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steam train charge/lighting system conversion to solid state.

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m3vuv:
heres the schematic.

floobydust:
I think it will get quite hot. Make sure the 2N3055 is sitting flush on the heatsink, it looks caught on a lip. What is your field winding resistance?
The circuit design seems for a 9R field and I could not get more than 2A happening.  Transistor power dissipation is 14W at 24V and 21W at 28V so it will heat up. If that is a stud mount diode, it will make a lot of additional heat.

I found pics of dynamo and regulator test stands. It might be worthwhile to run it there.
Dynamo test rigs
http://www.gw-svr-a.org.uk/frankenstein.html
http://www.gw-svr-a.org.uk/kidderminster_works.html

m3vuv:
luckily they have a test rig,heat is a concern,i may use a bigger heatsink with fan cooling,im there on wed so will find out.

David Hess:
So they want to keep the existing shunt wound generator and convert the regulator to solid state?  Oddly enough, I did that once with a Pinto because the electro-mechanical regulators you could buy became so unreliable.  The look on my neighbor's face when he saw me with an oscilloscope and impedance bridge hooked to my car was worth it.

It basically comes down to modulating the field current to regulate the output.  Lots of switching regulator controllers can do it (I used a 78S40 the first time) and now probably some integrated switching regulators but it will require detailed design to replicate all of the functions of the original circuit.

You might be able to find a simplified circuit intended for cars from the 1960s and 1970s.  Something basic could be done with a zener diode and some bipolar transistors if you wanted to do a fully discrete design.

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