Voltage Drop - Electrical Issues

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Jun 20, 2007
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'71 Commando 750
Boyer mark3 ignition
Tympanium Regulator/Rectifier

I've been having problems for several months starting my bike. Kickback and dozens of kicks to get it started...sometimes giving up because it won't start.

I have a SLA battery (1 year old) and a Battery Tender to use as needed. Seems my battery won't hold a charge very well. I started hooking up a multimeter up to see the charge. Noticing that sometimes when it's fully charged, turning the key (no real big drop in voltage), and kicking it, it will start first or second kick..no kickback.

BUT, most of the time now, once I turn the key, the voltage drops immediately to under 10 or 9 volts. I know then, it's no use trying to kick it as I'll break my foot and basically won't get it started.

When it was starting (hasn't in a long time now), I could ride a bit, and then eventually it'd start sputtering and dying on me. Especially when I turned the headlamp on...basically slowing down or being at idle it would cut out.

Regardless, the situation now:
Turning the key on drops the voltage. Headlamp doesn't even come on. Very faint pilot light is on. If I fiddle with the dipswitch on the left handle where the highbeams, etc. are, I can get it to light up (bright). Of course, doing that the voltage drops even more, like around 8 or even 7. Flipping the switch up or down doesn't do anything, but pushing/holding on it puts on the brights. Also the high-beam flash button works. I'm thinking the push on the dipswitch is just activating how that button works. So probably nothing worth noting there.

I noticed the red light (warning light assimilator, right?) is not on when I turn the key either. I did the test from my manual to pull the brown/white wire from it and touch it to earth. It lights up. Which the manual suggests MAYBE an alternator issue (or something else?). I haven't tested it yet.

Here's the (not-so) funny thing. A while back, when my friend basically rebuilt most other (non-electrical) aspects on my bike, he lost the key to the ignition. Before I got a new one, in his haste he hot-wired it because he was very excited to see how well the bike ran. He rode it a little bit, and remembers that the regulator/rectifier got REALLY hot. At the time, we didn't even know what the unit was. But now, understanding what it does, it starts to make sense in relation to my problems.

So the questions:
1) Do the symptoms sound like maybe it's just a fried regulator/rectifier? And if so, how can we test?

2) Do the symptoms sound like something common/different?

3) Alternator. Should we go thru the trouble of testing it? And/or would one problem (regulator/rectifier) also cause another problem (alternator) or visa versa?

Our first instinct before thinking more on this, was grounding out wires. I probably SHOULD get a new wiring harness anyways. But, I've done the lazy-man's testing... with the multimeter on the battery and ON, I wiggle wires all over the bike, to see if the Voltage moves up or down (suggesting something loose or grounding). But it doesn't. (just the initial drop in power when turning the key on). So...

4) Does it sound like something other than grounding wires, whereby I can worry about my wiring later?

Utlimately, both of us still learning as we go about the Norton, I'm wondering if just the basics of what I've told you sounds like it points to something specific/common.

Several posts have sounded CLOSE to my issue. L.A.B. had some other posts that sounded intriguing. Love to get his take on this. :wink:

Thanks..
Rich
 

L.A.B.

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rich1000 said:
I've been having problems for several months starting my bike. Kickback and dozens of kicks to get it started...sometimes giving up because it won't start.

The kickbacks being a classic symptom of low voltage at the Boyer ignition box, and, as you have described the voltage appears to drop rapidly at times when the ignition is switched on, so it would seem to be either a faulty or failing battery (it could have been damaged if the charging system has blown -more on that later) or a heavy power drain possibly from a partial short circuit?

rich1000 said:
I have a SLA battery (1 year old) and a Battery Tender to use as needed. Seems my battery won't hold a charge very well. I started hooking up a multimeter up to see the charge. Noticing that sometimes when it's fully charged, turning the key (no real big drop in voltage), and kicking it, it will start first or second kick..no kickback.

So does the battery hold a charge when disconnected from the bike?
And if you then connect a headlamp or brake light bulb to the battery terminals does the bulb stay bright? I would expect a fully charged battery to keep the bulb reasonably bright for at least an hour or so?
If it will then I would think that the battery was OK, and would expect the problem to be elsewhere? Electrical fault finding is more a process of logical elimination rather than random guesswork, so once the battery is considered OK (and eliminated) then you can move on from there.

You said it is an SLA battery, but which type/size? And what is its Amp-hour rating?


rich1000 said:
When it was starting (hasn't in a long time now), I could ride a bit, and then eventually it'd start sputtering and dying on me. Especially when I turned the headlamp on...basically slowing down or being at idle it would cut out.

Which would seem to show that the charging system isn't working (for whatever reason?) or the battery is not holding a charge?

rich1000 said:
Turning the key on drops the voltage. Headlamp doesn't even come on. Very faint pilot light is on. If I fiddle with the dipswitch on the left handle where the highbeams, etc. are, I can get it to light up (bright). Of course, doing that the voltage drops even more, like around 8 or even 7. Flipping the switch up or down doesn't do anything, but pushing/holding on it puts on the brights.

There could be a fault somewhere in the switch unit, or switch circuit wiring and this could be no more than a dirty switch contact, or something inside could be broken leading to a partial short circuit? That could be one reason for the rapidly discharging battery? Although I would expect you might have had fuse blowing problems?
Are you using the correct type British 30mm fuse (35A *blow* rating) or if you are using a different type of fuse (blade type etc.?) then 15A or 20A *continuous* type?

rich1000 said:
I noticed the red light (warning light assimilator, right?) is not on when I turn the key either. I did the test from my manual to pull the brown/white wire from it and touch it to earth. It lights up. Which the manual suggests MAYBE an alternator issue (or something else?). I haven't tested it yet.

The 'silver can' type assimilators can be unreliable, and can cause charging problems if they go wrong, which could also damage the original rectifier apparently, I do not know if a faulty assimilator would damage a Tympanium unit or not-maybe?
Try disconnecting the assimilator completely and see if it makes a difference, although if the damage has already been done then it's probably too late?

rich1000 said:
Here's the (not-so) funny thing. A while back, when my friend basically rebuilt most other (non-electrical) aspects on my bike, he lost the key to the ignition. Before I got a new one, in his haste he hot-wired it because he was very excited to see how well the bike ran. He rode it a little bit, and remembers that the regulator/rectifier got REALLY hot. At the time, we didn't even know what the unit was. But now, understanding what it does, it starts to make sense in relation to my problems.

Without knowing what your friend did to hot-wire the ignition it is difficult to say if this caused the problem or not, but I would suspect that a very hot Reg/Rec is not a good sign, so it may have blown? That may also account for the high current drain from the battery if it has blown but I cannot be sure about that?

rich1000 said:
Do the symptoms sound like maybe it's just a fried regulator/rectifier? And if so, how can we test?

Basic test:
With the battery fully charged, connect the voltmeter to the battery terminals, then start the engine (if you can?) the voltage should rise from battery voltage to around 13.5-14.5V when the engine is revved with the lights off? If the voltage does not rise, or if it rises above that level (unlikely I think, in this case?) then there is a good chance the Reg/Rec is faulty, the only other options would be a faulty alternator stator or a wiring fault (stator to Tympanium unit or Tympanium unit to battery wire or earth/ground connection? If it all points to the Reg/Rec unit being faulty then somebody like A O Services could check it if you sent it to them (but I suspect there is somewhere closer to you?) Or you could buy a new unit?

rich1000 said:
Does it sound like something other than grounding wires, whereby I can worry about my wiring later?

Unfortunately it isn't possible (or wise) to rule anything out at this stage? As it could just be a simple wiring or connection problem? Or a faulty (ignition/kill/lights) switch?

I would suggest (once you have established that the battery is OK) that you disconnect as much of the wiring as possible including the charging components so that only the ignition system is connected and see what difference it makes to the voltage drop problem (even by-passing the ignition and kill switches if necessary).
If you then start to get consistently better voltage results you will at least have removed the high current drain problem, so you would need to work back from there by re-connecting the wiring a circuit at a time until the fault re-occurs.

Info:
http://www.oldbritts.com/17_01233.html
 
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Great thoughts. Okay, so I began with the battery, which seems like a no-brainer, but certainly I should have already looked into this. I got it tested and it's faulty. It was a Westco 12V, 9A SLA.

So, before I move on to some of your other thoughts, I'll go with a new battery and see what happens then.

I've never been able to get a proper recommendation on an SLA battery for the 750 Commando. So, any thoughts on brand/model I should get? I just assume an SLA should be the way to go because it's "one less thing to worry about on the Norton."

Thanks.. i'll report back once I get the new battery in there.

rich
 
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I would be buying a new battery for sure. Another AGM is best but watch those Battery Tenders. An AGM battery needs high volts and low amps for short times like four hrs max. All of the battery" Tenders" I have tested are just over 12 volts when they need to be 13-14 and they are near an AMP when the need is about a half of one. Everyone should know what the charging system is doing at certain study RPM's With a volt meter and a hand held AMP gage you might find that your bike is treating the battery the same way as the Tender, Low volts too many AMP's many find that they have to run with the lights on.
 
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Makes sense.. thanks for the tip.

Can you provide some suggestions on the following?

My previous battery that is seemingly bad now, was a Westco 12V9-B (YTX9-BS) - 12V, 9A, 120 CCA. Not sure where I got that recommendation, and if it was ok?

I've seen this one recommended for the Commando 750: Westco 12V14L-B (YB14L-A2) - 12V, 14A, 190 CCA.

Which one would you suggest, or would both fit your recommendation?
--

Second, the battery tender I'm using is the Deltran Battery Tender Jr: 12V, 750mA:
http://www.batterystuff.com/battery-cha ... -0123.html

Any experience with that one, or anything to be concerned about there?


Again, I'm going to go ahead and get a new battery and see how it reacts, and report back. Hopefully that's all it is, but I'm guessing I won't be done tracing the next issue once the battery is figured out of the equation.

Thanks..
 

L.A.B.

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rich1000 said:
I've seen this one recommended for the Commando 750: Westco 12V14L-B (YB14L-A2) - 12V, 14A, 190 CCA.

Which one would you suggest, or would both fit your recommendation?


Some 'recommended' batteries will be for the electric start 850 MkIII model, so a modern type battery of approximately 9AH should be quite adequate for a non-electric start Commando, the CCA (cold cranking amps) rating really being irrelevant for non-electric start models.

From what you have now said, I would expect that fitting a new battery could solve all the problems of light dimming and bad starting, but I would also recommend that the charging system be checked and monitored, as a fault in the charging system could have been the reason for the premature battery failure, if for instance the voltage is exceeding 15V. I did originally say that overcharging was unlikely to be a problem, but as the battery has now been found to be faulty which could be the result of it being overcharged, then that cannot be eliminated.

I would still be a little concerned about the regulator unit: "getting REALLY hot" as you said previously, I don't know how hot those Tympanium units are supposed to get, as they are not common in the UK, perhaps others here who have had experience of them could give their observations regarding how hot these units normally get? If there was any doubt about the regulator functioning correctly then (personally) I would just replace it.

Modern AGM type batteries should hold their charge for considerably longer than standard type lead-acid batteries, and are not damaged by this as a normal lead-acid type could be.
My own Westco AGM type electric start battery was left over the winter period without being given any top-up charging, and it fired the bike up easily on the starter afterwards, and I did the same with the previous Odyssey battery with the same result.
 

Ron L

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Unlike the Podtronics or Sparx, Tympanium regulator/rectifiers have no heat sink, so should be mounted on a plate of aluminum or in the air stream to remove heat. I have noted that when they are not mounted in this way they can develop a fair amount of heat. However, I have yet to see one fail because of this. YMMV!
 
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Hi all - Even with a poor battery there should be no voltage drop when you turn the key on.

I had a voltage drop as well & traced the the problem to the brake light switch which had moved & therefore the light was always ON, (causing the voltage drop).

You will need to find the source of your power draw......... Was the bike always doing this or is this a more recient development?
 
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Yeah, it seems weird that even if the battery is bad, that it would just show a big drop in power as soon as the key is turned. And when it first started happening, it only happened sometimes. Recently it is always happening. We'll see when I get the new battery though.

As for the regulator/rectifier, my friend only noticed the heat when he hotwired it for a few rides (he was a little ancy before I had gotten a new ignition lock). That just keeps sticking out of my mind: hotwire + super hot reg/rect = these current issues. Where it's mounted now (on frame, under seat), I believe is the suggested place for it. And as you said, normal heat issues probably wouldn't make it fail.

Once I get the new battery, I'll test the reg/rect per the suggestion of L.A.B. earlier. They're pretty inexpensive, so if I suspect that after the battery is replaced (if I can get the bike to start), I'll just get a new one.

Certainly wiring issues sticks out as a possible issue, but wanted to start with some suspected possibilities: i.e. battery, reg/rect, alternator

Last dumb question, what type of fuse should i have on it? 20A, 25A, 35A? Does that really matter much?

Thanks
rich
 

L.A.B.

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rich1000 said:
what type of fuse should i have on it? 20A, 25A, 35A? Does that really matter much?


Yes it does matter. The original would have been a single 35A 32mm British glass fuse.

British fuses of this type are referred to, and marked with the blow rating, unlike many other fuse types which show the continuous rating, so if you intend to use a different type of fuse like the automotive blade type or even a 25mm glass fuse then these are marked with the fuse continuous rating which is approximately half the blow rating, so an equivalent fuse to a British 35A glass fuse would be one of around 17.5A.
The nearest blade type equivalent would be either a 15A (Lt. Blue) or 20A (Yellow).
 
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Going off what L.A.B. said earlier, i second the notion of overcharging being what ruined the battery, and i think a bad reg/rec is what probably caused it. The regulator part of it's supposed to keep the voltage going to the battery at a level that won't overcharge it, a maximum of about 14.5 - 15V i think. If the reg/rec is toasted it could have the effect of a constant closed circuit, meaning the alternator is basically supplying voltage directly and unrestricted to the battery, whether it's 8V or 18V. Overheating also suggests that since it probably gets hot from outrageous amounts of current flowing through it at high revs when alternator output is high.

Personally, i wouldn't run a new battery in it until you put a new reg/rec on there first, or at least test to make sure the old one's working properly. If it's not regulating the alternator voltage to the battery properly, it's just going to end up overcharging and frying your new battery.
 
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Understood... thanks. I believe it's a combination of the two as well.
So, how can I test the reg/rect without using the new battery on it? According to L.A.B.'s method, I would need to get the bike started and see what the volts move to (if anything) when started and revving it.

Although we suspect it's the reg/rect, I want to get some proof before paying another $50 for a new one. And I agree as well that I probably shouldn't mess with the new battery if the scenario you're talking about is happening.

thanks
Rich
 
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Not sure about which wires to hook up to exactly since i don't have a Tympanium (or even an assembled Commando at this point... :? ), but i think what you want to do is hook up your voltmeter to whatever the output wires are coming out of the reg/rec, whichever ones end up going to the battery. Probably have to start the bike with a Battery Tender hooked up to the old battery at this point too since it won't have enough juice by itself. Might not even need the battery, just the BT, but i'm not really sure.
Once it's running, start reving up and measure the Tymp output. Typical alternators put out 14-15V when running (at least modern ones do), so if it stays above 15V at any point there's probably a problem. Even 14.8-15V is pushing it a little bit in my opinion. Obviously pay special attention to the sustained output around your typical cruising RPM.
According to the Old Britts site Tympaniums also have 2 year warranties, in case you just got it recently...
 

L.A.B.

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Testing using the new battery for a few minutes should not do it any harm, and the voltage will be monitored during that period, so any under or over charging should be noticed quickly enough. Connecting the meter across the battery terminals for the test should be enough.
 
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Pardon my ignorance, but isn't the function of the Zener diode to eliminate overcharging by diverting extra current to the aluminium 'Z' plate thus using it as a heat sink, or am I totally off track.

Mike.
 

L.A.B.

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There is no Zener fitted in this case, as the function of both rectifier and regulator is done by the Tympanium unit.
 
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Mike, you're right - the zener uses the Z plate as the ground since it passes excess current to the plate. That current does create heat though, hence the zener being mounted to a big exposed hunk of metal to dissipate the heat.

But like Les said, using the Tymp does away with the zener altogether.
 
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