The issues surrounding lithium batteries.

[Kyle Communications]

The Savannah's come with a 50amp blade style fuse and holder...that is well more then needed for the DC side of the regulator

 

Normally I have never seen fuses in the AC side

[Markdun]

Mark based on your post, I've been trying to locate the most suitable fuse for my battery (small, lightweight). My electrical mates think 150 A is overkill for my a J2.2. Are your Jabs 4s or 6s (and would that make any difference to the size of fuse needed?)

 

In trying to relocate this thread, I came across a related discussion a few years back with this interesting contribution from a well-respected source:

https://www.recreationalflying.com/threads/battery-isolator.23440/#post-264636

Actually I have 3 fuses in the engine bay.A 150A for the starter motor

[Markdun]

Actually I have 3 fuses in the engine bay.A 150A for the starter motor, a 50A for the supply to the cabin and everything else, & a 15A on one of the AC wires going to the voltage regulator. I did have a 100A for the starter motor , but it blew, so I upped it to 150. The 150 and 50 amp fuses are mounted on the battery box with one large wire about 12cm long going to the positive terminal of the battery. I copied the set up from a friend’s Tecnam where we had to change one of the fuses which had corroded through (plane left outside in the rain by training school). The fuses in the AC charging wires is the one supplied with the Powermate regulator. It’s just a standard automotive inline blade fuse. BTW don’t use the fuses with a wire in a glass tube; the wire bends and work hardens with vibration, then breaks. Yeh, I know the Jab engines don’t vibrate, but I do have a friend who has an engine failure because of this.... the fuse was to his high pressure fuel pump on an EFI. Only use fuses where the fuseable element is supported.

[Kyle Communications]

I will always have a battery isolator within reach of the pilot in any aircraft..its your only true safety if there is a fire...first sing of smoke then kill the supply to and from the battery.

Mine in the girlfriend was mounted on the pax side on the front crossmember within easy reach while I was flying

[Markdun]

I will always have a battery isolator within reach of the pilot in any aircraft..its your only true safety if there is a fire...first sing of smoke then kill the supply to and from the battery.

Mine in the girlfriend was mounted on the pax side on the front crossmember within easy reach while I was flying

I’m no expert, but: if the isolator is a an electrical controlled solenoid even once turned off, you still have power to the isolator/solenoid control switch. If its a mechanical switch, it means you either have the battery in the cabin or a bunch of large heavy copper wires in there with you that will still be live too, or a mechanical link to the isolator if it’s remote from you. And if your electrical fire is due to a short in the AC side of your charging system and/or the voltage regulator, isolating the battery will not affect this. Finally, assuming an electrical fire is due to a wire overheating and burning the insulation on the wire & then cutting through your wingspar, that would be due to excess current... which would be prevented by an appropriate sized fuse or circuit breaker. There is one scenario I could contemplate, and that is a lightning strike. Andeven then, I’m not sure an isolator would help. I experienced a lightning strike on a yacht...it vaporised the vhf antenna, the current flowed down the antenna coax to the vhf radio, which caught fire, releasing all the magic blue smoke that makes all things electronic work, and there to the ground bus and to the engine to earth in the saltwater through the gearbox and prop. All, and I mean ALL, electrical items connected to the negative bus, switched on or not, was toast. FWIW & that’s not much, I use an old aircraft battery isolator solenoid as a 200A relay on the yacht to power the electrical anchor winch. Finally, that smoke in the cabin might not be electrical, it just might be that your trusty plastic oil catch can decided to spray 50ml of old engine oil onto your exhaust (don’t ask)!

[Old Koreelah]

...If its a mechanical switch, it means you either have the battery in the cabin or a bunch of large heavy copper wires in there with you that will still be live too, or a mechanical link to the isolator if it’s remote from you. ..

 

Another possibility: a reliable remote control. I have a weighted, spring loaded lever next to my right knee, connected by a wooden rod to the battery's earth terminal. (The actual connection is the rounded tip cut off the brake lever of my first bike- a Speedwell - which slides forward to connect the earth cable with one engine mount nut.)

Despite the very light spring pressure holding it there, it has reliably carried starting current for a decade.

 

I have the battery behind the firewall, technically in the cabin, but being LiFePO4, I trust it more than a lead acid unit.

[Thruster88]

I will always have a battery isolator within reach of the pilot in any aircraft..its your only true safety if there is a fire...first sing of smoke then kill the supply to and from the battery.

Mine in the girlfriend was mounted on the pax side on the front crossmember within easy reach while I was flying

This is how it has been done on all certified aircraft since the dawn off time, a combined master/alternator switch allows all electrical power (battery and alternator output) to be shut off in fire or forced landing situations. Not sure how manufacturers are handling the self exciting permanent magnet alternator types found on jabiru/rotax machines.

Edited August 31, 2020 by Thruster88

[Kyle Communications]

A solenoid requires power to operate of course. The isolator I used in my aircraft is the removeable key type. A proper make/break switch. All the wire in my aircraft is tefzel...no auto style wire at all. The battery in the sav was right down the back the first port of call is the isolator then everything forward of that is controlled. It wouldnt matter what you had as a isolator if the battery burst into flames. You are most likely to have a severe fault forward of the isolator . I like the big clunky switches that give me a open circuit...I ahve seen too many solenoid/contactors locked shut in my time

 

You can wire it like the picture above no issue but like on any heavy machinery they still have that final part that isolates the battery completely..thats what I like

[Markdun]

This is how it has been done on all certified aircraft since the dawn off time, a combined master/alternator switch allows all electrical power (battery and alternator output) to be shut off in fire or forced landing situations. Not sure how manufacturers are handling the self exciting permanent magnet alternator types found on jabiru/rotax machines.

[ATTACH type=full" alt="images (5).jpeg]55972[/ATTACH]

I’m sure this set up is reasonably safe. But just to be clear: the logic of a system being ancient and on ‘certified’ aircraft means nothing. It’s the same as the fable of the farmer with the sick cow.

[Markdun]

A solenoid requires power to operate of course. The isolator I used in my aircraft is the removeable key type. A proper make/break switch. All the wire in my aircraft is tefzel...no auto style wire at all. The battery in the sav was right down the back the first port of call is the isolator then everything forward of that is controlled. It wouldnt matter what you had as a isolator if the battery burst into flames. You are most likely to have a severe fault forward of the isolator . I like the big clunky switches that give me a open circuit...I ahve seen too many solenoid/contactors locked shut in my time

 

You can wire it like the picture above no issue but like on any heavy machinery they still have that final part that isolates the battery completely..thats what I like

Agree

[Markdun]

Another possibility: a reliable remote control. I have a weighted, spring loaded lever next to my right knee, connected by a wooden rod to the battery's earth terminal. (The actual connection is the rounded tip cut off the brake lever of my first bike- a Speedwell - which slides forward to connect the earth cable with one engine mount nut.)

Despite the very light spring pressure holding it there, it has reliably carried starting current for a decade.

 

I have the battery behind the firewall, technically in the cabin, but being LiFePO4, I trust it more than a lead acid unit.

Old Koreelah, here is a photo.

[Old Koreelah]

Sorry, been absent from this discussion for too long. Is that your 150A fuse?

[Thruster88]

Agree

I’m sure this set up is reasonably safe. But just to be clear: the logic of a system being ancient and on ‘certified’ aircraft means nothing. It’s the same as the fable of the farmer with the sick cow.

I strongly disagree with your statement that being certified and tested over a long time means nothing. In the certified world faulty design or parts result in an airworthiness directive, owners bitch and moan about it but it makes aircraft safer. Am not aware of the sick cow fable.

A solenoid requires power to operate of course. The isolator I used in my aircraft is the removeable key type. A proper make/break switch. All the wire in my aircraft is tefzel...no auto style wire at all. The battery in the sav was right down the back the first port of call is the isolator then everything forward of that is controlled. It wouldnt matter what you had as a isolator if the battery burst into flames. You are most likely to have a severe fault forward of the isolator . I like the big clunky switches that give me a open circuit...I ahve seen too many solenoid/contactors locked shut in my time

 

You can wire it like the picture above no issue but like on any heavy machinery they still have that final part that isolates the battery completely..thats what I like

The battery isolation switches rely on a spring for the disconnect just like a solenoid so I don't see any difference if they become welded. If the master solenoid was failing in certified aircraft there would be an airworthiness directive.

 

Farm/heavy equipment need after market battery isolation because while most circuits are cut by solenoid (often a long way from the battery) the alternator remains connected to the battery 24/7. Faulty alternator, dead battery BTDT. A master solenoid positioned AT THE BATTERY just like the certified aircraft will give that same complete isolation.

[Markdun]

Sorry, been absent from this discussion for too long. Is that your 150A fuse?

That’s two fuse holders. The bottom one has a 150A fuse (starter motor), the top one I think has a 50A and goes to the master switch on the panel and a 25A circuit breaker.

[Markdun]

I strongly disagree with your statement that being certified and tested over a long time means nothing. In the certified world faulty design or parts result in an airworthiness directive, owners bitch and moan about it but it makes aircraft safer. Am not aware of the sick cow fable.

 

The battery isolation switches rely on a spring for the disconnect just like a solenoid so I don't see any difference if they become welded. If the master solenoid was failing in certified aircraft there would be an airworthiness directive.

 

Farm/heavy equipment need after market battery isolation because while most circuits are cut by solenoid (often a long way from the battery) the alternator remains connected to the battery 24/7. Faulty alternator, dead battery BTDT. A master solenoid positioned AT THE BATTERY just like the certified aircraft will give that same complete isolation.

Thruster 88 it seems the rest of my reply didn’t make it. But I wasn’t responding to ‘certified and TESTED’, but your previous statement which was ‘old and certified’. I maintain that just because it was done that way in the past, and even if it worked, it’s sometimes worthwhile to look at alternatives. The ‘old certified’ isolators I have come across probably worked reasonably well (‘worked’ as meaning providing reasonable safety), but they weighed a substantial amount. But I think the safety provided by a battery fuse provides similar safety for a big weight saving, and if I’m doing a power off out landing, not having to turn off the battery isolator is one less thing to distract me from getting my landing just so.

The sick cow fable. Farmer A who had a sick cow attended the local annual field day. Farmer A explained to another farmer, Farmer B, about the sick cow’s symptoms. Farmer B responded that he had had a sick cow with the same symptoms and that the generally accepted approach was to treat the cow in a certain way. The next year Farmer B saw Farmer A again at the annual field day and asked A how it went with the sick cow. Farmer A responded that he did what Farmer B suggested, but the cow died. Farmer B then remarked that his cow also died when treated that way too.

[Thruster88]

Thruster 88 it seems the rest of my reply didn’t make it. But I wasn’t responding to ‘certified and TESTED’, but your previous statement which was ‘old and certified’. I maintain that just because it was done that way in the past, and even if it worked, it’s sometimes worthwhile to look at alternatives. The ‘old certified’ isolators I have come across probably worked reasonably well (‘worked’ as meaning providing reasonable safety), but they weighed a substantial amount. But I think the safety provided by a battery fuse provides similar safety for a big weight saving, and if I’m doing a power off out landing, not having to turn off the battery isolator is one less thing to distract me from getting my landing just so.

The sick cow fable. Farmer A who had a sick cow attended the local annual field day. Farmer A explained to another farmer, Farmer B, about the sick cow’s symptoms. Farmer B responded that he had had a sick cow with the same symptoms and that the generally accepted approach was to treat the cow in a certain way. The next year Farmer B saw Farmer A again at the annual field day and asked A how it went with the sick cow. Farmer A responded that he did what Farmer B suggested, but the cow died. Farmer B then remarked that his cow also died when treated that way too.

Mark, I am certainly not against new ideas, however the fuse idea is just plane silly. To do its job of cutting all electrical power so the risk of fire is reduced it must be capable of carrying the starter current. A fuse of this size will produce a mega spark and or burn all the small wires before blowing, you will be toast. The master solenoid used in certified aircraft also provides a method of stopping the starter if there is a malfunction with the start circuit. I don't post to be a smart a or to piss people off. I see the forum as a virtual pub full of interesting characters. ?

[RFguy]

Well I might have an IGBT switch/CB. Since I am used to switching 6000 amps for brain stimulators...

[Kyle Communications]

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