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I am currently embarking on a project that requires 4 brushless motors. Let's say the KV rating for each motor is 1400kv and requires a 30 A bi-directional ESC for each motor, and that I want to power it using a SINGLE power source which is 12 V, 30 A.

I know I can solder all the positives together and connect it to the positive and all the negatives to the negative and the ESCs would receive power and would power the motors.

My question is: what is the effect of connecting multiple motors to ONE power supply like this? Do they start sharing current? Will it affect the RPM/performance? For example, when you add more brushless motors, will this start affecting the performance of the other motors? Does the 12 V get divided by 4 - because I am connecting 4 brushless motors? Is the case the same with the amp rating; does it get divided?

If it will, is it better that I buy a regulated bench power supply so I can control the V and A ratings?


I have a follow up questions. I am now looking to purchase DC 12V 83.3A 1000W Power Supply and will use 4 brushless motors A2212 1400KV Brushless Motor. I have checked the Motors and they require 11.1 V and Load Current: 19.0A Power:210W. From my understanding the power supply I am looking to purchase would meet the requirements to run the motors at full torque. Am I correct is the power supply adequate or am I missing something?

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    \$\begingroup\$ You should have you learned about parallel connections by now. So whatever happens there with one real world caveat: Real batteries and voltage supplies have a series internal resistance so the more current you draw, the more voltage will sag. If you have not learned about series and parallel yet, go read about it now. It's more important than your immediate question. \$\endgroup\$
    – DKNguyen
    Nov 30, 2021 at 15:05
  • \$\begingroup\$ A 30A voltage-regulating, current limiting supply is really expensive. By all means get one if you can actually afford one. Your money is better spent on an oscilloscope if you don't have one yet. \$\endgroup\$
    – DKNguyen
    Nov 30, 2021 at 15:11
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    \$\begingroup\$ @DKNguyen a good 30A power supply is expensive. You can get a lot of power supplies in that range for dirt cheap. The quality shows though. \$\endgroup\$
    – Stiddily
    Nov 30, 2021 at 15:14
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    \$\begingroup\$ @Stiddily One with adjustable current limiting? Because even cheap no-name voltage and current adjustable supplies that supply 5A I see are like $500USD. If you give up one or both adjustments the price does drop a lot. \$\endgroup\$
    – DKNguyen
    Nov 30, 2021 at 15:15
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    \$\begingroup\$ If each motor requires 30A and your power supply is limited to 30A, you can only run 1 motor at full torque at once. If that's acceptable, enforce the limitation in software. That's fine for a crane or robot, not so much for a quadcopter. (Which must lift a 120A supply) \$\endgroup\$
    – user16324
    Nov 30, 2021 at 15:17

2 Answers 2

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I know I can solder all the positives together and connect it to the positive and all the negatives to the negative and the ESCs would receive power and would power the motors.

Yes, that is what you will do. For easier maintenance I suggest wiring each ESC to the 'common' power supply wires through high current polarized connectors like this. If the cable from the power supply is long (> 100 mm) then you should wire a few large low-ESR capacitors across the common connection point, to reduce voltage spikes caused by cable inductance. The cable should be rated to take the combined maximum current of all 4 motors.

what is the effect of connecting multiple motors to ONE power supply like this? Do they start sharing current? Will it affect the RPM/performance?

The power supply will have to deliver the combined current of all the motors. The motors won't 'share' the current - each will draw whatever current it wants, independently of the others.

If the power supply voltage sags at higher current there will be some interaction between the motors. With a well regulated power supply this effect should be minimal.

Does the 12 V get divided by 4 - because I am connecting 4 brushless motors?

No. You are making a parallel connection, so each ESC gets the same voltage. (this should be obvious - how could it not be so when each ESC is connected directly to the 12V supply?)

Is the case the same with the amp rating; does it get divided?

Not quite. The total current is the sum of each leg (ESC/motor) in the parallel circuit.

Since your power supply is only rated for 30 A, you will need to ensure that the motors don't draw more than that. That could mean each motor drawing up to 30/4 = 7.5 A, or two motors drawing 20 A each and two drawing 5 A each, or any combination that adds up to no more than 30 A.

The current each motor draws depends on mechanical loading and throttle level. Your ESCs are rated for 30 A each, but that doesn't mean they will draw that much or even be limited to that much.

is it better that I buy a regulated bench power supply so I can control the V and A ratings?

It may be useful for testing. Once you have determined how much voltage and current is required you can then switch to a suitably rated fixed power supply.

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  • \$\begingroup\$ Thanks you for the answer everything makes so much sense I did know about Parallel and Series but I was for some reason thinking that because the ESC is in between the motor and PSU and because all positives and negatives would be connected would make it a series! that's where my confusion was. I am now thinking to buy 2212 10T 1400KV Brushless Motor + 30A - bi directional Brushless ESC * 4 and the power supply would be : DC 12V 60A Universal Regulated Switching Power Supply 720W. I want to buy a good power supply so in the future if I change out motors or esc's I have a good power source. \$\endgroup\$ Dec 1, 2021 at 7:30
  • \$\begingroup\$ I have a follow up questions. I am now looking to purchase DC 12V 83.3A 1000W Power Supply and will use 4 brushless motors A2212 1400KV Brushless Motor. I have check the Motors and they require 11.1 V and Load Current: 19.0A Power:210W. From my understanding the power supply I am looking to purchase would meet the requirements to run the motors at full torque. Am I correct is the power supply adequate or am I missing something? \$\endgroup\$ Dec 1, 2021 at 11:34
  • \$\begingroup\$ 19A * 4 = 76A, so that power supply should be sufficient. FYI here's some test data for a motor similar to yours bhabbott.net.nz/A2212-10.html \$\endgroup\$ Dec 1, 2021 at 19:21
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The ESC ought to be as close as possible to the motors due to the high frequency PWM and high currents.

Motors in series are current sharing. In parallel, it is called voltage sharing.

But considering DC motors take ~ 10x the rated current on full start unless you limit the startup acceleration like 3ph-VFD, the parallel mode will be expensive or lossy.

Consider the ESR of the battery string (*n) relative to the DCR of the coils as Pd is proportional to R. Parallel mode increases driver losses while series mode demands a greater voltage breakdown on the drivers.

The servo acceleration controls the currents to the motor and from o load to full acceleration can be a ratio of 100:1 for bursts which is difficult to regulate on flyback SMPS. A more stable power supply approach would be a suitable battery with a float charger to maintain the average load current.

But remember this. Voltage load regulation error (%) is simply the % ratio of source ESR to load DCR for the worst-case step current or Rs/(Rs+load DCR)*100% This is true for all regulators. A "COTS" PSU with full protection might also be adequate if sufficient power margin is chosen in a forward full-wave converter and the ESC drivers can handle the back-EMF and inertia as coasting generates voltage and braking dissipates power.

Never overestimate the wisdom of silent down-voters!

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  • \$\begingroup\$ Thanks the information you have given is very useful, especially the fact that the ESC ought to be as close as possible. I have one more query regarding the decision I have made for purchasing DC 12V 83.3A 1000W Power Supply and will use 4 brushless motors A2212 1400KV Brushless Motor. They require 11.1 V and Load Current: 19.0A Power:210W - theoretically will the PSU be sufficient to power the 4 brushless motors at max torque at the same time - although I probably would not want to make them work at 100% probably at 80% but I am just interested to know if I am correct. \$\endgroup\$ Dec 1, 2021 at 11:41
  • \$\begingroup\$ It depends how far the motors are apart to share one ESC with 1 supply or 4 ESC and 4 supplies with ganged controls. ?? what are the distances involved and where will losses come from ESL,Rs of cable and what is ripple current on PSU load, also how much EMI on load depends on very low Z impedance connections to ESC from cable length and L/C ratio with ESR ratios. These affect supply regulation as a motor load can be very dynamic depending on speed change ramp control, motor inertia brake load dump. Will the ESC handle full stop current surge or will you prevent that by design. \$\endgroup\$ Dec 1, 2021 at 16:52
  • \$\begingroup\$ There are many things that can go wrong not defined in your question. I would go with 4x 30A ESC's with PE shielded busbars or twisted Litz wire pairs for power distribution. \$\endgroup\$ Dec 1, 2021 at 16:53

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