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Old Dec 20, 2010, 04:39 AM
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Question about motor and lipo

Hi. I am new the electric plane. Would like to ask a very noob question.
If a motor is recommended to use a 25C lipo, wats the pros and cons of using a high discharge lipo ie.45C lipo? Will the motor burn out?
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Old Dec 20, 2010, 05:09 AM
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Motor will only draw the current it requires

Higher 'c' rated pack will have a slightly higher voltage under load, meaning more motor rpm's

Cheers
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Old Dec 20, 2010, 05:25 AM
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So if the motor is drawing lesser than the lipo is supporting, any disadvantage? For example, the motor is drawing about 30amp and i m using the nanotech 45~90C lipo, is there any disadvantage?
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Originally Posted by crusey_aus View Post
Motor will only draw the current it requires

Higher 'c' rated pack will have a slightly higher voltage under load, meaning more motor rpm's

Cheers
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Old Dec 20, 2010, 06:19 AM
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Originally Posted by SpoonEK View Post
So if the motor is drawing lesser than the lipo is supporting, any disadvantage? For example, the motor is drawing about 30amp and i m using the nanotech 45~90C lipo, is there any disadvantage?
You are mixing specifications. 30 amps is an absolute current requirement. In order to determine the correct battery you have to specify it's mah capacity and voltage. Just saying the battery is 45 to 90C doesn't give any information about the battery's capacity.

For instance if you have a 3s 800mah 45C battery it can supply 36 amps. But at that rate it will fully discharge in just under a minute and a half.
However a 3s 3000mah 20C battery will supply 30 amps for 6 minutes.

Glen
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Old Dec 20, 2010, 06:28 AM
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The C (capacity) rating of a battery is a measure of how many amps (or current) your battery can deliver at one time. Your system will only take the current it needs proper voltage is what you have to be careful about. Think about it, most homes in the US have 15 amp outlets but you can plug anything that runs on 110v from a low draw alarm clock all the way up to a toaster.

A 1000mAh 20C battery can put out 20amps. 1000mAh=1amp x 20 =20 amps. A 1000mAh 45C battery can deliver 45 amps. The 45C battery won't last any longer than the 20C version but it can put out over twice the amperage in the same period of time. A higher C rating won't hurt your system as a matter of fact a higher C rating will make your battery run cooler with less stress. The down side of higher C rated batts. is that they are little more expensive and they generally weigh a little more

BTW, C rating does not effect the net voltage of a a lipo battery max voltage per cell is 4.2v a 3s battery is always 12.6v when it is fully charged regardless of the C rating.
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Old Dec 20, 2010, 06:37 AM
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Originally Posted by SpoonEK View Post
If a motor is recommended to use a 25C lipo, wats the pros and cons of using a high discharge lipo ie.45C lipo?
PROS= battery will run cooler CONS= price and weight will be more
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Will the motor burn out?
Not from using higher C rated pack. The above post explains why.
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Old Dec 20, 2010, 07:00 AM
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Originally Posted by Arkansas Travelr View Post
BTW, C rating does not effect the net voltage of a a lipo battery max voltage per cell is 4.2v a 3s battery is always 12.6v when it is fully charged regardless of the C rating.

Not sure what you are trying to say in that statement, nobody mentioned the fully charged voltage of a pack

'C' ratings are determined by the internal resistance of the cells / pack

Under load higher rated packs will and do hold a higher voltage

Cheers
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Old Dec 20, 2010, 07:21 AM
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Another thing to keep in mind is many of the cheaper lipo brands may not deliver their stated C rating so it's not a bad idea to up your C rating if you buy cheaper packs. If you are new to lipos you'll also want to follow the "80% rule" try not to use more than 80% of your batteries mAh rating during flight (1000mAh batt only use 800mah). This will help your battery last more charge cycles.
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Old Dec 20, 2010, 07:24 AM
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Thank alot guys!! I have better understanding now.
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Old Dec 20, 2010, 07:25 AM
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Originally Posted by Arkansas Travelr View Post
BTW, C rating does not effect the net voltage of a a lipo battery max voltage per cell is 4.2v a 3s battery is always 12.6v when it is fully charged regardless of the C rating.
Only true with NO load. As soon as you put a load on, the voltage will drop. A battery with a higher C-rating will drop LESS than one with a lower C-rating so you'll end up with a slightly higher voltage UNDER LOAD...which is exactly what was stated .

Steve
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Old Dec 20, 2010, 07:32 AM
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Sorry. One more question. Anyway to calculate the flight time?
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Old Dec 20, 2010, 07:39 AM
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Depends on throttle usage

Minimum flight time = battery-capacity (Amps) / motor discharge rate (Amps) * 60 minutes.

So, 1500mAh battery, 10A motor discharge, 1.5 / 10 * 60 = 9 minutes.

Of course, then you have to factor in things like being safe, so cut that back to 65~75% to leave yourself enough power to safely land.


Paul.
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Old Dec 20, 2010, 07:43 AM
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Thankyou!!
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Originally Posted by pldaniels View Post
Depends on throttle usage

Minimum flight time = battery-capacity (Amps) / motor discharge rate (Amps) * 60 minutes.

So, 1500mAh battery, 10A motor discharge, 1.5 / 10 * 60 = 9 minutes.

Of course, then you have to factor in things like being safe, so cut that back to 65~75% to leave yourself enough power to safely land.


Paul.
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Old Dec 20, 2010, 07:57 AM
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Quote:
Originally Posted by crusey_aus View Post
Not sure what you are trying to say in that statement, nobody mentioned the fully charged voltage of a pack

'C' ratings are determined by the internal resistance of the cells / pack

Under load higher rated packs will and do hold a higher voltage

Cheers
Sorry I misunderstood you I now understand what you are saying a higher C capacity battery will hold its voltage at a higher level during the discharge. Thanks for the info I didn't know that pro aspect of C rating.

Since the OP is new to electrics I stated the max volts per cell/pack because I didn't want them to think a higher C battery would deliver higher max cell voltage.
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