3850mah vs 3000mah

[wilinfla]

I am running an E-flite 90 with a castle 120HV speed controller on a 7.5 pound stik with an 18x7 prop. I have a 6s 3850mah 45c battery for it which I think is a good combo. I have a couple 6s 3000mah 25c batteries sitting around, how do you think they would work with this combo? I'm wondering if they will be powerful enough and provide decent flight times. Thanks.

[dahawk]

Wil,

There should be no reason the 3000mah 25 will not work. Flight time might vary slightly but check the math here:
http://www.wattflyer.com/forums/show...=power+systems

You'll have plenty of thrust

-Hawk

[JetPlaneFlyer]

The only issue with the 3000mAh 25c batteries might be their ability to provide enough amps while still holding their voltage.

Theoretically a 3000mAh 25C battery should be good for 75Amps (3000mAh/1000 x 25C = 75Amps). But some brands of battery have very optimistic C rating, also as batteries age their effective C rating decreases.

How many amps does the system pull?

[kyleservicetech]

Originally Posted by wilinfla

I am running an E-flite 90 with a castle 120HV speed controller on a 7.5 pound stik with an 18x7 prop. I have a 6s 3850mah 45c battery for it which I think is a good combo. I have a couple 6s 3000mah 25c batteries sitting around, how do you think they would work with this combo? I'm wondering if they will be powerful enough and provide decent flight times. Thanks.

Methinks a 3000 Mah battery might be a little light for an E-Flite 90 motor. www.motocalc.com predicts about 45 Amps for this combination.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=65869

[wilinfla]

My main concern is that I would have extremely short flight times. I am going to check the numbers tomorrow to see what they are pulling. What should I be looking for?

Will

[JetPlaneFlyer]

I don't think flight time would be too bad, probably in the 6-7 minute bracket. maybe a little more or less depending on how hard you fly.

[kyleservicetech]

Originally Posted by wilinfla

My main concern is that I would have extremely short flight times. I am going to check the numbers tomorrow to see what they are pulling. What should I be looking for?

Will

Depending on how much current and throttle you're pulling, flight times would be around 5 minutes or so with little reserve flying time.

If your ESC is a Castle Creations ICE series, this unit records all important data like amps, volts, watts, RPM and so on during a flight. This data and can be downloaded after a flight to your computer. Providing you've got the Castle Link dongle for doing that.

I've programmed my CC ICE series ESC's for a one second per reading, which for me has worked out well.

[wilinfla]

I do have the data link for the ESC. I want to run evrything tomorrow and see what it's pulling. I'll see what it shows me. I am still new to electrics, thanks for the advice.

Will

[hayofstacks]

You could always run two 3000 mah batteries in parrelell and double your amprage. And flight times if it can blance out okay like that.

[kyleservicetech]

Originally Posted by wilinfla

I do have the data link for the ESC. I want to run evrything tomorrow and see what it's pulling. I'll see what it shows me. I am still new to electrics, thanks for the advice.

Will

Let us know what your system results are. A lot of us wattflyer readers are interested.

[wilinfla]

I ran it today and it showed max current was 25.5 and max watts was 475 with the 3000mah battery.

Will

[kyleservicetech]

Originally Posted by wilinfla

I ran it today and it showed max current was 25.5 and max watts was 475 with the 3000mah battery.

Will

Ouch
Since Volts equals watts/amps, that's 475/25.5 equals 3.1 volts per cell. that's not very good for a decent LiPo battery. Those LiPos I've checked are closer to 3.6 Volts at the same type of load.

Just ran some 4000 mah cells, and at 65 Amps they measured 3.7 VDC per cell.

Did you recently charge your Lipos? If so, methinks your LiPos are running near the end of their life???

[JetPlaneFlyer]

Yep, if the numbers are accurate and if that was with freshly charged batteries then the batteries are ready for the trash I'm sorry to say Flying with those batteries means you would be hitting low voltage cut-out right away.

You haven't been leaving them fully charged while in storage by any chance?

Steve

[wilinfla]

This is the first time I have used the castle data so I need to check and make sure that I did it right. The battery is actually brand new and it was charged, I haven't cycled it any yet though. I looked at a previous run with the 3850mah battery and the max current was 35.1 with max watts at 801 which are much better numbers. It's cold in the garage today so I will play with it again tomorrow to see what I can get. I want to check all my connectors as well.

Will

[JetPlaneFlyer]

If it was really cold then that will pull down the battery voltage

[wilinfla]

It is a little chilly in the garage, about 40f. I ran it again and the numbers were a little better at 495 watts and 24.5 current. Would a smaller prop help the numbers?

Will

[JetPlaneFlyer]

If you keep the battery in your house for a few hours to warm up before testing then that will rule out low temperatures causing problems. Your numbers still dont look great that's about 3.37V per cell which is still poor for a fresh battery running at what should be 1/3rd of it's C rating.

What brand of battery are they?

A smaller prop will reduce watts and amps.

[kyleservicetech]

Originally Posted by wilinfla

It is a little chilly in the garage, about 40f. I ran it again and the numbers were a little better at 495 watts and 24.5 current. Would a smaller prop help the numbers?

Will

These electric power systems are critical on prop size, and battery voltage. An apparently small change in either one can result in a significant change in amps pulled and watts input.

Dropping your voltage by about 20% results in watts input dropping by about 40 or 50%, while using the same propeller.

Or, dropping your propeller diameter by about 20% while using the same battery results in the watts input dropping by about 50%.

[hayofstacks]

See if you can ballane it with both 3000mah batteries.

If you can, then try them in parrelel. This will double your power, and capacity.

Your batteries probably can't handle the current. Not a high enough c rating.

[JetPlaneFlyer]

Originally Posted by hayofstacks

Your batteries probably can't handle the current. Not a high enough c rating.

They are 25c and 3000mAh.. That 'should' mean they are good for 75Amps (3000/1000 x 25 = 75). 25 amps shouldn't be any problem at all to any 3000mAh LiPo, unless the batteries are performing below 10c.

wilinfla,
What brand are the batteries and what's it's history? You say 'brand new' but has it maybe been in storage for a while and if so was it fully charged during storage?

[nidly]

Originally Posted by hayofstacks

You could always run two 3000 mah batteries in parrelell and double your amprage. And flight times if it can blance out okay like that.

This would be what I'd do. I like longer flight times though.

[wilinfla]

Thanks for all of the advice. I ran it up yesterday for 8 minutes on the ground, the numbers are getting better. It was max current of 28.7 and max watts of 576, both batteries are about the same. After 8 minutes on the ground the batteries were reading 3.92 per cell so maybe it won't be too bad. I usually fly this plane slow at reduced throttle, if I can get 6 minutes flight times I will be happy. I bought these 2 batteries because they were a closeout at only $40 each.

Will

[wilinfla]

I did another run and the numbers keep looking better. I got 610 watts with a current reading of 24.5. I also stated the wrong c rating, they are 30c not 25c. I am assuming that cycling the batteries is helping with the numbers.

Will

[JetPlaneFlyer]

Originally Posted by wilinfla

I did another run and the numbers keep looking better. I got 610 watts with a current reading of 24.5. I also stated the wrong c rating, they are 30c not 25c. I am assuming that cycling the batteries is helping with the numbers.

Will

Well that's 4.14v per cell, which is too good to be true!

I think whatever you are using to measure the data is probably giving inconsistent results. It's impossible that the exact same system would give more watts but less amps, if the battery had improved you would have more of both. But anyway, it sounds like the batteries are providing more than enough power to go flying on, so probably no point in worrying about it too much.

[nidly]

I'm not sure how the castle system works , but it is easy to get funny numbers by reading all the maximums. The only accuracy is when all 3 data points are at the same time.

In otherwords the highest current and highest watts may occur at the LOWEST voltage and if those numbers were all figured up it would give a bad reading. I suspect that that may be what's going on here. It can skew the data either way.

Max power is max power , but max current can occur from snapping the throttle and get a "false" high reading along with a "false low voltage"

I think that to be consistent , I have used my bad watt-meter to get readings at WOT and pick the current and voltage readings at the same time. They always agree with power readings then. My set up is pretty crude compared to yours.