PMA / Sparx Headlight Issue

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genericdesignstudio

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1982 xs special with a PMA from Hugh, Pamco ignition, and a small Sparx cap. I have a switch wired in to kill all the lighting when kicking the bike, and an on-off-on switch that controls the headlight (Bates style with h4 55 watt bulb).

The bike fires up first kick, and can handle the lights perfectly fine with the headlight high/low set to off. The "parking light" in the bates style headlight works fine as well. Besides this issue with the headlight it's running golden!

However, when I go to flip on the high or low beam, the bike instantly dies. I've tested the power at the sparx and all the way up to the on-off-on switch and it's at a consistent ~14v when idling around 1500 RPM. I'm positive I have the headlight correctly connected after testing it on a spare battery. Went through and completely re-wired the bike yesterday and double checked that all the connections are solid. Brake light is super bright, etc...

I have an LED taillight, and then a small speedo and tach, but I wouldn't think they would be drawing too much power?

Kind of at a loss, any ideas would be greatly appreciated!
 
Why don't you try using a battery on the bike in place of the capacitor. A battery is a source of power, meaning current and voltage. A capacitor is a source of mainly voltage.........it can't supply any amount of real current.

With cars/trucks and the stock XS650, when the engine rpm is low and therefore a low amount of current available, the battery takes over and supplies the current that the alternator can't at that low rpm.
 
retiredgentleman said:
Why don't you try using a battery on the bike in place of the capacitor. A battery is a source of power, meaning current and voltage. A capacitor is a source of mainly voltage.........it can't supply any amount of real current.

With cars/trucks and the stock XS650, when the engine rpm is low and therefore a low amount of current available, the battery takes over and supplies the current that the alternator can't at that low rpm.
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retiredgentleman thanks for the response!

I would prefer staying away from a battery for the time being, though I understand the argument. I already had an issue with a severed PMA wire that fried a battery and left me stranded quite a ways from home, leading to my decision to go with just the cap. I do also understand the benefit of having both the cap and a small battery, and would consider that option if necessary.

Going to look this evening at disconnecting the lighting for the tach / speedo and see if that makes a difference, next step I think would be to try and track down a 35w bulb or go LED for the headlight as well.
 
On a related note, it would be great if anyone could offer recommendations on how to figure out how many watts my PMA is generating (I know the max is 200, then probably considerably less at idle), and what my accessories/ignition are pulling... Wasn't able to find too much information on the topic.
 
if it dies instantly like that, check for a short to ground in the headlight circuit. some old style headlights have one of the terminals grounded to the headlight housing, so make sure you aren't sending 12v+ on that leg.
 
jamesgs4 said:
if it dies instantly like that, check for a short to ground in the headlight circuit. some old style headlights have one of the terminals grounded to the headlight housing, so make sure you aren't sending 12v+ on that leg.
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That was my first intuition... I think I checked that off though, unplugged the headlight bulb and was getting a solid ~13.5 - 14v when checking the ground and power in the actual plugs for the headlight socket. Also it's a brand-new 5 3/4" bates replica headlight with wiring and grounds that I just did yesterday.
 
genericdesignstudio said:
retiredgentleman thanks for the response!

I would prefer staying away from a battery for the time being, though I understand the argument. I already had an issue with a severed PMA wire that fried a battery and left me stranded quite a ways from home, leading to my decision to go with just the cap. I do also understand the benefit of having both the cap and a small battery, and would consider that option if necessary.

Going to look this evening at disconnecting the lighting for the tach / speedo and see if that makes a difference, next step I think would be to try and track down a 35w bulb or go LED for the headlight as well.
Click to expand...

The fact that you had a PMA problem, which in turn killed your battery, does not reflect negatively on the design of batteries. Lead acid batteries are very rugged, but perhaps you had another less durable type.

No, the lighting on the tach/speedo, is so small, that any normally working alternator can easily handle that small current.

You have the wrong logic when you want to lower the wattage on your bike. Your bike's electrical system needs to be balanced, when you are using a PMA. If you reduce the wattage to far, the regulator will have a harder time to keep the voltage from going too high when you are at highway speeds. The regulator has to consume the extra wattage that the headlight does not use. If your PMA and its regulator are working correctly, you should have no trouble using a 55 watt headlight.

In most cases a stock type (field excited alternator) is a much better design (more versatile ) than a PMA. The stock alternator has no trouble with different wattage headlights, taillights, or ignitions, because its regulator simply reduces or increases the field current as required. The PMA always cranks out full current, proportional to rpm, and hopes that the regulator can handle it.
 
yeah, sounds like a dead short. draw your wiring diagram and post it, might shed some light(pun intended) on the situation.
 
jamesgs4 said:
yeah, sounds like a dead short. draw your wiring diagram and post it, might shed some light(pun intended) on the situation.
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full


Here you go... This is pretty much it minus the "kill" switch on the way to the coils.
 
Switching the headlight on kills the bike, that would lead me to believe in a dead short (as mentioned above)

But, just to make sure your PMA is operating properly, check your voltage at the Capacitor with the bike idling, and then with a bit of throttle (headlight off is ok) and then, with the volt meter hooked up, flip on the headlight on and see if it's killing the voltage immediately, or a slow drain...

Running, you should see 12.9-14.5V at the cap. 200W is max output (we are seeing about 225 on some of our stators, at around 3900 RPM) and of course less at idle. Batteryless and with a Capacitor, its not uncommon for the headlight to blink/flash a little bit, and pull the system down to 10V or so if idling under 1,000 RPM or so.

Also, you can check all of the wattage of your lights, and see if it's overwhelming the system. Headlight is 55/65, taillight is??, Indicator Light is?? etc...

IF you are not seeing good voltage at idle, with the bike off, unplug the regulator and check for resistance between yellow wires on the stator. You should see .7-1.0 Ohms between any and all wires. If not, remove the stator and check all your connections, and the soldered connections between the stator leads and the yellow wires.

Hugh
 
genericdesignstudio said:
Thanks Hugh. I'll check the voltage as described. If it is a dead short, how might I identify that? I've checked for exposed wires multiple times.
Click to expand...

It could be as simple as having the headlight wired wrong, its simple to do, and happens more often than not. If looking at the back of the headlight with 3 terminals, and the headlight it oriented properly (Top of the headlight being furthest away from you) then the left terminal will be the ground (I'll try to take and post a pic) - I myself have even wired them wrong, and they still work, but have a HUGE draw - which of course doesn't work so well on a batteryless system...
 
Thanks again Hugh.

I went through and checked a couple of things off the list last night.

Headlight is wired correctly, left side (green) is connected to ground, high / low to my on-off-on switch. I put the rubber damper for the headlight bucket back into place (it had fallen off at some point), and took a wire brush to my ground for a good scrubbing. I also disconnected the "parking light" to reduce the additional draw there.

One of those things or the combination of all of them solved the issue!

As a side note, voltage at the regulator was proper, as was the resistance between wires for the stator.
 

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