rcflyeri

I want it all, more power, duration and weight savings. Can I use lipos with a standard sp 400 and esc ? Will I burn up the motor with a 3s pack? Can I time the flight to save the lipos from discharging too far? This is for a Kyosho Spree Sports with a geared 370, Great Planes mini reciever with built in 30 amp esc . My standard Soar Star is great but I want more. Thanks

theHarpmanDan

rcflyer,
You can use a 3s1p with the right gearbox/prop setup. If you do not do your homework right, you will fry that motor in short order! But with the right prop, and throttle management, you can get 30+ flights out of a standard s400


theHarpman

Matt Kirsch

My Feedback: (21)

Exactly right. A 3S pack has a higher voltage than the 6, 7, or 8-cell NiMH packs you'd normally use. This makes the motor spin the prop faster, which makes it draw more current, more Amps. Too many Amps, and the motor overheats and burns up.

You can mitigate this somewhat by using a smaller prop, but with a cheap can 400, you still have the high RPM problem. The bushings don't hold up to the extra RPMs very well, so the motor will wear out quickly.

lwien

Throttle management...................I'm using a 3s TP1320 in my 400 E-Starter.........Flies great at a quarter to half throttle..............

pikeman401

My Feedback: (1)

Anyone care to comment on the question about timing the flight to protect the lipo pack from going too far down?

lwien

Sure Pikeman. I will.

I've been using Lipo's with non-friendly lipo esc's for awhile now.

I use a Futaba 7c transmitter that will allow me to mix my throttle with the timer so that the timer will go on at a set throttle setting and go off at a set throttle setting. I also purchased an inexpensive digital voltmeter from radio shack.

When I first get the batt, I would fly her for 10 minutes, bring her back in and do a voltage check. Then take her up again for another 5 minutes and do another voltage check. After a few times of doing this, I get a pretty good idea of flight times before hitting that critical discharge point. I also can also detect a pretty obvious loss of power once the Lipo's are reaching this point and I land immediatly, but again, typically, I'll land before that happens because of the voltage readings and setting my timer accordingly. I've taken voltage reads on the batts after doing this, and so far, I have never discharged the lipo's below 3.3v per cell.

So, my first line of defense of over-discharging my lipo's is my timer. My second line of defense is a sense of a loss of power. If I feel that I need a third line of defense, an ESC with an adjustable low-voltage cut off would be in order, but so far, I have not felt the need for it.

Hope this answers some of the questions....

Wyohi

My Feedback: (1)

Just bought a Automatic voltage cut off device from FMA. Will shut your can motor down with your present controller for li-poly Batterys . Works with most older speed controllers it says . no need to time flihgt.

lwien

Yeah there is, and here's why. I bought a Li-Saver about two weeks ago and never used it. It's basically the same thing as the FMA device. The problem with these auto-detecting devices are that they adjust the LVC based upon the voltage that it sees when you first hook them up. In my case, I will fly multiple times on one charged lipo. The problem in doing this, is that when you take off on the second or third time on a lipo that is not fully charged, these auto-detecting devices can miscount the cells in the pack, and if it does, and you are totally depending on this device, then you can be looking at one blown lipo-pack.

Also, if you fly a mix of Lipo's and NiMh in the same plane, these devices can be a real pain.

Wyohi

My Feedback: (1)

He does have a point I had not thought of. Mine is on back order till march. You would have to recharge after each flight & this could be a pain. Got to regroup & think on thei. What do you mean it is a pain when you go from li-po to other battery I thought it would sense the voltage & make the proper changes for cutoff??

TaSaJaRa

I use lipos on my JustGoFly 400F powered Slow Stick. I have used these with no problem at cut off. The 2 ESC's I have used on this setup are Motor Max 20/25 and E-Flite 20a
I have run both to cut-off. The thing is they will auto detect fine on a full charged battery, But never fly and disconnect the battery then reconnect it for another fliight without recharging it to full. The auto detect WILL misread the battery. Before the brushless motor I used the stock 300 on lipos with a KoKam 20 ran it to cut-off many times no problem.
The only time you would have a problem if you do, is if you hook up a battery that is not fully charged.

Short Video of how well my SS takes off on a windy day with the 400F
http://static.rcgroups.com/gallery/d...g_Thompson.wmv

rcflyeri

Thanks for all the info! How about if I use a 2s1p in my Spree Sports 370 gear drive, time the lipos. That would be less volts than an 8 cell 600mah that I use now. I would save weight but have less volts which would save the motor. But is it enough voltage? I think a 3s1p would be better if I manage the throttle.

Thanks again.

Soarstar
Spree Sports
Kyosho foam Cessna
Tower electric glider
Puddle Jumper

inedesca

I do not see why these cut off devices should read wrong when a 3S is low and confuse it with a 2S since the lowest voltage for a 3S is 9 volts and the max voltage for a 2S is 8.4 volts, they never ovelap.
If it reads more than 9 volts it is a 3S if it is less than 9 volts it is a 2S.
Or am I wrong?

regards

lwien

Here is a quote from the instruction manual from the Li-Saver..........

"The Li-Saver resets each time a battery is plugged in. The cutoff voltage is determined from the initial voltage. If a mostly discharged battery is plugged in, the Li-Saver may interpret it as a pack with one fewer cells than it actually has. Hence, the calculated cutoff voltage may be lower than 3 volts per cell. Always plug in a charged or mostly charged pack for proper cutoff."

coolboarder

My Feedback: (9)

Howdy!

coolboarder

My Feedback: (9)

Whoops!

Not to beat a dead horse, but what should i do with a 3s1p lipo with a 50 amp esc and a cheap direct drive 480?

Throttle management or new esc?

Thanks,

lwien

If you plan on going up and flying the battery down on one flight and you don't plan on switching out that Lipo with nimh during the day than a lipo friendly esc is the ticket.

But.........if you do plan on multiple flights on one Lipo charge and you do have a lipo friendly esc, just make sure that you set it manually for the correct LVC and disable the auto-cell-detect feature.