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HobbyKing SBEC Quality - or lack of...

PostPosted: Mon Aug 23, 2010 7:55 am
by pwy
A while ago I bought this switching BEC from HobbyKing http://hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=10313&Product_Name=Turnigy_5A_(8-40v)_SBEC_for_Lipo_ for a project that never materialised.

A few weeks ago I built a new glider, a 2.6m Discus I intended to use for aerotowing. When I was looking for a suitable receiver pack I found that the glider balances perfectly with a 3s 1800mAh LiPo. Remembering the BEC I bought earlier I thought that should be a perfect setup good for a weekend of fun without having to recharge the receiver pack. Assembled everything and had a few successful flights.

Last weekend I decided to swap the Spektrum AR6200 receiver for a Weatronic receiver. The main reason was that I wanted to use my shiny new Weatronic telemetry system I received just a day earlier and the secondary reason was that I'm slowly changing over from Spektrum to Weatronics.
Ok, done that, reprogrammed everything. Not very difficult as the glider only uses ailerons, rudder, elevator and a tow release. Then the stir-test on the bench (moving all the sticks together as fast as I can) and the Weatronics module started complaining loudly about link loss. Looking closely at the receiver I could see the red led flashing for a split second. Took the memory card out of the Weatronics module and checked the log on my PC. And there it was... stirring the sticks created peaks of about 3.5A for a very short time (rather big metal geared servos) and every time this happened the 5A rated Hobbycity BEC dropped the voltage enough to cause a reboot of the receiver!

Went then back to the Spektrum receiver and tried to reproduce this issue. Indeed, the Spektrum receiver rebooted as well. Only difference was that the Spektrum receiver did it silently but the loss of control was significantly longer than with the Weatronic.

I have never noticed anything in flight but usually my stick movements are not that wild like on the bench test ;) I also never noticed the Spektrum receiver flashing (indication of brownout) but the receiver is not visible from the outside and I usually switch it off without looking at it so it may have happened.

The fix was easy, the Hobbycity BEC went into the bin and was replaced with an Align BEC rated at exactly the same 5A but actually performing to it's specification.

The moral of the story.... If it's too cheap it probably doesn't do what you expect and never, never trust Hobbycity BECs ;)

Re: HobbyKing SBEC Quality - or lack of...

PostPosted: Mon Aug 23, 2010 8:10 am
by RCModelReviews
As I've said elsewhere in these forums -- my preliminary testing of cheap Chinese BECs shows that most are vastly over-rated in terms of their current capabilities!

A full review of a range of available SBECS and UBECS is due shortly.

Re: HobbyKing SBEC Quality - or lack of...

PostPosted: Sat Sep 18, 2010 8:29 pm
by pushinoldrc
A full review of a range of available SBECS and UBECS is due shortly.


I have been looking into the UBEC market for utilizing LiPo batteries for my Wife's GS Corsair. I have cobbled a servo buss system that will be controlled by a relay that isolates the battery from the buss when power is removed from the reciever via a switch. The VR that I was planning to use is an LM317 variable regulator. I was using it for testing in a homemade 5' wingspan glider, taking power from the 11.1v battery lead, when I started having brown outs (72Mhz) and lost control for momentary periods. The problem seemed to be caused by excess current drain through the VR as it was VERY hot after I landed the plane and took the wing off.
I want to find a regulator, or BEC that is capable of producing enough current for 8 High Torque servos as the TP SG-5010 series. I am not sure what the current requirements for this size of a system would be, but I have reasonable faith in the LiPo technology for such a task.
I have lost too many airplanes due to cheap China NiMh battery failure.

Re: HobbyKing SBEC Quality - or lack of...

PostPosted: Sun Sep 19, 2010 12:54 am
by RCModelReviews
pushinoldrc wrote:I have been looking into the UBEC market for utilizing LiPo batteries for my Wife's GS Corsair. I have cobbled a servo buss system that will be controlled by a relay that isolates the battery from the buss when power is removed from the reciever via a switch. The VR that I was planning to use is an LM317 variable regulator.

The LM317 is rated to a maximum of 1.5A -- and that's if the amount of power being dissipated doesn't cause it to go into thermal shutdown first.

I want to find a regulator, or BEC that is capable of producing enough current for 8 High Torque servos as the TP SG-5010 series. I am not sure what the current requirements for this size of a system would be, but I have reasonable faith in the LiPo technology for such a task.

Since each of the 5010 servos can draw 1A+ and you have 8 of them then you'll need a BEC with at least an 8A capacity if you want an absolute assurance you're not going to get any shutdowns. An SBEC is more likely to deliver those current levels than a linear one because it is far more efficient. A linear one might need a lot of cooling and will thus be quite heavy.

I have lost too many airplanes due to cheap China NiMh battery failure.

What about just using a 2S 100mAH A123 pack for your receiver & servos? These are relatively cheap, lightweight and can deliver over 50 amps without blinking. With most receivers and servos now rated to work at 6V, they don't need any regulation either.

Re: HobbyKing SBEC Quality - or lack of...

PostPosted: Mon Sep 20, 2010 1:13 am
by pushinoldrc
Thanks for the quick response. I have been reading your articles on the A123 packs, and now believe this is the cheapest, most effective, and trouble free way to go. The cost of these packs seems quite high (because I am squeaky cheap), but I have been spending a lot of money and time trying to trust Chinese NiMh batteries. We will have around $1200 and over 500 hours into this airplane, and I HAVE to trust the servo/receiver power. You stated "2S 100mAH A123 pack", do you mean 2S 1000mAH A123 pack?
Thank you for all you do!
Bryan

Re: HobbyKing SBEC Quality - or lack of...

PostPosted: Mon Sep 20, 2010 1:40 am
by RCModelReviews
Ah yes -- my bad :-)

I meant a 2S 1100mAH A123 pack. You can put these together for under $20 if you buy the cells and a 150mm servo extension (which becomes the wiring) from HobbyKing.