PMA wattage help

krza

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Hey all.

I'm running a 200W PMA with a MOSFET regulator in my 1975 XS. I can't run a small battery (7ah AGM) because the wattage output from the PMA is too high and I run minimal electrics (35W/55W headlight and LED tail light). I know I'm causing all my own problems here with the electrical system, but looking for a solution anyway.

Can I unplug or unwind a winding on the stator to reduce wattage and run a small battery? I have a pretty small custom battery box and can't run a bigger battery (like a 14ah).

Thanks.
 

Jan_P

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Thinking out loud here Not knowing the setup or wiring . Does the fuse burn.?
Correct Voltage kept in check
But to high Current ... Amperes
A resistor in series that cause a drop One that can stand heat ?
Or a bypass resistor to ground perhaps one that can be regulated with a knob.to Ground ?
 

arcticXS

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Why such a puny headlight? On all my single headlight bikes, I run a 55/60 or 80/100 watt headlight. Surely, your regulator should be able to cope with the excess power, if it is designed for that PMA, and mounted where it gets some cool air flow. Also, your ignition must draw some power, maybe another 50W?

If your PMA is 3-phase, it should be possible to disconnect one leg when power requirement is low. In fact, I have seen this on an OEM setup on an other Japanese 650 parallell twin, namely the Suzuki GR 650 Tempter. I was helping my cousin troubleshoot some charging issues, when I came across this setup.
The GR has a small daytime driving light just below the ordinary headlight, and that comes on automatically when the engine is running. And only 2 of the 3 AC wires from the stator of the PMA to the RR are connected at this stage. Only when the main headlight is switched on, the third leg from the stator becomes connected to the RR. Actually a pretty clever way to prevent the excess power from "cooking" the RR, and simple as well. Just takes a relay controlled by the main light switch.
 

krza

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Why such a puny headlight? On all my single headlight bikes, I run a 55/60 or 80/100 watt headlight. Surely, your regulator should be able to cope with the excess power, if it is designed for that PMA, and mounted where it gets some cool air flow. Also, your ignition must draw some power, maybe another 50W?

If your PMA is 3-phase, it should be possible to disconnect one leg when power requirement is low. In fact, I have seen this on an OEM setup on an other Japanese 650 parallell twin, namely the Suzuki GR 650 Tempter. I was helping my cousin troubleshoot some charging issues, when I came across this setup.
The GR has a small daytime driving light just below the ordinary headlight, and that comes on automatically when the engine is running. And only 2 of the 3 AC wires from the stator of the PMA to the RR are connected at this stage. Only when the main headlight is switched on, the third leg from the stator becomes connected to the RR. Actually a pretty clever way to prevent the excess power from "cooking" the RR, and simple as well. Just takes a relay controlled by the main light switch.

thanks for the reply.

The headlight is just an H4 bulb that is pretty common, I have looked for other higher wattage options but haven’t found anything.

The AGM battery I run seems to be destroyed by the charging system amperage, I’ve gone through a few of them now. The MOSFET handles the voltage but I don’t think it does anything about the excess amperage (if I understand correctly). The way I see it, I don’t need the 3 phase charging system because my amperage draw from the lighting and ignition are so low.

I think my question here is how do I disconnect one winding from the stator to ensure I don’t do damage? Is it just a matter of disconnecting a wire from the stator to the regulator?

Thanks.
 

arcticXS

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Yes, if you have 3 wires from the stator, and the resistance between any two of them is the same, it should be fine to disconnect one.

However, there is no way your charging system can "push" excess current through (into) your battery if the voltage is within the normal range (13.5 to 14.5 V approx.) So if your voltage is as it should, any battery problems is caused by something else. Vibration, heat or just a bad battery.
 
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krza

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Yes, if you have 3 wires from the stator, and the resistance between any two of them is the same, it should be fine to disconnect one.

However, there is no way your charging system can "push" excess current through (into) your battery if the voltage is within the normal range (13.5 to 14.5 V approx.) So if your voltage is as it should, any battery problems is caused by something else. Vibration, heat or just a bad battery.

Gotcha, thanks.

I’m not super knowledgeable about electrics generally, so I could be way off but here’s what I understand based on a thread in this forum, a comment from pamcopete specifically:

“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.”

Based on that, to run a 7ah battery I’d need a .7 amp excess of amperage to charge the battery. Like I mentioned I think, in short, that my electrical system is too low draw, combined with too small a battery, for the amount of excess amperage.
I don’t want to convert back to a stock charging system, and I can’t fit a bigger battery.
 

MacMcMacmac

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What >exactly< is the problem you are having? Most XS owners would love to have a charging system that puts out too much current, 200W is the same as the stock XS charging system output, so you really shouldn't be having any problems. If you are overcharging your battery you have a regulator/rectifier problem, which is not unusual since most of these pma systems ship with garbage regulators. Unhooking one of the phases is a half assed way of trying to solve the issue.

Don't run a higher wattage headlight or your battery will most likely run flat.
 

gggGary

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The problem comes when the regulator is forced to bleed off the excess current/voltage by heating resisters. It's hard on the regulators. High quality (I'll say it) Japanese made regulators can handle it better, but just add a few incandescent light bulbs? Because like Pete sez, PMA output should be fairly closely matched to the normal load.
SHINDENGEN is a popular and well respected brand, watch out for counterfeits...
 

Jim

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but I don’t think it does anything about the excess amperage (if I understand correctly).
Gotcha, thanks.

I’m not super knowledgeable about electrics generally, so I could be way off but here’s what I understand based on a thread in this forum, a comment from pamcopete specifically:

“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.”

Based on that, to run a 7ah battery I’d need a .7 amp excess of amperage to charge the battery. Like I mentioned I think, in short, that my electrical system is too low draw, combined with too small a battery, for the amount of excess amperage.
I don’t want to convert back to a stock charging system, and I can’t fit a bigger battery.
What Pete was alluding to was excess current to charge the battery. Too little and the battery takes forever to charge. Too much can destroy a battery. But this just refers to the max current used to charge it.... and the max is determined by how low the charge is in a battery... the lower the charge, the higher amperage going in. That's not a constant. As the battery comes closer to 100% charge, the lower the amperage will be... eventually going to zero at 100%. Unless your battery was regularly ran down to 50% or so of it's charge, it's highly unlikely overcharging killed it.
 

gggGary

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At the very least get a voltmeter on it, see what kind of voltage you see while riding. You might note that a major PMA supplier offers "up grade" regulators.
 

Jim

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Sorry to disagree Jim. Overcharging=overvoltage Either one will kill a battery.
The OP stated "The AGM battery I run seems to be destroyed by the charging system amperage."
I only addressed the question of amperage killing a battery. My point was it's doubtful excess current killed it.
Never claimed or implied it was the only way to kill one.
 
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krza

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What >exactly< is the problem you are having? Most XS owners would love to have a charging system that puts out too much current, 200W is the same as the stock XS charging system output, so you really shouldn't be having any problems. If you are overcharging your battery you have a regulator/rectifier problem, which is not unusual since most of these pma systems ship with garbage regulators. Unhooking one of the phases is a half assed way of trying to solve the issue.

Don't run a higher wattage headlight or your battery will most likely run flat.

*exact* problem is this:

I replaced the stock charging system with a 200W PMA (was a totally clapped out barn find bike for $700 and needed it, as the rotor did not pass charging system diagnostic test). I also built a small battery box to have a minimal look, it fits a generic 7ah AGM power sport battery. The 7ah AGM batteries stop holding charge after a few rides/one long ride. The batteries won’t hold charge and show low voltage, which I’ve always assumed means they were ruined by the charging system somehow.

I replaced the regulator with a MOSFET regulator from Revival Cycles, it is rated to 500W. But the battery issues seem to persist.

The regulator has a good set point and the charging system seems to work correctly, it shows max of 14.2v when the bike is running with a new battery in it.

Again, in my uneducated approach, I assumed unplugging one lead from the stator would reduce wattage and take care of any over charging of the battery.
 

gggGary

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Guess in my usual stone age way I'd do a little 'sperimenting. perhaps run with a larger lead acid "for a bit" Never had much luck with glass mat batteries. but haven't used many. My lithium battery trials on an XS haven't gone well either. :redface:
I don't see a lot of harm in dropping out one of the three phases. Assuming a Y phase set up. Guess the only question is to leave it open or ground it. Might want to install a switch on that lead.? Again run a voltmeter where you can see it.
 

krza

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Guess in my usual stone age way I'd do a little 'sperimenting. perhaps run with a larger lead acid "for a bit" Never had much luck with glass mat batteries. but haven't used many. My lithium battery trials on an XS haven't gone well either. :redface:
I don't see a lot of harm in dropping out one of the three phases. Assuming a Y phase set up. Guess the only question is to leave it open or ground it. Might want to install a switch on that lead.? Again run a voltmeter where you can see it.

I had a lithium battery burn up on this XS as well, a Shorai LFX19A4-BS12. The problem is that was before I put the MOSFET regulator in it, and I think the standard solid state regulator rectifier was set too high and I’ve heard lithium batteries don’t like too much voltage.

What’s a Y phase setup? and yeah would be good to know if better to disconnect or ground it.
 

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Spontaneously disconnection of one phase sounds wrong
ArticXS says it can be done but there is a risk as I see it

What’s a Y phase setup? and yeah would be good to know if better to disconnect or ground it.

Y system in 3 Phase as in the wall socket is used since the system is balanced .Not sure the English words
Ground and Zero is used here Plenty if you google
Just grabbing one there might be better

https://www.fluke.com/en-us/learn/blog/power-quality/balanced-three-phase-ac-power

Since the alternating current has a Sinus wave form in each phase the aim is to get no current in the Y central Point.
No current in Zero
the sum of 3 sinus waves is Zero
the sum of 2 Sinus waves is not Zero
Take one phase away and the balance is disrupted
To do that the Wiring and Loads must be taken into consideration. Inductive or Capacitive
And the wiring in this case not known at this point in time

I Would suspect overcharging ..The regulator giving the right Value but not all the time

AS Gary says
Again run a voltmeter where you can see it.
 

650Skull

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If i am understanding this guy right, he explains the working differences between a shunt and series Reg/Rect, the series Reg/rect, Regulater changes how it runs once it reaches a certain voltage and drops one of the 3 phase's and runs on 2 wires for a period then swaps the 2 wire sequence and the timing of the sequence. This makes the series reg/rect run cool

https://www.stromtrooper.com/threads/regulator-shunt-verses-series.435073/#post-5575668
 

arcticXS

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We still do not know whether the OP's PMA is single phase or three phase (easy to check though, is there two or three wires coming from stator to regulator/ rectifier)
If there is just two wires, i.e. single phase, then a wire cannot be disconnected or grounded.
 
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