Dashcam off delay using Panasonic LT4H timer and Azatrax relay

D

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I've been thinking about setting up a timer relays for my cameras as a way to leave them running when the car is left in a parking lot while precluding forgetting them on overnight and draining my car battery. After a lot of research and learning about relays, I figured out that the best way to accomplish this is with an off delay relay which can connect devices to battery power when energized by ignition power, and wait a set period of time before turning off battery power.

After a lot more research I discovered that there are digital relays referred to simply as "timers" that do this but also allow adjustment with buttons. The one unit I could find that could possibly hold up to the temperatures in a vehicle was the Panasonic LT4H-DC24VS which is rated for 55 Celsius (131 Fahrenheit) and it happens that it seems to be the easiest to control as it has a rocker button for each digit. It also has several modes of operation unlike a simple off delay relay. The 24V means it can handle up to 24V DC, and they also make AC versions. The S refers to screw terminals, as opposed to other versions made to fit into special relay sockets. http://www.newark.com/panasonic-electric-works/lt4h-dc24vs/timer-multifunction-12-24vdc/dp/67C7777

The next thing I learned was that the LT4H isn't like a typical automotive relay, it is triggered using a simple switch. So if you were to try to trigger it using the car ignition power, it could be damaged.

I figured that would be a simple obstacle to surmount but it turns out relays are more complicated than I thought. They require diodes and resistors to protect the control circuit because upon switching off the physical motion generates a current in the coil which goes backwards and can be very high voltage! Additionally, automotive relays are bulky and require sockets. I found one relay that is compact, cheap, has built in rectifier diodes to protect the vehicle, and has simple screw terminals--- a model railroad relay made by Azatrax https://www.azatrax.com/track-power-relay.html

The Azatrax relay is energized by the ignition power tapped from the fuse box, which acts as a "start" switch to control the LT4H. The LT4H has tiny dip switches that let you choose between several modes of operation. The one I selected connects the "common" and "normally open" terminals as soon as the relay's "start" switch is triggered. Common is getting power from the a constant power fuse tap. When the Azatrax relay loses power, that opens the "start" switch and the LT4H starts counting down.

Everything is housed in a cubby compartment built in to the fusebox door on my VW Golf. The wires are all gathered with a European terminal block and connected to the fuse box and output wires with a JST SM connector.

It works great and is easy to adjust. If I need to turn everything off immediately, I just press the "reset" button on the LT4H

P1030556-20180803-Edit66.jpg P1030563-20180803-2.jpg P1030569-20180804-2.jpg P1030566-20180804-2.jpg
 

WeedeaterDM

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I do like the how much of a variable control you get with that setup. I haven't looked at the specs, but I would venture to guess it can handle more of an amp load than the Power Magic Pro. Are you planning on adding a low voltage cut off to your project in the future as well? Tinkering is so much fun, even if it does cost more than buying something that does the same.
 
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I do like the how much of a variable control you get with that setup. I haven't looked at the specs, but I would venture to guess it can handle more of an amp load than the Power Magic Pro. Are you planning on adding a low voltage cut off to your project in the future as well? Tinkering is so much fun, even if it does cost more than buying something that does the same.

It can handle 5 amps so not a huge amount. If I get a Blackvue camera with the Power Magic Pro included then I'll have a voltage cutoff, otherwise I'm not worried about it
 

Mikk36

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And all this could theoretically be replaced by a simple low-powered chip (think something compatible with arduino or similar, for example) and a mosfet driver.
Granted, you wouldn't be able to change the timer settings on the fly, but then again, you'd have far more control using code.
 
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And all this could theoretically be replaced by a simple low-powered chip (think something compatible with arduino or similar, for example) and a mosfet driver.
Granted, you wouldn't be able to change the timer settings on the fly, but then again, you'd have far more control using code.

The challenge with a microchip custom programmed would be reliability and if you set it up with a screen, buttons, etc you end up spending much more
 

Mikk36

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Indeed, which is why I didn't say that You should have gone that route, but that it could have been an option for those not wishing to deal with all these discrete units.
 
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Indeed, which is why I didn't say that You should have gone that route, but that it could have been an option for those not wishing to deal with all these discrete units.

I think you'd need more discreet units though, because you'd have to use a relay to send a signal to the microchip, and you'd have to use another relay to switch the power. But you could get more complex, for example have a GPS system that knows to reduce the delay time to a few minutes when you stop at your home or your work, but if you stop anywhere else keep running for a few hours
 
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