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I recently got an electronic engineer to make a design of a circuit for me. He completed everything except for the fact that he never included in the design a way to detect when the battery was running low. I asked him to include this but he just claimed he couldn't do it for whatever reason. So now I'm trying to figure out myself how to add this to the existing design.

By browsing answers to similar questions I came across this question: Low battery detection the first answer mentions voltage supervisors and from what I've read it sounds like the ideal solution to my problem, the thing is that I'm not sure which one would be the correct voltage supervisor to detect when a 3.7 volts battery is low.

I've been looking around and from what I've found I think the NCP301LSN20T1G Voltage Supervisor would be the appropriate one to use, but I'd like to make sure I'm not making a mistake here. My background is in programming not in electronics so I apologize if this is somewhat of a innappropriate question for this site.

Thanks for any help!

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  • \$\begingroup\$ can your micro and circuit continue to run down to 2V? It's hard to say without a schematic. \$\endgroup\$ Commented Aug 17, 2015 at 14:42
  • \$\begingroup\$ The microcontroller I'd be using is a Pic16f628A and this is the schematic that was given to me: drive.google.com/file/d/0B1l1yYc-l28lZ0VKRWFKSno3XzQ/… \$\endgroup\$ Commented Aug 17, 2015 at 14:47
  • \$\begingroup\$ eevblog.com/forum/projects/… \$\endgroup\$
    – jippie
    Commented Aug 17, 2015 at 16:20
  • \$\begingroup\$ What is the battery chemistry. Depending, this can be very dangerous and you found yourself a bad EE. \$\endgroup\$
    – mcmiln
    Commented Feb 7, 2016 at 17:59
  • \$\begingroup\$ @mcmiln It's a lithium battery I'm using, don't know much more than that regarding it's chemistry. In the end I didn't bother using voltage supervisors, and instead I changed the microcontroller I was using to one that had an ADC and I used it to keep track of the battery's voltage \$\endgroup\$ Commented Feb 8, 2016 at 0:16

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NCP301LSN20T1G has a treshold voltage of 2.0V, while NCP301LSN36T1G has 3.6V. I guess 2V is too little for monitoring 3.7V battery.

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  • \$\begingroup\$ yeah you're right 2 volts would probably be too little, from what I understand the circuit requires at least 3.3 volts to operate so that should be my maximum threshold, 3.4 volts would probably be better, I'll try googling to see if I can find a better fit! \$\endgroup\$ Commented Aug 17, 2015 at 15:05
  • \$\begingroup\$ Think I found it but would like confirmation from someone more knowledgeable than I, am I correct in saying this ie.rs-online.com/web/p/voltage-supervisors/6864784 would do the job? \$\endgroup\$ Commented Aug 17, 2015 at 15:08
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If batteries are improperly treated, they can puff up, heat up, and outgas. This sometimes leads to fires if the battery is big enough. It is important for all batteries to measure for undervoltage, overvoltage, under/over current, and improper temperature. I generally recommend using a specific battery supervisor to deal with what you can.

There are so many cheap ICs specific to battery monitoring and it generally saves you battery lifetime as well. The IC can do a great job of stopping battery drain after the cutoff as well as giving the proper conditions during charging. This comes a little down to if the charger also needs to be on the device, but if not, there are very small devices for protection without charging(look at QLCSP packages).

You can use a micro for battery monitoring, and in fact it is becoming more common, but I won't use one for more than monitoring temp. What happens when your micro gets too low in voltage and the battery keeps draining? What about when your code hangs for sampling? There are also cases where there is a short under the micro and current draws from the battery at well over the specified discharge rate. Lithium batteries can only be discharged at generally 1C. Sometimes .5C and sometimes up to 2C. In these cases you want that separate IC to be your buffer.

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  • \$\begingroup\$ The batteries I'm using already have an onboard protection circuit that takes care of these things so I shouldn't have a problem with that, good info for anyone searching for this question though! \$\endgroup\$ Commented Mar 4, 2016 at 6:01
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You could use the onboard programmable voltage reference and comparator and compare reference to devided supply voltage. No extra parts required except resistor devider. You could also do this with the capture/compare pwm module. Probably been done before, may even find code for this if you know what to search for.

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