Winter cycling/battery charge-discharge strategy

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bardbe   100 µW

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Winter cycling/battery charge-discharge strategy

Post by bardbe » Jul 31 2018 9:28am

Maybe not the right time of year for a question like this, but hard to wait a few months for answer that's been on my mind for some time already :)
I have been riding a Bafang BBSHD throughout last winter commuting 45km each day, lowest temp about -7 deg C. The battery has been charged indoors both home and at work, so when I started riding, the battery was warm and stayed at a good temp the whole way, because of the large current draw from BBSHD. Now I have built a larger battery that doesn't need recharging at work, and is permanently mounted to bike, so indoor charging is not possible anymore. So now I want to clarify the following.

If I start in the morning with a charged battery that has been in the shed during the night, it will be cold, but heat up rather quickly when riding because of large (initial) internal resistance when cold. At work it will also get cold, so when I head back I will have the same situation, loosing some capacity to heat up battery. Since battery is warm when I get home, my plan is to hook it up to charger ASAP, and then the current from the charger will keep both the charger (Satiator 5Amp charge) and battery at a good temp, even if shed temp is below 0 deg C. In that way I avoid charging a cold battery, which I know can damage it, and it will be full for the next day.

Does this sound like a good plan, or will it cause reduced life cycle of battery? The biggest question is probably what is the lowest internal temperature of a battery pack one can start riding without causing significant reduction of battery life (standing for 7-8h at work outdoors the battery internal temp will maybe approach outside temp, but maybe not if I insulate it somewhat?). Active heating before riding is not an option, as I will need current from battery to do so.

Any opinions and preferably experiences on this issue? I've tried to search for this case, but haven't found a thread that covers it completely


dustNbone   10 kW

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Re: Winter cycling/battery charge-discharge strategy

Post by dustNbone » Jul 31 2018 5:23pm

The tricky part is going to be the sitting outside below freezing for 8 hours. I don't think any practical amount of insulation is going to be sufficient to prevent the battery from getting much colder than you want it.

One option you could use is a low amperage charger set to a lower than normal voltage, say 4.1 or 4.05V per cell, and leave that plugged in during the time it's sitting idle outside. It should trickle enough energy through to keep things at a decent temperature, if you combine it with some kind of insulation around the battery itself.

Another thing people have done is to use some nichrome wire and a PWM controller, possibly also a thermostat, to build a very small heater inside the battery box. It would only be drawing a tiny amount of power, a few watts at most, just to keep things above say 5 degrees C. Again, you'd want to insulate as much as practical.

I ride all year too, and it does get cold here sometimes, but I've always made a point of taking my battery inside if I'm going to be leaving the bike for more than an hour or so. I also bring it inside when I get home, so it's warm when I need it.

markz   100 GW

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Location: Alberta Canada

Re: Winter cycling/battery charge-discharge strategy

Post by markz » Jul 31 2018 7:29pm

I've been thinking about this

Warming the battery when its outside.
Sparkfun type heating pads that work off a dc voltage, wrapped around your main pack.
or just buy the carbon tape and diy ... ated-vest/

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RustyKipper   10 W

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Location: Rotherham UK the land of flat caps and wippets

Re: Winter cycling/battery charge-discharge strategy

Post by RustyKipper » Aug 02 2018 7:23am

Both my bikes have silicone heater mats fitted. I have a 4 pin charger plug that delivers the charging current as well as 12V to the heaters when required, this keeps the battery warm while charging.

With my ice bike the battery capacity is a bit tight for a 14 mile commute especially in snow so on really cold days I can preheat the pack. When at home I use a small 1A wall wart power supply, If I'm at work I use a small lead acid battery. This system works like a charm. I think the total heating power is about 10W, I have a thermometer on the bike with the sensor in the center of the pack so have a fairly accurate indication. A half hour of heating will get the pack from about -5 to about 10 C. The ice bike has really good insulation so will stay warm for a good few hours. My regular bike battery has a 30 odd degree temp rise in riding so in the summer has to shed heat so I can't insulate it.
2017 Cotic BFE hardtail MTB
Sram 9 speed twist grip
CST rear drive
5P10S 16Ah home built battery with built in block heater
Con121 12FET controller
Sapim 2.3mm black stainless steel spokes
Sunringle 26 inch rims
26 x 2.1 Swarble Marathon Mondail tires
650gm downhill inner tubes --essensial
Shimano Zee 4 pot calipers front and rear
200mm / 203mm rotors
Thudbuster suspension seat post -- essensial
150 Mile per week muddy commute

bardbe   100 µW

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Re: Winter cycling/battery charge-discharge strategy

Post by bardbe » Aug 04 2018 10:57am

In my case, I will not have access to plug in heater at work, and at home I can in cold days put it inside house or put some heating pads around it. It is hard to find some numbers at what temp one should not load battery. -10C is mentioned as a limit, but if your close to the limit, what discharge rate is safe in regards to battery life, before the self heating will kick in and warm the battery enough to be in the safe zone. I suppose this is hard to answer without a proper scientifical test procedure. Any links to such papers would be very interesting. I guess I just need to test it out for myself when winter comes. One indicator would be how the range will be affected, compared to summer, and if I will not make it roundtrip, I'll just need to go back to original setup.

Thanks for input

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