Using LM334 and Thermistor and Maybe a Comparator to Create Battery Charger that Reduces Current When NiCd or NiMh Battery Hits Certain Temperature?

[brockrwood]

I ran across LM334 current source IC's (TO-92 package) on sale at Electronic Goldmine:

https://theelectronicgoldmine.com/products/g27186
It seemed to me that I ought to be able to use an LM334 and a thermistor to sense when a NiCd or NiMh battery hits a certain temperature that indicates "full charge" of the battery.

When that temperature is reached, couldn't the LM334 or maybe the LM334 and a comparator reduce the current to something tiny, like microamps, to "cut off" the charge?

I found a circuit idea at bristolwatch.com (Mr. Lewis Loflin's website) that had a circuit I thought might work:

https://www.bristolwatch.com/ccs/LM334_sensors.htm
If you have been reading my other posts in this forum, you know that I have been breadboarding a very simple constant current (low current) NiCd/NiMh battery charger using the LM317 and LM350 voltage regulators.

But even at low current, at the "full battery" point, I want the charge to stop.

Any circuit ideas are welcomed!

I want to use some secondhand NiCd 12V batteries and a secondhand 10.8V NiMh battery as the launch power source for LPR rocket launches.

I guess the circuit would need a “latch” feature or some sort of hysteresis when the temperature level is sensed.

Hmm. Maybe this circuit using thermistors and an LM311 comparator is better way to go. It is pretty complicated.

https://www.electronicsmaker.com/em...on/TEMPERATURE CONTROLLED BATTERY CHARGER.pdf
Once an analog circuit gets this complicated maybe it means I should learn how to use a microcontroller? I have been resisting.

- Brock

 

[OverTheTop]

You mention that your circuit will need a latch to switch to trickle charge when the temperature goes up. The circuit you linked to has all the functionality you need. It is also a good way to learn about comparators and also making flip-flops with gates. The current control for charging is the same as your earlier mentioned current source. There is also a resistor to set the trickle-charge rate. No coding needed. Don't underestimate using analog and basic logic for functionality. It can make for some very reliable hardware.

FYI, if I can do something without a microcontroller I usually do. I have a lot of experience with them so it isn't a technical hurdle that steers my designs .

LM334 is a blast from the past. I did a biofeedback thermometer and a few other things with them back around 1980 or so.

 

[neil_w]

I like the idea of using a little micro for something like this because it makes it easy to play with different behaviors. But of course if you can get it do basically do what you want without the micro then it saves the extra work of coding.

 

[David Schwantz]

Way easier

 

[brockrwood]

The last link from my post shows a comparator (LM311) controlling a 4011 IC wired as an RS flip flop.

I am new to this. I think I will scale back my expectations and just use an op amp or a comparator IC to sense when the “full” voltage is reached, and turn on a big, bright LED to get my attention.

 

[brockrwood]

After much head scratching I have finally figured out what the “open collector” output on the LM311 means and how to connect a “pull up” resistor to the output pin to make the output switch on.

So much to learn.

 

[brockrwood]

I wish the datasheet had included this diagram of the internal arrangement of the LM311. It would have prevented many hours of confusion.

 

[tsmith1315]

I have been resisting.

 

[brockrwood]

I know, I know. Get with the program. OK, I will find the Arduino starter kit and learn how to use it.

Another member of the forum likes these microcontollers. I will also order one of these.

https://picaxe.com/hardware/picaxe-chips/picaxe-08m2-microcontroller/

 

[tsmith1315]

I know, I know. Get with the program.

My eyebrow was raised for the pun!

 

[Grog6]

There's a lot more to charging a li-ion battery than that. If you want to avoid a fire, I would recommend one of these circuits:
https://www.ti.com/power-management/battery-management/charger-ics/products.htmlThere's several (needed) ways to terminate charge, the most important is the slope of the charging current, and voltage. Charging one badly will kill it quick, and one way to do that is a trickle charge. They aren't as lossy as lead batteries, and a trickle charge will overcharge it, leading to a nice hot lithium fire. I saw that done on a lab bench, with a power supply. Our boss was not amused.
The flashlight it was in made a cool rocket for a bit, tho. Standing on an aluminum rocket fueled by a lithium fire is way funnier than it sounds, as long as it's not you melting your shoe off.

If you use a micro, just be sure to implement all the rules. You'll need voltage, current, and temperature.

 

[cls]

I know, I know. Get with the program. OK, I will find the Arduino starter kit and learn how to use it.

Another member of the forum likes these microcontollers. I will also order one of these.

https://picaxe.com/hardware/picaxe-chips/picaxe-08m2-microcontroller/

Arduino is friendlier for newbies.

 

[sghioto]

There's a lot more to charging a li-ion battery than that.

Nothing was mentioned about charging li-ion batteries, this thread is about NiCd and NiMh batteries.

 

[Grog6]

Oh, The thermistor threw me. I don't usually watch those much, they're very forgiving. Trickle charging them for a long time will bring out the memor effect on the nicads, tho. Use a relay with the 311 to disconnect the charger when it's full, and implementing the high/low charge thing can be done by grounding a resistor on the ground pin of those regulators. Good luck with it!

 

[brockrwood]

I just used the LM311 to sense the voltage on the battery and turn on an LED to let me know it is time to take the battery off of the charger. Dispensed with the temperature sensing idea.

I was going to use a red LED as the “full charge” indicator but decided to use green instead.

Took me a while to figure out how the “open collector” output on the LM311 comparator works.





The red LED is just the indicator that charger circuit is powered on.