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Old Jan 06, 2013, 10:15 PM
harv_d is offline
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I have question for you guys about regulating voltage. The plane im putting together has 8 servos. Im planning on using a castle BEC to regulate the voltage. my question is:

If i use a 3000mah 3s lipo, will that last longer than running a 3000mah 2s?

harv
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Old Jan 06, 2013, 10:49 PM
Lardog is offline
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Considering some batteries (not hobby lipos) have their capacity indicated at "Watt hours" then it would stand to reason the a higher voltage 3000mAh pack should last longer at a given current rate.
Old Jan 07, 2013, 07:26 AM
dand2k is offline
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If your BEC is a linear mode type, it will draw the same current from both batteries and they will last the same time, but it will dissipate more heat with the higher voltage battery as "waste" because it has to drop more voltage in the regulation process. Linear mode types are not very efficient.

If your BEC is a switching mode type, then it will be more efficient and will make use of the extra voltage and draw less current from the higher voltage battery, and it will last longer. But most inexpensive BECs are linear mode types.

However, if we consider the BEC as a constant load with resistance R, then the current I(2s) = V(2s) / R and I(3s) = V(3s) / R. In this case, the current is greater for the 3s battery, and therefore the 3s battery will not last as long as the 2s battery.
Last edited by dand2k; Jan 07, 2013 at 07:56 AM.
Old Jan 07, 2013, 11:56 AM
MCSGUY is offline
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aka JetMan Joe
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Quote:
Originally Posted by harv_d View Post
I have question for you guys about regulating voltage. The plane im putting together has 8 servos. Im planning on using a castle BEC to regulate the voltage. my question is:

If i use a 3000mah 3s lipo, will that last longer than running a 3000mah 2s?

harv
Since the CC Bec is a switcher as opposed to a linear and If I were doing the calculations I wouldn't model it as a constant load, I'm with Lardog. I think the 3S would last longer. You could do a test on both types for the same duration and load and see which one takes more mah to recharge. Maybe lock the same robust servo at full load for 60 seconds, or something similar.
Old Jan 07, 2013, 01:22 PM
mark_q is online now
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KG7TTQ - Las Vegas
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3S will last longer. It's a power problem, plain and simple.
If you disregard losses and inefficiencies...

At 1C:
A 3S 3000mah battery will provide 3 amps x 11.1 volts for one hour or 33.3 watt/hours.
A 2S 3000mah battery will provide 3 amps x 7.4 volts for one hour or 22.2 watt/hours.

If your electrical system, on average consumes 25 watts, the 3S battery will give you 79.9 minutes of run-time.
On 2S you will get about 53.3 minutes of run-time.
So, the 3S will last 1-1/2 times longer.
RCG Plus Member
Last edited by mark_q; Jan 07, 2013 at 01:31 PM.
Old Jan 07, 2013, 04:19 PM
cryhavoc38 is online now
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Why didn't they run? A pass???
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Quote:
Originally Posted by harv_d View Post
I have question for you guys about regulating voltage. The plane im putting together has 8 servos. Im planning on using a castle BEC to regulate the voltage. my question is:

If i use a 3000mah 3s lipo, will that last longer than running a 3000mah 2s?

harv
One thing that the others might be forgetting is that the CC BEC Pro reduces max amp output as the input voltage climbs.
it would be advisable to use no more than a 3s pack for input voltage with those 8 servo's.


Max continuous current varies with the input voltage. The ratings are:

Input Voltage: Max Continuous Output Current
16V 15A
24V 13A
32V 11A
40V 9A
48V 8A
Last edited by cryhavoc38; Jan 07, 2013 at 04:35 PM.
Old Jan 07, 2013, 11:39 PM
egaus is offline
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Quadrophenia
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I'm curious about your 2s/3s plane with eight servos.

e
Old Jan 08, 2013, 12:07 AM
SupaTim is offline
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Don't get too excited, it's still pumpin gas through the business end...
Old Jan 08, 2013, 01:23 AM
cryhavoc38 is online now
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Why didn't they run? A pass???
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Quote:
Originally Posted by egaus View Post
I'm curious about your 2s/3s plane with eight servos.

e
I'm fairly certain he is planning out the electronics power for a gasser
Old Jan 08, 2013, 09:15 AM
harv_d is offline
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Chip Hyde double vision
Old Jan 08, 2013, 10:27 AM
cryhavoc38 is online now
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Why didn't they run? A pass???
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Harv, assuming the roads are clear..what day were you thinking of coming down?
Old Jan 08, 2013, 11:27 AM
harv_d is offline
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Yes. I plan on coming down Friday evening. Figured I'll stop by your place first on the way down. Pm me your address.
Old Jan 08, 2013, 12:33 PM
cryhavoc38 is online now
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Why didn't they run? A pass???
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Quote:
Originally Posted by harv_d View Post
Yes. I plan on coming down Friday evening. Figured I'll stop by your place first on the way down. Pm me your address.

done
thanks
Old Jan 08, 2013, 01:15 PM
stevelmaa is online now
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Hey guys. I've got a couple large outrunners for sale if anyone is interested, priced cheap to sell
https://www.rcgroups.com/forums/show....php?t=1804350
https://www.rcgroups.com/forums/show....php?t=1804344
Each one would work great in a 10s set up for a 12-13 Ilb plane. Also have some 18x8 Xoar props
https://www.rcgroups.com/forums/show....php?t=1804363
And I have 2 TFR6 FR Sky Futaba Fasst compatable receivers, I'd let both go for 30.00. Thanks everyone.
Steve
Old Jan 08, 2013, 03:40 PM
Vitter is offline
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Gas Monkey Vic
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Quote:
Originally Posted by harv_d View Post
Chip Hyde double vision
NICE! I love biplanes


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