I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc and
open at, say, about 12.7vdc. Is such a device available - if so where? OR what
can I put together to operate in such a manner??

The application: I want to AC power an RV refrigerator with an Inverter from
the vehicle DC charging system but automatically disconnect when RV battery is
not being charged, ie, to prevent powering Inverter from RV battery.

Ray
--
Must view with Fixed Width Fonts
\\\//
(o o)
*----------------------ooO-(_)-Ooo------------------------*
---- REMEMBER ----
+++++ Those who IGNORE history are doomed to repeat its mistakes!! +++++

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Government is not reason; it is not eloquence; it is force! Like fire,
it is a dangerous servant and a fearful master." -- George Washington
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
No God, No Peace!
Through Jesus,
Know God, Know Peace!
~~~~~~~~~~~~~~~~~~~~~

Could this be what you are looking for?:

http://www.yandina.com/hints.htm

Automatically disable your refrigerator when there is no 12V charging
source.

This is a simple way to make sure you don't discharge or even destroy your
house battery by forgetting to turn off your refrigerator load. Many
installations only have the capacity to support the refrigeration while on
shore power or when the engine is running. But a manual switch is often
forgotten when you start the engine, wasting refrigeration time, or even
worse, you forget to turn it off and deplete your battery after the engine
is turned off.

The process can be automated by installing a Combiner 50 between the
refrigerator and the battery. One red lead goes to each, and the black
ground lead is connected to the 12 volts negative. Whenever a charging
source raises the battery voltage above about 13.3 volts, the combiner will
close and supply the refrigerator. When the voltage drops, it will
disconnect. The built in timing circuits in the C50 will prevent short
cycling that is detrimental to refrigeration motors. No power is used by the
C50 when the refrigerator is not running.

If you want to be able to manuall override the automatic control and allow
the refrigerator to run while no charging source is available, you can add a
small switch to the remote control feature of the Combiner 50.


Jim Pook
www.jimsfishing.com



"R. A. Piziali" wrote in message
...
I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc
and
open at, say, about 12.7vdc. Is such a device available - if so where?
OR what
can I put together to operate in such a manner??

The application: I want to AC power an RV refrigerator with an
Inverter from
the vehicle DC charging system but automatically disconnect when RV
battery is
not being charged, ie, to prevent powering Inverter from RV battery.

Ray
--
Must view with Fixed Width Fonts
\\\//
(o o)
*----------------------ooO-(_)-Ooo------------------------*
---- REMEMBER ----
+++++ Those who IGNORE history are doomed to repeat its mistakes!! +++++

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Government is not reason; it is not eloquence; it is force! Like fire,
it is a dangerous servant and a fearful master." -- George Washington
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
No God, No Peace!
Through Jesus,
Know God, Know Peace!
~~~~~~~~~~~~~~~~~~~~~

In article ,
"R. A. Piziali" wrote:

I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc and
open at, say, about 12.7vdc. Is such a device available - if so where? OR
what
can I put together to operate in such a manner??

The application: I want to AC power an RV refrigerator with an Inverter
from
the vehicle DC charging system but automatically disconnect when RV battery
is
not being charged, ie, to prevent powering Inverter from RV battery.

Ray


This can be accomplished witha simple diode combiner. No moving parts
and fairly cheap.

Bruce in alaska
--
add a 2 before @

You need a circuit like the one on:
http://www.ncws.com/rcrock/lowbat.htm

If you replace the LM336 and its 3K resistor with a 10K little
thumbwheel potentiometer (volume control), hooking the wiper arm to
the minus input to the LM311 voltage comparator and the two ends
between battery + and - terminals, you can adjust the trip point all
over the place to suit your needs.

Replace the little alarm beeper with a small 12V relay that will turn
your big control relay on and off remotely mounted at the inverter's
DC power source. The little relay contacts, being isolated, will
prevent the big relay's coil from kicking high voltage into the IC
destroying it.

The LM311 is a voltage comparator IC, made for this service. Its
output (hooked to the piezo buzzer in the schematic) switches from off
to full on whenever the voltage at the + input crosses the voltage set
on the - input. This will click the relay ON any time the voltage
drops below your set point. If you power the big control relay from
normally closed contacts on the little relay powered by the IC, any
time the little relay is energized, the big relay will be
de-energized, turning off the fridge. I like this because if this
circuit fails for some reason, the failure mode is to leave the fridge
ON, not off, continuously....protecting your food in an emergency
scenario.

As this circuit draws virtually whatever the tiny control relay draws,
a few milliamps, there's no reason to ever turn it off. Just put its
source to the breaker the inverter is running from.

Once set by the variable control, it'll stay that way for years.

To adjust it is simple. Turn the charging on, and adjust the control
so the inverter runs. Turn the charging off and adjust the control
back until the inverter shuts off at the desired voltage. You can
adjust the shut-down point to anything you like.....leaving the
inverter on until the battery voltage drops to X volts.



On Sat, 25 Oct 2003 22:13:20 -0700, "R. A. Piziali"
wrote:

I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc and
open at, say, about 12.7vdc. Is such a device available - if so where? OR what
can I put together to operate in such a manner??

The application: I want to AC power an RV refrigerator with an Inverter from
the vehicle DC charging system but automatically disconnect when RV battery is
not being charged, ie, to prevent powering Inverter from RV battery.

Ray
--
Must view with Fixed Width Fonts
\\\//
(o o)
*----------------------ooO-(_)-Ooo------------------------*
---- REMEMBER ----
+++++ Those who IGNORE history are doomed to repeat its mistakes!! +++++

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Government is not reason; it is not eloquence; it is force! Like fire,
it is a dangerous servant and a fearful master." -- George Washington
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
No God, No Peace!
Through Jesus,
Know God, Know Peace!
~~~~~~~~~~~~~~~~~~~~~



Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

(Larry W4CSC) wrote in message ...
You need a circuit like the one on:
http://www.ncws.com/rcrock/lowbat.htm



That's interesting. I have a similar requirement, to drive a low power
fan (draws approx 180mA) whenever the battery is receiving charge from
a solar panel. For this it makes no sense to use relays. If I flip
the connections to the comparator, does it then bleep above the
threshold voltage ???? How much current can the circuit take - ie
could I then power the fan directly ??

You can probably detect that my understanding of electronics
is at the vodoo level !

Thanks


Steve (no the other one)

It won't drive the fan, directly. The IC (probably) can only sink
50-100 ma and the motor will kick high voltage on shutdown so I
wouldn't attempt it directly. HOwever, for this little load a 12V
reed relay for a buck or two to key up the motor would work great.
The IC keys the relay and the reed contact keys the motor....

Radio Shack has nice little 12V relays that are little blue bricks
with wire pins sticking out. Those would be great for this
application, too.


On 27 Oct 2003 01:38:16 -0800, (Steve)
wrote:

(Larry W4CSC) wrote in message ...
You need a circuit like the one on:
http://www.ncws.com/rcrock/lowbat.htm



That's interesting. I have a similar requirement, to drive a low power
fan (draws approx 180mA) whenever the battery is receiving charge from
a solar panel. For this it makes no sense to use relays. If I flip
the connections to the comparator, does it then bleep above the
threshold voltage ???? How much current can the circuit take - ie
could I then power the fan directly ??

You can probably detect that my understanding of electronics
is at the vodoo level !

Thanks


Steve (no the other one)


Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

In article ,
says...
You need a circuit like the one on:
http://www.ncws.com/rcrock/lowbat.htm

If you replace the LM336 and its 3K resistor with a 10K little
thumbwheel potentiometer (volume control), hooking the wiper arm to
the minus input to the LM311 voltage comparator and the two ends
between battery + and - terminals, you can adjust the trip point all
over the place to suit your needs.

Replace the little alarm beeper with a small 12V relay that will turn
your big control relay on and off remotely mounted at the inverter's
DC power source. The little relay contacts, being isolated, will
prevent the big relay's coil from kicking high voltage into the IC
destroying it.

The LM311 is a voltage comparator IC, made for this service. Its
output (hooked to the piezo buzzer in the schematic) switches from off
to full on whenever the voltage at the + input crosses the voltage set
on the - input. This will click the relay ON any time the voltage
drops below your set point. If you power the big control relay from
normally closed contacts on the little relay powered by the IC, any
time the little relay is energized, the big relay will be
de-energized, turning off the fridge. I like this because if this
circuit fails for some reason, the failure mode is to leave the fridge
ON, not off, continuously....protecting your food in an emergency
scenario.

As this circuit draws virtually whatever the tiny control relay draws,
a few milliamps, there's no reason to ever turn it off. Just put its
source to the breaker the inverter is running from.

Once set by the variable control, it'll stay that way for years.

To adjust it is simple. Turn the charging on, and adjust the control
so the inverter runs. Turn the charging off and adjust the control
back until the inverter shuts off at the desired voltage. You can
adjust the shut-down point to anything you like.....leaving the
inverter on until the battery voltage drops to X volts.



On Sat, 25 Oct 2003 22:13:20 -0700, "R. A. Piziali"
wrote:

I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc and
open at, say, about 12.7vdc. Is such a device available - if so where? OR what
can I put together to operate in such a manner??

------------------

The LM311 circuit described should do the job, but does not have ANY
hysterisis and could "chatter" (on-off). Also, I would filter the
supply voltage.

A resistor connected between the 311 output (right side) and the "+"
input will add hysterisis. That is, turn on at voltage 1 and turn off
at voltage 2, rather than a single on/off point in voltage. The value
will depend on the amount of hysterisis desired and the other component
values (8K2 and 10k resistors). The resistor value can be calculated or
determined experimentally... Probably somewhere from 10K to 1 megohm.

I would add a 0.01 Uf ceramic cap across the +- chip leads and a 50 to
100 Uf at the power feed, maybe some ferrite too. ...Keep the false
triggers at a minimum...

Instead of a small relay a medium sized transistor would reduce the
moving parts and drive the big relay. The NPN circuit below will invert
the "sense" (logic) of the circuit. Should drive most all relays is you
use a 3-8 amp pwr transistor. The diode (1N4004 or equal) "snubs" the
inductive kick-back from the relay coil.
....Inversion can be done by swapping +- inputs too.

| To +
|
X
X 1000 ohms Lg Relay coil
X | /C---------^^^^^---------- To +V
| 200 ohms |/ |--Diode-| Cathode
------/\/\/\/\------| NPN
B|\
| \E
------ to Negative (ground)


Another (non-inverting) method using a PNP transistor.

| /------ To + voltage
1000 ohms B |/ E
-----/\/\/\/\-------- |
|\ C Rly coil
| \-----^^^^^^---- To neg (ground)
| Diode |
Cath

If My ASCII art is trashed and you need to know, email me for a better
drawing. - where MyCall=KZ4AK.

73,
Woody

As his trip point voltages will be either well below the trip point
when the charging is off or well above the trip point when it's
charging, I didn't figure he'd need it. Thanks for the suggestion,
though.



On Tue, 28 Oct 2003 03:28:17 GMT, Woody wrote:

In article ,
says...
You need a circuit like the one on:
http://www.ncws.com/rcrock/lowbat.htm

If you replace the LM336 and its 3K resistor with a 10K little
thumbwheel potentiometer (volume control), hooking the wiper arm to
the minus input to the LM311 voltage comparator and the two ends
between battery + and - terminals, you can adjust the trip point all
over the place to suit your needs.

Replace the little alarm beeper with a small 12V relay that will turn
your big control relay on and off remotely mounted at the inverter's
DC power source. The little relay contacts, being isolated, will
prevent the big relay's coil from kicking high voltage into the IC
destroying it.

The LM311 is a voltage comparator IC, made for this service. Its
output (hooked to the piezo buzzer in the schematic) switches from off
to full on whenever the voltage at the + input crosses the voltage set
on the - input. This will click the relay ON any time the voltage
drops below your set point. If you power the big control relay from
normally closed contacts on the little relay powered by the IC, any
time the little relay is energized, the big relay will be
de-energized, turning off the fridge. I like this because if this
circuit fails for some reason, the failure mode is to leave the fridge
ON, not off, continuously....protecting your food in an emergency
scenario.

As this circuit draws virtually whatever the tiny control relay draws,
a few milliamps, there's no reason to ever turn it off. Just put its
source to the breaker the inverter is running from.

Once set by the variable control, it'll stay that way for years.

To adjust it is simple. Turn the charging on, and adjust the control
so the inverter runs. Turn the charging off and adjust the control
back until the inverter shuts off at the desired voltage. You can
adjust the shut-down point to anything you like.....leaving the
inverter on until the battery voltage drops to X volts.



On Sat, 25 Oct 2003 22:13:20 -0700, "R. A. Piziali"
wrote:

I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc and
open at, say, about 12.7vdc. Is such a device available - if so where? OR what
can I put together to operate in such a manner??

------------------

The LM311 circuit described should do the job, but does not have ANY
hysterisis and could "chatter" (on-off). Also, I would filter the
supply voltage.

A resistor connected between the 311 output (right side) and the "+"
input will add hysterisis. That is, turn on at voltage 1 and turn off
at voltage 2, rather than a single on/off point in voltage. The value
will depend on the amount of hysterisis desired and the other component
values (8K2 and 10k resistors). The resistor value can be calculated or
determined experimentally... Probably somewhere from 10K to 1 megohm.

I would add a 0.01 Uf ceramic cap across the +- chip leads and a 50 to
100 Uf at the power feed, maybe some ferrite too. ...Keep the false
triggers at a minimum...

Instead of a small relay a medium sized transistor would reduce the
moving parts and drive the big relay. The NPN circuit below will invert
the "sense" (logic) of the circuit. Should drive most all relays is you
use a 3-8 amp pwr transistor. The diode (1N4004 or equal) "snubs" the
inductive kick-back from the relay coil.
...Inversion can be done by swapping +- inputs too.

| To +
|
X
X 1000 ohms Lg Relay coil
X | /C---------^^^^^---------- To +V
| 200 ohms |/ |--Diode-| Cathode
------/\/\/\/\------| NPN
B|\
| \E
------ to Negative (ground)


Another (non-inverting) method using a PNP transistor.

| /------ To + voltage
1000 ohms B |/ E
-----/\/\/\/\-------- |
|\ C Rly coil
| \-----^^^^^^---- To neg (ground)
| Diode |
Cath

If My ASCII art is trashed and you need to know, email me for a better
drawing. - where MyCall=KZ4AK.

73,
Woody


Larry W4CSC

"Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!"

(Larry W4CSC) wrote:

As his trip point voltages will be either well below the trip point
when the charging is off or well above the trip point when it's
charging, I didn't figure he'd need it. Thanks for the suggestion,
though.




When the charger shuts off, the battery voltage will slowly (more or
less) drop to the lower trip point. Whilst in that region, the
comparator could "chatter". I always use a bit of positive feedback in
a circuit like this to avoid the chatter.
Larry Bradley VE3CRX
Remove "removeme" from my e-mail address for direct mail
Ottawa, Canada

(use the e-mail address above to send directly to me)


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There is a very simple way to do this; you connect a relay to the oil light
switch on the engine[s] that drives the alternator[s].
The positive side of the relay coil goes to the ignition circuit.
This is the standard setup for separating a house battery from the start
battery with a relay, so avoiding the voltage drop from diodes.
The advantage of using the oil light instead of the ignition, is that the
engine will [normally] start before the load is added.
Not as clever as those comparator circuits, but sure is easy!
Regards, Mark Holden



"R. A. Piziali" wrote in message
...
I have need of the following:

A relay that will handle a 15amp load and close at about 13.0-13.4vdc
and
open at, say, about 12.7vdc. Is such a device available - if so where?
OR what
can I put together to operate in such a manner??

The application: I want to AC power an RV refrigerator with an
Inverter from
the vehicle DC charging system but automatically disconnect when RV
battery is
not being charged, ie, to prevent powering Inverter from RV battery.

Ray
--
Must view with Fixed Width Fonts
\\\//
(o o)
*----------------------ooO-(_)-Ooo------------------------*
---- REMEMBER ----
+++++ Those who IGNORE history are doomed to repeat its mistakes!! +++++

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Government is not reason; it is not eloquence; it is force! Like fire,
it is a dangerous servant and a fearful master." -- George Washington
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
No God, No Peace!
Through Jesus,
Know God, Know Peace!
~~~~~~~~~~~~~~~~~~~~~