I have a 24v 5A power supply that I'm using to power a 1A rated motor (I haven't tested the inrush current as yet but from what I've read it could be up to 5x the rated output).
I also want to use this to power my arduino and ESP8266 so bought a couple of buck converters for 24-5v and 5-3.3v respectively. These are non-isolated
My question is, am I putting my circuit boards in danger by having the grounds connected when the motor is starting? If so, what can I do to protect them?
Thanks in advance!
My question is, am I putting my circuit boards in danger by having the grounds connected when the motor is starting?
No.
If so, what can I do to protect them?
You don’t need anything.
The inrush current or stall current as it is called is very easy to calculate. Just measure the resistance of the winding and use ohms law with the voltage you are using to power this to calculate the stall current. So this is a problem for your power supply and it might take it out, that is trip the current overload, thus resetting your Arduino as well.
Tying the grounds together is not a problem - desirable in most cases.
What you should consider is the low resistance of the motor pulls the low-side leg of the motor (floats) UP to the supply voltage ‘until,’ it’s specifically pulled down to run the motor.
Grumpy_Mike:
No.
You don’t need anything.
The inrush current or stall current as it is called is very easy to calculate. Just measure the resistance of the winding and use ohms law with the voltage you are using to power this to calculate the stall current. So this is a problem for your power supply and it might take it out, that is trip the current overload, thus resetting your Arduino as well.
Thanks for that, measured at 21 ohms which is around 1.1A, must be rated for the inrush current rather than operating current? Shouldn't have to worry about it knackering my supply at least
lastchancename:
Tying the grounds together is not a problem - desirable in most cases.
What you should consider is the low resistance of the motor pulls the low-side leg of the motor (floats) UP to the supply voltage ‘until,’ it’s specifically pulled down to run the motor.
Cheers, what does that mean for me practically?
what does that mean for me practically?
Nothing. What will you be using as the motor driver or switch?
You should try measure the motor winding resistance again. This time, rotate the motor shaft VERY slowly while doing so, as the brush contact resistance can be quite variable. Take the lowest value that you measure.
jremington:
Nothing. What will you be using as the motor driver or switch?
You should try measure the motor winding resistance again. This time, rotate the motor shaft VERY slowly while doing so, as the brush contact resistance can be quite variable. Take the lowest value that you measure.
It's actually an enclosed diaphragm pump for an RO system so don't have access to the shaft. Controlled with a pressure switch, just using arduino to read a pressure sensor for data logging (and potentially as a backup)
Then your resistance reading is probably not reliable. One would expect a resistance 5x to 10x lower, for a pump rated at 1A continuous.
If you are using a non-isolated voltage converter to power the Arduino, then the Arduino ground and the 24V power supply ground will automatically be connected together, through the converter.
Yeah, that's what I expected, and I realise that re the ground, was reading the converter datasheet when it occurred to me it might be an issue to have them linked, seems not though?
Thinking about it, maybe the increased resistance from the water pressure is what gives it that rating, pump is rated to 9 bar
I would suspect that the rating you got for the pump includes the start up current as they are so close and that in practice when it is running the current will be much less. Mind you this will be a lot more difficult to measure than just putting a meter in series because of the phase angle between voltage and current. You would be better off putting a very low ohm resistor in series and measuring wth waveform on your scope.
Grumpy_Mike:
I would suspect that the rating you got for the pump includes the start up current as they are so close and that in practice when it is running the current will be much less. Mind you this will be a lot more difficult to measure than just putting a meter in series because of the phase angle between voltage and current. You would be better off putting a very low ohm resistor in series and measuring wth waveform on your scope.
I didn't think DC had a phase angle?
I don't have a scope unfortunately, nor an analogue meter
I didn't think DC had a phase angle?
DC voltage doesn't it is always constant but when you apply this to a motor the current is constantly rising and falling as the sets of inductors making up the rota coils get powered and not powered. So in effect you have an changing current signal. Sure it doesn't go negative but with any alternating value there are several ways you can express it, like peak, avrage and RMS.
Grumpy_Mike:
DC voltage doesn't it is always constant but when you apply this to a motor the current is constantly rising and falling as the sets of inductors making up the rota coils get powered and not powered. So in effect you have an changing current signal. Sure it doesn't go negative but with any alternating value there are several ways you can express it, like peak, avrage and RMS.
Interesting stuff, wouldn't have considered that at all.
I have some 1.6A time delay fuses, 600ms @ 2.75 x In (assume that means rated current). Worth popping one in to see if it blows?
The DC adapter that shipped with the pump is 1.7A rated, chinese though and theres not much reference material for the pump.
Interesting stuff, wouldn't have considered that at all.
Here is something else you might not have considered.
I once used this pulsing current to control the voltage on a model train set. It enabled me to have a slow start because I had a circuit called a phase locked loop with the current pulses and the train acting as the VCO ( voltage controlled oscillator ). This had the effect of raising the voltage until the train moved and then immediately shutting down the voltage to maintain the pulse rate at a slower speed.