Current Limiter for Main Bat?

Hi,

as we?re just installing a G3X system and renewing the electrical system, I?m thinking about to install a current limiter (ANL-60) for the main bat. The alternator itself has a circuit breaker, but according the vans electrical diagram the main bat does not have a breaker or limiter.
What do you think about that? Do you recommend to install a current limiter?
I took a look in the wiring diagrams of a Beech G36 and they do have a limiter for the main battery.

Thanks,

Kai

Kai,

The problem with putting a 60 amp current limiter on the main battery is that during engine start you're usually going to draw more than 60 amps, so it would probably blow your current limiter.

Your best bet is to have the battery relay as close as possible to the battery itself and to protect the battery cable as best you can. If you ever had a short, about the only remedy is to turn off the battery master relay and hope that your short is downstream of the relay.

Hope this helps.

Hello Pat,

thanks a lot. Yes, the relay is very close to the battery and the current limiter would be installed behind the path to the starter relay, just before the shunt. The starting current would not go through the limiter.

Kai

Download Bob Nuckolls's Book and scroll to back where the "Z" drawings are located. Z-11 is a basic aircraft wiring diagram. I think that what you have in mind is similar to the 60 amp ANL current limiter in Bob's drawing. The purpose of the current limiter is to protect the battery from a shorted alternator or associated wiring.
The aircraft main power bus is usually not protected except by the master contactor. When considering protection for the main power bus, weigh the odds of more failure points against the odds of the main feeder shorting to ground. Good workmanship and wiring practices will minimize the chances of short circuits.

I did not put one on the starter circuit but I do have one on the main bus feed that comes aft of the firewall to the VP-X (originally a fuse block). No way I am leaving such a fat and long wire unprotected....

The odds of a properly installed current limiter failing are very slim.

Good points, Brian

Kai
Lots of things have current Limiters between battery and source. Even Fords
It's there for one thing only a drop dead short.
These guys are right if you do professional wiring job and keep you main solenoid next to battery Great.
But I'm old and I believe in Murphy's Law.
Bill

The G36 limiter I'll bet is a whole lot bigger than 60amp.

Hi Bill,

you?re right, murphys law is always present...

I believe in "keep it simple" but also in "keep it safe".
The main contactor is directly next to the battery, but who knows what will happen if a current of 200amps is flowing and welding to contacts together.
A current limiter is another part which could fail, but i?m working since more than 10 years on King Airs and had them only replaced if there was a short (i.e. failed A/C blower).
I don?t want to have a burning AWG6 cable in my cockpit.
I think I will go with the current limiter.
Btw, yes the CL of the Bonanza has 100 Amps..

Kai

Can someone help me understand what is the difference between ANL-60 current limiter than a 60A circuit breaker?
Why should I prefer one over the other?

oren_rokach said:

Can someone help me understand what is the difference between ANL-60 current limiter than a 60A circuit breaker?
Why should I prefer one over the other?

Click to expand...

It's the trip time. CBs trip fast vs. Current limiters slow

Current limiters will accept peaks on top of their rating.

Thanks Igor,
So...
why do people tend to install ANL from battery to main bus, while installing CB from alternator to main bus?

Mich48041 said:

Download Bob Nuckolls's Book and scroll to back where the "Z" drawings are located. Z-11 is a basic aircraft wiring diagram. I think that what you have in mind is similar to the 60 amp ANL current limiter in Bob's drawing. The purpose of the current limiter is to protect the battery from a shorted alternator or associated wiring.
The aircraft main power bus is usually not protected except by the master contactor. When considering protection for the main power bus, weigh the odds of more failure points against the odds of the main feeder shorting to ground. Good workmanship and wiring practices will minimize the chances of short circuits.

Click to expand...

The purpose is actually to protect the wire and the alternator from the battery in the case of a short circuit.

Ed Holyoke

oren_rokach said:

Thanks Igor,
So...
why do people tend to install ANL from battery to main bus, while installing CB from alternator to main bus?

Click to expand...

Oren,

my interpretation is that during engine start there is an inrush spike in amps which a properly sized ANL can still handle without being blown if placed from batt to main bus. Anyway I think this practice is more common to multiengine aircraft or airplanes with multiple power sources where an accidentally blown ANL wouldn't kill the whole system..

On the alternator B lead it's more about philosophy. You could use an upsized CB, but this protection is not meant to be reset. That's why some builders prefer the ANL or another non resetable protection. Inspect/replace/troubleshoot the alternator or B-lead first, then replace breaker. I don't think a CB is forbidden here, however using the ANL instead avoids a possible pilot error to reset a hard fault.

Another point to consider is that keeping the alternator B-lead between alternator and starter contactor on the firewall hot side; you don't need to penetrate the firewall and take another fat wire to the inside of your cocpkit (another possible source of smoke/fire) With this design a CB would make no sense of course.. it all depends on system design goals.

A fuse in the starter circuit will drop voltage which will have an affect on starter performance.