# Winter and battery voltage drop



## miko81 (Apr 2, 2012)

Hi guys,

in Europe winter and low tem have come. This week in my town was belowe -15 celsius.

In my conversion I have Winston battery pack 31cell 200ah, nominal 96V 200AH, max charging voltage 108,8V,that is 3,51V/cell. While Iam driving during temp. around 0, voltage drops to 93-96V and car goes OK, but this week when it was -16 celsius voltage drops to 90V that is 2,9V/cell and stays on that voltage all time, when I stop it goes up to 103-104V. Later that day temp. was -3 and car workes OK and battery drop wasnt near that. 

I was wondering do you have souch big voltage drops during cold winter months? Do you heat yours batterys somehow? 
What are yours experience while during driving winter and cold days. 
My batterys are under hood and they are in box isolated with styrofoam 3cm.


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## piotrsko (Dec 9, 2007)

The chemistry of most batteries is at its happiest at temperatures that you find comfortable in short sleeve shirts. Remember this is a chemical reaction.

Anything below 70 Fahrenheit and performance suffers.

They need a heater.


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## Old.DSMer (May 18, 2012)

I drive in weather as cold as -20. Below that, I find my drivetrain is just too stiff and inefficient. No ICE to conduct heat into the tranny, so it feels like driving in syrup.

I used self regulating heat cable inside my boxes. And I built a small portable inverter so I can keep my cables "plugged in" while I'm parked. It can usually run about 3 hours before my portable pack goes dead. At home, I keep my warmers plugged into the wall all the time. I'm garaged, so it's relatively warm. But still not warm ENOUGH.

The cables draw between 80 and 200 watts depending on how cold it is. Most of the time, my pack stays around 10-15 degrees Celsius.

I have found that anything colder than +10 will result in excessive voltage sag. That also means the entire system becomes less efficient and range suffers dramatically.

Hope that info helps. Take a look at my build thread for more info on the cable and boxes.


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## rwaudio (May 22, 2008)

I drive in all weather, the car works very well, but like Old.DSMer mentioned in very cold weather the transmission is a bit thick. I don't think my 2wd front engine, rear transmission car is quite as bad as his since the transmission never really got as much heat from the engine as an ICE.

I also have battery heating, preset to 15C anytime the car is plugged in. This works very well and the car works great to the mid -30's Celsius, that's as cold as we've had so I haven't driven in colder weather yet. The cabin heat (4kw fluid heater) is just barely adequate below -25 though, doesn't keep you warm but keeps you from freezing. Heated seats help!

Long story short, keep the batteries as warm as practical and you can drive in any weather.


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## miko81 (Apr 2, 2012)

Thanks guys,

@rwaudio
how do you heat yours batterys, what kind of heater do you use? Some heating plates under batterys or something else? How many Wats are you using for heating batterys? +15 degree is weeeery nice!
You use 4kw liquid heater for car heating, I use 1,5kw and it is enough for defrosting windshield and heat a little bit car interior.

@Old.DSMer
are you using this typ off heating? 
http://www.ebay.com/itm/Under-Tile-...hash=item35ff58dedb:m:mv03dNeepoUp2_fcFMcgfIg 

I have sean some wires under yours batterys.


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## rwaudio (May 22, 2008)

miko81 said:


> Thanks guys,
> 
> @rwaudio
> how do you heat yours batterys, what kind of heater do you use? Some heating plates under batterys or something else? How many Wats are you using for heating batterys? +15 degree is weeeery nice!
> ...


I'm using heat tape, designed for reptile enclosures.
http://www.reptilebasics.com/heat-tape
(I didn't buy it there, but that's what a quick search came up with)

I have it attached to the bottom side of 0.05" aluminium sheet that the cells sit on. This protects the tape and evens out the heat produced. I have about 250w of heat and use a chinese temperature controller to turn it on/off. I have the tape configured in two identical halves that I put in series/parallel depending on if I'm connected to 120v or 240v using a volt meter with built in relays.

The charger is also configured so that it won't charge if the pack is less than 5 degrees C, the heaters come on when I plug the car into AC and the charger will just sit there till the pack has warmed up and then begin a normal charge cycle.

With the battery heating the car drives normally all the time. It takes a bit more energy, but it's well worth it.


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## Old.DSMer (May 18, 2012)

miko81 said:


> Thanks guys,
> @Old.DSMer
> I have sean some wires under yours batterys.


I used self regulating heat cable. No thermostat required. Less to go wrong  

Like this:
http://www.ebay.com/itm/381809152823


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## miko81 (Apr 2, 2012)

Thanks,

This was very helpful. I will see what I can buy in local store and instal under the batteries.

Thanks once more!!!


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## Old.DSMer (May 18, 2012)

miko81 said:


> Thanks,
> 
> This was very helpful. I will see what I can buy in local store and instal under the batteries.
> 
> Thanks once more!!!


Good luck, and stay warm!

+1 on the 4kW heater, barely -20. Mine is not as well insulated as RW.

+10 on heated seats. Made a huge improvement when I added them.


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## Moltenmetal (Mar 20, 2014)

I drive to zero degrees C with my Sinopoly pack and no colder, with no battery heating. I do see more sag in cold conditions but it isn't enough to worry about. If I had a car suitable for winter I would have removable insulation and heat tracing to keep the batteries warm, and I would have it plugged in all the time when the car is parked whether it is charging or not. Prismatic batteries have a lot of mass and comparatively little exposed surface area so they will take quite a while to heat if you don't keep them warm.

In summer, you don't want the batteries to heat up much at all either, so you either need heating AND cooling or you need removable insulation. The self heating isn't much, but battery capacity is lost quickly when you hold the cells at high temperature and high SOC- it is better to avoid both as much as possible.

Yabert is driving in -20 C all the time and he drives a lot of kilometres...He will have good advice for you!


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## Yabert (Feb 7, 2010)

> Yabert is driving in -20 C all the time and he drives a lot of kilometres...He will have good advice for you!


Well, only a dozen of day a year max. But a lot of 0 to -15°C days per year.
Anyway, same advice than other Canadian , heat your battery, drive train efficiency is terrible at cold temperature, etc...

My battery heating system with thermostat here: http://www.diyelectriccar.com/forums/showthread.php/smart-fortwo-ev-high-power-version-51472p31.html


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## miko81 (Apr 2, 2012)

I have order heat tape like rwaudio, it should come tomorow and I hope that I will install it tomorow. 

They have had only 80W so I will see how it will heat. I will put under batteries and from sides.


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## miko81 (Apr 2, 2012)

Finally I have install heaters. Under the hood are 20 cells (2P 10S) inside I have put heater 30W, I have bought heater 80W/m2 but in the box fits only 0,45m2 so that is 30W, box is isolated with 3 cm XPS. That box cant be opened easily so I dont know what is temp inside.
This is picture of heating tape:









In trunk I have aditional 42 cell (2P 21S), they are isolated only from two sides, from the top and from one side, another sides are car interior and seats. On this two sides I have put 10cm styrofoam and also I have put again 30W heater. 
Here is picture how heater looks before installing:









Yesterday around 16 oclock I have turn heating on, outside and in the car temp was +6C. I have left this thermostat in the box. 









This morning in 7 oclock outside was -3C and during night temp was going down to -7C.









Since I cant open easily box under the hood, I have open box in the trunk, the temperature in that box was +5C, temperature in the car was -1C and outside -3C.









The heater have heat batterys from -1C how much was in the car this morning to +5C, mutch better would be with 250W like rwaudio and Yabert uses. 
The car this morning was much better then usually when it is -3C. Batterys goes down to 94V (3V/cell) during peak (17kw) and stabilise on 98V (6kw) during normal driving. This morning batterys warent fully charged, on meter was showing discharged 60/200AH.

This heater is great, I should buy stronger one but I didnt know what to expect. I bought 80W/m2 and the stronger one is 200 or 220W/m2.

Thanke you all for help!!! I hope that this will help someone.


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