12v Self reseting switch question

[mg]

Hello,

I'm an officer with a small volunteer fire department. I'm not an
electrical engineer. We have a rescue van that we roll on almost every
call. We have a 12v light bar on the rear of the van. The light bar
has a yellow rotating light at the rear center. When we are on scene,
the yellow light is almost blinding. We would like to be able to turn
off the yellow light when we arrive on scene. We would like to put a
momentary switch some where near the rear door that will turn off the
yellow center light. The catch is that we want the switch to self
reset. At 4am after a long call, we don't want to add another item to
our crew. When we bring the van back to the station we turn all the
lights off. When the next call comes in and the van rolls, we want to
be able to turn the rear lights on again from the master switch on the
dash.

I've been sitting here trying come up with a diagram. My first thought
is to use a switch to control a relay. But, I'm not sure how to get it
to self-reset. I'm stumped. I'm open for any suggestion. Myself and
the rest of our crew would be very grateful.
--
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[Michael A. Terrell]

Hello,

I'm an officer with a small volunteer fire department. I'm not an
electrical engineer. We have a rescue van that we roll on almost every
call. We have a 12v light bar on the rear of the van. The light bar
has a yellow rotating light at the rear center. When we are on scene,
the yellow light is almost blinding. We would like to be able to turn
off the yellow light when we arrive on scene. We would like to put a
momentary switch some where near the rear door that will turn off the
yellow center light. The catch is that we want the switch to self
reset. At 4am after a long call, we don't want to add another item to
our crew. When we bring the van back to the station we turn all the
lights off. When the next call comes in and the van rolls, we want to
be able to turn the rear lights on again from the master switch on the
dash.

I've been sitting here trying come up with a diagram. My first thought
is to use a switch to control a relay. But, I'm not sure how to get it
to self-reset. I'm stumped. I'm open for any suggestion. Myself and
the rest of our crew would be very grateful.

You better make sure that you are allowed to modify the lights. They
are intended to protect you from other approaching vehicles.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[John O'Flaherty]

Hello,

I'm an officer with a small volunteer fire department. I'm not an
electrical engineer. We have a rescue van that we roll on almost every
call. We have a 12v light bar on the rear of the van. The light bar
has a yellow rotating light at the rear center. When we are on scene,
the yellow light is almost blinding. We would like to be able to turn
off the yellow light when we arrive on scene. We would like to put a
momentary switch some where near the rear door that will turn off the
yellow center light. The catch is that we want the switch to self
reset. At 4am after a long call, we don't want to add another item to
our crew. When we bring the van back to the station we turn all the
lights off. When the next call comes in and the van rolls, we want to
be able to turn the rear lights on again from the master switch on the
dash.

I've been sitting here trying come up with a diagram. My first thought
is to use a switch to control a relay. But, I'm not sure how to get it
to self-reset. I'm stumped. I'm open for any suggestion. Myself and
the rest of our crew would be very grateful.

You can link the reset to the turnoff of the vehicle lights. The relay
turns on in response to the pushbutton, and has a normally-open holding
contact bridging the pushbutton, as well as a normally-closed contact
powering the rotating light. But the whole thing is powered by the
light bar voltage supply, so it drops out as soon as the light is
turned off.

 

[Chris]

You can link the reset to the turnoff of the vehicle lights. The relay
turns on in response to the pushbutton, and has a normally-open holding
contact bridging the pushbutton, as well as a normally-closed contact
powering the rotating light. But the whole thing is powered by the
light bar voltage supply, so it drops out as soon as the light is
turned off.

John has it exactly. Copy this to M$ Notepad or any other fixed font,
print it out, and give it to your fire department's automotive
mechanic. He'll be able to do this easily:

+12V GND
| CRY1 |
| .---------------. Lightbar |
| | Lightbar | ||/ \.-./ |
|-o Control o----. ||-------( X )-----------o
| | Circuit | | /||N.C. /'-'\ |
| '---------------' o-----------| |
| | COM ||N.O. 1N5402 |
| | T ||------o----|<----------o
| | --- || | ___ |
| '---o o-------------o----UUU---------o
| RY1 |
| |
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Be sure to specify an automotive relay made for lamp loads that can
handle the current (holding, not switching, so you don't have to worry
about inrush current). It might be in excess of 20A. Just look at the
lightbar fuse rating for an idea of relay/contactor size.

Good luck
Chris

 

[jasen]

Hello,

I'm an officer with a small volunteer fire department. I'm not an
electrical engineer. We have a rescue van that we roll on almost every
call. We have a 12v light bar on the rear of the van. The light bar
has a yellow rotating light at the rear center. When we are on scene,
the yellow light is almost blinding. We would like to be able to turn
off the yellow light when we arrive on scene. We would like to put a
momentary switch some where near the rear door that will turn off the
yellow center light. The catch is that we want the switch to self
reset. At 4am after a long call, we don't want to add another item to
our crew. When we bring the van back to the station we turn all the
lights off. When the next call comes in and the van rolls, we want to
be able to turn the rear lights on again from the master switch on the
dash.


I've been sitting here trying come up with a diagram. My first thought
is to use a switch to control a relay. But, I'm not sure how to get it
to self-reset. I'm stumped. I'm open for any suggestion. Myself and
the rest of our crew would be very grateful.

You need a relay with "change-over contacts" (ie both NO and NC)

I'd go with one with spade connectors and a mounting hole, one
like that should be available at any auto parts place.

Run the relay off the same power that runs the light, when the power goes
off so does the relay.

If this diagram is garbled paste it into notepad etc....


v---------> to lamp
from switch __--
--+---------------o~~.
| . ^----.
| --- . |
`--o o------+-----|~| |
button | |\| |
| .--|_| |
| | |
`--|-----------'
|
-+-
//// chassis/ground





another way to do it would be to powe the relay coil off the interior light
when you open the door yellow light goes out, when you close it it comes back
on.


Bye.
Jasen

 

[Jamie]

Hello,

I'm an officer with a small volunteer fire department. I'm not an
electrical engineer. We have a rescue van that we roll on almost every
call. We have a 12v light bar on the rear of the van. The light bar
has a yellow rotating light at the rear center. When we are on scene,
the yellow light is almost blinding. We would like to be able to turn
off the yellow light when we arrive on scene. We would like to put a
momentary switch some where near the rear door that will turn off the
yellow center light. The catch is that we want the switch to self
reset. At 4am after a long call, we don't want to add another item to
our crew. When we bring the van back to the station we turn all the
lights off. When the next call comes in and the van rolls, we want to
be able to turn the rear lights on again from the master switch on the
dash.

I've been sitting here trying come up with a diagram. My first thought
is to use a switch to control a relay. But, I'm not sure how to get it
to self-reset. I'm stumped. I'm open for any suggestion. Myself and
the rest of our crew would be very grateful.

use a DPDT (double pole, double throw) relay. when the light rack is on
you can use the power from that. one pole of the Relay you will use the
NC (normally Closed) contacts (this is when the relay is not powered),
these contacts will be the switch that allows your power to run the
lights. with a momentary push button and using the power that runs the
rack (when on), you can energize the relay., the other set of contacts
will close which will connect the main power to the coil of the relay at
the same time. when you let go of your push button, the relay will stay
energized and your light will be off because the first set of contacts
are now open.
when the rack is turned off, the relay will also turn off because your
using the same power as the rack. so the next time you turn on the rack
your relay will also be in the off position which will have the NC
contacts on the first pole connected to power your light.

 

[CheapscateDave]

Hello,

I'm an officer with a small volunteer fire department. I'm not an
electrical engineer. We have a rescue van that we roll on almost every
call. We have a 12v light bar on the rear of the van. The light bar
has a yellow rotating light at the rear center. When we are on scene,
the yellow light is almost blinding. We would like to be able to turn
off the yellow light when we arrive on scene. We would like to put a
momentary switch some where near the rear door that will turn off the
yellow center light. The catch is that we want the switch to self
reset. At 4am after a long call, we don't want to add another item to
our crew. When we bring the van back to the station we turn all the
lights off. When the next call comes in and the van rolls, we want to
be able to turn the rear lights on again from the master switch on the
dash.

I've been sitting here trying come up with a diagram. My first thought
is to use a switch to control a relay. But, I'm not sure how to get it
to self-reset. I'm stumped. I'm open for any suggestion. Myself and
the rest of our crew would be very grateful.
--
Email hint - Everything after the @ is spelled backwards.

There are only 10 types of people in the world:
those that understand binary, and
those that don't.

Please explain if you want to only turn off one light in the light bar
and have the others remain in operation. If this is what you want then
you will need to alter the connections inside if the light bar unless
each light in the bar has a seperate external connection.
Either way I would suggest a DPDT relay and a button to activate it.
The button should be of the N/O type and connect one side to the
chassis(ground). The other should go to one side of the relay coil and
the other side of the coil to the power in the light bar. Connect the
o/p contact to the chassis(ground) and the n/o contact to the relay
coil where the button is attached. If the Light bar has room for the
relay then only 1 wire will need to exit the light bar to the button.
Using the other set of points of the relay, connect the o/p to the
power provided to the bar and the n/c point to the light that you want
to be out.
Dave
30+ year fire truck driver.

 

[Gerhard]

You better make sure that you are allowed to modify the lights. They
are intended to protect you from other approaching vehicles.

Michael A. Terrell
Central Florida

A safer solution might be not to switch the rotating light completely
off , but to dim the light by wiring two bulbs in series.

Just use the suggested relay circuit (see other posts) and wire a
second lamp across the normally closed relay contacts.
When the normally closed contacts open, the rotating light
will be supplied via this extra lamp.

I hope the wiring for the rotating motor can be separated from the
wiring of the lamp, else the motor might stall with the reduced
voltage available.

By selecting different wattage lamps (or even wiring two lamps
in parallel) across the normally closed relay contacts will allow you
to set a comfortable brightness (dimness for the rotating light.

Gerhard van den Berg
CSIR

 

[mg]

Thanks to everyone for their ideas. We installed a relay and a
momentary switch. This was suggested by Chris and Jason. We had to run
a new wire to the light bar to control the amber light. We used a
standard 20a automotive relay. It works quite well.

We put the switch just inside the door. This way someone could open
the door and turn the light off. We had some of our crew try it out.
Everyone is happy.

Thanks again for everyone's help,
--
Email hint - Everything after the @ is spelled backwards.

There are only 10 types of people in the world:
those that understand binary, and
those that don't.