jbflier

I have been flying a Funtana 40, AXI 4120 w/Jeti 70 ESC, UBEC, (2) ThunderPower 3s2p 4200mAh and a 14x7 APC electric prop. My batteries seem to be fine (warm) after 1-6 minute flight, but I after I complete the second 6 minute flight they are conciderably warmer; almost hot. Is this normal? Maybe I should try a different size prop? I simply sport fly (loops, rolls, lumpshawhatevers, etc) and am having a ball with it, but don't want to do any harm to the batteries. Thanks in advance..........

Greg Covey

Hi John,

It's difficult to determine what you consider to be "hot". Typically, if you can hold them in your hand and they seem warm to hot, you are ok. Ideally, you want to keep the pack temperature below 150 degrees F. The real issues come from the fact that the center cells in the pack have no cooling so they are even hotter than the outside ones you can feel.

FMA will be selling temperature strips as a "Skyvolt Accessory" item soon. You could get some of these and see how hot your packs are really getting.

One way to limit the heat build up in your packs is too keep your flight time just a bit shorter. In other words, don't use all the capacity. Cooler packs will last longer.

Good luck!

jbflier

Thanks for the quick reply Greg. You may not remember, but you were a great help when I was getting into electrics. In fact, I enjoy it so much I thought about converting a little larger plane this winter, but I have an issue with the battery costs. The batteries in my Funtana are not too hot to handle, but I guess I'm just a little gun shy with the newness to lipo's. I did notice a slight swelling of the casing on both packs. Is this normal also? I've been using an Astro 109 for charging and per your suggestion, charging thru 2C and fly. I think I will pick up a temp gage for now, and then look at those temp strips when they are available. Does the 14x7 prop size seem about right? Again, thanks for the help/info.......

Greg Covey

John,

Yes, that prop size is good for your setup. Remember that you can always start with NiMH packs and then later convert to Lithium if you really like the way the plane flies but want longer flights or a reduction in weight.

Here are some views of the new Skyvolt packs due out next month. Notice the variable temperature strip on the front that can return to ambient after a cooling period. It allows you to monitor the pack temperature and modify your air flow cooling, if needed. On the back are two very high temperature dots that will stay black when tripped beyond 160 degrees and 180 degrees F. These affect the warranty policy since that level of temperature damages the cells.

Note the air gaps between the cells in the pack for superior cooling. A proprietary separator is used to separate the cells in the pack and allow some level of compression to absorb blows. It is the center cells in a pack that take the most abuse from heat.

Since you cannot overcharge or under-drain any cell with the Skyvolt system, you are simply left with the responsibility to keep the pack under 160 degrees F and to not draw excessive current beyond the specifications.

Matt Kirsch

My Feedback: (21)

I've always said if it's hot enough to make you uncomfortable, it's too hot, period. Sounds like you're uncomfortable, so the issue needs to be addressed.

Which 4120 AXi are you flying (/14 or /18)? What's the configuration of the two 3S2P packs (3S4P or 6S2P)?

Oooh, I just saw you mention "swelling." That's not good. Means you're drawing too much from the packs.

The 4120/14 and 3S4P configuration should be okay. Those batteries should be cool as cucumbers.
The 4120/14 and 6S2P setup... That's a problem. Way too much voltage for the motor, way too much prop. Can you say, "meltdown?" Sure, I knew you could
The 4120/18 and 3S4P setup... Now, that's just plain silly. Way too low on Volts. Wouldn't be a useful setup.
The 4120/18 and 6S2P setup could be a problem. You've got 42 Amps of capacity in the pack, and you'd be drawing in the low to mid 40's with a 14x7 prop. You're right on the edge. Running around at full throttle like this for exteneded periods would certainly cause the heat to build up in the packs.

www.modelmotors.cz is where all the good info on AXi motors is kept.

jooNorway

I agree with Matt if you run the 4120/14, 6S is too hard. But if it is the 4120/18 it should be a good match on 6S, and the propeller is not to heavy load. In fact it should run quite cool. The only thing I would have done different is to throw away the APC and run it on a Graupner CamCarbon (Freudenthaler) folder which is more efficient.
Are you sure the ventilation is sufficient? A common mistake is to forget this, especially the outlets...
I have began to use mostly Flighpower Extreme 2- Carbon LiPo because they have a good carbon-covering and cooling-tabs between the cells to ensure sufficient airflow through the middel of the pack too. Think these are sold as Duraflight or something like that in USA...?

jbflier

Thanks for all of the great replies. My set up is an Axi 4120/18, Jeti 70 OPTO, UBEC, (2) ThunderPower 3s2p 4200 in series;(6s2p)....this is what was recommended by Hobby Lobby when I told them of my Funtana conversion..............

proptop

My Feedback: (8)

Guys...I've been following this thread with interest...
Hope you don't mind if I ask a question or two...
I have an AXi 4120/14 that I intend to put in my Funtana S40 and have bought an APC 14x7E as my starting prop.
I'll probably get the Jeti 70A ESC, but I am not sure about the batt. requirements.

I'd like to be able to do IMAC style manuvers, and maybe hover for a few seconds at no more than 3/4 throttle on a fresh pack.
Do you think 2 Kokam 3200 3 cell packs in parallel would be enough? Would you please "crunch" the numbers for me?
I've been flying electrics for a while now, but this is my first project bigger than a mini Funtana.

Thanks

Cubano8

I have the AXI 4120/14 on an SA Corsair. I'm using 13x8 prop and a TP 5s 6000mah pack. Flying for 10mininutes with throttle management, mostly a little over 1/2, upon landing the battery is just warm. I made a large opening on the firewall, and a outlet port hole for airflow, which is very Important for cooling issues.

Cubano8

Here are some pics...

proptop

My Feedback: (8)

Thanks Cubano8
I've been thinking of a 4S4P set-up now...what do ya'll think of that?

jbflier

Hi Matt; You mention with my set up and prop size, I'm on the edge drawing 42 amps from my batteries. Do you have another suggestion for a prop or battery? I do have a 15x7 APC-E.....Thanks for all of the help..........

Cubano8

Depends on your AUW. This SA Corsair came out on the heavy side of 8lbs, so I needed the extra 3.7volts. So I figured 5s= 18.5volts x 40amps = 740watts. This turned out very nicley, and pulled the plane at a little above average scale speed, at 1/2 throttle, or 20amps. I do need the extra power at takeoff since I fly off a grass field.

I always use this figure on scale planes 100watts per pound, then go from there to figure out my motor selection and Li-Po packs.

I am going to start on my next project soon. It is a 70" twin scale WWII Jap KI-45. Blue cor material. I'm hoping for a target weight of around 7 lbs, so two AXI 2826/10 and two TP4S4P should do it. But I will build it 1st, Glass it, add retracts, etc. then do my final calculations.