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Battery "Y" Harness - 4/1/2009 2:52 PM   
whagen01


 

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Status: offline 		I'm doing a glow-to-electric conversion on a Phoenix Sukhoi SU-31 .46. I'm in the process of selecting a motor/ESC combo equivalent to a 40 to 46 glow engine, one that puts out 700 to 800 watts - I'm not interested in aggressive 3D, just flying around. The range I'm looking at is equivalent to the E-Flite Power 32 or 46 motors. The batteries I'll be using are 2200mAh/3S1P/11.1V/25C LiPos that I use in my helicopter. I plan to make a "Y" harness to wire two batteries in series to provide the needed power for the airplane.

Here's where I need someone's help. I'm not sure how to calculate the expected power output of the batteries in series. I'm hoping that once I know that, I can make a better decision as to which motor would be the best match.

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RE: Battery "Y" Harness - 4/1/2009 3:15 PM   
-pkh-



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Status: offline 		Here you go:

Power (Watts) = Voltage (Volts) x Current (Amps)

So for two of your 3S packs in series (effectively a 6S pack):

Max Power = ( 2 x 11.1 ) V x ( 25 x 2.2 ) A = 22.2 V x 55 A = 1221 Watts

Since you only need 800 Watts, you can divide that by your pack voltage to get the max current draw that you need for a 800 Watt power system:

800 Watts / 22.2V = 36 Amps

This means you can pick a motor/prop combo that only draws 36A from your series packs to get 800W of power.

Since you have only 2200mAh packs, that's 2.2A hours, so your series packs will only last 3.7 minutes (2.2Ah/36A=0.061h=3.7mins) at full throttle (assuming 36A draw for the 800W setup). Rule of thumb is you can probably double that time for most flying, since you won't go full throttle all the time, so that may get you ~7 minute flights.

< Message edited by -pkh- -- 4/1/2009 4:05 PM >

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RE: Battery "Y" Harness - 4/1/2009 3:27 PM   
jumper666



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From: N. Richland Hills , TX, USA
Status: offline 		My guess is you already know this but here goes. Putting batteries in series raises the voltage. Connecting them in parallel increases capacity.

2X 3S 2200mAh packs in series yields a 6S 2200mAh 22.2V.....gain voltage and maintain capacity
2X 3S 2200mAh packs in parallel yields a 3S 4400mAh 11.1V...gain capacity/duration and maintain voltage

One suggestion for .40 to electric: http://www.modelflight.com.au/eflite/glow_conversion_040_brushless.htm

See if this link takes you to a model/motor/esc setup computer: http://www.modelmotors.cz/axisetuphobby-lobby/index.php?page=711&product=&kategorie=&serie=&motor=Sport&gram=112&ounce=&hmotnost=o

Motor comparisons: http://www.micronradiocontrol.co.uk/scorpion_data/comparison.html#scp30

Ready made Y harnesses:

Deans series: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXNKY9

Deans parallel: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXPTT6&P=ML

Deans parallel: http://www.maxamps.com/Deans-Parallel-Adapter.htm

" " : http://www.graysonhobby.com/catalog/product_info.php?products_id=184

" " : http://www.rctoys.com/rc-toys-and-parts/DE-HARNESS-2P/RC-PARTS-CONNECTORS-WIRING.html

Suggested powers:

50 - 70 watts/lb = min for light park flyers
70 - 90 watts/lb = trainer and slow flight
90 - 110 watts/lb = sport aerobatic & fast scale
110 - 130 watts/lb = advanced aerobatic & high speed
130 - 150 watts/lb = light 3d and ducted fans
150 - 200+ watts/lb = unlimted 3D

If I am correct, your acft AUW ~7lb. If that is close, your 800W is in the ballpark for the type of flying you want.

********************************

pkh, that info was helpful to me too. Thanks.

< Message edited by jumper666 -- 4/1/2009 3:38 PM >

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RE: Battery "Y" Harness - 4/2/2009 2:10 PM   
whagen01


 

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Status: offline 		Jumper and pkh

Thanks very much! That info was really helpful, but brought up another question I hadn't considered until now. The E-Flite Power 46 motor that I'm considering has an input voltage range of 14.4 to 19.2. Connecting the batteries in parallel will be below the required minimum voltage (11.1), but connecting them in series will be above the maximum voltage (22.2). Does that mean I should look elsewhere for a motor? Or is the Power 46 still capable of handling the power? Should I stop worrying?

Also, the flight weight of the Phoenix Sukhoi SU-31 .46 is listed as 6 lbs. I haven't actually weighed it, so I can't be sure. But I've heard that glow to electric conversions can actually reduce the weight of the model. If that's true, and the model I'm dealing with has no extra weight, then 800W should be more than enough. I hope

Again, thanks to both of you for your input.

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RE: Battery "Y" Harness - 4/2/2009 7:01 PM   
jumper666



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Status: offline 		whagen01, 4S is the recommended battery for the Power 46. If you run it on 3S's in parallel, I have run my 6' Telemaster on 3S, it will be doggy and you will NOT be happy with its performance. So, looks as if you have a couple of choices. New 4S's or another motor. For the weight of your acft, I would suggest stepping up to 4S's. Also, new 4S's can be useful in other builds. Buying a new motor for this acft would be useful for only this acft. I resisted moving from 3S to 4S until recently when I got my first two 4S acft. They are a real improvement over 3S. Cost of 4S was a real put off until I ran across the Zippy brand battery. Check out Zippy batteries at: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_listCategoriesAndProducts.asp?catname=ZIPPY+Lipoly&idCategory=235&ParentCat=85.

************************

I second patnchris's good remarks below about getting a watt meter. If one is going to do much outside of plug and play tested setups with electrics, he NEEDS to be able to determine exactly what a setup yields.

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< Message edited by jumper666 -- 4/2/2009 9:05 PM >

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RE: Battery "Y" Harness - 4/2/2009 8:14 PM   
patnchris



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Status: offline 		I've run my Power 46 motors on 5S for years, without issue.....You need to watch your current draw as well as voltage....Running it on 6S would make me cringe a little, however, if you stay within the parameters, I don't see where it would be a problem.....I would say that you really need to get an inline watt meter like the one MPI sells.....Then experiment with different prop sizes to stay within the parameters of the motor....As long as you stay below the rated watts and current draw, I don't see where it would be a major problem. Keep in mind that on 6S (two 3S in series) you can throw out all the mfg specs for prop selection.....Forget trying to run it on 3S.....To get any real power out of it you would need a prop the size of a heli rotor.....Pat



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RE: Battery "Y" Harness - 4/2/2009 10:58 PM   
vmsguy


 

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From: Woodville, WI, USA
Status: offline 		If I may make a suggestion...

You may want to purchase two 2S battery packs instead of one 4S. If you do, make sure they are the same mAh and C ratings as your current 3S cells.

When you do this, you can then "build" 2S, 3S, 4S, 5S, and 6S combinations, connecting any two batteries up in series. Just a bit more flexibility.

Granted, two 2S batteries will cost a little more than one 4S battery, but if you foresee yourself flying these size and capabilities of planes, the battery flexibility and interchangability could be worth the few extra dollars.. It might make "stocking up" a little easier to swallow too.

Just a thought...


Oh...! Another thought... Personally, I've gone away from Dean's connectors, and use bullet connectors instead. Why? It makes connecting batteries in Series easier. Just plug the negative bullet of one battery into the positive of the next, and viola! I use a male bullet on one pole, and a female bullet on the other battery pole. I just have to be consistent. 'course, it makes connecting batteries in parrallel a bit more difficult. Pick your poison.

< Message edited by vmsguy -- 4/2/2009 11:06 PM >

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RE: Battery "Y" Harness - 4/3/2009 1:57 PM   
whagen01


 

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From: Fairfield, CA, USA
Status: offline 		I'm coming to the conclusion that in order for this plane to get into the air, I would need the voltage of two of my Lipos in series, but the capacity of two of my Lipos in parallel. So what I'll do is take four Lipos, and put two sets of two in series, then connect both sets in parallel! That will give me a 12S 4P 22.2V 4400mAh power source! That should just about do it!

I'm kidding. Send the guys with the nets away!

Seriously, I'm trying to figure out a way to make these Lipos work because (1) I already have a lot of these particular Lipos for other applications (helicopters, sailplanes, etc) and (2) I don't want to buy any more Lipos! So I'm changing focus. Maybe I can use an electric motor I already have - The 430XL from my Trex 450 SE V2. My question is this: Would a gearbox-driven prop work in this application? Would the motor fit? Can that combination provide enough power? Or am I barking up the wrong tree? Again?

As always, thanks to everyone for their advice.



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RE: Battery "Y" Harness - 4/3/2009 2:13 PM   
patnchris



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Status: offline 		I'm not familiar with the powerplant you are referring to so I'll leave that to someone else.

As to using the existing packs.....Go for it......My buddy flys a Funtana 50X (Power 60 size) on 4 3S 2100ma lipos. He uses the series/parallel set up you suggest. What he did was make a removeable tray that the packs mount to and then installs the tray in the plane. If you search the different RC web sites you will find a modular Dean's connector that parallels two packs and a Y harness that series packs. I actually use the parallel connector as it is modular. (no wires) On my series connections I prefer to solder the Y connection directly to the ESC. I'm of the belief that the less connectors one uses, the less loss you will have.


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RE: Battery "Y" Harness - 4/3/2009 2:53 PM   
whagen01


 

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From: Fairfield, CA, USA
Status: offline 		Wow! I thought I was crazy for suggesting using four lipos! I guess not.

I'm still researching the possiblility of using a gearbox-driven prop with the Trex motor. But for now, I guess the 4-battery option is still available. Thanks!

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RE: Battery "Y" Harness - 4/3/2009 3:14 PM   
snuts


 

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From: camrose alberta, AB, CANADA
Status: offline 		whagen01,I have been very happy with the dualsky motors that I fly (10 now). They make a xm4250ca6, which 840 rpm/V 3 or 4 cell rated at 900w. they also make a xm4260ca6,which is 566 rpm/V 4 to 6 cell rated 1100w max. They might help you out, there must be others similar. I purchase here in Canada, and are very happy with the line. The only source that I have been exposed to state side is 2dogs rc, again there must be others. Hope this helps Snuts

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RE: Battery - 5/17/2009 2:22 AM   
speedy72vega


 

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Status: offline 		You also might want to check Rimfire motors by Electrifly. Very reasonably priced too. They have a motor, p/n 35-48-700 that would be perfect. 777 watts at 35 amps, and it's only 35mm wide. It is capable of running on 22.2 volts. At 700kv, is capable of spinning a decent sized prop also.

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