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RobbertPatrison

RobbertPatrison

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Great analysis, thanks.
Does it mean that on a fast highway trip directly after HPC session on a cold day the HV battery will not be cooled at all if you run cabin heating at the same time? Or car will enforce cabin cooling if some temperature limit was reached in the HV battery pack and HV battery requires cooling?
It will cool the battery because it is important not to fry the battery. I suspect that it will run the cabin heater in parallel. This simultaneous colling and heating wastes some energy and might not fully heat the cabin, but it is likely OK. The same happens when defrosting.
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Haha. Indeed: the 12V battery is a little small. That is probably to save cost and weight, but that will wear out the battery quicker. The small capacity also means that if you get stranded with a High Voltage battery failure, things may get pretty dicey quickly. After the 12 V battery drains dead, doors cannot be opened, or the car cannot be shifted from park.
Actually all three of our Prius batteries were Reall tiny as well!
When they started going bad, all kinds of errors, danger lights, the Triangle of death, you name it.
 

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I decided it was time to check out what is hidden behind the plastic of the frunk. Any maintenance - other than refilling wiper fluid - requires removing the frunk hardware. That adds to the shop cost as it takes time:
  1. Unclip the 3 plastic panels, with quite some force. Clips may fall off and need to be re-attached
  2. Detach several cover panels to remove 8 screws. Some of the screws did not turn easily due to poor threading: they seem to have been rammed in with oodles of torque on the production line.
  3. The frunk 'bathtub' is remarkably sturdy and heavy. It has thick metal reinforcements. It feels good, but I don't fully get why Ford did not try to save a little weight here.
This is viewed once the 'bathtub' is removed:
MacheUnderTheHood.jpg

Compared to the other EVs and cars I have opened, a few things stand out:
  • The plumbing is a royal mess. It seems as if Ford (+ its contractors) designed and placed the components without giving much thought about how they will be hooked up. Piping makes weird detours as a result. Compared to a Tesla MY, the MME has 3X more hoses and 3X more fluid according to Munro. That is a huge difference.
    It looks bad, but is it that bad? A large number of connectors increases the chance of leaks and adds a lot of weight. On the other hand, rubber hoses are cheap and off-the-shelf pumps are cheap. They can be repaired much easier. Looking at this, repair seems quite doable.
  • Given that the front motor is just 50kW, this seems quite large and bulky for what it does. The equipment in my old Chevy Bolt cranked 3X the power out of a hood area that is much smaller. It seems little effort was spent on compact design.
  • If you look down in the hole, the frunk could easily have been 3 inches deeper. The clumsy plumbing at the bottom could easily be moved out of the way. I wonder why this was not done.
  • The radiator fan blows against the frunk bathtub. This must be a hot place in summer.
  • I see 4 electric fluid pumps and a quad valve scattered on the bottom. More on that later.

I spent a little time decoding the mess of tubes that cool and heat. First, there is the motor and electronics coolant loop:
Screen Shot 2022-04-29 at 19.20.46 .jpg


This is a single large daisy chain loop that is cooled by the radiator. So large that it needs two push-pull pumps in series. There are two operational modes:
  1. L1 or L2 Charging, in which case the onboard AC charger produces up to 800Watts of heat. The heat is pushed through the DC/DC converter, the rear motor, and the front motor. Since the motors are not running, they do add additional heat.
  2. Driving, in which case most heat comes out of the rear motor and inverter (and the charger is off). The rear motor has an oil heat exchanger with its own oil pump. The front (non-GT) motor is water cooled only.
IMHO there is nothing really wrong with this setup for motor cooling. The battery and cabin loops, however, are another story. There are loads of pipes. It took me a while to make a good schematic:

Screen Shot 2022-04-29 at 19.21.15 .jpg



There are four loops that interact in intricate ways.
  1. Cabin heater loop: cabin pump->PTC heater->cabin heater core->diverter valve-> cabin pump
  2. Battery chill fluid loop: battery pump-> HV battery -> proportional valve -> chiller -> battery pump
  3. Battery refrigerant loop: compressor->condenser->valve->chiller evaporator->compressor
  4. Cabin cooling loop: compressor->condenser->cabin evaporator core->compressor
Each of these loops can be controlled independently. This means that the MME can cool and heat the cabin independently and at the same time (e.g. for defrost).
The MME can switch off the chilling of the battery and only cool the cabin. But it cannot chill the battery without also cooling the cabin. In practice that is probably OK.

All EVs share the AC compressor for both battery and cabin cooling. But the really odd design choice was that Ford decided to share a single PTC heater between the cabin and the battery as well. Most other EVs have a separate PTC heater in the battery loop. After all, PTC heaters are cheap and small.

This PTC heater sharing ik the MME adds a lot of messy plumbing. When heating the battery the diverter valve connects the two loops into one big one like this:
Screen Shot 2022-04-29 at 19.21.30 .jpg


The loop is: cabin pump->PTC heater->cabin heater core->diverter valve->battery pump-> HV battery -> proportional valve -> diverter valve-> heater pump. (!!)
In this heater mode, the refrigerant valve will be off, and the battery proportional valve feeds the fluid into the diverter valve.
It does mean that the cabin heater will always be on in case the battery needs to be heated. If the car is just charging, the cabin fan will be off so little heat energy will be lost there. When driving, some heat will be sent into the cabin by the blower. If this is undesirable, it could fire up the compressor to mix in some cooling.

It is a little odd that the PTC heater is just 6kW while it needs to service the cabin and the battery in parallel. That seems a little weak, but apparently, it works out OK even in cold climates. The small Chevy Bolt had an 8kW cabin heater plus a 2kW battery heater.

Overall, the heating and cooling system still works fine in practice. If you don't take the frunk apart you will be blissfully unaware of its messy complexity. Perhaps that is the reason why the frunk is covered so well.
Nice write up!
The tub bolts had a sealant and thread locker compound. I understand the thread locking but not the sealant. There is a drain in the tub after all....?

Edit: I figured it out. If you fill the tub with ice then the bolts could rust. The sealant prevents that. I should go back and reseal those fasteners.

I made some videos for my uncle and brothers to help explain to them how the coolant systems work. Or at least how I "think" they work. From reading this thread, it sounds like I am pretty close.

Links to video if you are interested....



 
 




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