Discuss Mk3 Sleeper Carriage, 120V DC supply? in the Electrical Engineering Chat area at ElectriciansForums.net

timhoward

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I have an interesting job/project coming up - a heritage railway has a Mk3 Sleeper Railway Carriage which they intend to use for volunteer accommodation.
It won't be moved from it's final resting place and they need it to 'work again'. It sounds simple....

I've had a good look at it and tried to find out as much as I can online, and talked to some clever people, and it seems the original electrical design is both ingenious and rather complex.
My understanding - 1000V used to arrive from the locomotive on the main supply that ran the length of the train. This powered a motor / alternator underneath the carriage to create a 400v AC 3 phase electrical supply.
This 400v supply powered the air conditioning, the hot water cylinder, and also a 'battery charger' that spits out 120v DC.
The 120v DC charges a bank of batteries, which in turn (with various tap-offs) powers the lighting, the fire alarm, some USB sockets, and actuators to put the coach into "vent mode" to allow air circulation. Without these the coach is pretty well insulated and a sealed unit, so without air conditioning no air moves and condensation / damp would be an issue. So the idea was if the main supply failed most important things still worked for a good duration and the vents opened.

I'm weighing up 3 options, firstly providing a 3 phase supply to the alternator outputs and keeping everything exactly original. This is rather hard and expensive due to the siting of the carriage and the availability of 3 phase. It's pretty unlikely this idea will be possible.

Second option would be to provide 120v DC to it, essentially pretending to be the battery charger, giving them most of the functionality and have the vents open. There's already a commando - style socket designed for battery charging marked 120v DC. The main reason for this post is about how I might provide the said 120v DC.
Is it loopy to consider making a circuit using step down transformer to 170v AC, and use 4 diodes and a capacitor to give 120v DC? I've never done anything quite as crazy as this and any advice would be appreciated!
I'd also provide some 230v circuits for a couple of heaters, a cleaning socket, and change the element to a 230v element in the water cylinder.

The final option is essentially a rewire replacing absolutely everything with a new 230v system, in which case the railway would have to sort out ventilation. That would obviously a very large job.

I'm grateful for thoughts - especially regarding how one goes about making 120v DC. Thanks in advance.
 

ImpededLoop

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What's the input of the on board charger, is it single phase or 3 phase? It might be easiest to just power the existing charger which would provide the DC power to get things going.

Which railway is it?
 
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timhoward

timhoward

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What's the input of the on board charger, is it single phase or 3 phase? It might be easiest to just power the existing charger which would provide the DC power to get things going.
Good question - I think 3 phase - but it's really hard to see where then currently have it parked. It's high on the list to verify.
Which railway is it?
Cambrian Heritage Railway.
If I still lived in Sussex and had it been the Bluebell or Lavender Line it sounds you have an interest and we might have teamed up ;-)
 

ImpededLoop

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Cambrian Heritage Railway.
If I still lived in Sussex and had it been the Bluebell or Lavender Line it sounds you have an interest and we might have teamed up ;-)
The Bluebell have some MK3 sleepers as well which I believe will need similar treatment at some point. They may be worth speaking to to see if they've got a plan for connecting them up.

I am a member but no time at the moment to volunteer unfortunately... It does sound like an interesting project! :)
 

Avo Mk8

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Is it loopy to consider making a circuit using step down transformer to 170v AC, and use 4 diodes and a capacitor to give 120v DC?
No, but a bit topsy turvy with those numbers. 120v rms will give you 170v DC after bridge rectifying, depending on the load Etc. You'll probably need less that 120v, dependent on how you regulate the DC.
I'm sure there'll be a commercial solution for this option, likely to be more stable and better protected than homebrew. Do you have an idea of kW load on the 120V DC?
Alternatively you might just be able to generate enough 3 phase 400v from a single phase 240v supply with an inverter, if the HVAC is 'modest' ?
 
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timhoward

timhoward

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Thanks for the interest and the maths correction. I'll report back when I've found out a bit more.
I need to figure out what equipment is being run on which DC tap-off voltages. It's quite a crude system in some ways, literally a tap off between certain batteries. e.g. the fire alarm is 24v DC.
Only when I have a complete list can I answer about the total power consumption on the DC side.

It's an interesting idea generating the 3 phase 400v. I haven't looked into the HVAC in detail yet either.
My understanding is that the 120V would need to be DC as it's charging a bank of batteries which in turn are tapped off for various purposes.
 

brianmoooore

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I was assuming that the batteries were redundant, now that there is a reliable, fixed supply. Much easier to produce a 24V DC PSU for the fire alarm than a PSU to charge what I presume are very high capacity batteries.
230 volt single phase to 400 volt three phase motor generator is a possibility. Fitted one or two of them over the years.
 
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timhoward

timhoward

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I was assuming that the batteries were redundant, now that there is a reliable, fixed supply. Much easier to produce a 24V DC PSU for the fire alarm than a PSU to charge what I presume are very high capacity batteries.
230 volt single phase to 400 volt three phase motor generator is a possibility. Fitted one or two of them over the years.
Yes indeed - I need them to drag the coach about 6 foot forwards so I can get to what proves to be the most pertinent bit underneath. Once I understand all of the DC tap offs and uses this might all get significantly simpler!
 

pc1966

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timhoward

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To date I've only had 25 minutes to look at it and I ran out of time so I'll report back on power requirements.
The main 3 phase load was the air conditioning which will not be used.
I reason that at least one DC load must need the full 120V but I haven't figured out what yet.
 

Avo Mk8

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To date I've only had 25 minutes to look at it and I ran out of time so I'll report back on power requirements.
The main 3 phase load was the air conditioning which will not be used.
I reason that at least one DC load must need the full 120V but I haven't figured out what yet.
Hi Tim
Found on the interweb. Probably doesn't add much to what you already know, but there is some indication of what is supposed to run off which supply (see image below):
Source:

There are rail forums where this topic gets a mention, and it seems 'a thing' for preservation societies to use Mk3 sleepers for volunteer accommodation, so this has been done by some before. You might get some help from such a group, if you haven't tried already!

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timhoward

timhoward

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Thank you. I'd already read the forum post, but the other document is new to me and very helpful.
I'm reassured I wasn't that far off - but it does look like I mis-identified the tap-off for the fire alarm, it looks like that might be for PA.

To me it looks as though the only sensible options are providing 110v DC for lighting and ventilation or a complete rewire.
I'll post some pictures when I'm able.
 

marconi

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My read in suggests to me the ETS is single phase ac or two wire dc at circa 1000V. It would be worth establishing what is the supply requirement of the motor driving the alternator. If ac you could consider a single phase 230 to 1000V step up transformer of circa 25kVA ( but check alternator kVA) and then keep the coach electrics as designed. Nice and simple and the coach would run everything installed which might have appeal to railway buffs.

Single phase transformer manufacturer - https://www.rbaker.co.uk/services/single-phase-transformers/
 
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timhoward

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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

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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

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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 ?
 
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timhoward

timhoward

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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

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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

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Lucien Nunes

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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.
 
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timhoward

timhoward

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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:
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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.
 

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Simon47

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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.
 

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