kiev
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Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Troubleshooting and repair for On-board Charger (OBC)

Wed Sep 29, 2021 8:33 am

i've used a hot soldering iron (dry tip with no solder) with a fat flat blade tip to heat up small areas of the epoxy. This seems to break it down somewhat to form a powdery layer that can be chipped and scrapped with the blade tip or other metal tools. This will mess up the tip for soldering unless you have a sal block to re-tin the tip, or just use a replacement tip.

Also a really sharp flat blade such as Xacto, etc can pry against the thin layer on top of the diodes to crack and flip that thin small layer on top to reveal the part numbers. The thin epoxy will crack with some verical pressure of the blade, then it can be pried off from the side.

You have some nice green color of the circuit board showing so you are doing great and its working. This is all new--never been seen board before.
kiev = kenny's innovative electric vehicle

philsuth
Posts: 26
Joined: Fri Apr 03, 2020 9:29 am
Location: Perth, Western Australia

Re: Troubleshooting and repair for On-board Charger (OBC)

Thu Sep 30, 2021 7:55 am

Another evening of mining. I used the Dremel, as well as working the epoxy with a old flat bit in the soldering iron (this was a good suggestion, thanks Kenny). I'm now thinking I may have done enough. I've removed all of the carbon and enough epoxy that I can see clearly where the failed capacitor used to be, and clear PCB below I can also see the top of the neighbouring capacitor.

Image

With access to the capacitor contacts I have confirmed that the short is gone, and that all of the diodes in the bridge are functional. I'm thinking that I can do an initial test as is this weekend, and solder another cap in parallel before back filling with epoxy if all is well.

kiev
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Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

Re: Troubleshooting and repair for On-board Charger (OBC)

Thu Sep 30, 2021 8:03 am

Is the other cap good? Can you get a reading of its value?

What is the approximate size of the device, length width height.

Great news about the diodes.
kiev = kenny's innovative electric vehicle

philsuth
Posts: 26
Joined: Fri Apr 03, 2020 9:29 am
Location: Perth, Western Australia

Re: Troubleshooting and repair for On-board Charger (OBC)

Thu Sep 30, 2021 3:59 pm

Good questions, should have thought of them myself. The remaining capacitor measures approx 3mm long by 2mm wide - from the x-ray its cremated neighbour was identical. Capacitance reads as 47-48nF.

philsuth
Posts: 26
Joined: Fri Apr 03, 2020 9:29 am
Location: Perth, Western Australia

Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Oct 03, 2021 1:27 am

So, I soldered it all back together again, leaving the pit in the waffle board as pictured above. I did proper joints rather than test tacking as the desoldering gun works very well with leaded solder and its slightly lower melting point. I put the boards back in, bolted the power board down with fresh heatsink paste, double and triple checked all the connections and the aux battery voltage (has been a while) crossed fingers, toes and every other imaginable appendage, and switched on.
...
...
It worked. No smoke, just all the normal charging noises. It pulled 12A @ 240V and did just what it was meant to. After three hours my imiev is now at 100% battery again.

Next move is to pull it out again, tidy up the waffle board and fill the pit, solder it together again, quickly test and then repot the main board. Haven't quite decided whether to try installing another cap to replace the cremated one or just to leave well enough alone.

One very happy (and more than a little relieved) iMiev hacker here.

JoeS
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Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Oct 03, 2021 7:23 am

philsuth, congratulations! Delighted your perseverance and skill paid off!
EVs: Two '12 Wht/Blu SE Prem., '13 TeslaMS85, three 156v CorbinSparrowsLi(NMC), 24v EcoScoot(LiFePO4)
EV Conversions: 156v '86 Ram PU, 144v '65 Saab96, 48v1kW bike
RIP(2021) ICE: Orig.Owner '67 Saab96V4, '88 IsuzuTrooper; '76 MBZ L206D RHD RV

Sandrosan
Posts: 43
Joined: Tue Sep 24, 2019 2:43 am
Location: Milan, Italy

Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Oct 03, 2021 1:23 pm

Hi Philsuth,

BRAVOOO! Your great passion and perseverance are amazing!

I am so happy for you

coulomb
Posts: 311
Joined: Sun Jun 10, 2018 8:32 pm
Location: Brisbane, Australia

Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Oct 03, 2021 3:24 pm

philsuth wrote:Haven't quite decided whether to try installing another cap to replace the cremated one or just to leave well enough alone.

I certainly would replace the capacitor. It may be assisting with suppressing of ringing, so leaving it out may stress the PFC MOSFETs, possibly leading to early failure.

philsuth
Posts: 26
Joined: Fri Apr 03, 2020 9:29 am
Location: Perth, Western Australia

Re: Troubleshooting and repair for On-board Charger (OBC)

Sun Oct 03, 2021 4:11 pm

coulomb wrote:
philsuth wrote:Haven't quite decided whether to try installing another cap to replace the cremated one or just to leave well enough alone.

I certainly would replace the capacitor. It may be assisting with suppressing of ringing, so leaving it out may stress the PFC MOSFETs, possibly leading to early failure.


Good point, and it raises several questions. Do you think it reasonable to assume that both capacitors (in parallel) were the same value? I presume the total capacitance required would depend on characteristics of the FETs and possibly the bridge diodes, all of which are buried deep in the epoxy. In the later units there was a single 1uF outside the epoxy, but this was coupled with a smaller inductor then the heavy duty 600uH monster mine is fitted with.

Also, why would you use two capacitors in parallel? Lower ESR?

philsuth
Posts: 26
Joined: Fri Apr 03, 2020 9:29 am
Location: Perth, Western Australia

Re: Troubleshooting and repair for On-board Charger (OBC)

Mon Oct 04, 2021 6:43 am

From my reading this evening the failed capacitor is there primarily to bypass high frequencies from the boost converter, and so reduce EMI. The design guides I read also suggest a low ESR cap, and this may be why a pair of them were used. I'm now thinking I'll replace the failed capacitor with another 47nF 500V chip capacitor - this will delay completion of my repairs a few days while I get the part, but I've come so far I'd rather do the job properly.

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