Testing a used 40-amp alternator

[batavicus]

This question must have been posed before, but I can't seem to locate it, so here goes: is it possible to test a 40-amp alternator before trying to install it? If so, then how? The 28-amp on my 1994 non-ABS, non-farkled (except for a 12-volt socket for the GPS) ST1100 appears to be working fine. The alternator came from a wrecked '01 with 29,000 miles. Before buying the motor, I watched video of the wrecked bike running, and everything the seller told me has thus far proved true. (In addition to the alternator, I kept the starter, carburetors, coils, and exhaust pipes; the motor I sold to a shop.)

Suggestions? Perhaps I should drive the bike another summer before changing? (Next summer, a long trip to Canada is planned) The voltmeter consistently shows 13.9-14.1 volts at cruising speeds. The voltmeter isn't much, but I'm looking more for a change than for the exact number. The bike has about 51,000 miles on it and except for Hot Pump Seizure Syndrome, since corrected with the fuel pump from the above mentioned engine, the bike has given me no trouble. Does sitting hurt the alternator? It's been in a draw in my tool chest in my garage for 2-3 years now.

 

[Bush]

Your non farkled 28 amper could easily go another 50,000 miles with no problems, as long as the wiring is well inspected and maintained often. Eliminating the red 3P connector and soldering those three yellow wires is a good preventative measure and check the VRR connector for discolouration (signs of overheating). Your 40 amper won't go bad sitting, in a dry location. Can't help with a bench test for it though.

 

[DeanR]

I have a local alternator repair shop nearby. He bench tested my used 40 amp that is waiting to be used. Just need an adapter so he can hook it up to his belt drive thing. (the shop had one, and so does John Oo here).
It was putting out good power. For around $100 he can rebuild it if necessary.

 

[Oldbikefixr]

Alternator connectors seem to have been problematic beginning in the late 1970's Hondas. Just a slight amount of corrosion inside the connector will cause minute arcing...which causes more corrosion...more arcing....until there is some significant heat damage which will ultimately lead to a short...usually in the stator coils.
A good preventative measure is the disconnect the halves and inspect for corrosion or arcing damage (little black spots). If the contacts are still clean, clean them more with electronic contact cleaner. When that is dry, connect the halves and fill the wire entry points with a silicone based dielectric grease. Force some into the gap at the mating flange of the plastic connector. Then make this a periodic inspection item.
On all the bikes on which I have noted some heat damage here, I have replaced the stock connector with a waterproof trailer connector with enough wires of the same gauge. Pep Boys has a good assortment locally. If you go this route, solder, don't twist and tape...that's just relocating a potential problem.

 

[batavicus]

Thanks to all for the replies. I guess I'll keep my 28-amp and maintain it carefully until it shows signs of failure. Any opinions on how much strain would adding two Clearwater Darlas (combined 48 watts) put on the alternator? Having seen Mike Martin's chart, the draw would still be under the capacity. Does operating the alternator close to full capacity shorten its life?
Would changing the tail light to an LED and possible saving 1.5 or so amps make any difference?

 

[John OoSTerhuis]

You should be OK with those aux lights, David. But monitor your voltmeter and turn off the lights when it starts to drop too far, ~12.8V, IMO. Like in stop-n-go traffic with frequent use of the brakes and the fan running. Your tail light reflectors were not designed for LEDs. For optimum conspicuity, stay with the OEM bulbs with the filiment positioned correctly for the reflector. JMHO

John

 

[wjbertrand]

If it were me I'd remove that 3P connector and solder the wires directly. If it ever goes out, you'll have to upgrade anyway so won't need that connector.


-Jeff

 

[batavicus]

Thanks to all who replied with advice. Ok, the 28-amp stays on the bike for now and the 40-amp stays in the tool cabinet, but the 3P connector is going, or at least getting a good looking over.

 

[Jim Van]

If it were me I'd remove that 3P connector and solder the wires directly. If it ever goes out, you'll have to upgrade anyway so won't need that connector.


-Jeff

+1 Same here.

 

[Jim Van]

Thanks to all for the replies. I guess I'll keep my 28-amp and maintain it carefully until it shows signs of failure. Any opinions on how much strain would adding two Clearwater Darlas (combined 48 watts) put on the alternator? Having seen Mike Martin's chart, the draw would still be under the capacity. Does operating the alternator close to full capacity shorten its life?
Would changing the tail light to an LED and possible saving 1.5 or so amps make any difference?

SuperBrightLEDs.com had some decent LED lights for a lot less than the Darla's, BTW. Not as good, but decent and a heck of a lot less $$ than the Clearwater's.

 

[batavicus]

Ooh, those look pretty good, Jim Van, and indeed, a lot cheaper. I've also run across the Denalis on-line. Does anyone have any experience with them? I try not to ride too much at night, especially not in the Texas Hill Country because of the all the deer. (Deer...that reminds me--it's almost time to sight in my ancient Swedish Mauser carbine, which went from being a backup pickup gun into my favorite. It's dead on the money at 100 yards with the cheapest ammo--not bad for a 99-year-old piece--oh wait, wrong topic. On the ST, I want to MISS the deer.)