voltage cutoff

--
Do you want to completely disconnect the battery from everything or do
you just want to disconnect one or several circuits from it if its
voltage falls below 11 volts?

Just the item on the curcurit.

device

11

--- When the voltage falls below 11V and the item gets disconnected, do you want it to:

1. Get disconnected permanently so that you later have to reconnect it manually, (with a momentary pushbutton switch) or:
2. Get connected again automatically if the voltage subsequently rises to say, 11.5V?

If you choose 1, then when the controller disconnects the item it will also disconnect itself and will draw no current from the battery unless it's reconnected again manually when the battery voltage is higher than, say 11.5V.

If you choose 2, then the controller will disconnect the circuit from the battery, but it (the controller) will still stay connected to the battery so it can detect when the battery voltage gets back up to, say, 11.5V, and reconnect the item automatically. Since the controller will always be connected to the battery it will always draw a small current when the item is disconnected, probably less than

10mA, so a car battery wouldn't even know it was there.

When replying, please bottom post or I will not respond.

-- John Fields

: > >I am looking for someone to built or somewhere to : > >purchase a little device : > >that will cut the current off if the voltage of a : > >car battery drops below 11 volts. : > --- : > Do you want to completely disconnect the battery from everything or do : > you just want to disconnect one or several circuits from it if its : > voltage falls below 11 volts?

This is a little more complex than is obvious from the statement. Depending upon the total load, and the percentage of that load represented by the circuit you wish to disconnect there will be a difference in battery voltage. So as you remove the load the voltage rises and (reconnects?) the load, which drops the voltage, ...

More detail of a more positive indication of whether the circuit turns on automatically or only manually is needed, as is a percentage of the total load (if Known).

Do you only want one?

See.....

Newsgroups: alt.binaries.schematics.electronic Subject: RE: voltage cutoff question from s.e.misc - PowerSwitch.pdf Message-ID:

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

A TL431 with two resistors as a voltage divider on the adjust pins (and a small capacitor from adjust to ground to prevent oscillating), will give you the turnoff point. Put a pot in the middle of the two resistors to give some adjustment.

Add a PNP power transistor for the higher current (you didn't say how much current you needed).

On July 3 I posted that sort of structure to a.b.s.e:

Newsgroups: alt.binaries.schematics.electronic Subject: RE: voltage cutoff question from s.e.misc - PowerSwitch.pdf Message-ID:

except I used a power FET, and I put some hysteresis in it to avoid "chattering".

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.