View Full Version : BEC Current capacity and Beastx

02-16-2012, 09:44 AM
I read in the CC Forum that the max current up plied by a Phoenix 25 A ESC is inadequate for a micro beast.

Max bec current for that unit appears to be 1.5A @ 5 volts.

Is there a risk running that bec with a micro beast on a Gaui X2?

02-16-2012, 10:24 AM
I think you mean the Phoenix25. It has a linear BEC. According to the Phoenix User Guide, it can supply 3A with a 2s. For a 3s it will be less. The limit of a linear BEC is the heating it gets dropping the pack voltage to 5V. With a 3s 12V setup, drawing 2A for example, that would be 14 watts--- (12-5)V*2A. That's a lot of heat to dissipate. With a 2s pack the heating is only (8-5)V*2A =6 watts for that same 2 amps.

I am using one on a TRex250 microbeast setup, with stock Align 410's and 420 servos (3s packs). The BEC definitely warms up, even on the bench. I just bought a VoltMagic that I can plug into my receiver to see what the BEC voltage is doing throughout a flight. Maybe I can check that out on the next flight. Of course the temps are on the low side around here, so there might be issues in summer heat.

I do believe the older Phoenix 25 did have 1/2 the current capability, so maybe that is what you are referring to.

02-16-2012, 05:16 PM
There have been no issues reported by people using the stock gaui esc (2A linear BEC) on the X2, it gets pretty warm but still works fine.

The miniJazz I use has a 1.5A switching BEC, its never had an issue, so I would say the average draw of the X2 is 1.5A or less. You should be fine IMO.

02-17-2012, 11:32 AM
Did a bit more thinking (always dangerous!).

The only spec I have ever seen for the Phoenix 25 (I am taking about the latest version), is that with a 2s lipo pack, it is limited to a 3A draw at the BEC voltage of 5V.

Depending on what you use for the voltage of a 2s pack (it clearly varies over a flight due to discharge, and also with load), you can convert this "spec" into a wattage limit for heat (same math I used above). So for example, if I use the fully charged 8.4V, then the linear BEC is dissipating (8.4-5)V*3A~10 watts. If you use 7.4V for the 2s lipo, then you get 7.5Watts. So the BEC limit is somewhere between 7-10 watts of heating.

If you assume this is the heat limit of the BEC, then if you run with a 3s pack, you need to calculate the voltage difference between the pack terminal voltage, 12.6V (4.2V/cell or 11.7 V (3.7Vcell) and the 5V output of the BEC. This gives 7.6V or 6.1V for the two cases. If you divide this into the 7-10watt figure, you can get an output current limit is 1-1.5A, depending on your particular choice.

So I would say the OP 1.5A limit would be a reasonable 3s limit. Not sure actually what his GauiX2 pack is --3s or 2s??

02-17-2012, 11:42 AM
I had this issue on my Trex250 with a beastx all you need to do is add

Spektrum Voltage Protector SPM1600

it solved my problem

02-17-2012, 03:05 PM
This from Castle

"The output will depend on which Phx 25 you have. The older version is 1.5 &
the newer is 3amps. I have attached a pic to help you identify what you

See pic

I have the newer one.