Last gasp alternator?

I took the battery off the bike this afternoon and it was showing 12.21v. I stuck it on charge and within half an hour it was up at 14.5v. The charger unit has a Fully Charged light that comes on - and it hadn't so presumably it may have edged up further given time. Lacking patience however, and having other things to do, I took it off charge and within about 15 minutes I checked again and it seemed quite stable at 12.85v.

I have to admit at this point that when I disconnected the battery from the bike, I found that the negative battery terminal bolt was only finger tight....oops!

Previously john_holmes wrote:

If the alternator is good then its further down the line but before that do a simple test on the battery, charge it and connect a voltmeter and see if it gets to 14V, and off charge then see how long it takes to drop to 12.6V or so. New batteries do fail.

The powerbox has a capacitor inside, these can fail just like the Lucas blue 2MC, one reason not to fit one.

Refitted the battery this morning, still reading about 12.6v incidentally. No difference in charging terms - in fact slightly worse. With only ignition on I could only get the red light to dim slightly at about 3000 rpm, but it didn't last.

So I guess it must be either the Power box or the low voltage warning device itself? The Power box has been on at least 20 years, the warning light thing about 10 years. How do I eliminate the innocent party here?

Dave

Previously Neil Wyatt wrote:

I can't speak highly enough of the Boyer power box, I have three fitted to bikes so far and none have failed. A blown fuse or a dead battery the powerbox will get you home, as long as your alternator is putting out a charge. That is the question!

Further to the above, I happen to have in my posession a brand new and unused Boyer Power box - so a straight substitution is possible! Just a thought though; on the fitting instructions it warns that the unit must not be used in conjunction with a "charging warning light simulator". It advises that If the bike has one, it should be removed! I can't recall what the clever piece of after market electronics on my bike is called, see original note in this thread for description, but I bought it from Al Osbourne I think after the original Norton piece of kit - the warning light assimilator, was involved in setting fire to my bike some years ago!

Before I substitute this new Power Box I need to be sure that it is likely to survive the experience.

Dave

Previously Neil Wyatt wrote:

Interesting Dave, my 650 has a Boyer power box fitted and later fitted a charge warning light bought from Paul Goff. (Boyer electronic ignition fitted too)

The reason for the warning light was because I could only get the ammeter to get out of negative until higher revs or about 50 mph in top without any lights on. Air gap was the problem and with the correct rotor fitted all was well .

The bike has only done 400 miles since being put together but I'll be out on it this weekend. (It knocks a lot at low revs but that's another story)

My point is that I didn't trust what the ammeter was telling me, hence the charge warning light. But both instruments were actually correct. Have you checked your main fuse, as the power pox should bypass this in the event of failure? Your battery appears sound. If the main fuse was blown then a fitted ammeter would also be bypassed (With a power box) and the needle remain central. Therefore, I would expect a charge light to remain on but that depends how it is wired up. Maybe Paul Goff could advise with regard to his charge warning light?

I fitted a resettable fuse to mine some years ago so I wouldn't need to carry a spare. I did check to see whether it had popped but it was fine.

I would like to think the "charging warning light simulator" is the same as the "warning light assimilator" particularly as I replaced mine about 7 years ago and have been running perfectly well up to now. My warning light device is a dinky little solid state black box with three wires attached which lives in the headlamp nacelle by the way. ....

The thing I changed my warning light assimilator for is a dinky little solid state black box with three wires attached which lives in the headlamp nacelle. I would guess that would be pretty reliable?

Which leaves only the Power box . Although I regularly suspect the ignition switch of all manner of games having replaced three of them in the life of the bike so far.

In the absence of contrary advice I will swop out the Power box, just because I have one here, and report.

Dave

Finally got a chance to run the bike against the voltmeter. The results were not spectacular. The battery read 12.48 before starting, and climbed to 13.4 after about 20 seconds at a steady 2000 rpm. If I held it at 3000 I could hget it slightly higher - about 13.6 - but very slow increase.

So, comparing the facts;

The alternator on its own will happily blow a headlamp bulb although it doesn't score well against the static resistance test.

Voltage across the battery with engine running appears not wonderful and, as originally discovered, not enough to extinguish the red light when headlights are on.

I still have a new power box which I could swap over, so maybe that's the next step? Any other ideas?

Thanks, I will get to that this weekend and report back!

Gentlemen, the problem has been resolved by replacing the Power Box. It was more than 20 years old so I have no room to complain. Luckily I had an unused new one, still in original wrapping, which I bought secondhand about 8 years ago, so happy days.

Regarding the earlier test, I did indeed fail to mention the test to earth part of the static test procedure - but I did do that bit of the test and it was fine. My only concern was the relatively low resistance measured across the two wires, which I mentioned.

The red light now goes out as soon as the bike fires up and, with all lights on, goes off at about 2000rpm, which is probably what it did before.

Thanks for all suggestions and comments - much appreciated,

Dave