Seattle/Renton/Bellevue/Kent Area 3DHS or just 3D Pilots - Page 737 - RC Groups
 Jan 06, 2013, 10:15 PM Registered User 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
 Jan 06, 2013, 10:49 PM ex-noob 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.
 Jan 07, 2013, 07:26 AM Registered User 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.
Jan 07, 2013, 11:56 AM
aka JetMan Joe
Quote:
 Originally Posted by harv_d 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.
 Jan 07, 2013, 01:22 PM KG7TTQ - Las Vegas 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. Last edited by mark_q; Jan 07, 2013 at 01:31 PM.
Jan 07, 2013, 04:19 PM
Go Hawks!
Quote:
 Originally Posted by harv_d 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.
 Jan 08, 2013, 12:07 AM Owner/Operator at NorthWest RC Don't get too excited, it's still pumpin gas through the business end...
Jan 08, 2013, 01:23 AM
Go Hawks!
Quote:
 Originally Posted by egaus 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
 Jan 08, 2013, 09:15 AM Registered User Chip Hyde double vision
 Jan 08, 2013, 10:27 AM Go Hawks! Harv, assuming the roads are clear..what day were you thinking of coming down?
 Jan 08, 2013, 11:27 AM Registered User Yes. I plan on coming down Friday evening. Figured I'll stop by your place first on the way down. Pm me your address.
Jan 08, 2013, 12:33 PM
Go Hawks!
Quote:
 Originally Posted by harv_d 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
 Jan 08, 2013, 01:15 PM Registered User 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
Jan 08, 2013, 03:40 PM
Gas Monkey Vic
Quote:
 Originally Posted by harv_d Chip Hyde double vision
NICE! I love biplanes