DumbDawg

My Feedback: (3)

Crappy flying weather so all I ca do is look at the birds. I installed a switch on the K2 so I can plug in a bat and then turn the heli on or off with a switch. Dig'n thru my tool box and finding tons of 'Oh smeg I didn't know I had one of those" things... I found a ubec as well.

I am running a 40A Emax esc on the K2. I'd gotten the esc with a motor combo I'd bought a long time ago and when cooked a previous esc put this one on, works great.

So question is... should I put the ubec on or not!!! I think I'm starting to get a litllte to heavy now with the bulky 40A'r , 2200 Mah bat's and the switch I put on. I'm positive it will lift it all but will likely be as quick and nimble as a 300lb Turkish ballerina.

What says you all???

happy fly'n

Druss

Be careful with that switch, make sure it's capable of handling 25-30amps. Most switches that are used in RC are meant for use with 4.8v or 6v receiver batteries which power the receiver and electronics and therefore pull less than 10amps. Putting 11.1v and 30amps through that switch may fry it in mid air.

DumbDawg

My Feedback: (3)

I will def be on the watchful side... I used an automotive toggle switch so I'm hoping it will work ok. I'll keep checking it to see how warm it gets.

Thx bro

kianhon

Put your UBEC if you want a cooler ESC. I find it useful to me cuz daily I fly 7 packs non-stop with Idel Up. Jerk my throttle alot cuz is really windy up here in Michigan

funflier

where is the toggle installed in relation to the circuit as I cannot think of any automotive toggle switch right off that is designed to handle say 20A DC (thats why they make relays). As for a bec or a UBEC (stepping bec) it will make no diff at all on either the temp of your esc or your run time, unless your into a heavy digital setup. and the the extra 10 seconds more or less is really hard to cound.
If you wanted to make your esc run cooler you can do more for it by cutting off the cover just around the metal heatsink, and installing a heatsink. If your a fanatic like me and have too much time on your hands you measure the temp with a probe of the ESC with and without a UBEC after you run it full power on a bench... I have a link somewhere on the specs on one common ubec and will will look it up and post it.
Mean while here is a link to the people that probably know more about it then anyone do far down there.
http://www.dimensionengineering.com/ParkBEC.htm
BTW Zimatosa took his ubec off as it was just extra weight.

kianhon

I pulled this out from Helifreak forum. Read it and you will understand more about UBEC.

What is a BEC?
BEC stands for Battery Elimination Circuit and that is exactly what it is.

What does a BEC do?
Before lipos and advances in battery technology, the normal method of powering a receiver was through a seperate NiCd battery pack providing 4.8v to the receiver and servos. As battery technology progressed the BEC was introduced to replace the 4.8V receiver pack (making the model lighter) by drawing power from the higher voltage main pack and dropping it down to 4.8V for the rx and servos. So quite simply the BEC eliminates the need for a seperate power supply for your receiver and servos.

What is the difference between built in and external BEC's?

Generally the BEC found in an ESC is a linear voltage regulator (or linear mode bec), quite simply the way these work is to take the input voltage (11.1V on a 3S lipo) and outputs 5V to the rx. The problem is that it has to dispose of the excess 6.1V and to do this it converts it to heat. Generally these linear mode BEC's are rated at 2-3 Amps, however what the manufacturers do not tell you is that this rating is only true with a 6V input. Using a 3S (11.1V) input the BEC will only deliver around 0.5A before it starts to overheat. Linear BEC's rarely reach more than 50% efficiency and can run as low as 10-15% efficiency.

Generally external BEC's are switching voltage regulators (or switched mode bec), these do not care about input voltage and can run up to around 30V+ input. A switching regulator works by taking small chunks of energy, bit by bit, from the input voltage source, and moving them to the output. This is accomplished with the help of an electrical switch and a controller which regulates the rate at which energy is transferred to the output (hence the term “switching regulator”).

The energy losses involved in moving chunks of energy around in this way are relatively small, and the result is that a switching regulator can typically have 85% efficiency. Since their efficiency is less dependent on input voltage, they can power useful loads from higher voltage sources.


A quick Comparison

Lets take our beloved belt as an example. It uses an 11.1V input and the Esky ESC has a 2A linear BEC. In order for the BEC to output 5V/1A the current flow into the BEC has to be at least 1A so the power on the BEC is 11.1V * 1A = 11.1W however the useful output power is just 5V * 1A = 5W so the BEC has to convert 6.1W of power to heat causing it to get very hot. This gives it an efficiency of just 5W/11.1W = 45.%

Now lets say we disable the onboard BEC and replace it with an external switched mode BEC like the Hobbywings 3A UBEC. For the switched mode BEC to output 5V/1A the current flow in is just 0.50A (actual test data), so in this case the power on the BEC is 11.1V * 0.5A = 5.6W with a useful output of 5V * 1A = 5W meaning the BEC only has to convert 0.6W of power to heat and runs at an efficiency of 5W/5.6W = 89%

Do I need an external (switched mode) BEC

If you are using digital servos or more than 3S Lipos then yes definitely as the linear mode bec's will overheat trying to provide any useful output.

If you are running spektrum 2.4Ghz receivers then it is highly advisable as they draw significantly more current than a normal receiver and are very susceptible to voltage drops. If your linear bec is trying to provide a lot of current it will overheat and fail to provide the correct voltage causing the spektrum receiver to reboot.

Rosebud6

Radio Shack had em. I I put 2 deans connectors on for set up so I dont have to unplug the battery.

@kianhon

I know what you mean about MI weather, Other than Saturday, its been just beautiful for flying though.

Druss

How does a ubec not affect the heat in the esc? The built in bec is linear and produces quite a bit of heat so if you're not using it, then there's less heat.

funflier

Opps should have said little diff rather then no diff.
Measured diff in heat was using a sep bec to was between 2 and 3 deg C when measured off a Dynam 25 amp ESC and a 3S pack, with and without a external UBEC from diminsion engeering over the period of 3 min at about 30% power on my Esky 3900 motor and a Spectrum 6100 rx with all the stock esky servos and a Telebee gyro connected. I used a fluke temp prob to measure the temp of the heat sink. I cut off the heat shrink in the area about the size of a pencil erraser on the top of the ESC to measure it directly off the heatsink of the esc it's self.
I think someone on RC groups posted something about the same some time ago or had a link to a mfg tech sheet on the diff in temp on a 2s pack and with or without the uBEC
I am not saying that there is NO heat diff but it is minimal.
All bec or Ubec produce heat just that the Ubec produces less of it converting and is more efficent however the truth remains that unless your using a 4s pack or have a digital system your not really going to benifit with a ubec. Most of the mfg agree on that.

Druss

I hate to say it but I'm more interested in what the heat diff is at 60 or 70% throttle, and not at the heat sink. The heat sinks in most escs I've seen are not attached well. An infared heat gun pointed at various components within the esc will show much higher temps than the heat sink will.

I expect that most esc manufacturers would not say anything bad about their products.

I'm not saying that you're completely wrong but if I can notice the temp difference by hand with on my esc's using an ubec then it's got to be more than 3 degrees.

I might just have to run this experiment myself.

funflier

itchy fingers supposed to read 12 to 13 deg C
Actually a inferred gun would be a lot better as I think that tiny tip on the probe may not the best thing for measureing a surface temp with sue to the limited surface area it has contact with.