kymike

This is my first experience with brushless motor setup. I replaced the motor that came in a gws e-starter with an e-flite 370 brushless motor and phoenix 25 speed controller. I kept the gws 6.6:1 gear box and 1080 prop. The motor bolted right in. I built a 3s 15oo ma battery pack from 3 kokam batteries I had. All batteries had the same specs. but I can't remember the discharge rate. The speed controller is set at a 9 volt cut off. The problem is that the motor cuts off when I give it full throttle or try to climb fast. I tied the plane to my workbench and put a voltage tester on the battery while giving full throttle. The voltage drops below 9 volts so I believe the speed control is cutting off power to the motor. I want to be able to fly at full throttle and do some aerobatics . My question is why is the voltage dropping so low? Could the discharge rate of the batteries be to low for this set up? I tested the amp draw under full throttle and it is about 15 to 20 amps. I suspect the battery pack just isn't enough but I'm not sure. What battery requirements do I need if that is the problem. Thanks for helping.

jonnyjetprop

My Feedback: (3)

The kokams at best can support a 12 amp discharge rate. Running two packs in parallel should fix the problem.

John

Foamaholic

My Feedback: (1)

You could set a soft cutoff on the esc if it isn't set for it. I think the default setting is soft though.
If that doesn't fix it you could program a lower cutoff voltage, like 5 volts for even 4 volts.
I know that's too low for the lipos, but if you make sure to land when power begins to fade you will be okay.
I doubt if your setup is pulling over 10 amps.
My esc always cut off until I lowered the voltage cutoff.

kymike

Thanks for the advice. I'm not sure I know what you mean by a soft cut off on the speed controller. Also, would it be better to use a battery that has a high discharge rate? If my set up is drawing around 10 amps should the battery have a discharge rate of 10 amps or higher? Would this help keep the voltage from dropping to much under load?

Foamaholic

My Feedback: (1)

Don't exceed the amp draw of the battery pack's rating, or it ruins lipos.
If the rating is 10 amps then don't exceed that. The best way to know for sure is with a meter like the AstroFlight Whattmeter. It's probably saved some of my batteries. With it you know exactly what you are drawing. Shows, amps, watts, and volts. It's easy to use and almost indispensible.
The instructions with Castle controllers tell how to program it for cutoff, etc.
The soft cutoff slows the motor down without cutting it off. The hard cutoff cuts it as soon as voltage drops below the cutoff voltage you have set.

kymike

Thanks for the help. I found the cutoff type instructions for my phoenix 25 and I understand the differences. I will also lower the cut off to 7.2 volts and land when batteries show they are weakening. I will also double check the amp draw under load with a meter and buy the appropriate batteries. Thanks again for helping.