11 volt shutoff circuit

[crunch53]

Can someone help me with this?

 

[Nigel Goodwin]

The inverter itself should shut down when the battery gets too low, it's a standard feature - as draining the battery too low damages them.

 

[crunch53]

The inverter is shutting power to the light but stays on itself and just keeps beeping. That's why I want to shut down power to it completely.

 

[Nigel Goodwin]

The inverter is shutting power to the light but stays on itself and just keeps beeping. That's why I want to shut down power to it completely.

If it's shutting power off to the light then the inverter is shutting down, all that's left is low power indication circuitry - try measuring the amount of current it takes?.

If it's the 'beep' you don't like?, 'adjust' it with a large hammer 8)

 

[crunch53]

It's the beep and the little fan in it that keep running. Wouldn't want to keep the mice awake at night if it decided to run down then. :lol: It's probably not a good idea to have the battery run down too far either.

 

[Nigel Goodwin]

It's the beep and the little fan in it that keep running. Wouldn't want to keep the mice awake at night if it decided to run down then. :lol: It's probably not a good idea to have the battery run down too far either.

Are you sure they don't shut down after a while anyway?, you might also consider the small amount of current they take, probably not enough to concern the battery at all.

Do you have a circuit diagram of the inverter?.

 

[audioguru]

"adjust it with a large hammer!"
Hee, hee, hee, hee, hee, ...... :lol:

 

[crunch53]

No, I left it beeping for over an hour today just to check. It's a Portawattz 300 inverter. I have no diagram. Is it that hard to do a circuit for it? I was hoping to just connect the coil of the relay to the battery and somehow sense when the voltage got below a certain point shut power off to the inverter until the voltage got above 12 or 12.5 volts and then come back on by itself.

 

[Roff]

Here you go. You should be able to connect the relay contacts in series with either the + or the - terminal on the inverter.

 

[crunch53]

Do I understand you right? I need to put the relay in my inverter.

 

[Roff]

Do I understand you right? I need to put the relay in my inverter.

No. The inverter just connects to the N.O. contacts of the relay. It does exactly what you want it to do - switches the inverter off when the battery voltage drops below 11 volts, and back on when it gets up to 12 volts.

 

[crunch53]

OK, so I just need to make that circuit then right. What do I need to change if I want those voltages a little different?

 

[Roff]

OK, so I just need to make that circuit then right. What do I need to change if I want those voltages a little different?

As designed, the hysteresis is about 1 volt. The pot determines the switch points. In other words, if you set it to switch off at 11 volts, it will switch back on at 12 volts. If you set it to switch off at 10 volts, it will switch back on at 11 volts. You can change the amount of hysteresis by changing the value of R2. To double the hysteresis to 2 volts, change R2 to around 75k. The pot should still allow you enough threshold adjustment range. The pot will affect the hysteresis to some extent.
We could make a circuit with independent (non-interactive) on and off points, but it would require more parts.

 

[crunch53]

I see said the blind man. Thank you very much. I think it is just ewhat I want. It looks doable.

 

[justDIY]

forgive me if this is too simplistic of a solution, and it doesn't offer automatic turn on...

take a small "wall wart", like one 12vdc output, maybe 100mA at most, and run it off the AC side of your inverter ... all the wall wart will do is keep a relay turned on... as soon as the inverter cuts off the AC power (to the wall wart) the relay will open, cutting power off to the inverter.

perhaps you could wire in a push button switch (with a diode to stop current flowing backward into the wall wart) which could temporarly connect the battery to the relay coil, kinda like a push to start.

 

[crunch53]

I don't see why that wouldn't work either. It is simple which is one of the things I am looking for. I'm not sure how much more that will take out of the battery though. Do I hook the switch up between the plus side of the battery and the plus side of the relay? I just need to decide whether I want it to come on automatically like the other circuit or if I want to push a button. Thanks to everyone so far for all your help. I really appreciate it.

 

[justDIY]

in regards to taking extra energy from the battery, the only additional load is the relay coil, which you're paying for in either situation.

for turning back on, you nailed it ... a lead from battery positive with a switch to the positive relay coil terminal... and have a diode in-line with the poisitive lead coming from the wall-wart, so current cannot flow from the battery into the wall-wart.

I suppose a magnetic type wall wart with a linear regulator would be wasting some energy as heat, but it would be insignificant compared to any real load like a lights, television, etc. If you really wanted to optimize it, use an AC powered relay, so no energy is wasted on converting AC to DC... you would need to bypass the relay to turn the gizmo back on however. Or use a switching type wall-wart, they have a really high efficiency.

 

[crunch53]

Sounds good. Thanks.

 

[ljcox]

If I understand what you want, it is to switch off the current that is being drawn from the battery when the voltage falls to 11 Volt. Ron's circuit will do this, but there will still be some current drawn by his circuit.

This could be avoided by connecting the Vcc line of Ron's circuit to the + side of the inverter.

And connect a push button switch across the relay contact.

You press the button to start the inverter and, if the voltage falls below 11 V and the relay releases, you will have to manually restart (ie. push the button) when the battery is recharged.

Edit, I have attached a drawing