This question came up on the EFlight mailing list that I am on and I thought I would share.

Q:  I am still puzzled as to why two brushless ESCs wired to the battery, all in series, should seemingly interfere with each other.  As far as the  ESCs "know", surely the battery is just the power supply, or is some sort of info passed between ESC and battery?

A:  When the ESC draws power from the battery, current flows through the ESC from the negative battery lead to the positive battery lead. If the ESC does not need power from the battery at that instant, it doesn't allow current to pass between the battery leads (if it did, it would be acting as a short across the battery lads).

In any series circuit, the current must be the same throughout that entire circuit. A particular component can only get current if nothing upstream or downstream is blocking the flow.

If one of the ESC's is in its "off" phase (such as between poles in ts motor's rotation) and not drawing current, then the rest of the circuit also has no current. That ESC is acting like a switch, and it only cares about what its motor needs. It has no way of knowing, and doesn't care, what might be going on with the other components on the series circuit. If the other ESC needs power at that instant, then it's out of luck. Likewise, if the second ESC is in its "off" phase at the instant when the first ESC needs some, then the first ESC is unable to get the current it needs, when it needs it. In fact, the only time that large currents will flow in the circuit is during those rare moments when both ESC's simultaneously need lots of power. Of course that also assumes that this constant turning off and turning on by these multiple ESC switches doesn't cause both of them to crash their microprocessors and have to reboot over and over.

If you wire the ESC's to one battery in parallel, then each ESC can draw from the battery whatever it needs, whenever it needs it, regardless of what is going on with the other ESC, at least up to the maximum capability of the battery.

Answer courtesy of Don Stackhouse of DJ Aerotech www.djaerotech.com