Hi guys, hopefully not that dumb of a Q.

I recently converted a Cessna 182 .40 size to electric. Using a Phasor 45/3 and a Castle 70 amp that I had, I was advised and bought 2 seperate 4c 4000mah Li-po's.


Once I started rigging it up, I noticed I had plenty of power and time on one pack. Being the E-rookie I am its my understanding that adding packs in parallel only adds capacity or duration (flight time). With flight times above 15 minutes in capacity, and wanting to be a nice guy at the field not hogging up the pin taking 10 minuteflights:

WHY so much batteries? Was it just a 'here comes a fat wallet, lemme sell this guy 2x the batteries he needs' or is it really better to double the battery weight and flight times? Am I missing something else here?

I'm wanting to do a Corsair Hangar 9 conversion and the battery setups I read about are pretty substantial in size, duration AND cost. Why so much there??

well, a big reason is that the discharge ability of the battery is related to its size. say the battery can support 10c discharge, your 4000mah batteries can put out 40A each at that rate. if you put them together in parallel, now you can draw 80A. What I would suggest is, Invest in a whattmeter, then you can find out how many apms youre drawing. if its more than the discharge rate of 1 of the batts, then use both. if its under, well, you have an extra battery, now you get twice as much flying

Ok, so you are telling me that if my amp draw is too high, I'll cook the battery pack else not have full potential of the motor.

Checking the amp draw will tell me if the batteries can 'push' as hard as the setup will draw right?

Ok, fair investement since I've dumped nearly all my gas stuff in favor of elec.

With that setup and a 'cheap' pack as I described, what kind of watts should I be looking at for one, or deciding on both packs?

well, really, you want to be looking at amps. the motor will try to draw as much as it needs regardless of the batteries ability. so yes, it would cook the battery if its too high. the prop used has an effect on this, the bigger the prop, the more amps.
By Cheap pack, I assume you mean one that doesnt have a super high discharge rate.... lets assume it can handle 8c (pretty common) that means youre looking at about 32A per battery, or 64A combined in parallel. Just as a guess, Im gonna say you will need both batteries.
Watts is an expression of the amount of energy used by your motor setup. I believe the general rule is that you need to produce 50W per pound to achieve a rolling takeoff.... 75W/lb for decent aerobatics... and 100W+/lb for 3D.

hope that helps...

This is VERY helpful thanks.

Well I'm going to get a whatt meter and see where I am. After 10 or so flights on the single battery, easily cruzing at 1/2 throttle with plenty of authority to climb out (Cessna, not CAP232) I'm real interested in knowing what the real numbers are.

quick easy test in your situation is: how warm are the batteries when youre done? if theyre getting any more than just warm, its probably not good, but if theyre cool, then it should be fine

I have a temprature gun and I have been checking. After a 12 minute flight I'm at or under 100deg. Today, with a wonderful day I came back and checked it at 98 degrees after 12 minutes. Motor is super cool too.

My understanding is 120 degrees is your danger point, is that correct?

I dunno about actual temps, but 100 doesnt seem too bad

I believe the critical point for LiPolys is either 140 or 160 degrees F. Either way, you don't want them to get that hot. 120 degrees is uncomfortably hot for most humans to hold on to, and I always advise that if the battery feels too hot to you, it's too hot.

Ok one more... has anyone checked out the Hyperion meter instead of the Astro Whatt Meter? Is it worth the $90?

I'm not a tightwad, but if it isnt really needed for a sport modeler lemme kno~!