Edgeomatic

My Feedback: (2)

Hey guys, I am having some problems with power and flight times. I have an axi 2208/34 with a castle creations 8amp controller. I have some 340mah 3cells, a 720, and some 1500 and the only ones that give the motor any power the the 1500's. My small batteries all of the sudden don't hold a charge or the don't put out the power. I use this set up on a shockflyer and all of the sudden everything is going bad. Is the motor shot, the ESC, or the batteries? I use a smartcharger 2500 if that helps.

Thanks for your help

jdetray

Have you used a wattmeter to monitor the battery performance under load? Perhaps your smaller packs can't deliver enough current and their voltage is dropping under load.

Let's assume your motor draws 5A. To provide that much current, your 340mAh packs would have to be rated at almost 15C. Are your 340mAh packs rated that high? Even if they are, the flight time at 5A with such a small pack will be very short.

A formula for calculating approximate flight time is:
flight time in minutes = (capacity of battery/current consumption) x 60

So if we have:
340mAh pack
5A (or 5000mA) current comsumption

We can plug in the numbers:
flight time in minutes = (340/5000) x 60 = 4.08 minutes

That assumes you run the batteries until they are totally depleted -- not a good idea with lipos. So actual flight time will normally be less than the calculated value -- maybe 3 minutes? And this assumes that your 340mAh packs can even deliver the required current (5A in our example). Perhaps you are expecting too much from those small packs, in terms of either the current available or in the flight times.

The 720mAh pack will do better.
flight time in minutes = (700/5000) x 60 = 8.4 minutes

Again, that's an idealized value probably never reached in actual flying. Maybe 6 minutes or less in actual flying?

Another thing to check. What is your battery voltage fresh off the charger? A fully charged 3S pack should measure right around 12.6V. If it is much lower than that, it could indicate your charger is not doing its job or that the battery is failing.

- Jeff

Edgeomatic

My Feedback: (2)

See thats what I don't get about all of the electric stuff. The 340s I have would fly my shockflyer for 9-12 minutes to what I would call extreme flying (plane is never still). Now it won't even fly for 1 minute. The 720 would fly it for almost 20 minutes.

jdetray

If nothing about the plane or its power system has changed (same plane, same motor, same prop), then I would suspect that either the batteries have gone flat or the charger is no longer charging the batteries to full capacity.

Measure the battery pack voltage after charging. A fully charged 3S pack should measure 12.6V, and a 2S pack should measure 8.4V. If the fully charged pack voltage is much lower than that, then either the battery or the charger has problems.

- Jeff

Edgeomatic

My Feedback: (2)

the batteries mosthave gone nad then because I have had a friend charge the batteries with his charger and it is a lot nicer than mine.

jdetray

What is the voltage of your battery pack after it has been charged?

- Jeff

Troy-RCU

My Feedback: (1)

Your pack sounds like it is certainly had it, done, kaput! I should also warn that once a lipo is at it's end in life, it can be more prone to "incidents" including puffing and fire. A small lipo like that can not take the same abuse (ie: current) as your bigger packs so you can't compare the two. Are they hot after a flight? That's an easy sign that usually means you're over doing it. Your packs should be just mildly warm to the touch.

You still haven't noted what brand of cell it is or what the manufacturers "C" rating is. Not all lipos are the same, you could be using lipos meant for ho-hum lazy park flyers when you're trying to huck it hardcore!!