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Old Jan 03, 2014, 02:41 AM
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United States, CA, Orange
Joined Aug 2013
50 Posts
Question
SPC voltage reading lower than actual pack voltage?

History, my A9 is around 7 months old, has the latest firmware as do all my receivers.

Been running my A9 on a lot of my models, most if not all run 3S lipos. As far as I could tell the SPC voltage displayed on the screen was spot on to the pack voltage in the aircraft.

Just built a Katana 50ep with a 5S setup, an Optima 7 receiver and noticed that the SPC voltage is reading a few points lower than the voltage as read by any of my volt meters.

For example, today I put a fresh pack that has only ever seen 5 charge cycles in my plane, and instead of reading 20.9v that the pack was at I was seeing 20.6v - 20.5v on the A9's screen. This is resting voltage with the BEC switched off, so the only load is a non spinning motor.

This isn't a huge issue, but I really don't want to have to guesstimate an offset when it comes to my low voltage alarm, and really don't have the time while flying 3D to glance at the screen and do quick math to figure out what voltage I am really at.

I guess I could swap receivers and see if that helps.

Any ideas?
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Last edited by icedomin8r; Jan 03, 2014 at 03:04 AM.
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Old Jan 03, 2014, 05:08 AM
Registered User
Joined Aug 2002
5,811 Posts
Quote:
Originally Posted by icedomin8r View Post
History, my A9 is around 7 months old, has the latest firmware as do all my receivers.
Been running my A9 on a lot of my models, most if not all run 3S lipos.
As far as I could tell the SPC voltage displayed on the screen was spot on to the pack voltage in the aircraft.
Just built a Katana 50ep with a 5S setup, an Optima 7 receiver and noticed that the SPC voltage is reading
a few points lower than the voltage as read by any of my volt meters.
For example, today I put a fresh pack that has only ever seen 5 charge cycles in my plane, and instead
of reading 20.9v that the pack was at I was seeing 20.6v - 20.5v on the A9's screen.
This is resting voltage with the BEC switched off, so the only load is a non spinning motor.
This isn't a huge issue, but I really don't want to have to guesstimate an offset when it comes to my low
voltage alarm, and really don't have the time while flying 3D to glance at the screen and do quick
math to figure out what voltage I am really at.
I guess I could swap receivers and see if that helps.
Any ideas?
"so the only load is a non spinning motor." = leads? also some switches incorporated with BEC units have
a residual current draw even when switched off, e.g. Turnigy 10A..
Your other tests should also be through same circuit so same parameters are included.
Then check the wire and solder to SPC port and yes, try another transceiver to ensure matter is repeated
Check the section on leads and pin sizes about half way down:
. After Market Accessories - Caution re Switches, Leads etc.

ex Hitec USA Support Forum Sticky:
Aurora 9, AFHSS 2.4Ghz Module, Transceivers_Receivers & Telemetry,
- FAQ, Setups & Tips

Much more information available under sub sections
"ESC & BEC - Setup to prevent majority of all RF Problems, Brownouts & Crashes"
"Glitches & Jitter in Receiver, Servo & ESC - Causes and Cures"
below
"Radio Systems, Accessories, Alterations and FAQ" at
Alan's Hobby, Model & RC FAQ Web Links

Alan T.
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Old Jan 07, 2014, 02:16 AM
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United States, CA, Orange
Joined Aug 2013
50 Posts
FWIW, I swapped out another Optima 7 and sure enough the voltage reading was spot on.

Not sure if I should contact Hitec about this or not. I purchased the receivers back in July.
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