Would like to use something like a single or dual internally compensated 741 that can have a adjustabile 6 to 7 volt pull in point & about a .3 vdc lower drop out point . It will be used to control a 12 vdc relay that pulls .3 amps when energized.

This will controll the charging on 2 small gasoline motors battery charging. They have alternators & rectifiers. But no control of the battery being over charged. So the SPST relay needs a adjustible pull in setpoint & a adjustabile drop out setpoint.
A website with a diagram would be fine.


Thank you for any help.
Rich

 

A 555 operating in the bistable mode is closer to what I need ?

 

You could use a comparator, such as the LM339 or LM393. You set their trip point by a resistor divider and hysteresis feedback. Here's an article on that.

Depending on the required relay coil current you may need to add a transistor driver at the comparator output. Also be sure you add a transient suppressor diode across the relay coils (cathode to positive end).

What's the supply voltage? If it's the battery voltage itself, then you will need to add a resistor and zener diode to provide a stable V reference voltage.

 

You site is excellent. The 555 has too large of a hysterisis minimum range.

Are there OP AMPS with onboard reference supplies that will survive being powered by the extreme variations of a Lead acid battery in a boat or mower enviroment ? With voltages from 0 volts..dead battery... to 14.5 vdc maximum fully charged?
I will add a transistor booster stage for the relay, 300 ma. load operating on a 14.5 volt battery.

Thank you.
Rich

 

You site is excellent. The 555 has too large of a hysterisis minimum range.

Are there OP AMPS with onboard reference supplies that will survive being powered by the extreme variations of a Lead acid battery in a boat or mower enviroment ? With voltages from 0 volts..dead battery... to 14.5 vdc maximum fully charged?
I will add a transistor booster stage for the relay, 300 ma. load operating on a 14.5 volt battery.

Thank you.
Rich

I think you need a comparator, not an op amp. There are lots of comparators with built-in references.Give us more details of what you are trying to do if you want design help.

 

I came across this 5 amp regulator. Will fly with it.

Thank you both for the helping to get a old brain going again.

Best wishes to both of you.
Rich