[Ken Currell]

Hi

I just bought my first elecrtic motor

I have lots of cells I can use.
I have a choice of using 1.5 amp Makita Lithium Ion or 2.3 amp A123 cells.

The specs on the A123 cells are awesome but I can't find any specs on what voltage / cell to set the cut off on my ESC.

It is a Castle Creations Phoenix 80 ESC.

Thanks

[moo]

I would guess around 2.5 Volts per cell from the datasheet.

Clickety

[Ken Currell]

Thanks Moo

Just what I needed.

Good site.

[rcpilot]

I would not recommend setting the cutoff at 2.5volts. These cells drop voltage to around 2.5, 2.6volts under load of around 40 AMPS, you might loose your plane with a cutoff at wrong spot. Phoenix can be programmed for cutoff at any voltage, so set it to 1.5volts per cell. These cells don't get damaged like lipos, so its safe to set the cutoff at that level.
Just my opinion though.

[Ken Currell]

Originally Posted by rcpilot

I would not recommend setting the cutoff at 2.5volts. These cells drop voltage to around 2.5, 2.6volts under load of around 40 AMPS, you might loose your plane with a cutoff at wrong spot. Phoenix can be programmed for cutoff at any voltage, so set it to 1.5volts per cell. These cells don't get damaged like lipos, so its safe to set the cutoff at that level.
Just my opinion though.

I agree that the cells don't get damaged but when I looked at the discharge curve of the cells the voltage seems to drop rapidly around 2.6 volts. If I set it at 1.5 I could lose the plane because my bec might cut off and I could lose all signal from the receiver which would cause the motor to shut down.

Thanks for your input

[rcpilot]

Originally Posted by Ken Currell

I agree that the cells don't get damaged but when I looked at the discharge curve of the cells the voltage seems to drop rapidly around 2.6 volts. If I set it at 1.5 I could lose the plane because my bec might cut off and I could lose all signal from the receiver which would cause the motor to shut down.

Thanks for your input

I don't quiet get you, what I am saying is that if you set the LVC at 2.5/cell, there is a chance of LVC kicking in way too soon as the cells have flat discharge curve around that mark, setting it lower than 2.5 will allow you to use the capacity of the pack.

You didn't say how many cells you are using and how many amps. When you said Phoenix 80, I am assuming you are using something that needs nhigher amps and voltages, in that case the BEC in the ESC is disabled with a 3S or more cells.

Let me give you an example;
You take off fully charged with an LVC set to 2.5/cell, you are flying around and pull full throttle which causes a rapid drop of voltage down to 2.5V/cell the motor is going to be cutoff by the LVC, although you have battery capacity left, but the LVC is kicking in because you set the voltage close to what the dropped voltage is for the cells under load.

[Ken Currell]

Sorry, but I am new to electrics and I may have mixed up my facts from something I read elsewhere. I understand what you mean about setting it too high.

The esc is 80 amp but the price was right.

I will be using 5 A123 cells or 4 lithium Ion cells for each battery pack.
I prefer to use the A123s if they will fit in my plane.

My motor will draw 50 amps max, 40 for 10 min, but I expect to only use 30 to 35 to fly with.
Since it is my first electric I am using a LT 40 so the batteries should fit.
There are probably a few other things I should tell you. BUT WHAT are they?

Thanks

[roscoe]

Here is my $.02. First, use a flight battery to get started, your LT40 will not notice the weight. Set your LVC at 1.5-2 volts, and use a timer for your test flights. Set a conservative time, say 3 minutes for arguments sake. After the timer goes off, land, and charge the battery. Make a note of how much charge goes back in. If it is, again for arguments sake, 1300 mah, set your flight timer to 4 minutes, and repeat the process. Soon you will know what the pack's maximum flight time is, and you are not in danger of loosing control of the aircraft. You can switch to Bec or Ubec later on to save the weight.

[Ken Currell]

Good idea
At least it is a starting point.
I can always add another pack if it will fit.
These A123 cells are fairly large.

Thanks for the advice.

[rcpilot]

Agree with Roscoe totally.

Now that you have given your setup, with 5S A123, disable the BEC on the phoenix 80 by removing the red wire out of the recvr connector. Use an external battery pack either a NICD, Nimh or a small lipo with a regulator down to 6V. Then fly it a few times and measure how many mahs the flight takes and then follow that duration as Roscoe pointed out.