Current draw - stationary vs. in flight?

Getting ready to fly a new foamie (e-foamie Revolution 3D), with the recommended AXI 2212/26 motor, Phoenix-25 ESC, Kokam 3C 1500mah battery, and using the recommended props of either a 12x3.8 or 11x4.7 the current draw at max throttle drops the battery voltage to hit the 9V cutoff when testing it just holding the airplane in position. I've monitored the voltage with a DVM and it is hitting the 9V mark with the 1500mah batteries, but a 4200mah holds up (but is too big for this airplane). Haven't tried a amp meter yet, as I don't have anything that goes over 10a. Has anyone experimented with the current difference between loading it down in a stationary position vs. what might be expected in flight???

TIA

Don

Reply to
CRaSH
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The current draw will drop a bit in flight - exactly how much depends on the prop, RPM and airframe drag. In my experience, testing with an air compressor blowing into the prop saw the current draw drop from 11A to 10.5A on an 8x6 prop, but I don't know if the air compressor stream actually related to anything real.

What I did notice is that while the current draw in flight tends to be less, as soon as you pull up into a static, or close to static manouver, ie a hover, the load becomes the same as holding it in your hand, and the battery cutout will trigger if the pack can't deliver the amps.

Reply to
Poxy

With such fine pitched props you are likely to be flying right up to pitch speed and might see as much as 40% or more current reduction in motion.

BUT this is a 3D plane, and unless it can hover at less than 60% throttle, that is where its likely to approach static draw.

Kokams are perhaps the worst cells for voltage drop under power as well, and in fact probably the worst cells period.

If the motor is holding up, switch to another brand of cell. I'd say polyquest would suit the sort of price performance bracket you are looking for.

Reply to
The Natural Philosopher

That's what Tim at E-foamie's replied, also... Until I upgrade my battery inventory I guess it'd be wise to do my 3D practice at a 3 mistake altitude, and maybe prop down a bit if hitting cutoff... Current stock should be good for my maiden shake down and getting used to how it flies though. So far all my airplanes fly better than I do anyway.... d:->))

Yep, Tim also recommended Poly or TP (which is what my 4200mah pack is, used in a Pigi)

Thanks....

Reply to
CRaSH

Finally got around to putting a ammeter in the battery circuit, just noticed my bench meter does go to 20a, whereas my travel meter is limited to 10a. Which didn't matter much, because the 2212/26 motor seems to top out at

10.5a on a 3S2P 4,200mah TP, using some skinny test leads (alligator clip kind) that undoubtedly limited things a wee bit since I already had the connectors off the ESC, and tried props from 11x7 down to 9x6 without much difference.. Motor is rated for 12a. Unfortunately, the 1,500mah Kokam go to their knees at 6 amps! A little surprising and it looks like the general concensus is correct. A TP-2100 3S 10-12C is only one oz heavier than the Kokam, but the TP-1320 would be nearly one oz lighter, so now do I want show time or air time?? With my skill level, air time may be needed more... Decisions, decisions, decisions......
Reply to
CRaSH

I have come to believe that a cut off voltage of 9.0V on a 3s system i

a very conservative setting. At 9.0v a lipo still has a lot to give. always set my cut off voltage to no higher than 8.4V. I get more ru time from the batteries with no ill effects. I have one system set t

7.2V cut off. Because I draw 25 amps and have very long leads from th motors to the esc then on to the battery. I believe I have about a 1 drop between the battery and the motors due to the long wires, esc etc. So the battery still does not go below 8.2V. But bein conservative with lipos seems to be the norm

-- harolds

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Reply to
haroldsb

Not if its being run at a sesnible discharge rate - i.e. a safe one, about 75% of manufacturers claims, or 50% of Kokams...

Generally when it clips 9v, uyou have 95% of the capoacity gone.

Only if you really cane the pack will its voltage drop velow 9v with any significant capacity left.

I
Reply to
The Natural Philosopher

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