Advice for a 16x2 LCD heater - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: December 31, 2013, 02:34:45 pm
content: Hi all, I'm working on a device that use a classic, cheap 16x2 LCD screen. The device will be exposed sometimes a low temperatures (max -5 C) and since at that temp the crystals response is very slow, I need a solution to heat up the LCD screen.The only commercial solution I've found is a very thin and adhesive transparent film heater that runs at 12V, that must be applied on the rear part of the glass screen.Unfortunately those films doesn't come in 16x2 size (and cannot be cut due to their working principle) and even if I could use a bigger screen their cost is very high since they are not available as single items.I was thinking to glue 4X1W resistors to the metal chassis that holds the glass in place and drive them to generate heat, but I don't know if this a good solution (since the glass has a low thermal conduction, I fear that heating only the chassis is not enough).Do you have any advice about other ways to heat solve my issue? (except changing display technology)

author: Rerouter
author_rank: Super Contributor
timestamp: December 31, 2013, 02:38:06 pm
content: nicrome wire looped a few times around the back driven off a constant current source?

author: babysitter
author_rank: Frequent Contributor
timestamp: December 31, 2013, 02:46:19 pm
content: Place the heater resistor somewhere under the LCD, allow air gaps and let the raising warm air reach it.In the old times when germanys telco was still the state-owned "Deutsche Bundespost", the public phones had a heater resistor near the dial. The resistor was mounted in a kind of "chimney" which gave some advantage over well, no chimney.

author: mcinque
author_rank: Unknown
timestamp: December 31, 2013, 03:44:48 pm
content: Thank you for your advices! For both methods, I will need something to control how much heat it will be dissipated, that cuts off the resistors when the temperature rises over a threshold. Since I should use 2W power dissipation with 170mA I guess I can use a PTC to do it. What do you think?EDIT: I cannot use a PTC, the resistance rising curve is too far from the temperature I need! (around 18°C, while PTC start from 70°C)

author: dannyf
author_rank: Super Contributor
timestamp: December 31, 2013, 03:57:35 pm
content: A transistor (TO220 for example) controlled by a mcu or a temperature sensor would function like a heater. A TO220 can confortably dissipate 10w and more with TO247/3P.

author: holozip
author_rank: Unknown
timestamp: December 31, 2013, 04:15:28 pm
content: How about a 16x2 sized PCB with 35um traces arranged in a back and forth pattern? That way it'll be perfectly sized to mount on the back of your LCD display.3D printers use a similar concept for their heated print beds:http://reprap.org/wiki/PCB_HeatbedMaybe you could hack up something like one of these:http://www.dual-star.com/index2/Rider/heated_grip_kit1.htm

author: strangelovemd12
author_rank: Regular Contributor
timestamp: December 31, 2013, 04:20:23 pm
content: Is this battery powered? Assuming you don't need super high efficiencies (4W @ 33% average duty saves ~1kWh/yr) you might try looking for a solution that doesn't overheat at ambient temp, but serves to keep the screen warm enough to function satisfactorily at -5 then run it constantly.Is there anything inside that you can just overclock when it gets cold?Generally speaking more small resisters spread around will be more efficient. Also note that thermal transfer from a cylinder to a plane is terrible. Maybe square package ceramics? Probably less practical is making a small board almost solid with SMDs. I bet it'd coat up with thermal paste real nice. Might try that for one of those "keeps your coffee warm" electric coasters, actually.Edit: holozip came in with a more clever idea while I was typing. Guess I guessed the printer beds were Peltiers. Then you could put a fridge under it. God knows there's enough time for a drink or two while it's printing.

author: dannyf
author_rank: Super Contributor
timestamp: December 31, 2013, 04:27:33 pm
content: QuoteYou just need to put the temperature sensor next to the heater and use negative feedback. The heater would then only turn on if the ambient / heater is cold.Look for some OCXO design - Elektor has something like that awhile ago.

author: strangelovemd12
author_rank: Regular Contributor
timestamp: December 31, 2013, 04:43:07 pm
content: dannyf, that should work fine as long as everything is reasonably stable. As the heat flow gets more complicated and variable, you move towards having to err closer towards always on. My remark was more about looking for the simple solution.OP, what are the expected temp fluctuations inside the device due to the other circuitry? How much/constant of a current does it draw, or is the screen mounted away from the main circuitry?

author: Rufus
author_rank: Super Contributor
timestamp: December 31, 2013, 04:44:38 pm
content: For a similar problem the solution was an array SMT resistors and a temperature sensor on a custom flex circuit.

author: dannyf
author_rank: Super Contributor
timestamp: December 31, 2013, 05:03:24 pm
content: QuoteHere is an example of how it could be done.M1 is the heater (a mosfet in this case), and Q1 is the temperature sensor (=Vbe multiplier) mounted to the heater - it serves as a feedback mechanism.At 0C, the heater allows Ids of 0.7amp -> dissipating 3.5w. At Q1 heats up, its Vbe goes down, turning off the heater gradually: to eventually 0.3w @ 40c.Obviously, you will need to adjust the numbers (R2/R3) for your particular implementation but that's the gist of it.In the real thing, they use kapton cable for more even heating and a comparator for more precise cut-off. But the basic principle is the same.

author: mcinque
author_rank: Unknown
timestamp: December 31, 2013, 05:24:27 pm
content: strangelovemd12: Yes, it is battery powered, it runs between 12 and 9 volts and drains 150mAh at the maximum voltage. It must stay on for at least 24H (I can use maximum a 2.2Ah LiPo ).dannyf: thank you for your schematic! I was just simulating the attached scheme before reading your kindly post, it looks similar.When the PTC reach 25°C has 120R, and toghether with the 270R resistor it will turn off the FET.I'd like to shut off the current to the heater when the temperature rises over 25°C, so I think a PTC and a FET should work well.What do you think about it?

author: mcinque
author_rank: Unknown
timestamp: December 31, 2013, 05:44:23 pm
content: Quote from: strangelovemd12 on December 31, 2013, 04:20:23 pmYes, I would use 10x 10Ohm small resistors under the LCD.

author: ConKbot
author_rank: Super Contributor
timestamp: December 31, 2013, 05:50:26 pm
content: https://www.sparkfun.com/products/11987no need for a heater, operating range is -40 to +80C, dont know what characteristics may change, or how sunlight readable you need your LCD to be.

author: dannyf
author_rank: Super Contributor
timestamp: December 31, 2013, 06:00:43 pm
content: QuoteI wouldn't bet my life on product spec from sparkfun.

author: ConKbot
author_rank: Super Contributor
timestamp: December 31, 2013, 06:07:25 pm
content: Quote from: dannyf on December 31, 2013, 06:00:43 pmI wouldnt bet my life on a product spec from TI eitherQuoteEither way, its OLED instead of LCD, so its going to operate over a broader temperature range than LCD, but possibly at the expense of being able to read the display with sunlight directly on it.

author: mcinque
author_rank: Unknown
timestamp: December 31, 2013, 06:22:16 pm
content: Quote from: ConKbot on December 31, 2013, 05:50:26 pmThank you for the advice; well... the oled tecnology should be a lot less sensitive to cold with no liquid crystals that "freezes", but is much more expensive (and I should change my code because of new oled library).Unfortunately the "operating" range doesn't tell us about the display response: the datasheet ofthis LCDwich is the one I'm using, says "operating range -20 to +70C" but I've tested it with freeze spray and a thermocouple: at 0°C the display takes two seconds to refresh!!

author: ConKbot
author_rank: Super Contributor
timestamp: December 31, 2013, 09:41:24 pm
content: Mouser carries some OLED displays too, I dont know how much better their datasheet would be, but they are more expensive than the sparkfun unit. Depending on production quantities, it could be cheaper than rigging a heater. The company that makes the displays sold on will certainly be more willing to give advice on if it would work than or not than sparkfun though.Failing that, I'd check out thin kapton heaters (I'd use Omega in the US, dont know about international suppliers) and see if you can slip them behind the backlight diffuser for the LCD. If youre feeling daring, straighten out the tabs that hold the bezel on, take the LCD apart and put the heater (which you can get ahesive backed) on the back of the LCD diffuser) and reassemble the stack. It should work fine if they are using zebra-strips to connect the glass to the pcb.

author: sacherjj
author_rank: Frequent Contributor
timestamp: December 31, 2013, 10:00:35 pm
content: Have you looked into high temperature range liquid crystal? I know the display company we met with in China had some medical device LCDs that needed to respond in all temperature ranges. This may not be an option if your quantity is low.A quick search turned up a few, such ashttp://www.lumex.com/images/Lumex_ExtremeTempLCDs.pdfI think it makes more sense spending money on a display that works in the temp range, than to try to bend the temp range to the display.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: December 31, 2013, 10:17:17 pm
content: Some thoughts...- This thing consumes the best part of 2W. With an ambient temperature of -5C, it ain't gonna be -5C inside the case! If the upper ambient temperature spec allows, a sealed case will keep all of this heat inside nicely, especially if the case is non-metallic. If you can place the voltage regulators near the display, so much the better...- I would be highly untrusting of the freezer spray plus thermocouple experiment. You'll get a whole range of random temperatures, depending on the thermal mass of the items covered in frost, and the thermocouple will only be in vague contact with part of it. Put the thing in the freezer for a while, monitoring the temperature with a thermocouple thermally bonded to the glass.- If the LCD really doesn't work, given the above, then it's the wrong technology and heating the damn thing up is just crazy - every way you look at it!Sorry! Itmightbe reasonable if it's a custom LCD with annunciators or similar (like the German telephone), but here it's just text. Other than code (trivial excuse!), why is OLED out? It won't have an appreciable lag at low temperature - it's a diode!- Alternatively, VFD would work, and they are available in 16by2 compatible versions (meaning no code changes):http://www.noritake-itron.com/subpages/productse/vfmod7000.htm- e.g. GU112x16G-7806A - I've used these a lot, and they have no problems at low temperatures. They take more current than an LCD (without backlight) or O-LED, but no-doubt less that you're proposing to waste with a heater. And they can be switched off by software when not needed.- LCDs are commonly used in cars, and they work fine below freezing. Yes, they might be slightly "laggy" before the interior heater starts to work, but what's the big deal? After all, they are only telling you non-critical information like the time and radio station you are tuned to. Actually, why is the lag a problem in this application - you're not trying to scroll text or anything? Can a rethink of the UI contribute towards an acceptable compromise?- An old-school incandescent backlight might be a "nicer" solution, if you can work out the mechanics and optics.- What if your heater system goes wrong?https://www.eevblog.com/forum/microcontrollers/lcd-display-fault-any-ideas-what-would-cause-this/Good luck, whatever you go with!Mark

author: cellularmitosis
author_rank: Unknown
timestamp: December 31, 2013, 10:57:56 pm
content: mcinque, I have noticed at least two distinct backlight constructions for the common hd44780 boards which have become ubiquitous and cheap recently. One variant of these boards draws 20mA for the backlight, and another draws 200mA! If you can find a source for the latter, you might not need a heater at all.Unfortunately, I can't remember where I got the 200mA variant. It was either dealExtreme or ebay, but I recall that the display/backlight configuration was red on black.

author: Stonent
author_rank: Super Contributor
timestamp: January 01, 2014, 02:24:02 am
content: I was thinking if there's anywhere in your circuit that you're using a 7805 to drop 12 down to 5, mount that near the LCD to heat it up.

author: strangelovemd12
author_rank: Regular Contributor
timestamp: January 01, 2014, 06:24:50 am
content: Dannyf- that should work fine as long as everything is reasonably stable. I understand how could be implemented, my concern was mostly that a dynamic or conditional (dT thermocouple/dT of screen element) makes it less and less useful. If the environment is too variable, the case an unpredictable insulator, etc., it is basically just taking a stab in the dark. Such things could also make this system a huge PITA to tweak to the right values.Don't get me wrong, it is still a decent solution, and may be the simplest one that is practical in this situation.Ditto on the freeze spray tests not being the best method. I second a proper freezer test, though the result might be identical.I'll try resubmitting another suggestion in verse: OC below 0C; key to frost free LCD if you ask me.

author: mcinque
author_rank: Unknown
timestamp: January 01, 2014, 09:55:28 am
content: Quote from: Stonent on January 01, 2014, 02:24:02 amIt might be good, but since it must dissipate 1,5W I've put the heatsink out of the case, otherwise in summer I would have heat problems instead cold ones, since I can't use a jumper to disable it when the season is hot. Moreover putting the regulator under the LCD wouldn't allow me to control the heatingQuote from: sacherjj on December 31, 2013, 10:00:35 pmThat modules has 15-20W heaters to keep the glass warm. It's too muchQuote from: Mark Hennessy on December 31, 2013, 10:17:17 pmYes, I use a closed plastic enclosure, and I was thinking the same. But I must test the worst scenario.Quote from: Mark Hennessy on December 31, 2013, 10:17:17 pmmmm... you're right.Quote from: Mark Hennessy on December 31, 2013, 10:17:17 pmYou're right, unfortunately for me I forgot to consider this LITTLE issue at the start of the projectQuote from: Mark Hennessy on December 31, 2013, 10:17:17 pmYes, i'm scrolling text and fast response is needed. Unfortunately I cannot rethink the UI...Quote from: Mark Hennessy on December 31, 2013, 10:17:17 pmmmm, i must investigate about this solution.Quote from: Mark Hennessy on December 31, 2013, 10:17:17 pmOf course LCD will be cookedQuote from: Mark Hennessy on December 31, 2013, 10:17:17 pmThank you for your suggestions and thoughts!I will try the freezer method and if it fails, I will try the oled

author: DTJ
author_rank: Super Contributor
timestamp: January 01, 2014, 10:24:59 am
content: Two points:Have you looked at heaters made by "Minco"http://www.mod-tronic.com/Minco_Flexible_Heating_Elements.html?gclid=CKn2uarh3LsCFUshpQod2UgAgwAlso resistors are available in TO220 packages.

author: Frant
author_rank: Regular Contributor
timestamp: January 01, 2014, 01:44:18 pm
content: Instead of display heating, which is complicated and energy inefficient, I would recommend choosing an adequate LCD. For example, a German company Electronic Assembly (www.lcd-module.com) offers the EADOG series, specified for the temperature range from -20°C to +70°C. There are several sizes, formats and backlight options. Their current consumption is in hundreds of microamperes (without backlight).

author: mcinque
author_rank: Unknown
timestamp: January 01, 2014, 02:43:42 pm
content: Quote from: Frant on January 01, 2014, 01:44:18 pmThey only specify operating temperature, but is the same of sparkfun: -20 to +70. They don't specify the response time at -10.And using them I should correct my code because they haven't hardware contrast. However thanks you for sharing!Quote from: DTJ on January 01, 2014, 10:24:59 amI've requested a quote, thank you.Quote from: DTJ on January 01, 2014, 10:24:59 amYou're right! I could use a to220 format with a heatsink.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: January 01, 2014, 04:48:10 pm
content: These are the types of environments that VFD and OLED displays excel in. Being as they are emissive technologies, they do not typically have the same temperature dependence issues.Sent from my EVO using Tapatalk

author: calexanian
author_rank: Super Contributor
timestamp: January 01, 2014, 05:32:06 pm
content: I think your resistor idea is good. I would actually use 1/2 or 1/4 watt series string of lets say 20 resistors with a thermistor in the middle, and a op amp and a Darlington to drive the thing. a 1/4 watt or 1/2 watt resistor even at half its rating gets nice and toasty. Perfect for keeping a display warm. Clearly power drain is not much of a concern in this application. I would say a watt or two would be more than adequate provided the display is not in direct contact with sub zero temps. In that case i would recommend an additional lens over it for protection.

author: babysitter
author_rank: Frequent Contributor
timestamp: January 01, 2014, 07:10:13 pm
content: You might find stuff that tells you the temperature without using a dedicated thermistor or such, if your driving µC has a ADC you could even use of the heating resistors as thermistor. Switching on the heater for a fraction of a second once per hour will tell you the current through this one, giving insight about the resistance of the whole set. a heating resistor string you could switch off for a while and look at the temperature decrease rate to decide if you stop heating.Also, using a backlight LED for the LCD might be a viable temperature sensor, too.

author: calexanian
author_rank: Super Contributor
timestamp: January 01, 2014, 07:27:47 pm
content: Nevermind. I see it is battery powered. Just go with an oled display if you can afford it.

author: dannyf
author_rank: Super Contributor
timestamp: January 02, 2014, 02:12:35 am
content: Kapton heaters are fairly expensive, and may not be necessary in this case.I would pick a black-on-yellow lcd with backlight. Take out the backlight + associated defuser. In its place, put in some heater wires wrapped in heatshrink. You can reuse the contacts on the lcd for that. It will heat up the lcd screen from behind. The black on yellow is picked as they work well without backlight.

author: Andreas
author_rank: Super Contributor
timestamp: January 02, 2014, 04:13:10 am
content: Quote from: calexanian on January 01, 2014, 07:27:47 pmThe OLED will use 30 mA even when it´s not cold outside. A LCD consumes about 1-2 mA.The last 3 OLEDs that I used survived not longer than 1-2 years after first power on.Even when not used most of the time.With best regardsAndreas

author: mcinque
author_rank: Unknown
timestamp: January 02, 2014, 12:44:34 pm
content: mmm... since the device and lcd will be mounted on a panel inside a case like thisI was considering that maybe the best solution is to simply put a heater inside the case, since the heat will mostly remain inside.I could use two film resistors on the inner side of the alluminium panel like in the attachment.That resistors will heat the panel and so all the case, and the heat will be monitored by a one wire ds1820. Since the case will be mostly closed during power on, the heat will remain inside and the lcd should be warm and responsive when I open the case.What do you think about it? Any suggestions or comments?

author: mcinque
author_rank: Unknown
timestamp: January 02, 2014, 12:49:55 pm
content: I forgot: there is any math formula to calculate the power required to heat the alluminium frame?I guess I should keep in mind- external temperature- thermal leakage of the case- thickness andi size of the alluminium panel

author: dannyf
author_rank: Super Contributor
timestamp: January 02, 2014, 01:24:35 pm
content: Basically desired temperature rise (desired temp - ambient temp) and the device's thermal resistance (size, shape, etc.). Thermal mass comes into play in terms of how fast you can increase temperature, a concern if you are going to take the device through quick temperature transitions (from inside of a heated vehicle to frigid outdoors, for example).

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: January 02, 2014, 01:30:37 pm
content: This is all speculation and circular discussionsAs I said before, how do you know it's necessary with the heat being generated by the existing circuitry being trapped in that cosy warm box?Get the box, mount the LCD in there, and - assuming the rest of this isn't built yet - put your battery plus a resistor that dissipates the same heat as your completed circuit. Put it in the freezer, measure the temperature of the outside of the box, and measure LCD. If you can drive the LCD with your prototype as it exists, so much the better.You can't fix the problem until you've defined it. Right now, it's all just noise...If it is indeed a problem - which is quite possible given that someone apparently thought that scrolling text on an LCD would be a good idea - then O-LED or VFD is the answer. Or a wide-temp LCD. Don't be proud!I am amazed that so many people think that actively heating an LCD could be a good solution. And I'm astonished at the complexity that people are dreaming up for something that needs to be 100% reliable. Trust me, a good engineer needs to be able to step back and look at the bigger picture.Sorry if that sounds like a rant - I am trying to help, I promise

author: AndyC_772
author_rank: Super Contributor
timestamp: January 02, 2014, 01:36:17 pm
content: ^^^^^^^ This. Every word of it.

author: Frant
author_rank: Regular Contributor
timestamp: January 02, 2014, 01:40:38 pm
content: Quote from: mcinque on January 02, 2014, 12:44:34 pmDue to the mass, the enclosure volume and other thermal parameters of the solution you proposed, the heating will be slow and it will require a significant amount of energy. Water condensation inside the enclosure has to be considered. The whole thing will cost you more, and cause much more trouble than using a display designed for such conditions.A good, but expensive solution are intelligent LED alphanumeric display modules made by Avago and Osram (Digikey: Product Index > Optoelectronics > Display Modules - LED Dot Matrix and Cluster).

author: mcinque
author_rank: Unknown
timestamp: January 02, 2014, 08:05:57 pm
content: Quote from: Mark Hennessy on January 02, 2014, 01:30:37 pmBecause I've put the heatsink outside the case. This because with a warmer weather the heat being generated inside wouldn't dissipate anymore and the temp would rise dramatically, because I'm using a waterproof case, so no air leakage. And because of this I can't use a fan to cool the inside when it's hot, otherwise I would lose the waterproofing.Quote from: Mark Hennessy on January 02, 2014, 01:30:37 pmI'm not exactly scrolling text (I've said that only to give the idea), try to think it like a digital VU-Meter: something that require a good screen response.Quote from: Mark Hennessy on January 02, 2014, 01:30:37 pmI've a loooot to learn.I'm here to do it, hearing your opinions and sharing ideas. I'm ready to step back whenever is needed.I've no problem to use an OLED or a VFD, but this would raise the project costs, and since I should make a dozen of this, I was investigating a solution that would let me use the old, cheap lcd modules.Quote from: Mark Hennessy on January 02, 2014, 01:30:37 pmDon't worry, I appreciate your thoughts

author: dannyf
author_rank: Super Contributor
timestamp: January 02, 2014, 08:36:46 pm
content: QuoteMe too. Worse yet, there are even numerous commercial products that do precisely that - heat up LCD screens.Those people are nuts.

author: Bloch
author_rank: Unknown
timestamp: January 02, 2014, 08:43:41 pm
content: Quote from: dannyf on January 02, 2014, 08:36:46 pmYes wow to heat up a display to +10° Celsius are just nuts !!!Do you keep yous LCD in the fridge in the summer ?

author: ConKbot
author_rank: Super Contributor
timestamp: January 06, 2014, 04:43:38 am
content: Quote from: dannyf on January 02, 2014, 08:36:46 pmThere is a wide spectrum of answers for any problem that range from optimal, to death trap, just because a commercial solution exists, doesnt mean its optimal. There are a ton of variables that contribute to what is the best solution.Lets say you have a widget, which is powered by mains, has a user interface LCD, was normally used in temperate climates etc, and a customer wants 5 units that work outdoors in Alaska. By all means a heated LCD would be the best solution, no change to firmware, if you have margin on your power supply for the extra power, great, just a drop-in solution, you can charge them a nice chunk of NRE for custom work, and bam, done.But for this, since its a) currently still in design, b)battery powered c) a whole lot of vagueness on the application, quantity, required certifications, etc. Going for a heated LCD could be a easy swap in, with reduced battery life, or it could require a ton of work.Drawing a lot more power? Bigger batteries. Bigger batteries? Different charging circuit and/or BMS, and they might no fit in the current case. New case? Gotta get the mechanicals re-done, and you need to re-design a bunch of circuitry too.Also just because a heated, or a normal LCD and heaters is cheaper on the BOM than an OLED doesnt mean its cheaper in the end. If youre putting a kapton heater on the back of the backlight diffuser, then someone has to take apart the LCD, add the heater, etc. Or someone has to mount resistors in non-standard ways and do it all up. Maybe doable in house for a low-production run. Getting someone else to do it? Labor is going to add up quick.Even heating the whole product, with chassis mount resistors is manual labor, not as intensive as retrofitting a heater onto the LCD, but manually wiring something up is going to add cost.The person with all the details (thread starter) needs to step back, evaluate the needs, gather solutions, figure out the actual costs, pros, cons for each solution, and figure out what optimal is.That being said, on just about any battery powered test equipment that a single person can carry I'd expect a heater, just for the LCD to be a majority of the power consumed, and to not be the best solution, though there is always exceptions.

author: mcinque
author_rank: Unknown
timestamp: January 06, 2014, 11:51:31 am
content: Quote from: ConKbot on January 06, 2014, 04:43:38 amExactlyQuote from: ConKbot on January 06, 2014, 04:43:38 amI'm doing it.The real issue is that I realized only now that SOMETIMES this device MAY be exposed to cold climates and when done it SHOULD work acceptably, but unfortunately I've engineered this thing forgeting this "insignificant" possibility.Anyway, I want to say "thank you!" to everyone that has replied to this post sharing his ideas and thoughts: I appreciate it.

author: ConKbot
author_rank: Super Contributor
timestamp: January 06, 2014, 02:43:40 pm
content: Quote from: mcinque on January 06, 2014, 11:51:31 amWasnt directed at you, just at the people making declarations of the 'best' choice without knowing/considering all the details. Even something such a lead time and availability can make a decision as to what is used. Ive just recently wrapped up a project which needed to run in very low temperatures. Low temperature li-poly cells were a good choice, but their lead time was long, and if they came in, and werent low-temperature enough, there wouldnt be enough time to re-work a solution. We ended up designing for heaters and extra heater batteries to hedge our risk of not completing the project in time. But the low-temp lipo cells arrived in time, and performed as we needed. So in the end the widget came out lighter, with a longer run time, and cheaper. O0