A year or so ago, I said to a friend of mine, who happens to be a longstanding Yamaha dealer, that my old Norton had an electrical problem. He replied that a Norton WAS an electrical problem. I think that he is correct.

My 1970 Roadster has had a longstanding problem of losing charge, and being totally incapable of running for any time with the headlight on. Almost all of the time that I have been riding it – the last few years, the ammeter on the headlight (it is one of the earlier models that still has this) has had the needle firmly in negative territory; only when I am at highway speeds at about 4000 revs would it waver into positive. As the bike runs Boyer ignition this pretty soon translated into missing and stalling.

In order to resolve that issue I have recently installed a Sparx three phase alternator, and Sparx regulator rectifier. That was not without issue – the system initially did not put out the voltage that it should have. It transpires that the new spark plug leads that I bought and thought were not resisted leads – they are connected to 5000 ohm resister caps as recommended – were resisted leads – I have not tested them but the manufacturer’s helpline advised that they were resisted to about 900 ohms. With those leads on the regulator would only put out a maximum of 12.5 volts, and the ammeter still ranged between about -12 and -4 during most rev ranges. I have now changed the leads to copper leads – with the 5000 ohm caps, and that appears to have cured the problem; the regulator is now putting out 14.1 volts and 3 amps at idle, and 14.69 volts and 12.3 amps at between 3000 and 4000 rpm with the headlight on. The alternator is putting out about 15.5 volts from each of its three phases at idle, raising to over 30 volts at revs. So I am happy with my Sparx system.

However, the ammeter on the headlight still points to negative for most of the time, except when I am on the highway at 4000 rpm; when it fluctuates wildly but appears to hit positive. With the headlight on at say 2000 rpm it will show -12 amps. Is that normal? Or is it an indicator of a problem somewhere in the circuit that is taking all of the power that is being generated by the alternator and regulator? Or is it just what is to be expected to be used through the ignition system – and brake light; and headlight when it is on?

Could it be that the ammeter is defective, and if so, how can I test it? If I did not have the ammeter, as later models don’t, I would not be aware of any potential issue. I am not aware of any issues with the running of the bike – but since curing the spark plug leads issue I haven’t had the opportunity to go for a long run to see if any issues arise if I have the headlight on for a few hours. I am running a new 7ah battery.

How about sticking a real multimeter on it.

The local Harbor Freight has them for about US$3, so they can be had pretty cheaply.

That will tell you more than a 50 year old ammeter.

Frankly, I would do the voltage checks that you appear to have done and then either replace the ammeter with a new one or, preferably, bypass it completely. It sounds as if the output is OK from the alternator so all that's really necessary is to ensure all connections are clean. Remember that ALL elec power runs through the ammeter so any problem there becomes a problem elsewhere.

Cars used to have ammeters too but went to voltmeters because the ammeter itself and/or its connections can affect the entire elec system.

Re the spark plug wires...spark plug wires would not be expected to have any effect at all on output from the charging system. Are you sure that the only thing that was changed that caused the voltage to rise was the spark plug wires?

I would go through the entire elec system, breaking/cleaning/remaking all connections. After breaking them. clean the connections with something like De-Oxit and then coat the terminals with di-electric grease and re-connect them.

MexicoMike wrote:Re the spark plug wires...spark plug wires would not be expected to have any effect at all on output from the charging system. Are you sure that the only thing that was changed that caused the voltage to rise was the spark plug wires?

Insufficient HT resistance causes "overloading" of the Sparx regulator.
Sparx (Tri-Cor England) warn about this:
http://www.tri-corengland.com/acatalog/Alternators.html

**Single & Three phase boxes***
Due to the sensitive nature of both the single and three phase boxes it is VERY important to fit spark plug caps of the 5000ohm resisted type.
Failure to do so will cause overloading.

So too much HT resistance may also cause problems.

I would say that if your Boyer started missing, then there probably is something going on and your ammeter was just telling you about it. If your wiring and switches are original then it wouldn't be wouldn't be much of a stretch. I installed an ammeter on my bike and it oscillated a lot till I rewired the loom, now it's steady. You might have a closed short or bad connection that isn't enough to pop the fuse but it's enough to drain current. What's the rating on the fuse you're using?
The thing to remember about ammeters is that they don't measure the output from the charging system directly, they only show how much current is going into or coming out of the battery. When the battery is topped off, which is almost all the time, the ammeter reads zero. It doesn't matter if it's 2000rpm or redline.

"
Insufficient HT resistance causes "overloading" of the Sparx regulator. "

Interesting! That's the first time I have ever heard of a spark plug wire affecting the output of a charging system. But clearly it is an issue with the Sparx. After reading the response I immediately went to the garage and ran the bike with resistance/non resistance wires, checking the load in both cases and there was no difference at any RPM with the oem Lucas electronic components/Lucas 3 wire alternator (180W as I recall). Wonder why there would be so much effect on the Sparx?

Do you still have the stock capacitor under the seat? I wonder if it is breaking down. As I understand it that results in a high resistance short. Which would only get worse as voltage climbs.
Russ

The thing to remember about ammeters is that they don't measure the output from the charging system directly, they only show how much current is going into or coming out of the battery. When the battery is topped off, which is almost all the time, the ammeter reads zero. It doesn't matter if it's 2000rpm or redline.

Bob - are you able to expand or clarify that? Maybe I'm seeing questions that are not really there, but it is things like this that really show up my ignorance on electrical issues. I understand you to be saying that the ammeter measures output from the battery, as opposed to output from the alternator, which in turn in connected to the battery which is connected to the main circuit. I have wondered whether current from the alternator goes through the whole of the main circuit as well as the battery, but your statement suggests not - that it goes to the battery and the current from the main circuit is generated from the battery. If the battery is topped off ie fully charged -as mine is - brand new and most times hooked up to an intelligent charger - then it reads zero. Therefore when the bike is started and the coils are taking electricity to create sparks, and a light is on, then presumably it is normal for the ammeter to show a drop in available current - ie to hit negative - as some of the current is being used. But if so, then would not the battery put out more current to compensate and bring it back to zero, and if the battery is fully charged would not some of the current that is going to the battery from the alternator effectively be utilised to bring the main circuit back to zero or into positive? That should bring the amperage in the main circuit back to zero almost instantly?

Another thing that I struggle with (probably even more basic than electricity 101) is the difference between, and relationship between volts and amps, and after reading another thread on alternators yesterday, watts, and even ohms - and the relative importance between these measurements. I'm not asking for a deep explanation of this (I can go back to Wikapedia), but when testing the circuit for current with my voltmeter, what measurements should I be checking? Is the amperage that important?

Incidentally, I replaced the loom when I rebuilt the bike, so generally all the connections are good. I have taped over (as opposed to cutting off) the various connectors that I am not using. I think that my various earth points are good, but will recheck them.

Ammeter is not susposed to be wired directly inline with battery, but isolated
by another circuit, Assemulator?, that only allows current to flow in ammeter to show if more or less watts being consumed than produced but Not the total amount of current-amps flowing though system. Volt meter better to monitor which side of equation you're on. Trixie Combat has ammeter just to fill the hole, not wired but still wavers like normal just from engine vibes. Tough task to try to seal one to hold dampening oil w/o messing up the lens. There are small circuit boards available that allow only the excess hi or lo to show up instead of direct wire to battery that loses a few more precious watts, ie: pressure pushing amont of electrons against resistance.

Oh yeah there should not be any effect of ignition system on the charging or regulation as battery should isolate and dampen that small drain of maybe max 5 watt's intermittently. I'd also check the big blue can as mentioned as its a like a small battery too that absorbs spikes of charge and fills in for fast discharge dumps like horn and spark coils and winkers.

Chris T wrote:the ammeter on the headlight still points to negative for most of the time

Hmm, same characteristics as the ammeter on my Triumph TR4A. The generator charges normally but the ammeter isn't sure what to do. I'd chock it up to the age of the ammeter and its inherent inaccuracies.

hobot wrote:Ammeter is not susposed to be wired directly inline with battery, but isolated
by another circuit, Assemulator?, that only allows current to flow in ammeter to show if more or less watts being consumed than produced but Not the total amount of current-amps flowing though system. Volt meter better to monitor which side of equation you're on. Trixie Combat has ammeter just to fill the hole, not wired but still wavers like normal just from engine vibes. Tough task to try to seal one to hold dampening oil w/o messing up the lens. There are small circuit boards available that allow only the excess hi or lo to show up instead of direct wire to battery that loses a few more precious watts, ie: pressure pushing amont of electrons against resistance.

Oh yeah there should not be any effect of ignition system on the charging or regulation as battery should isolate and dampen that small drain of maybe max 5 watt's intermittently. I'd also check the big blue can as mentioned as its a like a small battery too that absorbs spikes of charge and fills in for fast discharge dumps like horn and spark coils and winkers.

With the stock setup all the battery current (except for the horn) DOES pass through the ammeter, so if it goes open charging stops though a 2MC might keep the bike running. It is possible to convert to a shunt ammeter, if the gauge fails the battery still charges and the shunt (which is just a low value precision resistor) can be close to the battery to simplify the wiring. There is a good page on ammeters vs. voltmeters at http://www.egauges.com/ATM_Tips.asp?TipPage=voltmeterammeter.htm I'm using a LED voltage indicator myself and it work well

THEY used to say , throwing a 6 to 8 inch wire across ( wired in ) let the ammeter do its thing , and if it didnt , it did .