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Jul 31, 2012, 05:00 PM
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PSU powering 3 reversible ESC + 3 outrunner dc motors causing the PSU to trip.

Suffice it to say I have a PSU modified to run for all intents and purposes as a benchtop power supply. The only modifications were simply stripping all lines and combining like rails, added a bleeder resistor, and tied the sensor on line to a 5+ V rail to allow the PSU to turn on (needs a small load in order to function). Simply this was the easiest way to get this old dell 300W PSU to function as a power supply for alternate use.

I am only using the 12+ V rail on the PSU and am powering three reverse type electronic speed controllers which are tied to 3 outrunner dc brushless motors. according to the label on the PSU i should be able to get up to 14 amps on the 12+ volt rail which these motors shouldn't be exceeding even at peak (I measured the amperage to be around 2-3 amps per motor). However after turning it on and engaging the motors the PSU will sometimes trip, needing to be reset (turned off for a few seconds then plugged back in). This behavior is not consistent but will only occur after engaging the motors at full throttle and letting off the throttle and trying to go to full throttle, sometimes I can power all motors and ancillary components all on the 12v rail just fine for extended periods of time, yet sometimes it won't run the motors for but a few seconds before tripping off.

Do the ESCs themselves return a back EMF to the power source, i.e. battery, or in this case my PSU which might cause the psu to trip? Any suggestions about any of this would be greatly appreciated. Thank You.
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Jul 31, 2012, 09:07 PM
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Bruce Abbott's Avatar
Originally Posted by late_fee View Post
I measured the amperage to be around 2-3 amps per motor
Peak current at startup will be higher. What motors are you using, and what is the load?
Aug 01, 2012, 09:59 AM
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RPM/v: 1100kv
Dimensions: 36 x 24mm
Shaft: 4.0mm
Voltage: 11.1v
Weight: 76g
No-load current: 1.8a @ 11.1v
Max Current: 32A
Max Watts: 280W
Mounting Holes: 44mm

Cont. Current: 18A
Burst Current: 25A
Car Size: 1/18th
Battery: 2-3 Cell Lipo / 4-9 Cell Ni-XX
L-BEC: 5V / 1A Output
Motor Type: Sensorless Brushless
Size: 30 x 26.1 x 13.8mm
Weight: 26g (Including wires)
Motor Plugs: 3.5mm Bullet type
Battery Plug: Required
On/Off Switch: Yes
Reverse: Yes

Sometimes I have initiated the startup and ran all 3 escs + 3 motors on full throttle for close to 10 minutes while also powering some additional components. If it does shut the PSU off it happens after I engage throttle and then let off. Thanks for the help.
Aug 01, 2012, 05:23 PM
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Bruce Abbott's Avatar
Originally Posted by late_fee View Post
If it does shut the PSU off it happens after I engage throttle and then let off. Thanks for the help.
Does the PSU shut off only when you throttle back? If so then the ESC may have its 'drag brake' function enabled. This feeds voltage spikes from the motor back into the PSU when throttling back, possibly causing the over-voltage cutout to trip. Make sure that the drag brake function is turned OFF.

Another possibility is that the PSU has poor regulation at light loading, and the sudden drop in current draw causes a momentary voltage spike. Try adding an external low-esr capacitor bank (1,000uF or more) and a larger bleeder resistor (12 Ohms or less) on the 12V output.
Aug 05, 2012, 08:22 AM
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I don't know if this is any help, but the multiple 12v rail supplies I've seen don't say the 12v is split in two on the sticker, and are really 7A on one rail and 7A on the other.

I knew this cheap method of advertising more amps would lead to this. Imagine all the poor saps that ended up with their video card and cpu on the same rail, and had to buy a new supply, even though they were only using 51% of what they had.

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