Tuesday 8 June 2021

Triumph Tiger 955i: checking your motorcycle alternator and replacing a regulator rectifier

I tested the Tiger's alternator today. This is found under the round cover on the bottom left side of the bike.  I've lined up a MOFSET regulator/rectifier for the Tiger after some concise and clear advice from PSPB's FB forum where you always get clear advice instead of a bunch of internet mouth-breathers jumping in with what they don't know.

The Triumph OEM reg-rectifier isn't available and costs nearly $400 while also being an inefficient silicon controlled rectifier (SCR) shunt type reg-rectifier.  The one coming is a metal oxide semiconductor field effect transistor (MOSFET) based unit that is both faster and more efficient both thermally and in terms of providing steady voltage to the battery.  

With a new reg-rectifier coming, I took the advice on PSPB's FB forum and tested the alternator.  To make sure you're getting clean AC power you test the three wires going into the alternator for resistance (they should all show similar resistance between them).  The result was a steady 0.5ohms across all the connectors, which bodes well.

The final test is to make sure nothing is showing infinite resistance to ground on the bike.  Once again the alternator in the bike showed good wiring with no infinite resistance to ground on any of the wires:

The next step will be to wire up the new reg-rectifier when it gets here (should be early next week) and then see how things go.  The one I was able to find is wired for my specific Triumph (though Triumphs and Ducatis from the era both seemed to share the same unit).  With the new reg-rectifier wired up I should be good to go with the Tiger again and hopefully the (new over the winter) battery isn't having to carry the bike like it was and I won't have the stalling issues that have been plaguing me.


The reg-rectifier came in from Amazon right quick and I just installed it.  Having just brimmed the tank I didn't want to get the 24 litre monster off again to install it, and installing it with the tank in is tricky, but I managed it.

The kit came with replacement connectors, which is good because the ones on the bike disintegrated when I took them apart.  I was liberal with the dielectric grease and it all went together well.

I fired up the bike and it's now producing a very steady 13.9v and when I rev the engine nothing changes (before it would drop to barely 12.1v suggesting that while the motor was spinning above idle the battery wasn't being charged.  I didn't run the bike hot as I was in the garage with an impending thunderstorm going on outside but the readings I got suggest the strange electrics are resolved.

If you're experiencing regulator rectifier issues usually shown through an overcharging or undercharging (as was my case) battery, look up MOSFET type reg/rectifiers for your model of bike and save yourself a lot of time and money trying to chase down OEM replacements that simply don't exist.

The plan is still on to get the Tiger to 100,000kms by the time it turns 20 years old in 2023.

I wish Blogger weren't so stingy with headers or I'd alternate between the Tiger TMD logo and the new Concours TMD logo as I now have two functional and quite different bikes on the road.