[CharlieWaffles]

I have an SD-8 installed as a backup alternator on my IO-540. I do not have a shunt installed on it's output so I am unable to see an Amperage draw on it when it is activated (and primary alternator is disabled). But when I load shed down my system down to about 3As, increase RPMs to 1800 the voltage goes from 14.7 (on primary alternator) down to 13.2V when on the SD-8.

Is this the expected voltage for the SD-8 when operating or is it possible the SD-8 isn't properly outputting to the main bus?

 

[AltonD]

Yep. The SD-8 external regulator is always on-line and picks up when voltage falls to the setpoint. On my SD-20, it is 13 volts.

 

[Andy Hill]

NB @ 1800RPM [Engine] max Output of the SD-8 is ~3.5A, so if you are pulling about 3A you are near maxing the SD-8 out.

The -1 regulator [PMRIC-14] should push out nominal 14V and according to the diagram is adjustable. However, I would "load shed" everything you can to get a true reading, and/or do at Max RPM.

 

[RV-4]

SD-20 INSTALLATION

Hi Alton

I just looked at your construction log to see how you mounted the Current Limiter/shunt of your SD-20 B/U Alternator but the pictures came out kind of fuzzy.

I'm installing one on my -4 as we speak and I wonder if it will be possible to see any pictures you may have.

Thank you for your help.

Cheers

Bruno
[email protected]

 

[Mich48041]

When a battery is first disconnected from a charger, or main alternator in this case, its voltage is expected to be slightly above 13 volts. A better test of the SD-8 would be to go flying at cruise RPM with the main alternator off. If the voltage remains above 13 for an extended period of time at reduced load, then yes, the SD-8 is working.
Joe Gores

 

[airguy]

When a battery is first disconnected from a charger, or main alternator in this case, its voltage is expected to be slightly above 13 volts. A better test of the SD-8 would be to go flying at cruise RPM with the main alternator off. If the voltage remains above 13 for an extended period of time at reduced load, then yes, the SD-8 is working.
Joe Gores

And if you're going to do that - don't turn your main alternator back on with the engine at full RPM, you'll give the regulator fits and the resulting voltage spike is tough on it. Get your engine RPM down (either on the ground or slow speed flight) before re-energizing your main alternator field. Be kind to your electronics!