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Battery Isolation Switch

Tcheairs

Well Known Member
I would like to mount a battery isolation switch on the firewall of my RV7A. Has anyone done this safely? Photos? I should be able to reach it through the oil access door on the upper cowling..

Thanks
 
I would like to mount a battery isolation switch on the firewall of my RV7A. Has anyone done this safely? Photos? I should be able to reach it through the oil access door on the upper cowling..

Thanks

Use welding cable and place the switch in the ground cable.
 
I have not done this, but it seems that the marine people have a lot of good products.
 
the marine people have a lot of good products
… and the truck and racing car industry… search for Automotive Battery Isolator Switch, or Kill Switch.
 
I'm surprised no one asked "why"..There seems to be a slight "leak" somewhere in my system even with the battery master off and I have been unable to find it with pulling circuit breakers. All large boats have battery isolation switches and it's for that very reason.

The only (quality) isolation switches I have found online are designed to be placed on the + side. My positive cable is connected to a solenoid and the only thing that would isolate the battery completely would be shutoff at the + cable. I'm on my 3rd battery for the past 12 months.

I realize that this presents a significant safety issue and I had hoped someone had come up with a mount. It's not rocket science and I should be able to come up with something with lots of insulation on the terminals.

Thanks to all
 
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I'm surprised no one asked "why"..There seems to be a slight "leak" somewhere in my system even with the battery master off and I have been unable to find it with pulling circuit breakers. All large boats have battery isolation switches and it's for that very reason.

The only (quality) isolation switches I have found online are designed to be placed on the + side. My positive cable is connected to a solenoid and the only thing that would isolate the battery completely would be shutoff at the + cable. I'm on my 3rd battery for the past 12 months.

I realize that this presents a significant safety issue and I had hoped someone had come up with a mount. It's not rocket science and I should be able to come up with something with lots of insulation on the terminals.

Thanks to all

I just installed a battery switch in the boat I'm finishing and am a bit confused about your comment about switches being designed for the + cable. The switches I've used are just two terminals, the switch doesn't know which side of the battery is connected. If you put the switch between the battery ground terminal and the airframe the battery is isolated and no drain can occur. I put the boat switch on the ground side.
 
Might be easier to just find the source of the battery drain and fix it.
 
I just installed a battery switch in the boat I'm finishing and am a bit confused about your comment about switches being designed for the + cable. The switches I've used are just two terminals, the switch doesn't know which side of the battery is connected. If you put the switch between the battery ground terminal and the airframe the battery is isolated and no drain can occur. I put the boat switch on the ground side.

What Sam said. The switch doesn't know or care about polarity. The primary reason it is marked that way is for idiots out there in the wild that have no clue how to install, they see the markings and follow the directions. It cuts down on calls to the company help line.
 
I'm surprised no one asked "why"..There seems to be a slight "leak" somewhere in my system even with the battery master off and I have been unable to find it with pulling circuit breakers. All large boats have battery isolation switches and it's for that very reason.

The only (quality) isolation switches I have found online are designed to be placed on the + side. My positive cable is connected to a solenoid and the only thing that would isolate the battery completely would be shutoff at the + cable. I'm on my 3rd battery for the past 12 months.

Thanks to all

I just figured you looking to secure your aircraft.

Unless you have electronic ignition that needs to be connected 100% of the time to the battery, there should be no draw at all with the master off.

Do like Walt suggested, fix the problem. Don't just Band Aid it.
 
Checking for parasitic loads on battery.

With the battery contactor shut off, disconnect the cable from the negative terminal of the battery. Measure the voltage between the now disconnected negative battery cable and the negative battery post. If the voltage is zero, then there is no parasitic load or leak. This can be confirmed by repeating the test with the meter set to measure current. To prevent ammeter damage, start with the meter set at a higher current scale and work your way down to measuring milliamps. If there is leak, knowing the milliamps will give a clue as to what the culprit could be.
 
I think having a KILL switch is a great idea.
Now, that said I do not have one on my RV. But, when I went to Houston from Washington with my high cube work van full of tools (van and tools about $50,000.00) to work on her house for 8 weeks I put one in the engine compartment so nobody could easily steal my van.
Simple to install and has a separate plug like plastic key to re-engage the power.
I used it for an anti-theft device on that truck, But, have used them on our race cars in the past. Mounted on the dash for fast access and guaranteed power cutoff.
Art
 
I think having a KILL switch is a great idea.
Now, that said I do not have one on my RV. But, when I went to Houston from Washington with my high cube work van full of tools (van and tools about $50,000.00) to work on her house for 8 weeks I put one in the engine compartment so nobody could easily steal my van.
Simple to install and has a separate plug like plastic key to re-engage the power.
I used it for an anti-theft device on that truck, But, have used them on our race cars in the past. Mounted on the dash for fast access and guaranteed power cutoff.
Art

Thread drift starting... :)

Doesn't that just make your kill switch a SPF item?
 
Whether it's simpler or not, it's still yet another SPF in the system.

I'm sorry, but I find the idea of "hidden kill switches" silly.
 
As with any electric dependent aircraft, required power will bypass everything
and connect direct to the battery bypassing any failure points.
 
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I'm going to try the voltage leak check again through a negative ground with my multimeter and I will also check for amperage leak. I think I may have had my meter set wrong when I tried the test before..
 
Battery leak found

Dan, confirmed the leak today. Multimeter in amps mode connected between grounds. Found a 07.91 leak in the mili amp mode. Pulled cbs and the leak is on the autopilot servo cd. All the other cbs checked no leak. I'm sending you an email with a photo of the reading because I haven't yet figured out how to post photos on this forum...

Well..here's a link to my Google Drive photo which is the best that i can do.

https://drive.google.com/file/d/1eHu4QcrPY9mj-OMu2u-ImAkZChdnR33v/view?usp=sharing
 
Glad you found it

Why.... was my first thought when I saw your post but I didn't want to mess up your thread and drift off to some pro and con argument on kill switches.
Now that you are on to a solution I am sure you'll put that kill switch idea out of your mind.
There are places for kill switches, I don't think airplanes are one of them, IMHO.
 
So, what are your suggestions for trouble shooting the leak in the autopilot system? For me..kill switch until I can get it to Vic Syracuse's shop for the annual inspection in a couple of months.

Of course I could use the circuit breaker as a switch in the meantime...(a definite no no)

I am a non builder, non mechanic, and a non automotive electrician
 
How is the electrical current getting past the master battery contactor?
Is there an E-Bus? If so, do you normally shut off the E-Bus along with the master switch?
Do you have a wiring diagram for your aircraft?
 
Drain

So, what are your suggestions for trouble shooting the leak in the autopilot system? For me..kill switch until I can get it to Vic Syracuse's shop for the annual inspection in a couple of months.

Of course I could use the circuit breaker as a switch in the meantime...(a definite no no)

I am a non builder, non mechanic, and a non automotive electrician

Remove the negative terminal. Remove the positive terminal. Connect a voltmeter in amps configuration set to the maximum. One lead goes to the positive battery terminal. The other to the positive lead. Voltmeter is in series. Make sure the leads can't touch ground or other wires. Reconnect the ground side. Read the voltmeter. Change scale down as needed till you read amps or milliamps. Write it down. Have someone inside pull breakers one at a time till the voltmeter shows zero. That's the drain circuit. Autopilot? Hopefully it's one device. If not, disconnect devices on that curcuit till the meter reads zero. Disconnect ground. Disconnect the amp meter. Reconnect positive. Reconnect ground.
Probably not the right way but that's how I would find it.
 
Semantics

A kill switch was that thing on a motorcycle that stops the engine. The lights, etc, would still work on my old bikes even when I hit the kill switch to coast into the driveway too late at night.....

A battery cut-off switch is a device for disconnecting the battery from the vehicle voltage bus. On an aircraft, unless the ignition is completely battery dependent, a battery cut-off switch has no impact on the continued operation of the engine.
 
Dan, confirmed the leak today. Multimeter in amps mode connected between grounds. Found a 07.91 leak in the mili amp mode. Pulled cbs and the leak is on the autopilot servo cd. /url]

And this was done with the Master OFF??

"How is the electrical current getting past the master battery contactor?
Is there an E-Bus? If so, do you normally shut off the E-Bus along with the master switch?
Do you have a wiring diagram for your aircraft?".... I think Joe hit on it.
 
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Dan, confirmed the leak today. Multimeter in amps mode connected between grounds. Found a 07.91 leak in the mili amp mode.
Pulled cbs and the leak is on the autopilot servo cd. All the other cbs checked no leak. ..

Looks like you are reading the ground strap from the engine. Not good.

What is the other end of the cable with the white boot connected to??

You may not be reading your actual loss. You need to measure from
the firewall ground to the battery (-) post without any other wires
connected to it when you are taking the reading. Look for any extra
wires connected to the (+) post or the hot side of the solenoid, and
follow it.
meter.PNG
 
Yes, I did measure between the negative battery lead to the ground strap of the engine. I will check again using the firewall ground..However, ground is ground is it not? I am measuring current flow through the battery either way. I understand that current flow can be measured either on the positive side OR the negative side of the battery. I just don't like the possibility making SPARKS!

I do have a backup 12v Odyssey battery installed and it does supply the E bus through a switch on the panel. It's charge from the alternator can also be controlled via a switch. I have had no voltage loss issues on the backup battery.

The only leak I have is with the autopilot servo cb "in". I have pulled and reset all 24 circuit breakers and that is the only cb that indicates a leak. When I pull the autopilot servo cb, the multi meter indicates 0.00 (no leak)

As I see it, my choices are:

1. Take the plane to an electrical system guru immediately. Yes, I do have a schematic

2. Install a temporary battery shutoff on the ground side until the plane goes in for annual next month.

3. Use the autopilot servo circuit breaker as a switch until I can figure what the h...is going on in that circuit.
 
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Choice #3

Thomas,

In some circles, using circuit breakers for switches is a no no.

I'm retired from a major airline that had crews pull over a dozen circuit breakers if the airplane was going to overnight. They got reset by the first crew in the morning.

I see no downside to pulling the circuit breaker until your upcoming condition inspection with Vic. Rather than resetting it for every flight, I would only reset it when the autopilot was desired.
 
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Yes, I did measure between the negative battery lead to the ground strap of the engine. I will check again using the firewall ground..However, ground is ground is it not? I am measuring current flow through the battery either way. I understand that current flow can be measured either on the positive side OR the negative side of the battery. I just don't like the possibility making SPARKS!

I do have a backup 12v Odyssey battery installed and it does supply the E bus through a switch on the panel. It's charge from the alternator can also be controlled via a switch. I have had no voltage loss issues on the backup battery.

The only leak I have is with the autopilot servo cb "in". I have pulled and reset all 24 circuit breakers and that is the only cb that indicates a leak. When I pull the autopilot servo cb, the multi meter indicates 0.00 (no leak)

As I see it, my choices are:

1. Take the plane to an electrical system guru immediately. Yes, I do have a schematic

2. Install a temporary battery shutoff on the ground side until the plane goes in for annual next month.

3. Use the autopilot servo circuit breaker as a switch until I can figure what the h...is going on in that circuit.

The engine ground strap is to ground the engine to the firewall / (-) battery. The way you are testing your leak is to the engine that is not properly grounded because you disconnected it from the grounding source (unless there is another strap connecting the engine to the firewall) and is reading your leak through control cables connected to the engine.... throttle, mixture, carb heat.

Best to pull the circuit breaker when not using the A/P until the gremlin is found.
 
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