Making your own BEC by Fireup

[fireup]

Even though the T500 comes with an ESC with an onboard BEC, some may still want to run an external BEC for different reasons. I start this thread to discuss the use of such device and how you go about doing it.

If you want to run off the flight pack, you need a BEC that can handle the cell count of the flight pack. Align's current stand-alone BEC's are linear regulators and design to use with a separate 2s pack. You need to use a "switching" type BEC that can handle high cell count. You can get switching BEC made by CC or Medusa, but because some have asked me which one I use, I will show how to build one using a switching regulator module made by Texas Instruments. The module are pretty much pre-assembled, you just need to add some capacitors and wires.

The module I'm currently using is model: PT6883, It can supply 5Amp continues and I've run it on 10s on my 600 for 10+ months now. But because this module will soon be discontinued, I will be using model: PTN78020W. (has similar spec and 6Amp) All the parts can be purchased from Digi-key.com

I wired it up as in Fig. 24 in the datasheet, so you'll need the following parts for this configuration:
Datasheat: http://focus.ti.com/lit/ds/symlink/ptn78020h.pdf

Qty - Digikey part #
1 - 296-20517-ND (PTN78020WAZ - REG SW 2.5-12.6V 6A SMD)
1 - 13.0KXBK-ND (Resistor to set for 6.0V)
1 - 445-2879-ND (Capacitor 2.2uF 50V)
2 - P5184-ND (Capacitor 300uF 63V)

1 - servo plug/wire
1 - two spare wires
1 - heatshrink tubing (A034C-4-ND) clear 3/4" or (A100C-4-ND) clear 1"

Here's different resistor value you can use if you want different output voltages:
5.0V - 21K ohms
5.5V - 16.4K ohms
5.8V - 14.3K ohms
6.0V - 13.1K ohms

8.0V - 5.99K ohms

The value don't have to be exact, you can use 20K ohms for 5V or 13K ohms for 6V

If you want to make a 3Amp version, you can use this part instead of the first item
296-20524-ND (REG SW 2.5-12.6V 3A SMD)

Bob also made a video on BEC101:
https://www.helifreak.com/showthread.php?t=55538

[HeliBurns]

Kevi, have you done any testing with regards to any RFI generated by the ISR.....the spec says that it's switcher is typically 550kHz...do you have acces to a spectrum analyzer?

[Finless]

Hmmmm seems this would be best as a sticky in a more common forum? This can be helpful to other helis not just the 500....

But where to put it? Maybe in 2.4 radios?

Bob

[fireup]

Originally Posted by HeliBurns

Kevi, have you done any testing with regards to any RFI generated by the ISR.....the spec says that it's switcher is typically 550kHz...do you have acces to a spectrum analyzer?

No, I just have a digital 100Mhz scope, I don't have an FFT module for it or a spectrum analyzer.

[TRex888]

Fireup: If you send me one I can do a EMC scan for you. I will return it when done. I run a 3m emissions test chamber in the UK and can measure from 30MHz to 1GHz (up to 18GHz if need be). You will need to provide some kind of passive load as any emissions from the load cannot be separated easily.

The testing we do is to FCC Class B limits. I can go lower but the measurements will be extrapoluated rather than truely calibrated.

[Pinecone]

HeliBurn,

What I was talking about is that some ESC require power from the BEC (optoisolated ones, or those without internal BECs). In that case you NEED to connector power back to the ESC so it works. The ESCs on my Huricane 550 and Quick of Japan EP8 are both like this.

[heliboy88]

Just wanna ask if a 3 Amps output external BEC will be good enough for the t500 with say 3 x hs5245MGs, GY401+9257 and using AR7000 Rx?

[HeliBurns]

Pinecone...I'm not sure I understand....

If a SportBEC would work for this situation you describe, then this design will work.

[fireup]

Pinecone, in that case, just don't cut the red lead on the ESC and let it get power from the Rx.

Originally Posted by heliboy88

Just wanna ask if a 3 Amps output external BEC will be good enough for the t500 with say 3 x hs5245MGs, GY401+9257 and using AR7000 Rx?

I'm sure 3 Amps will be plenty. I think someone measured the current once and it was under 1.5Amps

[heliboy88]

Thanks a lot for the heads up Kevin, i'm using this http://www.aero-fever.net/product_in...roducts_id=389 in my 450 Trex, do you think it's safe enough to use this on the T500 if i'm planning to use 5s 3300 pack?

[skid]

I could have sworn I read that Aligns new esc had switching bec.

Fearture:
¡´5-6V step-less adjustable BEC output allowing custom voltage setting to match servo specification.
¡´BEC output utilizing switching power system, suitable for 7.4-22.2V (2s-6s) Li battery, with continuous current
rating of 3A, and burst rating of 5A.
¡´Three programmable throttle speed settings to support quick throttle response.
¡´Include soft start and governor mode.
¡´Small and compact PCB design for lightweight and simple installation.
¡´Large heat sink for optimum thermal performance.
¡´Highly compatible to work with 98% of all brushless motors currently on the market.

[fireup]

Sorry I miss word it. Align ESC that comes with the 500 has a switching BEC internal to the ESC. The Align external BEC that is used with the 600 is linear.

[dj_rpr]

ive got a spare sportsbec around, is it worth putting this on or just flying the heli with the align esc and onboard bec?

[Jaso]

I've flown about 6-7 flights on mine so far with no problems at all .
If that helps .
Last fly I gave it a fair smackin and no problems .
I have the stock esc set to 6 volts or actually 5.8 when read on a meter out of RX socket .

[HeliBurns]

heliboy....in short, no...

[HeliBurns]

heliboy...their advertised features are very vague...

everyone knows that a switcher is more efficient than a linear....what BEC would ever overload an ESC...the question is if our rx, gyro, and servos would overload our BEC with respect to current draw...

Over what temp range was that BEC tested at full current load, what ripple voltage is output when tested....why oh why would we throttle up ~$1000+ of equipment that depends on a $12.50 part is beyond comprehension....the state of the art T. I. switching regulator alone costs $19.50 in lots of 100, not to mention the PCB, ancillary components and fabrication and manufacturing costs.....

No offence intended....just concern.....

[Pinecone]

OK, ONE MORE TIME.

The SportBEC automatically disconnects the positive lead from the ESC to the Rx to disable onboard BECs. Great, nice feature.

BUT some ESCs do NOT have a BEC at all, Gaui 50 Amp, Align 75 Amp, Castle HV line, etc. So on those you have to power the ESC from the external BEC.

If you use a SportBEC, you cannot connect it in line with the ESC because the ESC will get no power. So you have to run both the ESC and BEC to the Rx. Pain.

So, if we are doing a BEC from scratch, why not put a jumper or switch in it so that you can chose to connect or not connect the positive to the ESC to either power the ESC or disconnect the internal BEC, respectively? Just makes it more universal.

Also, I asked in the other thread, but never got an answer, is it better to use the 6883 running in its upper votlage range or the 6884 running at the bottom. Would the 6884 provide more headroom for less voltage sag?

[th3tick]

Originally Posted by Pinecone

BUT some ESCs do NOT have a BEC at all, Gaui 50 Amp, Align 75 Amp, Castle HV line, etc. So on those you have to power the ESC from the external BEC.

Not to confuse the issue, but is this true for all BEC-less ESCs? My Jazz 55-10-32 has no BEC, but I out of habit put an extension on its throttle lead with the red wire disconnected, yet it works fine.

John

[fireup]

Originally Posted by Pinecone

Also, I asked in the other thread, but never got an answer, is it better to use the 6883 running in its upper votlage range or the 6884 running at the bottom. Would the 6884 provide more headroom for less voltage sag?

I have not compare the two in details, but I think it makes no different which one you use. I choose the 6883 because I already had it laying around from a different project.

Originally Posted by th3tick

Not to confuse the issue, but is this true for all BEC-less ESCs? My Jazz 55-10-32 has no BEC, but I out of habit put an extension on its throttle lead with the red wire disconnected, yet it works fine.

John

The Jazz55 has no BEC but power itself off the main pack, that's why you only need the common and signal wire.

[Shawn Behrens]

The 6 & 3 amp align bec units designed for the trex600e are switching regulators (bec). The 2 in 1 unit made for the 600N however is linear. All of these units however call for only a 2s input.
shawn