor coach is turned by the drive shaft and after say 5 mins running at above say 40mph you would have enough charge and power being generated by the alternator to start a cool but not cold engine
just make sure all but essential lights are off

I doubt it, just like it's not true for a car. Otherwise, the battery wouldn't be charged if the unit was sat idling stationary. The alternator needs to be connected to the output of the engine but before whatever it is that engages the engine with the wheels - some kind of mechanical or hydraulic gearbox for a Sprinter, I would guess.

big all · 26 May 2019

MichaelAMW said:
I doubt it, just like it's not true for a car. Otherwise, the battery wouldn't be charged if the unit was sat idling stationary. The alternator needs to be connected to the output of the engine but before whatever it is that engages the engine with the wheels - some kind of mechanical or hydraulic gearbox for a Sprinter, I would guess.

we only drove 101/117/ 119 at redhill so either my 25 year old memories are wrong [on numerous occasions

]or the units you talk about are different to the ones we had

61653 HTAFC · 26 May 2019

It's worth noting the difference between a jump-start and a bump-start. The former is using jump leads from another vehicle's battery. A bump-start (or push-start) is using gravity (or pushing/towing) to start the engine without using the battery.

If any rail-based diesels old or new can be bump-started you'd need a bit of a downhill run!

MichaelAMW · 26 May 2019

big all said:
we only drove 101/117/ 119 at redhill so either my 25 year old memories are wrong [on numerous occasions ]or the units you talk about are different to the ones we had

The OP was about Sprinters, which have some kind of hydraulic drive, even if there's a mechanical gearbox in there somewhere too. I'd be interested to know how a "bump start" works on a 1st-generation DMU.

big all · 26 May 2019

if you read all the quote connected to the first post it mentions you dont bump start an engine you get enough charge in the battery to start it

ironically my posts count related to this post is 579 one off the 119s we used to drive

Highlandspring · 26 May 2019

MichaelAMW said:
I'd be interested to know how a "bump start" works on a 1st-generation DMU.

It doesn’t because there’s a fluid flywheel between the engine and the epicyclic gearbox. In any case if you tried it you’d just wreck the gearbox, freewheel and final drive.

MichaelAMW · 26 May 2019

big all said:
you dont bump start an engine you get enough charge in the battery to start it

OK, but here's my failure to understand: the alternator has to be connected to the engine, so that it charges even when stationary, and the alternator needs to be connected to the wheels if dragging the unit will charge the battery. So, unless there's an intermediate drive shaft of some sort, that drives the alternator but can be separately and independently disconnected from both the engine and the wheels, the dragging along to charge the battery process will also turn the otherwise dead engine, which probably isn't that good for it and would be a significant resistance.

MichaelAMW · 26 May 2019

Highlandspring said:
It doesn’t because there’s a fluid flywheel between the engine and the epicyclic gearbox. In any case if you tried it you’d just wreck the gearbox, freewheel and final drive.

Well, without that level of precise detail, that's kind of what I wondered myself.

JModulo · 26 May 2019

MichaelAMW said:
OK, but here's my failure to understand: the alternator has to be connected to the engine, so that it charges even when stationary, and the alternator needs to be connected to the wheels if dragging the unit will charge the battery. So, unless there's an intermediate drive shaft of some sort, that drives the alternator but can be separately and independently disconnected from both the engine and the wheels, the dragging along to charge the battery process will also turn the otherwise dead engine, which probably isn't that good for it and would be a significant resistance.

On a sprinter (156 for example) the driveline is; Alternator - (Auxiliary Shaft) - Engine - (Carden Shaft) - Gearbox - (Carden Shaft) - Final Drive / Wheelset. If you're dragging the unit that isn't running all that happens is the wheels and final drive turn, which would then turn the carden shaft to the gearbox. The engine isn't running and no gear is engaged in the box, therefore no drive is taken up via the gearbox so the shaft just rotates and nothing is transmitted from the engine side. For the alternator shaft to turn the engine would need to turn, which wouldn't happen unless it was running.

37057 · 26 May 2019

For 185s, they're fitted with a load reduction relay which sheds loads if there's no engines running or loss of 3 phase supply.

If left in this state and the battery voltage drops below 82v then the unit will shut down automatically (by a low voltage relay fitted to each car) to prevent damage to the cells.

To get it started again its nessessary to lower the threshold of this relay slightly and trip any MCBs throughout the train which aren't essential and that may take some loads such as lighting and ventilation fans etc.

This is usually enough to to be able to start an engine and once an alternator begins to produce 3 phase down the train for each battery charger the job is done and all MCBs and LVRs can be reset to normal condition.

Its the same for 350s too except there's only one set of cells and a single LVR and its the auxiliary compressor and pantograph/VCB rather than a diesel engine!

MichaelAMW · 26 May 2019

JModulo said:
On a sprinter (156 for example) the driveline is; Alternator - (Auxiliary Shaft) - Engine - (Carden Shaft) - Gearbox - (Carden Shaft) - Final Drive / Wheelset. If you're dragging the unit that isn't running all that happens is the wheels and final drive turn, which would then turn the carden shaft to the gearbox. The engine isn't running and no gear is engaged in the box, therefore no drive is taken up via the gearbox so the shaft just rotates and nothing is transmitted from the engine side. For the alternator shaft to turn the engine would need to turn, which wouldn't happen unless it was running.

Thanks for that. I didn't have the detail but you've confirmed what I thought/assumed - that big all's suggestion that towing the unit would turn the alternator is not, in fact, correct, because the transmission is not engaged. Interesting, from what you've said, that the alternator is actually the *other* side of the engine from the gearbox and wheels.

big all · 26 May 2019

you isolate

MichaelAMW said:
Thanks for that. I didn't have the detail but you've confirmed what I thought/assumed - that big all's suggestion that towing the unit would turn the alternator is not, in fact, correct, because the transmission is not engaged. Interesting, from what you've said, that the alternator is actually the *other* side of the engine from the gearbox and wheels.

you isolate the final drive for towing
i was talking about a dead motor coach on a say 3car with all the movement being via the good end so final drives engaged so not bump starting as such but when enough charge in the battery from movement to start normally

Billy A · 26 May 2019

Highlandspring said:
It doesn’t because there’s a fluid flywheel between the engine and the epicyclic gearbox. In any case if you tried it you’d just wreck the gearbox, freewheel and final drive.

You won't be trying it on a train because you'll need the engine running to provide hydraulic pressure but in principle you can tow start a vehicle with a fluid coupling or torque converter provided the hydraulic pump is turned by vehicle movement. It was at one time quite common to design road automatic transmissions this way.

JModulo · 26 May 2019

Billy A said:
you can tow start a vehicle with a fluid coupling or torque converter

If you want to wreck it, yes.

Billy A · 26 May 2019

MichaelAMW said:
The OP was about Sprinters, which have some kind of hydraulic drive, even if there's a mechanical gearbox in there somewhere too. I'd be interested to know how a "bump start" works on a 1st-generation DMU.

They use what's called a hydrodynamic transmission. One fixed gear driven either by a torque converter (lots of slip, so first speed) or a fluid coupling (less slip, so second speed). Newer units have a high gear driven by a second fluid coupling, so third speed.

Steve Harris · 26 May 2019

MichaelAMW said:
Thanks for that. I didn't have the detail but you've confirmed what I thought/assumed - that big all's suggestion that towing the unit would turn the alternator is not, in fact, correct, because the transmission is not engaged. Interesting, from what you've said, that the alternator is actually the *other* side of the engine from the gearbox and wheels.

big all said:
the alternator on the dead motor coach is turned by the drive shaft provided the drive shaft is not isolated and after say 5 mins running at above say 40mph you would have enough charge and power being generated by the alternator to start a cool but not cold engine
just make sure all but essential lights are off

big all said:
we only drove 101/117/ 119 at redhill so either my 25 year old memories are wrong [on numerous occasions ]or the units you talk about are different to the ones we had

Looking at the posts above its clear big all is talking about first generation DMU's when the OP's question was regarding second generation DMU's.

Admittedly the OP asked a plethra of questions in one post which does make it hard to understand who is answering which question.

Billy A · 26 May 2019

JModulo said:
If you want to wreck it, yes.

No wrecking required. The old Borg Warner boxes that much of the UK motor industry used at one point would allow it. Wasn't encouraged partially because of the speed needed, but it was possible. Older Mercs used to do it too (and the manual said that you could!)

JModulo · 26 May 2019

Billy A said:
No wrecking required. The old Borg Warner boxes that much of the UK motor industry used at one point would allow it. Wasn't encouraged partially because of the speed needed, but it was possible. Older Mercs used to do it too (and the manual said that you could!)

Ill go bury my head in the sand... :rolleyes:

big all · 26 May 2019

yes i apologise i was talking first generation and starting a dead end via movement in normal service
i apologise if i caused any confusion

Ken H · 27 May 2019

MichaelAMW said:
The OP was about Sprinters, which have some kind of hydraulic drive, even if there's a mechanical gearbox in there somewhere too. I'd be interested to know how a "bump start" works on a 1st-generation DMU.

i did actually mention 1st gen.

Steve Harris · 27 May 2019

Ken H said:
i did actually mention 1st gen.

Indeed you did. You also mentioned Sprinters (2nd gen).

Perhaps if your five questions had been numbered, it might of saved confusion on who was answering what. Just a thought.

Ken H · 27 May 2019

Steve Harris said:
Indeed you did. You also mentioned Sprinters (2nd gen).

Perhaps if your five questions had been numbered, it might of saved confusion on who was answering what. Just a thought.

good point. ta

TRAX · 27 May 2019

To bump-start a car, you have to have a manual transmission, because you have to engage a gear, preferably second, press the clutch, start making the car roll, and at the appropriate speed you gently release the clutch to make the wheels and transmission link up with the engine (that’s the ‘bump’); the motion of the wheels and the transmission will make the engine run too, thus starting the firing process of the engine, thus starting the engine, and this will make the alternator turn to charge the battery.

You can’t bump-start a car with an automatic gearbox as you won’t be able to tell the gearbox anything. Considering the fact that you can’t select the gears on a second- or third-gen DMU, be it hydraulic or mechanical transmission, you can consider the situation similar to a car with an automatic gearbox.

Thus, you can’t bump-start a second- or third-gen DMU.

Bump-starting doesn’t take the alternator into account, as this will only turn if the engine runs. So just forget about the alternator. The aim of bump-starting is starting the engine. Only the running engine will provide electricity via the alternator on a car with a dead battery.

starting a dead DMU

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