UPDATE on Lights causing LM-3S to overheat?

[CPRail]

Reference my previous post:https://rpug.pdc.ca/index.php/topic,1679.0.html

This weekend, I pulled out all the bulbs and replaced them with surface mount LEDs. I wired them up, including the resistors on the negative side. Went to hook them up on the board and couldn't get them to work.

Pulled out the old multimeter and we are getting juice to the connections, which I expected as the original light-bulbs were working.

Then, when taking the loco off the rails, I almost burnt my fingertips on the whitish-gray resistors (I'm guessing) hanging on the bottom of the board just above the flywheels! See photo 4.

Wok the heck? Keep in mind, I had the light functions turned on for maybe 30 seconds prior to testing with the multi-meter. The rear resistor was cooler than the front, but still warm. I'm guessing that is due to it driving the gyra-lite so the voltage goes up and down, while the headlight one is constant. NOTE: I did not have any LEDs or bulbs hooked up when I checked with the multi-meter.

Time to pause and ask the experts!!

Guess I found why the LM-3S was getting overheat messages with these little Chernobyls sitting under the board!

So, couple of questions:
1. What causes those resistors to get Rocket Hot in such a short period?
2. How do I test these surface mount LEDs before hooking them up to the module board?
3. What am I doing wrong?

[CPRail]

Adding pictures

[CPRail]

Last set of pics.

[G8B4Life]

At that size and body colour those are likely to be inductors, not resistors. If so they are part of of an RF suppression circuit on the motherboard. I've never heard of them getting hot to the touch before though. Anyway, if they are inductors it's best to remove them (replaced by a plain wire) as they just cause trouble for modern control gear. I talk about the why they are there briefly in this post.

Let's make sure they are inductors though, As I've just located a resistor with the same apparent size (but different colour, resistor brown) on a motherboard here. You'll need to check the under side of the circuit board to see what they are labelled as to 100% absolutely confirm. If they are labelled as L such as L1, L2 then they are inductors. If labelled as R such as R1, R2 then they are resistors.


I don't recall asking this simple question, did you ever get the over temp warnings when running without the lights on or having the lights on while not running? If we didn't ask/try this we could have saved ourselves a whole lot of searching.

- Tim

[CPRail]

Hey Tim,

Let me check on the components. Now that the lights are disconnected, I can do a test run as well. Stay tuned.

[kellanphil]

What was the result?

[CPRail]

Sorry guys, we had the first really nice days of spring here on the weekend (FINALLY), so no train activity due to being outside enjoying the weather! Of course, it was gloomy and snowy all day yesterday in punishment. Mother Nature is a harsh mistress...

I'm doing the tests tonight and will update in the morning.

[CPRail]

Here are the results (see photos). The grey items on the bottom of the board sure look like resistors to me, but I'm not an expert - I only play one on TV.  One location is marked R1.

All running was done on test rollers as I don't have a continuous loop of track. Throttle was set at 75% for all tests. Load was set to about 25-30% on the HC. There was a 5 minute cooling period between the first run (in reverse) and the subsequent run (in forward). I removed the shell immediately after each running test to check temps.

Test 1 was 15 minutes in reverse, headlights/gyralites were off.

Test 2 was 20 minutes in forward, headlights/gyralites were on.

After Test 1 the grey resistors where cool to the touch, the LM was slightly warm.

After Test 2, the front grey resistor was rocket hot (headlight), the rear was uncomfortably warm (gyralites), the LM was noticeably warm - you could feel the heat from the outside of the shell.

While you can see the LM temperature increasing, I suspect if I had an actual load and was able to let it loop, it would increase faster.

Next steps?

[gregeusa]

OK, just checking we are on same page. from april 7

you replaced all the original incandescents with LEDs, and you added resistors.

(no value was given for the resistors!)

in the same post you say the LEDs were not hooked up when you tested with a meter...

right here, those resistors on the board overheating without the LEDs connected makes no sense whatsoever...

if this is true, if you have the right resistors that connect to the function outputs, your board is damaged..

I think we need pictures of the board, with the "resistors" circled and verified what they are connected to..

Greg

[gregeusa]

update, I could not see the pictures when replying...

OK, your components hooded the the LEDs are resistors, not inductors...

they have 5 bands, so they are precision.. what is hard is to read the sequence, since the tolerance band is not the typical gold or silver (of course since they are high tolerance, i.e. 5% or better)..


brn-brn-blk-blk-brn  (100 ohms)  (cannot read the other way, the first digit cannot be 0, i.e. black)

so 10 ohms times 1 = 10 ohms...

if that is right (measure with meter), no kidding you have the wrong resistors!

what is the common voltage? (not mentioned) but if 12v, then ohms law gives you 1.2 amps!

Greg

[CPRail]

Hi Greg,

Ask and you shall receive!

The resistors come up just behind a bunch of diodes on the board. I've marked the resistor connection and where the headlights connect (this is the "front" of the board - gyralites are connected to the "rear" part of the board with a similar setup). I've also circled the resistors.

Resistors I attached to the LEDs are 1KΩ - I used the same resistors when wiring up my Rapido B36-7 and it works fine.

I'll have to measure what is coming across those resistors.

For the common, where is the best place to measure?

[gregeusa]

usually the common wire is blue... let me look at the manual:

ok, blue wire in the diagram:
https://ringengineering.com/RailPro/Documents/LM-3Instructions.pdf

so 1k should be fine, I guess I could not see that some of the lines on the resistors were brown, not black... it would be very good to test the resistors with an ohmmeter to be sure, they sure looked black...

have you tried the decoder with the leds connected but not the motor?

Greg

[CPRail]

To clarify, I did not add the resistors on the board, that is how it came. I added the 1KΩ resistors in line with the LEDs as per the below photo. Maybe I have too many resistors in play?

I note that the board I have in my loco is NOT what the Athearn P/N shows as being...

Maybe I have dud LEDs. Now that I soldered the 1KΩ resistors to them, is there a way to test the LEDs without them being hooked to the loco? Can I connect them to an AA battery, like one can do with an incandescent bulb?

[gregeusa]

so more resistance should lower current, so that should not cause overheating

having shorted LEDs could, or if they were wired in backwards.

disconnect the LED and resistor and test on your supply voltage, you have not indicated your max track voltage, but again guessing it is 12 volts or so.

Greg

[G8B4Life]

Here are the results (see photos). The grey items on the bottom of the board sure look like resistors to me, but I'm not an expert - I only play one on TV.  One location is marked R1.

All running was done on test rollers as I don't have a continuous loop of track. Throttle was set at 75% for all tests. Load was set to about 25-30% on the HC. There was a 5 minute cooling period between the first run (in reverse) and the subsequent run (in forward). I removed the shell immediately after each running test to check temps.

Test 1 was 15 minutes in reverse, headlights/gyralites were off.

Test 2 was 20 minutes in forward, headlights/gyralites were on.

After Test 1 the grey resistors where cool to the touch, the LM was slightly warm.

After Test 2, the front grey resistor was rocket hot (headlight), the rear was uncomfortably warm (gyralites), the LM was noticeably warm - you could feel the heat from the outside of the shell.

While you can see the LM temperature increasing, I suspect if I had an actual load and was able to let it loop, it would increase faster.

Next steps?

You didn't run the test without using the motor, ie standstill. however I don't think you'll need to.

Yes those resistors are resistors, The R1 marking confirms that but we did need to confirm it; I've not seen that body colour on that size resistor before. The value is 150 ohms though (brown-green-brown-gold).

Anyway, I'm confident I've been able to ID the board now (consequently lifting the LM off the board may have given this away too). It appears to be an older Digitrax product that Athearn put in their models and I found a home drawn circuit of the board here: http://www.pacificcascaderailway.com/converting-an-athearn-pc-board/. It's certainly looks like it's designed for bulbs/globes/lamps, and in fact I'm surprised you get the LED's to work at all (circuit simulation says it shouldn't!)

Anyway from what I can work out is your passing about 90 mA on each of the front and rear outputs which is about 1.2 watts of heat generating power each output at the same time, so no wonder the poor LM was toasting. From what I can see you can either toss the board and start again with a new motherboard designed for LEDs or you'll have to get rid of more components on the motherboard; namely the 4 smd diodes at each end, and maybe more.

- Tim