Mk3 Sleeper Carriage, 120V DC supply?

[timhoward]

I think that there are configuration options on the EHT control panel to switch in a rectifier, meaning that the 1000V incoming supply can be AC or DC to suit the locomotive in question. On the face of it this would be viable.
Other considerations are the noise / environment issues with running an MA all night, and the additional maintenance required. The MA units are reportedly not known for long periods of trouble-free operation.

 

[marconi]

My last input is I read the MA has voltage and frequency stabilisation I suppose because the supply is from the locomotive's diesel generator whose output will vary as it's traction output loads up and down. I hazard a guess that is it this stabilsation which fails. It may be possible to do without the V and f control since the mains is rock steady in f and volt drop negligible with suitably sized cabling to and from the transformer.

Please if you would keep is abreast - and we love pictures

 

[Avo Mk8]

Tim, just to state the obvious, that many posts here have mentioned 120V DC, including the suggestion of a PSU, but the 'spec' seems to be 110V, as you put in your recent post #14.
There are 110V high-current PSU's available. I presume it matters that it's 110 rather than 120 ?

 

[Rockingit]

Take the MA off the carriage and place remotely to overcome the noise issue? You'd potentially then just have a standard 415v 3ph to distribute back to the carriage inputs....

 

[timhoward]

Tim, just to state the obvious, that many posts here have mentioned 120V DC, including the suggestion of a PSU, but the 'spec' seems to be 110V, as you put in your recent post #14.
There are 110V high-current PSU's available. I presume it matters that it's 110 rather than 120 ?

Thanks - yes I'd got 120 in my head for some reason, it's certainly 110 as you say. I think there's automatic load shedding of 2/3 of lighting after DC drops below 86 volts, and I'm assuming it's not super critical.
I've been in my shed and found two 6A 48v DC supplies and as a temporary proof of concept setup I'm thinking I'll put them in series with extra diodes between output terminals to prevent back-feeding if one powers up alone. I stress that is a temporary fact-finding tool not the final solution!

Take the MA off the carriage and place remotely to overcome the noise issue? You'd potentially then just have a standard 415v 3ph to distribute back to the carriage inputs....

Thanks, yes, could do that. It's probably worth checking the relative prices of a 230 -> 1000v step up transformer compared to a 230v 3 phase converter, neither of which I have in my head!

 

[pc1966]

Thanks - yes I'd got 120 in my head for some reason, it's certainly 110 as you say. I think there's automatic load shedding of 2/3 of lighting after DC drops below 86 volts, and I'm assuming it's not super critical.

OK.

I've been in my shed and found two 6A 48v DC supplies and as a temporary proof of concept setup I'm thinking I'll put them in series with extra diodes between output terminals to prevent back-feeding if one powers up alone. I stress that is a temporary fact-finding tool not the final solution!

Worth a go to see how it work out.

Thanks, yes, could do that. It's probably worth checking the relative prices of a 230 -> 1000v step up transformer compared to a 230v 3 phase converter, neither of which I have in my head!

I would try and avoid depend on any electro-mechanical convertor, they are noisy and relatively short lived (between servicing).

Do you know the AC frequency range that is acceptable? If 50Hz works then probably a VFD would do, but you would need to check with the supplier if it can be used on non-motor loads, etc. Of course you can also get dedicated converters but cost might start to creep up.

 

[pc1966]

Here is one from MachineMart, seems reasonable price (£430 on 25 Nov 2021) but more checking needed:

Clarke PC60 - 5.5HP Phase Converter - Machine Mart - Machine Mart

www.machinemart.co.uk

 

[pc1966]

Here is one from MachineMart, seems reasonable price (£430 on 25 Nov 2021) but more checking needed:

Clarke PC60 - 5.5HP Phase Converter - Machine Mart - Machine Mart

www.machinemart.co.uk

Just looked at the manual, it is not suitable for this sort of job. Relies on phase-shifting capacitors and a step-up transformer, has no N output.

Oh well, seemed too good to be true. And it was!

 

[Lucien Nunes]

I would make the specific voltages needed by the specific loads to be powered. If something takes 24V, power it with 24V. Bypass the battery configuration and certainly bypass the MG. Transforming and rectifying is easy and maintenance-free but battery and DC machine maintenance are hard, dirty work. Yes make the 110V DC with a transformer-rectifier, no need for sophistication if the loads are designed to cope with the varying voltage of a battery, just reasonable smoothing.

 

[timhoward]

Thanks. I agree, most systems that are needed run 110v DC so this is the main goal.
I spent another half hour there today as light was fading. Sorry, no interesting photo's yet. I did find a handy guide to the multitude of under-body compartments on the back of the services cupboard door:

This in turn confirmed that all of the EHT stuff that I'm not so interested in is on the easily accessible side, and compartments B,C,D,H,J and L are the other side completely blocked by a platform wall....typical!
Undeterred I searched more inside, and managed to find someone with the right railway key to open the inner consumer unit/services cupboard (not the typical square T key!). I've certainly found the main 110v bus bar and breakers, as well as a changeover switch for the entire carriage between Off, Aux (110v) and AC, so I have some points of reference in the wiring for further testing and circuit tracing now.
Next time I'm there I'll definitely take some more interesting photos.

 

[Simon47]

How about ...
Have them remove the batteries from the battery compartment, and install a couple of DC power supplies (others have already posted links for some units). It sounds like you need one for 110 or 120V, and another for 28V. Connect these to the terminals that would otherwise be connected to the batteries - you might need to "follow the cables back" to find fixed terminals rather than free cable ends, or you might make up a "dummy battery" just to hold insulated terminals in the right places to act as fixed connections. It shouldn't be too hard to find somewhere to bolt a bracket with power inlet connector to. You could potentially disconnect the generator to battery connection - I'm guessing this would be a diode rectified output from the alternator so in theory not needed, but might be worth disconnecting so there's less stuff powered up when it's not needed.
That would allow you to leave everything exactly as it originally was, so they could remove your PSUs and refit the batteries if they ever wanted "as original" operation.

 

[Sparkgap]

If all you are after is running the lighting have you checked inside the fittings? IIRC the standard fittings are only DC to allow for the battery backup and have a built-in inverter. Might just be as simple as bypassing the inverter and running AC direct, poss through a transformer. Other thing, is it ALL fittings on DC or just a proportion?
Even if they aren't using the A/C I expect they will need the mechanical vent side of it to run and provide fresh air, vols accommodation can get quite whiffy!!

 

[timhoward]

If all you are after is running the lighting have you checked inside the fittings? IIRC the standard fittings are only DC to allow for the battery backup and have a built-in inverter. Might just be as simple as bypassing the inverter and running AC direct, poss through a transformer. Other thing, is it ALL fittings on DC or just a proportion?
Even if they aren't using the A/C I expect they will need the mechanical vent side of it to run and provide fresh air, vols accommodation can get quite whiffy!!

Thanks for the response. My current understanding is ALL the lighting hangs off breakers on the 110v DC bus bar. I completely agree that the fittings will almost certainly have inverters in, the irony of converting AC to DC and then back again is not lost on me.
I also completely agree that the vent side will need to run, and that requires DC as far as I can tell.

My current plan is to investigate the transformer that is currently already there to charge the batteries. I'm assuming this will be single phase, and it may be suitable to supply enough current with some smoothing added for the lighting and ventilation requirements. At the moment I can't get to that compartment due to a platform wall.
There is a 2nd coach which was a buffet car at the other end of the railway - in that one they have started again with a 230v supply, so I'm going to ask if I can remove some redundant kit (the charging transformer) for investigation /testing. This sort of thing has to fit around paid jobs, so it will be slow going!

 

[Simon47]

I would have assumed, probably incorrectly, that they would have tapped windings on the alternator connected to the battery via a 6 diode bridge. Design the system right and you get the right AC voltages at the same time as the right DC voltage - but possibly at the expense of a slightly distorted AC waveform.
A bit like how sewing machines used to have an AC motor with integral (pedal operated) clutch & brake, plus a tapping off the winding for the work lamp.

 

[timhoward]

I would have assumed, probably incorrectly, that they would have tapped windings on the alternator connected to the battery via a 6 diode bridge. Design the system right and you get the right AC voltages at the same time as the right DC voltage - but possibly at the expense of a slightly distorted AC waveform.
A bit like how sewing machines used to have an AC motor with integral (pedal operated) clutch & brake, plus a tapping off the winding for the work lamp.

Thank you for that thought.....it's interesting and certainly one way of doing it.
I really need to get into compartment D and see what "Battery Charger Transformer" actually entails.