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05-26-2020, 02:43 AM
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Join Date: Dec 2018
Location: Tel-Aviv Israel
Posts: 175
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Alternator circuit breaker
I noticed some are purchasing 70A E-T-A alternator circuit breaker which costs 150$, while ACS offers a 30$ one
Any reason for 5 times the price?
https://www.aircraftspruce.com/catal...ickkey=2054789
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Oren Rokach
4X-ODU
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05-26-2020, 03:54 AM
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Join Date: Sep 2007
Location: BC
Posts: 1,674
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I don?t follow the logic of a resettable alternator circuit breaker on the panel. The wiring from the alternator will be sized to handle all the current the alternator can make. But if the alternator was to fail a certain way, it could ask for everything the battery can deliver which is much more amps. So...put an inexpensive current limiter (large fuse) on the engine side of the firewall near the battery in-line of the wire going to the alternator. See...
https://www.amazon.com/Blue-Sea-Syst.../dp/B000K2K7TW
And a fuse sized for the alternator max output that the wiring can handle, see
https://www.amazon.com/Blue-Sea-Syst.../dp/B01LBPMZ14
If this ever blows, you will not need to try to reset it. Your voltage will drop from alternator output voltage (14+ V) to battery voltage (12.5) in short order letting you know you?ve lost the alternator and go from there. If you have an engine monitor with alarm functions, set to around 13 v to let you know the alternator is offline.
Bevan
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05-26-2020, 05:46 AM
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Join Date: Dec 2018
Location: Tel-Aviv Israel
Posts: 175
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Thanks Bevan! makes sense completely
Still ... very curious 
what makes a circuit breaker 150$ worthy
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Oren Rokach
4X-ODU
RV-10 QB
Cabin top installed, doors completed!
Wings almost done
Blog:
https://4x-odu.blogspot.com/
VAF 2020 dues paid!
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05-26-2020, 06:48 AM
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Join Date: May 2013
Location: Sherman, CT
Posts: 794
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Quote:
Originally Posted by Bevan
I don?t follow the logic of a resettable alternator circuit breaker on the panel. The wiring from the alternator will be sized to handle all the current the alternator can make. But if the alternator was to fail a certain way, it could ask for everything the battery can deliver which is much more amps. So...put an inexpensive current limiter (large fuse) on the engine side of the firewall near the battery in-line of the wire going to the alternator. See...
https://www.amazon.com/Blue-Sea-Syst.../dp/B000K2K7TW
And a fuse sized for the alternator max output that the wiring can handle, see
https://www.amazon.com/Blue-Sea-Syst.../dp/B01LBPMZ14
If this ever blows, you will not need to try to reset it. Your voltage will drop from alternator output voltage (14+ V) to battery voltage (12.5) in short order letting you know you?ve lost the alternator and go from there. If you have an engine monitor with alarm functions, set to around 13 v to let you know the alternator is offline.
Bevan
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I agree,
If your alternator CB pops, you don't want to reset it. I also have a current limiter installed on the firewall versus a CB in the cockpit. This is a simpler system that does not require another high load circuit on the cockpit side of the firewall. Keep a spare current limiter onboard and troubleshoot once you get back on the ground.
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05-26-2020, 12:06 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,597
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To the original question, the $34.50 70amp breaker is just fine - I used this breaker on three RVs.
You want a 70amp breaker to avoid nuisance trips as will happen with a 60amp breaker on a 60amp alternator. Keep in mind that a 60amp alternator is nominally rated - so it can easily exceed 60amp output if you load it up - for example a depleted battery.
I mount the breaker on the engine side of the firewall so this is not something I reset in flight. But - I still prefer using a breaker.
Carl
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05-26-2020, 01:02 PM
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Join Date: Aug 2010
Location: Newport News, Va
Posts: 325
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60A alternator uses 60A ANL current limiter
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05-26-2020, 03:19 PM
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Join Date: Mar 2014
Location: Bratislava, Slovakia
Posts: 203
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Quote:
Originally Posted by oren_rokach
Thanks Bevan! makes sense completely
Still ... very curious 
what makes a circuit breaker 150$ worthy
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resettable
temperature compensation
tight tolerance product -mil grade/commercial aviation?
trip free ops
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Igor
RV-10 in progress
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05-26-2020, 07:13 PM
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Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,039
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Quote:
Originally Posted by johnbright
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That depends. ANL type fuses tend to be Slow Blow, but not always. If you use a 60A Fast blow it may blown more times than you feel comfortable with. A 60A Slow Blow is a better option to prevent nuisance failures. Most alternators are capable of between 10 - 25% greater power output than rated for about 10 seconds. With fuses and circuit breakers you size them to protect the "wires" not the equipment.

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Galin
CP-ASEL-AMEL-IR
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