Battery insulation/warming?

[RagingGrandpa]

11 hours ago, InfiniteWheelie said:

I didn't test the battery without insulation

Aww... without a baseline, data is meaningless :/

[InfiniteWheelie]

On 12/16/2021 at 9:41 AM, RagingGrandpa said:

Aww... without a baseline, data is meaningless :/

Well I would have needed to pierce the shrink wrap and find a place to slide the probe in, and secure it inside so it didn't wear away at the cells as it rattled. I was just focused on getting the insulation on as it was quite difficult and time consuming. Really anyone with a Sherman in cold climate could buy one of these cheap temp probes from amazon and test it themselves.

The results won't be meaningless though. It's pretty obvious the Sherman or any uninsulated wheel will quickly get close to ambient temperate before too long. On my most recent ride in single digit temperatures, I sustained about 10c above ambient while riding for hours and draining about 75% of my battery (rough guess). Like I said I'll post some logs once it gets a little colder. If it works, it works. It doesn't necessarily need to be compared directly to uninsulated as common sense already says uninsulated doesn't work for long (or I wouldn't have bothered with this).

Edited January 13, 2022 by InfiniteWheelie

[InfiniteWheelie]

Since I've been testing the insulation for a while, was the mod worth it for me? Yes, because it was an easy and quick way to get riding this winter. It'll likely keep my battery above freezing for most, if not all of the winter. Although I doubt most people would want to pay the $180 USD it costs.

After maybe two hours of riding the battery settles at a stable temperature of about 10°c warmer than outside (which has been hovering around 0c). Perhaps temperatures of -10°c or colder outside would cause to battery to reach 0°c, I'll have to wait and report back. I've noticed that when taking extended stops the temperature does seem to fall more, so the batteries probably generate some noticeable (but not drastic) heat. By the way, I've had no heat issues when using the stock 5 amp charger.

Is this the ultimate solution? Obviously not, but it's better than nothing for me. The ultimate solution would be silicone heating pads (which I couldn't implement in time for winter). Imagine having 20°c batteries even after hours of freezing temperatures. I'm sure they could be done "DIY" with enough effort put in, but it would be amazing to see this come standard from the manufacturer (perhaps surrounded by a sealed plastic case). I don't think it would add too much cost or complexity, and would be a great selling feature.

 

Edited December 26, 2021 by InfiniteWheelie

[TantasStarke]

How long does it take the batteries to come back up to temp after being left inside? Been wondering how long realistically to wait to recharge after winter riding to avoid charging a dead cell, would be some amazing info for the community

[mrelwood]

For freezing temperatures I tend to wait for at least an hour, the batteries are packed deep inside the wheel after all.

 But it would be nice to hear if @InfiniteWheelie has checked how fast the temp gets back up!

13 minutes ago, TantasStarke said:

to avoid charging a dead cell

Not sure what you mean by this though. A dead cell is a dead cell, waiting won’t make it resurrect. Cold cells just have a low limit for the charging current (all the way down to zero), which is why we wait for them to warm up.

[TantasStarke]

8 hours ago, mrelwood said:

For freezing temperatures I tend to wait for at least an hour, the batteries are packed deep inside the wheel after all.

 But it would be nice to hear if @InfiniteWheelie has checked how fast the temp gets back up!

Not sure what you mean by this though. A dead cell is a dead cell, waiting won’t make it resurrect. Cold cells just have a low limit for the charging current (all the way down to zero), which is why we wait for them to warm up.

Sorry meant to say charging a frozen cell, late night lol

[InfiniteWheelie]

It's hard to give an exact time for heating back up since I haven't been scientific about it. A rough ballpark answer is about 2+ hours. For example one time after going inside it took roughly 1.5 hours to go from 10c to 15c. Reaching 20c+ probably takes around 3-4 hours (based on experience and a rough guess). I usually just plug it in before bed, which lately tends to be around 4 hours after I get home. By then the battery is always at least 15c+ (even when starting in the single digits). I mention 15c+ because that's the minimum temperature I choose to charge at in order to baby the battery. I know it's a little vague but maybe that helps.

Edited January 14, 2022 by InfiniteWheelie

[TantasStarke]

4 minutes ago, InfiniteWheelie said:

It's hard to give an exact time for heating back up since I haven't been scientific about it. A rough ballpark answer is about 2+ hours. For example one time after going inside it took roughly 1.5 hours to go from 10c to 15c. Reaching 20c+ probably takes around 3-4 hours (based on experience and a rough guess). I usually just plug it in before bed, which lately tends to be around 4 hours after I get home. By then the battery is always at least 15c+ (even when starting in the single digits). I mention 15c+ because that's the minimum temperature I choose to charge at in order to baby the battery. I know it's a little vague but maybe that helps.

No yeah that's great info, seems it rises give or take 3c an hour for your wheel, so around 4 hours seems to be good to stay in the safe zone, the batteries would have to fall to less than -10C to still be frozen by the time you'd plug it in. Thanks for the data

[InfiniteWheelie]

To give a minor update, I've now taken the wheel out for long rides in below freezing temperatures (negative single digits). Oddly the battery seems to stay higher above ambient the colder it gets. I mentioned the battery staying roughly 10c above ambient in positive single digits temperatures. In negative single digit temperatures it was often something like 12-14 above ambient. For example I believe at -8 outside, the battery remained around +5 (13 degree difference).

Regardless it's clear now that even -10 will not cause the battery to hit 0. The next milestone I want to test is -15c, to see if the battery still stays above 0. If my observation about lower temperatures having a reduced effect is true then maybe it could. I'll have to wait and see.

 

Edited January 14, 2022 by InfiniteWheelie

[InfiniteWheelie]

For anyone wanting to do this modification on their wheel, here's the information summarized. Keep in mind this was fairly difficult, especially since I was learning as I went and winging it. It was only by luck that it BARELY worked out in the end. If you're not handy, patient, and detail oriented you probably shouldn't waste your time and money. That said it can be done, especially with the knowledge I gained.

For this project I decided to use aerogel which the best insulation material you can buy. As mentioned above I used a product called Pyrogel® 2250. It's the thinnest aerogel insulation sheet available at only 2mm. This is very important because any thicker and this wouldn't have fit inside my Sherman (or any other wheels I suspect). It's available online from a US company called Pacor Inc. What you want are the sample sheets here https://www.pacorinc.com/standard-length-aerogel-insulation/try1-sample-kit. They are currently $45 each, and you need one per battery pack. This 16" x 16" sheet is big enough for Sherman packs, and should work for any wheel. They also sell big rolls if needed https://www.pacorinc.com/standard-length-aerogel-insulation/pyrogel-2250. Keep in mind 2250 doesn't come in a dust-free variant, so you want to wear gloves and probably breathing protection. I did handle it without gloves at times and it did seem to irritate the skin slightly. I didn't wear a mask but tried not to shake up too much dust. I seem to be alright but I don't encourage it.

The first step is to dislodge the battery packs and remove all tape/foam from the packs and case. Using a heat gun can help, but I wouldn't use it on the battery, just for removing things from the case. When peeling the sticky foam off the packs, it helped to go very slowly and carefully so it came off smoothly. If it doesn't come off smoothly it can be very difficult and time consuming to pick off.

Next I cut 14.25 x 14.25 pieces using a tape measure and a long square. I wrapped it around so the seam was vertical, and joined it on a 90 degree edge of the pack. Use one of the two edges next to the panel, so any slight overlap doesn't cause space issues. I then taped the vertical seam to hold it in place. This leaves the top and bottom open. I then folded the edges into a triangle shape (like wrapping a gift), and finished by taping the two long edges over each other. If you don't know what I mean watch a gift wrapping tutorial and see how they close the ends. It's important that you take your time to pull the insulation very tight to the pack throughout the whole process. Use lots of tape to hold it tight and cover every seam completely to trap air.

In the top corner with the wire you have to make a slit (maybe a couple of inches long) to allow the wire room. I tried 45 degrees first (straight diagonal), but this wasn't ideal as I had to trim a little more after closing the ends. Just try to judge where the wire will lay to cut a better angle. This wire connecting the two packs is very short, so it needs room to bend out naturally otherwise the packs won't go back in.

After that was done I used 220 mm wide shrink wrap to seal it all. I believed I tried cutting a 16" piece which was a little too big, then trying a 15" piece which worked pretty well. I sealed it up with a heat gun at around 150c I think. I started by heating the middle and working my way outwards. I then trimmed the ends a little with scissors. Note this leaves an oval hole in top and bottom revealing the insulation. I guess there's a way to avoid this using 2 pieces like the factory wrapping job, but I didn't bother and there wasn't room for more thickness anyway. Come to think of it this may be an unnecessary step, and the packs would probably fit back in better without it.

I then managed to stuff the packs back in which was an extremely tight fit, as there was literally 0 room to spare in every dimension (meaning it had to be coaxed in). It's astounding it actually worked. The panels didn't go back on 100% perfectly. There's a very small gap on the seams, and I didn't dare tighten the screws past about 80%. With patience and coaxing at least the panels did go back on, and without any problems so far. The new Sherman Max is using bigger 2170 cells so I don't believe this modification is possible for that wheel. The side panels have been modified by removing the ribs, and possibly other slight changes. I'm considering buying these panels to relieve pressure on the battery packs, and hopefully close the panels 100%. I'll keep an eye out for that.

I also used this Bluetooth temperature probe from amazon to monitor it https://www.amazon.ca/dp/B08V1HGYMX/ref=twister_B095W9WXR4?_encoding=UTF8&th=1. The probe was taped to the bottom of the pack itself (meaning the open end you fold), underneath the insulation. There's lots of room there because of the way the pack slants due to the cylinders stacking. It has a long wire which connects to the module. I taped the module inside the controller compartment since the space above the battery was a little bit too small. It's right in the very front next to the fans, there's a little empty void there. I was going to use one for each pack but there was just no space for extra modules. There are probably units with multiple probes which would work, but you only really need one since the packs should be basically the same temperature.

 

Edited January 14, 2022 by InfiniteWheelie

[RagingGrandpa]

Have any photos of your install?