Battery isolator solenoid- legal requirement in 19 reg aircraft?

[danny_galaga]

Thought I'd asked this before, but couldn't find the thread. As per title, do you legally need one? I have a basic mechanical battery isolator at the moment. If I don't legally require one, I'd rather save the weight and extra complexity. I think when I asked before you guys convinced me about the virtue of a starter solenoid warning light so I know if the starter is still engaged. So I have that and the mechanical battery isolator .

[facthunter]

I like your  MECHANICAL Battery isolator. Solenoids can always stick or weld contacts. I know because I've had it happen and a fire resulted.  Nev

[Thruster88]

I like the mechanical master isolation. Good thing is it can go on the negative side of the battery for complete isolation.  

[RFguy]

Mechanical is good !

On the master breaker  ? For an LSA ? You'd need to consult the ASTM for LSAs

Probably not required because Jabirus have hot wires through the firewall and no isolator and they also have fires.... (should be the subject of an AD but .....) 

or maybe they are required but there isnt a competent body to check this stuff ? 

Danny, you could substitute it for a 200A relay as a master (IE starter runs through it also) , I've posted an affordable , reliable  professional  option a few times. 

 

 

 

 

 

 

 

 

[danny_galaga]

1 hour ago, RFguy said:

Mechanical is good !

On the master breaker  ? For an LSA ? You'd need to consult the ASTM for LSAs

Probably not required because Jabirus have hot wires through the firewall and no isolator and they also have fires.... (should be the subject of an AD but .....) 

or maybe they are required but there isnt a competent body to check this stuff ? 

Danny, you could substitute it for a 200A relay as a master (IE starter runs through it also) , I've posted an affordable , reliable  professional  option a few times. 

 

 

 

 

 

 

 

 

My isolator as it happens is on the negative purely because it was easier to install on that side. For the purpose of this thread solenoid=relay. As a auto sparky we always referred to them as solenoids to differentiate from regular (30amp 70amp etc) relays. 

 

So long as I don't legally need an electrically operated isolation switch of any sort, I'm not going to install one. If it's a legal requirement I will of course.

[facthunter]

They should have more sense than mandate electrical.  Nev

[Blueadventures]

4 hours ago, danny_galaga said:

Thought I'd asked this before, but couldn't find the thread. As per title, do you legally need one? I have a basic mechanical battery isolator at the moment. If I don't legally require one, I'd rather save the weight and extra complexity. I think when I asked before you guys convinced me about the virtue of a starter solenoid warning light so I know if the starter is still engaged. So I have that and the mechanical battery isolator .

I recommend mechanical battery isolator on positive from battery.  Isolates aircraft after use and you can isolate any time during a flight if required.  Not much weight; heaps of benefit; I believe.

[danny_galaga]

If there is anything written about it, can anyone point me in the right direction? Ra Aus technical manual?

[facthunter]

You are only Isolating a battery. Why does it matter which terminal is OPEN? Nev

[danny_galaga]

I only ask because an LAME apprentice was in the hanger and we were talking about it. He was pretty confident you HAVE to have on in GA, but wasn't sure about 19 rego...

[Blueadventures]

22 minutes ago, danny_galaga said:

If there is anything written about it, can anyone point me in the right direction? Ra Aus technical manual?

I can't answer; however convention is two solenoids in the circuit (master and start).  In my build I only fitted a start solenoid, isolation switch on batter supply positive and most of my toggle switches are switch / circuit breakers and have 5 additional fuses in the circuit.

 

It's also like fuel systems and weather to fit a gascolator or not;  I did and always would.

 

Cheers 

 

PS how far off is the taxi runs and then flight?

Edited July 3, 2023 by Blueadventures

[facthunter]

Are we talking about a master switch or a battery isolator?  The location  of the battery would affect whether this could be done reliably..   Nev

[Old Koreelah]

Danny I can’t help with current legalities, but when I’ve consulted RAA about my build, they’ve simply quoted the broad rules about 19-reg which didn’t mention such details.

 

Rules aside, having a foolproof way of disconnecting the battery makes sense. (I don’t trust those cheap isolators with a red plastic key: even if turned to the OFF position, a slight press on the key reconnects the current.)

 

I installed a home-made isolator that automatically disconnects the (-) side of my battery in the event of a prang and use it as part of my startup checklist.

A lever near my right leg is weighted with a small lump of lead, so that rapid deceleration swings it forward, pulling back on a wooden rod that releases the contact. This is made from the round tip of the aluminium brake lever off my old Speedwell bicycle. When contacted, it sits neatly into a nut on the end of the top right engine mount. Simple and reliable.

 

I have no idea what damage could result if I feel the need to disconnect the battery in flight. The alternator would be spinning without anywhere for its current to go. Any advice welcome.

[facthunter]

It's the regulator that sends the varying current  in the non permanent Magnet set up.. Magnet types used on some motorbikes  just supply lights when they are turned on. but may blow stop lamp filaments obviously with some overvolting happening with only one small bulb being on. I've had other DC systems where you could disconnect the battery and everything would still work fine while the generator or  alternator was working. This depends on the quality of the regulator.   Nev

[danny_galaga]

The isolator I'm using, yet to be tested is a small motorcycle screw type. Winding the knob out disconnects, and if you really need to you can wind it all the way out until the lead falls off. 

[facthunter]

That might fail the "quick and easy" test.  I would think a GANG switch with a large  contact  area would do the Job. It's got to stand the starter cranking AMPs.  Nev

[onetrack]

Disconnecting an alternator from the battery while the alternator is producing current will cause serious damage to it, at the very least blown diodes, a damaged regulator, perhaps totally fried windings.

Alternators produce high voltage AC current initially, which is converted to DC current by the regulator. A sudden disconnect of the charging circuit can see that AC current spike to unacceptably high levels, and cause damage to the alternator.

Of course, a damaged alternator that needs to be replaced is a small price to pay to avoid a cabin or fuselage fire!

[danny_galaga]

Well, I would rather not have anything at all but everyone insists that if I don't have an isolation solenoid/relay then I should have a mechanical isolator. Clearly it's not something you would  disconnect while the engine is running. It's for emergency use only.

Edited July 3, 2023 by danny_galaga

[facthunter]

To me, it's a no  brainer that having the ability to disconnect the Battery in flight is vital from a safety viewpoint..  Be one of the first actions in an "ELECTRICAL , Smoke /or Fire" situation  Nev

[kgwilson]

To answer the question definitively. There is NO legal requirement to instal a battery isolator in a 19 registered amateur built aircraft. Wiring is entirely up to the builder. You can instal motor vehicle cables or certified tefzel cables and the switch gear can be anything you like so long as it works & considered safe by you the builder. When the pre-flight inspection is carried out, that is done by you and observed by a L4. 

 

Personally I have nothing that will isolate the electrical system except a 30amp fuse on the firewall for all electrical power to the master to deal with a direct short and various size fuses and circuit breakers for the various bits of electrical equipment in the cabin. The quality of the wiring installed will be determined by the knowledge and experience of the installer.

 

If I had a lithium battery I would instal an isolator but even that may not prevent a runaway internal circuit failure.

 

I've seen some terrible installations with cables bundled allowing for electromagnetic interference, too close to hot surfaces, poor joins and bad insulation some even showing bare wire, cable runs throgh drilled holes with no grommets or glands, the list goes on.

Edited July 3, 2023 by kgwilson

[facthunter]

In a car when smoke starts coming out from under the dash or under the bonnet you just pull over and get out of the thing. There's not many situations WORSE than an in flight fire. .   Nev

[Old Koreelah]

2 hours ago, onetrack said:

 A sudden disconnect of the charging circuit can see that AC current spike to unacceptably high levels, and cause damage to the alternator...

The next question: is there some way to divert that energy before it does damage?

[facthunter]

How does a disconnect (open circuit) cause a CURRENT spike? It MIGHT cause an over voltage depending o how the regulator works..  . You'd get high current if you "shorted out" the terminal  The diodes are rectifiers full wave or half wave so they would probably fry because of the short circuited current load.   Nev

[danny_galaga]

The AC coil doesn't really 'know' where to stop with voltage. If open circuit, and therefore no load it tries for infinity. 

[kgwilson]

1 hour ago, facthunter said:

In a car when smoke starts coming out from under the dash or under the bonnet you just pull over and get out of the thing. There's not many situations WORSE than an in flight fire. .   Nev

I agree but there is always a limit to what can be done to minimise the risk of a fire. The risk will decrease with the preventative meaures taken but the tradeoff is added complexity and weight. Even the addition of items to help with prevention could cause other problems should they fail to operate as required. So there is a compromise to be reached and be determined by the builder. Good quality components correct wiring protocols, procedures and continued preventative maintenance will minimise the risk of failure. If these things are properly carried out the risk will be minimised to a level that is acceptable to the builder.

 

Statistics from the US show that in 2022 there were 1,529.9 fires in petrol powered cars per 100,000 sales or 1.53% and this was all fires, not just those caused by electrics. The vast  majority were fires caused by accidents and fuel spilled onto hot engines For EVs the number was just 0.025%. So the conclusion is that the risk is extremely low without adding extra prvenative measures.

 

If after looking at statistics and analysis you still think extra measures are required either do them or don't fly. I am happy with the knowledge of having wired the aircraft to very high standards and the risk of fire with the system I have installed is very low so as to not bother me.