spotty electrical problems

[cod 121]

With older wiring harnesses and components have any of you found a good way to determine what's behind occassional quirky electrical problems?

 

I posted around a month ago about having a battery charging problem with my 418-A and with the help of a wiring diagram that one of you posted, I was able to solve it but now it appears to have returned and I'm puzzled as to why.  I've checked the stator output and it's around 32 VAC (it's a twin Kohler) and the rectifier was putting out 14+ VDC, I also cleaned all of the connections and replaced the negative battery cable.  Now I'm beginning to wonder if perhaps there are issues as the engine warms up the heat affects the rectifier or perhaps the wiring is corroded throughout the length of the wires themselves but I wish it was something simple like a flat tire or having a rod sticking through the block as those are obvious, this electrical stuff is voodoo to me.

 

That said, any advice would be greatly appreciated.

 

Thanks in advance - Cod

[Jeff-C175 7,206]

It probably would have helped to continue the previous thread so we had 'history' of the problem... so here is the link to the original for reference as to what you've done already:

 

 

 

Now I'm beginning to wonder if perhaps there are issues as the engine warms up the heat affects the rectifier or perhaps the wiring is corroded throughout the length of the wires themselves

 

Why do you think it's a 'heat related' problem?  Does it work properly when it's cold, EVERY TIME?  and ONLY acts up when it's HOT?

 

I doubt the wire is corroded... I've seen corrosion going down a wire maybe an inch or so, but never the whole length.

 

I recently replaced the rectifier/regulator on my KT17 twin because it was intermittent.  Sometimes it was fine, sometimes not.  There was no rhyme or reason... cold or hot, day or night... didn't matter... when it wanted to act up, it did.

Edited August 18, 2013 by Jeffpicks

[bean 85]

I got rid of my 73 8hp, because I couldn't chase down a charging problem. it would work in the short term, but if I ran it for a long period of time, like you are describing with a heat issue, it would run the battery down. this was very annoying, because the charging system was designed to just charged the battery, and didn't supply energy to the ignition coil. the engine ran off of the battery. when the battery was dead, you could not start the engine. I would have to remove the battery, charge it, re-install, and it would fire right up and be fine. unfortunately, I was usually on our other lot, 5 miles from the garage.

it had been a problem for previous owners, evident by the wires coming from the stator having been spliced at least 4 times. it finally got so annoying, I took it apart in the garage one night and parted it out. I threw out the stator & regulator,

those intermittent electrical problems can be a real headache. you can keep throwing new parts at it, and never get it fixed.

it's like taking your car to the dealer, and everything is fine. and then beaks down on the way home.

Edited August 18, 2013 by bean

[cod 121]

It probably would have helped to continue the previous thread so we had 'history' of the problem... so here is the link to the original for reference as to what you've done already:

 

 

 

Now I'm beginning to wonder if perhaps there are issues as the engine warms up the heat affects the rectifier or perhaps the wiring is corroded throughout the length of the wires themselves

 

Why do you think it's a 'heat related' problem?  Does it work properly when it's cold, EVERY TIME?  and ONLY acts up when it's HOT?

 

I doubt the wire is corroded... I've seen corrosion going down a wire maybe an inch or so, but never the whole length.

 

I recently replaced the rectifier/regulator on my KT17 twin because it was intermittent.  Sometimes it was fine, sometimes not.  There was no rhyme or reason... cold or hot, day or night... didn't matter... when it wanted to act up, it did.

Thanks for the response Jeff and the reason I thought it might be heat related was that when the tractor is completely cold, it fires right up with no problems but if I turn it off once it's been running for a couple of hours, turning the key does nothing.  I can get it running with the key in the "run" position and jumping the soleniod and that's when I check the ampmeter and see that it's only putting out slightly more than 12 volts.  I suspect that the battery recovers between mowing so there's enough amps to start it when it's cold but I have to assume that there's a small drain when it's running that keeps it from having enough power to start it when it's warm.  Just before logging  in, I went out with a voltmeter and after sitting for 25 hours, the battery measured 12.5 VDC, the beast fired right up but this time I kept me eye on the ampmeter and it showed an output of 12+ volts and I measured 12.4 VDC with the voltmeter.  Tomorrow I'll pop the rectifier off the block and see unconnecting and reconnecting the leads makes a difference. 

 

Somehow I tought there was a way that one could measure the resistance of the rectifier itself to see if it was in a certain range to tell if it was good or bad and I was thinking of measuring it cold and then baking it in an oven to get the same reading when it was warm.  Luckily "she who must be obeyed" is working tomorrow evening so I'll have plenty of time to clean up if I vaporize the rectifier in the oven...

 

Cod

[oldredrider 2,553]

Before you go to the trouble of "baking" the rectifier, make SURE it is well grounded. Check all of your grounding points. Heat and vibration can have negative effects on bad wiring.

[cod 121]

Just to update, I went surfing and found an article about testing Kohler rectifiers at this site "http://www.smokstak.com/forum/showthread.php?t=72708",  and so I went out and disconnected the rectifier and measured the resistence as the author suggests.  So looking down onto the rectifier with the 3 spade lugs in the 6 oclock positon, and the voltmeter set for 2000 ohms, I placed the negative probe on the center spade( and when I placed the positive probe on the left spade I found that I had 0 resistance, while probing the right spade yielded inifinate resistance.  Reversing the probes as suggested in the article yielded the same results so I figured the rectifier was bad.  I also started the tractor up and checked the stator voltage and I found 28 VAC at idle and 34 VAC at high idle so I believe the stator is working as it should.  Turning the tractor off, I reinstalled the rectifier, started it once more and tried measuring the voltage from the wire the connects to the center spade and the battery ground and found 12.4 VDC.  All this seemed to confirm to me that the rectifier was bad so I called Jack's Small Engine and the had a replacement rectifier in stock so I took the old down and bought a new one as they are less than a mile from where I live.  On returning home, I proceeded to try and measure the new rectifier to see what it read and low and behold, the reading were IDENTICAL.  Needless to say I was somewhat preturbed thinking that I had blown $50+ and this might not fix the problem.

 

Today I brought the tractor up to the garage where I can see, and went through all of the wires from the stator leads to the key switch cleaning every contact and connection as best I could as I saw oldredrider's comment and I did not want to install the new rectifier if there was a chance that the old one was okay.  After cleaning everything I bought out the voltmeter and checked all wires to make sure they were okay and everything passed.  With all that done I started it up and the voltmeter read 14+ volts.  I let it run for about 10 minutes and the needle on the voltmeter slowly went back to 12+ and when I measured the voltage I found 12.5 VDC.  I shut it down for about 5 minutes (more gas) and when I went to restart it, turning the key did nothing.  Jumping the soliniod got it running and intially the voltmeter read 12+ but then it jumped up to 14+ and stayed there. I let it run for another 5 minutes and then drove it back to the shed and the voltmeter was still at 14+ when I shut it down.

 

At this point I'll keep and eye on the voltmeter and see what happens but I really would prefer not to have to field strip the charging system every couple of months just to keep the battery alive.  I also apologize for the long posts but if I've got to ask for help I'd prefer to explain what I've been trying so someone might be able to clue me in on something I'm overlooking.  It's great to see so much useful information in one place.

 

Cod

[Jeff-C175 7,206]

Man, I wish I lived a mile from Jack's... I wouldn't have to bother Lauren half as much as I do!

 

In that smokestack thread, the fella Arkie that explained that you had a full wave rectifier is completely WRONG.  The tests he described would be valid if it were in fact a full wave rectifier... but it's not.  I guess nobody there knew enough to call him on it... the guy that posted just before him, MARK, had it right.  One thing to add to his post though, at full throttle you could have as much as say 38 - 40 VAC on the stator terminals.

 

Those reg/rect are based on what is called an SCR.  You WILL have direct short between the B+ and ONE of the AC terminals.  The other terminal won't really give you any solid data as to whether it's good or bad, and depending on which ohmmeter range you use you could well get different readings.

 

Testing the r/r on the machine with the engine running is the best test you can do.  If you've got adequate voltage from the stator, and from ground to the B+ terminal does not give you at LEAST 13.5 volts anywhere from say half throttle to full throttle (it can go lower at idle) then you either have a bad r/r or a bad ground.

 

If your battery is 'soft', it IS possible for the voltage to go above say 14.7 or so at full throttle, but if the battery is good, it should not go higher than that.

 

You should see the SAME voltage at the battery as at the B+ terminal when the engine is running.  If you do NOT, you need to look at the condition of the ignition switch.  The output of the R/R makes it's way back to the battery THROUGH the iggy switch.  It's very possible to have intermittent connections there.

 

On my machine that I recently repaired, I actually had BOTH a bad R/R AND a bad iggy switch.  I somewhat believe that the the iggy switch problem contributed to the failure of the R/R but don't want to test my theory and blow up my new R/R.

 

Set your meter up on the ohms scale.  Pull the connector from the iggy switch.  Put one ohmmeter lead on the B terminal and the other on the R terminal.  Turn switch ON.  You should see O ohms... direct connection... wiggle the key around... push in and out... watch the meter while doing this... if you see the meter jumping around, you have a bad switch.

 

Might as well check all the switch connections while you are at it...  leave one lead on the B terminal... do same as above for the I terminal and the A terminal.  Leave the lead on the A terminal and turn the key to the START position.  You should see that connetion go OPEN.  Move the meter to the S terminal.  With key in RUN it should be OPEN.  Turn key to START and connection should go to ZERO ohms...

 

If any of these switch tests are erratic, replace the switch.

 

Did you try the new R/R yet?

Edited August 20, 2013 by Jeffpicks

[Save Old Iron 1,571]

Those reg/rect are based on what is called an SCR.  You WILL have direct short between the B+ and ONE of the AC terminals.  The other terminal won't really give you any solid data as to whether it's good or bad, and depending on which ohmmeter range you use you could well get different readings.

 

 

 

Perfectly correct.

 

I did an autopsy on an R/R several years back to purposely see if any external diagnostics were possible. As Jeff states, the RR is SCR based. Yes, it is a diode per say but one that has a "third leg" on it that needs to be triggered to put it into operation. Similar in principle to a starter relay that will not pass current unless a voltage is applied to its trigger terminal.

 

 

Same idea with the SCR inside the RR unit. Unless the trigger leg sees a voltage less than 13.something, it will not trigger the SCR to allow current from the stator thru the SCR to charge the battery . This is exactly why the battery voltage must be able to reach the RR thru the ignition switch. There are "electronics" in the RR body that need to be powered up to allow the RR to function.

 

 

 

 

Yes, you will measure a direct short from the B+ terminal to one of the AC terminals as they are physically riveted together inside the RR case.

 

 

 

 

 

 

 

I know I have a better pic of the terminals riveted together. I'll try to post it up later this week.

Edited August 21, 2013 by Save Old Iron

[Save Old Iron 1,571]

Heat can be a trigger to cause an RR unit to fail but it might be easier to bring a hair dyer outside and blow it on the regulator than to shake and bake an RR in the oven. If it is a bad electrical connection in the RR, by the time the RR cools down enough to handle, the failure might just reset itself.

 

Another way to thermally "challenge" an electronic unit is to freeze spray the unit. Freeze spray is available at electronics stores like radio shack.

 

I might suggest just monitoring the new unit and if it fails, grab a voltmeter and do a few checks to see where the issue lies. Don't just assume it is in the RR.

[Jeff-C175 7,206]

I'd just like to add a tiny bit here...

 

On the Kohler twins, possibly depending on age, the R/R is more likely to have the three terminals in a straight line, next to each other.  The physical appearance of your R/R will possibly be different.

 

It doesn't change the function though, those two terminals are still connected together.

[cod 121]

Shorter update this time but first thanks to Jeff and SOI for their posts and I'll check the switch wiring this weekend.  The switch is only a month old so I hope it's good but I'll check it anyway.  At this point I have not install the new rectifier as the old one seemed to have healed itself and both the old and new rectifiers have their terminals in a straight line.  Unfortunately on the new one, the overall height of the unit is shorter and instead of the terminals coming out of the side, they come out underneath with a 90 deg bend to get them in the same position as the original.  If I have to install the new one, I made a couple of brass standoffs to raise the rectifier off of the block so I can connect to the terminals and aviod the flywheel. 

I'll post more once I get more info.

 

Cod

 

PS  The pictures and wiring diagrams are VERY helpful SOI and I also saw where you were working on refurbishing the circuit board which may happen sometime this winter once I get a larger magnifing glass...

 

Thanks again!

[Save Old Iron 1,571]

My mistake - you may be talking about the "Onan" style RR units.

 

 

Either way, same philosophy. Two terminals are staked together electrically and there is nothing to be gained by measuring the Resistance of the third to any other terminal.

[cod 121]

Finally had a chance to go over the charging circuit and everything seems fine.  No cracked or pinched wires, and I get 0 ohms for resistance readings as well.  I did take the battery out and put it on a charger for about 8 hours to try and make sure that it was fully charged.  I measured the voltage going into the battery at 14.5 V and when I disconnected the charger I measured 13.8 V.  I had some errands to run so it sat for a couple of hours and when I checked it again it was down to 12.7 V.  A friend of mine told me that it might have what's known as a "surface charge" and lent me his load tester to check the battery with.  When I tested the battery I found that it was almost at the bottom of the weak section of the guage so I'll find out if I'll have to get a new one sometime this winter when I hitch up the snowblower and go to use it.  Luckily winter isn't too rough here in Maryland and shovels always work.

[WH nut 553]

When you say you jump across the solenoid to restart it, it tells me you need to be looking at the starting circuit not the charging system

[cod 121]

Thanks for all the info gents I really appreciate it and here's the latest on the 418-A.

 

Finally got tired of cleaning connections and checking the wires so I replaced the old rectifier with the new one and the charging problem went away.  With the tractor running the voltmeter reads 14+ volts so at least the battery is getting a charge and I suspect the old rectifier must have been on it's last legs when I got the tractor.  The replacement rectifier was made by Stens and I had to raise it off of the block to get the connector in place.  The picture the Chuck posted looks like the one I purchased and perhaps one could mount it in a similar fashion the the picture as you wouldn't have to shim it up and the next time I have the beast in the garage I'll check that option out as the only problem I can see would be that the sealant on the bottom of the rectifier would be more exposed to the weather.

 

My next problem to solve is getting the tractor to start after it's been running for an hour or so.  When it's cold ( first start ) it fires right up but once to engine is hot, turning the key does nothing and I have to jump across the solenoid terminals with the key on run to get it to fire off.  I don't thim the solenoid is going bad but I didn't think the old rectifier was bad either...

[Jeff-C175 7,206]

 

perhaps one could mount it in a similar fashion the the picture as you wouldn't have to shim it up and the next time I have the beast in the garage I'll check that option out as the only problem I can see would be that the sealant on the bottom of the rectifier would be more exposed to the weather.

 

Actually, the sealant is supposed to be up.  The aluminum case is a 'heat sink' and should be exposed to the air from the cooling fan on the flywheel.  Yeah, turn it over.

[Save Old Iron 1,571]

COD, good call the regulator replacement.

 

BUT,

 

The RR unit needs to be mounted with the "sealing compound" in the upward direction.

The majority of the RR body needs to be in the cooling air stream produced by the flywheel. The airflow over the cylinder heads also SIGNIFICANTLY cools the RR body at heavy charge currents.

[cod 121]

Saw Jeff's and Chuck's posts so when I got home from work I flipped the rectifier over.  The old was mounted with the fins away from the flywheel and it never occurred to me that perhaps the one I replaced was on wrong.  I took a picture to post with this message but my phone is smarter than I and until I figure out where I left the user guide you'll just have to imagine what it looks like!

 

Thanks again guys!