Should the Regulator be too Hot to Touch?

[freddy3]

Should the green resistor(?) on the regulator plate become too hot to touch within one minute of the engine starting?

The bike is a stock 1972 XS2, which I've owned since '75.

Last week, a day after I'd washed the bike like I normally do, within a couple of minutes of starting the engine, both battery leads along with the in-line battery fuse (behind the left-side cover) and rectifier became so hot that I couldn't touch them. I shut the bike off and then disconnected the battery leads. I've never seen battery leads get hot like that!

After everything cooled down, I tried to start the engine again, but the battery was then dead. No green neutral light came on in the tach (or is it the speedo?....whichever). So I charged the 2 year-old Die Hard battery and tried again the next day.

This time, the bike started normally and the battery leads were cool, but I found that the wires leading from the rectifier to the battery fuse (under the left-hand side cover) were again very hot, as well as the center bolt in the rectifier body that holds the rectifier onto the frame were scalding hot! So I shut the engine down and inspected the rectifier, since I'd had a similar problem many years ago (which turned out to be a bad rectifier).

As it turned out, the inside of the rectifier was pretty corroded (I have a feeling that water's getting into the rectifier body when I was the bike and it then rusts and corrodes) and it looked like the corrosion may've bridged some of the rectifiers, causing them to short. So I took the rectifier apart and cleaned it out thoroughly, removing all of the corrosion and potential shorts. It looked nearly new.

Upon restarting the engine, all the components that had previously gotten hot seemed to be fine. So I took the bike out for a 3-hour drive and as I was just a few blocks from returning home, the engine started to die while sitting at a stop light. Cutting to the chase....the battery had discharged. Or, it wasn't getting charged?

So I checked the voltage regulator to see if it'd been damaged by the heat the previous day and found it was putting out ~14.9 volts to the battery, which is within the normal range. Otherwise, everything seemed fine except that the green resistor on the voltage regulator plate is becoming too hot to touch within a minute of starting the engine.

My question is whether it's normal for that resistor to get so hot (and I just never noticed it before), or does that indicate that the regulator, rectifier or some other component is defective/damaged (even though the system's sending the correct voltage to the battery)?

 

[freddy3]

Anyone? Bueller?

 

[plane_ben]

What is the static voltage on the battery? You should have right around 12.9 to 12.8 for a good battery. Your system might be overcharging to compensate a bad battery.

 

[freddy3]

Static voltage = 12.9.

 

[retiredgentleman]

14.9 volts is too high; it should not go over 14.5 volts. Your regulator is old and tired and is struggling to do its job.

Congratulations on owning that bike for that many years.

Your regulator and rectifier have both done their job amazing well for that many years, but its time to retire them.

Do yourself and your bike a favour.................replace the regulator with an automotive NOS solid state regulator. I use the Standard VR115 but there are others as well. Replace the rectifier with new dual bridge rectifiers. Reliability will be greatly increased.

 

[freddy3]

Thank you for that, retiredgentleman, but both the Clymer and Yamaha Service Manual (I'm looking at it now) specify the proper voltage range coming out of the regulator (to the battery) to be between 14.5~15 volts, which is right where it's at. So it seems like the regulator's doing its job correctly.

Still, I'm confused as to why that resistor's getting so hot, so fast. Again, it' may've always been that way (which is basically what I'm trying to find out with this post) and I just never had a reason to check it, but my gut tells me it's not supposed to be that hot.

Is anyone else in a position to just start their bike, let it run for a few minutes and touch that resister to see how warm/hot it is? If it's hot on other bikes, then it's probably supposed to be that way.

 

[xjwmx]

I don't have your kind of regulator, but I found this diagram. Your regulator is at the bottom right. I think the big resistor is the one on the left there. Inside the regulator is an electromechanical switch. I would open it up if possible, and check to see if it is corroded stuck. There's a path there where the resistor can conduct straight to ground from 12v. I'd clean it up inside really good and put it back together and see what happens with the resistor. I think in there there's a way to adjust the output voltage too.

 

[freddy3]

Thanks, xjwmx. The regulator has two sets of contacts, both of which I sanded/cleaned yesterday (they weren't bad to begin with). Unfortunately, that made no difference. The regulator, otherwise, looked very clean throughout. That is, nothing burned, dirty, rusted, corroded, loose, etc. Even the "hot" resistor's still got it's original green paint/sealant intact.
Very strange.

 

[xjwmx]

In that case, figure out how to adjust its output voltage. If it is misadjusted enough it would probably have an effect similar to being stuck.

 

[freddy3]

I can adjust the voltage (there's an adjustment screw inside the regulator), but I'm already measuring the correct voltage (14.9vdc) in step 3:

And that's why I'm stumped. That resistor gets blazing hot within a minute after starting the bike, but the bike seems to be running fine and I've got correct voltage at the battery.
The $64,000 question is whether that resistor's hot on other bikes? If so, then it's probably normal to get hot and I just never noticed it before. But if the resistor remains at or near room temperature on other running bikes, then I'll need some further diagnosis.

p.s. I've actually got a replacement (NOS) regulator (Yamaha part number: 1L9-81910-50-00), but it differs slightly from the one that's on the bike (the replacement has a black painted cover (mine is unpainted) and lacks the adjustment screw). Although it's otherwise the same and the part number is correct for my year/model bike, because it lacks the adjustment screw, I'm hesitant to install it unless I have to.

 

[plane_ben]

I just checked my resistor. I'm running the exact same reg/rec, and I'm getting warm after couple minutes, but not hot. My output at the battery while at high idle(holding the throttle open)is 14.5 volts. I'm still suspecting your battery. Try isolating, and do a load test, and see what the output is then.

Resister could be shorting out also. Is the ceramic cracked anywhere on the resister?

 

[freddy3]

I just checked my resistor. I'm running the exact same reg/rec, and I'm getting warm after couple minutes, but not hot. My output at the battery while at high idle(holding the throttle open)is 14.5 volts. I'm still suspecting your battery. Try isolating, and do a load test, and see what the output is then.

Hmmm... You might have something there (in bold). The battery charged fine and seems to be holding the charge without any problems. But I wonder if the battery might've gotten damaged (internally) when this first happened?

In case you missed it in my original post, it was finding the battery terminals scalding hot that initially told me I had a problem. It was only after I disconnected the battery (after it'd cooled down!) and started troubleshooting the charging circuit that I found the hot fuse leads (since replaced), regulator resistor and hot/corroded (since cleaned and no longer hot) rectifier.

Resister could be shorting out also. Is the ceramic cracked anywhere on the resister?

No, that's the weird thing. As hot as it got that first day, I would've expected it to've burned off or, at least, turned brown. But it looks just fine. But since yours is only warm, which is the way I think it's supposed to be, there's definitely something wrong here.

 

[xjwmx]

If the resistor is failing and getting lower in resistance, it would make it hotter than normal. So measure the resistance of the resistor and compare it to the stamp on it.

What I would do is adjust the voltage down to about 14-14.5. At first glance, the higher the output voltage, the more time it spends in the zero current 'rotor on' position, which would make it inversely warm to voltage. But - with the higher output voltage, when it's in the rotor off position there's more current through the resistor, heating it more So, I would adjust the voltage down and see how it feels. An extra load on the regulator, like a short somewhere or a bad battery, etc., wouldn't heat the resistor more. Only higher voltage would.

 

[freddy3]

If the resistor is failing and getting lower in resistance, it would make it hotter than normal. So measure the resistance of the resistor and compare it to the stamp on it.

I did that yesterday. The resistor measures 0 resistance, measured at the ends of the resistor (regardless of polarity). I thought that was kinda odd, except that I get the same readings from the resistor on the NOS regulator (the one without the adjustment screw under its cover).

What I would do is adjust the voltage down to about 14-14.5. At first glance, the higher the output voltage, the more time it spends in the zero current 'rotor on' position, which would make it inversely warm to voltage. But - with the higher threshold voltage, when it's in the rotor off position there's more current through the resistor, heating it more So, I would adjust the voltage down and see how it feels. An extra load on the regulator, like a short somewhere or a bad battery, etc., wouldn't heat the resistor more. Only higher voltage would.

I'm not sure that reducing the voltage by <1 volt would make a big difference, but it's worth a try. I'll give it a shot this evening and report back with the results.

 

[xjwmx]

The resistor reads zero because you're reading the resistor with the switch in the at rest position. In that position it has zero ohms parallel with it. Push the switch free of that contact and then measure the resistor.

 

[freddy3]

You know, I think you're right. I'll check it again this evening.

 

[freddy3]

Okay, somehow I measured the resistor incorrectly the other day. Today when I measured it again, I'm getting ~1meg impedance when I first hook up the ohmmeter. But, immediately, the resistance then starts dropping. I didn't do an extended resistance test to see how low it would ultimately drop down to, but after about 30 seconds, the resistance dropped to ~.325k (and still dropping). However, for comparison, the resistor in the NOS regulator behaved exactly the same way, so I don't think that indicates a problem.

I did another check of the voltage at the battery terminals with the bike running at 2500rpm, which returned odd results. Initially, when I placed the DVM's leads on the battery voltage, it reads ~15.75vdc. But, almost immediately, the voltage begins to vary +/-.5vdc. It varies slightly up/down for about 15 seconds and then it suddenly drops to ~13.5vdc and then slowly works its way back up to ~15.75vdc +/- .5vdc. This pattern then repeats every 15 or so seconds. Not sure what that means???

Since I had NOS replacements for both the regulator and rectifier on-hand, I figured I'd try swapping both units to see if that cools the hot regulator resistor. Unfortunately, it made no difference. The resistor on the NOS regulator did the same thing. Unlike the original regulator, the NOS part doesn't have the adjustment screw, so it doesn't allow me to lower the voltage at the battery to see if that might affect the resistor. But since the NOS regulator did the same thing, I kinda think that rules out the regulator or an adjustment at that point being the cause of the hot resistor.

Now, there's also a relay on the (right-side of the) bike right below the regulator:

I've also got a NOS replacement relay, but I wasn't sure if the relay has anything to do with the charging circuit, so I didn't try swapping it out for the NOS part.

So, what I currently know:
1) The hot resistor isn't being caused by a faulty regulator or rectifier, since it continues to heat up with the NOS replacement parts.
2) The battery's being both overcharged (15.75vdc) and underchanged (13.50vdc), but in a repeating pattern.
So do any of these new details produce an epiphany for anyone?
I'm about as stumped as a completely stumped thing.

 

[xjwmx]

Consider measuring the resistor a test. If you can't do that, it's hopeless.

 

[650Skull]

Never mind

 

[freddy3]

Consider measuring the resistor a test. If you can't do that, it's hopeless.

I'm not sure I follow you?
Tonight, I measured the resistors on both my current regulator as well as the one on the NOS regulator, and they both measured the same. Oddly, but the same.

Either way, since the resistor on the NOS regulator got hot just like the resistor on the original regulator, I'm not sure what I'd be gaining from additional measurements of them? Since both resistors get hot, doesn't that eliminate the regulators/resistors, themselves, as being the source of the problem? I'm leaning more towards your previous suspicions about the battery being the problem. Are you no longer thinking that?