New build, now in arctic environment

[Bor_Ed]

This is my first posting on the forum so be gentle
The bike I built is cheap 100eur city mtb and I added www.ev-power.eu rear kit to it with their 36V 10Ah battery.
Is there clear process for the battery burn-in for temperatures below -15°C? I have done first couple of cycles (around 20km/14ml) to first bms cutout.
What kind of power and range I'm supposed to get from the 36V 500W direct hub motor and 36V 22A 9cont controller in these temperatures without ruining the controller and the battery? I'm pretty confident that the motor itself can handle the temperatures.
Pic for the prelimenary setup is at http://i.imgur.com/UTqlz.jpg .

 

[amberwolf]

Best thing to do is keep the battery warm, as it's performance will need to be seriously derated at those temperatures.

Keep the battery inside when not in use, and insulate the battery case very well. Open up the case when inside the house/etc. for charging, so the BMS doesn't overheat and cook while balancing/etc.

 

[neptronix]

A lithium battery will perform extremely poor below freezing. So will SLA, etc.
22A on a 10AH lifepo4 battery is going to perform poorly to begin with. That's a little over 2C.. those batteries should be used at more like 1-1.5C for best performance.

So you have the worst case scenario - a weak battery weakened even further by freezing temperatures.

You need to keep the battery warm.. electric glove warmers seem to work well. This should provide a big improvement in power.

I did some tests here, check it out. http://endless-sphere.com/forums/viewtopic.php?f=14&t=35668

 

[Bor_Ed]

Interesting read...
Need to wrap the battery with some insulation apparently and try to be light on the throttle for next months.

 

[neptronix]

80% capacity at -20C? maybe if you disable your low voltage cutoff because it will sag so bad that a 36v battery will act like a 24 volt battery or worse due to voltage drop.

Get a turnigy watt meter, cycle analyst, or something else and see what your results are. Otherwise these are only educated guesses.

 

[Bor_Ed]

Currently I have only educated guesses, that's true.
I'll get some sort of power monitor to the finalized setup to see the real usage of the setup.

 

[MadRhino]

My high C rate Lipos perform well at -15, it is around -20 that I start to notice a clear difference of capacity. If they are not left outside and start the ride warm, I can do 20Km at -20 without any loss of performance or range. Most of the time, one would ride slower in very cold weather anyway, because of the extreme wind factor and bad road surface. That alone is enough to give my battery packs some extra range in the winter. Letting them freeze outside makes for a loss of performance and range, but I believe it doesn't damage the cells at all.

This might be different with other chemistry, smaller wiring, lower C rate...

 

[neptronix]

It is. You've got plenty of C rate to spare, especially if you are using a big pack.

At a little under 0F, my 20C lipos started acting like they were 3C. Not a big deal.

 

[Drunkskunk]

Beer cooler.

you have a good looking setup, but for the best performance from your battery you should add a beer cooler to the rear rack, and keep the batteries in that. you'll find the batteries perform best around 20C. So keep them indoors when not in use, and keep them in the bag while being used, they should stay warm enough.

I live in Texas, we get the opposite extreams here. it can get to 45c in the summer, and I use a cloth sided cooler as a battery bag, with the kind of jell packs you freeze to keep beer cold or sprained ankles from swelling. It makes a real diffrence.

Its actualy good for Lithium batteries to be cold when being stored, so no harm from the temp, but they perform better when around 20C.


My head hurts from converting everything to metric. I think I'll go have another beer.

 

[dogman dan]

I disagree that lipo doesn't sag in cold weather. It just depends on how you carry it. My desert oriented battery box is built to be a nice heat sink instead of a nice insulator, and I can feel the cold affect my bike in much milder temps around freezing.
Could be, it's the wiring that's affected as much as the battery. But in any case, cold slows the bike down dramaticly. Start the ride warm, and within a few blocks the power drops a lot.

But that's my speed dropping, Ah avaliable seems to be pretty similar. So it sags but seems to keep a lot of it's capacity.

With cold lifepo4 battery, I did see a noticable drop in capacity when comparing riding at 30F to riding at 90f. (0-30c?) I'd lose about 20% capacity.

But since you are riding in really cold weather, I'd look at insulating everything till you get into above freezing. For sure start with a room temp battery, and put it into an insulated bag or beer cooler of some kind. Line the box with foam, whatever works. I'd even insulate the controller just a little bit, mabye just put it into a plain uninsulated cloth bag to keep wind off it. This will let the controller heat itself a bit. Once warm weather returns, the controller needs to come back out of the bag.

You might put a hot pack in the bag with the battery too. You can get ice packs that also works as hot packs. You just pop em in the microwave to make em warm. Get those at the drug section of the store.

The motor itself will make enought heat to keep itself happy. But you can get a tiny bit of condensation inside, which can freeze and lock up a bearing. Won't be much of a problem till it gets to being above freezing part of the day.

Range? It depends on so many things. My rule of thumb for 36v is 1 ah per mile. But that's a battery sizing guide to get enough reserve to reach a goal reliably. 15 miles should be possible on 10 ah, riding at 20 mph or so, draining the battery 100%.

Leave new batteries on the charger a long time, so the battery can continue to balance itself better and better. Plugged in overnight is convenient anyway.

 

[Ykick]

Lipo sags very bad the colder it gets. I've been testing a loose RC Lipo cell in the freezer around 0-5F. At room temp this cell holds around 3.6-3.8V during most 1C (5A) load. Left in the freezer overnight between 0-5F the same cell spends majority of discharge 3-3.3V at 1C. I had to use Lilo setting to achieve a lower voltage cutoff for my iCharger to monitor.

The odd thing to me, with that amount of sag, the capacity remained roughly the same (80%) that it had at room temp. The cell didn't seem to be any worse for wear once it warmed up - capacity returned at the normal temp sag voltage.

My uneducated guess is that the cell can sag to lower voltages without damage at lower temps than at warm temps. The practical challenge would be if your LVC system is calibrated for room temps it probably won't allow you to discharge the battery enough to get any capacity out of it at low temps.

My commute allows me to start with a room temp battery but I park in an unheated alley while at work so my battery settles to whatever ambient outside temp we're experiencing. 25F' and below is where I really notice the sag and to help minimize that I double my usual capacity for the cold weather. That seems to limit the sag enough and after a couple blocks the internal heating of the cells starts to soak in and it delivers a decent level of performance for my ride home.

Based on these experiences I've set my cold weather cutoff to around 15F.

BTW - my co-worker drives a Chevy volt and based on the vehicle computer during warm weather he was seeing 40miles on the battery pack. When temps started dipping into the mid 20's F' battery range dropped to around 28 miles.