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Author Topic: Accessory Control Relay  (Read 30049 times)
AA4PB
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« on: September 10, 2013, 09:40:24 AM »

I have an IC706mkIIg in my pick up that is powered directly from the battery. Now that I'm not driving the truck to work every day, I've noticed that the radio, even though off, drains the battery to the point that it won't start after about a week. I have a new battery and the alternator is working correctly. I've started unplugging the power cable from the radio after use so that it doesn't drain the battery.

My solution was to add a 40A automotive relay to control battery power to the radio and powered the relay coil from the vehicle accessory line to ensure that the radio was not powered when the ignition key was removed.

An added benefit turned out to be that when power is removed or applied "cleanly" with the relay, the IC706mkIIg remembers if it was ON or OFF at the time power was removed and returns to that state when power is reapplied. Now if I start the vehicle with the radio ON, it will switch off while the starter is cranking and then turn back on (with all the same settings) as soon as the engine starts. With no power applied to the radio during cranking, it is also protected against possible voltage spikes from the starter motor.

I tested my IC-756PRO and find that it also remembers the ON/OFF state when external DC power is removed.

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K6LCS
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« Reply #1 on: September 10, 2013, 03:11:10 PM »

You might consider one of these ...

http://www.powerwerx.com/batteries-chargers/dc-automotive-timer-lvd-battery-guard.html

It features ...

-User adjustable shut down delay: 2, 15 or 30 minutes and 1, 2, 3, 4, 5, 8 12 hours.
-Rugged, water proof construction. Easily installed in engine compartments or high vibration environments.
-Low voltage disconnect: Automatically shuts off at selectable LVD value.
-Super low standby current draw of 4 mAh will not drain your battery.
-Smart! No ignition wire is required.
-Overvoltage protection: Automatically shuts off at 16V with Auto reset.

Read more: http://www.powerwerx.com/batteries-chargers/dc-automotive-timer-lvd-battery-guard.html#ixzz2eX0gtGd9

Available from ...
HRO-Anaheim
714-533-7373
http://www.hamradio.com

...or directly from Powerwerx.

Clint Bradford K6LCS
« Last Edit: September 10, 2013, 03:31:33 PM by K6LCS » Logged

Clint Bradford, K6LCS
http://www.work-sat.com
AA4PB
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Posts: 13032




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« Reply #2 on: September 10, 2013, 05:24:39 PM »

That would work, but it's $80 vs $4.50 for the relay  Wink
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K5LXP
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« Reply #3 on: September 11, 2013, 03:34:27 AM »

That would work, but it's $80 vs $4.50 for the relay  Wink

November 2012 QST had a time delay DC control relay project/kit article.

Mark K5LXP
Albuquerque, NM
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WX7G
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« Reply #4 on: September 11, 2013, 07:16:32 AM »

AA4PB,
with 168 hours in a week, and the battery probably able to to lose 40 amp-hours of charge and still start the truck, the radio would have to draw 1/4 amp or more when switched OFF.

Does the radio really draw this much current? Have you measured the OFF current?
« Last Edit: September 11, 2013, 07:20:29 AM by WX7G » Logged
K5LXP
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« Reply #5 on: September 11, 2013, 08:05:27 AM »


the radio, even though off, drains the battery to the point that it won't start after about a week.

the radio would have to draw 1/4 amp or more when switched OFF.

This was a topic on the 706 group a while back and I measured mine on the bench.  My 706MkIIG drew less than 5mA when off.  This is many times less than the other parasitic loads in a vehicle, so I wouldn't consider the radio to the the problem unless there's a fault with it.   I've heard of cases where there were faults in the PA that can cause the radio to draw current when off, but any appreciable amount of power would make the radio warm.   A few minutes with a multimeter will tell.

Mark K5LXP
Albuquerque, NM

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AA4PB
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« Reply #6 on: September 11, 2013, 09:27:10 AM »

The constant current draw is only a few milliamps. However, after setting in the garage for about 10 days I came home to find the radio cycling on and off quickly by itself. Since I also have an SGC tuner powered from the radio's tuner connector, the tuner was cycling too. After charging the battery, no more cycling. The radio has always powered itself off when the input voltage reaches about 11.5V. I expect that the switch circuit was cycling as the voltage dropped and that in turn caused the radio plus tuner to draw even more average current. Because the switching issue starts at only 11.5V you can't take that many AH from the battery before you start having problems.

Anyway, removing power when the truck is going to be left for a week or more solved the problem for me. The devices that provide solid-state low voltage sense to cut power are fine but seem like added expense and effort when a simple $4 relay powered from the accessory line will work. This is how we used to install commercial mobile radios years ago.


I haven't look into details of Icom's power switch circuit, but since it remembers whether it was on or off when external power is removed it must be tied into the processor or memory in some way. I see from the schematic that the finals always have power applied to them, even when the radio is off.

I just downloaded a service manual. The power button is simply an input to a processor port. That means that the processor is powered all the time, probably running in sleep mode. That could explain things going "flaky" at low input voltages.
« Last Edit: September 11, 2013, 10:06:46 AM by AA4PB » Logged
K5LXP
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« Reply #7 on: September 11, 2013, 10:07:42 AM »

Because the switching issue starts at only 11.5V you can't take that many AH from the battery before you start having problems.

Only about all of the Ah.  With essentially no loads applied to a lead acid battery, open circuit voltage of 11.5V is "dead".  So either the battery is bad, or something is pulling it down to that point.  As WX7G points out, you'd have to burn through 40Ah or more to discharge a battery to this point.


Quote
The devices that provide solid-state low voltage sense to cut power are fine but seem like added expense and effort

Basically saves the trouble of tapping into a switched ignition circuit.  Have to agree it might not be worth the trouble.  Mine is somewhere in between, with an RC and switching transistor controlling the relay providing a time delay from key on to radio on, and key off to radio off.  Dead bugged it right on the relay body and potted it in silicone.


[/quote] it remembers whether it was on or off when external power is removed it must be tied into the processor or memory in some way.[/quote]

Probably no way to really know for sure which way since it's a custom device.

You bring up a good question about what happens at low input voltage.  But, the battery has to run down to that point for that to happen, so there's still something external to the radio, or a radio fault that's causing this.


Mark K5LXP
Albuquerque, NM

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AA4PB
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« Reply #8 on: September 11, 2013, 10:29:23 AM »

I was lucky. The fuse panel by the door has blank (unused) positions and one of those has switched accessory power on one side. Found it with a multi-meter and simply inserted a wire into the clip.

My radio could have a problem, but it only draws a few mA at 13.8V when off and it works fine otherwise.
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WX7G
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« Reply #9 on: September 11, 2013, 11:22:33 AM »

It sounds like the radio cycling ON/OFF is only a symptom of the battery being discharged by a parasitic load (not the radio) in the vehicle.
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M6GOM
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« Reply #10 on: September 12, 2013, 03:27:02 AM »

The constant current draw is only a few milliamps. However, after setting in the garage for about 10 days I came home to find the radio cycling on and off quickly by itself.

You've got problems elsewhere if the radio is only drawing a few milliamps.

Next time you park the truck up, turn the transceiver off, remove the battery earth terminal and connect a multimeter/ammeter in series on at least a 10A range between the battery earth lead and the battery terminal. It'll tell you how much current is being drawn. If its more than 100mA or so which the alarm will use you've got an issue.

In the past I've known it to be switches for the trunk light so the 5W bulb in the trunk has been constantly on and the owner completely oblivious as like a fridge its always on when you open the trunk but in these cases it wasn't switching off when it was closed.
« Last Edit: September 12, 2013, 03:29:03 AM by M6GOM » Logged
AA4PB
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« Reply #11 on: September 12, 2013, 05:33:30 AM »

Except that if I unplug the radio (or use the external relay) then I don't have the issue. Now it is quite possible that the battery was not fully charged when the truck was parked. At the time I was driving it to work which was only 1 mile away. So, in the morning the engine was started and driven a mile and then the same in the afternoon. Its possible that starting took more capacity than what the alternator could replace during the short drive time. It was also winter time so the battery capacity was likely reduced somewhat by the cold.

Once the voltage got low, the radio started pulsing on and off which took the battery even lower. I never did fully analyze the problem with meters in order to determine the exact mechanism because unplugging the radio solved the problem so I went with that. At any rate, I don't like the radio turning itself on (and off) regardless of the applied voltage or battery condition. The relay provides a positive way to make sure that can't happen.
« Last Edit: September 12, 2013, 05:36:47 AM by AA4PB » Logged
K1CJS
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« Reply #12 on: September 16, 2013, 05:15:22 AM »

The relay idea is fine--for convenience, but a simple on-off toggle switch in the radio/tuner power line would serve the same purpose.  Sometimes the old methods will work just as well--if not better.  73!
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AA4PB
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« Reply #13 on: September 16, 2013, 10:07:07 AM »

I considered a switch but decided it was easier to put the relay in the engine compartment than it was to attempt to mount a switch on the dash and run heavy power wires to it. In addition, there is no way I can forget to turn the relay off unless I leave the keys in the ignition.  Wink
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K1CJS
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« Reply #14 on: September 16, 2013, 10:54:25 AM »

...In addition, there is no way I can forget to turn the relay off unless I leave the keys in the ignition.  Wink

Good point that wasn't considered in making my reply.  73!
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