Hitec 7955TG power consumption

[Skippykix]

I have been running 7955's (unregulated) all the way around on my new Aeroworks 100cc YAK and have noticed that they are sucking the life out of my reciever batteries (2 X Fromeco 5200's on a Smart-Fly power expander Pro). The first set of recorded flights was 7 flights for a total of 132 minutes = 6738 mah usage. The second set of flights was 8 flights totaling 155 minutes and used a whopping 8029 mah. There is no binding on any servos and they are all programed dead on, 30 flights so far and zero issues. Just wanted to give you guys a heads up if your deciding on setting up your planes this way to make sure you have the juice to back them up, BTW they are fast as hell in this configuration. Makes you wonder if the new 7950's or 7940's are going to require a lot of juice as well? Anyway just a heads up, happy hucking!!

Forgot to add this all equals a smidge over 51 mah of consumption per minute of flight time.

[The Dirt Doctor]

Did you use the Hitec programmer to make sure the throws were equal throughout the entire sweep of the "ganged" servos? If not, the ganged servos may be fighting each other.

Bobby aka TDD

[Patrick H]

I got five that started out consumng 550mah per flight. After about twenty flights they consumed about 330mah. They may just need to be broken in.

[jamesrxx951]

i don't understand they need to be "broken in" it's an electronic device. they either work or don't no braking in. now if it was tight gears then that might be it but you would notice tight geartrain.

[Skippykix]

	Quote: Originally Posted by The Dirt Doctor
	Did you use the Hitec programmer to make sure the throws were equal throughout the entire sweep of the "ganged" servos? If not, the ganged servos may be fighting each other. Bobby aka TDD

Bobby aka TDD,

Yep, I used the good old HFP-20 and programmed all of them to a nats ass. No buzzing or binding what so ever throughout the entire throw of the servo, still uses 51 mah per minute of flight time.

[scott m lyons]

Mine do the same thing now.They are in a 35% extra and at first they would pull 700mha in 3 flights each a123 pack.Now they pull 1000mah in two flights.I went through the plane and checked for binding and everything seems fine.I am using a sf eq10 for servo matching.

[mike18421]

I have 5 7955's in my 30% Pilot RC Extra 300 and it pulls 1300mah in 5 flights or about 260-270mah a flight.

[Tired Old Man]

Amazing. Five 7955's and one 4721 consistently pull an average of 480 ma from each of two 2,300 A-123 batteries in my 35% Edge over the course of three flights. Flight times per flight run from 14 to 20 minutes. They've been using the same since they were first installed over 60 flights ago.

I must be doing something very wrong to be using less energy per flight than you other folks.

[Kevin B]

T.O.M. I am with the rest of the crowd on this one... I can't explain it either.... My set-up has always used more power than others have listed. I agree that there must be some binding somewhere. I bought the eflight voltage measuring device that Tom F. recommended and I can read the voltage, but I must be a dummy cause I can;t figure out how to use it. And while we are somewhat on the subject of A123, why haven't any of the manufacturers came out with a charger that will charge multiple A123 packs? I know that fromeco has plates for the cube, but the amperage is limited...

[jamesrxx951]

my cellpro 10 charges 2 a123 packs at the same time. and at high amp's too, i limit the charge to lower amp's because of the connectors that i use.

[Skippykix]

	Quote: Originally Posted by Tired Old Man
	Amazing. Five 7955's and one 4721 consistently pull an average of 480 ma from each of two 2,300 A-123 batteries in my 35% Edge over the course of three flights. Flight times per flight run from 14 to 20 minutes. They've been using the same since they were first installed over 60 flights ago. I must be doing something very wrong to be using less energy per flight than you other folks.

Ok maybe I need to be a little bit more specific on the setup, I AM USING FROMECO 5200 LION BATTERIES AT 8.4 VOLTS NOT A123's, AGAIN LITHIUM ION BATTERIES (YOU NO THE ONES THAT CHARGE TO 8.4 VOLTS), NOT A123's.. Operating the 7955's unregulated at 8.4 volts seems to increase their appetite for mah.

[JimC-MD]

If voltage goes up 10% in a circuit the amperage will increase 10% as well.

[jamesrxx951]

	Quote: Originally Posted by JimC-MD
	If voltage goes up 10% in a circuit the amperage will increase 10% as well.

no less. if voltage goes up then amp draw goes down. you have a higher working voltage to do the work thus need less amps to do the job.

[JoeAirPort]

Actually JimC is correct. If the impedance of the load stays the same you will draw more current. And Hitec says their servos will draw more current at higher voltages.

jamesxx951, in the things I design at work, we re-wire the load to be higher impedance/resistance at higher voltages. This makes sure the power is the same at both voltages...which makes the current be exactly 1/2 at double the voltage. This is probably what you are talking about. In the case of the servo, the power goes up since raising the voltage raises the current...because the impedance of the servo doesn't change (P=IV, P=V^2/R).

[jamesrxx951]

actually one thing i didn't think of is the higher voltage at the servo will increase power, i was thinking that it was the same power output. thus if a motor has a given hp rating at a certain voltage and the amps are at a giving spec then if you increase the voltage but keep the hp the same then amp draw goes down.