22KW OBC FAILURE INSIGHT & POSSIBLE SOLUTION

[Murph7355]

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In Taycan we have also done an experiment where we empty the original Taycan modules, empty them of the original LG pouch cells and reassemble them using CATL prismatic cells, welding them to make the same voltage as the original module with LG cells, welding the in module BMS voltage sensing wires… Done

I have built an experimental test Taycan battery (for my own test use only) in this way with CATL prismatic cells as opposed to LG pouch cell. Obviously this is not a commercial solution because I have no resources to perform the calculations and risk assessment etc that such a repair would need to be deemed safe and in this case as a matter of fact I have no way to guarantee it. So I cant sell it.

But just as a experiment, I think I’m the only person in the world who has driven a Taycan powered by CATL prismatic batteries LOL
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Do you have this installed yet?

I can see this sort of work being a big market eventually, and interested in how far you've got with it, what it does/could do for things like weight, longevity, range etc

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[whitex]

Using high quality proper chargers will help. The cheaper the charger the more ripple. Ripple makes this existing problem way worse (pushing the mosfets further towards self destruction).

How so? EVSE (a.k.a. AC charger) is just a glorified extension cord with some signaling and safety built-in. All it does it switch the wall AC ON or OFF (typically via relay), no voltage or current conversions/limits. In other words, when the EVSE is supplying the power, it just connects the car to the wall supply.

 

[whitex]

At the time when this OBC was designed, there was no MOSFET with a higher amperage rating that would do the job. This was the only choice.

They could have use 2 parallel MOSFETs in place of one, each carrying approximately half the current (not perfect balance due to manufacturing variations on the MOSFETS, but in this case should lower both paths to under 30A easy).

 

[ct14garage]

How so? EVSE (a.k.a. AC charger) is just a glorified extension cord with some signaling and safety built-in. All it does it switch the wall AC ON or OFF (typically via relay), no voltage or current conversions/limits. In other words, when the EVSE is supplying the power, it just connects the car to the wall supply.

I stand corrected. When writing this for some weird reason I was thinking of DCFC (and how egregious those cheap ones are). So I wrote the same about EVSE. Wasn’t thinking much.

EVSE (AC Chargers) are no more than glorified switches. They don’t and cannot fix ripple which is a major part of this issue. Even if you buy the most expensive EVSe it won’t make a bit of a difference

 

[ct14garage]

Do you have this installed yet?

I can see this sort of work being a big market eventually, and interested in how far you've got with it, what it does/could do for things like weight, longevity, range etc

Yes I have a battery completely finished and can be installed in any car and driven as normal.

I’ve briefly driven a car with this battery.

1. Definitely didn’t DC charge ?
2. Definitely didn’t floor the car (max discharge current or even closer) ?

This is not a viable commercial solution. It’s just a crazy experiment. There are no safety studies done. There are even no warranties.

The CATL cells I used (that I had access too) aren’t rated for the discharge/charge currents Taycan would see when using it’s max power output (or input). It could end in a bad bad fire.

Nobody is gonna commercialize this, just a crazy experiment.

 

[ct14garage]

They could have use 2 parallel MOSFETs in place of one, each carrying approximately half the current (not perfect balance due to manufacturing variations on the MOSFETS, but in this case should lower both paths to under 30A easy).

That adds more complexity circuitry (and thus cost) to ensure they wont blow up due to Vth differences, RDS differences, Gate charger differences (as you said manufacturing variations)

Likely they would still blow up (whether more or less frequently than the current approach, I have no idea)

 

[whitex]

That adds more complexity circuitry (and thus cost) to ensure they wont blow up due to Vth differences, RDS differences, Gate charger differences (as you said manufacturing variations)

Likely they would still blow up (whether more or less frequently than the current approach, I have no idea)

It's done in the industry all the time. I’m almost certain it's done in the motor inverters already (for much larger currents than charging, I doubt they found a single transistor to carry full current of the rear motor) too, so someone at Porsche knows how to do it. Here is an app note from TI explaining the considerations for such configuration:
https://www.ti.com/lit/pdf/slpa020

My point is that just because higher rated MOSFET was not available when they designed the OBC, it's no excuse for using it outside the spec like this. It's just poor design, penny wise, pound foolish. Perhaps they outsourced the design to some interns too to save money, and the interns haven't yet covered parallel MOSFETS in class.

 

[simcity]

OBC's seems to be a weak point on many cars. Had mine fail on my Tesla at the almost 5-year mark. That was a 3-phase unit too.

You'd think this was fairly basic electrical engineering design and implementation. Nothing particularly funky here.

I hope the same doesn't happen to me again in the Porsche out of warranty.

 

[anonymouse]

Too bad that Porsche’s “solution” for J1.2 cars was to delete the option altogether and cap charging at 11kW.

They forgot to tell the marketing department, though, because 22kW pops up in a few places in their PR.

 

[MrB]

Well, mine has just blown. Again. This’ll be number 4. Mercifully the lease is up in a few months and I’m off to try a different manufacturer. Frankly, I think the Maserati Folgore series will be more reliable than this car has been (and I mean it, Stellantis EV tech, which underpins this and my wife’s Fiat 500e seems bang on in comparison as her car has had literally one warranty fault - a stuck latch on a manual charge port door). It has managed the feat of being simultaneously both the best and worst car I’ve ever owned. I won’t miss the aggro but I’ll miss the drive.

 

[F1Ruaraidh]

It's done in the industry all the time. I’m almost certain it's done in the motor inverters already (for much larger currents than charging, I doubt they found a single transistor to carry full current of the rear motor) too, so someone at Porsche knows how to do it. Here is an app note from TI explaining the considerations for such configuration:
https://www.ti.com/lit/pdf/slpa020

My point is that just because higher rated MOSFET was not available when they designed the OBC, it's no excuse for using it outside the spec like this. It's just poor design, penny wise, pound foolish. Perhaps they outsourced the design to some interns too to save money, and the interns haven't yet covered parallel MOSFETS in class.

Absolutely is done all the time in inverters. Tesla have been doung it for years even with SiC.

 

[prj]

Well, mine has just blown. Again. This’ll be number 4. Mercifully the lease is up in a few months and I’m off to try a different manufacturer. Frankly, I think the Maserati Folgore series will be more reliable than this car has been (and I mean it, Stellantis EV tech, which underpins this and my wife’s Fiat 500e seems bang on in comparison as her car has had literally one warranty fault - a stuck latch on a manual charge port door). It has managed the feat of being simultaneously both the best and worst car I’ve ever owned. I won’t miss the aggro but I’ll miss the drive.

Porsche has extended the warranty on the OBC last month. At least in the EU - that is 5 years.

They are also in process of refunding me the 4000 euro that I paid for replacement when mine popped in the 3 months I did not have warranty on the car (you have to wait for 3 months after purchase to be able to buy Porsche Approved warranty in the EU).

The dealer wouldn't do it, but a polite message to contact at porsche de in German did the trick.

 

[MrB]

Porsche has extended the warranty on the OBC to match the warranty on the battery last month. At least in the EU - that is 8 years.

They are also in process of refunding me the 4000 euro that I paid for replacement when mine popped in the 3 months I did not have warranty on the car (you have to wait for 3 months after purchase to be able to buy Porsche Approved warranty in the EU).

The dealer wouldn't do it, but a polite message to contact at porsche de in German did the trick.

Hi,

Thanks for that, I’ve been told today that Porsche are to replace it (number 4) as “goodwill” so somewhat short of an admission of a problem but at least it’ll be replaced. Hopefully it’ll last until the end of October when the car goes back but, for now at least, and after 4 years of endless warranty jobs of various sizes, I’m done with Porsche.

 

[prj]

In my case nothing to do with goodwill as the warranty shows now until 2028 on the charger.

 

[freeforall]

In my case nothing to do with goodwill as the warranty shows now until 2031 on the charger.

@prj how do you check the OBC warranty ? Are you able to check it on your own or you ask the dealer ?

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