Can I put 2 ice 75A bec in parallel

[hemiblas]

I'm working on an A10 project that will use 2 70mm fans that pull 64A max each on 4S and decided to go with dual ice 75s. I've been reading and everyone has an opinion on if its better or worst to do this. I would like a difinitive answer from Castle if possible on this one, and also welcome any member comments on the forum. I've read the internal bec of the castle controller already uses 2 chips in parallel for the bec. I would keep the bec wires intact (no shortening) and put them in parallel and connect them up to the radio. I dont think my servo load will be over 5A for this plane. So my questions.
1. Is it possible without any harm to the controllers?
2. Will one bec do most of the work while the other helps out when the voltage drop falls below the rating of the other?
3. Will both BEC's provide equal current since they are so closely matched keeping them operating at a cooler temp?
4. If one fails, does the other one kick in and take over providing a level of redundancy?
5. Is it better to just unplug one of the red wires from one of the controllers and let the bec of one do all the work?

Thanks for the help on this one.

[suicideneil]

1. Wiring 2 escs to the same ( throttle ) channel on the receiver is quite common practice and totally harmless, lots of guys running dual VXL setups ( frickin' traxxas v-twin bollocks ) do this.
EDIT: only with linear BECs though.

2. When in Parallel, both BECs will do half the work all the time, regardless of how much work there is to actually do- that's the nature of parallel wiring.

3. See above. Since they are doing half the work, there shouldn't be as much voltage droop under the same load ( compared to a single esc / bec setup ).

4. If one fails, then any number of things might happen. The BEC also often powers the brains of the ESC, so you may experience total loss of power/control on one esc ( flying on one engine ). The remaining ESC / BEC should still be able to power the servos though so you can safely land under power & with full control. Another possibility of having the BECs in parallel is that the dead BEC takes the other one with it- this is certainly true if the BEC that fails send full pack voltage ( ~16.8v ) to the receiver when it fails ( hence lots of dead rxs & servos when some car ESCs fail ), which is ofcourse hooked to the other BEC / ESC.

5. Perhaps, if one BEC has enough current to power all the servos then it might be safer to isolate the other from the RX. Hobbyking sell external BEC's which have a built-in redundancy, 2 BECS-in-one as it were- if one fails the other takes over.

[Joe Ford]

Not with switching BECs like on the ICE series of controllers. That is true with the linear BECs though neil. With switching BECs you should disable one of the BECs as they can fight each other if the voltages become exactly the same. If worried that one will not supply enough current, use a separate regulator like a CC BEC or CC BEC Pro.

[suicideneil]

Ooh, did not know that- will keep it in mind for the future.

[BrianG]

A little late posting to this thread, but FWIW, I've done a little experimenting with paralleling switching BECs (using the common LM2596 chip).

What seems to happen is that one invariably has a tad bit higher output voltage, so that is the one that handles most of the load. If the voltage sags a little, the other BEC starts to "help". When that happens, the current provided by each seems to "see-saw" so it appears they are sort of fighting each other (not really fighting - more like flip-flopping). The output current is higher than what each would be able to provide individually, but it's not exactly cumulative. And efficiency is not as high either.

I've tried adding a diode to the output of each to help isolate each BEC circuit, and it does help the see-sawing (but the higher V one does handle most of the load at first), but then you get the extra ~0.7v voltage drop, so whatever gains in efficiency are achieved by the isolation are negated by the losses of the extra diodes.

So, in the end, it is better to simply use a single BEC that has the current output required rather than try to shoehorn two lesser BECs.

However, DimensionEngineering BECs can be paralleled. I'm sure BEC design has a lot to do with whether they can be effectively paralleled or not, so YMMV.

[hemiblas]

Thanks for the info guys. After putting so much $$$$$ into this kit, I dont want to do anything to risk it crashing.

[hemiblas]

Quick question for maybe Brian or Neil.
Since I am disconnecting one of the red wires from one of the ESC could I reroute that red wire to lets say the red wire that would run the retracts and keep the signal from the receiver. That way my retracts would not be run from the same BEC running the rest of the system and the other BEC would be powering only the retracts to help lessen the load on the rest of the system?
Thanks again.

[suicideneil]

You'd still need a ground wire also to power the retracts, so one of the esc's built-in BEC would need to be connected to the retract, with just the signal wire going to the rx. The other esc's BEC would be providing power to the rx and the other servos connected to it.

That's how it would work in my tiny mind anyway...