# Battery warming - Soil Cable + space blanket?



## gdirwin (Apr 7, 2009)

I bought mine from here:
http://www.morelectricheating.com/default.aspx?page=item%20detail&itemcode=WRAPON52020

They have light duty and heavy duty types, as well as some with built-in thermostats and others using external thermostats.

I am using 2 heavy duty cables (front and rear battery boxes) routered into the bottom layer of insulation, 20ft each with built in thermostats, 100 watts each (should be plenty). They will be plugged in on a timer when the car is plugged in over-night (and possibly during the day when I am at work).

I will try to design boxes that have insulation that can be removed in summer for air-flow...

Still waiting for batteries, so very early in my build (2001 REV4) - no experience yet though.


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## dtbaker (Jan 5, 2008)

cool... now I am wondering if these kind of cables would be ok if run off the DC main battery pack?! Issue is to keep batteries warm while outside at work.... I know the ceramic heater cores are fine running on DC as long as appropriate switch is used....


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## gdirwin (Apr 7, 2009)

DC and the heating cable itself should be okay, but I am not sure about the thermostat to turn off the power... You could use an SSR (solid state relay) and an external temperature controller... See my thread for a ceramic heater controlled by a temperature controller (to control the interior temperature):
http://www.diyelectriccar.com/forums/showpost.php?p=162803&postcount=22

The controller is about $40, each DC SSR relay is about $30, and a temperature sensor is about $5. If you have 2 banks, I believe you can also buy controllers with dual inputs...


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## Amberwolf (May 29, 2009)

If interested, there is a thread on ES about some insulation materials:
http://www.endless-sphere.com/forums/viewtopic.php?f=7&t=15509&start=0
________
SweetHotty cam


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## racunniff (Jan 14, 2009)

dtbaker said:


> Has anybody tried using Soil warming cables to line bottom of battery boxes? They have built-in thermostats to 74 degrees which sounds perfect....
> http://shop.ebay.com/items/soil hea...&MT_ID=69&tt_encode=raw&adgroup_id=1253902054
> 
> How about in combination with lining box with cheapo 'Space Blanket' foil? I am thinking this would be super easy to put in the fall, and remove in spring... or maybe just leave in if batteries don't generate much heat?
> ...


I'm using them, but not to line the bottoms. I've put them between the batteries - see these links:

http://volt914.blogspot.com/2009/12/battery-warmers.html
http://volt914.blogspot.com/2010/01/warmers-installed.html

I don't have a precise way of measuring the battery box temperatures, but at least I have verified that, once the boxes are warm enough, the thermostats on the cables are turning on and off periodically, and the boxes feel warmer to the touch than the surrounding environs.


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## Voltswagen (Nov 13, 2008)

DT
Would it be possible to use an Electric Blanket (the kind our wives love)
to heat the pack in cold weather?
Many AC powered heating devices, such as Hair Dryers, use Diodes to convert AC to 120v DC. 

I am currently setting up a Hair Dryer Defroster System for my Beetle. (1500 watts of instant heat)
In fact *you* were the one who suggested that I run the Hair Dryer straight off my pack. Good idea.

Since the Hair Dryer already has the Diodes, if I power it thru a 20amp DC breaker (not a toggle switch  ), I can run it directly off my 120v battery pack and the Diodes don't have to convert anything, they just pass thru the DC current.

Wouldn't an Electric Blanket, using a 20amp DC breaker, operate in the same manner? If so, it could easily be removed in warm weather when it's not needed.
Roy


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## dtbaker (Jan 5, 2008)

electric blanket, or these Soil warming things since they have a built-in thermostat is what I would HOPE would work. I am not an expert in that sort of thing so was hoping someone will chime in and say 'yes, that works great. '

An electric blanket might not be as good since the switch is rated for AC, and might fry or weld itself together under DC..... ?

I may just order one of these Soil warmers and see what happens when connected straight to DC.... only a $30 investment.


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## Voltswagen (Nov 13, 2008)

Dt 
What if you used a 20amp DC breaker to switch it on and off like I will do with my Hair Dryer.
I tested the Hair Dryer using a straight connection of the power wires to my battery pack without the breaker and the Hair Dryer's own switch on High. It worked fine but I only ran it about 5 minutes or so under full load. Maybe I should run a longer test?
Roy


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## dtbaker (Jan 5, 2008)

Voltswagen said:


> Dt
> What if you used a 20amp DC breaker to switch it on and off like I will do with my Hair Dryer.
> I tested the Hair Dryer using a straight connection of the power wires to my battery pack without the breaker and the Hair Dryer's own switch on High. It worked fine but I only ran it about 5 minutes or so under full load. Maybe I should run a longer test?
> Roy


yup, this is what I am thinking.... 20 amp breaker, manual switch... It would be really nice if I could leave a regular plug so I could use house power at night when charging pack, and then switch to pack power during the day.

When you 'tested' direct connection, did you get major spark/arc, or not too bad?


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## Voltswagen (Nov 13, 2008)

Small spark........nothing big.


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## Guest (Jan 25, 2010)

Check out this site. www.heatline.com and click on komensator. This is a self regulating heating cable. I talked to the Company founder and owner some time ago. He was quite talkative and seemed like he would be easy to business with.


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## racunniff (Jan 14, 2009)

racunniff said:


> I'm using them, but not to line the bottoms. I've put them between the batteries - see these links:
> 
> http://volt914.blogspot.com/2009/12/battery-warmers.html
> http://volt914.blogspot.com/2010/01/warmers-installed.html
> ...


Well, I *was* using them. They have burned themselves out after only a few cycles. Not sure whether the foam keeps too much heat next to the cables, or what, but they definitely destroyed themselves.

http://volt914.blogspot.com/2010/02/of-mice-and-men.html


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## dtbaker (Jan 5, 2008)

racunniff said:


> Well, I *was* using them. They have burned themselves out after only a few cycles. Not sure whether the foam keeps too much heat next to the cables, or what, but they definitely destroyed themselves.
> 
> http://volt914.blogspot.com/2010/02/of-mice-and-men.html


very interesting..... I am forgetting, did you plug them into regular AC wall current, or wire up to your DC traction pack voltage?


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## racunniff (Jan 14, 2009)

dtbaker said:


> very interesting..... I am forgetting, did you plug them into regular AC wall current, or wire up to your DC traction pack voltage?


I had a separate 120VAC line for the heaters. So, I was running them at their rating. I suspect they were designed for having moist soil all around them to conduct the heat away - the aluminum plate was not enough.


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## dtbaker (Jan 5, 2008)

racunniff said:


> I had a separate 120VAC line for the heaters. So, I was running them at their rating. I suspect they were designed for having moist soil all around them to conduct the heat away - the aluminum plate was not enough.


a real shame... you put a lot of work into the installation! Perhaps they overheated because the thermocouple was away from the heat source, and couldn't 'tell' when it was hot enough?

I just got some stuff from heatline.com which is self-regulating between .5 and 6 watts per foot. Its more expensive than the soil-warmer cord at $3.50/ft but can run off either AC or DC and doesn't require any thermocouple or sensor, so still less than the Farnum pads + control. I have not tested yet.

I was going to wire to my DC pack only, but am now thinking that if it looks like it is going to work I may wire a switch so I could run from either pack (during the day) or AC (at night while charging). I don't want the draw from the pack messing up the charge cycle....


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## RKM (Jun 9, 2008)

Dan,

I'm wrestling with the "heat the cells" issue right now as well. I've learned that the TS cells really like summer temps. 

Space is limited for adding additional insulation to the batt boxes. At a minimum, I will be using a self adhesive, foil backed fabric to act as a radiant barrier to heat transfer. I will also be placing 5/16 (uncompressed thichness) of foil/bubble wrap beneath the cells. Farnam heating pads will be placed above this insulation and beneath the cells (http://store.kta-ev.com/farnambatteryheaterpad.aspx). 

Each of the five boxes will use an inexpensive thermal switch. The switches will open above 15C. I'll install these switches at the top of the cells and should be able to play around with location and insulation to achieve a cell temp closer to 20C.

The heaters will potentially be on whenever my pair of chargers are plugged in. The heat will only be active on AC, not connected to the pack. There will be a total of 350W among the five boxes.

That's the plan. Will let you know how it works out.

Rob


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## gdirwin (Apr 7, 2009)

I noticed that you had cut/shortened some of the heating cables - how much did you cut off? This will reduce the total resistance, thereby increasing current and the load - maybe causing them to heat up too much...


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## dtbaker (Jan 5, 2008)

sounds very similar to what I am planning.... I have very little space for insulation, so was going to line boxes w/ 'space blanket' and go with either this heatline stuff, or the Farnum pads.... The Farnums may well be the way to go since they have greater surface area and probably give more even heat, but at $15 per unit they get pricey. :sigh:

Do you have a picture/post of the thermal switch you are using?


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## RKM (Jun 9, 2008)

dtbaker said:


> sounds very similar to what I am planning.... I have very little space for insulation, so was going to line boxes w/ 'space blanket' and go with either this heatline stuff, or the Farnum pads.... The Farnums may well be the way to go since they have greater surface area and probably give more even heat, but at $15 per unit they get pricey. :sigh:
> 
> Do you have a picture/post of the thermal switch you are using?


Dan,

I chose the Farnam pads because they are very thin at only .080", that's very important for my installation. I think they are likely easier to install and perhaps less prone to damage from contact with the bottom of the cells (I don't have the space to router a protective channel into insulation as Garth plans to do). I, too, expect that the heat will be more uniform. I'll be using 10 of these at a cost of $150. The thermal switches are $8 per, so another $80. If this, plus a few more dollars worth of insulation will convince the cells that it is summer all year round, it will be well worth it! 

I'm picking up the switches on Friday, will post a pic.

Rob


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## dtbaker (Jan 5, 2008)

RKM said:


> The thermal switches are $8 per, so another $80.
> I'm picking up the switches on Friday, will post a pic.


cool.... where are you getting the switches, and why are you putting one per pad? Can you not put the pads in series and just use one switch?


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## RKM (Jun 9, 2008)

dtbaker said:


> cool.... where are you getting the switches, and why are you putting one per pad? Can you not put the pads in series and just use one switch?


Oops. My mistake. I'll be using five in my car (ordered ten total, five for a friend), one per battery box. The five boxes have varying numbers of cells, heating pads and also varying amounts of insulation. I want each box to have its own thermal switch to achieve a more uniform pack temp.

I'm getting the switches from a local supplier. You'll want to find a US dealer to avoid crossing the border. I'll post the specs and a photo.

On the box cooling side, I'm using a single thermal switch, located in the box which should warm up the fastest, to control all the box cooling fans. This setup will run whether the car is charging or driving (off DC).

Rob


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## Dave Koller (Nov 15, 2008)

dtbaker said:


> Can you not put the pads in series and just use one switch?


Dan
Wouldn't they be in parallel at *120 volts, 35 watts each heater pad*. This looks like a good deal - you think *they* will be prone to hot spots with all the battery sitting on top and pushing down?


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## tomofreno (Mar 3, 2009)

> Wouldn't they be in parallel at *120 volts, 35 watts each heater pad*.


 Yes. If you put them in series you won't get much current through them, and not much heat. They are designed for 120VAC input. I have 10 in parallel for a total of about 350W.


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## dtbaker (Jan 5, 2008)

really? if you did'em in series + to - like you do the batteries wouldn't it just look like a single big 350w heater as far as the current goes? I'll go either way on this one not really having the best grip on circuits, but was just looking to not have to run multiple sets of wires back to a power junction. would it not be the same as: v-<-pad+-pad+-pad+>v+


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## racunniff (Jan 14, 2009)

dtbaker said:


> really? if you did'em in series + to - like you do the batteries wouldn't it just look like a single big 350w heater as far as the current goes? I'll go either way on this one not really having the best grip on circuits, but was just looking to not have to run multiple sets of wires back to a power junction. would it not be the same as: v-<-pad+-pad+-pad+>v+


You have to use Ohm's law - V = IR. If your "350W heater" is based on 120V, then:

1. It consumes roughly 3 amps (350 / 120)
2. Resistance (R) is V / I is 120 / 3 is 40 ohms
3. In parallel, two heaters would have 20 ohms resistance
4. In series, two heaters would have 80 ohms resistance
5. In parallel, two heaters would consume I = 120 / 20 or 6 amps
6. In series, two heaters would consume I = 120 / 80 or 1.5 amps
7. In parallel, two heaters would dissipate 6 * 120 or about 700 W
8. In series, two heaters would dissipate 1.5 * 120 or about 175 W

You can see how it works - heaters are simple resistors, so it's easy to figure out. Two identical heaters in parallel produce twice the heat. Two identical heaters in series produce *half* the heat.


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## dtbaker (Jan 5, 2008)

duh, it's all coming back to me now... good thing I didn't have to DESIGN any of these circuits!


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## RKM (Jun 9, 2008)

Dan,

Just got my Farnam heaters. Plugged one into 120VAC and it warmed up to about 45C within about 5 minutes! The surface temp is fairly uniform, varying perhaps 4C at various locations. This temp was measured at only 10C ambient.

The thickness is actually only .045", .080 at the four rivets and .125 where the pair of wires connect.

I'm pretty pleased and think it will be the solution for me. Will likely be a week or so before I start to install. Will take pics and post.

Rob


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## gdirwin (Apr 7, 2009)

gdirwin said:


> I noticed that you had cut/shortened some of the heating cables - how much did you cut off? This will reduce the total resistance, thereby increasing current and the load - maybe causing them to heat up too much...


Hi Racunniff - I didn't get an answer to how much you cut out of each cable - I am about to install heating cables and hope to get the to bottom of why yours failed...


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## drdonh (Aug 8, 2008)

Hi,

I thought I would share my attempts at a battery warming solution, where details can be found on my blog:

ev-a40.blogspot.com

It uses the guts from electric battery warmers for heat, and pet tererium temperature controllers to set the heat. I already have my batteries in insulated boxes, but natural heat generation from daily use and charging didn't quite keep up room temperature in the boxes once the outside temperature got below zero. This solution is perhaps not the cheapest way, but hopefully should work (I'm not done yet). The heat would only be on when plugged in for charging.

Don


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## JRP3 (Mar 7, 2008)

I was thinking of using those as well, but not taking them apart. Why did you pull them out of the bags?


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## drdonh (Aug 8, 2008)

Hi JRP3,

The warmers have a fibre insulating backing that made the units too thick, and the size didn't exactly match the bottom dimensions of my boxes. By using the wire and foil only, I could better stretch or compress the wires across the surface to be heated. 

Don


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## INCONCEIVABLE (Feb 19, 2008)

My lecar has had soil heating cables warming the batteries since before I owned it. I've had it about 4 years now, and have had to replace only one of the two cables. I'm very happy with the system.
The cables are woven through corrogated plastic sign board, about 1" or 2" spacing, and placed under the battery packs. A small 3 battery size pad up front under the hood and a large 7 battery size pad in the back seat area. They each have their own thermostat placed on top of the pack. I believe the soil cable came with an attached thermostat, that was removed and a small houshold ($10 from Lowe's) replacement thermostat is being used.
The car is plugged in all the time when I'm not using it. The three stage chargers keep the batteries on float, and the warmers keep the batteries between about 65-75 degrees. I actually haven't checked the temps lately, the batteries in my temp sensors are in need of replacement! Durring the warmer seasons I unplug the heating pads.
The batteries have 2 inch foam insulation around most sides and tops. Insulated like this they only loose about 10 degrees parked at work overnight (graveyard shift) when the temp is in the teens, which thankfully isn't very often 'caus I work outside!
Here is a link, but I noticed the pictures are not updated to show the current installation, so I hope my description was good. Sorry.
http://www.evalbum.com/1190

EDIT.....NOTE: Updated photos on evalbum!

Eric.


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## RKM (Jun 9, 2008)

Installed more insulation, heating pads and thermal switches this weekend. Huge job to remove the pack and reinstall!

I'd said I'd post pics of the switch. Its normally closed and opens at 60 F (55 -65 range). The Farnam 35W heaters are at the bottom of the box, four in this box. There is bubble foil insulation and a heat resistant foil fabric beneath the heaters.

Haven't had the heaters running yet, too warm in the shop. Tested them before installation though. Very thin, seem to work great. 

Test drove the car with a warmish (12C) pack, great performance. The cold pack (-5C to +5C) was very sluggish with huge voltage sag. 

Rob


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