Hello world!
I would like some recommendation on what IC to use for building a device (electrolysis machine) that can limit the current to less than 20 mA and be able to reverse polarity for a voltage at around 24V.
Any recommendation for maybe a DC motor controller that has current limiter via external resistors or Ref Voltage pin.
Any other device that can do this that I can control via Arduino?
Cheers,
How many times per second do you need to reverse polarity and how much time at each polarity? If you already know the voltage, 24 volts, and you limit the current to 20mA, then you can quickly compute the series resistor value.
Have you tested the project with just a relay doing the polarity reversing? An Arduino can easily control that.
I don't won't to use relays...
I also know how to do the coding for the polarity change interval (ex. every 5 minutes)
I just need recommendation on a external device, ex: DC motor controller that has current limiting capabilities, basically, if I set the current limits to 20mA, then I can short the output and only 20mA current will pass. I am aware of current limiter device like the LM334 (adjustable current source), but it's only good for 10mA max and would need to be installed on the Vin of the device and not on the output because of the polarity changes.
I was looking at the DRV8871 H Bridge DC Motor Driver Board that could be a possible driver.
I also have 10K digipots that could be used to set the max current limit....
But, I'd like to know if anyone else build something like this other than using a motor controller.
Thanks
You set your current limit with the resister in series with the motor power!
What is the typical resistance of your electrolysis apparatus?
The problem is that I am not driving a motor and the load resistance will change (decrease) with the electrolysis process.
probably from 2K to 30k ohms...
That is fine. Since your source voltage does not change choose the resistor to limit the short circuit current to 20mA. Then no matter what the load is, the current cannot go above 20mA.
Yes I will try this...
P.s, I have place a small 24v bulb in series for now in case of a short, nothing will explode... LOL
Cheers
What resistance and wattage did you compute for the series resistor?
probably around 2.4k for approx 2.5mA, haven't done it yet R=V/I
I'd like to use a digipot in this circuit, but not rated at that power, so will have to do some digging...
If your limit is 20mA, then that is the value that must be used in the resistance calculation, Ohms Law!
20mA would be the max, i'd like to go lower current...
If your guess is correct, at 24V, the apparatus will draw between 0 to 0.8 mA. You don't need a 20 mA current limiter.
It would be a very good idea to measure the resistance.
That is much different that limiting current to 20mA.
OK I call the power company and ask if they had any resistors for my project...
They ask for the power rating, so I said it was for 20 thousand amps (20mA is 20 thousand amps right!!)
They said yes, but it’s expensive, I ask how expensive? They said EXPENSIVE....
I ask if they can provide a picture...
It's seems a little big for my project, any comments???
LOL
Nice, start heating your soldering iron... 
By the way, why you want to complicate your life with some cinese motor driver boards, that you don't know how they behave with few mA loads? Just wire your power supply to current limiter ,from there to relay and finally to electrodes. You can use lm317 with pot to regulate current and single tiny DPDT signal relay for polarity swap.
This will be how I will set it up, waiting for the Adafruit INA169 Analog DC Current Sensor to get here tomorrow. The relay is to short the output of the electrodes so I can read the current draw via my Nextion Display via a dedicated button on the touch screen...
This circuit will allow me to change the electrodes voltages from 24 V to 40 V and adjust the max current from 2mA to 12.5mA approximately.
Cheers,
