Dyehard

I'm in the process of assembling a Great Planes Mini Super Sportser which will be used to give my grandsons some flight time. At the hobby shop today I was talking about which battery to use and the answer I recieved from the guy working there has me somewhat confused. My options were a 2000MAH eight cell nickel metal hydride or a three cell 1320MAH Li-po, and the hobby shop guy said that the Li-po pack would run much longer than the nickel metal hydride pack. While I'm quite new to electrics, that doesn't make any sense to me. The last I heard 2000 MAH was more than 1320 MAH. Given that the throttle is set to produce a certain RPM, I would think that 2000MAH would last longer. With the throttle wide open, I would think that the 11.1 volts of the Li-po pack would cause the motor to draw more current, produce more power, and run down even faster. Maximum power and minimum weight are not my requirements, the longest run time is. I would appreciate any views on this.

Trogdor the Burninator

Well, the weights of the two packs are dramatically different. So, while the larger capacity nimh technically has more juice, if you have to run the motor at full throttle to maintain enough airspeed to keep that brick aloft, maybe you will run it out sooner!

I think you get it overall but don't discount the weights. Anyway a 1320 does great in sub Speed 400 type motors which I think comes with this plane(?) However, most of those motor don't take the voltage of 3 cell lipos too well and quickly burn out.

I guess for a good recommendation I'd need to know what motor/gearbox/prop is used but using stock brushed motors you might be better off with a 2100 2 cell lipo... run forever and so light you don't need to be heavy on the throttle to stay up.

Trogdor the Burninator

Well, I got interested and looked on Tower and this plane is a little bigger and heavier than I thought. It does use a geared speed 400 so the 3 cell is probably a good choice, however since the voltage is higher (runs the motor faster) you might want to drop the prop load a bit to keep it from overheating. a 1320 would run it but speed 400s arent too terribly efficient so you might want to go with a thunder power 2100 3 cell for about 70 bucks for more flight time. That should last a good long time and be reasonably light (~5 ounces)

Tall Paul

You might let the smoke out of a conventional 400 brushed motor with a 3 cell lipo.
2 cells might be a safer option.

Dyehard

Ok, thanks for the opinions and ideas. I was already worried that 11.1 volts might be a bit to much for the stock motor, but I hate to drop back to 7.4 volts. That should cause a fair drop in performance from using a 9.6 volt pack. The airplane is fairly large and maximum performance is not the goal. Thunder Power lists the weight of their twe cell pack at 5.4 onces, I would think the eight cell nickel metal hydride pack probably only weighs a couple onces more and the little Super Sportster should handle that pretty well. I still haven't gotten a definative answer to my original question. Given that you just hold the plane in your hand for a static run, which will run longer, the 2000 MAH pack or the 1320 pack?

Matt Kirsch

My Feedback: (21)

Well, you wouldn't do an extended static run like that, unless you like burning up your motor... Theoretically, though, the 1320 would go dead far sooner at maximum throttle, because A) the higher Volts cause it to draw more Amps, and B) it has a smaller capacity. Realistically, you'd have a cooked motor, and probably a cooked LiPoly too...

In real-world flying, as was mentioned above, you would probably see at the very least, a wash. The lighter LiPoly makes it so the plane doesn't need as much power to stay aloft. Plus, the higher voltage causes the prop to spin faster, so you will also use lower throttle levels there as well.

A 2000mAh NiMH weighs approximately 1.6 ounces per cell. 8 cells... That's 12.8 ounces vs. 5.4 ounces for the 1320 LiPoly.

HOWEVER, you're pushing that 1320 pack to the limit, AND you're pushing the 400 motor well beyond its limit. A 2S 2100 Thunder Power LiPoly would be more appropriate.

I see you're worried about the lower voltage. The reduced weight in this case will more than make up for the reduced voltage. Plus, that reduced voltage isn't as much as it seems. 7.4 vs 9.6? Nah. Try 8.0 vs 8.8. The LiPoly will hold its voltage better under load, especially this high-discharge Thunder Power pack. A fully charged 2S LiPoly will read 8.4 Volts. A fully charged NiMH 11.2 Volts. Under load the NiMH will drop to around 1.1 Volts per cell, while the LiPoly will hang out around 4 Volts per cell.

gwright

actually a 6V sp400 geared and propped appropriately to get the current down to 7 or 8 amps works really well on 3S lipo. Most sp400 setups recommended draw in the 10 amp range with 8 cells, so about 80 watts or so. Re-gearing and/or re-propping for 8 amps with 3S lipo gives you a touch more inpute watts than that, so power is roughly equivalent, but with lower amperage and higher current you have a slightly more efficient setup, plus the weight is down. A 3S 2100 thunder power pack is around 5 and half ounces, so it's equivalent to the standard 8-cell 1000mah hydrides normally used, and at 7 amps would compute to 18 minutes runtime at full bore, but you'll be much less than that in the air, so you'd probably see half hour or more flights.

Dyehard

I was hoping that static run comment might get some real info that I could digest. It looks like it's between a two or a three cell 2100 Lipo pack. I think I'll try the two cell pack first, if that doesn't do it I'll go for the three cell. Thanks Trog, Matt and Gary.

Dyehard

Just did a little checking. The original 1100 mil pack that Great Planes suggusted for the plane weighs a little over 6 oz. The 2000 mil pack that the hobby shop ordered instead, without asking me, weighs a whoping 13.7 oz. Ouch! That's ruled out. I checked the Thunder Power site again, the 2100 mil two cell pack comes two ways, one is with a JST connector. What's a JST connector? Price is the same either way.

Trogdor the Burninator

A JST connector is a cheap connector that is not designed for the current levels that these batteries can put out. They just seem to have become the standard with the cheapest equipment available. Some packs even have thinner gauge wire with the packs having jst connectors vs. packs with no connector. weird.

Jst is worthless for everything but the lightest of equipment and you're much better off converting to deans or some other quality connector. But that's just my opinion!

pikebishop

the 2000 will run signifigantly longer than the 1320. are you aware you will absolutly need a special charger for the lipos? nimh in the 1100 range will fly this without being overweight. kan or hecell in seven or eight cell configuration.

Dyehard

I'm sure the 1100 Mil nimh pack will fly it ok but the guy at the hobby shop said it was out of stock at Great Planes. I guess I need to check with Radical RC and see what they have. I still think I will go with the two cell 2100 mil Lipo. I already have a Triton charger, that should charge the Lipo pack ok. Where would be a good place to order the Deans plugs. A friend of mine bought an electric plane with lipo pack and Hacker brushless motor while we were at the Toledo Convention last spring so I know what the Deans plug looks like, but I haven't had to buy any myself. Half the effort in getting into a new segment of the hobby is learning the sources for the items required.
The whole reason for this post is that the guy a the hobby shop tried to convince me that an 1100mil nimh pack would only run the little Sportster around five minutes, the 2000 mil nimh would maybe double that and the 1320 Lipo pack would run it over a half hour. That didn't sound feasible to me. The results from this post have comfirmed my suspicions and added quite a bit to my meager store of informtion on electrics. Thanks everone, I appreciate the effort.

Trogdor the Burninator

allerc.com
parkflyermotors.com
balsapr.com


these guys are good and probably all have Deans connectors. Do some searches on soldering Deans connectors for some ideas. If you solder one on without being connected to its mate, the plastic can melt a little and get the metal a little misaligned making separating them difficult! This is with the Ultras, not the micro connectors. 2100 2S should be equivalent to a lighter (~2oz or so?) 7 cell nimh or so, also consider upgrading to the 3S later for more power when you get bored with the 2S and just prop down a little to keep the components cool enough.

Have fun!

pikebishop

I usually buy loose cells from dynamoe electrics and build my own packs it's cheaper that way and you get exactly what you want.

pikebishop

just checked over at dynamoe and kan 1050's are 1.50 / cell. all the pack building supplies you could need are available also.

Matt Kirsch

My Feedback: (21)

www.cheapbatterypacks.com. If you're a soldering novice and you want your custom packs NOW, try them.