Dimming headlight/gauge back lights??

[ippytattoo]

I was doing a little work on my bike, Deep South XS, and got my headlight wired up tonight. I was running my bike to check and make sure that both the low and high beams were working properly and found something very odd. Both functioned as expected but when I raised the rpms from idle the headlight and gauge back lights dimmed, I would have figured they would have gotten brighter not dimmer. I am sure it has to do with the non-standard battery I am currently testing (a 12v battery from a computer battery back-up) to see if it will work as it is about half the size of a standard battery. I have yet to test the voltage at the battery with higher rpms but at idle (600-700 rpm) I am getting 13.5v. I am running a PMA swap with all new wiring and and new headlight socket. Has anyone out there run into such a situation? If you have what did you find to be the culprit?

 

[ippytattoo]

Well I just did some voltage tests at the battery and I got a drop to 9.0v when the rpms were brought up to 2000 rpm with the test battery. I then hooked up a standard battery and repeated the tests I got 12.6 with ignition swith off, 12.3 with ignition switch on not running, 13.4 at idle and 14.5 at 2000 rpms. Looks like the smaller test battery is a no go, too bad really it would have been a nice choice for the setup I would like to run. Anyone running the ultra small batteries see anything like this?

 

[xjwmx]

It doesn't make any sense unless your computer backup battery has some kind of overvoltage protection built in, that's kicking in to burn off the current and lower the voltage.

 

[jamesgs4]

I had the same problem with a small 0.8ah battery as well. I ended up using a sparx capacitor from lowbrow. Before I switched to a pma, I would get over a years use out of the small battery.

 

[xjwmx]

Ah. If the little battery is being overcharged it may be changing internally so that its internal resistance gets lower which drops the voltage. If that's what's happening, current limit the charging and you should be able to use a little battery fine.

 

[ippytattoo]

I hadn't thought of it changing internally. How would I go about limiting the charging current, add a resistor in the positive from the regulator? I may have to do some further testing and research.

 

[xjwmx]

Yes. By "changing internally" I meant something happening due to it being used out of spec. or being overcharged.

You could find the maximum charging rate for the battery, and also find out how it reacts to pulses if that's what the PMA produces, and also if pulses of some duty cycle affects the current you can use. The R=V/I formula would give you the value of the resistor, where I is the max charging current allowed you found for the battery and V is 14V or whatever, and the wattage you need for the resistor is given by W = VI. If you can use little batteries Hugh has some suggestions I'm sure. I'd wait for him to chime in with his experience with his PMA. The resistor would go just between the output of the PMA and the battery. Everything else would come directly off the battery, as usual.

 

[pamcopete]

1. The output of the regulator would still have to go directly to the load so the alternator can carry the load when it is producing enough current to do so.
2. The resistor would go between the load and the battery.
3. You would then need a suitable diode in parallel with the resistor so that the load is fed from the battery through the diode when the PMA is not producing enough current to carry the load.

However, with the resistor between the output of the PMA and the battery when the PMA is carrying the load, the battery would no longer act as a filter and the voltage would fluctuate , so you would have to install a capacitor directly on the output of the Reg / rect to act as a filter to stabilize the regulator.

 

[rezsst]

i had problems with mine dimming and flickering it turned out to be the brushes. 1980

 

[ippytattoo]

I did some research into current limiting last night and found the circuits to be more complicated than I wanted to tackle and find somewhere for another little box so I got a Sparx capacitor coming. Looks like it is time to alter my wiring just a little. I will be removing my main relay and using my key switch for just the coil/pamco since it is rated at 7A. 7A should be good for the Pamco w/ Ultimate coil from Mikes shouldn't it Pete, I think I read in an earlier post that they draw about 1-1.5A combined.

 

[pamcopete]

i had problems with mine dimming and flickering it turned out to be the brushes. 1980

PMA's do not have brushes.