Charging voltage too high?

[SteveD]

Wow. I guess one good thing about my multiple 4 buck HF meters is that I can check them against each other if I need to. I'd never heard of one going bad like that.

One for the car, one for the bike, one for the shed, one for the house.....http://www.ebay.com.au/itm/HOT-NEW-LCD- ... 2a3adeee32

[Hoof]

Beware - that $4 voltmeter is exactly the same as the one I had - I've gone up market now ($10)
Sealey MM20 Digital Multimeter 8 Function with Thermocouple Brand New......but I think I need to start getting things in 3 s' so I can obsessively cross check!

“Electricity for example was considered a very Satanic thing when it was first discovered and utilized.”
― Zeena Schreck

[Ken in Oklahoma]

Beware - that $4 voltmeter is exactly the same as the one I had - I've gone up market now ($10)
Sealey MM20 Digital Multimeter 8 Function with Thermocouple Brand New......but I think I need to start getting things in 3 s' so I can obsessively cross check!

I'm a fan of those $4 Harbor Freight meters. Actually I got most of mine free. In various magazines there is a Harbor Freight 'bargain' ad, and (in the past anyhow) they have often offered it for free just stopping in the store. I have given a few of them away to friends in need (who apparently aren't big Harbor Freight customers). I've had two meters fail (other than dead batteries) but mine have always given virtually the same voltages. And if you know the voltage of a dry cell batteries, a quick check of the meter can be performed using that as a reference.

Ken

[CafeR65]

Hi all,

I'm new to the forum and I have exactly the same reported fault as 'Hoof' who started this thread - however my voltage is CONFIRMED high by three seperate meters.

When starting and revving up above 2000rpm from cold the battery voltage appears normal, creeping up from 13 to mid 14's and momentarily settling in this range, however as the bike continues to warm up staying at the exact same rpm, the voltage starts climbing again before eventually capping out at 17 volts. The voltage also stays high until the rpm drops back below 2000 or so. If I let the bike cool down for 30 minutes or so the process simply repeats next start.

To fill you in on my troubleshooting efforts so far I initially suspected that my voltage regulator was faulty. I had an electronic style regulator fitted already since my rebuild circa 2012 and even though it shouldn't really ever fail I replaced it with another electronic style regulator but the test results were exactly the same.

Since reading this thread I have also carefully checked all of my wiring connections as outlined in the earlier responses by 'Barry' and can find any faults. My D+, D- and DF wires are all connected where they are supposed to be, wires are in good condition and there are no short or open circuits.

Even though I am an electrician of sorts I am pretty much stumped here and since this was the much only forum/thread I could find on the internet that addresses an OVER voltage problem I thought this would be a good starting point to ask for help. Any assistance or advice you can offer is most appreciated.

Cheers, Michael

[barryh]

Welcome Michael.

What the voltage regulator should do is control the current to the rotor by chopping it on and off rapidly once the voltage set point is reached such that the average rotor current is reduced and the desired voltage output is maintained. With full current to the rotor, the charging voltage will always rise to 17 volts or more when the engine is revved. If you are seeing 17 volts the only logical conclusion you can come to is that the regulator current isn't being reduced, so either the set point is wrong, if it's an adjustable regulator, or the regulator is faulty. As mentioned earlier in the thread, when fault finding is difficult, you can't make any assumptions, particularly that a new part can't be faulty or indeed that several new parts can't be faulty. The fault does sound temperature related which suggests that the regulator is the problem. Substituting a known good regulator would be a next step. If you tell us where you are, and there is another member nearby, perhaps they could help with that.

[Rob Frankham]

Hi,

You can say, without much doubt that the voltage regulator isn't working. This can really mean only one of two things (a) the regulator is defective or (b) the connections are wrong.

Leaving aside the possibility of a second defective regulator the most likely cause is that the D- wire isn't connecting to ground. This wire is a little unusual in that it grounds to the spade terminal on the left hand (looking from the front) brush connector on the alternator itself. If the ground wire isn't - well - grounding then the regulator won't work and the output of the alternator will always be at max.

This and a dodgy regulator are about the only two possibilities that will cause the output to go high. I would suggest that you double check that connection and, if that doesn't do the job, try a third regulator.

BTW, were you aware that it is pretty much essential to disconnect the battery when removing or replacing the engine front cover. Failing to do so can easily lead to a short that will play havoc with the diode board or... possibly... the regulator.

Rob

[CafeR65]

Thank you both Barry and Rob for your respective answers, I was worried if I wouldn't get a response at all digging up such an old thread.

I understand/agree with your logic but unfortunately I don't have another regulator available for further troubleshooting at this time, so is there another way I can prove that the VR is at fault without a substitute VR?

Perhaps if I disconnect the VR plug or the DF terminal whilst the engine is running and see the voltage drop? Also just a thought; even though my D- terminal measures less than 1 ohm to ground maybe I should measure this again while the engine is hot to see if it is going high resistance?

I'll try both of these things this morning and see how it goes, really hoping to find a smoking gun here that gives me the confidence to cough up for a third VR...

Btw i'm in Brisbane Australia which I suspect is the opposite side of the world to most of the members here! Either way I am gratefull for the responses and will be sure to report back with any findings.

Michael

[Kurt in S.A.]

There are general voltage regulators that can be purchased for testing...it's a "simple" 12v regulator. Check this page for some common substitutes:

https://ibmwr.org/index.php/bmw-parts-substitutes/

Kurt

[CafeR65]

Thanks Kurt.

Just a small update; after nipping up all the electrical related nut's and bolts around the alternator, brush block and diode board and also re-tensioning the tangs on all the regulator spade terminals to make sure they are gripping tight I went for a test ride and the problem seems to have improved, sort of - this time I had to ride longer, further and at higher RPM before the voltage finally spiked up to 17 again. I stopped the bike almost imediately and measured D- to ground at the brush block (i'm was riding with cover off) and it was still less than 1 ohm so I don't think this is the issue. I'm now wondering if the brown wire between the VR and brush block could be intermittently going open circuit with high vibration or heat or both? Also one thing I still havn't tried is removing the DF terminal at the brush block with the engine running, maybe I should do this just to prove that the alternator output voltage is not somehow running away on it's own accord?

Anyhow I'll continue trying anything I can think of until i've exhausted all options and am forced to replace the VR (again).

[gspd]

I don't know if this will help but I recall ripping my hair out (I had hair back then) chasing down a similar intermittent overcharging issue about a hunnerd years ago.
It turns out that the regulator wires had been pinched/damaged where they go into the engine and were making intermittent contact with each other and therefore by-passing the regulator intermittently. I'd check the 3 regulator wires (blue, black, brown) from end to end before proceeding.