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Author Topic: Low Voltage Disconnect  (Read 4483 times)
K0JEG
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« on: May 25, 2012, 06:09:43 AM »

In my old car, I had my TM-d700 mounted under the dash, with a puck GPS connected to the battery via a lighter adapter with some powerpoles on the cable. It was fairly easy to remember to unplug the GPS when I was away from the car.

In my new car, I mounted the radio unit in the trunk, along with the same setup for the GPS puck. However, out of site means out of mind, and I have already left the GPS running overnight. Since I don't run this vehicle every day it will eventually kill the battery. The way I've run the power cables doesn't make it simple or easy to put a switch on the dash (and I like the look of a clean dashboard, at least for now).

So I was looking at getting a low voltage disconnect. The only ones I've seen are from Powerwerx, and look fairly expensive. Anyone know of a better option?
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W8JX
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« Reply #1 on: May 25, 2012, 06:28:32 AM »

How about simply mounting a 17ah or bigger gelcel in trunk and using a 12 volt relay that has its coil feed for ign accessory circuit.  When car is on it charges battery, when it is off the battery is isolated. This would safely run GPS for many days if you forget to turn it off and would be pretty transparent. You could also just simply use a relay as above between rig and battery or feed it off a switchable ign accessory circuit.
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KF5JOT
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« Reply #2 on: May 25, 2012, 07:00:27 AM »

Why not grab a switched power wire to power the GPS instead of going direct? Key on and the GPS will power up. Key off and off it goes.
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W8JX
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« Reply #3 on: May 25, 2012, 12:15:41 PM »

Why not grab a switched power wire to power the GPS instead of going direct? Key on and the GPS will power up. Key off and off it goes.

I agree but I thought with it switching a coil on relay would let him still feed it directly from battery through relay.
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K0JEG
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« Reply #4 on: May 26, 2012, 07:17:30 AM »

Good ideas, all. But I was hoping to not have to run more wire if I could help it. I'll poke around the stereo amp (on the other wheel well) and see if there's anything I can tap.
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KB3HG
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« Reply #5 on: May 26, 2012, 09:52:00 AM »

Another approach maybe? The cigarette lighter does it stop supplying power when the car is turned off? If it does have power lost star a timer that can switch power of to the GPS or Activate a timer to cut power. possibly a 555 type timer circuit construct timer for some preset time that is convenient for you say 15,20 30 minutes what ever you want. That way power is switched off to selected devices.
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K1CJS
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« Reply #6 on: May 27, 2012, 05:34:27 AM »

Good ideas, all. But I was hoping to not have to run more wire if I could help it. I'll poke around the stereo amp (on the other wheel well) and see if there's anything I can tap.

All that will get you is either a constant power supply even with the key off, or a power supply that is only on when the stereo is switched on.

The answer is simple.  Get a twelve volt constant duty relay and connect its contacts into the power line you have already.  Get the power to energise it from wiring that is on only when the key is in the run or acc position.  That way, the power to the rear radio equipment will only be available when you want it to be.
« Last Edit: May 27, 2012, 08:31:09 AM by K1CJS » Logged
KJ4RQV
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« Reply #7 on: May 27, 2012, 07:10:28 AM »

I don't know if this would work for you but I run my portable rig with a 12v LiFePo through a MFJ battery booster. When the LiPo gets to 10 volts it shuts off the current from the battery and I know to re-charge and prevents damage to the battery. The cut off voltage point can be adjusted.

Maybe something like this would help to avoid a completely discharged battery.

This unit also keeps the output at a steady 14 volts to the radio.
YMMV
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K0BG
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« Reply #8 on: May 28, 2012, 05:34:21 AM »

Here's the best answer: http://www.westmountainradio.com/product_info.php?products_id=apo3_pp
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W8JX
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« Reply #9 on: May 28, 2012, 06:01:23 AM »


Not the best solution really. Best solution here is a ignition switched power feed.
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K5LXP
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« Reply #10 on: May 28, 2012, 07:14:19 AM »

OMG, all of this crap for the sake of running a *single* 22ga wire?  A GPS puck draws maybe 75mA.  Run it to switched ignition and be done with it.


Mark K5LXP
Albuquerque, NM
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K1CJS
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« Reply #11 on: May 28, 2012, 07:27:11 AM »

The TM-d700 draws more than 75 ma.
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K0JEG
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« Reply #12 on: May 28, 2012, 08:25:58 AM »

OMG, all of this crap for the sake of running a *single* 22ga wire?  A GPS puck draws maybe 75mA.  Run it to switched ignition and be done with it.

Better yet... OMG, all this crap for the sake of not remembering to shut off the GPS when you park the car. Just use my brain and be done with it!  Cheesy
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M6GOM
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« Reply #13 on: May 28, 2012, 11:59:28 AM »

Better yet... OMG, all this crap for the sake of not remembering to shut off the GPS when you park the car. Just use my brain and be done with it!  Cheesy

(looks fondly at Green Light Labs GPS710)

....I don't need to worry about such things.  Grin
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KE4DRN
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« Reply #14 on: May 30, 2012, 05:03:26 PM »

hi

Tie into the power line that runs to the fm radio.

73 james
« Last Edit: May 31, 2012, 08:41:44 PM by KE4DRN » Logged
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