[piwhy]

Hello,

I would like to know if someone already deep studied or reverse engineered the insulation monitoring device integrated on the BECM module of the chevy volt Gen1 ?
I know that it's not the most appropriated forum category but I know that's is probably where I can potentially find this kind of informations.
At the same time I'm also looking for someone that already measured insulation values of a complete chevy volt without and with official GM coolant inside with a megohmeter ?

I'm currently fighting with capricious Chevy volt on which I've tested insulation of all the HV parts independently, with very good values on all of them including the battery pack, but the car's IMD still measuring a low insulation value.

So I started to reverse engineer the IMD to find any problem on it and I'm looking for references values of battery/modules insulation.
For the moment I get >2000MOhms @500Vdc on the total battery pack without coolant and >30MOhms when it's full of official GM coolant. I can't imagine that this value is considered too low by the IMD...

So i'm interrested by any reliable informations on this topic.

Thanks.

 

[kennybobby]

The ceramic chip capacitors would be high on my list of culprits.

i see several long resistor chains making up voltage dividers to drop HV down to lower levels.

Nissan laef does a test similar to this using a low frequency AC.

 

[remy_martian]

Is this in the car (and what car) or on the bench?

 

[piwhy]

This is the IMD (Insulation Monitoring Device) which is integrated on the BECM board in the Chevrolet Volt Gen1 (2011-2014).
I've started to draft the measuring circuit which seems to be pretty common. Measurement principe is well explain is this document for example: http://journal.it.cas.cz/62(2017)-1B/Paper 03 Han Peng.pdf
I'm not fully confident on some references for the moment but that's the basis.
I get 6.2Mohms of insulation @500V with a megohmeter between ground and HV minus and ground and HV positive input which is more or less the resistor chain value. Is there a more reliable way to check these chip capacitors ?
Thanks

 

[remy_martian]

Again, is this in a car or on a bench?

If in a car, which one?

 

[piwhy]

Again, is this in a car or on a bench?

If in a car, which one?

In a car. As I wrote before in the Chevrolet Volt Gen1 2011.
This IMD is integrated in the battery pack of the car.

 

[remy_martian]

So, it's in a Volt, then?

Take it to the dealer.

 

[piwhy]

So, it's in a Volt, then?

Take it to the dealer.

Ahah good luck to find any dealer capable to diagnose and repair the insulation monitoring device in a battery pack.
In the best case scenario it will propose to replace the whole battery pack. In the worst to sell you a brand new car...

Thanks for your nice recommandation but that's not the plan.

 

[remy_martian]

This is clearly something a dealer won't touch, and you appear to me to be weaseling the location of the IMD vs saying whether this is your own contraption (I image processed your scrap piece of paper, lol):

And being your own contraption, the Volt pack is not happy with it, so you're looking for a defeat. If that's the case, you should spell out what you are doing so you can get ideas from people here of how to remedy the fault.

 

[kennybobby]

Are you sure that the 6M resistor strings are connected to chassis ground? Or is that tied to some other ground plane.

 

[piwhy]

This is clearly something a dealer won't touch, and you appear to me to be weaseling the location of the IMD vs saying whether this is your own contraption (I image processed your scrap piece of paper, lol):

And being your own contraption, the Volt pack is not happy with it, so you're looking for a defeat. If that's the case, you should spell out what you are doing so you can get ideas from people here of how to remedy the fault.

Hi Remy, indeed this paper comes from the left drawer of my desk I used this draft paper to scribble the circuit diagram of the IMD circuit... This document was an RFQ from a potential client in 2019, as you saw for agriculture applications. It could have been my last mobile phone invoice or wathever piece of paper guy ! Nothing confidential and nothing related to the subject we discuss here. I've a company in France, we design battery pack for small series vehicle, motorcycles, ebike, ... we have our own technology based on cylindrical cells and honestly we have a pretty low interest to use or distort a >10 years old battery pack design for any other application.

You're welcome to imagine whatever weasel story if you want but I personally own a 2011 Chevrolet Volt (or more precisely a French "Opel Ampera") since 2016 on which I've random insulation problems for 2 years now. Because of lack of time I didn't had time before to investigate on it until now. As you can see below this is the car and the battery pack where the IMD is integrated :

I only try to bring my expertise and my technical ressources with the help of the EV community to move forward on a technical issue that concerns more and more Chevy Volt today.

 

[kennybobby]

It's nice that there are reference designators for all the components so the board could be easily traced out.

Any manufacture logo on the wide leg spacing devices, is marking code W216SC04 ?

Maybe some sort of isolation or opto coupler device?

 

[piwhy]

Are you sure that the 6M resistor strings are connected to chassis ground? Or is that tied to some other ground plane.

Yes as you can see in red, the center of the resistor chain is connected to the ground through a 0ohms resistor. So yes to my great surprise on this car you I always have half of the HV battery pack voltage on the car frame.

I'm looking for full pinout diagram of the BECM but this voltage reference created by resistor chain is connected at least to the overall plan and to the both mx34 black and gray connectors (pin circle in red)

 

[piwhy]

It's nice that there are reference designators for all the components so the board could be easily traced out.

Any manufacture logo on the wide leg spacing devices, is marking code W216SC04 ?

Maybe some sort of isolation or opto coupler device?

I have difficulties to find the W216SC04 reference. There is a "M" logo on it which seems to be Matsushita/Panasonic logo so the most probable reference is a custom/prototype/old version of AQW216 photoMOS component. But I'm not 100% sure at the moment. These solid state relay are probably used to connect bias resistor when insulation monitoring is activated.

 

[remy_martian]

That is not chassis ground. That's the board ground. Chassis ground would be connected through the missing device above the one your highlighted red run is showing.

 

[kennybobby]

If you are reading a voltage or 6Mohms to chassis, then inspect/replace any shorted little ceramic caps marked in the photo

 

[piotrsko]

Ok, I must be dumb, but I have issues with just half the pack voltage being grounded through anything. How and where are you measuring this ?

Is your coolant conductive? Premix should be DI or distilled.

 

[remy_martian]

Those resistors are locally grounded on the board - "ground" is a common return for the circuits on that board.

The four caps KB circled are the only connection to chassis on that board - the schematic is wrong.

 

[piwhy]

That is not chassis ground. That's the board ground. Chassis ground would be connected through the missing device above the one your highlighted red run is showing.

You're right Remy, that's board ground. And the surrounded plan is the car ground and the two references are not supposed to be at the same potential. But when I connect HV on IMD input I get the voltage divider reference (half of the battery pack voltage) on both plan (board ground and surround chassis ground).
And that's propably the point @kennybobby I think that your remark about ceramic cap in the the corner was very pertinent ! I only have 50kohms insulation @500Vdc between board ground and chassis ground !

 

[remy_martian]

Caps are easy to R&R and, technically, you can probably run the car without them...