Power question

[+benjamin921]

I think I know the answer to this question (no) but I an going to ask anyway.

 

Someone has asked me if there is a way to have a GPS unit power on when the power to a vehicle gets turned on.

 

I.E. In a fire truck when you want to start the truck up you must first turn the batteries on.

Is there a way to have the GPS unit power up after the batteries are turned on and with out having to push the power button on the GPS unit?

 

My answer is no but on the slim chance I had to ask.

Sounds confusing but I need to know for sure.

[+Prime Suspect]

For handheld units, probably not.

 

[mcb]

I know someone figured out how to do it with a Garmin III+ and maybe a few other Garmin units. They had to take the units apart and a few simple componets to make some new connections to get it to work. Its definitly beyond my limited electronic skills but if you are really interested go to google and search the sci.geo.satellite-nav newsgroup. I am pretty sure I read it there. Just a sec......

 

Yep!

 

http://groups.google.com/groups?hl=en&q=turn+on+gps+power+auto+mod&btnG=Google+Search

 

Good luck if you try it. I would be too scared to do it.

 

Later

mcb

 

GPS-Yote

[m2fun]

The current Garmin V powers off in 20 seconds after the ac adapter power is turned off. The older units II and III (I think) remained on after the ac power ended. A buddy direct wired a II in his Land Rover that was powered when the vehicle was started.

 

Garmin does offer a direct wiring cable for ac power. Without making any modifications to the GPS V unit programming you would need the unit to be on at all times. There may be a way to modify the programming of the GPS V to bypass the 'on' button and start when ac power was received.

 

I have not tried the Etrex AC power to compare to a GPS V.

[+park2]

These things draw so little power, I just let mine run for days at a time. My G12 drew like 60mA which would kill an average truck battery in about 2 months.

 

Is there any circuits that stay live so you can just leave it on or might it sit too long?

[+GOT GPS?]

Neat idea on vehicles with power door locks, is to wire that to a circuit that sends a momentary signal to the GPS's Power button circuit, to cause the unit to power on.

 

The GPS has an internal circuit that when the power button is pressed, it causes a power-on sequence. From the Key activated power door locks, you would have a wire going to the GPS, that is tied to the GPS via a relay that mimics a power button keypress. This means voiding the warrenty, if you still had one.

 

Could somebody come up with a schematic diagram for something like this??

 

My home page about GPS units and information

[+Desert_Warrior]

What you want to do is quite simple really. It could get a little more complicated, depending on your GPS. My E-Trex needs about a 2 second push on the ON-button to make it fire up. This is probably a longer duration than you will have using the door-lock command. I would do it with a 2 pole latching relay, and an electrolytic cap for the holding voltage. I would set the cap to charge instantly as the circuit energized, then let the cap discharge through the resistance of the relay coil slowly. The length of the contact timing would be set by the resistance of the coil and the capacity of the cap. Note, a 12VDC relay needs only 7-8 VDC to hold, but the full 12 VDC to pull in, so this would be a help too.

 

If you only need a momentary contact, a single pole single throw relay will do it fine.

 

Mike.

[+Desert_Warrior]

Originally posted by park2:

These things draw so little power, I just let mine run for days at a time. My G12 drew like 60mA which would kill an average truck battery in about 2 months.

 

This is because the average car/truck battery is designed for a huge power surge, then an immediate recharge. The average lead-acid car battery is really only usable for about 10-% of its capacity before it sustains damage. OTOH, a deep-cycle battery is much more suited for the long-slow discharge you are talking about. But... they are not designed for that sudden surge of starting power.

 

Your G-12 at 60mA is good. My E-Trex is 150mA running normal, and 220mA with the back-light on.

 

Anyone wants a disertation on battery capacity and current drain... ask. Otherwise I will not bore the group here.

 

Mike.

[+Renegade Knight]

quote:

---

Originally posted by KD9KC:

Originally posted by park2:

These things draw so little power, I just let mine run for days at a time. My G12 drew like 60mA which would kill an average truck battery in about 2 months.

 

This is because the average car/truck battery is designed for a huge power surge, then an immediate recharge. The average lead-acid car battery is really only usable for about 10-% of its capacity before it sustains damage. OTOH, a deep-cycle battery is much more suited for the long-slow discharge you are talking about. But... they are not designed for that sudden surge of starting power.

 

Your G-12 at 60mA is good. My E-Trex is 150mA running normal, and 220mA with the back-light on.

 

Anyone wants a disertation on battery capacity and current drain... ask. Otherwise I will not bore the group here.

 

Mike.

---

 

I agree the simplest solution is to leave it on and wire it direct to your battery. It wild even be relativly cheap to add a second 'assorey' battery to run the GPS and save your main battery for starting.

[+benjamin921]

Some really good answers and comments, thanks.

 

If there is a hard wire to it, lets say a II+, will the unit turn on as soon as there is power to it with out having to push the power button?