skylogger
Posts: 76
Joined: Sun Dec 14, 2014 3:54 am

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

Fri Sep 07, 2018 8:16 am

Hi KIEV:
All of my posts from 29th of August onwards are regarding this 2nd OBC 17 SKYLOGGER#2 that I've been working on.
The first OBC 13 had the Twisted 39k resistor, blown 2x 1000pf caps in the doghouse and the 20 amp fuse in MCU Blown.
That was all that was required to get it running again.

So far on this 2nd OBC 17 SKYLOGGER#2 , the 20 amp fuse in MCU was blown, the 2x 1000pf caps in doghouse blown, one of the 4.7R resistors in the doghouse was blown, and the Relay in the doghouse you could hear click on activation, but contacts would never close to zero ohms.
I think that once I replaced the fuse, and 1000pf caps, I tried testing in car, and it seemed to detect AC input for a few minutes but then stopped charging. There is probably still some shorted component that is causing more than 16 amps to be drawn, which has now damaged the 4.7R resistor and the Relay during that test. Once I get the replacement relay and resistor replaced, I'll still need to see what other fault is causing the input current to be too high. Earlier, Coulomb suggested using a current limited power supply with an AC output of around 50v
applied to the AC input of the OBC. Buying one of these is not in the budget just at the moment. I have a few 2:1 mains transformer that get used to convert 240V to 120v which was used on some USA equipment to be used in Australia. I was thinking of putting 2 of these one after the other, so I end up with 60vac that I could put a 5 amp fuse in series with. Another thing that I was thinking about trying, is a portable "stick" arc welder. This is basically just a variable transformer with an adjustable output that max at around 50v. I could either leave in or take out the rectifier, and connect the output with a 5 amp fuse to the AC input of the OBC.

Before I try any of these things, Now that I have the waffle board removed from the main board, I'll continue ohming out the areas that I could not get to previously. Its a shame that in the final rectifier bridge section, there is a point where the two bridges are connected together, but there is no test point that can be accessed due to potting in the waffle. I guess that since I can go across the whole bridge array and see a 2x diode drop, that would look like something else if any of the 4 inside diodes were shorted. I was worried that one of these diodes would get damaged by the same inductive kick that killed the 2x 1000pf caps since the output filter feeds back to them. So far that all looks ok on the meter.

I can see a normal diode drop across the protection diodes that are across the IGBTs, but that's not much of a full test. Since the waffle is seperated from the PCB now, I was wondering if I used a 12v supply with a 10k series resistor connected to the gate of the IGBT, would a ohm meter show a difference across the output of the IGBT pins comming out of the waffle, or would I need to setup some other pullups or pulldowns to get a bias?

coulomb
Posts: 175
Joined: Sun Jun 10, 2018 8:32 pm
Location: Brisbane, Australia

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

Fri Sep 07, 2018 6:54 pm

skylogger wrote: I think that once I replaced the fuse, and 1000pf caps, I tried testing in car, and it seemed to detect AC input for a few minutes but then stopped charging. There is probably still some shorted component that is causing more than 16 amps to be drawn, which has now damaged the 4.7R resistor and the Relay during that test.

Initially, I thought that the resistor or relay failure might have been the original cause of the charrger failure. But with a little thought, I agree with most of your assessment. I think that the 4.7 Ω resistors must have been intact for the test, and failed after the few minutes. Hence, no more AC detection. But I think that the relay contacts may have been burned before the test. The pre-charge resistors allow the 3 220 μF capacitors to charge and the charrger to actually charge at very low power, but of course they will drop way too much voltage as the current ramps up. In fact, maybe the relay is the only problem now, apart from the extra 4.7 Ω resistor, and when these are replaced, it might all just work. But of course, it would be good to gain confidence about this. Replacing the relay means the full power of the mains is available for blowing up IGBTs :shock:

Once I get the replacement relay and resistor replaced, I'll still need to see what other fault is causing the input current to be too high.

As indicated above, I think there's a moderate chance that there isn't such an other fault. The normal mains current of over ten amps is too much for the resistors, if the relay isn't shorting them.

Earlier, Coulomb suggested using a current limited power supply with an AC output of around 50v

Actually, I use around 50 V DC. The charrger doesn't care; it will rectify whatever you give it. I was going to say that a ~37 VAC source (remember that 50 V will rectify to some 71 VDC before diode drops) isn't nearly as safe as a current limited DC source, but due to the 3 220 μF capacitors, the current limiting will have little effect. The capacitors with enough voltage will have enough energy to destroy the IGBTs before the current limiting can come into effect. Perhaps you could use a 12 VAC or even DC plug pack to connect to the mains. There isn't a lower limit, because the power supply doesn't come from the mains, but from the auxiliary battery. In fact, you might be able to use your 13.8 VDC power supply to power the mains input and also the 12 V input, wiring them in parallel. There should be isolation to prevent problems with that. Unfortunately, without intervention, the PFC front end will probably work really hard and turn that 13.8 VDC into ~400V for the IGBTs to switch. The Elcon/TC charrgers had mains detection, and disabled the PFC section if the mains was not detected. We don't know if these Nichicon charrgers have this detection and disabling.

I guess that since I can go across the whole bridge array and see a 2x diode drop, that would look like something else if any of the 4 inside diodes were shorted.

Yes, the fact that you can't separate the two paralleled bridges doesn't really matter at this point. As you say, any single diode shorting should be detectable.

I was worried that one of these diodes would get damaged by the same inductive kick that killed the 2x 1000pf caps since the output filter feeds back to them. So far that all looks ok on the meter.

Excellent point. But I think the IGBTs have a reasonable surge current rating, so they might survive where the capacitors literally explode.

I can see a normal diode drop across the protection diodes that are across the IGBTs, but that's not much of a full test.

True, but considering the usual failure mode of IGBTs (total meltdown and short circuit, or alternatively fused bond wire and hence open circuit), seeing these normal voltage drops is quite a good sign. I'd say very roughly a 75% confidence that they are OK.

Since the waffle is separated from the PCB now, I was wondering if I used a 12v supply with a 10k series resistor connected to the gate of the IGBT, would a ohm meter show a difference across the output of the IGBT pins comming out of the waffle, or would I need to setup some other pullups or pulldowns to get a bias?

That sounds reasonable; I think it should work. You might have to come down a bit with the 10k series resistor; there may be something like a 10k pulldown from gate to emitter already. Though I've seen values as high as 47k. 1k from 12 V (12 mA) isn't going to blow up these large devices. I'd use the diode range on the multimeter, rather than ohms; often ohms range are designed to be lower voltage so as not to turn on semiconductors, and diode ranges are higher. My second hand Fluke can even slightly light up blue LEDs (near 3 V). I just used another multimeter to check it: 0.15 V on the ohms range (auto ranging, so that's the 40 megohm range), and 3.76 V on the diode range. Other multimeters may not have as large a difference, but still.

[ Edit: "merely work really hard" -> "probably work really hard" ]

kiev
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Re: Troubleshooting and repair for On-board Charger (OBC), DC-DC Converter

Fri Sep 07, 2018 7:08 pm

Thanks for clearing up the question about which OBC you were testing.

i think coulomb was suggesting that you can use a DC power supply of about 50-60 VDC with an adjustable current limit in order to make probing measurements and not cause additional damage--an AC supply is not necessary. The DC will pass thru the diode rectifier bridge and charge up the 3 big caps, then the PWM switching of the Boost stage can be measured or seen on your scope to prove that it is working. Hopefully your waffle plate is intact and undamaged.

Your data and findings re-affirms my thoughts about a weak Aux battery.
If the 5V coil drive supply gets drop-outs due to a poor 12V supply, then the contacts in the AC input relay would be experiencing excessive chatter and internal arcing which coats the conductive contact surface with carbon. Now it is a high-resistance contact and eventually the relay wasn't carrying any current, but it was routed thru the two 4.7R precharge resistors. Those are fairly tough resistors, but they weren't sized to handle the full current required to operate the OBC.

In addition the AC detection circuit picks off the AC signal downstream of the relay contacts--the cutting in and out of the OBC during your test was a sign that the relay contacts were frosted and the processor was getting confused. If you pull the DTCs with the MUT i predict you will have a stored code in the EV-ECU for
either:
Code No. P1A10: On board charger power supply relay circuit, low input
Code No. P1A11: On board charger power supply relay circuit, high input

If you could read the OBC data items the code would be either 06 or 27, for abnormal AC input voltage or current, or taken from the FSM:
=============================
Code No. 04: Control Power Supply Voltage Abnormal. This is recorded if:
For more than 10 seconds, the on board charger control power supply voltage is less than 7.2 V.
or
For more than 10 seconds, the on board charger control power supply voltage is more than 17.6 V.

Code No. 04 PROBABLE CAUSES:
The auxiliary battery is failed.
When jump-starting at more than 17.6 V from the outside of the vehicle.
The installation of the auxiliary battery terminal is failed.
The DC-DC converter is failed.
Open circuits of on board charger power supply, short circuits to earth or damage; poor contact of connector
The on board charger is failed.
==========================
So my thoughts are pointing to weak or old Aux batteries as the main culprit common to all these failures on the forum. The specific manifestation of burnt and blown parts is related to which cascade of events gets triggered.
kiev = kenny's innovative electric vehicle

coulomb
Posts: 175
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Location: Brisbane, Australia

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

Fri Sep 07, 2018 7:10 pm

skylogger wrote: The part number on the relay is K1AKOO5W-KW I soldered some wires to the coil pins and supplied 5v to the relay and could hear it click.

Hopefully you were careful to get the polarity correct; there is likely a diode or other circuitry across the relay coil that could be damaged by a low impedance 5 V power source if connected the wrong way around. It's a significant pain getting these relays off the board, so testing in-situ is a good idea.

Something to keep in mind if other readers attempt this sort of thing.

Also be aware that giving power to the relay may also liven up the whole 5 V circuit, which may have consequences. So make sure you have no other power connected when you do this, or gates could start turning on, etc.

Another consideration is that if the relay doesn't pull in, it may be because something else is dragging the 5 V supply down. This was especially the case with the Elcon/TC charrgers, which ran the relay off the 15 V power supply (via a 68 Ω resistor), and plenty of other power gear (gate drivers, PFC chip, PWM chip, and a quad NAND gate) would often effectively short out the 15 V power rail.

coulomb
Posts: 175
Joined: Sun Jun 10, 2018 8:32 pm
Location: Brisbane, Australia

Re: Relay as root cause?

Fri Sep 07, 2018 7:24 pm

kiev wrote: Code No. 04: Control Power Supply Voltage Abnormal. This is recorded if:
For more than 10 seconds, the on board charger control power supply voltage is less than 7.2 V.
or
For more than 10 seconds, the on board charger control power supply voltage is more than 17.6 V.

With the 17.6 V figure mentioned twice, it sounds like these error codes respond to the voltage of the auxiliary battery, as read near the charrger input. That seems to imply to me that they expect the charger to work more or less successfully down to around 7.2 V. I find it a stretch to imagine that an auxiliary battery that operates window winders, headlights, etc well enough to not be immediately suspect would fall to 7.2 V while charging. However, the sudden switch-on of a coolant pump or the like might cause a brief brownout, which might cause the relay to partly drop out. But a relay that pulls in at less than 5 V will likely not drop out at more than ~2 V, so I'm still a little sceptical.
Last edited by coulomb on Sat Sep 08, 2018 11:58 pm, edited 1 time in total.

kiev
Posts: 996
Joined: Sun May 03, 2015 7:15 am
Location: The Heart o' Dixie
Contact: Website

An Aux battery weirdness story

Fri Sep 07, 2018 8:17 pm

i bought my car ~ 3 years ago and it was only ~3 years old at the time, and it still had the original OEM 12V Aux battery. i drove it the first year without doing any maintenance or worry, but sometime into the 4th year i started having troubles. The car would randomly quit and throw the HV ! warning, go to turtle mode and other weird stuff. i might have to try several times to re-start, leave the key off for several minutes then re-try etc. No pattern developed to give any clues of why this was happening.

i checked the Aux battery and it was reading ~12.8 OCV, so it seemed ok to me--i kept driving it and putting up with the occasional stall which was becoming more frequent. It was bothering me and very troubling that it could just die for no good reason while on the road...not a good thing in traffic.

Eventually i decided to just get a new Aux as part of the troubleshooting process--it was still reading "good" at OCV, but i was getting desparate. And the new Aux seemed to solve that issue, no more stalling. i think some other folks were having the same random issue around the same timeframe, same year car, same OEM Aux, etc.

So now we are seeing 17 OBC failures within the past 6-8 months. The poll results are not complete, but i suspect a commonality that those with failures were still using the original 6 year old OEM Aux battery.

i got a report this week of another OBC failure from someone not on the forum--they replaced his 6 yr old OEM Aux battery as part of troubleshooting, but the OBC is bad. Price is too high, the car is for sale.

It may be difficult or impossible to prove the weak Aux battery theory, but my stalling experience and its resolution leads me down this path. i will keep an open mind and i'm willing to test other theories and look for bad parts and the smoking gun...

But if you are still using an old Aux, please save yourself grief and get a new one before the something hits the fan...

Here's the link to FSM for this code, there are strange phrasings due to translation from Japanese to English:
Code No. 04

Also a link for testing the 12V AUX battery.

They have a three-part criteria with an open-circuit, charging, and loaded voltage test.
It must have a no-load OCV of 12.4V two minutes after running the headlights for 15 seconds, and
It must be have OCV of 12.4 or more after 6 hours of charging at 5 Amps, and
Under load it must measure higher than a minimum temperature-dependent voltage ranging from 8.5 to 9.6V (-15 to +21C) after 15 seconds of discharging @130 Amps.
Last edited by kiev on Sat Sep 08, 2018 4:32 am, edited 1 time in total.
kiev = kenny's innovative electric vehicle

electronpusher
Posts: 45
Joined: Sun Jun 25, 2017 3:11 am

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

Fri Sep 07, 2018 8:43 pm

I cannot collaborate this, as it is only the sellers word, but when we bought the car, he said that he had the Aux Battery replaced because the car would not power up. So the battery is supposed to be about 1 year 4 months old, the battery indicates it is good, but the battery is rather tiny. So possibly it is undersized for the car, which may be why we are seeing this issue in our car a year after purchase, hence why I want to buy a larger AUX Battery.

I am about to drain the coolant in our car, and remove the DC/DC Converter, remove it and the upper board and start the diagnosis of the DC/DC Converter. So now for a recap on we know about our car so far.....

  • We have both snubber caps on the riser board blown
  • We have the MCU Fuse blown
  • Our BMU was replaced by Mitsu at our expense :/
  • We have the MCU Fuse on order (4 weeks delivery)
  • We have replacement snubber caps on order, should arrive next week.

So from everyones experience thus far with diagnosis and repair of the DC/DC Converter, what is the recommended diagnosis process.

Do we need to remove the black stuff in the dog house, or can we mount the new snubber caps on the riser (I know the rise is for SMD, not sure if it is possible to retro fit through the hole onto it or not).

Do we need to remove the board from the waffle plate, or can we do the diagnosis and repair with it attached to the waffle plate?

Can the board with the dog house etc be removed without desoldering?

Also I have a bench top lab power supply, multimeter, can I use this for testing. I also have a 2 channel oscilloscope, as well as a good Hakko solder station. I do not have a rework station, but we do have a rework station at uni (electrical engineering school).

coulomb
Posts: 175
Joined: Sun Jun 10, 2018 8:32 pm
Location: Brisbane, Australia

Re: Another relay to suspect

Fri Sep 07, 2018 8:52 pm

kiev wrote: i bought my car ~ 3 years ago and it was only ~3 years old at the time... Eventually i decided to just get a new Aux as part of the troubleshooting process--it was still reading "good" at OCV, but i was getting desperate. And the new Aux seemed to solve that issue, no more stalling.

Yeah, that's interesting. Something crazy must be happening with the 12 V system when the auxiliary battery goes weak.

Here's the link to FSM for this code, there are strange phrasings due to translation from Japanese to English:
Code No. 04

That brings up another possible culprit: the A-06X relay (not the mains relay inside the OBC, the one with many fuses nearby that supplies 12 V to the charrger). A combination of heat, vibration , age, dirt and moisture might have affected this component or its socket (if it has one). Maybe the OBC doesn't draw enough current to "wet" the contacts and keep them clean, though I think that's about 20 mA, surely it would draw that. If it gradually built up a layer of oxide, it might make the OBC more sensitive to marginal auxiliary battery condition. In fact, it might be more effective to replace a $5 relay than a $100 auxiliary battery. Just a thought, though I have no idea how to test it. Maybe put a multimeter on the charrger input and tap the relay with a screwdriver, perhaps wiggle it in its socket (if removable).
Last edited by coulomb on Sat Sep 08, 2018 5:15 am, edited 1 time in total.

kiev
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Location: The Heart o' Dixie
Contact: Website

A-06X Relay swap

Sat Sep 08, 2018 5:06 am

That's a really good idea, the relay is located up front in the fuse/relay tray. There are numerous tiny relays, closely packed in the tray and they are difficult to grab and remove. But if an OBC has failed in a car, then it makes a lot of sense to swap out the little A-06X relay also.
kiev = kenny's innovative electric vehicle

skylogger
Posts: 76
Joined: Sun Dec 14, 2014 3:54 am

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

Sat Sep 08, 2018 6:59 pm

Hi Coulomb:
I'm glad we have these little chats, Too bad I did the relay test, before I discussed with you what I was going to try.
I did see that the relay coil (on the relay itself) was not polarized, and I had the top PCB disconnected, and the waffle board removed,
so I did not think polarisation of supplying a test voltage to the relay coil would matter. Turns out, the protection diode D301 is still there, just to the side of the doghouse, so I managed to blow that up when I tested the relay. Good thing that its just the relay, the D301, and Connector CN1 Involved (since the top PCB was not plugged into CN1 at the time) so I'm sure nothing else got damaged. I pulled a SMD Diode off another scrapped piece of equipment and replaced D301, So when the relay comes in from Digikey I should be back to square 1.
So kids don't try this at home unless you are a trained professional :-) or at least get the polarisation correct.

I did a post-mortem on the relay that was in the doghouse. I bent the contact back so you could see both contacts.
It looks like there is no obvious burnt contacts, but if you zoom in, there looks like a bit of oxidation.
Also I thought this relay had two sets of contacts and they were being used parallel so there was some redundancy,
but now that I have chopped off the top of the relay, I see it is a Single Pole Double throw. Out of the four PCB pins for the
contacts, One of the pins is a Not used. The PCB is laid out so that the Normally closed pin is connected to the centre contact pin, and the
Normally open pin is is connected to the not used pin. If I had not already got it on order, I would have probably ordered a different version of the relay that was double pole single throw, so there would be two sets of contacts in parallel and offering some redundancy on the same PCB footprint. Here is a photo of the contacts:
Image

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