Pressure testing batteries

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Dala

Well-known member
Leaf Supporting Member
Joined
Oct 28, 2018
Messages
464
Location
Finland
AKA Air leak inspection
So here's something that's good to know when testing used batteries. I recently examined the 40kWh that is soon going into a customer car, and found a small puncture in the top casing. After informing the customer, and then repairing the small puncture, it was time to pressure test the battery.

So a bit about pressure testing. The batteries are by design "waterproof", this specific model can be fully submerged for a few minutes/hours? without any issues. But they aren't 100% waterproof, some water will get in thru the high voltage harness pins overtime, so it's not possible to store the batteries underwater. So to test the batteries, a pressure tester is needed. There is an official tool, but since it's not possible to buy it I'll have to make my own.

Here is the port on the battery used for testing. It's just a bolt with a copper washer, next to the high voltage connections.
oBFrmRd.jpg


And here is my improvised tool using some scraps. It's just the same bolt type, with a hole drilled thru it. I put some threads into the bolt head, and attached a hardline pipe and hose to it. It then gets a bike tire pressure valve on the end, which a normal bike pump can be attached to. Tada, 0€ testing tool.
7FPnVdk.jpg


And finally here is the official procedure from the FullServiceManual.
uIxL6jh.png

YPkaHdm.png

oQZgMGi.png

HO7doZS.png


And yes, the battery passed the test :)
 
Nice work, as always, but where do you find a gauge and pump that can operate at 1.6kPa/0.232 PSI ? That seems tiny compared to most applications and I wouldn't know where to find that kind of equipment. Just curious as the check valves on my bike pumps are iffy at best when inflating bike tires and I can't imagine any consumer pressure gauge being that accurate.
 
Ebay has them(Precision Air Regulator), but I think the manual is overly cautious to not have you pop the breather valves out (these are the ones that should go first). So you might get away with a bit more pressure if you're lucky. But better safe than sorry :)
 
The mildest pressure test ever. A blood pressure kit would be overkill if not for the volume.
 
Hey Dala, finding a precision air tester this sensitive seems difficult, especially at short notice given new lockdown restrictions. I thought that a 30mb gas test gauge would work ok.

https://www.screwfix.com/p/monument-tools-30mb-gas-test-gauge/80090?_requestid=306135

it has the bonus of being widely available and locally sourced (for the UK at least)

30mb == 0.435113 psi approximately so it feels like its in the ball park of 0.2 and 0.23psi

found an m8 bolt in my collection but its a cap head with an internal hex (from bike parts) It also maybe too long looking at your photos. Not sure whether to try to use this or buy a stubbier one to modify.

Lastly I am wondering about air valves to ensure that when I'm pumping air in the surge doesn't break the gas gauge so having a tee and a valve seems sensible to me. Another frustrating hurdle to overcome to break the seal safely on the leaf battery. (or rather put the seal back again)

Edit
Just bought the gauge from toolstation (similar to screwfix) and some m8 tensile 20mm bolts for modification. Kind of difficult to source cheap flange head ones so I am hoping that this doesn't matter too much. I really want to get my car back on the road. One thing that concerns me it that the head of these bolts (setscrews) might not be deep enough to accommodate a thread for putting an adaptor onto it. The bolts were only £0.70 pence for 10 so its worth a try anyway.
 
whereswally606 said:
found an m8 bolt in my collection but its a cap head with an internal hex (from bike parts) It also maybe too long looking at your photos. Not sure whether to try to use this or buy a stubbier one to modify.

Note that you can buy bolts with holes already drilled in them ('vented'):

https://www.mcmaster.com/93235A351/

93235A351p1-b01-digitall@3x_637015804812093173.png


Not sure that's exactly what you need, but could be close.
 
I managed to drill through a flange head bolt almost identical to the one that was in the pack. In the end however we never did the pressure test. I was concerned that the pump (bike foot pump) would cause too large a spike in the pressure and blow some of the seals.

The good news is that my external pre-charge resistor has fixed the car. I hope that it will continue to work but if it blows again I can easily access it near the pack disconnect in the passenger footwell centre. most the parts I used were from cpc farnell so that this could be repeated by others with the same issue on their gen 1 Leafs. I would say though that it would be cheaper to use the 33 ohm cement replacement but you will have the same issue if the relay sticks in the future when the 12v goes low in the cold.
 
I found a manomenter with almos high precision 0-160 mBars e.g. 0.0 -> 0.16 bars (17€). The hardest part was to create a reliable tool without almost any leak. A single little air bubble leak that is visible underwater after 1 minute is almost 0.02 mbar.
After almost removed this leak (near the gauge) with new and conical teflon wrapping I was able to reduce to 0.02 mbar after 8m.
Some design aspects:
1) rod metrics for pression test is 12/125
2) I wasn't able to find any hydraulic connector with with metric nor in specialised places => need to build it getting an enough large rod drilling a hole.
3) The rod have to be enough large to add a bolt screwed with teflon in the middle of the rod leaving space from one side to screw into the battery with a plastic gasket and on the other side to introduce into a 10mm tube with tube tie (added silicon between tube and rod to avoid air leak.
4) Due to high precision of the measurement, probably would be better to used a armored tube to avoid to change pressure due to change of tube position of change in weather conditions.
5) due to 4 => measurement have to be done without moving at all the measurement device.
6) A design aspect: Due to dimension of the pressure gauge, it is necessary to pur it far from the battery rod otherwise there is no space to screw the rod into the battery due to HV connector just by side of the pressure rod.
7) A design aspect: Added a hydraulic faucet to avoid any leak from bicycle tube valve.

photo_6050703030313140911_y.jpg
Below the complete test device. For testing purpose, in the image below on the right, there is a rod closing the hole of the main drilled rod that will be screwed in the leaf battery (with plastic gasket).
Note the length of the tube connecting the rod to the gauge to allow to screw the rod without touching he HV connector that do not allow rotation due to the size of the gauge.
Probably the simplest, cheaper and reliable tool to use is that already shared https://www.screwfix.com/p/monument-tools-30mb-gas-test-gauge/80090?_requestid=306135 that I was not able to find other than in uk ebay market.
photo_6050703030313140912_y.jpg
 
AKA Air leak inspection
So here's something that's good to know when testing used batteries. I recently examined the 40kWh that is soon going into a customer car, and found a small puncture in the top casing. After informing the customer, and then repairing the small puncture, it was time to pressure test the battery.

So a bit about pressure testing. The batteries are by design "waterproof", this specific model can be fully submerged for a few minutes/hours? without any issues. But they aren't 100% waterproof, some water will get in thru the high voltage harness pins overtime, so it's not possible to store the batteries underwater. So to test the batteries, a pressure tester is needed. There is an official tool, but since it's not possible to buy it I'll have to make my own.

Here is the port on the battery used for testing. It's just a bolt with a copper washer, next to the high voltage connections.
oBFrmRd.jpg


And here is my improvised tool using some scraps. It's just the same bolt type, with a hole drilled thru it. I put some threads into the bolt head, and attached a hardline pipe and hose to it. It then gets a bike tire pressure valve on the end, which a normal bike pump can be attached to. Tada, 0€ testing tool.
7FPnVdk.jpg


And finally here is the official procedure from the FullServiceManual.
uIxL6jh.png

YPkaHdm.png

oQZgMGi.png

HO7doZS.png


And yes, the battery passed the test :)

AKA Air leak inspection
So here's something that's good to know when testing used batteries. I recently examined the 40kWh that is soon going into a customer car, and found a small puncture in the top casing. After informing the customer, and then repairing the small puncture, it was time to pressure test the battery.

So a bit about pressure testing. The batteries are by design "waterproof", this specific model can be fully submerged for a few minutes/hours? without any issues. But they aren't 100% waterproof, some water will get in thru the high voltage harness pins overtime, so it's not possible to store the batteries underwater. So to test the batteries, a pressure tester is needed. There is an official tool, but since it's not possible to buy it I'll have to make my own.

Here is the port on the battery used for testing. It's just a bolt with a copper washer, next to the high voltage connections.
oBFrmRd.jpg


And here is my improvised tool using some scraps. It's just the same bolt type, with a hole drilled thru it. I put some threads into the bolt head, and attached a hardline pipe and hose to it. It then gets a bike tire pressure valve on the end, which a normal bike pump can be attached to. Tada, 0€ testing tool.
7FPnVdk.jpg


And finally here is the official procedure from the FullServiceManual.
uIxL6jh.png

YPkaHdm.png

oQZgMGi.png

HO7doZS.png


And yes, the battery passed the test :)
I worked as a test engineer for a defense contractor where we performed "Leak Down" testing on our underwater vehicles. This involved an initial vacuum purge and hold at reduced pressure followed by a dry nitrogen back-fill. This was repeated at least twice to reduce the chances of any moisture remaining inside. Dry nitrogen was employed instead of air to prevent moisture forming on internal electronics as the vehicles commonly operated in the presence of large and rapid temperature gradients. I've often wondered if something similar would be in any way beneficial in this application.
 
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