Charging system issues.

[Loctite77]

A bit of back story here, I have ALL new electronics on my 76cb750f. Spent the spring and summer replacing every wire, relay, switch, light etc. everything except the alternator. I used an earthX lithium ion battery and a RR combo unit from Sparck Moto.

I recently installed a new aftermarket oil tank which I had to relocate the RR to make room for. Lengthen the wires coming from the alternator and mount it under the seat cowl. After I did that I went for a little ride and everything seemed fine. Came home did a few things and was going for another little ride a few hours later. Cranked up and was letting it warm up and the battery died and it shut down. That's strange so I pull out the multi meter and crank it up again and check voltage at the battery. slowly dropping at idle from the low 11 v on down. When I open the throttle voltage climbs back up a bit to the low 12v range but a soon as I go back to idle voltage drops and battery quickly dies.

Great I think, bad charging system. Put the battery on the tender for the night and worry about how to diagnose the issue. This morning I go check it out again and this time with the battery fully charged, I have a solid 12.5v at idle and am getting the low to mid 13v at 3-5k rpm. Would a fully charged battery cause the charging system to act differently vs an almost dead one? Or do I have an issue somewhere?


Yeah Son!
[/quote]



Yeah Son!

 

[hillsy]

Was it charging properly before you changed the wiring? If that's the case, then it's more than likely bad connections (earth) in the charging circuit.


Right now it's not charging enough - you should have closer to 13v at idle and around 14v at 5k rpm.

 

[Loctite77]

To be honest I never checked until just recently when I relocated the R/R so I am unsure what it was doing before. I had taken it on a few longer 40-50 mile rides before and never had a problem with the battery so it was likely fine.

What do you mean by "charging circuit"? Any likely areas to check for better connection?


Yeah Son!

 

[irk miller]

He probably means the field coil circuit. The field coil is notorious for causing charging issues on these. It's something I'm dealing with on my 77, as well. If you hook up a meter set to check ohms to the green and white wire coming from the field coil, you should get 7.2 ohms, or very very close to that. Above 7.8 or below 7.0 is an issue. What I discovered on mine, and it's common on many bikes, is the connectors behind the shifter cover has gotten brittle from heat. The copper oxidizes and the connections become bad. As a result, I was getting 7.8 ohms on my reading. The bike could maintain a charge at idle, but after a long ride it couldn't keep up and often would drop below 11.6v. I'll replace the the wires by soldering silicon insulated wires in place, after sanding the copper clean with fine grit sand paper, then cover with fiberglass insulating tape. Before the repair, results of my charging system readings were often not consistent since vibration might've loosened things or the the connector vibrated to a better spot. A loose connection will also create enough heat to oxidize the copper and make it produce higher resistance.

This may or may not be your issue, but it's a test you need to do.

 

[Loctite77]

Thanks for the great feedback Deviant. I'll take a look at testing the field coil.


Yeah Son!