I'm a little dim, are you?

[davem222]

Hey guys,
SO this may be a controversial topic, but I just got my 79 2F running great (mostly thanks to all of you guys) with a Pamco, Hugh's PMA and a Sparx Capacitor. I know everyone talks about the headlight dimming at low idle, and I definitely have that. My questions are this: 1) does it matter? Should I be concerned longterm for the health of the bike/circuitry or is it no big deal? and 2) How long will it take at idle, if I don't rev it at all, to just go dark, and if it does, should I care (mechanics-wise. Obviously I should care if it's night time and I can't see lol). Thanks

Dave

 

[scabber]

How dim is dim? On the stock system It dims but you can still see with it. The PMA shound put out more volts at idle or why buy it. I set my idle at 1500RPM. with the stock system. Check your battery voltage at idle 1200 Rpm normal. I don't have the PMA system so just guessing it should put out more volts. The wires no harm done.

 

[pamcopete]

Hey guys,
SO this may be a controversial topic, but I just got my 79 2F running great (mostly thanks to all of you guys) with a Pamco, Hugh's PMA and a Sparx Capacitor. I know everyone talks about the headlight dimming at low idle, and I definitely have that. My questions are this: 1) does it matter? Should I be concerned longterm for the health of the bike/circuitry or is it no big deal? and 2) How long will it take at idle, if I don't rev it at all, to just go dark, and if it does, should I care (mechanics-wise. Obviously I should care if it's night time and I can't see lol). Thanks

Dave

It would help if you installed a 35 Watt headlight and an LED tail light. When stopped at a light with brakes on, the brake light burns 27 Watts and the tail light 8 Watts. An LED brake light burns less than a Watt.

However, the downside to this remedy is that the PMA regulator is a shunt type that works by shunting excess current to ground and converting the current to heat. If you have a higher wattage headlight, tail light etc., then there is less excess current for the regulator to burn, so you should read the instructions that came with the PMA and regulator as well as consult with the source to find out what is the best combination of lights to use without frying the regulator.

 

[retiredgentleman]

It would help if you installed a 35 Watt headlight and an LED tail light. When stopped at a light with brakes on, the brake light burns 27 Watts and the tail light 8 Watts. An LED brake light burns less than a Watt.

However, the downside to this remedy is that the PMA regulator is a shunt type that works by shunting excess current to ground and converting the current to heat. If you have a higher wattage headlight, tail light etc., then there is less excess current for the regulator to burn, so you should read the instructions that came with the PMA and regulator as well as consult with the source to find out what is the best combination of lights to use without frying the regulator.

Some very good points there Pete. With the PMA/regulator combo, you are always trying to balance load to the supply. However the suppy cannot be controlled, since it generates 100% as much as the rpm allows. A PMA is a similar to driving a car with one foot fully down on the accelerator, and the other foot pushing on the brake to slow the car down.

The stock alternators work quite well, because the regulator controls the rotor current/strength of the magnetic field. It has the ability to reduce the magnetic field as the rpm increases (but gives full magnetic field at engine idle). It still is a benefit to be kind to your alternator by using a 40 watt headlight and an LED tail/brake light. 1200 rpm works just fine with the stock alternator.

 

[pamcopete]

RG,

Yes, the engineers for OEM PMA's really try to balance the load to the PMA output. My '73 CB450 even has a set of contacts in the headlight switch that disconnects two of the three stator windings when the headlight is off to avoid frying the regulator.

 

[osteoderm]

Excellent thread. I puzzled over this for awhile when deciding how to wire my lights, and came up with what I believe is a reasonable compromise.

I have 6 lights that are on with the keyswitch: 2 LED taillights, two LED front marker lights, 1 LED plate light, and a 6W incandescent pilot bulb inside the headlight housing (visible in my avatar). This way, there's always some load besides the ignition. The headlight is a 60W/55W halogen, switched separately. Since the bike didn't have an always-on headlight as stock (1974), I didn't get too worried about wiring it as such.

For starting and cold idling, I can leave the headlight off. I habitually run with the headlight on, but if I forget, the 4 markers and pilot light keep me amply visible. This way, I have some control of the load on the charging system. Useful? Maybe not, but at least I have options.

 

[retiredgentleman]

RG,

Yes, the engineers for OEM PMA's really try to balance the load to the PMA output. My '73 CB450 even has a set of contacts in the headlight switch that disconnects two of the three stator windings when the headlight is off to avoid frying the regulator.

That is interesting. I have never heard of switching such as that. So they are switching from a 3 phase alternator to a single phase alternator when the headlight is turned off..................those Japanese engineers are so clever.

 

[pamcopete]

That is interesting. I have never heard of switching such as that. So they are switching from a 3 phase alternator to a single phase alternator when the headlight is turned off..................those Japanese engineers are so clever.

Well, except that they did not think of what happens if your headlight burns out during the day and you do not notice it and continue to run with the headlight switch on with all three phases working. I think it's because they were in a pre mandatory headlight on in daylight era, so you would not have your headlight on during the day and you would notice it at night. In any event, you are supposed to turn off the headlight if it burns out (Huh? ) The interesting part is that the headlight consumes 2/3 of the available PMA output.

 

[XSLeo]

#1 Not really, as soon as you bump it up off idle the voltage raises enough to get full brightness on the headlight.
#2 With the cap it will run forever at idle and never go dark. It will just stay at the dim level it is at. A battery of about stock size or a bit smaller, the dimming won't be quite as noticable. It may get dimmer after a few hours at idle, but not much.
Leo

 

[davem222]

Leo, thanks for the clarity. Everyone else, amazing info. I feel like I just learned so much that my brain is bleeding. The good kind of brain bleeding though.

Dave

 

[Rexxis]

Awesome thread!

 

[Purplezinger]

Some very good points there Pete. With the PMA/regulator combo, you are always trying to balance load to the supply. However the suppy cannot be controlled, since it generates 100% as much as the rpm allows. A PMA is a similar to driving a car with one foot fully down on the accelerator, and the other foot pushing on the brake to slow the car down.

The stock alternators work quite well, because the regulator controls the rotor current/strength of the magnetic field. It has the ability to reduce the magnetic field as the rpm increases (but gives full magnetic field at engine idle). It still is a benefit to be kind to your alternator by using a 40 watt headlight and an LED tail/brake light. 1200 rpm works just fine with the stock alternator.

FYI 40 watt H4 bulbs are rare (at least I've not found them locally). However a Internet search turned up this source: http://store.candlepower.com/4512vh4hebu.html

 

[XSLeo]

I was just browsing the Candlepower site. They list a 35/35 watt bulb too.
I have one of thier replacement motorcycle lens reflector units in my 75. I like the beam of light it throws. It shines less up and down, as in at your feet and in the tree tops, and projects more light out front where you need it.
On low beam it has a spot of light high and to the right. This helps you see things along the side of the road better, like animals and people.
I'm using a 55/65 watt bulb from Harbor Freight. About $7. It is very white, just a slight blue tint.
I also run LED tail/brake lights and turnsignals. Even with the LED's it's a good idea to make sure all the connections in the lighting circuits are clean and tight.
Leo