Hello,
I trying to build a battery overvoltage "battery charger" cutoff circuit. I must be in error because what I keep trying isn't working. I am trying to build a power cutoff when a battery reaches a predetermined higher voltage. I wish to use a zener diode of perhaps 16 volts to provide a trigger to the mosfet, which in turn drives a relay to cutoff the 110v to the charger.
I got the mosfet to turn on with low voltage at the gate and off with high voltage at the gate, so I think that part is ok. (hope you can see the attachment diagram) ; but when/if the zener breaks down it doesn't give a positive enough signal to the gate to of the mosfet to turn it off?
I've tried all different voltage at supply from 12 - 15.6v , and many different resistors for R1 (100, 200, 15k, 47k , etc ), also tried zeners rated 10, 12 and 15 volts. It may be that the Vgate has to be higher than the Vdrain but I'm unclear on howto do it?
Any help would be appreciated. I guess I'm really rusty anymore (getting old), but rather than waste another day trying myriad of different setups, i thought I'd just ask the experts.
I got another zener setup to work fine using an LED that tells me when batteries are low voltage (LED when voltage drops to 11 volts on 12v batteries). But this is a little beyond that.
**To limit a 14.4 volt NIMH battery from being overcharged, unfortunately normal battery chargers when they "seem" to be at 0 amps are really still feeding about "up to" 1 amp (shumacher etc all have same problem), this can in the case of lead acid 12v batteries boil away the water ruining the battery over a week or two (so don't ever leave the charger on for more than it takes to charge the battey fully or about 6-10 hours using 15 amp charger). In the case of NIMH batteries its even worse, the nimh actually can overheat and catch fire (nimh voltage actually goes down just very slightly when fully charged which is very hard to detect with); this slight v drop can result in metling as NIMH batteries can tend to hog the juice once fully charged and most chargers aren't smart enough to know its already fully charged.
I trying to build a battery overvoltage "battery charger" cutoff circuit. I must be in error because what I keep trying isn't working. I am trying to build a power cutoff when a battery reaches a predetermined higher voltage. I wish to use a zener diode of perhaps 16 volts to provide a trigger to the mosfet, which in turn drives a relay to cutoff the 110v to the charger.
I got the mosfet to turn on with low voltage at the gate and off with high voltage at the gate, so I think that part is ok. (hope you can see the attachment diagram) ; but when/if the zener breaks down it doesn't give a positive enough signal to the gate to of the mosfet to turn it off?
I've tried all different voltage at supply from 12 - 15.6v , and many different resistors for R1 (100, 200, 15k, 47k , etc ), also tried zeners rated 10, 12 and 15 volts. It may be that the Vgate has to be higher than the Vdrain but I'm unclear on howto do it?
Any help would be appreciated. I guess I'm really rusty anymore (getting old), but rather than waste another day trying myriad of different setups, i thought I'd just ask the experts.
I got another zener setup to work fine using an LED that tells me when batteries are low voltage (LED when voltage drops to 11 volts on 12v batteries). But this is a little beyond that.
**To limit a 14.4 volt NIMH battery from being overcharged, unfortunately normal battery chargers when they "seem" to be at 0 amps are really still feeding about "up to" 1 amp (shumacher etc all have same problem), this can in the case of lead acid 12v batteries boil away the water ruining the battery over a week or two (so don't ever leave the charger on for more than it takes to charge the battey fully or about 6-10 hours using 15 amp charger). In the case of NIMH batteries its even worse, the nimh actually can overheat and catch fire (nimh voltage actually goes down just very slightly when fully charged which is very hard to detect with); this slight v drop can result in metling as NIMH batteries can tend to hog the juice once fully charged and most chargers aren't smart enough to know its already fully charged.
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