Never did get analog electronics

[CrashDude]

How about this for a simple circuit.

Pot feeding a SPDT relay. Hook LED and resistor to the "off" pole, adjust POT for cutoff voltage. 4 components.

Would cutoff be too un-reliable?

If not, i'd use a PIC with A/D cause I don't get analog :-).

Robert

[Mr.RC-CAM]

What are you trying to build?

RC-CAM

[BMatthews]

Battery cutoff?

If so you're on the right track but you gotta wire in the primary set of poles so they turn around and cut off the power to the relay as well. So the power goes through the normally open contacts and then to the relay's coil and the rest of the downstream circuitry. Then you add a push to arm switch across these same contacts. Pushing the momentary switch clicks the relay on and then it holds itself on until the low voltage point is reached. If you don't do it this way the batteries will recover in a second or two and click the relay on again. Sets up a constant chatter that's NOT what you want.

And if you want a "tripped" light then use the second contacts as you're suggesting.

BTW, this isn't analog other than the pot. It's digital in it's simplest form..... But then most of you around here are too young to remember RELAY LOGIC.... :D

[Gary Warner]

Your circuit may set up an oscillation. As the coils are opened out of circuit, the battery voltage may recover enough to energize the coils again. This assumes an RC application and where the battery voltage will recover if the load is reduced. Plus the relay coils will consume some degree of current, hindering the batteries performance. Maybe not good if this is a receiver battery. And the POT might need to be of a higher wattage value than you are willing to use.

Better to use a latching circuit. If you are familiar with the PIC's, just test out the value of the ADC (like on a PIC16C71x) to "window" the latch or what ever you need (don't forget to LPF the sensing AD input). With DIP micro switches you can even write the program so the parameters are field programmable. The PIC can also sink 150ma on it's open-collector outputs (more than enough to drive an LED).

Other options are an analog latch with a comparator and an RS flip-flop (KJ might be better for better startup status). SCR's and other type of circuits are possible too. Just remember to window or latch the output to avoid battery voltage rebound.

[Bruce Abbott]

A relay requires a lot more current to operate than to release, so 'oscillation' should not occur. However, if a change-over contact is available you might as well use it to latch the relay, as it saves a bit of power in the off position, and could also be used to turn off some other device. In any case, an arming switch will probably be required to bypass the variable resistor, otherwise the relay may not pull in on a fully-charged battery.

This type of circuit used to be quite popular as a simple alternative to an ESC. The motor starts when armed and runs until the battery goes flat. The circuit might look something like this:-

[jrb]

This link might help: http://www.marcee.org/Articles/BatteyPackDischarger.htm