in the interest of providing feedback: had a fire this evening. a fet burnt up, I think it was shorting from drain to batt neg. I’ll have to be more careful with soldering on the next one.
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Shaman, thank you for sharing this with the community. I was the one having this issue, and I will try to answer the questions here and probably provide some advice so that you dont blow up your diodes.
The DRV’s ground pad from underneath is unsoldered wehn received from JLCPCB, at least on my batch of 10, i couldnt see any solder from underneath.
When I powered up the FOCer, it blew up D1, which I thought was a diode problem, i replaced D1 but it happened again. So I contacted @shaman and he pointed that it is a DRV issue. So this time I replaced D1 and powered the FOCer with 5V and gradually went up, any higher than 5V would result in a humming noise from the board. I measure the 5V rail and it was not regulating correctly. Therefore I advise you all to power your FOCer with 5V the first time and go up 0.5V. At 6V, measure the 5V rail, and if it any higher than 5.3V, and you hear humming, then do the following:
Get some hot air on the drv, start with 300C for 20 secs, and 380C until the drv pins are nice and shiny. Of course, pour in lots of flux beforehand. Remove the drv only when it is hot enough. Dont pull as this can damage the pads and render the whole PCB useless. Set the drv aside and add some solder to the ground pad with a soldering iron and some flux. Too much solder will result in the solder squishing out and shorting the pins. Give the pins a gentle swipe with the soldering iron. Dont put to much solder or it will bridge. put back the drv in place and gently applyl hot air at 380C. Let cool. Check i there are any solder bridges. I have a video about removing solder bridges on youtube.com/fungineers if you need it.
The drv should be OK now. Power with 5v and go up gradually. The 5v rail and humming noise should be fixed.
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Is there any easy test you can do with a meter to determine whether the DRV is soldered to the pad?
Also, could we not simply add solder from underneath rather than removing the chip?
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I just messed with a couple of mine. I tried to inspect them to see if I could tell whether they were soldered to the pad. There was no obvious evidence that they were, but it’s not at all clear to me that I’d be able to see that through the hole in the bottom. So I went ahead and gave them a bit of solder through the hole.
I then did a continuity check between AGND (Pin 28) and the pad to check it. After soldering it checked out. Now I kind of wish I’d done the continuity check before adding the solder. I’ll probably do that when I open up my TwoWheeler.
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I’m measuring 0,86 Ohm between the pad and AGND (the wires from my meter are about 0,5 ohm). I didn’t have any problems with powering on and detecting and running a motor (ebike 250W) in FOC. I did have some problems at first with usb but they just went away on its own. So maybe that was just a bad connection. Should I also add solder to the pad to be sure?
Just tried the diode tester method on a cheap focer v2
You will still get a reading of around 2.616V on the power input pins if the drv GND pad is soldered correctly
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If anyone has an extra 1 or 2 of these around let me know. Haven’t been around long enough to do a GB but would love to try this out regardless
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There are still units available from Group Buy Batch 2. I can send them internationnaly.
got another board together, working very well, no issues so far.
safe batt current is around 35A continuous, is that what it’s recommended to leave max batt current at?
What about motor current?
is it a good idea to use the DRV8301 OC mode? if so, what OC adjustment?
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Max batt and motor currents are 35A and 70A respectively but this depends on the thermal management of your rig. With airflow you could do a little higher.
Leave the drv OC mode disabled as it should be for default.
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Cant wait to use these beauties, got six from somebody instead of those nasty non existent neoboxes C:
Had the same issue myself with 3 FOCers that I assembled, yesterday I tried to fix one of them.
I removed the DRV, applied a bit of solder to the ground pad, and reflowed the DRV. I made sure that the pins are cleaned and not shorting. Powered ON the FOCer and nothing happened - LEDs didn’t light up, 5v rails didn’t output any value. I then increased the voltage of my lab supply (stuipd idea) from 5v to 12v, and then a little bit of smoke came out near AMS1117-3.3 (U1) or TJA1051T/3/1J (U4), not quite sure which one, the area near them was a bit hot as well. I guess the DRV wasn’t soldered properly, although I didn’t see any legs on the DRV that aren’t connected well to the PCB.
Whats the recommended way of hooking up an led strip to these for a diy onewheel?
So what do I probe with my multimeter? On the 10 I have, 3 measure 2.6V between the top of R20 (PWRGRD) and the bottom of R48, the other 7 measure 1.4V unlike the 2.9V doomy said.
Also, the datasheets for the 8301 on LCSC show pin 8 as AGND, not pin 28. Yet when I use Charclo’s method to test I get continuity on all 10 boards between pin 28 and the pad.
If someone could write a solid method of testing these boards I’ll buy you a sixpack.
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Looked at the datasheet wrong, PWRGRD is actually pin 4 and not pin 2, the 3 functional ones measure 2.4v between pin 4 and the bottom of R48. the other 7 still measure 1.4V yet continuity checks out 
I went from this datasheet…
It shows AGND on Pin 28
are you using kapton tape instead of thermal pads?
if so, how has performance been?
Yeah, i dont worry too much about performance, more about no getting shorts. I think even with 2 layer kapton tape the heat transfer should be better than 1mm silicone pad but i could be wrong.
@Minimadness
I have to confirm this with a unconnected gnd pad. But if you measure the input of the focer with the diode tester you should get 2.6v. If it is higher ~2.9V the connection to the GND pad is bad.
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Thanks for the reply, could you clarify which points I specifically have to measure? Also I’m measuring my boards without all the other components soldered, just bare smt assembled parts from jlcpcb. I was measuring between these solder points:
With ground on the top of R20 and positive on the bottom R48 I measure between 2.6V and 2.7V on the good ones, and 1.428V on the bad ones consistently.
With positive on the top of R20 and ground on the bottom of R48 I measure 2.43~ on the good ones and 2.33~ on the bad ones, there is clearly a distinction
I was referring to the cheap focer v1 in my link! R48 is a completely different resistor. On the v2 you can just measure between the 2 input pads.
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