[SOLVED] Smart Power 3 not working after attempted reboot

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[SOLVED] Smart Power 3 not working after attempted reboot

Post by paulcrawford »

I received a Smart Power 3 last week and in the beginning it worked fine. I connected the left hand output to my N2+ and the input to a Hardkernel 15V power supply that I originally got with a Smart Power 2. I use a lithium battery as a UPS on the N2+ so the output from the SP3 goes into a Y cable that feeds both the battery and the N2+. The power supply that came with the battery has a voltage of 12.6V so that is what I set the output of the SP3 to. I updated the firmware to get the output on telnet and that worked fine until today when I could not get any response on the SP3 IP address. When I looked st the SP3 screen I noticed that the WiFi connection icon on the top right was not green and the description below indicated that it was not connected to WiFi. I thought the best thing to do would be to restart the SP3 so I unplugged the 15V input power, but the screen did not go blank. I realize now that the battery voltage from the N2+ was probably feeding back to the SP3 and preventing it from shutting down. When I plugged in the input again I heard a dull pop and then that characteristic electronic burning odour. Then the screen went black. After realizing that the output was probably feeding back I unplugged it as well but plugging in the input with no output did nothing and the screen was still black. I opened the box up but saw nothing obviously burned.

Is there any possibility of repairing the SP3?

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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

Wow, that's an interesting case - exceeding output voltage over the input voltage.

The Buck converter has a high side MOSFET switch that has a parasitic diode, letting the current flow through it backwards. What happens next, I'd have to check on the schematics, but one thing for sure, nothing good.

Many things could have gone wrong, but since even the display is nonfunctional, i don't think there is much to be salvaged from this unit. :(
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Re: Smart Power 3 not working after attempted reboot

Post by odroid »

We will try reproducing the issue with an external power source soon.
Then, we can check which components would be damaged.
Give us a couple of days.

BTW, what was the output voltage settings on the Smart Power 3?
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paulcrawford (Thu Dec 16, 2021 9:24 pm)

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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

Thanks @odroid. The output voltage setting I used was 12.6.

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Re: Smart Power 3 not working after attempted reboot

Post by odroid »

We could reproduce the problem. We connected a bench top power supply to the SP3 output port and removed the power source of the SP3.
Immediately, the STPD01 DCDC converter and a couple of near PCB patterns showed a short period of fire. :o

The DCDC converter IC STPD01 seemed to be permanently damaged and showed something internal short circuit condition.
But, the SP3 could turn on if we connected it to my PC via USB cable.
It means there should be no other fried components probably. Please try connecting your SP3 to a 5Volt USB port to check the status first. Don't connect the main power source for this test.

After replacing the fried STPD01 and adding some wires to repair the burned PCB patterns, the SP3 is working fine now.
If you really want to keep using the UPS battery after repairing, you need to place a diode (20~30Watt grade) between UPS input and SP3 output to prevent the reverse current perhaps.

BTW, mouser and some other famous IC distributors seem to have enough stock at this moment.
https://www.mouser.com/ProductDetail/ST ... qHUQ%3D%3D
I hope you have some soldering skill and tools to replace the QFN type IC.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

I have removed the STPD01 and I can see that there are burned traces on the PCB.
1639835996718 copy.png
1639835996718 copy.png (2.02 MiB) Viewed 668 times
Rather than replace the chip and add new wires, would the SP3 work on the other channel alone or do both channels need to be present and working?

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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

Holy... smokes..

As far as I can tell from my experience with SP3 firmware, it should work with a single channel only. Hardware wise both channels should be independent.
It is certainly not prepared to work in such conditions and may hang or do other unexpected stuff, waiting for the answer from nonexistent chip. Actually, your input on that matter would be appreciated.

That is, of course, assuming nothing else got damaged.

Just be mindful pure carbon is conductive. You'd like to make sure that battlefield is cleared up before you proceed.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

I will try cleaning up the board. Do you think 99% isopropyl and a brush would do anything or do I need to be more aggressive? Once I get it clean I will try the single channel output to try to rescue this device. I will and another photo for review post-cleaning.

@odroid, would a 1N5041 diode work to protect the SP3 output? It is rated at 3A but because of the forward voltage drop of 1V I would need raise the output to about 13.6V so the power would be about 41W. What do you think?

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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

1N5041 is a Zener diode and is a terrible choice for this application. Don't!
You want a Schottky diode with 5A or more current rating. Power rating isn't that important in this application, nor switching speed. A Schottky rectifier diode might be a good choice.
I can help you select a diode if you have a preferred shop nearby and share their website.

Cleaning the board with alcohol certainly won't hurt. If you feel like it, you may remove surrounding resistors just to be sure. Capacitors may be removed as well, but that is not expected to change anything.
In my mind, care must be taken to avoid short circuit between U1's input voltage and anything else. Just use a ohm meter to make sure this is the case.
U1 input voltage is - and I'm just guessing here - on the lower end of your photo, where two capacitors can be seen.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

Apparently I am not very good at selecting diodes! :oops: The highest current capacity I could find at my local shop is 3A: https://secure.sayal.com/STORE2/details.php?PID=3147284. If that current capacity is OK, will the 20V rating be OK or would the 40V be better. All the same price anyway.

I have cleaned up the damaged area by scraping out the burned PCB material. It seems that there was a copper ground plane below the top layer so it went too. I also removed all of the resistors and capacitors (except C3 and C44) around U1 and then cleaned the entire area with 99% isopropyl alcohol.This is a picture of the final state:
1639947783515 copy.png
1639947783515 copy.png (512.2 KiB) Viewed 626 times
Do you think it looks OK?

As I do not have the diode yet, I assume that I could test the other channel without it as long as I remove the output connector before disconnecting the input power. That is how I used it first and it was fine until the removed the input power to reboot the SP3. What do you think?

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Re: Smart Power 3 not working after attempted reboot

Post by smitna »

paulcrawford wrote:
Mon Dec 20, 2021 6:31 am
Apparently I am not very good at selecting diodes! :oops: The highest current capacity I could find at my local shop is 3A: https://secure.sayal.com/STORE2/details.php?PID=3147284. If that current capacity is OK, will the 20V rating be OK or would the 40V be better. All the same price anyway.

I have cleaned up the damaged area by scraping out the burned PCB material. It seems that there was a copper ground plane below the top layer so it went too. I also removed all of the resistors and capacitors (except C3 and C44) around U1 and then cleaned the entire area with 99% isopropyl alcohol.This is a picture of the final state:

1639947783515 copy.png

Do you think it looks OK?

As I do not have the diode yet, I assume that I could test the other channel without it as long as I remove the output connector before disconnecting the input power. That is how I used it first and it was fine until the removed the input power to reboot the SP3. What do you think?
What's about RMA for your device?
I think we have an other reason to ask what's about the status of:
- real current protection
- backlight off after power off (I think/hope a firmware problem)
- logging freezes after some time (I think/hope a firmware problem)
- and now the risk to connect batteries or something like that to the output (charging etc.?)

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Re: Smart Power 3 not working after attempted reboot

Post by odroid »

@paulcrawford,
Could you turn on your Smart Power 3 after cleaning the PCB?

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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

Yes, it does boot and connects to WiFi when the USB C port is powered. Do you think it is safe to connect the input 15V power with nothing connected to the output on the right channel (the only working one)? If so I could at least check the no load voltage at the output.

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Re: Smart Power 3 not working after attempted reboot

Post by odroid »

Please hold on.
We've been testing some diode samples to protect the reverse current flow from an external battery. We will post a test result very soon.

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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

I will hold on of course. I will not connect the output to the UPS battery permanently until I get a diode in the output circuit. I still wonder though about connecting for a test, as I did when I first got the SP3, which worked fine for several days. The problem occurred only when the input power was disconnected. The input power is also connected to a 120VAC UPS so there is almost no possibility of it not providing power accidentally. If the output power is disconnected before the input power then there should be no problem as that is almost the same as it running right now on USB power with no load, except that I still have not connected the input power yet.

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Re: Smart Power 3 not working after attempted reboot

Post by lsc1117 »

@paulcrawford,

I have tested with SK54 schottky diodes.

http://www.smc-diodes.com/propdf/SK54%2 ... 0REV.-.pdf

There is no issue on this circuit when the voltage is supplied backward. But, there may be about 0.4V voltage drop.
And It's better to use Axial type diodes, not SMD.

We didn't have a UPS, so we used a power supply unit instead.

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Last edited by lsc1117 on Tue Dec 21, 2021 11:05 am, edited 1 time in total.

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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

paulcrawford wrote:
Mon Dec 20, 2021 6:31 am
Apparently I am not very good at selecting diodes! :oops: The highest current capacity I could find at my local shop is 3A: https://secure.sayal.com/STORE2/details.php?PID=3147284. If that current capacity is OK, will the 20V rating be OK or would the 40V be better. All the same price anyway.
Yes, I think you have found the best diodes for your application the shop can offer. :) SK54 proposed by @lsc1117 above would be great too.
I encourage you to google a datasheet of a diode that you selected and look through its outstanding features :D
Pick the one rated for the highest voltage, if the price is the same. This is the voltage the diode can withstand while blocking current, so in theory your battery voltage would be enough.
paulcrawford wrote:
Mon Dec 20, 2021 6:31 am
Do you think it looks OK?
No, it looks like a disaster. :D
But you did an excellent job of cleaning it all out. I'm pretty confident it should not cause random short circuits from now on.
If you have a separate lab PSU at hand, it would be wise to supply SP3 off that lab PSU with some 15V and 0.1A current limit to prevent total destruction if there is still something wrong.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

mctom wrote:
Mon Dec 20, 2021 5:50 pm
Yes, I think you have found the best diodes for your application the shop can offer. SK54 proposed by @lsc1117 above would be great too.
I encourage you to google a datasheet of a diode that you selected and look through its outstanding features
Pick the one rated for the highest voltage, if the price is the same. This is the voltage the diode can withstand while blocking current, so in theory your battery voltage would be enough.
I did get the data sheet https://www.st.com/resource/en/datasheet/1n5822.pdf and it seems that the lower voltage one (20V) also has the lowest voltage drop (0.475V vs 0.525V for the 40V) so I think I will go with that one. Do you concur?
mctom wrote:
Mon Dec 20, 2021 5:50 pm
If you have a separate lab PSU at hand, it would be wise to supply SP3 off that lab PSU with some 15V and 0.1A current limit to prevent total destruction if there is still something wrong.
As it happens I do have a lab PSU so I will use it as the input of the PS3 and we will see what happens.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

I set up the PS3 with a lab PSU at 15V and maximum current of 0.1A as input and no output connected. It boot fine, connected to WiFi but would only output 5V, although the output was set to 12.6V, on the right channel. I disconnected the input, connected it again and then connected an N2+ without a UPS battery. Finally the output went to the required 12.6V and the N2+ booted. So it seems like a success.

Here is a photo of the setup:
IMG_1387.png
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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

Wow, you really did your homework here!

About the diode, well spotted, the maximum forward voltage drop does differ by 0,05V between the two.. I think any of these two models will do.
Keep in mind voltage drop on a diode actually depends on the forward current, temperature, and varies from diode to diode. So in worst case it's gonna be 0.525V, but in the best case close to 0V (See Fig. 10-1 and 10-2).
paulcrawford wrote:
Tue Dec 21, 2021 1:03 am
It boot fine, connected to WiFi but would only output 5V, although the output was set to 12.6V, on the right channel.
Did you measure this voltage, or was it displayed on SP3?
I expect firmware to be really confused about the lack of one chip, so it may have shown wrong value to begin with. If the output voltage was indeed 5V (measured independently), that would mean SP3 had a hard time configuring outputs. 5V is the default voltage setting of the buck converters, I believe.

Of course, I suggested 0.1A input limit just for booting SP3 and making sure it's not suicidal. For powering N2+ you'd want to set this limit much higher. And input voltage may be 19V too. :)
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

mctom wrote:
Tue Dec 21, 2021 1:16 am
Keep in mind voltage drop on a diode actually depends on the forward current, temperature, and varies from diode to diode. So in worst case it's gonna be 0.525V, but in the best case close to 0V (See Fig. 10-1 and 10-2).
Yes I did notice that the voltage drop that I will have will be less than the maximum levels stated. It is interesting that the higher the temperature, the lower the voltage drop. At the operating current of an N2+, probably around 0.2 to 0.3A, it seems unlikely that the junction temperature would be much above 25°C but we will see what happens. The issue is, of course, that the PS3 will include the power loss in the diode as part of the output power that is logged. But for normal operation that would be say 0.3V and 0.25A or 0.075W compared with say 2.5W for the N2+ so only about 3% so not so bad! And if the diode heats up bit, it will be even less.
mctom wrote:
Tue Dec 21, 2021 1:16 am
Did you measure this voltage, or was it displayed on SP3?
I expect firmware to be really confused about the lack of one chip, so it may have shown wrong value to begin with. If the output voltage was indeed 5V (measured independently), that would mean SP3 had a hard time configuring outputs. 5V is the default voltage setting of the buck converters, I believe.
Not with a voltmeter but an N2 would not do anything so I think it probably was 5V. No matter though as it is working now. And I believe that the default output is 5V as well since that is where both channels were when I first started the PS3 (before the issues).

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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

paulcrawford wrote:
Tue Dec 21, 2021 1:50 am
It is interesting that the higher the temperature, the lower the voltage drop.
This is true for all silicon diodes and bipolar junction transistors. :)
This is also why connecting a few diodes in parallel to share their load doesn't work, as the hotter one conducts better, thus gets even hotter. The load will never balance.
paulcrawford wrote:
Tue Dec 21, 2021 1:50 am
it seems unlikely that the junction temperature would be much above 25°C but we will see what happens.
Ah, but you can work that out.
Junction to ambient thermal resistance is given in datasheet, 80 K/W. (That's Kelvins per Watt).
You already estimated power dissipation at 0.075W.
So, the product is 6 Kelvin, or 6 degrees Celsius. That's the junction temperature rise compared to ambient temperature. Insignificant. :)
paulcrawford wrote:
Tue Dec 21, 2021 1:50 am
The issue is, of course, that the PS3 will include the power loss in the diode as part of the output power that is logged.
If you find it bothersome, you can rewire buck converter feedback node to include a diode - this way you'll always get the proper output voltage, and correct logs.
BUT this way you'd introduce a path unprotected by the diode. To work around that, you would have to add a high resistance on a feedback node, something around 100k, which may be a source of errors on its own.
This is actually a common practice in space industry. I'd show you a relevant example if I could. :)
paulcrawford wrote:
Tue Dec 21, 2021 1:50 am
Not with a voltmeter but an N2 would not do anything so I think it probably was 5V. No matter though as it is working now. And I believe that the default output is 5V as well since that is where both channels were when I first started the PS3 (before the issues).
I fear this may happen again. Keep an eye on that, don't burn a low voltage circuit by accident if your SP3 really has issues changing output voltage.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

Thanks again for all of your help. You really are brilliant.

All I need to do now is get the diode and solder it onto the output lead then verify the voltage drop with my DVM and determine an average offset on the logged power consumption. I think that is simpler than rewiring the feedback node etc.

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Re: Smart Power 3 not working after attempted reboot

Post by mctom »

Oh stop it you, I'm just an electronics engineer that loves to brag about it. ;)
I don't know what your background is, but I take it you must pursue a similar trade, or are an exceptionally quick learner.

If you don't plan to modify feedback loop you can always use the diode externally. No soldering required, unless you mean soldering to your usual power supply leads. :)

On the other hand, I think this is already understood what caused the failure - From SP3's perspective, output voltage must never be higher than input voltage, which will always be true unless you unplug the PSU from SP3 with battery still connected to the output.
So either you remember about that, or always use diode for protection, with all the drawbacks that you have already identified.
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

mctom wrote:
Tue Dec 21, 2021 5:28 am
I don't know what your background is, but I take it you must pursue a similar trade, or are an exceptionally quick learner.
Actually I am a retired professional engineer in the wastewater treatment field. All of my electronics knowledge comes from "Google".
mctom wrote:
Tue Dec 21, 2021 5:28 am
If you don't plan to modify feedback loop you can always use the diode externally. No soldering required, unless you mean soldering to your usual power supply leads.
Yes external diode so that it is part of the device to be powered rather than the power supply. And yes soldering similar to what @lsc1117 showed earlier today.
mctom wrote:
Tue Dec 21, 2021 5:28 am
On the other hand, I think this is already understood what caused the failure - From SP3's perspective, output voltage must never be higher than input voltage, which will always be true unless you unplug the PSU from SP3 with battery still connected to the output.
So either you remember about that, or always use diode for protection, with all the drawbacks that you have already identified.
I thought about doing it without the diode and just remembering to disconnect the output before the input. Since the present arrangement has the input on UPS it will be very difficult for it to be disconnected from it's AC input, but nonetheless, if the N2+ has a UPS, there is still a risk losing the second, and only now, output on the SP3. I think prudence says put in the diode and live with the power loss, which can easily be dealt with in software.
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Re: Smart Power 3 not working after attempted reboot

Post by lsc1117 »

I have changed the pictures above to make it more clear.
In the previous pictures, only SP3 could supply power to N2.
Now both UPS and SP3 can supply power to N2.

download/file.php?id=15111
download/file.php?id=15110
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Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

Yes, those photos show exactly how my N2+ is connected if the power supply is replaced by a battery.

Thank you for making it very clear.

paulcrawford
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[SOLVED]Re: Smart Power 3 not working after attempted reboot

Post by paulcrawford »

I noticed that the Wiki for SP3 has been updated to include reference to this topic. Thank you for that!
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odroid (Wed Dec 22, 2021 9:21 am)

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