Finding a power source when motor is run

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overworked

Copper - Posts: 133

Joined: November 09, 2004

Location: Australia

Posted: November 10, 2004 at 5:32 AM / IP Logged

I need to find a power source that will give me 12 volts only when the motor is running, I thought of using one of the ignition lights using a relay set for NO anyone got a better idea?

Asmodeus

Silver - Posts: 393

Joined: September 02, 2004

Location: United States

Posted: November 10, 2004 at 9:21 AM / IP Logged

There is are plenty of keyon keyoff power wires running through a car....All you have to have is a test light or a Multi Meter to find them....Turn the key to the ACC position and find a hot wire then turn the key off and see if the same wire has 12v on it with key off ..if not you have a switched power supply...

Finding a power source when motor is run -- posted image.

Making the World A Louder Place

overworked

Copper - Posts: 133

Joined: November 09, 2004

Location: Australia

Posted: November 11, 2004 at 2:01 AM / IP Logged

Yeah not quite what I was after, I need power only when the motor is running so if the Key is "ON" but the motor isn't running then there is no power but if the motor is running there is power, otherwise I would just find a hot innition wire and use that,

What it is being used for is this, My company is doing a fleet install for a mobile forklift repair comp and they need to be able to draw 12 volts at 110amps to supply power to the electric forklifts, now the owner is saying that his drivers are all halfwits and with the old system the drivers would do it without the car running and drain the battery in a matter of minutes, so if the charging line was only hot whilst the motor was running then there would be a constant power source from the altenator albeit not 110 amps but it would at least stop them from draining the battery unless they had it hooked up for a long period of time.

In case you were wondering, yes they do go through a lot of batteries and regulators. Thanks Guys

From another bloody Newbie!

dxav

Silver - Posts: 314

Joined: September 11, 2002

Location: United States

Posted: November 12, 2004 at 8:24 AM / IP Logged

How did you make out on this one, overworked?

I was thinking about they system you have explained, and it seems to be quite difficult.

Since the battery supplies voltage constantly, whether the motor is on or not is inconsequential. You have 12VDC on the terminals if it is hooked up or out of the car.

They thing that bothers me is that is you would need a sense line from the actual motor to a input on the car's computer. This would have to be completely seperate from the battery or charging system, though. And since the motor is not electronic (just electronically controlled, perhaps), this would be hard to accomplish.

One thing you could consider is monitor a motor function separately (like RPMs for instance). If a line can sense this 'signal', a second isolated battery could be electronically 'turned on'. It would be easy to sense an analog input with only a bit of electronics.

Just a thought..... I am interested in seeing what others have to say.

Unless I am totally wrong on this one, don't really know much about mechanical things.

DXAV

overworked

Copper - Posts: 133

Joined: November 09, 2004

Location: Australia

Posted: November 12, 2004 at 8:38 AM / IP Logged

Geez dxav that sound more difficult then my plan!

1) Hook relay to ignition light to switch relay ON when light goes off(i.e. Motor is running)

2)The relay then in turns activates a solenoid linked directly to the battery suppling power down the lines.

3)when ignition is switched, relay is thrown off killing power to the solenoid causing the solenoid to release thus stopping the flow of power.

Any ideas? or have I pretty much got it sorted or am I just a sparky butcher?

dxav

Silver - Posts: 314

Joined: September 11, 2002

Location: United States

Posted: November 12, 2004 at 12:35 PM / IP Logged

Yes, I see where you are coming from. I guess I was overthinking what you asked. I figured that there is no voltage coming FROM the engine at anytime.

A light is being supplied from the battery, so I see how that can work.

Not sure on the solenoid portion of the project.

Have you gotten anything working yet?

DXAV

bdl666

Silver - Posts: 330

Joined: December 31, 2002

Location: United States

Posted: November 12, 2004 at 2:54 PM / IP Logged

Depending on the car there should be a wire on the alternator that only shows 12volts when the motor is running and the alternator is doing it's thing. I had to find this wire when installing a cheap no name remote starter on a 2003 Corolla, the rs didn't have a tach sense wire and it wouldn't work without the Alternator sense(weird, I know).

dxav

Silver - Posts: 314

Joined: September 11, 2002

Location: United States

Posted: November 12, 2004 at 5:12 PM / IP Logged

Yeah, that is kinda what I meant. Thanks bdl.

DXAV

overworked

Copper - Posts: 133

Joined: November 09, 2004

Location: Australia

Posted: November 12, 2004 at 8:31 PM / IP Logged

Yeah I got it working the only problem I have is finding a solenoid big enough to handle the current draw, I tried using a starter solenoid but it just burnt out

geepherder

Platinum - Posts: 3,668

This member consistently provides reliable information

Joined: October 27, 2003

Posted: November 15, 2004 at 8:55 PM / IP Logged

Here:

https://www.the12volt.com/installbay/forum_posts.asp?tid=25129&KW=ford+starter+solenoid

My ex once told me I have a perfect face for radio.

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