Low voltage problem '78 XS650

[krza]

Hey all-

I'm at my wits end with a charging issue with my '78 XS650. Here's the situation:

I have an HHB PMA installed for a few years now, with a small SLA battery and no electric start. Charging system is super simple: just the PMA, SLA, and reg/rec. The issue is that batteries are getting boiled off, which leads me to believe the reg/rec is to fault. I'll replace the battery and the bike will run strong for a while until the battery is cooked and then I have to replace the battery again. I replaced the reg/rec with a new 3 phase hoping that would solve the issue, but it persists. Any ideas? Bad ground maybe? Ground wire too small? My ground seems solid, and it's a 14 gauge wire.

Any help appreciated.

 

[pamcopete]

The battery is receiving too much current when charging from the PMA. The regulator has nothing to do with it. The battery is just too small. The regulator is a voltage regulator, not a current regulator. The PMA puts out its maximum capability current at all times.

Talk to Hugh about possibly disconnecting one of the winding's from the PMA to reduce the current.

 

[krza]

The battery is receiving too much current when charging from the PMA. The regulator has nothing to do with it. The battery is just too small. Talk to Hugh about possibly disconnecting one of the winding's from the PMA to reduce the current.

Thanks for the reply Pete!

Would it just be more reasonable to get a bigger battery? Is there a specific amperage battery I should look for?

Thanks much!

 

[pamcopete]

Thanks for the reply Pete!

Would it just be more reasonable to get a bigger battery? Is there a specific amperage battery I should look for?

Thanks much!

Add up the current that your electrical system uses. Subtract that from the max current from the PMA at 3,000 RPM and higher. The difference is what is available to charge the battery. A 200 Watt PMA produces about 200/14.5 = 13 Amps. Your typical electrical system uses about 10 Amps of that leaving 2 Amps to charge the battery which should be about 10 % of the Amp Hour rating of the battery or about 20 AH. Typically, we bend the rule a little and go with a 14 AH battery with a 200 watt PMA.

Other power management schemes can also be used to allow you to use a smaller battery. The battery only has to be charged if it has lost some of its charge due to things like waiting at the stop light with the headlight on, so turn the headlight off when waiting at the stop light. I have a relay in my '81/H that turns off the headlight when I shift into neutral. You can also install LEDs to reduce the power needed for the brake light. If you can manage to not discharge the battery down to about 11 Volts, then it will not draw its maximum of 10% AH rating so it doesn't matter if the PMA is capable of providing that amount of current or not.

However, there is a trade off with reducing the power consumption and that is that the regulator works by converting excess current into heat, so if you reduce the load, then the regulator may overheat so be sure it is mounted in a place that gets lots of fresh air.

Another method of PMA power management is to increase the load with, say, a higher wattage headlight so there is less current to charge the battery. That would work if you turned off the headlight when stopped.

So, basically you have to balance the electrical load, battery AH capacity and power rating from the PMA. You can't change one without also changing the others.

 

[retiredgentleman]

Hey all-

I'm at my wits end with a charging issue with my '78 XS650. Here's the situation:

I have an HHB PMA installed for a few years now, with a small SLA battery and no electric start. Charging system is super simple: just the PMA, SLA, and reg/rec. The issue is that batteries are getting boiled off, which leads me to believe the reg/rec is to fault. I'll replace the battery and the bike will run strong for a while until the battery is cooked and then I have to replace the battery again. I replaced the reg/rec with a new 3 phase hoping that would solve the issue, but it persists. Any ideas? Bad ground maybe? Ground wire too small? My ground seems solid, and it's a 14 gauge wire.

Any help appreciated.

As Pamcopete has said, the charging system needs to be balanced, when using a PMA.
Using small batteries, small wattage headlights, and LED tail/turn lights, makes for an unbalanced system. I guess they don't tell you that when they sell you a PMA.

The stock type alternator works better on these bikes. Unlike a PMA, the stock alternator can easily reduce voltage/current at the source (alternator output), which prevents boiling the electrolyte. With the stock system, low wattage headlights, and LED lights work very well.

Go back to a stock alternator, with a 14 amp/hr battery, and all your battery troubles will be gone.

 

[krza]

retiredgentleman, I hear you, the stock system on my bike was fried and I picked up the HHB PMA after reading lots of forums and hearing good things.

Pamcopete, I don't know much about DC electrics (obviously), so I have one more question for you before I try a 20ah SLA: someone mentioned somewhere in a forum (I can't find it now) something about adding resistors to the system to help with high amperage charging. Does this sound familiar or did I misunderstand what they were talking about?

Thanks much to everyone participating here. I really appreciate the help.

 

[pamcopete]

krza,

If you are going with a 20AH battery, then you need not concern yourself with overcharging. If you want to use a battery with a smaller AH rating, like less than 10AH, then, yes, you can install a resistor going to the battery, but that resistor has to be bypassed in the other direction with a suitable high current diode so you will get the full current available from the battery when the PMA is not producing enough current to carry the load.

 

[krza]

Ah, I see. Again, appreciate the help here. Running a simple electrical system like mine, the resistor and diode would live where in the charging system?
I'm essentially running this diagram, except with an electronic ignition (one of yours Pamco Pete, that I bought from a friend):
http://cdn.xs650chopper.com/wp-content/uploads/2009/09/noid-chopperwiringdiagram.jpg?2786c5

Thanks, and at this point I feel like I owe you beers!

 

[pamcopete]

You may also have to install a capacitor in the line coming out of the regulator because the battery may not provide the smoothing effect it normally provides. Of course, you could just replace the battery with a capacitor and never mind all this complication.

 

[krza]

Thanks once again Pamcopete.

I took your advice and grabbed two Sparx capacitors from Triumph Spares Scheme here in Portland, and wired them in parallel and pulled the battery from the equation.

I ran it, and at idle it had around 12v at the posts on one of the capacitors at a time, and under load it immediately came up. Around 3k RPMs I saw about 14.7v at the posts. Is this normal, or is that high?

Next time you're in Portland Pamcopete, beers on me all day! I was talking to some other motorcycle guys (pretty savvy dudes), and we were all impressed with your 12v DC knowledge. But maybe we're a bunch of head scratching idiots.

 

[pamcopete]

krza,

14.7 is OK. Was that with the headlight on or off?

 

[krza]

Pete-

That was with the headlight off, but I can do a quick test with lights on and report back.
T H A N K Y O U !

 

[krza]

Hey @pamcopete . I'm resurrecting this thread. I ran this system with a capacitor setup for some years, but I've decided to go back to a battery. I totally forgot about this issue with the 200w stator and the battery size, and I toasted a 14ah Shorai lithium iron battery first, and then a 10ah AGM battery as well. I dug this thread up and remembered your advice. Wondering if it's possible to run a bigger Shorai lithium battery like the LFX19A4-BS12, which is 19ah instead of 14ah. My other way forward might be to disconnect a winding from the stator. Wonder what you think. Thanks!

 

[Rasputin]

Later Norton Commandos ran a 3phase PMA system with two Zenner diodes using the aluminium footrest mounting as a heat sink.
The excess current is shed away as heat above 12.7v.
Something to think about.