Servo electrical consumption

[coyote12]

I have a LongEz with skyview D700 system with a roll servo.
My long just have a small B&C alternator (actually more a dynamo) which output is limited to 15Amps at cruise, but very limited at low RPM between 1.5 - 4 Amps during taxi.
1) My plan is to power the servo only inflight to avoid to high electrical consumption. Is there any concern if the servo is powered lately, and not during SV boot ?
2) I have tested several max torque, and it looks like 30% is double of the sliding value. Is the current consumption of the servo proportionnal to the max torque ratio ?

 

[dynonsupport]

1) If the servos have power going to them but are not actually flying the aircraft, they draw negligible power. They're only pulling current when they're pulling on the aircraft, basically
2) Current consumption is proportional to the max torque, though I don't know if it's completely linear without consulting some others around here. I'll check in with our EEs.

 

[coyote12]

Thanks for the answer, than i have another question :
what happens with my system if i had a battery SV-BAT-320 when i taxi at idle, and the alternator is producing less than what total avionic is sucking.

Doc says "An SV[ch8208]BAT[ch8208]320 is fully charged when it reaches 12.25 volts ... the SV[ch8208]BAT[ch8208]320 is only charged with SkyView detects your alternator/generator to be online."

What if my generator is online, but do not produce enough ?
Does the system switch to battery automatically ?
Can the system put down my main by trying to charge the battery when generator output is low ?

Finally, is there an interest for me of adding a battery to help my generator during taxi and other low generator output, or will it make the situation worse ?

 

[dynonsupport]

SkyView only knows the voltage it's receiving, so it makes all it's decisions based on that. Here are the rules, assuming you have a battery on the SkyView:

1) Voltage is above 12.25V: SkyView runs on master power and charges battery

2) Voltage is above 10V, but below 12.25V: SkyView runs on master power but does not charge battery

3) Voltage is below 10V: SkyView runs on battery

If you are at idle and the alternator output is low, then your voltage can't be above 12.25V, since you are actually running on the aircraft battery, which is a 12V battery. You are actually slowly discharging the aircraft battery. If you did this for a long time, you'd get to 10V and then we'd switch to the backup battery.

If the charging of the SkyView is the last straw in your alternator's output, what will happen is that SkyView will try to charge, the voltage will drop, SkyView will stop charging, the voltage will come back up, and then SkyView will try to charge again.

There is no need for an additional battery in the plane.

 

[coyote12]

So if i understand well :
- I can power up the servo at start-up as they draw negligible current when they are is std-by
- adjusting the torque ratio to 30% reduce the servo current consumption at roughly 30% of the doc values
- it is worth installing a SV-BAT to my system as it will support my sytem during low alternator output, and charge only if the alternator output is enough.

Thanks Dynon for the clarification and responsive answer !

 

[jakej]

FWIW - if I was in this situation & wanted startup & idle rpm voltage stability ops then I'd fit another smaller battery say 5-7amps connected via a diode to the main electrical system so that it will give you the 12 + volts (while idling - has to be a 'good' battery) and therefore will also be charged when engine is operating at flying rpm. This battery would only be connected to the avionics that are necessary on the ground ie radio or EMS etc, what ever suits you.

Jake J

 

[dynonsupport]

coyote12:

-Yes
-Yes - roughly, give or take some percentage that we don't have firm number for
-We think so, but we're biased since we sell the things . Note that the battery does a bunch of neat things like detecting whether the alternator's outputting enough to let the battery be charged, but do know that it doesn't power the servos or the transponder module. Everything but though.