voltage all over the place??????

THE AXE

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Hello all i hope someone can help me with this... this is a long story but ill try to keep it short so you keep reading...my problem is that the voltage goes crazy as soon as i test up the line from my reg/rec ....my set up right now.. all my wires are on quick connects or pig tails until i figure this out...the bike is an 1980 xs650 .i have a PMA make and model not sure,it was on bike when i got it.. 3 phase reg/rec for honda magna (new).. sparks cap..(new).dyna DC3-1 3ohm coils.(new) . 7mm leads with non resistor caps....points and condenser (new) ... right now i have disconnected the head light and tail light just to be sure i dont get any miss reads from a bad wire or short, i know this will make the voltage a little higher with no draw but i am taking that into account... i run my PMA into my 7 point 3 phase reg/rec. 3 wires from PMA into 3 wires on reg/rec.. (PMA tests all 3 leads even with 4-6 volts depending on RPM) pig tail two reds out from the reg/rec to one main power line (14 gauge) to my sparks cap then to a 20 amp fuse followed by a 15 amp kill switch followed by a 7.5 amp fuse to my coils... the two ground wires are pig tailed and run to my cap then to my rear motor mount that has been ground to metal on the engine and the frame both sides....(this line is 10 gauge) and test 0.06 ohm's when off as quick as my voltage meter gets there by touching its two leads together..and 0.06-to 0.10 when running..the bike runs great takes half a kick to start my valves are set my points are set my cam chain set timing set.... the thing is it has always burnt out head lights....and then my last set of coils went so i started checking volts, right at my reg/rec (the first connection is 3 inches from the reg) it reads a steady 12.5 - 14.8 volts as soon as i work up the line say another 3-5 inches it goes crazy by the time i work up to the cap it is unreadable because it is flashing so quick but i see 19 and i see some times a minus???? i have grounded the hell out of this bike and it does not change, the motor has a good ground to frame... i am at a loss???? bike runs great out pulls all my friends xs650's but it will keep burning up electronics if i cant fix this problem... i just cant understand how it can read the right volts at the reg and then go so wrong 3 inches away???? it seems to be feeding back the line but why??please anyone i am out of ideas.....thank you for reading this what i see has turned into a short novel.
 
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Digital DC voltmeters have "sampling times", and can show bizarre behavior on noisy DC lines. Sounds like the combination of low-resistance coils and Sparx cap are creating enuff DC noise to challenge the regulator. Simple test would be to replace the Sparx cap with a battery, then see if voltage stabilizes...
 
Hmm interesting, never thought about that, but i did swap out the cap with a dead bike battery for a test...it did give a slightly more steady reading right by the reg/rec steady at 12.4 (idle) but still went nuts up the line??? would a good battery test different?? But now you have me thinking maybe i should try a 5 ohm resistor caps on the plugs to knock down the noise? could it be that simple???
 
Sure throw on any old pretty good 12 volt, a car boat lawnmower (not running) battery use jumpers if nothing else. I got no expertise with this but caps and voltage all over the place seem to go hand in hand. What headlight bulbs are you using?
 
I use halogens H4 12 volt 60/55 , but i am sure correct me if i am wrong even if i am running a cap i should see about 12-14 volts at the head light bucket. but that far up the line it is as i say jumping around so fast i cant say for sure what i am getting but i see flashes as high as 19 and the negative sign even come up from time to time..
 
Also the brake bulb seems to last a long time ( probably not as sensitive to volts?) and after about 40 -50 hours on the bike the coils start to fail...i have used stock coils and mikes green coil and now have a dyna coil on it...not riding the bike scene i put new points coils condenser reg/rec and cap just running it long enough to test it.
 
If you heat a capacitor, lets say by your exhaust, you create CO2 internally causing a voltage fluctuation. Try putting it in a different place.

Other thing possible......RF
Plug caps? Plugs? Do you have a radio on when checking system? Live near radio tower? Etc

Perhaps far fetched but hey it how I am.

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To see how much 'noise' is on your DC circuits, simply switch your testmeter to AC volts, and probe in the same places you tested before. Ideally, you'd like to see 0 volts AC. But typically can get 0.5 volts AC. Above that indicates too much fluctuation on the DC supply lines, and it's time to fix or redesign the circuits.

Prevailing wisdom here is to use coils of no less than 4 ohm primary resistance on a points system. Less than that can stress (arc and heat) the points. And, that may not be a proper match for the stock ignition condensors.

The noise that's suppressed when adding 5K ohm plug caps is in the RF (Radio Frequency) range, and only applies to the high-tension secondaries of the coils, not the DC power side.

Digital VOMs (Voltage/Ohms Meters) can have poor interpolation of varying DC voltages (cheap units). Depends on how cheaply or how well they're designed. It could be taking a snapshot, or predictive over a slope, or averaging a slew over a specific timeslice, or computing using RMS (Root Mean Square) algorithms (expensive units), or ...etc.

A better way to diagnose DC supply noise problems is with a good scope. That would allow you to analyze the noise waveform, to see if it's caused by feedline resistances, excessive momentary draws, missing pulse from rectifier (like a bad diode), poor voltage regulation, ...etc. Then, solutions could be tested, like different Sparx cap value, or battery, fixing a rectifier, isolated/common power and ground tie points, different regulator, ...etc.

The rabbit hole can get deep. But, others are running similar configurations successfully. So, it could be something simple. Just gotta find it...
 
How big is your capacitor? Is it duff? A cap of at least 4500 MF (Lucas Blue Cap size) should work okay to smooth out any voltage fluctuation. Smaller? I don't know.

Tom

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Thank you TWO MANY so you say the 5 ohm plug cap is just for radio noise OK that makes sence, i am at work right now so i will get a better meter from the shop and see if that gives me a different reading...you say i should be useing a higher ohm rated coil, i may be misinformed here but i was looking at the xs650 direct site and they sell a 3.3 ohm (the green high output one)to replace the stock 4 ohm coil for what they say is for bikes with points?? i could have ordered a 5 ohm...that said the condencer is doing its job i have a small blue spark right at the points with no arcing at all, the points are new as are all my electronics (product of trying to fix my problam) so i can not tell if they are waring excessively or not yet. i still cant get past the good volt reading right at the reg/rec and then the crazy jumping up the line....all new tested electronics new wire re worked tested grounds...it a deep rabbit hole indeed.
 
Hey there Chizler the Sparks cap is mounted just under the coils with lots of wind getting to it and i always run a fan on the bike when idle testing it.. Tomterrific i think the Sparks cap is 10,000 but not sure, lots of guys useing this cap with good results and its the one that comes with hugh's kit and that guy know's his stuff from what i have read...also i bypassed the cap and tested with a battery it was a little more steady right by the reg/rec but again move up the line and voltage all over the place... stumped!
 
TWOMANYXS1Bs Thank you thank you thank you...I took a really good meter home from work last night and that did it!!! my meter was i guess picking up the noise and giving me a bad reading. the one good thing that came of this is i now have the best grounded bike in Vancouver and i learned a good life lesson. thank you so much for your help everyone.. One odd thing is the ac power out of my PMA gives the same reading on all three line but does infact drop from 7 to 4 when at a higher RPM ??? maybe that is normal? but all i know is its a nice steady 12 ish at idle and 14.7 at high RPM...

thank you again

Axe
 
Glad to be of help, AXE. Hope it gets you closer to solving your headlight burnout problems.

Readings of AC voltages on 3-phase systems (1-2, 2-3, 3-1) can be tricky. If you study 3-phase waveforms, and see how each line is out-of-phase with the others, then look at the voltage potential between any 2 lines, you should be able to see that those differential voltages are much less than the actual voltage swing of any single line. It gets trickier when the voltage regulator starts to clamp those lines. Need a chalkboard here...
 
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