|Jul 18, 2010, 05:28 PM|
The BEC Tester UPDATE June 23 2011 - first post now has a list of all tests
The BEC Tester
There seems to be quite a few questions about BEC's on this Forum.....
So not daring to trust the ratings on various ESC’s with built in BEC’s…. I devised this “BEC TESTER” to verify the sustained amp rating of any BEC, either built into an ESC, or separate UBEC.
The BEC Tester is a simple device that uses common 3157 dual filament automotive bulbs as load devices.
The dual filament bulbs have a “tail/parking light filament” and a “turn/brake light filament”.
The tail/parking filaments will impose approx 0.36 amp loads @ 5 volts, and the turn/brake filaments approx 1.3 amp loads @ 5 volts.
I installed pin jacks so I could easily plug in a couple of meters, one to monitor voltage and the other for amps.
A switch installed on each bulb filament allows various loads to be imposed on the DUT (device under test).
Wiring the tester is quite simple as the attached schematic shows.
For the first test I tried a Turnigy Plush 40 amp ESC with a built in switching BEC that is rated at 3 amps.
I used a 3 cell LIPO to power the ESC/BEC and ran the test for a full ˝ hour.
Ambient temperature was 80 degrees F.
I had 2 turn/brake filaments and 2 tail/parking filaments switched in to impose the load on the BEC.
The BEC voltage began at 5.297 volts with no load.
With approx a 3.03 amp load, the voltage dropped to 4.36 and the BEC reached a temperature of 213.5 degrees F.
The BEC showed no sign of failing/glitching and delivered it's rated current of 3 amps for the duration of the test.
I ran the test again at approx 3.5 amps and after 10 minutes the BEC went into thermal shut down. (forgot to check the temp
Voltage dropped to 1.2 V, not anywhere near enough to operate servos or receiver.
I will be testing other UBEC's and ESC's with built in BEC's as I find time.
Hope this helps somebody.
EDIT: June 23 2011: UPDATE: Here is a list and links by post # of all BEC tests so-far...
1. this post... duh... Turnigy Plush 40A ESC with 3A switching BEC.
34. Turnigy 3 - 5A switching BEC http://www.rcgroups.com/forums/showp...0&postcount=34
44. CCBEC 10A .....update in post 47 http://www.rcgroups.com/forums/showp...5&postcount=44
57. DE Sport BEC 1.25A .....update in post 61 http://www.rcgroups.com/forums/showp...2&postcount=57
92. T-Bird 36A ESC w/linear BEC http://www.rcgroups.com/forums/showp...4&postcount=92
107. DE Park BEC 5V 1.25A http://www.rcgroups.com/forums/showp...&postcount=107
108. DE Park BEC 6V 1.25A http://www.rcgroups.com/forums/showp...&postcount=108
119. DE Park BEC retest http://www.rcgroups.com/forums/showp...&postcount=119
125. HobbyWing 5 - 7.5A switching BEC Good one ) http://www.rcgroups.com/forums/showp...&postcount=125
141.Turnigy 5 - 7.5A switching BEC http://www.rcgroups.com/forums/showp...&postcount=141
152. CC IceLite50A ESC w/ 5A BEC .....update in post 155. http://www.rcgroups.com/forums/showp...&postcount=152
180. Turnigy SBEC 5A (stinker) http://www.rcgroups.com/forums/showp...&postcount=180
191. Turnigy 8 - 15A switching BEC http://www.rcgroups.com/forums/showp...&postcount=191
195. Hyperion HP-TICOOL-BEC 4 - 5A switching BEC. http://www.rcgroups.com/forums/showp...&postcount=195
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|Jul 18, 2010, 05:51 PM|
The ESC will, of course, create it's own heat, but if it's mounted in airflow the "extra" heat should not be a problem.
Bench testing this way really puts the BEC to a torture test as far as heat goes, since there is no airflow....
and if it's going to "thermal", it will do so much faster on the bench.
|Jul 18, 2010, 06:02 PM|
|Jul 18, 2010, 06:09 PM|
With this setup i'm guessing you'll end up with the same value as in the spec. You need to test with motor running and prop attached (or dummy load of some sort). The esc that comes with the Radian shut down with only 2 standard servos connected. The manual states that you can only run the motor for 2 minutes or it will shut down. In most cases I think the motor will be a bigger source of making the esc shut down.
Is there any esc that has one thermal fuse for esc and one for the built in bec?
|Jul 18, 2010, 06:10 PM|
Ya, not surprising.
I did test an E-Flite 20 amp ESC that has a linear BEC rated at 1.5 amps.
The trouble with Linear BEC's.... The amp rating is usually for a 2 cell input.
If you use it with a 3 cell then you have to "derate" the BEC by about half.
The E-Flite 20 very quickly went into thermal shutdown at 1.36 amps with a 3 cell.
I'm pretty sure the Radian ESC has a linear BEC.
|Jul 18, 2010, 06:41 PM|
|Jul 18, 2010, 06:55 PM|
What if you use a ESC rated for 40 amps but then have a motor/prop combo that only pulls 25 amps?
Of course not everyone goes overkill on ESC amp ratings, (but I do.. )
Really, if you have done your homework and use an appropriately rated ESC for your power system and the ESC is mounted in air flow...
....then "how hot will it really get"?
Do you really think a PROPERLY chosen power system, where the ESC can easily handle the load of the prop/plane AND is mounted in airflow, is going to heat up so much as to affect the BEC?
I bet those documented (show me please) cases of overheat were instances where components were NOT chosen properly and did NOT have sufficient airflow.
If you consistantly run your equipment "On the edge" then you deserve the failure, or at least you should expect it.
My purpose in making this tester is to find out "where" the BEC will fail, and will it deliver it's rated amps.
Once I know that, then I can calculate the total amp draw of my flight system, (I have a servo amp tester too) and if it is too close to the max tested draw of the BEC then I know I need to use a separate BEC or find some other solution to powering my flight electronics.
Again... my pupose in this testing is find the ACTUAL rating of any BEC I happen to use.
Combined with ACTUAL KNOWN MAX amp draw of my flight electronics (servos and Rx) I can, with very reasonable certainty, determine if the BEC is REALLY going to deliver the amps when I need it most.
I want to avoid "running on the edge" of my electronics ratings.....
.... and I DON'T want to "guess" at it.... I want to KNOW what the real ratings are.
|Jul 18, 2010, 06:58 PM|
North vancouver, B.C. Canada
Joined Apr 2008
Thats why when you want to use a 4 cell battery as an example, some esc's can't handle the extra voltage and a separate bec is needed or a separate rx pack.
proper airflow is esential to conduct a test like this, it will make the world of difference for reality purposes.
holding the esc or separate bec in your hand and feeling the temperature, is a simple test, if it gets too hot to touch, it is over taxed and not a good one to use.
remember when you are flying with a tilt servo for the camera, the wind can really cause lots of constant draw on that particular servo
|Jul 18, 2010, 07:01 PM|
On my Skywalker, I will be running a Turnigy 40A Plush ESC, which has the built in 5V 3A BEC built in. I will be running a motor which requires a 40A ESC... Some may say that I am foolish not to run a separate BEC. Is this the case? I haven't seen any reports of the Turnigy ESCs failing... An adding a separate BEC ads noice and an extra fail point (or else, maybe it could be called safety redundency?). Is there a history of failing ESCs, because the BEC was maybe overloaded?
When I connect my watt meter to my plane, with everything on, but no motor running, it registers 0.5A. That's servos, 500mW Video Tx, Camera, Radio Rx, mic. Wiggles the servos like a mad man, and it goes to 0.9A. I'm WAY under the in built BEC rating. Move an elevator up,a nd push down on it, simulating wind resistance, and there isn't a change in the readings.
So, I'm still not sure I need a BEC.
"I ran the test again at approx 3.5 amps and after 10 minutes the BEC went into thermal shut down. (forgot to check the temp Voltage dropped to 1.2 V, not anywhere near enough to operate servos or receiver."
So, you were overloading the BEC, and after 10 minutes, it failed? That's pretty expected, no? Infact, lasting 10 minutes is pretty good!
|Jul 18, 2010, 07:15 PM|
I can hook a amp meter to my servos, each one, one at a time.
I test them on the bench by "stalling" them to see each servo's MAX amp draw.
The following is just "for example".....
Lets say the servos I use have a stall amp draw of 0.4 amps and I have 4 servos on the plane.
4 X 0.4 = 1.6 amps is my MAX servo draw. Absolute worst case.
Add whatever your Rx draws.... say 0.5 amps.
Now we have 2.1 amps total.... again ...."worst case" now add a little "headroom"..... say another 0.2 amps....
= 2.3 amps total draw at the very outside.
So my 3 amp BEC should be fine EVEN WITH the additional "heating" from the ESC operating.
And if the ESC is properly rated and in airflow like it should be.... then....
Yes, I'd say that was pretty good for that BEC to run for 10 minutes at 3.5 amps. a full .5 amps outside it's spec.
I really wish I had remembered to check the temp.....
I don't feel like repeating the test to find out.... after all this IS a Brand new ESC....
|Jul 18, 2010, 07:30 PM|
I thinks that's a pretty good tick of approval for the ESC (Was it Turnigy?). And also, a nice thumbs up for running an ESC only. Now, my other issue is that my ESC is planned to be inside the fuselage, with NO airflow. I think THAT might be asking for trouble.... So, I may need to reevaluate my ESC positioning.
Thanks for the testing, galaxiex.
|Jul 18, 2010, 07:37 PM|
Yes, it is the Turnigy Plush 40 amp ESC.
I was leery of the 3 amp rating for the BEC....
Not anymore, I believe that BEC will consistantly deliver it's rating of 3 amps, provided sufficient airflow, and provided you don't overload the ESC motor side of it by having a power system that draws 50 amps or more!!!
Yes, in your case I would def. get the ESC out in the air flow.
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