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5KW BLDC Motor Controller wiring

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Tommycat:
Keep in mind that the resistor has to be able to handle the wattage produced. I notice that Kelly controllers recommend a 1K/10watt pre-charge resistor for their controllers up to 72 volts.


As at 52 volts and 1.5 amps = 78 watts.   :o

But with a 1K resistor at 52 volts = .052 amps = 2.7 watts.

Granted it's only for a short duration...  But even with this seemingly large increase in resistance, I would think charging would take place in a matter of a few seconds.

Jusp:
Correct, and thanks for reminding. I was just ordering some 100Watts resistors. These are not typically available in micro electronics stores :)
I am still not sure what the capacity is that I need to charge, and wanted to stay on the safe side, so am ordering a few, 30, 50 and 100 ohms. I prefer a bit higher because that gives a gentler current, but also want to keep the charging time down. As soon as I have the resistors I will put a voltage meter on it during charging to see what I am dealing with.

Jusp:
Ah, 1k. I was still working from Alan's suggestion of 30 Ohms. 
1k gives a way more common wattage that I can buy around the corner.
Let me try that first. I can at least determine the capacitance with them.

Jusp:
Just to conclude this thread, here is what I will end up doing.

First, an 1kOhm shunt resistor does not work:  this indeed starts charging the capacitors, initially increasing the voltage to the controller, but the controller starts booting around 27V, drawing too much current at that stage for the voltage to increase any further towards the full 54V.

However, a 100 Ohm resistor is able to bring it up to about 49V. The remaining 5V can then be safely bridged by closing the contactor, after which the motor controller is in business. I am using 10 resistors of 1K each in parallel. Each of them is rated 1watt, which is a little bit low, but this appears to give no problem in practice because the current through them tapers off quite quickly.

Attached is a sketch of a simple microcontroller circuit using two relays, that first connects the battery to the motor controller via a 100 Ohm shunt resistor for a few seconds via Relay1, then activates the contactor via Relay2 (and releases the shunt) for bringing the motor controller in full contact with the battery. Note that this circuit is powered by my 12V house battery. The microcontroller requires 5V, which is provided by a 7805 voltage regulator. The total component cost is lower than $20, available at any microelectronics store or web site. I am using Digikey.com (relay part no Z2352-ND ). Note that I have not mentioned here anything about the (simple) program that runs on the microcontroller. Anyone interested in that shoot me a message.

Of course, having a microcontroller available now opens up other possibilities. For example, I can place it between the throttle and the motor controller to gradually increase or decrease the motor RPM towards the throttle setting in order to prevent the motor from jerking the propeller shaft. But that is another post :)

Thanks again Alan and Tommycat, for getting me going on this

Juul

Jusp:
Ai, too hasty with this diagram: the contactor coil should still be in the 12V circuit.
Here is the update. One relay only, plus the ZJ400D

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