esc-battery compatable?

[Louis Benjamin]

Hello, i need some expert help please!!!

i`m a newbie to electric flight(and this site)

I have thunder tiger obl36/11-40a outrunner brushless motor, 3700mah 11.1v 3s1p li-po batteries, and an E-pro sp50a-bec-air esc. i have fully balanced charged the lipo at 3.7amp but i am only getting about 3minutes of flight(full throttle for take off then on half for the remainder until there is a noticable loss in power and i have to land. the esc only has a program set up procedure for 2 cell li-poly 5.6v and 3 cell li-poly 8.4v......are these two compatable? . thanks louis

[Tim Mackey]

The ESC should be set to activate the LVC at the 3 cell setting of 8.4V ( 2.8V per cell )

It sounds like you are pulling too many amps through your rig, and this is very likely due to the wrong prop.

Can I suggest you read the 2 x articles I did recently in the mag...they are now published here on the forum if you missed the mags. Heres a link to part 1...they are both on the the forum at the moment.

[Louis Benjamin]

i`ve just read the articles thanks.   i had set the esc to the 8.4v setting as this was the factory default anyway. the prop i have on at the moment is an 11x7 which was recommended with the model. what size would you suggest i try?
  cheers

[Tim Mackey]

That prop spounds about right for the motor actually - I dont know of these tt outrunners, but a quick google shows them as being 1180Kv

• Voltage range: 8~10 cells | 3x Li-poly
• KV rating: 1180 RPM/V
• Max efficient current: 20~45A
• Shaft diameter: 5mm / 0.197 in.
• Dimensions ø x L: 36 x 47.7 mm / 1.417 x 1.877 in.
• Weight: 165g / 5.82 oz.
• Propeller Recommended: 10 x 5 / 11 x 7 / 12 x 6

However the opening blurb states that ...

"Each and every motor is designed for use with 2 to 5 cell lithium polymer batteries". The spec above however shows it as happy up 3s with those props, and this is misleading to beginners. To runj any electric motor which is "normally used" wuith a 3s pack on a 4s or a 5s would require a considerable reduction in prop size to keep the current manageable. Anyway, besides all that rambling - what is your problem ? Well assuming the prop size is OK for the motor, why are you running out of juice so quickly?? -

1. is the battery fully charging corectly to 4.2V per cell.
2. is the battery in good condition - what brand is it?
3. have you another pack you could borrow / beg / to try
4. how much charge goes back in after it flight
5. is all the wiring and connectors up to standard
6. what current IS being pulled - did you invest in a whattmeter or similar ?

It does sound as though the battery is flagging rather than the LVC activating -  as this usually results in the motor beiong stopped or pulsing on and off, and you say "there is a noticable loss in power and i have to land".

[Louis Benjamin]

thanks Timbo,

As u said in your first post, it was the prop. i have just tried a ACP 11x5.5 prop on it and i`m getting 10mins flight......even on full power!!!!. with a little throttle control,  i`m sure i`d get 12-13 mins per flight.   

The batteries i`m using are a flightpower evo25 and a tornado proffesional 22c-both are new. They are taking over an hour to balance charge now, whareas it was only charging for around 40 mins before.

thanks for your help, i`m glad it was something easy to rectify

[Tim Mackey]

Good, glad we sorted it for you

[Terry Whiting]

Louis,  When I became interested in electric, I  read  many articals by Nigel Hawes, he stated anyone who is about to delve into electrics,  he advised the first item to purchase was a Watts meter, and this I did. I think  it's an extremely valuable piece of kit that no serious electric flight modeller should be without, could save you £'s in the long run. 

[Flash1]

you all recommend a watt meter but as a novice how do I know what to do with it and what is it for ?

[Nick Rigg]

You insert the meter between the battery (input) and ESC (output)

Then you can check the readings to determine current being drawn, watts produced, battery voltage and the amount of power consumed

By switching between different propellor sizes, you can see at a glance whether you're going to fry your motor or ESC, whether you'll have enough power to fly your model the way you want to and probably how long you'll be able to fly for. Bear in mind that this static test will not be exactly the same as when the model is flying, for example in flight the prop 'unloads' and consumes less power

[Bruce Richards]

A watt meter plugs between the battery and the ESC in the red and black wires. It shows you the current draw of the motor and the voltage maintained by the battery. It is usually only used for ground testing and not left in the model while in flight.

The reason you should be interested in these two numbers is that if the current is too high you will burn out your motor/ESC and damage your battery. If the voltage is too low (say less than 3v per cell under load on a fully charged pack) you either have a very poor battery or you are pulling too much current (amps). It will also show you how may watts the setup will draw and hence whether it will fly the model. Most Watt meters also show you the cumulative power used which will help work out how long you can stay in the air before that battery needs charging.

So a watt meter could save you a lot of time and monye in burned out/crashed stuff. 

[Flash1]

Thanks Nick & Bruce. Guess I will have to get one.

[Terry Whiting]

After 50 years of I/C flying I'm now totally electric. Many would say I'm over cautious as   I  NEVER install any combo (motor & ESC) in a model until it's been on my test rig, albeit prop or EDF. The Watt meter is the only instrument capable of  giving all the required info other than digital scales for static thrust.

                                               

[Tim Mackey]

AMEN