Basic Power Supply Requirement for RC Motor?

[centarix]

I have two RC motors designed for RC helicopters which both have the following specs: 16A, 11.1V.
I would guess the following power supply would work: 30A, 12V.
I am imagining this would result in 15 amps going to each of the two motors? The wattage is almost the same either way, the voltage should be too far off, but I'm not sure about whether it really works out in practice, or whether the amps can properly split that way between the two units? Or, if one of the motor fails does the other one then get cooked without a 16A fuse? Or, will the power supply automatically reduce to the amperage the device can handle?

They also list: 1470Kv/1470RPM/V and 800g max thrust which I doubt are relevant to this question.

I am a computer programmer trying to start into robotics and am now toying with some RC motors, so am outside my area of expertise. I'm using RC motors on what will start out as a boat though I plan to remove the motors and use them for a helicopter later on and so I got helicopter motors. For testing I want to use a standard outlet power supply and then later on add in batteries if things work out well.

Thanks in advance for any help with this question. I posted it to an RC forum but nobody seemed to know the answer as they all just use batteries and not a power supply.

 

[MikeHalloran]

The starting current of a DC motor can fry a simple power supply, and confuse a fancy one.

Use the batteries, or learn some expensive and painful lessons about power supplies.



Example: One time I specified some DC linear actuators for an application where battery power made sense. Our wizard sparky could not be dissuaded from designing a custom line-operated DC supply, that could deliver just a little more than the rated current of the actuators, maybe 20 A.

When the actuators came in, the QC department tested them as 'not working'.

The QC department was using very fancy power supplies with 'foldback current limiting', which they had preset to ~22 A, or a little more. ... and the actuators would not start on the folded back current, even on no load.

When tested from a battery with a simple contactor, a current transducer and a scope, it turned out that the actuators demanded something like 300 A for a few ms. They were working as designed.

I think the wizard sparky was eventually persuaded to use a battery, and design a custom battery charger.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Batteries can do amazing things. A standard alkaline AA battery can easily dump 10 A, thus making essentially impervious to load annoyances.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[itsmoked]

centarix; The motors will draw the current they demand and will not be "over currented" by the availability of 'excess' current.

The motors may demand more than is available as mentioned but depending on several factors it may mean nothing more than the motors don't come up to speed quite as fast as they could. If that doesn't matter in your case then the power supply will probably work fine.

That all said, if you're doing research and testing towards a future goal then doing everything as close to the future configuration means you'll be closer to the final results faster. So if you plan on using battery power in the end you really should just start with it as then you will get all the results up front. You'll get a feel for battery life, voltage sag, voltage decay, charge times, temperature excursions, etc etc. All stuff you won't get from using alternative power sources.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[centarix]

The feedback so far is very helpful. Thank you to itsmoked, IRstuff and MikeHalloran. I saw a Youtube video of someone who did manage to do testing on a standard power supply, but he didn't give the specs for it. So, I do plan to give it a shot. From the replies it would seem I'll want to try something much higher than 360 watts.

 

[IRstuff]

There may be other ways to skin this cat. Often, what's specified for a power supply is a steady state maximum power specification, i.e., your 360 W, and a surge specification that might be 3x to 5x the steady state for, say, 0.25 seconds. What this means is that the power supply can handle startup spikes, but won't be penalized by running a steady state output power that's only 30% of the design specification.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529