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R4 overheats on the AUX-PS r3B3 module (green PCB)
IMPORTANT: Only some BB3 kit version with 2 Mean Well LRS modules seems to be affected by this issue!
R4 is located on the AUX-PS module r3B3 that looks like this (i.e. green PCB version):
/Images/AUX_PS_r3B3.jpg)
Possible remedy (updated): install RC snubber 1 uF (X2 / 300 Vac) + 47 R (3-5 W). Use e.g. heat shrink tube to properly insulate capacitor and resistor terminals. Capacitor's terminal pitch could be from 15 to 27.5 mm.
R4 which limits the opto-triac current in the soft-start circuit overheats if BB3 is switched on continuously for several days.
An indication that you may have this problem is over-temperature protection (OTP) tripping for the AUX temperature sensor (inside IC2 which is near R4).
The soft-start (inrush current) limiter circuit was not new to the AUX-PS module: it was literally copied from the H24005 PSU in which it has been running properly for years. However, the H24005 does not use the Mean well LRS F-model (full range or autoswitch) but one that has manual input voltage selection (115/230 Vac). So basically it's another model! Soft start uses two triacs that are controlled via the opto-triacs OK1 and OK2. It turns out that the Mean Well F-model in some way affects the operation of the opto-triac even when there is no load. In the long run, i.e. if your BB3 is turned on continuously for a week or more, the power resistor that should limit the current of the opto-triac overheats so much that it eventually burns out. Why haven't I been able to notice this so far? For two reasons: I have BB3 active for at least 10 hours a day every day, and when I did continuous testing (which lasts for several days) then I did it with BB3 which had one modification on Mean well's which was one of the attempts to passes the current harmonics test. So I had 4u7/X2 capacitors connected in parallel at their inputs! Here are some pictures. The resistor that looks good to me but not to @goran-mahovlic is the R4 which is under increased stress from Mean Well's F-model:
R4 temperature if two F-models are connected without added capacitors at their AC inputs (230 Vac):
... and it increases further. If I connect a purely resistive load (230 Vac, 46 W halogen lamp) R4 temperature is just fine:
The same is true if I have capacitors added:
Detail of the connected capacitor on one of the Mean well's:
I can't test 115 Vac and 60 Hz here, I only have 50 Hz, but it seems that the situation is even more alarming. Fortunately, capacitors help in this case as well. Without capacitors (115 Vac / 50Hz):
... with added capacitors:
What will happen if R4 burns out? Soon after the power up DCP and DCM modules will report an error as they will get DC at their inputs only for a short time (as long as the soft-start sequence lasts when another triac will be used). In short, no further damage should be expected.
In the picture with the capacitor, do you also have another small component? Resistor or diode? At least on my screen, I can't tell...
@johnsonm I have asked the same - it is nothing important just resistor for quicker capacitors discharge after power down
The capacitor used is 4u7, X2 Kemet R46KR447050P1M. A bleeder resistor can be connected in parallel (470K to 1Meg):
It seems that only one capacitor is needed, even if three Mean well's are used:
I could only find 0.47uF on some old power supply
After adding it many problems just dispersed:
Resistor R4 is not overheating any more! With function generator I could repeatably get smoke out of DCP405 with setting voltage to 3.3V and current to 100mA with this capacitor it is working normally! AUX OTP tripped after long usage is gone I could not use function generator if OVP HW is set - it was activated in first few seconds, now it does not Current showing on channel without load was much more noisy
I have two channel BB3 with two mean wells.
I have two DCP405. Powered up for months now (usually around 15W per channel, rarely higher). Zero issues.
Today I've added two 1uF WIMA MKS4 10% 400V just to sleep better 🙂
Thanks everyone for sharing and @prasimix for transparency!
I'd not known about this issue. But just today after having my unit powered for 10 minutes I bumped the table and I get a CH1-Ch2 Error message. I'm in Australia so running at 230V,50Hz.
Opening my unit I saw this.
And I can confirm that it's R4. It appears to gotten hot enough to melt the solder, and then after a slight bump it simply fell off.
I could do some tests later with a thermal camera this week if you want some more data from systems running at 230/240V.
Weird - I'm in Australia, and after 10/15 minutes not seeing any significant heat on R4
I must just have the worst luck with my unit then. :laughing:
I've gone ahead and installed 2x 1uF X2 caps.
While it helps... the resistor still reached ~88.0C after 5m of idle operation. (Measured with a kapton insulated thermocouple.)
I also took a short video with a thermal camera. https://youtu.be/8bMoKZcSGj8
Unfortunately I don't own a radiometric unit, so I can't read off exact temperatures, only the thermal flux. The modified version I took a reading with the thermocouple right after capturing this video, which read 88.0C.
You can see the modified version does a bit better than unmodified.
My local electronics store didn't have 4.7uF X2 caps. But I can order some with my next Digikey/Mouser order. Any other ideas about why this is happening? Or things I should try.
Hmm yeah that's strange. Not sure if it's relevant but my unit has three meanwell LRS-150-48s instead of two. I have a few R46KW447000M1K on the way. Happy to post one to you when they've arrived
@gregdavill this is really strange since @goran-mahovlic reported that only single 0.47uF rectify this problem for him. I tested it on my side with 4.7uF as already reported. I still don't know why combination of two Mean Well's makes this problem. For the test could you please try to disconnect one Mean well and make thermo measurement once again? Thank you very much for your patience.
I tried right now two new Mean Well randomly selected from piles and another AUX-PS "green" version. Not the slightest change in temperature can be measured on R4. See pictures (I used a wooden stick to make it easier to see on the thermal image where the R4 is). Still don't know why is that.
Ok, obviously something is wrong with the combination of multiple Mean Wells. But not only the two LRS-150F but also the two IRM-10s located on the AUX-PS module. I did a new test and instead of just a capacitor I put an RC snubber 1uF + 47R (3-5W) on the AC input and now I have a significantly better situation. It seems that a little experimentation will be needed here.
I did repeat the test here with just one meanwell LRS-150F unit attached. I received the same result, temperature rapidly approached >80C within a few minutes.
Ok, as you can see I got better results with bigger RC snubber (since one exists on the AUX-PS module), it now looks like this:
Adding a 1uF / 47R to one unit does appear to help me a bit. This is brings my results inline with your initial testing, R4 climbs to around ~45C.
I tried right now two new Mean Well randomly selected from piles and another AUX-PS "green" version. Not the slightest change in temperature can be measured on R4. See pictures (I used a wooden stick to make it easier to see on the thermal image where the R4 is). Still don't know why is that.
So what happens if you swap the AUX-PS with the AUX-PS on the other unit where you saw the high temperature rise? I can you isolate whether it is one or two dodgy LRS on your original unit, or a variation in the AUX-PS module?
I tried to swap LRS modules, but not AUX-PS (where IRM-10s resides). I'll do that and report here.
Okay
I guess what I meant was
| AUX-PS module | LRS modules | Problem evident? |
|---|---|---|
| A | 1,2 | Yes |
| B | 3,4 | No |
| A | 3,4 | ?? |
| B | 1,2 | ?? |
I have very little experience with triac/AC circuits, but I've been poking around with my unit here.
I added the extra snubber circuit on both LRS-150F's. And removed R1/R3. Is it my understanding these simply aid in noise immunity for the gate? (But at the expense of extra current draw?) With these two mods my unit seems to function more correctly, with R4 only warming to ~28C (18C ambient) after 5m.
Not sure about the negative ramifications to this mod, but thought I'd share as an extra data-point.
For those of us without the hardware, where is the revision of this board source that is affected by this issue and same for the wiring diagram to the updated PSU modules?
For those of us without the hardware, where is the revision of this board source that is affected by this issue and same for the wiring diagram to the updated PSU modules?
- Affected AUX-PS module (Crowd Supply kit version): https://github.com/eez-open/modular-psu/tree/master/previous%20designs/aux-ps%20r3B3%20(Crowd%20Supply%20edition)
- Latest version (CE approved, assembled version): https://github.com/eez-open/modular-psu/tree/master/aux-ps
I have the green AUX-PS with three LRS-150F. I measured with the temperature probe of my multi meter, and it seem to be around ~37C (25C ambient) after 5 minutes with a load of 24V and ~13W and no modifications.
With a 1uF X2 capacitor and a 1M bypass resistor on one mean well it got down to ~35C with two ~33C. So I don't think I could reproduce this issue really.
@PyroDevil as already mentioned, this issue seems to affects kit versions with 2 Mean wells in the first place. So you're safe (i.e. with original RC snubber on the AUX-PS module), but you can add a bigger one if you like.
Some debugging thoughts:
- What is the current drawn on AC_OUT_L by all downstream components? A modest bandwidth current clamp to an oscilloscope required. Could this fail to meet Q2's latch/hold currents while still maintaining active downstream loads?
- What is the line input waveform at the LRS-150F terminals? Does any distortion correspond to discontinuities in the current measured?
- Do the loads (IRM + LRS) on all the AC/DC supplies attached to AC_OUT_L contribute to R4 getting stuck hot?
- (highly complicated) Would an isolated zero-crossing detect and driving PWR_DIRECT at each ZC help identify if Q2 isn't switching reliably?
Thanks Thomas for all your valuable suggestions. It seems that some more detailed investigation is needed. At the moment I think we have a good solution that does not require any intervention on the AUX-PS module which is already retired and will no longer be offered. Also in the future Mean Well LRS will be replaced with EPP model.
As I mentioned on Discord, I was concerned that the issue with R4 is due to the lack of a snubber across triac Q2 terminals. See the MOC3052M datasheet Figure 8 for an example snubber configuration. The snubber across AC_OUT_L and AC_OUT_N (or on the PSU) won't help as much as one across the triac terminals. Another option is to try the snubberless version of the BTA26. As the issue seems to only affect some units & configurations, it is hard to know whether that will be of help.
It is possible that the latch/hold currents of the triacs is the issue when combined with the lack of snubber, as they could be marginal especially at low ambient temperature. At idle, I measured a single LRS-150 PSU (-F or non -F) draws 45mA RMS at 110V 60Hz, and 86mA RMS at 240V 50Hz. In both cases the power factors were really low. With the -F PSU PF was around 0.010 at 110V and 0.022 at 240V. With the non-F PSU, the PF was 0.046 at 110V and 0.025 at 240V.
I have still not seen this on either of my BB3 units even with the problematic configuration of two -F PSU's at 240V, so I haven't been able to investigate/test this myself. I'm certainly no expert having only a few low power triac based designs under my belt.
