Could an inline fuse work to stop my longterm issue of headlight blowouts? Regulator replacement did not cure it. No issues found in wires. If I put a fuse on each of the low and high beam hot wires, might that work? If so, what amp rating for each wire going to separate 35 watt filaments in the 12 volt system?
A voltage regulator is a better solution.
With a fuse you'd have to keep replacing it every time it blew out.
P = I*V, so a 35W filament draws just under 3A on a 12V system.
Your voltage regulators brown terminal out isn't a ground but a voltage dump. It's grounded too close to headlights or another true ground .
I have used a nut and bolt and wrapped the out dump wire around it so if there are any spikes the bolt will be magnetized softening the spike before it grounds. I have mine on the tank which is isolated from ground.
Then again it's an old a3 so it's a short. The wiring is old and the solder points on switches go the rear has a flaw where it goes through the fender and body anywhere could cause the headlight to pop at WOT.
"Ground" is just another wire, it's nothing magical.
The voltage regulator needs a path back to both sides of the lighting coil, and on many bikes one side of that coil is connected to the frame "ground." Similarly on many bikes on side of the lighting circuit is connected to the frame "ground."
This is done to reduce cost. Wiring is expensive, and the frame is a big hunk of metal so why not use it (you do more or less have to use it on the ignition circuit, since the spark plug's return is through the cylinder head)
I don't know what you mean by "voltage dump." If you're worried about voltage spikes you can use a TVS (transient voltage suppression) diode, but given the very low frequency of moped power I strongly doubt that one is necessary.
Great advise on your problem..just one thing to add...are you sure it's not vibration causing the light to fail ?....
The regulators on points models is an AC system.
The magical"ground" is the overage control. It doesn't need to be connected for the bike to run.
Not a electro engineer just owned Tomos' for 2 decades.
Good advice and apologies, it’s an A35 Targa LX not A3 engine. Will check for dry solder joints as that has been an issue I’ve seen on other circuits this old. Will also check grounds but does anyone know where the brown wire from regulator actually attaches to the frame? I have heard something supporting what Slew said about getting the ground/voltage dump connection further from the draw of the headlight. Will give that a try too. I don’t think it’s vibration, this bike is less buzzy than my other Tomos. TVS sounds interesting but is like the fuse idea which I’m more familiar with.
Brian's correct, there is no difference between the ground and "voltage dump" point. They can share continuity, as they are meant to do. This is, by design, a shunt regulator. When a high voltage is seen across the circuit, it shunts to ground to protect the equipment.
Sure, you can pull that ground and you will still have lights, but the regulator will not function as designed.
My guess is that despite your claim that the wiring is fine, it's most likely a short somewhere in the aging harness, which is either shorting the bulb, or more likely: introducing a second V input into the circuit.
Either way, some time with a DMM will sort out the majority of your issues. I would not suggest wasting the time isolating the shunt ground from the regulator.
> ♣Slew Foot♣ Wrote:
> -------------------------------------------------------
> The regulators on points models is an AC system.
>
> The magical"ground" is the overage control. It doesn't need to be
> connected for the bike to run.
>
> Not a electro engineer just owned Tomos' for 2 decades.
We have a number of EEs here, including me.
If you want the regulator to do anything, it needs a path back to the lighting coil (in this case via the frame "ground"). Dillon's explanation is dead on.
> Ned Renner Wrote:
> -------------------------------------------------------
> does anyone know where the brown wire from regulator actually attaches to the
> frame?
Anywhere you can get a low resistance path back to the coil. Make sure there's no paint or grime in between the regulator and the bare metal of the frame.
> I have heard something supporting what Slew said about getting the
> ground/voltage dump connection further from the draw of the headlight.
That won't make a meaningful difference in this case.
Thanks. Will recheck wires and focus on insuring that the regulator is grounded.
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