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TR5/TR250 TR250 Alternator

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Marvin Gruber

Marvin Gruber

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Need some help please! I am bringing a one owner, original paint 250 back to life for a friend. He wants it back as original as can be. None of the big three have the original alternator but one said "Oh we supply wiring diagram to change it over". I get a std TR6 alt with newer style clips, wiring diagram showing the installation of the clips. Nothing about what to do with the existing external voltage regulator. Question is - I can leave the existing voltage regulator in the circuit? Or what do I need to change, I could look at the TR6 wiring and bypass.

Marv
 
I've had a car with this. You can only use one regulator. With the 6 alternator you need to bypass the regulator on the car. I also know that a good shop can convert a 15 ACR to a 15AC unit if you have the correct end cap to retain the wires.
 
Moss Motors lists the same part number for both the TR250, and the MG MIDGET 130-100 there is a real
simple conversion from generator to alternator and keeps the voltage regulator. You only have to move 2 wires--go to
www.mgaguru.com tech section at the top, in the search box "generator to alternator conversion" it shows the wiring diagram,
and the wiring change (2 wires--that's all) it doesn't make any difference that this is an MGA--I did this conversion on my Nash Metropolitan.
The conversion is the same---any car that can accept an alternator, and has a voltage regulator
 
If originality is important to your friend, it might be worth doing some looking. 15AC (not ACR) alternators are scarce, but they are still out there. (I believe the same unit was used on 68 MGB.) Find a non-working original and have it rebuilt.

If you do go the ACR route, you can keep the external regulator mounted, but it won't be functional. The wire to the warning light on the dash will have to be rerouted to the internal regulator.
 
Yes, 68 B had the same setup, my TR250 has an external regulator from a 68 B, and it is the same (except my car runs at 14 volts on the B regulator and 12.x on the old one, vagaries of time I suppose) anyhow, I have had two TR250s, my current car has the 15ac regulator, my first one, which was Original down to the bumblebee hoses, had a 15 acr, I was just looking at a pic last night (different device, too lazy to post a pic right now). My current car is fairly early production #2004, the other car with the internal regulator was somewhere in the 7000s
 
A local shop has in the past rebuilt 250 alternators for me but is now telling me he can't get parts. Will still try to find correct one but just in case, what is needed to reroute wiring to use a TR6 alternator. I'm thinking just a jumper at the external VR. Leave it in place for looks.

Marv
 
Thanks guys, all good leads. Jeff (TRopic6) has a rebuilt one he sending from HI. Still curious to know how to bypass external regulator and use more modern alternator.

Marv
 
Classic Motorsports has a nice article about generator to modern alternator conversion in the current issue. One major point the article mentions: modern alternators can provide much more current. As such, make sure the wiring / fuses are OK to handle the load - the load that can occur if a component has a short, not the load during normal operation.
 
The 30-ampere ammeter is another weak link. When I push-started my TR4 and the dead battery drew the full 62-ampere output of the aftermarket alternator, the current fused the ammeter immediately.
 
Easy enough to add a shunt around the ammeter, though; effectively making it a 60 amp (or whatever you want).
 
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