jsuffolk
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UBEC Keeps Burning Up my Pis

Tue Oct 23, 2018 10:56 am

Hi,
As many advised here in the forum I'm using a 5v 3A UBEC to power my Raspberry Pi Zero W:
https://www.dx.com/p/hobbywing-5v-6v-3a ... ubec-15149

The UBEC input is drawing from a 12V 230A lawnmower battery.

The output is directly into the 5v and GND pins. There are a few devices pulling power from the Pi's 3V:
two I2C devices (ADC and LSM303), a UART device (I moved the bluetooth UART to the mini-UART) and 2 4-channel relay boards (one is a DPDT relay board). For the relays I've disconnected the JD-VCC jumper and they are pulling 5V in parallel to the PI to power the relay, while the input signals and the regular VCC comes off the PI's 3V. In total I don't think these pull more than 3A, and none of the relays were switched on at the time of the problem.

All connections are made through a breadboard, but I'd like to move to something more permanent as soon as I'm confident that the power setup is working and I stop burning up pis.

I've burnt out two Pis now with this configuration, they appear to work for a while then poof. In the most recent time the Pi had been in use with no wiring changes for about 20 hours. It had been running for about 3 hours contiguously while I was debugging a program on it over SSH. The Pi was essentially idle (except for an active Wifi connection) and I went to copy some new code over winSCP and the Pi froze - green activity light was still on and solid green. I disconnected the power (jumper clips) and reconnected it to reboot the Pi, the power light didn't come back on. I pulled the pi out of the breadboard and tried connecting via a normal power supply from adafruit and sure enough it's toast.

Is it the UBEC that's killing my Pis or is it possible something else is awry like overheating? Perhaps somehow when I connect the high amp battery it's pulling more than it should for a split-second? Is there a more reliable way I can supply power than this UBEC?

pcmanbob
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Re: UBEC Keeps Burning Up my Pis

Tue Oct 23, 2018 12:23 pm

Hi.

Seeing as the UBEC has the option to supply 5v or 6v have you actually measured the voltage that it outputs using a meter ?
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mahjongg
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Re: UBEC Keeps Burning Up my Pis

Tue Oct 23, 2018 12:26 pm

Applying 6V to the PI will trigger its over-voltage protection diode, which will short the 5 Volt rail, and this blows the polyfuse.

Unless you manage to burn out the TVS diode, the PI will recover when its polyfuse self-heals.

You could try to use a cigar-plug adapter, but (for a PI3B+) you need one that can deliver 2.5A . cheap ones only do 1A, but for a zero that will be enough! The ones that you directly plug into the cigar plug are small, so they contain a switching converter, large boxed ones are less good, and often contain just an LM7805 linear regulator.

Normally you can screw open the adapter (most often by a unscrewing a ring around the tip), and then you can cut of the red wire (to the tip), and a black wire to the side springs, so you have wires to connect +12V to directly (red is the positive 12V input, black is GND). These adapters already have one or two USB ports.
Because they have USB outputs they should output no more than 5.25V, and no less than 4.75V, unlike "battery replacement units".

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HawaiianPi
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Re: UBEC Keeps Burning Up my Pis

Tue Oct 23, 2018 1:06 pm

mahjongg wrote:
Tue Oct 23, 2018 12:26 pm
Applying 6V to the PI will trigger its over-voltage protection diode, which will short the 5 Volt rail, and this blows the polyfuse.
It's a Pi0W, so no protection (and he's powering it from the GPIO expansion header, so even if it wasn't a Pi0...).

jsuffolk wrote:
Tue Oct 23, 2018 10:56 am
I'm using a 5v 3A UBEC to power my Raspberry Pi Zero W:

The UBEC input is drawing from a 12V 230A lawnmower battery.

The output is directly into the 5v and GND pins.
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aBUGSworstnightmare
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Re: UBEC Keeps Burning Up my Pis

Tue Oct 23, 2018 2:15 pm

5V is supplied to Pi and - in parallel - to relais coils...

Maybe you should search for the term 'induction voltage' and then add a few bucks for either a decent protection circuit or relais driver.

jsuffolk
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Re: UBEC Keeps Burning Up my Pis

Wed Oct 24, 2018 12:27 am

Seeing as the UBEC has the option to supply 5v or 6v have you actually measured the voltage that it outputs using a meter?
Yes, it's on the 5V jumper. I measured the output, was ok.
You could try to use a cigar-plug adapter, but (for a PI3B+) you need one that can deliver 2.5A . cheap ones only do 1A, but for a zero that will be enough! The ones that you directly plug into the cigar plug are small, so they contain a switching converter, large boxed ones are less good, and often contain just an LM7805 linear regulator.

Normally you can screw open the adapter (most often by a unscrewing a ring around the tip), and then you can cut of the red wire (to the tip), and a black wire to the side springs, so you have wires to connect +12V to directly (red is the positive 12V input, black is GND). These adapters already have one or two USB ports.
Because they have USB outputs they should output no more than 5.25V, and no less than 4.75V, unlike "battery replacement units".
Interesting. I thought the UBECs would be a switching converter as well, the description also mentions a filter to reduce noise. You're suggesting that the cigar-plug would have a tighter voltage range?
5V is supplied to Pi and - in parallel - to relais coils...

Maybe you should search for the term 'induction voltage' and then add a few bucks for either a decent protection circuit or relais driver.
This is a real possibility as the circuit is not protected against this. However, I'm skeptical that was the problem in this case as all the 12V relay circuits would have been off at the time of the problem and the NC state of the relays are ground to ground. Nonetheless, I think this is something I'll need to address.

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Re: UBEC Keeps Burning Up my Pis

Wed Oct 24, 2018 1:18 am

jsuffolk wrote:
Wed Oct 24, 2018 12:27 am
5V is supplied to Pi and - in parallel - to relais coils...

Maybe you should search for the term 'induction voltage' and then add a few bucks for either a decent protection circuit or relais driver.
This is a real possibility as the circuit is not protected against this. However, I'm skeptical that was the problem in this case as all the 12V relay circuits would have been off at the time of the problem and the NC state of the relays are ground to ground. Nonetheless, I think this is something I'll need to address.
The Pi0/Pi0W do not have the power protection circuits present in other Pi models. Also...you average multimeter isn't going to see transient spikes...and those may be what is killing your Pis.

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