Low Voltage Battery Disconnect

[BrentA929]

Hey Guys,

I have started a new project and need some assistance...

I found a really cool circuit (see attached) that I have been using for a while to discharge my batteries. It automatically shuts off at 12V (or whatever you set it to) and I can adjust the discharge rate by using different wattage lamps for the load. It is my "poor mans" version of John Bedini's load box.

Here is the thing...so, I have this circuit and I have a count-up timer that I use to determine the length of time it takes to discharge, but I want to hook them up together. I don't want to have to be there every time the battery is done discharging. It is quite the pain.

Any ideas?


Thanks, Brent

[Tom C]

so you start the timer by hand and then you want the timer to stop automatically?

Tom C

[Tom C]

everyone look at the comparator circuit on this device, very interesting!!

@ brent,

I think you could use the voltage out of the oscillator to drive a dual throw relay. we call them ice cube relays.

http://www.ebay.com/itm/like/1115930...lpid=82&chn=ps

when the voltage is on the relay is held open, as soon as the voltage goes off, the relay turns off and you can just make that side of the relay a switch closure, wire it right into the stop button on the timer. I don't think the timer will care if it is held on until you get to it. the timer button is probably just a dry contact switch with a few volts on it. you would not need much of a relay at all.

Tom C

[BrentA929]

Tom,

Thanks for your response...

So, here is what I was thinking. I could use the other side of the switch (S1) in the schematic to start the timer. There is a free spot available on the switch and fortunately it is on the "ON" side, so it can start the timer when the load is applied. Then I am wanting to figure out how I can automatically stop the timer when the load is disconnected. I hear what you are saying about the relay, but I am wondering if it will function correctly if it can only toggle back and forth. It seems as if you would have to start it then stop it then start it again to get it in the correct state to function being that the "start" and "stop" are the same button. Or maybe you would just have to push the switch twice to the "ON" position. I may have to breadboard it to see. Anyway, I was hoping that someone out there would know how I could close a switch/relay momentarily on an open circuit.


Thanks, Brent

[Tom C]

you can do that with a 555 and an opto.

Tom C

[BrentA929]

Hey Tom,

I'm all ears...your assistance would be greatly appreciated!


Thanks, Brent

[Tom C]

dig around here:

http://www.555-timer-circuits.com/driving-a-relay.html

I saw a circuit one time that used a pair of 555 timers. one for hi one for low. I would think since you need to reset the timer and add another battery you would only be interested in turning the timer "off" turn on the circuit push start on the timer, and let it turn off the timer at the cutoff.

Tom C

[BrentA929]

Got it working

Just an update...

I got it working! Not much of one to build a circuit from scratch, so I found something that fits the bill nicely. After much searching, I found a DEI 528T (pulse timer relay). It allows me to pulse the timer circuit when the light turns off or when the circuit opens. Pretty cool little product...used mainly in mobile electronics. It is built around a CD40107BE Dual 2-Input NAND Buffer/Driver for those that are curious.

My only complaint is upon powering it up, it cycles on and off. I can live with that for now...

Anyway, just thought I would share the progress.


Thanks, Brent