ahicks

My Feedback: (2)

To be blunt, I would not run that combo on a NiMh in a 20cc anything. To be fair, I think you're close. The likelihood of trouble may depend on the plane/flying style you're considering. 20cc powered 3D flight would be out of the question. With something like a 20cc Great Planes Revolver (or similar capable "sport" types) being flown hard, I'm betting you could easily be in for some trouble. With a 20cc Stick or Cub type flown conservatively (touch and goes only, or take off, fly a couple of laps, then land), your combo might be OK.

My opinion, FWIW, -Al

lamarkeiko

My Feedback: (1)

Al & speed, you guys got me convinced to purchase a LiFe battery for my receiver power. The plane this system is for, is a Four Star 120 l'm building now. I did some checking with Tower, and they have a Trinity 2300 LiFe for $31.99. I also checked with Hobby King, and I can get a Zippy 2500 MA LiFe from their West warehouse for $10.23.
Would these be acceptable? As for connection, I assume they will go straight to the receiver via the manual switch. I can still use the 4.8 V 2300 ma NiMH battery for the ignition. Is that correct?
Just to be sure, will the 6.6 V LiFe battery be safe to use by itself without regulator for receiver & servos?

Lamar

ahicks

My Feedback: (2)

Yes, for your 4*, you should be good to go with either of those, set up the way you're thinking.

When that plane is up and flying, suggest you keep an open mind on this, and read what you can find to learn more about it. You may find there are better ways (e.g. the BEC mod already discussed) that are popularly used in planes maybe one step up from your 4*.

kmeyers

Lamar let me throw this out there.

The whole flight uses very little electricity. What most guys miss is how much current is required for very brief fractional seconds. We often charge, fly and recharge, just to check flight needs. The flight needs are very small, one hour of your set up will be less than say 400 mah @ 6.6v.

When 2.4 first arrived 4.8 volts packs were browning out and causing receiver reboots. Instant current draws of lets say just for argument 2 amps would lower the system voltage. This was especially true on Nimh paired with digital servos because of there design.

So without a lot of tech stuff you can see that a 6.6 Life pack of 1500 mah would power a small plane for 1 hour and have 1100 mah left. Also the draw of your ignition at max RPM for 1 hour would be another 500 mah. So an IBEC would still leave you with 600 mah in reserve.

So the short is 1500 mah 2s 30C Life is comfortable discharging 45 amps for 2 minutes and Nimh is not. This is why we are using them. You would need some hefty wire and connectors, but, you should get the point.

I hope this helps.

.02

lamarkeiko

My Feedback: (1)

Al, speed & kmeyers,
I should be receiving my 2500 ma LiFe battery soon. The Rexel kill switch mod seems easy to do. Now, if I do that mod, is that LiFe battery enough by itself to power my complete airplane system (ignition, receiver, digital servos), and how many flights can I expect? Or is my best option to use my 2300 ma NIMH battery for the ignition and not do the kill switch mod?
Can the LiFe battery be charged without removing it from the plane, such as through the charge jack on my manual power switch.

Lamar

Flyfast1

My Feedback: (1)

Hi Lamar,

I may not have this right, but it appears that the power path for the receiver goes through the optical kill switch, which doesn't seem correct. The battery switch should provide power directly to the receiver and the optical kill switch should be connected between the receiver and the ignition. The optical kill switch should cut the power path from the receiver to the ignition module, but should not cut power to the receiver.

-Ed B. Edit: after looking at this again, perhaps this is just the way this particular optical kill switch is supposed to be connected?

ahicks

My Feedback: (2)

Yes, plenty of power available for the whole rig with a single 2500 LiFe. That's one of the bigger advantages of going this way.

You can charge the battery while in the plane.

You can also use that charge port to charge it, but you will need access the balance lead from the battery as well. Both need to be hooked up to balance charge.

My experience has been you'll have no trouble getting 3-4 flights on a charge. It would not surprise me if you found you could get twice that many. The way to find out for sure is to put a couple of flights on it and then see what it takes to charge it back up to full. Using the info you get there (let's say it takes 350mah) and knowing you can use up to 1250mah safely (1/2 the battery's capacity) you can see 7 flights shouldn't be too big a deal. You'll need to keep an eye on it for a while to get a good idea of what YOUR plane uses per flight.

kmeyers

Yep +1
You could easily be looking at 80-90 minutes flight time on a 20 cc model. But we sneak up to it with data and testing.

I love these computer chargers and the data they give us!

Data is power.

dirtybird

My Feedback: (5)

Considering that for many years I flew a much larger airplane on a 4 cell nicd(500MAH) I think you people are way overboard. Since we have the low voltage problem, I would feel comfortable with a 5 cell nicd. I dont do 3D but I dont think he is ready for that either.
Just my opinion.