Capacitors in KT Controller blown

[Sturmey]

I think that large carbon resistor is part of the regulated lower voltage and 5volt circuit. One end is connected to the 48/36v and the other end goes to the voltage regulators. Its shown in the bottom of the circuit diagram I have attached below as R62 and 82ohms/3watt but this resistor number and ohms value varies with different versions of the KT controllers as far as I know.
If you google 'KT controller circuit board' and select 'images' you will see examples of this resistor with different values on different versions of the controllers as photo below.
The fact that the resistor has 'blown' would lead me to suspect that there may have been a fault on the 5 volt line or that the voltage regulators may be faulty, so there is no guarantee that replacing the resistor will work. Also I suppose it would be wise to check the external wiring as a short on the 5 volt line could possibly cause this resistor to blow.
I have attached a pdf of KT controller general circuit diagram below if it helps.

.

 

[Balmy]

That too _could_ read 1K and it's failed open circuit: if it were more than 7K a smaller and cheaper one could have been fitted. The cause of failure still needs finding and fixing.

thx

 

[Balmy]

I think that large carbon resistor is part of the regulated lower voltage and 5volt circuit. One end is connected to the 48/36v and the other end goes to the voltage regulators. Its shown in the bottom of the circuit diagram I have attached below as R62 and 82ohms/3watt but this resistor number and ohms value varies with different versions of the KT controllers as far as I know.
If you google 'KT controller circuit board' and select 'images' you will see examples of this resistor with different values on different versions of the controllers as photo below.
The fact that the resistor has 'blown' would lead me to suspect that there may have been a fault on the 5 volt line or that the voltage regulators may be faulty, so there is no guarantee that replacing the resistor will work. Also I suppose it would be wise to check the external wiring as a short on the 5 volt line could possibly cause this resistor to blow.
I have attached a pdf of KT controller general circuit diagram below if it helps.

View attachment 63438.

Thx for the info. Are you suggesting i replace it with a 82 ohms/3 watts resistor?

 

[saneagle]

It needs to drop the voltage by around 20v at a current of between 100 and 200mA, so it'll be 100 Ohms to 200 ohms. Colour look like brown black brown, so 100 ohms. It's value isn't that important as long as itin that sort of ball park. The shunt would only overheat if you connected the battery with the wrong polarity, which would also soon blow the capacitors, or if a MOSFET has blown, so you should check them before going any further.

 

[Balmy]

You are right. I did indeed short the controllers positive with the negative, but the battery was not attached. I tested the resistor out of the circuit and it showed 198 ohms. I checked the mosfets, they are all ok. Visually the capacitors seem ok too.

 

[saneagle]

You are right. I did indeed short the controllers positive with the negative, but the battery was not attached. I tested the resistor out of the circuit and it showed 198 ohms. I checked the mosfets, they are all ok. Visually the capacitors seem ok too.

Shorting the wires without the battery is not harmful and it doesn't send any current goes through the shunt. Shunts are normally 0.005 ohms, so would dissipate 2w at 20A.

 

[Balmy]

Shorting the wires without the battery is not harmful and it doesn't send any current goes through the shunt.

Well i had a proper short, sparks and burning wires smell

 

[saneagle]

Well i had a proper short, sparks and burning wires smell

It's just a spark due to the high current. You get the same when you connect a live battery. It looks and sounds bad, but it's pretty harmless.

 

[Balmy]

It's just a spark due to the high current. You get the same when you connect a live battery. It looks and sounds bad, but it's pretty harmless.

I thought so too, i had that happen twice before and my controller worked fine, the 3rd time it happened i thought it would be fine, but this time the display came on but the throttle stopped working. The motor is fine, it works with another controller. I opened it up and found the shunt was a bit charred and the legs of the resistor had a bit of black char too.

 

[Ghost1951]

It isn't that easy to be certain whether the first band on that resistor is yellow or orange, but I reckon that picture looks like orange, brown, brown for the resistance values and orange for the tolerance value. If that is correct, that would make the value of the resistor 310 ohms, with a tolerance value of 0.05%

If the first band is not orange, but yellow, then the value would be 410 ohms and 0.02% tolerance. I can't be sure because the lighting and clarity is not ideal and the colours look a bit faded with age or heat stress.

Either way - the measured value of 198K is way off, so it is not right. Resistors are very cheap - even chunky ones. I can't see what physical size it is, but you need one of the same size to dissipate whatever power it dissipates. Maybe you could try and take some more photos to give a better idea of the colours in the resistor bands.

One more thing to say - and you likely know this, but just in case you don't, electrolytic capacitors have a polarity and they MUST be soldered in the right way around. Follow the orientation regarding + or - marked on the capacitors as they were originally. They go off with a bit of a bang and fling out rubbish if you put them in the wrong way around. Also it is important to make sure you get the right voltage rating. Certainly - don't under-volt them.

Here is a decoder for the resistor colour code if you can get a better idea of the colour bands.

Resistor Calculator

This resistor calculator converts the ohm value and tolerance based on resistor color codes and determines the resistances of resistors in parallel or series.

www.calculator.net

 

[Balmy]

View attachment 63440

It isn't that easy to be certain whether the first band on that resistor is yellow or orange, but I reckon that picture looks like orange, brown, brown for the resistance values and orange for the tolerance value. If that is correct, that would make the value of the resistor 310 ohms, with a tolerance value of 0.05%

If the first band is not orange, but yellow, then the value would be 410 ohms and 0.02% tolerance. I can't be sure because the lighting and clarity is not ideal and the colours look a bit faded with age or heat stress.

Either way - the measured value of 198K is way off, so it is not right. Resistors are very cheap - even chunky ones. I can't see what physical size it is, but you need one of the same size to dissipate whatever power it dissipates. Maybe you could try and take some more photos to give a better idea of the colours in the resistor bands.

One more thing to say - and you likely know this, but just in case you don't, electrolytic capacitors have a polarity and they MUST be soldered in the right way around. Follow the orientation regarding + or - marked on the capacitors as they were originally. They go off with a bit of a bang and fling out rubbish if you put them in the wrong way around. Also it is important to make sure you get the right voltage rating. Certainly - don't under-volt them.

Here is a decoder for the resistor colour code if you can get a better idea of the colour bands.

Resistor Calculator

This resistor calculator converts the ohm value and tolerance based on resistor color codes and determines the resistances of resistors in parallel or series.

www.calculator.net

Thx for the suggestions and the explanation. Yes it is indeed quite difficult to determine the colour bands of the resistor, in the pic i posted and also when i look at it. It is a large resistor 1.5 cms in size and grey in colour. The band colours are a bit confusing. My best interpretation is band1 is a light brown/ copper band, band2 is definitely black, band3 is darkish coffee brown and band4 is a metallic lightish brown although slightly darker than band1, but quite similar. Because i was unsure of the band colours i posted my query in this forum, in the hope that maybe someone knew for sure, the value of this capacitor, which would help me determine if it had blown and what value to replace it with. I do understand it is difficult to determine its value as all kt controllers have different value resistors as someone else suggested. I have attached a couple of new pics that are clearer and more life like.

 

[matthewslack]

I admire your desire to fix it, but the sheer messiness and low cost of a replacement would take me down a different route! Not forgetting that display and controller are best replaced as a pair.

 

[thelarkbox]

fwiw i was reading Orange Black brown/gold, 3, 0, x10, 5% 300ohm 5%

Bt now band #1 looks gold too ???

 

[Ghost1951]

Thx for the suggestions and the explanation. Yes it is indeed quite difficult to determine the colour bands of the resistor, in the pic i posted and also when i look at it. It is a large resistor 1.5 cms in size and grey in colour. The band colours are a bit confusing. My best interpretation is band1 is a light brown/ copper band, band2 is definitely black, band3 is darkish coffee brown and band4 is a metallic lightish brown although slightly darker than band1, but quite similar. Because i was unsure of the band colours i posted my query in this forum, in the hope that maybe someone knew for sure, the value of this capacitor, which would help me determine if it had blown and what value to replace it with. I do understand it is difficult to determine its value as all kt controllers have different value resistors as someone else suggested. I have attached a couple of new pics that are clearer and more life like.

Orange, black, brown? I have no certainty, but the new photo certainly shows the second denomination band as black, I previously thought that was brown.

If correct, it would be 300 ohm, and 0.05 tolerance. At 15mm, sounds like a 2 watt resistor.

Matthew's advice is sound, but if you really want to have a go yourself, it won't cost much to do it.

The capacitors shown in the first photo are 470 microfarad and 300 microfarad, 50Volt electrolytics.

You would need to get them with the leads coming out the same way. Typically, teh leads come out of the same end, but sometimes, electrolytics have wires coming out of either end.

This company is local to me and I can walk in and talk about what I want, but they are mainly an online dealer nowadays.

https://www.esr.co.uk/

 

[Balmy]

I admire your desire to fix it, but the sheer messiness and low cost of a replacement would take me down a different route! Not forgetting that display and controller are best replaced as a pair.

Yes i know they should be bought as a set and they are cheap. As i wrote in another post in this thread, i already have another set and have my bike up and running. I just find it a waste to throw away something that can possibly be repaired for a few cents. Besides it is quite a kick when you can do a little investigation and come up with a positive result, and if the result is not positive, then too you end up having learnt something in the process.

 

[Balmy]

fwiw i was reading Orange Black brown/gold, 3, 0, x10, 5% 300ohm 5%

Bt now band #1 looks gold too ???

I am confused too

 

[Sturmey]

I have an old but working cyclotricity kit (2017) 36v/14A Kt36ZWSR controller (label hard to read) in my hand at the moment. I have removed the end cover and can clearly see the shunt and the resistor. The shunt is discoloured, so I guess this is normal. The resistor has a red, black and brown band and a gold band at the end, so this would indicate 200 ohms. .

 

[Balmy]

Orange, black, brown? I have no certainty, but the new photo certainly shows the second denomination band as black, I previously thought that was brown.

If correct, it would be 300 ohm, and 0.05 tolerance. At 15mm, sounds like a 2 watt resistor.

Matthew's advice is sound, but if you really want to have a go yourself, it won't cost much to do it.

The capacitors shown in the first photo are 470 microfarad and 300 microfarad, 50Volt electrolytics.

thx for your response. The second one is definitely black, the 3rd definitely dark brown. The first one is light brown/ copper. Cant tell for sure. Yes i do get Mathew. I just like to tinker, thats how i ended up blowing it thrice . Both my capacitors are 470uf 63v.

 

[Balmy]

I have an old but working cyclotricity kit (2017) 36v/14A Kt36ZWSR controller (label hard to read) in my hand at the moment. I have removed the end cover and can clearly see the shunt and the resistor. The shunt is discoloured, so I guess this is normal. The resistor has a red, black and brown band and a gold band at the end, so this would indicate 200 ohms. .

thx for the effort. If you are right then my resistor is fine as it shows a reading of 198 ohms. Which only makes life more difficult, as i have to investigate further and find where the fault is at.

 

[Balmy]

Thank you everyone. I will order a few resistors in the values that you all suggested and try them. Hopefully it is the resistor that is the problem and hopefully one of them will fix the controller. If not i will try to find the fault in other areas and if i cant find it, i will bin it. It will take time and i will post and update somewhere in the future. cheers