coulomb
Posts: 175
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Location: Brisbane, Australia

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

Mon Sep 10, 2018 4:08 pm

ChristopheFR wrote: my Czero's charger is dead. One more!

Oh no!

... when I plug my charging cable, the green charging light on the cable box comes on for several seconds, I hear a few clicks to the cable and to the car, the car's blower starts a few seconds, then everything stops, no blower,

That to me sounds like the relay that is supposed to short the pre-charge resistors is not working, though that's just a guess based on similarity to other reports. With others, this situation quickly deteriorates to the charrger never coming on at all (because the pre-charge resistors fail open circuit). [ Edit: If I'm right, then that's a good reason to get the charrger out of the car as soon as possible, or at least not attempt to use the on-board charrger until then. ]

The only way to find out is to extract the charrger / DC-DC box from the car, as SkyLogger has said.

Sadly, it looks like you're in for a lot of inconvenience. Maybe it's only the pre-charge relay; if so, you should be able to get that shipped to you in a few days, and you might be back and running in a week, depending on your time. Your pre-charge resistors might have had a hard time of this, so it might be worth replacing them at the same time, especially if you can source them from the same supplier (e.g. Digi-Key or Mouser).

coulomb
Posts: 175
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Location: Brisbane, Australia

Re: Coulomb's relay theory

Mon Sep 10, 2018 5:09 pm

So my theory justifying the above is as follows. If the relay fails, then the 400 V bus charges as normal, and until the IGBTs are switching, there is essentially no load on the 400 V bus. So there is simply no way for the charrger microcontroller to know that the input relay has failed at this point. So it gets everything ready, perhaps does some handshaking with other vehicle computers, and if all goes well it starts ramping up the charge current in a few seconds. When the charge load is less than say 2 A, then the voltage drop across the two 4.7 Ω pre-charge resistors is less than 20 V, which is less than 10% of the mains. At two amps, the power dissipated by each resistor is I²R = 2×2×4.7 ~= 19 W, a severe overload, but they can probably take that sort of power for a few seconds. Note that with 10% less AC voltage available for charging, the PFC (Power Factor Correction) stage has to work 10% harder to maintain 400 V, so really it's 2.2 A at this point.

But when the charge power ramps up to say 920 W. so the current from 230 V would normally be 4 A, then the voltage drop across the pre-charge resistors is at least 40 V. That means the PFC stage has to work at least 17% harder, so it's really 4×1.17 = 4.7 A, which really means 44 V drop, so the current is really about 5 A, and each resistor is dissipating some 5×5×4.7 = 118 W. Surely at this point, they would fail open circuit. But there is a chance that they could fail high resistance, evaporating away some of the wire (assuming wire-wound types, as they appear to be), leaving some wire intact. This means that they would get even more heat with the same current, but the AC input to the PFC stage would drop even more quickly as the charge current ramps up. When the PFC stage input voltage drops below about 85 VAC, the charrger microcontroller would detect an error and stop charging. This protects the pre-charge resistors from further deterioration, so they might stabilise at a certain much higher than nominal resistance.

So my theory predicts two different outcomes, though one is more likely than the other. The more likely scenario is that the pre-charge resistors fail open circuit suddenly. When that happens, the 400 V bus collapses very quickly, which might cause stored energy in the output inductor(s) to cause the small doghouse capacitors to explode. These often fail short circuit, hence the fuse in the motor controller blows. We've seen plenty examples of this.

The other, less likely outcome is that the pre-charge resistors fail high resistance. As indicated above, this could cause the charrger microcontroller to terminate charging so quickly that the pre-charge resistors don't suffer much more degradation. This could be the situation with ChristopheFR's Zero. Alternatively, every time you fire up the charrger, it might be like playing Russian Roulette with the charrger; eventually it dies (because the pre-charge resistors fail open circuit), but it might get lucky and survive a few starts. Maybe ChristopheFR was lucky, and/or didn't try starting the charrger many times. Until the pre-charge resistors fail under load, you don't get the sudden stopping of charging, so you don't see the doghouse capacitors explode, and the DC-DC still charges the auxiliary battery.

One thing that bothers me with this theory is that any interruption of AC while charging should cause the doghouse capacitors to explode. Otherwise, when the input resistors fail open circuit, the charrger should quietly refuse to start from them on, and the DC-DC should continue to charge the auxiliary battery. I imagine that most charges would be via J1772, so if you interrupt the charge by taking out the connector, there is a digital signal to the charrger microcontroller, which allows the microcontroller to ramp down the current in a tenth of a second or so; that's all good. But surely sometimes the AC fails for other reasons: a breaker trips, the charge is via a wall plug and is turned off before the charge is complete, blackout, brown out, or a rat chews the power cord. I don't hear reports of on-board charrgers failing for these reasons.

The other thing is that there is considerable energy in the 220 μF capacitors, so that interrupting the AC input (which happens all the time 100 or 120 times per second due to the nature of alternating current), and these are presumably sized such that over the 8-10 ms between peaks of the mains, these capacitors can run the charger with only a minor dip in 400 V rail voltage. I realise that between peaks, the capacitors are still being charged via the PFC boost stage, but there is less current charging the 400 V bus capacitors between peaks. The current is sinusoidal, as well as the voltage; that's why it has good Power Factor. Kiev's theory about poor auxiliary battery voltage may explain this; if the IGBTs get too low a voltage on their gates, they could fail to turn on properly or at all. There might be some sort of desaturation protection, which causes the IGBTs to suddenly stop switching. However, in my very limited experience, desaturation protection is more of a gradual cut-back of gate pulse width than a sudden shut-off.

So I suspect that while the relay is the root cause of some failures, something else is causing the doghouse capacitors to explode. In Skyogger#1's case, we could blame the poorly manufactured 39 kΩ resistor, but this doesn't seem to be a common issue, at least so far.

Let the speculation continue :)

skylogger
Posts: 76
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Re: Troubleshooting and repair for On-board Charger (OBC), DC-DC Converter

Tue Sep 11, 2018 2:04 am

Hi Coloumb / KIEV:
I mentioned earlier that during the testing of the relay in the doghouse, that I accidentally blew up the protection diode on it's coil by putting wrong polarity during the test. I found a simular diode in a piece of scrapped equipment and replaced it with that while waiting on the relay to be supplied. Now that I think about it, I think I should look into making sure that I use a diode that will function properly.
It looks like the original diode was in a SOD-323 Package. I came across a diode in stock at Altronics called a Y0162 1N4148WS
It's not a power rectifier, just a signal diode, but it's the only one altronics sell in a SOD-323 Package.
Would this be suitable for protecting the inductive kick from the relay coil? The markings on the original diode are no longer readable.
The markings on the diode that I have currently(temporarily) put in place is "32J" but not sure what it's part number or specs are.

coulomb
Posts: 175
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Location: Brisbane, Australia

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

Tue Sep 11, 2018 4:31 am

The Elcon / TC charrgers have a BAW56 dual diode (usually marking code A1t or A1W), both rated at 215 mA, in parallel. This is for a relay with a 12 V coil, so it would have lower current than the 5 V coil. So I'd guess you'd need about a 500 mA diode, which is not going to be easy. Here is one though: https://au.rs-online.com/web/p/switchin ... s/7512730/ . Well, it's 100, actually, about AU$12 including GST. 5 working days for delivery, plus west coast and black stump penalties :( .

But maybe someone can post a photo of the diode; it looks like it's D301 on top of the board, just near a 45° angle change in the dog-house border, between the dog house and the two pulse transformers. @SkyLogger, one of your photos has it, but it's too blury to read as is. Maybe you have a higher megapixel version on your computer or in your camera that can read it. The 1N4148WS is probably rated at about 300 mA (repetitive peak forward current) and might well be good enough.

There is a small chance that the diode you scrounged, marked "32J", is a 2.7 V zener diode, which definitely won't do. Others are 5.6 V zeners, which might work for a while, but I suspect that zeners are too low current for this application. Perhaps test with a 9V battery and a 220 Ω to 1 kΩ resistor in series with the diode, cathode (striped) to negative; measure the voltage across the diode.

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

Tue Sep 11, 2018 5:16 am

D301 on my board has a roughened (etched?) appearance with no part number. Why go to the trouble to etch them?

It has a size of 0805 (LxW inch) with a square cross-section. The metal at the ends is just a thin vertical strip about .015" in width that doesn't extend to the top face. i can't tell if there are feet at the solder pad unless i remove one.

On the bottom layer there are 7 more similar-looking diodes (D317-322, 346) near the PFC chip, IC312, UC2854BDW.
kiev = kenny's innovative electric vehicle

footswitch
Posts: 9
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Location: Portugal

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

Tue Sep 11, 2018 9:10 am

Hi KIEV,

Can you add ChristopheFR to the list? It's the exact same symptoms as mine (#16).

I've been following your exchange of ideas very closely.
The fact that Christophe changed his Aux in 2015 makes me think that there's more to it - though the symptoms are different.
I'd say the thermal design issue can also play an important role - if everything is heated more than it should, failures can pop up from anywhere and everywhere.

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

Tue Sep 11, 2018 11:20 am

ChristopheFR wrote:...
While waiting to change the charger or to repair it, I recharge my "Z" on the Chademo socket at Ikea.

The apparent diagnosis: when I plug my charging cable, the green charging light on the cable box comes on for several seconds, I hear a few clicks to the cable and to the car, the car's blower starts a few seconds, then everything stops, no blower, no green light on the cable, and no fault on the cable or on the dashboard.

With the ignition key closed, when I take the voltage across the auxiliary battery, I get 12.4 volts
With the ignition key open, I get 14.5 volts.


Bon jour Christophe,

Your "failure" is quite different from all the rest here, and i hope that it will be an easy fix.

Your car, the EVSE cable, and the OBC all appear to be communicating normally, it is trying to start charging, but something is blocking that last step needed to turn on the transistors in the waffle plate.

The easy case is that i think you may have a blown fuse on the top board, or some sensor circuit on the bottom board is not sending the required signal to the micro controller chip on the top board. But in the worst case, it may be that components in the waffle plate have blown. Almost everything in the OBC can be purchased and replaced, except the plate.

It appears that your DC/DC converter section in the bottom of the OBC box is working ok, so the 20A fuse in the MCU is okay also.

Please pull the cover off and post up some pictures.
kiev = kenny's innovative electric vehicle

ChristopheFR
Posts: 20
Joined: Sat Aug 11, 2018 1:08 am

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

Tue Sep 11, 2018 12:58 pm

Hello tous,
Thank you for all your answers.

Kiev, do you think I have less malfunctions on my charrger because I changed my aux battery in 2015?

I will open Saturday, and I will take pictures. I will start by checking the fuses

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

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

Tue Sep 11, 2018 5:03 pm

Hi ChristopheFR,

It sounds different because your symptoms are different to the other charger failures, why that is we simply do not know at this point.

While I see merit in the Aux Battery theory, I am not completely convinced it is the Aux Battery just yet, since we had our Aux Battery replaced about a year prior to our DC/DC Converter failure, however, we do have a rather small battery (I think we can fit a bigger one in the battery box), and also have an after market amp, sub etc, which may have also cause the Aux Battery to go low.

When you open up your DC/DC Converter we can then see if it is the same problem or not.

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

MCU Fuse and Snubber Capacitor Failures

Wed Sep 12, 2018 2:23 am

One puzzle upon which i ponder, is how do both of these items get taken out? It appears to be a common failure mode in Australia and US, maybe not so much in France and EU.

If you look at the Output Filter, these items are at either end of the filter stage, the snubber caps at the beginning and the MCU fuse just after the OBC output line on the (+) terminal to the pack, just past the 20A fuse on the OBC board.

The little 20A fuse on the (+) inside the OBC has never been reported blown, neither has the little 20A fuse on the (-) side on the DC/DC board. Maybe that is good for us since they are soldered to the boards, whereas the MCU fuse is a screw terminal device and can be easily accessed under the small cover plate on the MCU, but that would be a clever designer to be able to control the failure's location.

But the commonality of the failed parts in the vicinity of the Output Stage should somehow be a clue.

Image
kiev = kenny's innovative electric vehicle

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