Battery isolator

Should we all be using these? I have never known a starter-solenoid to stick in the "on" position while the battery goes flat and the starter and ring gear get damaged, but it must have happened.

Is the risk of this happening worth the added weight and complexity of an isolator switch ? And would you even know the solenoid was stuck on over the noise of the engine?

If you were to do something about the risk, one way would be to put a second solenoid in series with the first I guess. The odds against them both sticking "on" at the same time would be very small.

Personally, I'm inclined to do nothing on the grounds that the engine should keep running so there is little risk of an engine failure during flight.

Any comments or experience?

... Bruce

A battery isolator would, I guess, should prevent any slow drain of the battery while the aircraft is stored between flights. Most people have them on boats except if the boat is moored and you need some current going to anti-electrolytic corrosion devices - not an issue with Aircraft!

On a risk management / probability basis I doubt the risk is one that needs to be managed - but I'm no expert. Be interesting to see if anyone has experience with isolators on aircraft.

I have an isolator as my key whith a push button for start. I would've thought there would have been quiet a few 19 reg with them.

You could wire an LED/12vdc indicator to the starter motor side of the start contactor/solenoid.. some units have an extra faston terminal for that reason.

If the solenoid remains closed after the start button/key is released, the LED remains illuminated. Thus warning the operator the starter still has power applied to it.

I have a master solenoid that supplies battery +ve power to the starter solenoid via a 4AWG cable, so when the Batt (Master solenoid) s/w is off, no power to starter or circuits anywhere.

I don't have an indicator for the starter solenoid, but the wiring is in place if I want to hook one in, haven't bothered so far as I think its low risk.

My Foxbat came standard with one. Sits on the bottom of the pilots seat (easy to reach) and has a red removable plastic key.

It isolates the earth/negative wire. I think it's a great idea and also acts as a security measure.

Similar to this one below.

All competition cars must have one within the driver's reach by the rules and many racing classes also must have one on the exterior of the car for a Marshal to switch the power off for the simple reason of electric fuel pumps can be turned off immediately in the event of an accident.

We had an incident with our glider tug - Cessna- which highlights the possible serious outcomes of a starter malfunction.

The starter jammed engaged. Nothing obvious happened on the takeoff run. The aircraft took off normally but at about the end of the strip, a burning smell filled the cockpit. Instrument chech looked normal except for high battery voltage. Then the cockpit filled with acrid smoke.

What happened was the starter, When run at speed was generating uncontrolled power. The risk was of cockpit fire.

I'm glad that my Lightwing has a battery isolator.

Note that an turning off the start solenoid source may not save you from this scenario.

Peter

indeed, isolating the battery from the rest of the system in the event of a stuck starter (where the motor is running!) will likely generate dead avionics/radios almost immediately. The battery in effect acts as a regulator. Its destructive to the battery (boils off electrolyte), but not as destructive as would be the case if it were removed from circuit.

Andy

My Foxbat came standard with one. Sits on the bottom of the pilots seat (easy to reach) and has a red removable plastic key.It isolates the earth/negative wire. I think it's a great idea and also acts as a security measure.

Similar to this one below.

 

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This topic has been discussed before, but I can't seem to find the thread(s). I installed an automatic battery isolator which disconnects the earth terminal on heavy landings or prangs. A lever near my right knee allows me to control it manually. It's part of my pre-start checklist and a useful bit of safety.

I'd suggest Bob Nucholls book 'The Aero Electric Connection' & the Advisory Circular "FAA AC 43.13-1B" (Acceptable Methods, Technique & Practices) should be mandatory reading - it sure could stop a lot of misinformation/misconceptions out there. For those who won't, or don't want to spend the money on items like Battery Isolators (which should be mounted within 150mm of battery) I'll ask this question --

Why do you have a fuel Tap ?

What are the 2 main sources of fire in an aircraft ? Answer -- Fuel & Electricity (battery). Most have a Fuel Tap (I hope) so why not have a tap (Isolator) for the battery, it's standard practice in GA aircraft & makes good sense IMO. Some RA Aus aircraft manufacturers seem the think that what is good design practice elsewhere doesn't apply to them so they cut costs by not including, what is considered essential equipment by others, in the design of theirs.

Another argument for a Battery Isolator is what happens if your Starter switch/solenoid (without battery isolator) stays stuck on ? You'd have to sit there watching the propellor turning until the battery runs flat - not a good look I have seen 2 homebuilt aircraft set up to do just that & they were 'certified' 101.28 types.

Jake J

My post above should not be read as being for or against, merely stating that in the case specified above mine such an isolator would do nothing. The solution of course is to turn off the engine.....if at all possible.

Andy

We had an incident with our glider tug - Cessna- which highlights the possible serious outcomes of a starter malfunction.The starter jammed engaged. Nothing obvious happened on the takeoff run. The aircraft took off normally but at about the end of the strip, a burning smell filled the cockpit. Instrument chech looked normal except for high battery voltage. Then the cockpit filled with acrid smoke.

What happened was the starter, When run at speed was generating uncontrolled power. The risk was of cockpit fire.

 

I'm glad that my Lightwing has a battery isolator.

 

Note that an turning off the start solenoid source may not save you from this scenario.

 

Peter

Thank Christ they don't make aeroplanes.

Anyhow back to aeroplanes.

Lightwings have them standard..............

What, pump up seats?

Clear Prop has ordered 10 of these to hold in stock...price will be around $14.95

Should we all be using these? I have never known a starter-solenoid to stick in the "on" position while the battery goes flat and the starter and ring gear get damaged, but it must have happened.Is the risk of this happening worth the added weight and complexity of an isolator switch ? And would you even know the solenoid was stuck on over the noise of the engine?

If you were to do something about the risk, one way would be to put a second solenoid in series with the first I guess. The odds against them both sticking "on" at the same time would be very small.

 

Personally, I'm inclined to do nothing on the grounds that the engine should keep running so there is little risk of an engine failure during flight.

 

Any comments or experience?

 

... Bruce

Dafydd, how does the current limiter fuse work? Suppose the stuck starter just continued to draw 149 amps?

Also, I'm learning (I think) that the starter motor being driven by the running engine can act as a generator and try to charge the battery at say 149 amps.

But I take the point about not knowing its happening.. its late in the day when you smell smoke.

... Bruce

Clear Prop has ordered 10 of these to hold in stock...price will be around $14.95[ATTACH=full]31662[/ATTACH]

They can be replaced with aluminium nuts. You can get these as nyloc too which adds some security to the risk of them coming loose.

Conductive grease should be used on alu nuts/copper stud as the two softer metals can bind.

The limiter rating needs to be less than the current rating of the starter leads (look up FAA AC 43.13-1 Chapter 11 for the current ratings). If you look at the copper cross-section of a 150 amp limiter, it's a lot smaller than any starter cable - less than 10%. The impact current when the starter contactor first closes is several hundred amps, but it only lasts for a fraction of a second, which the limiter can handle. I don't know whether it will protect the starter motor in all circumstances, but it will prevent the starter cable from setting fire to the aircraft. The trick is to find the smallest limiter that can withstand the normal starter usage. In my case, naturally I've never had another problem since I started using them, so I don't have a series of experiences to draw on.

The only sign of the problem in the Cherokee whilst my wife was flying, was that the fuel quantity indicators etc all went to zero. It wasn't until after they landed that the burned small from the battery box became evident. The whole exercise cost over $2000 (new starter, new ring gear), all for the sake of a lousy $15 starter contactor.

Battery isolators also add some small degree of security. Remove the red key and the engine can't start...another little thing that a thief will have to overcome

My Foxbat came standard with one. Sits on the bottom of the pilots seat (easy to reach) and has a red removable plastic key.It isolates the earth/negative wire. I think it's a great idea and also acts as a security measure.

Similar to this one below.

 

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I have the exact some one in my Savannah...about 12 bucks at Jaycar

here you go...under the front of the pax seat

I have the exact some one in my Savannah...about 12 bucks at Jaycar

well when i got mine 2 years or so ago i paid about that...i thought it was pretty cheap....oh and i have a trade card too so it would have been cheaper...so your probably right about the current price

The limiter rating needs to be less than the current rating of the starter leads (look up FAA AC 43.13-1 Chapter 11 for the current ratings). If you look at the copper cross-section of a 150 amp limiter, it's a lot smaller than any starter cable - less than 10%. The impact current when the starter contactor first closes is several hundred amps, but it only lasts for a fraction of a second, which the limiter can handle. I don't know whether it will protect the starter motor in all circumstances, but it will prevent the starter cable from setting fire to the aircraft. The trick is to find the smallest limiter that can withstand the normal starter usage. In my case, naturally I've never had another problem since I started using them, so I don't have a series of experiences to draw on.The only sign of the problem in the Cherokee whilst my wife was flying, was that the fuel quantity indicators etc all went to zero. It wasn't until after they landed that the burned small from the battery box became evident. The whole exercise cost over $2000 (new starter, new ring gear), all for the sake of a lousy $15 starter contactor.

So why not just use the Battery Solenoid switch which then can cut power to the Starter as is possible in a LOT of aircraft ??

Jake J