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Charging problem on an '81 R100RS

2 Posts
2 Users
Samuel Creasman
Posts: 6
Active Member
Topic starter

Was on a multiple day ride when I stopped to rehydrate at a Shell station on a very hot (94-95 degree) day. When I got back on the bike and started the engine, the Volt meter
pegged as high as it would go at over 16 volts. Bike ran normally, rode down the road for a couple of miles and stopped. Restarted the bike and it pegged again at over 16 volts. After a minute or two the volts dropped to 12 volts at idle. Riding down the road the volts held steady at 12.5 volts, no matter what rpm I was running. Stopped again to cool off and same thing happened again. Volt meter pegged at 16 volts and after riding for 3 or 4 miles the volt meter again dropped to 12.5 volts while running at speed.
What do I look at first?
Sam Creasman
RA # 12545

Posted : 09/09/2019 18:46
Richard W
Posts: 2529

Scot gave an excellent response.

• I can only add that the OEM voltage regulator is full of relays and contacts that are set to open and close at certain limits. Just like points ignition, those contacts needs cleaning and renewing every decade or so. That's the number one reason to find one of the newer, 3rd party voltage regulators which are all electronic. Those newer type do the switching in transistor logic rather than with mechanical springs, arms, and contacts. The increase in reliability should be blatantly obvious to even the staunchest Luddite among us.

• Then let me underscore Scot's point about newer sealed batteries (AGMs) needing a slightly higher charge voltage. With Rick's adjustable model you can dial the voltage right to the battery maker's voltage specs. Another big plus.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

Posted : 09/11/2019 01:14


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