SSN Fix: DIY Upper HV Pack Heat Exchanger (Cooling Plate) Removal

[Anti_Climax]

Depends on the temp. At 120-something it forces a stop. Below that is a range where it's degraded performance and below that a range where there's no error but it's totally bypassing the cabin evaporator.

[27ace27]

Interesting. I wonder if we have different BECM firmware or something. Mine never forced a complete stop, it just kept limiting performance until the car barely moved.

[Anti_Climax]

How hot did it get though? Was it a yellow warning or a red warning?

[27ace27]

Yellow, then red.

[Anti_Climax]

Had to unplug my charger and the car sat in the PHX sun all day. Can confirm, hybrid battery temp of 122 gave a "stop now" message.

Changed to "severely limited performance" with a red turtle at 121-120F. When it switched the battery indicator (which was up above 99%) showed 0 miles range and began counting up to 95+ miles.

At 118-117F the turtle went yellow and just "limited performance"

At 114-113F the warnings went away but AC was still fully redirected to the battery loop.

At 112-111F, the AC began working in the cabin.

[27ace27]

Good to know!

[27ace27]

Quick addendum here:
Ford addressed this issue in the 33.5 kWh packs by adding clamps to keep the cell stacks compressed. At first glance, this seems like something that it would to be easy to retrofit the 23 kWh packs with. However while there is plenty of research on compressing new pouch cells, I could not find any on compressing aged pouch cells.

My concern is that the pressure would crush the hollow heat exchanger plates and we'd be right back at square 1. The ideal solution would be to vent the accumulated gas somehow. While doing so safely is relatively straightforward, there doesn't seem to be a reliable way to re-seal the cells afterward, as the electrolyte contains a solvent which would degrade any adhesive patch. Since the electrolyte and the gasses that cause the cells to swell are both highly flammable, this makes such a solution a complete non-starter.

Unless I can find a way of reliably re-sealing the cells, I'll probably just try the clamp retrofit without venting the cells first. Maybe with a quick shutoff valve installed in the coolant loop

[27ace27]

Have found a further downside to this mod: at high-ish ambient temps (was seeing this at 90-100F), charging throttles hard.

This seems to be due to the onboard charger (SOBDM) overheating. As best I can tell, whether the car activates the chiller in the battery coolant loop is based solely on the temperature of the coolant going into the battery. When battery cooling is bypassed, this always reads ambient. So as long as ambient temps are below chiller activation temps, the SOBDM relies on ambient cooling.

I'm not even sure whether the coolant runs through the radiator yet. I'm thinking probably not though; the temperature of the coolant going into the SOBDM was ~124F when ambient was ~90.

[Anti_Climax]

You could potentially set up a temp sensor in the coolant stream and make it think it's in the upper pack.

And for sealing cells after degassing - perhaps something that isn't an adhesive in the traditional sense like epoxy?