1974 DT125A Regulator/Rectifier

[Diablo007]

*****Keep in mind the 1974 DT125A has an electric start and a12V electrical system*****


Tried to swap out the stock R/R for a Trail Tech unit today as the battery wasn't charging well.  I connected the wires to the TT unit as follows:
Motorcycle - Trail Tech R/R
Red - Red
Black - Black
White - Yellow
Green - Yellow

There was no current to the battery, the voltage was roughly the same before starting as after starting and did not climb when the RPMs were increased.  I'm guessing this has something to do with a 'floating' ground?  I've attached the TT instructions.

Also; here is a post that was on treatland's website regarding the R/R.

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"Wired this bad boy up to a capacitor and oh man, LET THERE BE LIGHT!!!

Black - Ground (- side or ground)
Red - Capacitor/Battery and lights (+ side)
Red/Yellow - Not used
Yellow 1 - input AC current coming from Stator
Yellow 2 - Also Ground

Wired up my pinto this way there was no need to float the ground. Voltage stays regulated around 13V - 14V (adjusted) with no issues.

The post on mopedarmy about wiring this up does not work and you don't have to float the ground."
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I did try grounding each Yellow wire individually to see if it would work.  There was no change.

I'm hoping someone has managed to get this to work...

[1976RD400C]

Do you have a wiring diagram for your DT that you can post up?

[m in sc]

its an excited field alternator since it thats older unit. you need a unit that will power the rings on the unit to exite the magnet.  the unit you used is for an permanent magnet unit and wont work. 

[Diablo007]

Thanks m,  as soon as I read your post it clicked in my head.  Doh.

I have a Rick's Regulator that I'm not using right now.  I can't remember the part number right now.  It's a universal model that will work with the RD350.  I'm guessing this would work?  It's been a while but I seem to recall doing something similar many years back converting a Honda R/R to work on a Suzuki.  Matching wires and not needing to connect any extra white (or yellow depending on the system) wires coming off the R/R.

Basically:
Motorcycle - R/R
Red to Red
Black to Black
Green to Green
Yellow to White
Disregard extra Yellow(s)
Green (if there is an additional) to Ground

Pics of the RD350 R/R attached, the one I have has no plugs prewired to it.
Sound correct?

[m in sc]

yellows are ac

im not sure about the rest. since honda uses green as ground and black as switched power it can get tricky. and green -should- be to field wire on alternator to power it if it follows yamaha wiring protocol, so you should be correct with your wiring.

[bitzz]

A quick google search says that thing has a combination starter/generator.
A regulator/rectifier designed for a  AC alternator won't work.

Does your setup have brushes? (dead give away)

[1976RD400C]

A quick google search says that thing has a combination starter/generator.
A regulator/rectifier designed for a  AC alternator won't work.

Does your setup have brushes? (dead give away)

Yes, that's actually a DC generator that uses a special voltage regulator. There is no rectifier, just a regulator, like a '55 Chevy. The regulator energizes the field coils (stationary coils) and the 12 volts DC comes off the brushes that are touching the armature (spinning rotor).  The regulator also connects the armature to the field coils in a series circuit to convert the generator to a motor for starting. It's a very special one of a kind regulator.

[m in sc]

shit. youre right. its iS a generator not an ac alternator. 

[Diablo007]

Thanks for the info.  Wiring diagram has been attached.  I also forgot that it is a generator and not an alternator.  Friend I bought the bike from went over all of that when we checked the timing.  My memory seems to be going, that or too many projects going on, probably both.

OK, so the reason for changing the regulator.  The motorcycle has had a LiFe Shorai battery for the past 2 years.  A couple of weeks ago it wouldn't start so I had to jump it with a uninterruptable power supply battery to get home from work.  Once started it ran fine with the idle adjusted so that it would not stall.  The lights on the bike have always been dim, so dim that riding at night is scary.  Found that out after getting stuck at work late one night.  I figured now would be a good time to swap out the R/R which I now know is only a regulator.  When the Trail Tech didn't work I troubleshot the regulator and found that it did need tweaking to get it to the manual's specs (pages for that attached in case someone needs the info).  After adjusting I'm only getting about 13.50 volts at the battery with the bike revved to 5000 rpm, from there it holds steady.  At idle ~1350 or so (I didn't use my digital meter as I just realized I do have one while typing  this) it only puts out about 13.05 volts.  This is too low for a LiFe battery so I'm surprised the problem took so long to surface.  It also seems low for a lead-acid battery.

Is there any reason I can't use the R/R I have?  If I'm correct the rectifier circuit just won't have to rectify anything.  A rectifier is basically comprised of diodes configured to only allow current to flow in one direction.  Only the regulator would do any work.  If this will not work does anyone have an idea on what can be done to improve the lighting?  I'm willing to lose the LiFe battery and go with a lead acid if necessary.  Maybe use the aforementioned regulator for a '55 Chevy?  Since I can't test the R/R I have until the weekend I figure I might as well see what ideas are out there.

[m in sc]

use a regular battery. .02

[1976RD400C]

   A voltage regulator for a generator has a cut out relay, AC alternator regulators don't. There is no way a AC regulator will work on a generator. The cut out relay disconnects the battery from the generator so the battery won't drain when the motor is shut off. AC alternators don't need that because of the diodes in the rectifier.
   When you turn the key on the reg powers up the field coil in the generator but the cutout relay (number 2 in your service manual pic) stays closed and the battery is still disconnect from the armature. After starting the motor the generator voltage rises and when it hits 13 the cut out closes and charging starts. If the engine stops or stalls the voltage will drop below 13 and the relay opens, disconnecting the battery from the generator. You can watch that happen. See if that #2 relay is pulling in after the motor starts. The #1 relay is adjusting the voltage to the field coil so the output of the generator is correct, 14-16 volts. It's showing how to adjust those relays in the manual.
    Observe the cutout relay after starting. If it is pulling in, measure battery voltage. If not high enough you may be able to adjust the #1 relay to increase voltage. If cut out does not pull in, check generator brushes, and check the resistance of the regulator coils to the specs in the manual.
   If you can't get the regulator working I think a VR20 is the automotive one that works the same way.

[m in sc]

   A voltage regulator for a generator has a cut out relay, AC alternator regulators don't. There is no way a AC regulator will work on a generator. The cut out relay disconnects the battery from the generator so the battery won't drain when the motor is shut off. AC alternators don't need that because of the diodes in the rectifier.
   When you turn the key on the reg powers up the field coil in the generator but the cutout relay (number 2 in your service manual pic) stays closed and the battery is still disconnect from the armature. After starting the motor the generator voltage rises and when it hits 13 the cut out closes and charging starts. If the engine stops or stalls the voltage will drop below 13 and the relay opens, disconnecting the battery from the generator. You can watch that happen. See if that #2 relay is pulling in after the motor starts. The #1 relay is adjusting the voltage to the field coil so the output of the generator is correct, 14-16 volts. It's showing how to adjust those relays in the manual.
    Observe the cutout relay after starting. If it is pulling in, measure battery voltage. If not high enough you may be able to adjust the #1 relay to increase voltage. If cut out does not pull in, check generator brushes, and check the resistance of the regulator coils to the specs in the manual.
   If you can't get the regulator working I think a VR20 is the automotive one that works the same way.

excellent advice. the generator regulator on my 62 ford works the exact same way. (of course). ^

[Diablo007]

Great information, thanks!  Now things make more sense.

The cut-off relay works properly per the specs in the manual.  The regulator can be set to the manual specs also, but when set the voltage at the battery is only ~13.50 volts.  I did play with it more to see if the voltage could be increased but stopped when it was at ~13.67 as I had adjusted the screw quite a bit for what seemed to be a small gain and did not want to burn out the regulator.  I'm planning on changing to a lead acid battery but the voltage still seems on the low side and I'm concerned that it won't effectively charge the battery.  I'm pretty sure the low charge voltage is why the LiFe battery worked for so long before the voltage dropped too low and the motorcycle would not start.  When I pulled it it was at about 12 volts.  It is still good, as in it had not dropped below the minimum charge necessary and I was able to charge it back to spec without any problems.  Seems the voltage was just too low to allow the motorcycle to start.  As mentioned jump starting it with a 12V UPS battery allowed me to get it running and get home, so the it is producing enough power to run the motorcycle and lights.  I did turn the lighting switch off though as having the motorcycle stall on the way home would have sucked.

If anyone has experience with this motorcycle and can confirm the charging voltage is correct and that they haven't had any problems, that would be great.  In any case I may just run it with a lead acid battery and monitor the battery voltage from time to time to see if it holds steady, or keeps dropping.  If it drops I'll try the regulator mentioned, or one similar.

It would be nice to find a solution that would give decent lighting for riding at night.  Just in case I get stuck at work late again.