91 ST1100 alternator concern

[SHEMWATSON77]

First off, Im not an expert and dont have the tools yet to adequately determine whether I have a problem. All I know is that my lights flicker when I rev the engine, so that at idle they dim. Also when I connected my heated grips there is a protection circuit that flickers showing that the voltage is reading lower than optimal. Ive heard alot about the poor stock alternators and so am concerned but should I be? I have a heated vest in the mail that Im going to run off a USB charger. Im hoping there wont be a problem. If there was what should I look for please?

 

[Slydynbye]

First things first, Check for a loose battery connection, then check the red connector left side of the bike.
Look for burnt terminals. with luck it's just bad connections or corrosion.

 

[Oldbikefixr]

+1 on the connections, check for corrosion and looseness per above.
Check out your battery.
Check out the VRR (voltage regulator/rectifier)
Inspect the wires form the alternator to the connector for overtemp indications.
Check every connector in the battery for burned insulation, corrosion (fuzzy blue/green and fuzzy gray).
Perform the resistance check on the wires from the alternator...wire to wire and wire to ground...there are three yellow wires.
You will be able to find details and photos if you search on "St1100 alternator'.

 

[ST Gui]

I have a heated vest in the mail that Im going to run off a USB charger.

Could you elaborate on that? Brand of vest and charger?

It doesn't seem like most USB chargers could handle the wattage of a vest. I haven't heard of a vest that runs off of a 5V supply (not that it means anything). Are you going to use a USB battery pack?



[Bit by the gator]

Ok a quick search showed a few of these but they run off a USB battery/charger and not a charger proper.

This one is runs off a 2A USB battery pack but is only 10W (5VDC@2A) so it might have to live underneath a stout jacket.

 

[Bush]

A heated vest running off a USB charger? Never heard of such an animal and frankly, I can't see a USB charger is going to supply sufficient amps to heat a vest. If there is something I don't know about this product that makes this work, please post a link to the maker.

You need a multimeter for basic tests. After you check the battery connections for tightness and look at connectors for signs of corrosion or overheating, everything else is guesswork if you don't have a multimeter to check resistance (ohms) and volts (AC and DC).

Lights dimming at idle and brightening when revving is quite normal with the 28 amp system you have, but that alternator was not designed to support many extra electrical accessories. There are only about 10 amps to spare once the bike's original needs are met. I don't know what your grips draw, or if there are any other add ons on the bike, so you may be at the limit already (higher wattage headlights draw quite a bit more too).

The Honda Service Manual can lead you through the steps required to test your alternator, or search for details on this forum, or the Archives of Wisdom.

 

[SHEMWATSON77]

You know what, I dont think I fully understood the ad. Maybe I cant run directly off charger. I do have a bank anyway but I was hoping I could plug right in to the charger on my handlebars.

 

[ST Gui]

but I was hoping I could plug right in to the charger on my handlebars.

The vest I linked to states that it runs off a 'battery bank' and not a charger. The the optional battery they provide is 10W. And it's small enough to carry in a jacket pocket.

In theory you should be able to run a vest directly off a USB charger if it's studly enough. Here are just a few that provide ≥10W (2.1A@5V).

The question becomes— are USB chargers designed to sustain that output for a protracted period? Some of these batteries take over 8hrs to charge but the current usually tapers off somewhat as the battery nears fully charge.

And what's the capacity of your charger? I'd be tempted to try it with an external USB charger first and then confirm the bike's charger is up tot the task. There are some cheap USB chargers out there.

But FIRST you need to fix your existing electrical gremlins.