Loop Alernator Conversion. Denso Alt Replacement ??

[Tom H]

I have a alt. conversion from Greg Fields with a Denso alt P/N 18504-6220 or 100211-1680. both numbers can be used for look up. It is in my Eldo police version with the police dash.

My alt was sounding like it may be time to get it serviced, so I found an aftermarket replacement that should have been correct by the P/N. It's mechanically the same, but not entirely correct electrically.

To make the alt light come on, you can ground the wire. The wire has 12V and when grounded the light comes on.

With the Denso, I turn the bike on with the key. Oil and neutral lights come on, pull the ignition switch on the dash and the alt light comes on and goes out when the bike is running. That is how it should be.

With the AM alt, when I turn the key on, the alt light comes on at the same time. Pull ign switch and the light is on. with the bike running the light goes out. Hmmmm!

All wires are hooked up correctly. So I wanted to know why it was working the light differently. I did a Google search and came up with a site that sells a kit sorta like Fields kit and it mentioned that the alt light can not be used on the police version with the dash ign switch, but civi it works fine. Huhhhh???

So I used my DMM to see why the AM made the light work differently. I'm not electrical engineer, so I have a bit of a time understanding what I'm reading on a DMM when it comes to more than Volts. With the help here I think I've got Ohms a bit figured out.

With the wires off both alts, I did find that the Ign and L connectors gave me a reading on my DMM's Continuity/Diode setting when the neg lead of the DMM was grounded to the alt and the pos lead on either connector.

Denso gave a reading of about 890 on the Ign term and about 1980 on the L term.

After market gave a reading of about 890 on both terminals.

Could this be why the light circuit does not work correctly?

Can I do/add something to make it work like it should?

I can use it with out the light working, just don't like that idea.

Any thoughts??

Thank you!!
Tom

[Kiwi_Roy]

With the Denso, I turn the bike on with the key. Oil and neutral lights come on, pull the ignition switch on the dash and the alt light comes on and goes out when the bike is running. That is how it should be.

With the AM alt, when I turn the key on, the alt light comes on at the same time. Pull ign switch and the light is on. with the bike running the light goes out. Hmmmm!
 

That sounds to me like they are both working with just a subtle difference

[eldoroddo]

I have the same alternator on my 73 Eldo police/California/whatever you wish to call it, and the light never worked.
I emailed Greg and he couldn't figure it out, either.
This was about 10 years ago or so.
The light not working drove me nuts until I learned to deal with it.
Whadda ya want for an alternator designed for a Hitachi forklift?

[Tom H]

Thanks for the replies.

The light works correctly with the Denso. I was concerned that the way the light is coming on as soon as the key is on could damage something in my wiring.

I guess the AM alt just has a bit of a ground to that connector as soon as the key is on.

Thanks again,
Tom

[eldoroddo]

"With the AM alt, when I turn the key on, the alt light comes on at the same time. Pull ign switch and the light is on. with the bike running the light goes out. Hmmmm!"

I've never used my switch on the dash. I just leave it pulled out at all times.
When I bought the bike from Mark at Moto Guzzi Classics back in 2005, he told me not to mess with the dash switch. "Turn on the petcock, turn the key to the first click, twist the throttle twice and hit the starter button. By the time you're done with a cigarette, the bike is warmed up."

Granted, this is in SoCal. I've never used the choke (yeah, yeah, I know...enrichener). I do occasionally make sure the cables are still free and everything's operating properly.

I'd love to see a pic of your wiring, maybe it's different than mine. I'll check my alternator part number when I can...I'm healing from back surgery.

[Tom H]

I have always used the dash ignition/kill push/pull switch. Just a habit I guess.

Also just to be clear, the AM alt does charge correctly, so unless there is a reason to not use the dash light, I'll just get used to it working differently.

Never use the choke either. Tried it a few times when I first put the bike together 35 years ago. The bike never did want to start with the choke.

Thanks again,
Tom

[Hahnda]

The deal with the Police bikes is that the light works for a while and then quits working after 10-200 miles. Put in a new alternator and the same thing happens. Civilan bikes, no issue.  At least this is the case with the alternators that I have been supplying with my alternator conversion kits.

Had an email exchange with Greg Bender and this is pretty much covers it-

On civilian motorcycles:

    The ignition switch cuts power to the dash bulbs.
    The ignition switch cuts power to the coil (which sends current to the alternator).

On police motorcycles:

    The ignition switch cuts power to the dash bulbs.
    The push/pull switch cuts power to the coil (which sends current to the alternator).

Since civilian machines don’t seem to have this problem, it seems to me that using the kill switch to turn off the motorcycle causes this problem (ignition switch remains on, push-pull switch is off). Therefore, if current is sent to the alternator through a circuit only powered by the ignition switch, the problem should be solved.

There is nothing special about tapping current from the coil positive terminal for the alternator. It is simply a convenient location. A wire could easily be routed to the fuse box instead, as there are open/unused spots available.

[Tom H]

The deal with the Police bikes is that the light works for a while and then quits working after 10-200 miles. Put in a new alternator and the same thing happens. Civilan bikes, no issue.  At least this is the case with the alternators that I have been supplying with my alternator conversion kits.

Had an email exchange with Greg Bender and this is pretty much covers it-

On civilian motorcycles:

    The ignition switch cuts power to the dash bulbs.
    The ignition switch cuts power to the coil (which sends current to the alternator).

On police motorcycles:

    The ignition switch cuts power to the dash bulbs.
    The push/pull switch cuts power to the coil (which sends current to the alternator).

Since civilian machines don�t seem to have this problem, it seems to me that using the kill switch to turn off the motorcycle causes this problem (ignition switch remains on, push-pull switch is off). Therefore, if current is sent to the alternator through a circuit only powered by the ignition switch, the problem should be solved.

There is nothing special about tapping current from the coil positive terminal for the alternator. It is simply a convenient location. A wire could easily be routed to the fuse box instead, as there are open/unused spots available.

I think I get at least part of the Civi vs. police issue. Since the civi never cuts power separately , it would be like leaving on the push/pull switch. You would never know that the AM alt is allowing the light to glow when it shouldn't be on the police version. Hmmm.

As long as it does not damage my wires, I guess I'll just get used to it working differently.

Thanks again,
Tom