SD8 Wiring - Try Again

[pvalovich]

I posted a similar question last weekend but got no response - so I'm trying again.

-8A with Aerosport IO-360. Bob N's Z13/8 architecture with a 40 amp main and SD8 back up. The Z13/8 diagram shows only one connection from the SD8 controller to a bus; the diagram included with the SD8 shows 2.

How did folks with an SD8 really hook it up? What am I missing?

[vic syracuse]

I just hooked up the output of the SD-8 to the bus through a fuse (10 amp). Seems to work fine. If the main alternator quits, just turn on the SD-8. I've tested it many a time to check for proper in flight operation.

Vic

[Fearless]

If no one gives you any feedback, call B & C directly and ask for some tech support. I know they have helped others in the past with wiring questions.

[rvator51]

Originally Posted by pvalovich

The Z13/8 diagram shows only one connection from the SD8 controller to a bus; the diagram included with the SD8 shows 2. How did folks with an SD8 really hook it up? What am I missing?

If you look at the Z13/8 drawing, you will see that it shows both wires as well. There is a 20AWG coming off the controller to a 2A c/b that goes to the Aux alt off/on switch.

Then, there is also a 14AWG wire that goes to the battery contactor. It
goes through an 18AWG fuselink instead of going through the 10 amp CB that is shown on the B&C installation drawing. You can use either one.

Does this make sense or did I get your question wrong?

Also, if you want the self-excitation feature, look at drawing Z-25 for how to wire it so it can self-excite.

[Camillo]

By the way, do you know if self-excitation is necessary or not?
I'm not sure of this. It seems an optional feature. Am I right?
Camillo

[rvator51]

Originally Posted by Camillo

By the way, do you know if self-excitation is necessary or not?
I'm not sure of this. It seems an optional feature. Am I right?
Camillo

This is my understanding. The SD-8 needs power from the battery to start producing power. If your main alternator and your battery both died at the same time, the SD-8 wouldn't be able to start producing power.

With the self-excitation capacitor and resistor added in parallel, the SD-8 can start up (self-excite) with the battery off line.

Its easy to add the extra resistor in parallel to the capacitor, so might as well for extra protection against a double failure of the main alt and the battery.

[Camillo]

Thank-you, rvator. You lighted my life! I was searching on the aeroelectric FAQ and on this site, but didn't get answers...

Actually, I understood that in Z-13/8 SD-8 is connected to battery. So, I didn't understand the needing of such mod. So, the mod allows SD-8 to operate even if battery is shorted or completely down. When you switch aux alt on, it will come always alive.

One more question: why Bob (Z-25 description/note 25) says that in this way SD-8 will come alive as soon engine has started. Won't it need aux. switch to be ON?

Thanks.
Camillo

[rvator51]

Originally Posted by Camillo

One more question: why Bob (Z-25 description/note 25) says that in this way SD-8 will come alive as soon engine has started. Won't it need aux. switch to be ON?

Thanks.
Camillo

Hi Camillo,
Good call on pointing out note 25 that shows the parts list to make the SD-8 self excite.

Until you apply ground to the Aux Alt relay by turning the Aux Alt switch to ON, the relay wont energize. With the relay not energized, no power can get from the SD-8 to the battery contactor. So even though the SD-8 may come alive as soon as the engine starts, you cant use the power it generates until you turn on the Aux Alt switch. So I think you are correct.

[Mike S]

The SD8 is a permanent magnet dynamo. It is not an alternator in the "normal" sense.

It will make juice as soon as the engine is running.

The controller/regulator may not let the juice thru though. This is what the "Field" switch controls.

In an actual alternator setup, the field switch controls the current flow into the alternators field, energizing the electromagnetic field, which then allows the production of power when the unit is running.

Overall, the SD8, and an alternator do the same thing------convert mechanical energy into electrical energy------they just do it a bit differently, and thus require different controllers/regulators, and hookup wiring.

[Camillo]

Ok. Thanks to everybody. I heard the longest hesitation would be panel planning (actually, I changed n times my mind...), but nobody told me of electrical architecture perplexity.

I started with Z-12. Then, when I realized that SD-20 needed a battery (so, in case of battery short or battery contactor failure, no juice), I abandoned it for Z-11. It has an endurance bus, so one can simply switch battery off and continue fly with MEL. Then, I thaught: I can always add a second smaller battery. But...why not go with Z-14 with an aux. non cranking battery. since I'm planning from scratch?

When I started considering Z-14, I was enthusiastic. Then, I understood that I couldn't probably make both alternators (L-40 and SD-20) work together; I turned down thinking using the main one with crossfield contactor closed; that I realized that having an aux. smaller battery will probably make problems in charging (since the different ampereage of the two batteries); then, when counting weight, I realized that adding a second Odyssey PC-680 would be too much...for a RV9. Maybe for a RV10 it would be the best choice.

Finally, I'm persuading myself on Z-13/8. SD-8 costs less and...weights less. It goes after battery contactor and let me save 1 amp. battery contactor coil current in case of main alt. failure. And now...it may work without a battery.

I ended as Bob predicted in his book. Time lost?

Camillo