Mk3 Sleeper Carriage, 120V DC supply?

[timhoward]

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]

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?

 

[timhoward]

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]

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]

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' ?

 

[brianmoooore]

Does the 120V need to be DC?

 

[timhoward]

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]

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.

 

[timhoward]

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!

 

[marconi]

How many running kVA at 400V three phase is now required? What switch on surge kVA required?
50Hz AC?