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I have designed a circuit that uses this low-battery-indicator: http://www.homemade-circuits.com/2013/05/low-battery-indicator-circuit-using-two.html

I use 4xAA Lithium batteries to drive an Arduino Pro Mini, some LEDs, a buzzer and a solenoid. The circuit diagram below shows the complete circuit. My complete Circuit

The circuit will be used in a buzz wire game that is placed outside. When the player completes the game the solenoid is activated to reveal some treats behind a trap door.

The solenoid is activated in three short 80ms bursts to make sure that the trap door mechanism is released. It fails to release one time of twenty but that is probably a mechanical issue.

The game is turned off while not in use and is activated by a switch when a lid is opened.

The game might be visited approx 5 times each week. Initially more frequently.

The target operating temperature range is from approx. +25°C in summer down to approx. -25°C in winter

Parts list:

  • 4 PCS of 2V 15 mA standard indicator LEDs
  • 1000uF 10V electrolytic capacitor
  • Arduino Pro Mini Processor
  • 1N4007 fallback diodes
  • 1% 1/4W metal film resistors of various values (see schematics)
  • 3V 15mA buzzer, operating voltage 2-5V
  • HK 19F 5 V relay, 125 Ohm coil resistance
  • JF-0530B 6V 300mA solenoid

Some current measurements:

  • Arduino and one LED: 36 mA
  • Arduino and two LEDs: 53 mA
  • Arduino, one LED and the buzzer: 56 mA
  • Arduino, two LEDs, the relay and the solenoid: 1.57 A

I set the low battery threshold indoors so that the low-battery-LED lights up at around 5.8 V.
The initial battery voltage reading with the circuit off is 6.5 V. With a 53mA load the voltage stabilizes at 6.1 V indoors.

But when I place the circuit outdoors for a while in approx 0°C the low-battery LED turns on even if the rest of the circuit works as intended. I measured the voltage outside and it reads 5.8V

When I take the circuit indoors again with the exact same batteries the low-power LED turns off and the Voltage level is back to 6.1 V

Is this a normal behavior? The circuit is meant to operate at -20°C. Will the voltage level be even lower at that temperature? Is there a way to prevent this from happening?

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  • \$\begingroup\$ Looks like you're using a base-emitter junction as the reference for your circuit. That's not going to be very stable with temperature. Consider using a voltage supervisor or reference. \$\endgroup\$ – John D Oct 31 '16 at 0:28
  • \$\begingroup\$ @JohnD I am a beginner at electronics so I do not understand what you are saying. Can you please elaborate? \$\endgroup\$ – MrDark Oct 31 '16 at 0:34
  • \$\begingroup\$ Do you mean that the complete circuit or just the low-battery indicator circuit will not be stable with temperature? \$\endgroup\$ – MrDark Oct 31 '16 at 0:41
  • \$\begingroup\$ @JohnD, what you are saying does not match what the OP is reporting. He is reporting that the ACTUAL MEASURED battery voltage is dropping to 5.8 outside. It is expected and desired that the low-battery light would come on at that Voltage. Of course there will be a tempco for a circuit that relies on Vbe. But that does not seem to be the problem right now. \$\endgroup\$ – mkeith Oct 31 '16 at 1:10
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    \$\begingroup\$ Based on a quick internet search, it is definitely expected that Lithium batteries will show lower discharge voltage at reduced temperatures. The effect will be even larger at -20C. Wrapping the battery with a thermal insulator may help (because it will self-heat a little during discharge). Just make sure it does not overheat when it is not cold outside. You could also modify your low-voltage warning to compensate for voltage droop at low temperature. \$\endgroup\$ – mkeith Oct 31 '16 at 1:17
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Batteries work on chemical reactions. Chemical reactions slow down at lower temperatures. This slow down shows up are a reduction of capability. I've been looking into this because the nimh batter pack I use to ride my bike to work is dying. Most bike lights now are Li-on. Since I ride in the winter this is an issue for me. There doesn't seem to be an exact agreed upon reduction, but it seems like the consensus is -10% at 0C and -20% at -20C. If you do a search you will find graphs that show the change in voltage, resistance, and capacity as a function of temperature and discharge rate. The problem is the graphs very from site to site.

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  • \$\begingroup\$ The most important effect of low temperatures on the battery is in the internal resistance, so the amount if voltage drop depends in the load. I bet that your bike light NiMH pack has at least one cell that already has too high resistance due to age, so adding age and low temperature makes the resistance too high and causes the voltage to drop too low. The OP is using a badly chosen threshold for low voltage detection anyway. On AA cells, it should be between 0.9 and 1.2 volts per cell. I would suggest a voltage at the high end for Li cells, so 4.5 instead of 5.8. \$\endgroup\$ – Michael Karcher Oct 31 '16 at 13:15
  • \$\begingroup\$ @MichaelKarcher, 4.5 V is too low for the solenoid to work. I tested it out and it stops working satisfactory at approx 5.4 V. I now have set the threshold at approx 5.6 V instead. \$\endgroup\$ – MrDark Oct 31 '16 at 20:04
  • \$\begingroup\$ If the other pieces of your circuit can handle 7.8 volts, you should consider adding a fifth cell to make use of the full capacity of your cells. Check the datasheet for typical discharge curves. If you are lucky, they include a low temperature curve, too. \$\endgroup\$ – Michael Karcher Oct 31 '16 at 21:23
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  • Every conductor has a Tempco or temperature coefficient, although NiCr wire is 10x lower than copper.

  • Every semiconductor has a temperature coefficient too and Bipolars have a NTC while some MOSFET"s have a PTC which makes them easier to gang in parallel for current sharing.

  • Diodes are used as disposable thermometers for this reason of -x mV'/C.

  • SLA batteries need a thermal compensated voltage reference for charging
  • Some chemistries like Lead Acid and some LiPo's drop capacity in cold temp and rise in ESR as well as some voltage changes.
  • every battery has a model of a chemical cell voltage, a very large capacitance, a small series resistance and some parallel leakage resistance, all dependent on individual chemistry characteristics
    • ESR (series R) is always inverse to Ah capacity and State of Charge (SoC) which is also temperature sensitive as batteries have more capacity at higher temps but also age at accelerated rates and risk secondary damage effects.
    • thus loaded voltage also drops more at lower temps due to a rise in ESR and reduced capacity

Basically everything has a thermal property, which you can look up in your reference sites on web

  • welcome to science
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  • \$\begingroup\$ Thermistors and Tempco resistors were made for this. \$\endgroup\$ – usajnf Oct 31 '16 at 2:33
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    \$\begingroup\$ also NTC ceramic caps moreso than PTC ceramic caps and NP0 is not NP Oh but NP zero as in closest match to zero tempco vs P100 (ppm/'C) or N1500 (ppm/'C) \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 31 '16 at 2:41
  • \$\begingroup\$ I long ago learned that almost everything is a thermometer. \$\endgroup\$ – mkeith Oct 31 '16 at 3:31
  • \$\begingroup\$ the secret in design is to manage thermal sensitivities and use compensation with diodes or passive parts or active thermal voltage compensation and determine your operating temperature range in specs up front.. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 31 '16 at 3:37
  • \$\begingroup\$ @Tony, Thanks for that overwhelming answer. It was a bit too much high level information for me to digest though. :-) Maybe in ten years I will revisit your answer and nod in unity... "Welcome to science" - no shit, Sherlock! ;-) \$\endgroup\$ – MrDark Oct 31 '16 at 20:14
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Lithium cells are badly affected by sub zero temperatures under some operating conditions - you should consult the data sheets to see what you can expect from the batteries and how they should be treated at very low temperatures.See references below.

I have read in numerous places that Lithium batteries are the best kind of battery for use in cold temperature. If there is any other kind of battery that out-performs them, please tell me.

A major problem is we do not know fully what you 'problem' is - or applicaton. You've described the hardware, which may be all the hardware but that's potentially not as it sounds. eg are "a few LEDs" indicator LEDs or 1 10 100 Watt lighting LEDs? ie what is the base, operating and peak current drawn and what is the mix of uses. What temperature and environmental conditions must the system operate in - eg is this a letterbox in a snow bank in Alaska, or a caving light or an occasional subzero use or ... . You say " operate AT -20C", is that AT, or down to and sometimes or usually or ...
AND the current affects the answer once the above is answered.

Here is a very good "Energizer L91 Ultimate Lithium AA cell product sheet](data.energizer.com/PDFs/l91.pdf). Presumably that's what you are using? Do I presume correctly? Not all brands are created equal - if you are using another brand or model of cell please advise, and the relevant data sheets must be consulted.
The graph at the bottom right of page 1 shows that for the L91 the mAh capacity is almost unaffected by temperature down to -40C. That's rather magical. At 250 mA you are down to under 50% capacity at -40C and at 1000 mA the battery is not a a battery. The graph to its left show how voltage and load relate and you can infer (possibly incorrectly) what may happen at lower temperatures.

A good 1st step is to tell us what you are trying to do. Application, load profile, temperature profile and why, ... .

It's possible that the voltage drop you are seeing is circuit or battery related. It is easy for you to determine which it is and about impossible for us given what you have (and haven't) told us.
That said - of your load is under 100 mA then it seems more liable to be your circuit than the batteries that cause the voltage drop.

If the solenoid does not work <~= 5.6V you have the wrong battery pack or the wrong solenoid. A good design MUST have more "headroom" than that.
SO more data please, as above. –


References:

Superb Cylindrical Primary Lithium Handbook and Application Manual - Energizer 21 page pdf. Much data on low temperature use. Note they rate the battery to -60C at lower discharge rates.

Eveready L91 application manual - similar to but differs from the above. Very useful 24 page pdf.

Lygte {whoever} review - useful

Batteryshowdown comparisons - many types L91 does very well on most energy metrics.


VARTA Primary Lithium Cells Lithium Manganese Dioxide LiMnO2 Sales Program and Technical Handbook - 50 page PDF - looks excellent.

VARTA AA 6106 cell very basic data sheet.

Battery comparison - as above. Varta & Energizer cells are comparable on energy and power metrics.


Related

Equivalents - various types

Other battery type comparisons

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  • \$\begingroup\$ Thank you very much for your informative answer! I have now updated the question with some more information. I was using Varta Professional Lithium AA series but I cannot find any specs online for them. I will switch too Energizer L91 instead! They seem outstanding! \$\endgroup\$ – MrDark Nov 1 '16 at 20:13
  • \$\begingroup\$ The more I think about it the main problem might be the solenoid's current draw and rated voltage. It should not be 1.57 A. It is rated 300mA at 6V by the seller on ebay \$\endgroup\$ – MrDark Nov 1 '16 at 20:20

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