Hot battery temps when using bike sitting in hot garage

[Offroader]

Normally my battery pack heats 10-15C when I use up the full battery capacity.

When starting at 20C my battery temps will maybe peak around 35C. This is totally OK for me and 35C isn't that hot at the end of my packs capacity.

With the summer coming, my garage can get as high as 35C. This means my battery temps may peak at 50C towards the end of my riding, because they are starting at such a high temperature.

Will this be a problem for 18650 cells? They list the operating range for my cells up to 60C. However, do you think running them to a peak of 50C will decrease battery life?



Any recommendations for something like this?

 

[flippy]

high temps are murder for lifespan.

i would recommend lowering the currents in hot conditions.

don't forget they have max operating temps, you should stay well clear of the limits. thermal runaway is no joke.

 

[dogman dan]

Living in my hot climate, I definitely don't leave batteries in the garage all summer. What I'm using daily comes inside, and what I'm not using a lot goes in an old fridge, not running, which stays somewhat cool all day.

But, in my experience, if they hit 35c as they discharge when starting at room temp, they don't really get a ton hotter if they start warmer. sure, there is an effect, but it's not been my experience that you still get the same amount of increase.

However, this could be mostly because I try hard to not push my stuff so hard, summer or winter. In particular, I slow down a lot if I know I'm in the last 20% of capacity.

 

[Offroader]

dogman, that is what I am hoping for that the batteries don't increase in temp so quickly if they are hotter.

I did have my old turnigy lipo packs in the hot garage for two summers and only found that I lost around 2-3% a year capacity and that also included usage. This makes me believe it isn't so bad keeping them in a hot garage. I guess the batteries also get the advantage of the cold garage during the winter which may help offset some of the heat losses.

The thing is my lipo packs didn't get hot under use because they were 20C compared to these 3500MAH 18650 cells I am using. So they probably didn't increase in temp when using the bike.

I may have to improvise here and bring in the bike in the house during the hottest days.

If my pack is starting off at 35C, at what battery temp would you stop using the bike?

 

[dogman dan]

I'm not sure, if you can't hold it in your bare hand with no problem, way too hot. So I'm saying where practical, keep a battery down to about body temp.

Sounds like you have a too big discharge rate for the new pack problem, nothing to do with the starting temp. Slowing down a lot towards the end of the discharge will help. That's when internal resistance is highest, and c rate lowest. I'd have to say that even in winter, it's still a big problem.

So,,,, uh,,,, Stop immediately?. Lower your amps before another discharge? Perhaps I'm too fraidy cat, but I hate to have a pack heat itself to more than ambient in summers peak temps. That's about 40c or less here, except for a few days a year. If it starts at 40c, I feel there is no damage if it doesn't heat much more than 5 more degrees centigrade from there. More, is obviously roasting that pack.

I would think much over 45 degrees centigrade would be bad. My garage, it can go way past 50c, so no way my batteries are asked to endure that. That old fridge might reach 40c on some summer days, but mostly stays no hotter than 30c all summer.

 

[Ykick]

RC Lipo performs best warm, almost hot. A year round commuter understands how they perk up in summer compared to winter.

100F (37C) storage isn’t anything I worry about or have noticed any practical degradation if/when stored in those conditions at low voltage 3.85V/cell.

As far as too hot when operating? Just below burning hand, 120F (49C) or thereabouts….

I say with strong conviction based on daily use approaching 7 years, 100’s of RC Lipo packs later - avoid sitting at full 4.2V/cell for more than a few hours. That’s “the one” which I believe makes most practical difference and reaps maximum life expectancy.

No other mojo/juju (except over discharge, obviously) makes any measurable practical difference to longevity, IMO.

Short charging (70-90%) is one way to achieve lower sitting voltages but also runs the risk of not having enough capacity for a ride. Merely top off before you head out, longevity doesn’t suffer. Oh, and don't trickle charge 'em...

 

[Uilleam Gilvoni]

My battery is constantly reached by sunlight when I leave at the university 2-4hours), normal temperature its about 25° C, should I cover it up or do something about it? I have a dolphin battery.

 

[Offroader]

My battery is constantly reached by sunlight when I leave at the university 2-4hours), normal temperature its about 25° C, should I cover it up or do something about it? I have a dolphin battery.

Do you have a temp gauge in the center of the battery to monitor the temps?

 

[dogman dan]

Stuff like that is what it is, and it is important that it's not full at that time. We have to use it in the real world. If you can park it in the shade, that's better of course.

I guess I need to clarify some about the garage.

My assumption was that a garage is hot, say 50c, then you pull in with a heated battery, plug in and charge. Then after it's full, it's sitting there still in 50c for 3 or 4 hours till sunset. That's the kind of thing to avoid in my opinion.

As for storage when not full at 100f,,35c ish,, I don't know if that's too hot or not. I have to go use them in those temps all the time, or park it for summer after 12 oclock. But my garage is way hotter than that in summer and I don't want to do that experiment with lipo.

I did keep my lifepo4 in there for a few years, full, and it seemed like they did fine. But now if I got another ping battery, I'd bring it inside and not store it completely full like I used to.

What I'm trying to say is if your garage, or where you park gets to 100f or so at the hottests, that's not so bad. The temps I'm saying avoid are 120-150f. For 4 or 5 months of the year here, asphalt streets reach 150F here.

But it's true,, the battery does perk up quite noticeably. I'm just not so sure the battery likes it,,, If your discharge rate is doing the heating. Big difference between having a warm battery, and having a set up that is roasting the battery.

 

[Offroader]

dogman you are in a whole other ballgame down there in Arizona. Here in NYC, it does get hot in the summer, but usually my garage will peak around 90F to 95F on the hottest days.

I think I may be alright with the temps, I started my ride yesterday at 32C right after charging and after 23 miles or 1400 watt hours, my battery was only around 36C. Seems to increase in temp a lot slower if the battery is hotter to start with.

I have a 3300 watt hour battery pack that is glued tightly together.

What surprises me is that charging this pack caused a rise from like 19C to 32C, when I only charged it at .65 amps per cell. Cells are rated at a max of 1.6 amps per cell. Seems the pack likes to rise to low 30's C easily and then doesn't heat up fast from that point.

 

[amberwolf]

Are the temperatures the same throughout the pack? Or is it only measured at that one point?

If you're not already doing this, you might check it with an IR thermometer with a small-spot focus point, to get an idea of if it is specific cells getting warmer than others, or if it's a whole-pack phenomenon.

Then you'll know if it's a cell problem or if it's just how that pack performs as a whole.

BTW. Dogman is in New Mexico....but I'm in Arizona. It's probably hotter here than in NM, but neither is much fun in the summer heat.

 

[dogman dan]

Definitely hotter in Phoenix. I'm at 4500 feet elevation. But it still gets hot here, and hotter in my garage.

But I happen to have a metal garage door that faces south, and no insulation in the garage. So my garage is really a type of solar oven. It gets hotter than outside in there on a summer day. If my garage peaked at 90f, I likely would not worry too much about the hot garage. But it would still be best not to put a heated up battery on the charger in there.

 

[Offroader]

Just wanted to write that I will be doing an 18650 test to see exactly how the cells fare in my hot garage, which has temperature fluctuations (75-95F) vs in my cooler more stable basement. (78F)

I have a bunch of unused 18650 cells from my battery build to do the test with.

From a preliminary test of a single cell that I left in my garage for a couple of months now vs a cell that was left in my basement, they both cycled with the same capacity.

What I plan on doing is placing 3 18650 cells in the garage, and compare those with 3 18650 cells in my basement and checking capacity at certain intervals to see if there are any differences in capacity. I will keep the cells at around 3.7 volts.

I may consider leaving a cell at 4.1 volts to see how leaving the cell with a high voltage degrades life when compared to 3.7 volts.

Will start another thread with this when I get everything started and update it with results.

 

[Lurkin]

It's kinda irrelevant I guess, given you have already made your pack, but would interesting to see temp dispersion of a glued pack vs pack with spacers vs pack with spacers and fans... I've read arguments both for and against gluing, primaily driven by pack size requirements than cell life. Further I've read some believe that gluing the cells so closely together allows the metal cell to transmit the heat to the outside of the pack. I've never really bought this theory because it doesn't really allow the temp to return to ambient centrally in the pack vs fan cooling via air gaps in cell spacers and the glue and heatshrink also act as insulators.

Food for thought. The nice thing about more active forms of cooling is the degree of control over the central pack temperature

I was considering doing something similar to snaths most recent non weld design, but to segregate the box on both sides allowing a gap between the two cells ends which could have fans blowing at least ambient air down the middle of the cells.

 

[Offroader]

It's kinda irrelevant I guess, given you have already made your pack, but would interesting to see temp dispersion of a glued pack vs pack with spacers vs pack with spacers and fans... I've read arguments both for and against gluing, primaily driven by pack size requirements than cell life. Further I've read some believe that gluing the cells so closely together allows the metal cell to transmit the heat to the outside of the pack. I've never really bought this theory because it doesn't really allow the temp to return to ambient centrally in the pack vs fan cooling via air gaps in cell spacers and the glue and heatshrink also act as insulators.

Food for thought. The nice thing about more active forms of cooling is the degree of control over the central pack temperature

I was considering doing something similar to snaths most recent non weld design, but to segregate the box on both sides allowing a gap between the two cells ends which could have fans blowing at least ambient air down the middle of the cells.

My pack glued together as a solid piece and surrounded by foam does seem to get hot fast. I notice when charging at a very slow rate (.5 amps per cell) it will heat from 22C to 32C.

Normal riding at 8KW, it can climb to 35c-40c depending on if I Just charged the pack before using and the pack is sitting in the 30'sC at start of ride.

Most of the time I won't heat the pack up above 35C and the max I ever got it to was 40C during the hot summer days. This is why I am not really worried about cooling so much because it isn't worth it if all I'm seeing is usually a maximum temperature of 35C, with only once ever heating it to 40C, and seeing these hot temps only in the peak of the summer.

During the cooler months when the pack isn't starting in the hot 30'sC temperature out of my hot garage, there is almost no problem at all with pack heating.

This of course all assumes that it isn't a big deal to heat the cells during my short time riding into the 35-40C range, it only gets that hot towards the very end of my riding.

Another thing to point out is that I rarely keep the bike at full throttle for continuous riding, like if I was riding on the highway. If I was to push the bike full throttle on the highway at 8KW or around 6.5 amps of my 10 amp rated cells, the pack would heat up very fast and I probably could heat it to 45-50C after 5-10 minutes of that kind of power. Riding in the city I would never be able to do that so that isn't and issue.

If you were using the cells in a street legal ebike designed for the highway, you would easily overheat the pack and would want some kind of cell cooling. It is important to have a temperature gauge on the pack when using 18650 cells. Surprisingly almost nobody uses a temperature gauge.

 

[Lurkin]

I imagine some people might rather not know :lol:

It would be really interesting if you could get some measure of your entire packs capacity now and test it again for degradation over time. I think those temps are too high to maintain long term cell life, but I guess the proofs in the pudding - measuring it is the only way to be sure.

Interestingly thought though - it really depends on what you perceive to be acceptable cell life. After all, batteries are improving at rapid rate - how long will you actually keep this pack anyway? We could be worrying about degradation which is irrelevant if replacement is on the (eventual) cards.

The measurements are the only way to know whether the rate of degradation vs pack replacement rate is acceptable to you. 8)

 

[Offroader]

I'll be able to measure the capacity when pulling the pack and cycling a single on my pack.

I also will get an idea about how my pack is doing by keeping an eye on the max-e watt meter. When the pack was new I get the following stats for a full ride from 4.1 to 3.3 volts



If I start to see that I'm getting lower than 2802 watt hours, I'll know roughly how much my pack is deteriorating. The Max-E watt stats are very consistent.

But like you say, I built my pack so big and don't think I have yet used a full charge in a single day. It would take me years (5+ years) before capacity loss would be an issue.

 

[wineboyrider]

I have two packs of 12s 16ah lipo packs after a ride the battery is usually discharged to about 45 volts. I put the discharged pack in my refrigerator in the garage and exchange it for the other already 45v pack and quick charge it for about 15 minutes with my 10.8 amp charger. I am hoping to get a few years out of these packs...

 

[wineboyrider]

FTR I live in NM a tad bit cooler than Dogman (not much) and my garage gets hot, but I think the lower humidity probably keeps it cooler than a more humid place.