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BrokenStraw,
You may have already gotten all the answer you wanted from the link that Brooks provided, but the B&C published info will always show using two circuit breakers to the regulator, one 5A for the field current and a 2A for the voltage sense input. The voltage sense input also keeps the low-voltage warning output working if the 5A breaker opens which it will if the over-voltage protection decides to step in. Some people have installed it using a single circuit breaker and jumpered the field supply input and the voltage sense input together. There are two downsides to doing this so you should understand those if you are considering doing that.
1. Having a second sense input that draws very little current (the 2A breaker) enables the regulator to accurately sense the bus voltage even if that path develops some resistance over the life of the aircraft. The split rocker switches used for battery/alternator master switches are notorious for developing some resistance through the contacts as the switch ages. If the two regulator inputs are jumpered together and powered through a single 5A circuit breaker and through the alternator switch, the resistance of the circuit will cause a voltage drop at the regulator input and since the field current varies, the amount of voltage drop varies. This causes the voltage regulator to see an inaccurate and sometimes varying voltage which results in a less stable bus voltage. So if you are willing to accept an increased risk of poor regulator performance and required maintenance down the road, the single circuit breaker option might be considered.
2. The over-voltage protection works by intentionally faulting the field supply input to ground which causes the 5A circuit breaker to open. The alternator will no longer be online and the bus voltage will drop. The B&C regulator provides an output terminal to drive a low voltage warning light which would provide an annunciation to the pilot that something is amiss. If the two inputs to the regulator are jumpered together from a single breaker, then the OV event that opens the breaker will also disable the low-voltage warning. This would not be acceptable if you are counting on the low-voltage warning from the regulator. However, if you have an EFIS or engine monitor that is providing a low-voltage warning independent of the B&C regulator, this is no longer a factor.
Another option that I'll mention is the new Silver-Flite series of alternators that B&C is introducing. These are internally regulated with built in over-voltage protection and will require only a single breaker feeding an alternator switch which then goes to the small alternator connector to turn it on or off. There is no output provided for low-voltage warning or alternator failure annunciation so you would need to rely on an independent means of low-voltage warning to detect alternator failure. The 60A belt driven unit has begun to ship and the 40A belt driven and 30A pad mounted units should begin shipping the end of March. These Silver-Flite units are a little less expensive than the traditional B&C units but when you consider that you don't have to purchase a regulator, the savings becomes much greater.
David Swartzendruber
Bearhawk LSA builder (nights and weekends)
Engineer at B&C (during the workday)
You may have already gotten all the answer you wanted from the link that Brooks provided, but the B&C published info will always show using two circuit breakers to the regulator, one 5A for the field current and a 2A for the voltage sense input. The voltage sense input also keeps the low-voltage warning output working if the 5A breaker opens which it will if the over-voltage protection decides to step in. Some people have installed it using a single circuit breaker and jumpered the field supply input and the voltage sense input together. There are two downsides to doing this so you should understand those if you are considering doing that.
1. Having a second sense input that draws very little current (the 2A breaker) enables the regulator to accurately sense the bus voltage even if that path develops some resistance over the life of the aircraft. The split rocker switches used for battery/alternator master switches are notorious for developing some resistance through the contacts as the switch ages. If the two regulator inputs are jumpered together and powered through a single 5A circuit breaker and through the alternator switch, the resistance of the circuit will cause a voltage drop at the regulator input and since the field current varies, the amount of voltage drop varies. This causes the voltage regulator to see an inaccurate and sometimes varying voltage which results in a less stable bus voltage. So if you are willing to accept an increased risk of poor regulator performance and required maintenance down the road, the single circuit breaker option might be considered.
2. The over-voltage protection works by intentionally faulting the field supply input to ground which causes the 5A circuit breaker to open. The alternator will no longer be online and the bus voltage will drop. The B&C regulator provides an output terminal to drive a low voltage warning light which would provide an annunciation to the pilot that something is amiss. If the two inputs to the regulator are jumpered together from a single breaker, then the OV event that opens the breaker will also disable the low-voltage warning. This would not be acceptable if you are counting on the low-voltage warning from the regulator. However, if you have an EFIS or engine monitor that is providing a low-voltage warning independent of the B&C regulator, this is no longer a factor.
Another option that I'll mention is the new Silver-Flite series of alternators that B&C is introducing. These are internally regulated with built in over-voltage protection and will require only a single breaker feeding an alternator switch which then goes to the small alternator connector to turn it on or off. There is no output provided for low-voltage warning or alternator failure annunciation so you would need to rely on an independent means of low-voltage warning to detect alternator failure. The 60A belt driven unit has begun to ship and the 40A belt driven and 30A pad mounted units should begin shipping the end of March. These Silver-Flite units are a little less expensive than the traditional B&C units but when you consider that you don't have to purchase a regulator, the savings becomes much greater.
David Swartzendruber
Bearhawk LSA builder (nights and weekends)
Engineer at B&C (during the workday)
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