headlight issues on 300 -12

[Peppito]

Hi!

I just bought a gasgas 300 -12.
It was in bad shape, but after some hours in the garage it?s starting to look like a bike again

But if got some problem with the head and tail light.
The previous owner has installed a rectifier and battery, i have like 14 volts dc from the battery, thats all good.

But att the headlight i have AC. If i start the bike the head and tail light has around 12 volts. But after like 1 minut if i rev the bike it decrease to around 8, and the lights dosen?t shine so bright anymore And after like 2 minute i have around 6 volt in the "front".

Anyone have any idea what i should do?

Thanks!

[Neil E.]

First thing is to check the headlight bulb wattage, should be no more than 35W if it has a stock bulb.

Second thing is to figure out if the battery is good. A worn out battery may charge up to the required voltage, but does not have any capacity to maintain it's output.

Charge the battery off the bike, then connect a tail light bulb to it using the brake filament. It should be able to keep the light bright for quite a while. If the light output is good for 20 minutes, the battery should be OK.

Charge the battery again and test your headlight. If it still has a big voltage drop, you will need to test all the connections and grounds. Run temporary wires from the battery directly to your headlight bulb. If there is only slight voltage drop then for sure you have an issue like broken strands near the headstock, etc.

[Neil E.]

My previous answer was based on your headlight operating on DC voltage.

You may have to trace wires and make a diagram to determine what the previous owner modified. Your headlight might be connected to AC, but I don't know what would create that kind of voltage drop as the revs are increased. Normally you get more output at higher revs. When an AC voltage regulator fails, your bulbs burn out from excess voltage.

What is the physical condition of the stator? Corrosion will reduce output.

[Peppito]

Thanks for your answer Neil.

The battery seems fine, and the regulator for the battery seems to work good also. Gonna try with a led light tomorrow on the DC side. I think i only used the battery for a led light that i haven?t got yet. So nothing is connected to battery.

You have right i have AC at the headlight. I gonna measure the voltage tomorrow ( can?t start the bike, because it?s middle of the night in sweden directly on the yellow wire from the stator.
I haven't looked at the stator yet, will do tomorrow.
Here in sweden the enduro people always talking about "solder the stator" if i understand it correctly the 2 coils will work as one. Could this have something to do with my problem?

Thanks again

[Neil E.]

Don't "solder the stator" unless you're repairing a broken connection. The yellow (and ground) provides AC power for lighting. This is regulated. The white wire (and ground) provides slightly higher AC voltage to be rectified into DC for battery charging.

If you measure voltage at the yellow wire, it should hold steady around 12 to 13 VAC as the revs increase. If the regulator is unhooked, you will see it increase dramatically.

A bad connection in the system will act like high resistance and possibly heat up causing reduced current flow and a resultant voltage drop. You have some investigation to do. Check all connections and grounds.

[Peppito]

Hi again!

This morning i tested this: Battery out, but the aftermarket rectifier still in with the white cable to + and - grounded in the chassi.
Then i measure the yellow cable direct from the stator. I had only like 1,5 volts AC. Strange, so then i removed the ground cable that goes to the rectifier. Then i hade like 22-30 volts, plugged in the original regulator and every things works like a charm! Steady between 12-13 volt.

So thats good.
But i wonder why i can?t use both system? It?s something wrong with the ground? Or is the aftermarket rectifier/regulator broken?
But i think it ok, when a measure the DC system on the battery i got a charging around 14 volts that seems ok to me.
I really want to use both system.

[Peppito]

Hmm! I was sitting with a cup of coffee and thinking my brain outs :=)
The aftermarket rectifier for AC, should that one be grounded? If i just connect that cable to the - at the battery and to the lights? should that work?

[Neil E.]

You can run a mixed system but the output from a fullwave DC rectifier must not be grounded. This is because the stock stator windings are already grounded and the DC rectifier will not work correctly if it's output is grounded.

In review: the single phase stator has three connections. Ground, yellow and white. AC output from yellow to ground, AC output from white to ground.

AC on yellow regulated only, AC on white rectified and regulated for battery charging. AC after rectification becomes DC, connect it directly to your battery.

The only issue is that an estart bike must be done differently because of the starter motor ground. All the discussion so far is based on a standard non-estart machine.

[Peppito]

Great! I think i got the problems solved! Thanks Neil!

[Peppito]

Hi again Neil!

After som more digging in the electrical system on my bike, i assume the other owner has wired the t/t rectifier with no floating ground, but have kept the original rectifier. But that sorted out now i think
But if i want to have ac for my stock headlight and brake light and DC for my helmet and extra headlight, should i ground the t/t rectifier? Because now it?s sits under the plastic battery holder.

Thanks