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Testing B&C Standby Alternator

RV9Otter

Active Member
I have a B&C gear driven standby alternator on my XP320 and am wondering if it can be tested while the engine is running from the cockpit, and if so, how?

My switches from left to right are Master, Standby-Alternator, Left Ignition, Right Ignition. My ignition is one mag and one electronic. My master switch has three positions, off, battery only, and on.

With the engine running, I turned off the master switch, turned on the standby-alternator switch and nothing, no power at all, not even battery.

So now, assuming the standby-alternator is functioning correctly, I presume the the master switch must be either left in the on position or battery only position. I'm concerned with just flipping switches from this point on as I don't know what would happen if I left the master switch on (main alternator) and then also turned on the standby-alternator.

I would think there would be some way to turn only the standby-alternator on and observe it powering the avionics, including a readout on the volts and amps.

Thanks,

Curt
 
I'm assuming you bought this aircraft flying. If you don't have the schematics, you can spending a lot of time guessing at the operation. Can you call the previous owner and ask them? Otherwise your only choice is to start trading wiring and reverse engineer the schematics.
 
SD-8 Requires a Battery

The SD-8 requires a battery to be on-line in order to work. So if you have the switches correct, then your master must be set to "battery only" and the standby alternator switched on.
 
I've Asked the Builder...

I've asked the builder and he thought the procedure that I used was correct. So, either it isn't, or the standby is not functioning.

The panel was built by Stein Air so I've put the question to Stein as well.

Thanks,

Curt
 
KRWalsh - Thanks...I'll Try That

KRWalsh:

Thanks...that was my next guess. I'll put the master in battery only and switch on the standby and see what happens.

Regards,

Curt
 
Once you have figured out which switch selections will allow you to shut down the main alternator, be aware that the B&C standby alternator requires quite a bit of rpm to produce rated output. If you test it at low rpm, it won't put out enough current to show any voltage increase. On my aircraft, I test it at 1900 rpm or more. I can select the main alternator off, shed the non-essential loads to get the current less than 8 amps, they select the standby alternator on while watching the system voltage, which rises to 12.8 volts.
 
You might consider starting the airplane with battery "ON" (obviously) but both alternators OFF. Note the voltage. Then turn on Standby Alternator and watch for a voltage rise. If it rises, the alternator is putting out "some" power which as previously stated, will be RPM dependant. I'm not sure but I suspect it will be safe to turn off the the standby alternator while it's producing power because it is a permanent magnet type. The voltage should then reduce to battery voltage. Then turn on the main alternator and again watch the voltage rise.

Be advised that turning off the main alternator while it's supplying current is claimed by some to be hard on the alternator. I don't know but can understand to a point how it could cause of brief stress and wouldn't do it myself intentionally.

Bevan
 
The SD-8 requires a battery to be on-line in order to work. So if you have the switches correct, then your master must be set to "battery only" and the standby alternator switched on.

Aeroelectric provides a diagram (Z-25) that includes a rectifier/resistor for self booting the SD-8.
 
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I didnt see what typ eof standby alternator, but the earlier poster is correct in that if it is an SD-8 you will not see any volatage rise at ground idle, especially after an engine start. It is a permanent magnet type of alternator and takes Lots of RPM's, usually 1800 to cruise rpm's to make any power. The newer standby alternators from B&C are much better in that they are REAL alternators and will put out power at lower RPM's, but keep in mind that on the accessory pad they are running much slower than off of the flywheel pulley.

No, you will not harm the main B&C alternator by turning it OFF. I ahve asked that question of B&C multiple times. It is the way I check my standby alternator in flight. In fact, I will let my standby alternator carry the load sometimes for 30 minutes or more while in flight. It is the BC-410 H and can output almost 40 amps. After all, when I need it I want it to carry the load, so I want to know it is working. My steady state load in flight is around 24-25 amps, and it carries the load just fine. However, the voltage is a little lower, around 13.8 vs. 14.4, which is normal.

There are 2 ways of installing the standby alternator that have the regulators. You can use a switch, as I did, or you can wire them both on all of the time, with the standby regulator set a few tenths of a volt lower than the main alternator. The standby will come on automatically in the event of a main alternator failure. In this config there is no harm in having them both on all the time.

Vic
 
Results of Today's Test - Normal?

O.K. Put the main switch on Battery, put the standby alternator to On, started the plane. With avionics on, voltage read 12.4 at idle and 12.8 at 1900 RPM.

Amps read what it usually reads.

I presume that since the voltage increased with RPM, that only thing that could account for the voltage increase is that the standby alternator is working normally.

The main alternator normally registers voltage around 14.1 volts, so the standby reads lower, again I assume normal.

I'll try it in flight next time at cruise RPM...see if the voltage increases even more.

Thanks everyone for the help.

Curt
 
Get the warning lamps wired

Curt,

You should think about getting the warning lamps wired on your system assuming it has B&C regulators.

I have a B&D main and a B&C standby alternator with B&C regulators. The lamp for the main alternator comes on only when there is a charging problem (low voltage). The lamp for the standby regulator flashes only when the standby alternator is actually charging the system. Without these indications you don't know which system you are running on.

The B&C backup regulator only comes online when the voltage drops below a preset level (around 13v but adjustable) which is also why you see the lower voltages when operating on the standby system. That allows it to come online automatically when the main alternator goes offline/fails.

Andy
 
SD-8 STANDBY

Vic, you are right about the "standby" alternator SD-8. I had them on all three of my Pitts S1's as the only alternator. B&C makes a great product, never failed ever, but it is not an alternator and I don't think it even has a regulator per se.
We are mixing two different types of technology, an alternator(MAIN) and a backup(permanent magnet). The master switch is not even a known as to it's operation: OFF,bat only,on. What does on do, turn the field on the alternator? What happens if you turn the master "off" and the standby "ON", does it power up the buss with eight amps, hope not.

I would trace back every switch, breaker, "master" wiring to really see how it was designed, a piece at a time. In an emergency when I turn a master "OFF", I don't want any power anywhere. You have electronic ignitions so.....more safety concerns. Just my two scents.. John
 
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