I've a charging problem with my Honda mini bike. It is Honda st70 1975 model and it has 6v electrical system. I measured 6v AC voltage before the diode and 3v DC after the diode at idle. These voltages increase at higher RPM but the voltage isn't sufficient to charge the battery even at full throttle. I've tried to solve the problem by changing the new selenium rectifier (not original) and I also tried a silicone diode with no luck. Where could the problem be?
Battery charging issue
- Thread starter Hondast70
- Start date
Just as info, the lighting coil as shown in the wiring diagram uses different windings depending on if the lights are "on" or "off", The green wire is used when the lights are off and the pink is used when the lights are "on". Glad you have a meter because it will come in handy finding the source of this gremlin.
It appears the green wire supplies less voltage when the lights are off and the pink wire is used when the lights are "on" to account for the juice being delivered to the AC lights.
It appears the green wire supplies less voltage when the lights are off and the pink wire is used when the lights are "on" to account for the juice being delivered to the AC lights.
I found a few notes on this type of lighting coil and how it should work on a UK version CT70 based on your schematic:
Green wire supplies AC thru the main switch and & headlight switch (off) to the selenium rectifier to charge the battery. You should see the battery voltage start increasing somewhere above 4000 RPM.
When the HL switch is in position 1, the pink wire is used to supply AC for the lights and charge the battery (thru the Se rectifier). Just be aware that the light will not be very bright and don't expect much charging to occur until 7,000 - 8,000 RPM.
When the HL is in position 2, the yellow wire is used to supply AC to the HL and charge the battery (thru the Se rectifier). You should see the battery voltage increase once you pass around 6,000. At a minimum, the voltage should be stable (not going up or down).
Notes for future reference:
- Not much difference in the green and pink windings
- 3 vdc at idle does not surprise me; the only winding that provides substantially more AC is the yellow winding. However, what surprises me is that you don't read 6vdc or whatever the battery voltage is? That is the reason I suggest you take a reading at the battery as well.
I could guess on possible causes but let's take a few more voltage measurements to minimize the confusion.
Green wire supplies AC thru the main switch and & headlight switch (off) to the selenium rectifier to charge the battery. You should see the battery voltage start increasing somewhere above 4000 RPM.
When the HL switch is in position 1, the pink wire is used to supply AC for the lights and charge the battery (thru the Se rectifier). Just be aware that the light will not be very bright and don't expect much charging to occur until 7,000 - 8,000 RPM.
When the HL is in position 2, the yellow wire is used to supply AC to the HL and charge the battery (thru the Se rectifier). You should see the battery voltage increase once you pass around 6,000. At a minimum, the voltage should be stable (not going up or down).
Notes for future reference:
- Not much difference in the green and pink windings
- 3 vdc at idle does not surprise me; the only winding that provides substantially more AC is the yellow winding. However, what surprises me is that you don't read 6vdc or whatever the battery voltage is? That is the reason I suggest you take a reading at the battery as well.
I could guess on possible causes but let's take a few more voltage measurements to minimize the confusion.
Thanks for the reply. I've been looking for a solution to this problem for ages. I have replaced original wiring harness with home-made wiring harness during the restoration so there is a small change that the electric wires are not correctly. So far, I have made measurements without the battery. I think I measured 3v DC with the lights on and the voltage went up to 5v. The brake light works ok with key on and engine off.
Sometimes during the measurements the voltage rose up to 9V at high RPM but I thought it was an error in the meter because every time after a short run the battery charge level had dropped closer to 5V. In addition, my Honda model has turn signals and a relay that need DC power from the battery as opposed to the wiring diagram. I’ll get back to this later this week by measuring the voltage across different options.
Sometimes during the measurements the voltage rose up to 9V at high RPM but I thought it was an error in the meter because every time after a short run the battery charge level had dropped closer to 5V. In addition, my Honda model has turn signals and a relay that need DC power from the battery as opposed to the wiring diagram. I’ll get back to this later this week by measuring the voltage across different options.
A couple of points to consider. 1st of all, it can be a touch difficult to make sense of readings beyond the rectifier without a battery in the circuit. You also run a high risk, more of a sure bet if you rev the engine, w/o a battery in the circuit.
If you've change the wiring, your simplest option may be to install a standard CT70 lighting coil and make a few changes such that it works and functions like a typical CT70. Now that may be simpler stated than done because I don't know which type of flywheel you have - Hitachi (unlikely), Mitsubishi or ND (Nippon Denso).
No where close to be an expert on ST70s but I have touched a few stators that were definably used on UK bikes.
I did some measurements directly after the diode (see picture) and the meter was grounded to the frame. The light switch has three options. When the motor was off, the voltage was 0. When the lights were on (1) or with the position lights (2), the charging voltage was 4.5V DC at high RPM. When the lights were off (3), the charging voltage rose up to 6V DC. This model features Hitachi flywheel and I have changed a new stator. The stator should be correct for this model.
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cjpayne
Well-Known Member
A 72K1 I used to have read over 6volts at idle(6.7.....I think)and with out the lights on. I measured mine at the stator/harness connection by poking the red probe into the connector and one on the engine guard bolt. I later made a set up so I could bolt that ground probe to the engine guard and hold the meter while ridding. I seem to remember the voltage went alot higher when ridding.
Btw, I'm no electrical genius on these bikes and they are hard for me to diagnose.lol. You may just have a bad connection somewhere or your stator is faulty. I've tried those new china ones before and they just dont last. I think they just cant take the engine heat for too long.
On the old stators, if the induction surfaces are not clean/shiny, it will cause voltage problems, just like the magnets not being clean.
With the engine off but key switch on, you should see ~6vdc at the place you added an "arrow" you added to the drawing. The main switch connects the positive side of the battery to the circuit when it's "on"
Here is what I would expect:
Not a lot of difference in the voltage you see on the battery when the lights are "off" or in position 1. Even then, maybe a little higher voltage at 6,000+ RPM. in position 1, the HL should not be as bright as it is it is position 2.
When the HL switch is in position 2, the HL should be the brightest and the charging voltage to the battery is the highest as well. If you don't see 6.8 to 7vdc + at 6K to 8K rpm on the battery, we'll have to did a little deeper.
The clean copy of the wiring diagram does help. Good to know the brake light works fine, nice and bright, only on when it should be. Something that I noticed, and a suggestion on something that may help.
It appears the negative side of the DC circuit is grounded at the HL bucket and this is the only place it is grounded. You may help things a bit by adding a jumper from the green/white (I think) directly to the frame or wherever you find is the easiest. If you measured 5.6 volts after checking the brake light, I tend to think the battery needs charging or you don't have a good ground for the battery.
Again, based on what I've seen with the few UK stators I've tested. neither the pink or the green wires from the stator provide much charging to the battery until 6,000 RPM or higher and it's still not a lot at wide open throttle. Even then, it takes a up to a minute or so to see the battery voltage rise much at all when the HL is on (pos II). The pink wire provides the most juice (pos II).
It may be worthwhile to temporally disconnect the headlamp, meter lamps and tail light bulb and see what you have in all 3 switch switch positions with the engine running. The battery voltage should slowing start to rise when the headlight switch is off (I) or in position II and rapidly rise in position III. Just be sure to reduce the RPMs if you start to see more 8 vdc directly on the battery.
Again, I would add a temp jumper to ground and check again before I tested without the lamps.
It appears the negative side of the DC circuit is grounded at the HL bucket and this is the only place it is grounded. You may help things a bit by adding a jumper from the green/white (I think) directly to the frame or wherever you find is the easiest. If you measured 5.6 volts after checking the brake light, I tend to think the battery needs charging or you don't have a good ground for the battery.
Again, based on what I've seen with the few UK stators I've tested. neither the pink or the green wires from the stator provide much charging to the battery until 6,000 RPM or higher and it's still not a lot at wide open throttle. Even then, it takes a up to a minute or so to see the battery voltage rise much at all when the HL is on (pos II). The pink wire provides the most juice (pos II).
It may be worthwhile to temporally disconnect the headlamp, meter lamps and tail light bulb and see what you have in all 3 switch switch positions with the engine running. The battery voltage should slowing start to rise when the headlight switch is off (I) or in position II and rapidly rise in position III. Just be sure to reduce the RPMs if you start to see more 8 vdc directly on the battery.
Again, I would add a temp jumper to ground and check again before I tested without the lamps.
I had a few extra minutes today to look over both the wiring diagrams you sent and review my notes from testing 3 different UK stators (none were Hitachi however). I noticed that some UK models used a 15 watt HL while others, like shown in your first wiring diagram, show a 25w HL.
I have actually tested a couple of stators that would only support a 15w headlight, but have one that not only will support a 25W HL....requires it.
So in your case, maybe we need to determine what the wattage of the HL should be in your ST70 UK Model?
I have actually tested a couple of stators that would only support a 15w headlight, but have one that not only will support a 25W HL....requires it.
So in your case, maybe we need to determine what the wattage of the HL should be in your ST70 UK Model?
Very nice looking bike!!!!
I searched high and low for an original ST70 owners manual and a corresponding parts list...and I found one of each. The owners manual specifies a 25W HL bulb (UK Only) but the parts list only shows a 15 watt. Not sure. Can post some pics of the pages if that helps.
I searched high and low for an original ST70 owners manual and a corresponding parts list...and I found one of each. The owners manual specifies a 25W HL bulb (UK Only) but the parts list only shows a 15 watt. Not sure. Can post some pics of the pages if that helps.