Low voltage protection circuit - disconnect when voltage drops below set point

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RogueRose

Joined Oct 10, 2014
375
I need to be able to disconnect a power source (battery) when the voltage drops below a certain point which will usually be about 3v but it would be nice to be able to get down to .9 - 1v for when I'm testing NiCd and NiMH batteries. I need to test the capacity of a number of Lithium cells as well as some NiMH and I have a tester that draws a constant load (up to 180w) but it won't disconnect automatically if the V drops past a point, which I'd like to then put a circuit in line to take care of this.

I'm guessing 10A will be sufficient but probably wouldn't be a bad idea to be able to do 15A.

Does anyone know of a pre-made board that can do the voltage monitoring and then disconnect w/ a relay?

Someone suggested this device and it looks like it has some features I need (including the lower voltages I need) but it also looks like a charger. I'm also not sure what the 220v input is used for and would 120 work alright (I only have 120 & 240vac).
https://www.ebay.com/itm/Battery-Charger-Discharger-Board-Under-Voltage-Over-Voltage-Protection-Module-Sx/323727475189
 

SamR

Joined Mar 19, 2019
1,796
Look at the 7665S CMOS Micropower Over/Under Voltage Detector chip and see if it works for you. It is an over/under watchdog chip with alarm setpoint outputs. Not a premade module but food for thought.
 

ScottWang

Joined Aug 23, 2012
6,873
An independent power supply, an comparator and a PNP bjt drive circuit (one 10K Rbe cross on b, e pins) and a low Rds PMOSFET or relay, something like that, the similar method as this.
 

crutschow

Joined Mar 14, 2008
24,318
That ebay module would appear to do what you want, as it can be used as a low-voltage discharge monitor, with a relay to cut off the discharge.
 

SamR

Joined Mar 19, 2019
1,796
That module doesn't say what the chip is and can't read it in the pic but sure sounds like the 7665...
 

Janis59

Joined Aug 21, 2017
1,057
There are rather much products realizing this undervoltage/overvoltage protection functionanality.
For example IRS2452; LB11696; Max6399 and more extended list anyone may get at the octopart.com search engine
 

AnalogKid

Joined Aug 1, 2013
8,302
That module doesn't say what the chip is and can't read it in the pic but sure sounds like the 7665...
Hard to figure the inductor on pin 2/6 ...

My guess is a uC under the display. Given the operating voltage range, I think the 8-pin chip is a buck regulator with onboard FETs.

ak
 
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