Ballast Resistor getting hot and smoking (2014)

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I have had 74 850 that has been in storage for the last 15 years. It was running when it was put away so i'm doing the usual things to freshen it up before attempting to start it. When I originallly checked for spark I did not have any on either side. I ultimately found that the points were so oxidized that they did not make an electrical connection when closd , I've cleaned them and no have sprk on both plugs.

The problem I have now is that after the key is on for a minute or so the ballast resistor gets so hot it starts to smoke. I checked the resistor and it is within spec at 1.9 or 2.0 ohms . I also checked the primary of both coils and they are also around 1.9.

One thing i did notice is that now when I measure across the set of points that is open, that it is showing as shorted to graound, as if it they were closed. I don't know what would cause this, but my theory is because there is a direct path to ground through both set of points the coils that are wired in parallel now represent only have of the load which increases the voltage drop on the ballast resistor.

I'll be the first to admit that I'm not an expert on pints, but shouldn't I measure infinate resistance across the open set of points?
 
Trixie Combat has her's get wire then paint to smoking before I caught it. Found ballast cracked so resisting current even more. Replaced it to get points firing again. Went bad just sitting up between engine blow ups. i tease about it being mean shoe elves but know its really Ozark swamp man messing with my stuff. Check wire run for failed insulation and weakened terminals. Grease the AAU and hope for the best. Many folks have ballast left over after converting to electronics so likely get an offer soon.
 
Skelly said:
I have had 74 850 that has been in storage for the last 15 years. It was running when it was put away so i'm doing the usual things to freshen it up before attempting to start it. When I originallly checked for spark I did not have any on either side. I ultimately found that the points were so oxidized that they did not make an electrical connection when closd , I've cleaned them and no have sprk on both plugs.

The problem I have now is that after the key is on for a minute or so the ballast resistor gets so hot it starts to smoke. I checked the resistor and it is within spec at 1.9 or 2.0 ohms . I also checked the primary of both coils and they are also around 1.9.

One thing i did notice is that now when I measure across the set of points that is open, that it is showing as shorted to graound, as if it they were closed. I don't know what would cause this, but my theory is because there is a direct path to ground through both set of points the coils that are wired in parallel now represent only have of the load which increases the voltage drop on the ballast resistor.

I'll be the first to admit that I'm not an expert on pints, but shouldn't I measure infinate resistance across the open set of points?

If the points are not going open when they are open then yes the ballast resistor will get hot and eventually burn out.
It sounds like something with the points is not assembled correctly. Jim
 
I am working from a faulty memory, but it seems to me I remember recording a grounded ignition until I disconnected the warning light assimilator. Basically, if you are trouble shooting the ignition circuit then you should make sure that is all you are testing. I am puzzled about the smoking ballast resistor as it would indicate high amperage. So I would assume there is a short somewhere, but then how are you getting spark at both plugs?

The coils are typically in parallel. So I wouldn't think that should be an issue. Make sure they are six volt coils and not twelve volt.

Russ
 
I think you have misplaced the insulator rings on the points. The point arm spring must be insulated below, on top, and in the middle so it does not short to ground. A fiber washer goes on first and then one with a collar that goes in the spring eye and has a flat on top. The wire goes on and must make contact with the point spring. The system is enegized when the points close and current runs through the resistor and coils to ground. When the points open, the field in the coil collapses and the plug is jolted to fire. It is quite common for people to not insulate the point spring properly or to make sure the wire makes contact with the spring. Have a look at how you have yours set up.
 
I think aceaceca's explanation is the most likely problem although in that case I don't see how you're getting sparks on both plugs?
Also bear in mind that having the ignition switched on without the engine running will cause the resistor to get hot when the points are closed, because the current is flowing continuously unlike when the engine is running when the current is being switched on/off by the points.
Hope this helps a little.
 
Skelly said:
I'll be the first to admit that I'm not an expert on pints, but shouldn't I measure infinate resistance across the open set of points?

No, not unless you were to disconnect the points wire from coil(+), otherwise what you are effectively reading is the continuity between the point contacts but in the direction away from the point contacts and not 'across' them.


daveparry said:
I think aceaceca's explanation is the most likely problem although in that case I don't see how you're getting sparks on both plugs?

If that had been the case, then there wouldn't be any sparks at all, as the coil/s would be permanently earthed/grounded.
 
Skelly said,

" I've cleaned them and no have sprk on both plugs."

That could be taken as "I don't have spark on both plugs"

Pete
 
Deets55 said:
Skelly said,

" I've cleaned them and no have sprk on both plugs."

That could be taken as "I don't have spark on both plugs"

Pete

I took it to mean "I've cleaned them and now have spark on both plugs".
 
I'm not sure if it is a typo or not either. Just figure I'd ask the question to be sure.

My thought is, for that resistor to over heat it must be flowing current through it. It has be finding ground some where. In which case there should not be spark at the plugs (I don't believe so anyway).

Occams Razor says start with the simplest solution.


Pete
 
Thanks all,

I had meant the post to say that I now have spark on both plugs.

i'm head out to the garage this mornign and I'll check it again. I doubt that there is anything wrong with the points insulator since I have not had it off.

I'm wondering if it may be the warning light assimultor.

I'll let you know how I make out today.
 
Disconnect the warning light assimilator altogether as a test, it won't affect the sparks or the running of the engine. I don't think that will be anything to do with your problems though, it is only concerned with charging indication.
 
Skelly said:
The problem I have now is that after the key is on for a minute or so the ballast resistor gets so hot it starts to smoke. I checked the resistor and it is within spec at 1.9 or 2.0 ohms . I also checked the primary of both coils and they are also around 1.9.

Did you check between the primary terminals and the coil casings?
 
Ballast resistors get hot - that is just the way they are. The smoking you described is probably nothing more than the burning dirt, dust and maybe some oil burning off the resistor windings. It is similar to turning the house heater on for the first time in the season which can set off the smoke alarms. Of course you don't want to leave the ignition on without the engine running because you are going to have constant current going through the ballast resistor and one of the spark coils which could overheat and possibly get damaged.

Now if the wires that connect to the ballast resistor are smoking, that means that your terminals to the ballast resistor are bad and need to be replaced. Possibly you may also need to replace some sections of wire as well.

When checking your points for continuity you need to isolate them from the rest of your circuit. In other words disconnect the points wire at the spark coil. What you were reading was continuity between the other set of points which were probably closed and possibly through other circuits such as the ignition warning light.

The warning light assimilator has nothing to do with your ignition system. However, those warning light assimilators also get hot when the engine is running. So if you notice this down the road someday this is normal and you do not need to be concerned.

It sounds to me like you are about ready to go riding. I hope this helps,

Pete
 
if key left on - the connected-active charging up coil should get way hotter than the ballast but the ballast should not get so hot to smoke dust, oil or wire installation. Bad terminal will heat the terminal area till solder melts but then limits current to heat ballast to even normal warm 6 volt conduction. Suspect short on out put side of ballast, constant earth shorted breaker, a coil shorted externally or internally to case to earth, which would not spark that plug, or luck of the draw old age ballast failure. If ya give up on the thinking testing solutions for electronic, hobot is collecting Norton ignition left overs.
 
Good evening all.

It has been a very fruitful day. After drawing this all out on paper , I finaly clued in that what I thought was a dead short across the open set of points was indedd the impedence that I was measureing across the primary of the coil that was tied to grpound through the other set of points. As Peterjoe described it a couple of posts back , when I took the negative lead of the coil that was connected to the close points , I measured an open circuit across the open set. I gues my first mistake wa susing the diode tester on my meter rather than actually loking at what the ohm value actually read. Like I said at the begining of this post, I never claimed to be knowledgeable about points.... :lol:

With respect to the ballast resitor smoking , this was infact just junk on the windings of the resistor itself. The previous owner of this bike actually covered the bike with WD40 before he stored it in his barn in 1998. A little while after that his interests turned to workworking and he built a workshop in the barn. As a result of this, the bike was covered in sticky sawdust. It is a bit of a mes to clean up, but the chrome and everything else is amazingly preservered.
I replaced the smoking ballast resistor wiht one that I had left over after installing a tri spark in my other 850. This one didn't smoke , but it got warm. I guess from what you guys are telling me , I can expect it to get hot if the key is left on. I wonder what will eventually happen if the key was left on? Would the ballast resistor fail forst or the primary of the coil? Do you think there is a risk of fire?
Anyway, once i had her all squared around I tickled the freshly clenaed carps. She fired on the first kick but died immediately. Another tickle of the carbs and she started and stayed running. It is zero degrees here today and there is snow on the ground, but i couldn't resist taking here around the block.
I can tell I need to clean the clutch plates and clkean and mostly rebuild the front brake master and caliber, but other than that the old girl is purring like a kitten.
Thanks Everyone
 
Glad you figured out your Commando joy juice. Still unusual report of stored Commando ballast smoking w/o a fault. You should leave key on a bit while fingering you gal to get idea of time it takes to warm up the first thing and which heats up most then will know where to look first next time you forget to key off with fresh battery. Coils would try to boil their oil in mine before ballast got frying hot. MIght even get an idea of how long before ballast heat reduces points voltage and by how much. I've warmed hands on hot fins more than once but better with gloves on.
 
Skelly,

I had this problem a few years ago. The resistor got hot and the engine missfired at certain revs.

I measured the resistor and all was ok but it still did not work. Never found out what was wrong with it.

Replaced the resistor and the problem went away!

Regards,
Per
 
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