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Discussion Starter #1 (Edited)
Hey guys, so i got my first bike a while back. This 75' suzi is a gorgeous little thing and i've fixed nearly everything on it now. the only problem still standing is the slow discharge of my battery when riding.

It comes to noones surprise that the old school dc dynamo charging system on this thing can be a little wonky and weird. rather than an alternator it has a DC charging system equipped with a stator field winding and armature winding.

I checked and cleaned the stator, armature, carbon brushes, and voltage regulator a few months ago and it all seemed normal, so reluctantly, To alleviate my unsolved battery drain, I added 2 SLA batteries parallel with the wet cell allready in it. with this setup I can get about 6 hours of riding in before the lights begin to dim, charging light comes on bright, ect.

I just performed an avid voltage test in the hopes that one of you may be able to diagnose whats going on. I figure it's one of two things, either my charging system is actually messed up and i just couldn't tell with my previous tests, or it has some sort of parasitic draw.

after a full charge the batteries were reading 13v. When the main switch was applied to give power to the tail light and accesories, the batts began to drain at about .01 volts per second. with the ignition switch on(power to coils from points) the drain was a little sporatic, but looked to be about 0.1 volts/second(note that I have 2 12v full size canister coils on it rather than bike coils, the old ones were shot and i couldn't find any actual aftermarket replacements)

with the engine idle at 1.8k the voltage was kindof sporatic, and would read anywhere in 12.2v to 12.4v and would momentarily drop to 5-7 volts every 5 or so seconds.
with the engine revved at 4k the voltage became more sporatic. at first it popped up to 12.6v, in a half a second dropped to about 5, then popped back up to 12.65, down to 5ish, up to 12.7 and so forth. it had momentary drops to a low voltage every split second but appeared to return every time to a higher and higher value. after about 30 seconds of revving the nominal voltage had climbed up to about 13.1 v.

Bear in mind that these readings are directly from the battery terminals. I remember doing a reading from the voltage regulator when revving and it was at like 14v like it should be.

Looking at my readings, I would assume that the battery is charging at that 4k rpm since the voltage keeps climbing a little every second? As for the momentary drops down to 5-7 volts, is that just a normal operation of a DC system or is something funky going on there? As for the timed decrease in voltage for the switches being on, is that a normal drag or does it seem like somethings drawing too much current?

any input would be great. i'm not a electricial by any means. i'm only an amateur mechanic. feel free to ask me any other questions, i've done a lot of tests to this bike so i probally have a response to any inquiry.
 

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Sounds like you are getting a momentary drop in charge probably enough to slowly drain your batteries. Have you checked the rectifier...also what kind of regulator does it have....points type? With the motor shut off what does the across battery voltage do?

ER is the man for this...
 

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Bear in mind that these readings are directly from the battery terminals. I remember doing a reading from the voltage regulator when revving and it was at like 14v like it should be.
This is a critical piece of information .......because it can't be true.

Well maybe.

The output of the R/R (regulator/rectifier) should be tired directly to the battery with a fairly thick wire.
If the voltage at the two ends of that wire are not the same, you have a bad connection there.

It is also possible that your battery is shorting out and dragging the whole system with it.

First you need to make real sure that your battery is good, probably by buying a new one and charging it up. Take those extra batteries OFF of it.
Then you need to check and clean ALL of the connections to the battery, regulator and charging components.

Resist the temptation to run it without a battery attached. That can blow the regulator.
 

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Discussion Starter #4
thanks for the responses guys. Aussie the bike doesn't have a rectifier because the dynamo puts out DC directly. and the regulator is an oldschool points system with two electromagnetic solenoids in it. i cleaned the gaps a while back. with the motor off and coils on, the batt voltage drops at a rate of about 1/10 volts each second. with the coils off and just the brake light and accessory lights on it drops at about .01 volts per second. with the main power switch off(the battery totally disconnected) it maintains voltage at about 13v.
 

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Discussion Starter #5 (Edited)
Easy Rider, that does sound like a weird descrepancy, i was following the manuals guide when i tested the cut in voltage directly from the regulator, and that involved unplugging the red wire leading from the regulator to the positive battery terminal, and routing it through a test light to ground. the manual then called for hooking up a voltmeter onto the red/green wire from the regulator then to ground. i can only assume the red/green wire is the dump wire that returns the current to the stator so no voltage is produced. So with these things hooked up, it then requested to rev the engine up monitoring the red green voltage and record the voltage at the instant that spliced light on the red wire turned on, which was about anywhere from 11.6 to 12 volts. slightly under the nominal recommendation of 12.0 to 13.5 volts. the over-voltage appeared normal though, it maxed out at about 15.5 (book calls for 15.4-16.6). I may just need to adjust the regulator...but the main battery may also be shot.

I bought the battery less than a year ago, a nice big wet cell, filled it, charged it to the max. but while i was trying to work with some wires a few weeks later i shorted it out. I had to physically unscrew the lead to break the circuit which took like 20 seconds. I suppose it may be possible i fryed that brand new battery doing that?
 

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What voltage does the dynamo put out and is it regular. Is it a magnet coil type with the magnet passing the coils. The gap needs to be accurate and free from any rust or crap build up. The regulator coils and points need to be in good condition and correctly gapped. I would check for a parasitic draw from the battery also. Switch things on and off...without them being connected...ie disconnect the horn and push the button to see if there is a voltage drop. Run the motor up to about around three/four k rpms and see if the voltage going to the battery stays stable.

You have a very old system and there could be an intermittent fault with either the dynamo or the regulator. Added to this the output of the dynamo will be just enough to keep the system working....does the headlight dim when stopped at a set of lights?...these old systems used to do this because the charging circuitry relied on rpm's to maintain it at an acceptable level of charge.

good luck... You may be better seeing if you can find a bike specific forum for this bike.
 

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Discussion Starter #7
yeah the lights do dim at stops if the batteries aren't fully charged, i was in full knowledge that that was typical. when the lights dim like this too my charging light will come on while at idle. i adjusted and cleaned my ignition points recently and checked the condensers. all good. ignition is fine. the regulator is the big confusion...i get the concept of the thing, but the wiring really hard to understand. unfortunately there are no adjuster screws on the regulator and no refrerence to adjustment in the manual, the most i could do to adjust would to be to carefully pry the point leads forward or back a little bit. i did notice however pulling it out that there is a little scorching mark on one of the points.

The generator doesn't have solid magnets in it though which is quite perturbing, it has a stator field coil of electromagnets that i guess induces the magnetic field that generates electricity from the armature. A few months back i cleaned the armature and commutator, and i checked the resistance across all the windings and it checked out just fine. voltage coming from the generator looked good too. i also put on new carbon brushes.

Ill get on checking for parasitic draw today...itl be tedious but it seems like it might be my problem. unfortunately i had to whip up this forum because their is hardly anything regarding this bike on the internet...hell i can't even find any info on dc dynamo systems either! i wish i could just replace the whole electrical system with a modern alternator setup lol
 

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I suppose it may be possible i fryed that brand new battery doing that?
Yes. Disconnect it and charge it up good and see how long it holds 12.6 or above....over the next 24 hours.

That mistake might have fried the regulator too.

Bottom line: If the battery measures 12.6 or more and that voltage goes UP when the engine is off idle, things are probably working as good as can be expected. A small battery tender is almost required equipment for old bikes like this........or a new battery about every year.
 

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Any arcing across the points probably means the condenser/capacitor is fried...there should be one somewhere in the regulator circuitry. Also check the points as they should also have one. Its function is to store the high voltage from the ignition and then release it quickly to avoid burning the points.

DC dynamos are a simple system the brushes and winding's have to be in excellent condition though as most are only just able to keep up with the battery and electrical systems demands...ergo the lights dimming at a stop. If you have even a small parasitic draw this will undermine it easily also any bad connections will have a similar effect so all switches and connections need to be free from any corrosion, be tight and, in the case of switches, work properly. A switch that is reluctant to fully engage will arc causing problems.
 

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Discussion Starter #10
ok so when running the bike there are no sparks across the regulator gaps, however I have had the dynamo cover off before and ran the engine and you can see the ignition points arcing up a storm. (brushes are new). i took the battery to autozone yesterday and they tested it under load, said everything was fine.

so i rode it up to my dads yesterday and the battery was starting to die pretty quick on me so we had a convo about these problems, he noted how my quick fix of using car coils on it may be my problem as they might be too big? it seems like a possibility considering that with the battery almost dead like this. with the accesories on, the batt dropped to about 11.9 and when i switched the coils on it dropped all the way down to 6-7 volts. i've heard of guys putting car coils on their bikes before without any problems, but i would assume that their modern charging systems probally have the umph to keep the battery nice and charged even with the big coils on, perhaps my old bike just can't handle it?
 

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Any severe arcing at the ignition points indicates the capacitor for them is toast. This in itself will not cause the battery to discharge but it may take more voltage to overcome the points being pitted. In some cases I have seen points welded together from arcing. I dont know what brushes you refer to in this instance...I know some of these bikes with dynamo supplied ignition have an adjustment to retard the spark for starting purposes...didnt think the Japs did this though. Car coils may well be too heavy...certainly for a six volt system to energise. They are also predominantly 12 volts.
 

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Discussion Starter #12
everything on the system is actually rated for 12 volts, so the coils i stuck on dont have a higher voltage rating...just " bigger". the brushes i was referring to are the carbon brushes on the commutator, just standard dc carbons. and the ign points do arc but i havent noticed any burn marks over the last few hundred miles. so yeah ill get some good aftermarket coils for the bike and hope that solves the problem. thanks aussie!
 

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with the accesories on, the batt dropped to about 11.9 and when i switched the coils on it dropped all the way down to 6-7 volts.
so yeah ill get some good aftermarket coils for the bike and hope that solves the problem. thanks aussie!
I don't think it will. Are those readings above with the engine running or not ??
A fully charged battery that drops to 11.9 with just the "accessories" on probably is not good......regardless of what the test showed.
There aren't any extra lights on it, are there?

And the important thing here is: What does the battery read when the bike is running ??
At idle and at fast idle.
It sounds to me like your charging system is shot.
 
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