Tesla High Voltage Battery Pack Information

Breathers, Vents and Umbrella Valves

Two Different Purposes

This section matters because when you repair your pack, part of the refresh process will involve installing a new combination of Breathers, Plugs and Umbrella valves and you will need to decide what combination is best. Breathers and Umbrella Valves are combined in this section, but they really serve two very different purposes. In short, the Umbrella Valves are emergency valves that bleed off pressure if there is a fire inside the pack. If the pack was sealed completely or not able to vent the pressure buildup during a fire, the pack itself could explode like a soda can rolled down a hill. In the vast majority of packs, the umbrella valves just sit there and do nothing and that's the way we want them! What we don't want is for them to gunk up with road debris and start letting road-spray or standing water into the pack.

Each pack has 14 module bays (7 per side) and each module bay has 6 round holes to accommodate the Umbrella Valve. The original packs had 84 Umbrella Valves. Someone can measure one and do some math to see how much emergency 'escape' volume that many valves provided, then they can look up how large a lithium battery fire to produce that much out gassing but someone at Tesla did and determined that 84 Umbrella Valves was complete overkill!

This is an original umbrella valve from a v1 pack. Notice the little grooves that keep it from sitting flush with the pack? All this seems to do in reality is collect gunk.

The rubber seems to be a different/better composition than the v2 umbrella valves. It seems softer but thicker and doesn't collect mildew like the v2 seems to.

Despite the subjectively better rubber, I don't like the stand-off grooves so I changed my packs to the newer style

Here is the v2 umbrella valve. Notice the smooth surface that will make a flat contact with the pack? The clips are also a different design - I don't know if one is 'better' and they both tend to break when pulling them down from outside the pack.

This rubber is a little thinner. The newest ones seem to use clear plastic while the early v2 types use a yellow/brownish plastic like you see in the plugs below. All of the used ones I removed from my v2 pack had black mildew on the rubber that wouldn't come off.

The basic function is the same for both versions. The clips hold it in place, the o-ring does the actual sealing in the pack bore/opening. If pressure builds up in the pack suddenly (i.e. fire), they will vent out as quickly as necessary.

Plugs

At some point, Tesla reduced the quantity of Umbrella Valves by 2/3, installing just 2 emergency (Umbrella) valves per module bay. The other 4 holes were filled with basic plugs. The plugs fit into the holes the same way but don't have the potential to gunk up with road debris and let water in.

Here is the plug used in the early v2 packs. In that first iteration, there were 4 plugs and 2 umbrella valves per bay except the front that has all plugs.

In the newest revision, there are 2 umbrella valves, 1 Gore breather (see above) and 3 plugs per bay except for the front that has all plugs.

It is handy to have some extra plugs available because you are supposed to replace the breathers with plugs for pressure testing.

Breathers

The battery pack is 'sealed' so it can withstand road spray on a rainy day but I would never describe it as 'water tight'. As the pack heats and cools and gains and loses elevation, it needs to be able to breath - there is a lot of volume there. The mechanisms by which it breathes is the other topic in this section. Each pack has at least one breathing mechanism to allow the pressure inside the pack to equalize so we don't get the 'oil can' effect of the case popping as it expands and contracts.

Breathing for the original packs happened with a small AGM silicone valve in the center of the penthouse cover. It is intended to open at .2psi. It faces up right at the base of the windshield so what happens if those little holes are full of water when it 'inhales'? The final version of our packs do not have this silicone valve.

There is also a PTFE breather on the bottom side of the pack under the coolant rapidmates (under the left-hand/driver's feet).

The Penthouse cover with the AGM Silicone Valve in the center

This is supposed to open at .2psi so it looks like this is a fail-safe (for sucking in at least) if the pack cools or descends altitude too quickly for the breather. The umbrella valves will burp off any pressure needed although it isn't ideal to have them open at all.

This is the cover for the PTFE Breather on the under side of the pack at the front/left. Do a bunch of breathers on the sides make this part redundant?

The top side - appears to be additional umbrella valves.

Gore Breather

The newest versions of the pack have these Gore breathers in 12 of the 14 module bays in place of one of the plugs. To recap, 12 of the 14 bays have 2 Umbrella Valves, 3 plugs and 1 Gore Breather. The 2 module bays behind the front tire (1 per side getting maximum road spray) have 6 plugs each. In the packs that have the Gore breathers in the sides, there is no Silicone valve in the penthouse cover. Note - there is a data sheet on the Gore breather attached below.

The newest umbrella valve kits have one of these for 12 of the 14 module bays. Packs that came with these don't have the AGM Silicone valve on the top of the penthouse.

These facilitate breathing of the packs and provide that breathing evenly distributed throughout - not just at the front like the v1 and early v2 packs. As you have read, the vast majority of C26/C27 corrosion failures happen at the front of the pack where the early packs breath.

I actually tracked down a data sheet on this part.

GORE_AUTO_Snap_Fit_Datasheet_Electronics_US - AUTO-003-DSH-US-JAN20.pdf

Time to make wild guesses!

So what is the best combination? Personally, (subjective opinion) I think it is best to install the breathers in the current spec and plug the AGM silicone valve on the Penthouse. I haven't been able to find the flow rate or any data on the PTFE breather at the front of the pack to see if it becomes redundant with 12 breathers in the side. I would also be curious for a 'math' person to do the volumetric calculations on how much volume the breathers need to flow and comment on the minimum quantity of breathers that would meet that need. Just like the early umbrella valves, I think the pack might be overly breathing with 12 of these. I don't think 'over breathing' is necessarily a bad thing and if you accept that the pack with breath X CFM for a given condition and then divide X by Y number of breathers to reach a value lower than the CFM any single breather will be asked to handle.

The best solution would be to have the pack breath the dried and conditioned air from the cabin and be completely sealed to the outside (except emergency pressure relief from umbrella valves) but that comes with the risk of the cabin breathing whatever nasty toxins a bunch of lithium battery cells decide to outgas. Other OEMs do this so why not Tesla? There is no perfect solution it seems. The good news is once you modify your BMBs so the bottom tab doesn't rub C26 and C27, moisture won't cause the same failure in your pack again so maybe this whole 'breather' discussion is a waste of keystrokes!

Page updated

Google Sites

Report abuse