[TCADMAN]

One possibility would be to put the batteries in an insulated box and run a 12 volt bulb directly off the batteries. A bulb such as used for a tail light bulb, which would be around 10 - 15 watts, seems appropriate. You would need to recharge the batteries periodically. The time between re-charges would depend upon the size of your battery bank.

I remember my father doing that with a 100 watt light bulb back in the 60’s. I grew up a mile or two from Lake Erie. It went down below zero several times a year there. He would run an extension cord under the hood and plug in a trouble light fixture with the 100w bulb. Close the hood and leave it on all night. I do remember him bringing the battery in the house a few times. We heated our camping trailer the same way. He made a light box with venting but no light escaped. It had 100w bulb in it.

 

[kenryan]

I remember my father doing that with a 100 watt light bulb back in the 60’s. I grew up a mile or two from Lake Erie. It went down below zero several times a year there. He would run an extension cord under the hood and plug in a trouble light fixture with the 100w bulb. Close the hood and leave it on all night. I do remember him bringing the battery in the house a few times. We heated our camping trailer the same way. He made a light box with venting but no light escaped. It had 100w bulb in it.

I think in a small insulated box, a much smaller bulb would do the trick.

 

[Checkswrecks]

I remember my father doing that with a 100 watt light bulb back in the 60’s. I grew up a mile or two from Lake Erie. It went down below zero several times a year there. He would run an extension cord under the hood and plug in a trouble light fixture with the 100w bulb. Close the hood and leave it on all night.

Grew up east of Cleveland and my Dad did that trick too.

Heaters like these work but realize that in testing, we use them to intentionally ignite cells and batteries.* Do NOT place them directly on the side/bottom/top of the cells!!! You want to distribute the heat evenly as possible in a box.

If you do put one directly on a cell and are using a temp controller, you are still massively shortening the life of the cell because heating the windings or layers will be so uneven. Electricity will always take the path of least resistance, which is where the wear will be, because the warmer area will be the easiest path.

(* While LiFePo4 generally is the safest of the lithiums, once it puts out a bunch of smoke the smell is almost impossible to get out of any cushions, fabrics, or nearby wood.)

 

[IsleofMan]

One possibility would be to put the batteries in an insulated box and run a 12 volt bulb directly off the batteries. A bulb such as used for a tail light bulb, which would be around 10 - 15 watts, seems appropriate. You would need to recharge the batteries periodically. The time between re-charges would depend upon the size of your battery bank.

A short length of fairy/christmas lights? I have an 18" string of lights in a cooler that holds the plugs and bricks for a an outside lighting system. The transformers need to be above freezing. Since adding the insulated cooler and the string lights, the system has never had an issue with the cold.

 

[GaryBIS]

Hi,
I bought a cheap Zooms LiFePo4 battery about a year ago mostly just to have one to experiment on.
I've done some cold weather related tests (I live in Montana) and I'll pass them along as they might be of some use for people working on solutions to the cold weather problem.

The first test deals with taking the Zooms battery from an inside environment and placing it outside overnight to see how fast it chills, and then taking it back inside and seeing how quickly it warms up just sitting in warm inside air.

The red line is a temp sensor taped to one of the Li cells.
The green line is the ambient air temp (outside for first part of test, and inside for the warmp part)
The blue line is a temp sensor taped to the outside of the battery case on the plastic.

No current was being taken out of the battery during this test.

The battery goes outside at 6pm with about 40F outside temp.

The battery temp pretty much follows the outside temp down through the night until 8 am the next morning and about 24F.
I take the battery inside then and watch how fast the battery temp comes back up to room temp.
It takes about 2 hours to get it up to 40F.
This means the outer surface of the cell is at 40F, but I did not have any way to get a sensor on the inside of the cell, or even between two cells as the cells were glued together.

Bottom line is that for this battery, the battery heated up at about 8F per hour.
If you were starting with (say) a battery at 0F, the warmup rate would be a bit faster, but it could take a long time to heat a battery soaked at 0F up to 32F just sitting in room temp air.

The Zooms battery has a lot of padding between the case and the cells, and this tends to insulate the cells from the warm air.
Note also that the case temp comes back up to room temp very quickly (not surprising), so a temp sensor just taped to the plastic case of the battery is not much good. It will lead you to think the battery has heated up, when if fact the actual cells are still cold.

For us, this cold soaked battery comes up as a practical matter as the van sits out in the driveway between trips in the winter, and it can easily be down toward 0F. If we decide in the morning we want to go on a trip that day, how to get the battery back up to temp in time?

Here are some pics of the Zooms battery taken apart and the test setup:

Zooms battery sitting on the front porch with the tempreature logger in a Ziploc bag

Cutting access hole into the Zooms battery case to get access to the cells to mount a
temp sensor. I later gave up on small access holes and took the whole top off
so I could pull the cells out.

The cells removed from the case.
The temp sensor that logged the battery temp was taped direcly to one of the cells.
Note the heavy padding between the cells and the case - not sure why they use so much,
but it is certainly going to act as insulation.

The battery taped back together with the sensors in place.

I have a couple other tests - self heating with current flow, heating with DIY heating pads, and temperature in battery compartment vs van temp.
I'll try to get them up tomorrow if there is interest?

Gary

 

[kenryan]

A short length of fairy/christmas lights? I have an 18" string of lights in a cooler that holds the plugs and bricks for a an outside lighting system. The transformers need to be above freezing. Since adding the insulated cooler and the string lights, the system has never had an issue with the cold.

Depends on the wattage. Heat will be directly related to wattage. If it's a 18 inch string of micro leds that might only be a watt or two. The other variables are how big is the box, how well is it insulated, and how cold will it get?

 

[javazoe]

I have the SOK 206aH with the built in heater and can say it works well. The BMS is relatively straightforward and Bluetooth. Lithium is the way to go if you can spare the extra $'s. The SOK 206 is also fairly compact they have a bit more of a cube dimension than say a 27 or 31. The lighter weight is also great, make hauling out much easier than traditional lead acid.

 

[T town]

Hi,
I bought a cheap Zooms LiFePo4 battery about a year ago mostly just to have one to experiment on.
I've done some cold weather related tests (I live in Montana) and I'll pass them along as they might be of some use for people working on solutions to the cold weather problem.

The first test deals with taking the Zooms battery from an inside environment and placing it outside overnight to see how fast it chills, and then taking it back inside and seeing how quickly it warms up just sitting in warm inside air.

View attachment 179846
The red line is a temp sensor taped to one of the Li cells.
The green line is the ambient air temp (outside for first part of test, and inside for the warmp part)
The blue line is a temp sensor taped to the outside of the battery case on the plastic.

No current was being taken out of the battery during this test.

The battery goes outside at 6pm with about 40F outside temp.

The battery temp pretty much follows the outside temp down through the night until 8 am the next morning and about 24F.
I take the battery inside then and watch how fast the battery temp comes back up to room temp.
It takes about 2 hours to get it up to 40F.
This means the outer surface of the cell is at 40F, but I did not have any way to get a sensor on the inside of the cell, or even between two cells as the cells were glued together.

Bottom line is that for this battery, the battery heated up at about 8F per hour.
If you were starting with (say) a battery at 0F, the warmup rate would be a bit faster, but it could take a long time to heat a battery soaked at 0F up to 32F just sitting in room temp air.

The Zooms battery has a lot of padding between the case and the cells, and this tends to insulate the cells from the warm air.
Note also that the case temp comes back up to room temp very quickly (not surprising), so a temp sensor just taped to the plastic case of the battery is not much good. It will lead you to think the battery has heated up, when if fact the actual cells are still cold.

For us, this cold soaked battery comes up as a practical matter as the van sits out in the driveway between trips in the winter, and it can easily be down toward 0F. If we decide in the morning we want to go on a trip that day, how to get the battery back up to temp in time?

Here are some pics of the Zooms battery taken apart and the test setup:




View attachment 179847
Zooms battery sitting on the front porch with the tempreature logger in a Ziploc bag


View attachment 179848
Cutting access hole into the Zooms battery case to get access to the cells to mount a
temp sensor. I later gave up on small access holes and took the whole top off
so I could pull the cells out.

View attachment 179849
The cells removed from the case.
The temp sensor that logged the battery temp was taped direcly to one of the cells.
Note the heavy padding between the cells and the case - not sure why they use so much,
but it is certainly going to act as insulation.

View attachment 179850
The battery taped back together with the sensors in place.

I have a couple other tests - self heating with current flow, heating with DIY heating pads, and temperature in battery compartment vs van temp.
I'll try to get them up tomorrow if there is interest?

Gary

Oh yeah, I’m interested.

 

[GaryBIS]

Hi,
Here is another test on the Zooms LiFePo4 battery.

This one looks at how fast the battery warms up when you put a load on it. Idea is that if the battery is below 32F, its not safe to charge it, but you can take a load out of it. Since the battery has internal resistance (albeit low) the battery will warm up as heat is dissipated over this internal resistance.

Bottom line is that with a load of about 12 amps, the Zooms 12 volt 100 amp-hr battery cell temperature goes up at a rate of about 2F per hour. This is pretty slow and uses quite a bit of juice. If the battery was at (say) 20F, and you wanted to bring it up to 40F for safe charging, it would take about 10 hours and use about 120 amp-hrs, which is more than the battery total capacity. It seems the internal resistance of LFP batteries is just to low to efficiently generate enough heat to be a good way to warm the battery - at least for this LFP battery.

Details:
I left the same temperature sensors on as for the last test, one to sense cell temp, another to sense battery case temp, and a third to sense air temp.

To provide the about 12 amp load on the battery, I used a coil of lamp cord that had about the 1 ohm resistance for 12 amp current flow.

The brown coil of wire on the left is the load - current is about 12 amps.
The clamp meter measures the current.
The battery is insulated from the bench with an inch of Polyiso.

The logger records the cell temperature, case temperature, and air temperature.
I also measured the temperature of coil of wire acting as the load.

It became immediately apparent that the coil of wire that was acting as the load was generating far more heat than the internal resistance in the battery. The coil got all the way up to 190F!.
Had I wrapped the coil of wire around the battery, I'm sure the battery cell temp would have gone up much faster!


Here is the data for the half hour test:

Time	Ibat (amps)	Vbat (volts)	Tbat (F)	Tcase (F)	Tamb (F)	Tcoil (F)
4:00 PM	13.6		55.86	57.8	58.1
4:04 PM	12.96		55.94	58	58.4
4:10 PM	12.13	12.9	56.1	57.5	58.7	165
4:15 PM	11.9	12.88	56.5	56.9	59.3	170
4:20 PM	11.74	12.86	56.5	56.5	59.3	180
4:25 PM	11.63	12.84	56.8	56.4	59.4	185
4:30 PM	11.54	12.82	56.94	56.5	58.8	190

I stopped at half an hour with only a 1F cell temperature rise.
The rise in cell temp with time is very linear.
Note how hot the coil of wire acting as the load gets.

So, heating with internal resistance does not seem practical? Anyone see a better way to use internal resistance to heat?

The next test is experimenting around with a DIY silicone heater pad taped to the cells.

Gary

 

[JackHubbs]

My concern is the solar panels charging the batteries in low winter temps when the van is setting parked.

Simple fix is to trip your solar disconnect switch to ensure it does not try to charge when left idle.

 

[GaryBIS]

Hi,
Here is another test on cold weather charging protection for my poor abused Zooms battery...

This one looks at placing two 25 watt, 12 volt heater pads taped to the bottom of battery plastic case.
The two silicone pad 25 watt each heaters are siliconced to the grey alum sheet metal pieces which are then taped to the battery plastic case bottom. The bottom of case temperature sensor can be seen between the alum plates - its in direct contact with the plastic case and not in contact with the alum ( but close).

The top of battery temperature sensor is duct taped to the top middle of the plastic case.
The battery terminal temperature sensor is clamped under the positive terminal bolt - clamped pretty tight.
The pairs of red pairs of red wires coming up from the heaters are later attached to the battery terminals.
The thinking on the temp sensor on the battery terminal is that it might get a better thermal coupling the Li cells than the sensor mounted on top of the plastic battery case and still does not require opening the battery case to get to the actual cells.

The battery was encased by 1 inch polyiso.
A polyiso lid with a weight on it was added for the test.

There are a total of 6 temperature sensors:

• Taped to the top of the plastic battery case
• Taped to the bottom of the plastic battery case between the two pieces of alum
• Taped to the bottom of the actual cells
• Taped to the top of the actual cells
• Clamped into the Positive terminal of the battery
• An ambient air temp sensor in the air about a foot above the battery

This first plot is for the case with the two 25 watt heaters hooked up in parallel (50 watts).

The top red line is the sensor taped to bottom of case between the two heater pads (but not touching the heating pads)

The purple dash line sensor is taped to the bottom of one of the actual Li cells

The purple dash-dot line sensor is taped to the top of one of the actual Li cells

The solid aqua line sensor is clamped under the positive battery terminal (the wire from the positive terminal attaches to the Li cells directly, while the neg terminal wire goes through the BMS)

The plot may be hard to read - I copy to the Windows clipboard and then paste it into a picture edit program so I can blow it up.

Clearly looking at how fast the bottom of the case gets up to 240F, 50 watts coupled to the battery case in this way is too much. The bottom of case temp was actually hotter in that the sensor was not directly above the heater pad. The plastic where the heater pad was placed showed some distortion, but appeared to survive pretty well.
I had meant to watch the temps and cut off the heating if it got to warm, but got distracted and came back to a case that was very hot and smelling.

Maybe worth noting that the bottom of cells temperature went from about 55F up to 125F over the 40 minutes - probably not good for the cells. Meanwhile, the top of cells temperature sensor went up less than 10F. So, heat does not rapidly move into the cells and equalize across the cells.

-------------
This plot is for the case of the two 25 watt heaters hooked in series. The amperage through the heaters was 1.1 amps, so total wattage for both heaters is about 14 watts (1.1 amps * 13 volts) - so, only about 1/4 of the wattage for the other test.

This 14 watt setup might be fairly close to being OK.
It takes 2 hours (4pm to 6pm) to get the average cells temp up 16F.
There is still a fair bit of difference in temp between top and bottom of cells - at end of test top cells is 74F, bottom 103F, for a difference of 29F. Not sure how good this non-uniform temperature is for the cells?
It does not take very long after the heater is turned off for all the temps to come together - so, maybe a half hour waiting period after the heater is turned off would be good before charging?

It would be a pain to damage the battery with uneven heating while trying to protect it from damage due to charging below freezing

One of the new LFP batteries with a heater built in wraps the heater around the sides of the battery - this might be a way to get more uniform heating. The new SOK heated battery puts the heaters between the cells, which seems like a good plan to me.

It appears that any way you slice it, warming up cold batteries before charging is not going to be a 10 minute thing.

The sensor clamped in the + battery terminal follows the top of cells temperature pretty well - so, this is good. With the heater on the bottom as for this test, it will underestimate the average temperature of the cells in that the top of the cells is their coolest part.

I think some kind of a temperature controller that would cycle the heater to prevent overheating the cells locally and could also be used to turn the heater off altogether when the cells get up to temp would be a very good thing?

Its clear that there is a lot of potential for damaging the battery if a lot of care is not taken in the design of the system.

On observation is that if the battery is in an insulated container, it would not take a lot of juice to just keep the batteries warm as the outside temperature goes down below freezing. The 2nd test used just over 1 amp-hr per hour and it heated the batteries up at about 8F per hour - so, (maybe) less than half and amp-hr per hour would keep the batteries from getting cold?

Just to follow up on the keep the battery warm rather than heat up a cold battery idea...
A 1 inch thick polyiso enclosure for 2 SOK size LFP batteries is about 7 sqft and would have an R value of about 6.
So, the heat loss per degree F of temp difference between inside and outside the battery compartment is (7 sqft)(1F)/(R6) = 1.2 BTU/hr-F or 0.35 watt-hr per hour, which is 0.03 amp-hrs per hour per degree F.

So, to (say) keep your battery at 35F when the temp around it is 0F would take (0.03amp-hr/hour-F) * (35F - 0F) = 1.1 amp-hrs per hour.

So, you could let the van go cold in 0F weather, and the battery could keep itself warm for 26 amp-hrs over a full 24 hour day.
Or, half that if the outside temp was 20F.
Not so bad?
The caution would be that you would have to be careful that the battery did not overheat in its insulated container. But, the LFP batteries have such low internal resistance to generate heat that it might not be a problem?

Any thoughts on this? Better ways to do it?

I have two of the SOK 100 amp-hr batteries in my van and so far have not taken any steps to provide a heater. But, we do enough cold weather camping that we will have to do something eventually. SOK has since come out with a heated version of my battery that also has a Bluetooth BMS for $590 (only $20 more than I paid for the unheated one). I would definitely have gone that way if they had been available.

If you like camper van tests, there are a few more on my site you might like... These are on various topics.
Feedback is very welcome!

Gary

 

[Checkswrecks]

GaryBIS -

You captured the heart of things with this statement: "It appears that any way you slice it, warming up cold batteries before charging is not going to be a 10 minute thing."

Followed by the testing and resulting observation that simply keep the battery in an insulated box and slightly above freezing doesn't take that much energy, especially since most conversions have banks with a minimum of 200 Ah.

Bravo!

As for your question about whether a temp differential across a cell is significant, the answer is that it ABSOLUTELY is. When we were dissecting cells during the 787 investigation*, the difference could be seen in the coatings across the windings, especially when looking with a microscope at the PE layers. You do want the cells to have the most uniform temp possible.

* I was the original launch investigator in 2013 and we went through $3.6 million in cells and batteries doing a wide range of temp and performance tests. These were largely done at UL labs and in Japan.

 

[GaryBIS]

GaryBIS -

You captured the heart of things with this statement: "It appears that any way you slice it, warming up cold batteries before charging is not going to be a 10 minute thing."

Followed by the testing and resulting observation that simply keep the battery in an insulated box and slightly above freezing doesn't take that much energy, especially since most conversions have banks with a minimum of 200 Ah.

Bravo!

As for your question about whether a temp differential across a cell is significant, the answer is that it ABSOLUTELY is. When we were dissecting cells during the 787 investigation*, the difference could be seen in the coatings across the windings, especially when looking with a microscope at the PE layers. You do want the cells to have the most uniform temp possible.

* I was the original launch investigator in 2013 and we went through $3.6 million in cells and batteries doing a wide range of temp and performance tests. These were largely done at UL labs and in Japan.

Hi,
Good to know about the importance of cell temperature uniformity.

Also good to hear about the 787. I was an engineer at Boeing in the Seattle area for 35 years - retired in 2000. Never got a chance to work on the 787 as the design work on it was just starting when I was leaving. Great airplane to fly in (with the updated battery system

Gary

 

[gregoryx]

@GaryBIS, thank you for this great research and documentation. Sooo much better than a bunch of internet guesswork! 🤘

 

[GaryBIS]

@GaryBIS, thank you for this great research and documentation. Sooo much better than a bunch of internet guesswork! 🤘

Thanks - I do love doing testing!

Gary

 

[njvagabond]

Thanks - I do love doing testing!

Gary

(FWIW - I R 1 2)

 

[Dman]

We have three 100ah Battleborn LiFePo batteries in our van. We live in coastal California where low temps are not common but have snow-camped for several days with lows around 10-12°F and highs maybe 28-30 but sunshine some days. Batteries are “inside” the van but not insulated nor heated. Zero issues with usage, but definitely some mornings where they wouldn’t charge due to low temp shutoff even when we had solar or alternator charging.

 

[NeilHunt]

You don’t say how you plan to heat the van for humans when it’s 0F? I have to imagine diesel, gasoline, or propane. Then I’m wondering whether you wouldn’t just leave the thermostat set to 30 for those nights you stay in a hotel with the van parked outside. For longer term storage, obviously you could just let the batteries chill, and avoid charging until they are warmed up (turn off the solar). Or add a heat pad plugged into shore power only.

 

[Wyocalm]

OP non-engineer, here. Thanks for all the input.
Seems like this can be managed fairly easily -- i didn't know that before.
For winter on the driveway, just shut the lithium electric system down -- can use van as non-camper as desired.
If we want to use it as a camper in winter, we can pre-heat by running the Timberline heater with shore power (didn't realize this was an option) -- this should also work (running the Timberline off the gasoline) for the possible night in a motel. Around here, many motels have plug-ins for engine block heaters -- could even use that to run the heat at night.
Thinking about how a heated battery works -- once it's up to temp, presumably the battery heats itself (so to speak) before the temp gets low enough to reject charging, keeping itself at a functional temperature.
Let me know if I am way off.

 

[brío]

Sounds about right.
The only real fly in the ointment is the absolute minimum storage temperature, which is almost always well below zero F. But, unless you live in a very mild location, you do need a plan for that eventuality.