Hello,
i’m interested in MIKROE 4414 digital reostat bsed on CI AD5175 but in my application the current that pass throught the reostat is 5V and up to 20mA (from raspberry).
On the AD5175 documentation, it is mentioned ±6mA but the oblective of a reostat is to vary the current and 6mA is very low.
Someone can help me to confirm the MIKROE 4414 is ok for my application and if not choose an otherone?
Many thanks.
The AD5175 would only be able to handle the 6mA for the load.
As for if the board would be able to work for your application. I would ask is the 20mA you were looking at the current that the digital pot will be seeing? or just the maximum that the raspberry pi can provide?
If the total amount that is needed for the application is 20mA(as in the pot will see this) then I would say that the MIKROE-4414 would not work.
If the total amount of current is only amount the pot draws through the load then I would think the MIKROE-4414 would be fine.
As for items that would be able to handle the 20mA or more.
I found the MCP41HV51-502E/ST
The 5K item the manufacturer lists can handle the 25mA
However I am not currently seeing a board with the “MCP41HV51-502E/ST”
MIKROE-4110 would have the 100Kohm version which can handle 6.5mA.
MIKROE-4110 MikroElektronika | Development Boards, Kits, Programmers | DigiKey
It maybe possible for them to make a version with the 5K item on it.
I would recommend reaching out to them to see if they would make these for your needs.
Contact us - MIKROE
Thanks a lot for the reactivity.
The objective is to simulate a current transformer (90A to 48mA but not the all scale will be use) and it’s like a 0-20mA loop but with a low voltage (2.5-5V).
I believe that the MCP4151-104E/P-ND may be a friendly option for breadboard use. It can hit that 20mA current discussed and maxes out at 25mA.
I am curious as to the method you are using to simulate the current transformer. Are you doing the conversion of current in software and simulating the output? A block diagram or sketch as to what you are doing may help us understand.
My project is to manage my vehicle charging box to take in account the solar production. This function is not native on my box and I have a TIC simulator with an current transformer input and an information output similar to the one of an energy counter.
For the current transformer input, I’m using the PWM output of a Raspberry PI 3B+ (settled at 50Hz / 50% to “emulate” an alternative voltage around) and a rotative potentiometer to manage the current.
It works fine but now I want to manage the value of the resistor with the PI, that’s why I think about a digital potentiometer. With I2C serial command if possible, easier to implement in Node Red.
I will add a voltage converter from 3.3V to 5V to increase the value of the resistor because the minimum value I need is around 50 Ohm. It’s important for the Digipot too because of the operating voltage often greater than 2V. With the PWM and the power of the CT input the voltage is around 1.2V with a 3.3V output.
I will probably need to put several resistor in parallel because the resistor I need is from 50 to 500 Ohm (with 3.3V) and 80 to 800 Ohm (with 5V). I need more precision for the lower value because the behavior of the CT input seems logarithmic.
With the rotative potentiometer and 3.3V output I have the following values:
In the same product range, wath do you think about the MCP4451-502 or MCP4452-502 , rheostat is enough no?
but in all cases I saw that:
Maximum output current sunk by any Output pin = 25mA → OK
Maximum output current sourced by any Output pin = 25mA → OK
Maximum current into PXA, PXW & PXB pins.±2.5mA, and it’s through this pin the current passes by no?
Finally, it’s easier to use a extension board but if not, i will use a componant holder.
Yes, you are correct:
Max current on resistor pins is only 2.5mA. I have not found a single digital pot capable of handling more than about 6mA steady-state. I think you’re going to have to try something else.
I have to say that I do not follow what you are doing above, but is there any way you could drive a controlled current rather than change resistance to do the same job? Perhaps something like the MIKROE-1296 SPI to 4-20 mA converter (I’m pretty sure it could go down to zero Amps). It communicates via SPI to control a DAC and the output of the DAC feeds a 4-20mA driver controlled by the voltage coming from the DAC.
thanks @David_1528
I need “alternative” voltage on the loop because of the CT input. (I try with DC voltage and it doesn’t work).
I created it by the PWM output (3.3V 50Hz and period 50%).
The voltage in the loop must be between 7.5 to 36V and there is an diode bridge on board.
It’s possible to use CC/CC converters like MU Series (3.3->5->12V for example).
But do you think it’s compatible with the PWM on the loop ?
Sorry but I’m not an expert just basic in electronic.
Warning, playing around with high power battery charging can easily lead to fires and explosions. Be very very careful and make sure your liability insurance covers you improvising high power electronics.
@PaulHutch
Thanks for your warning.
That’s why I want to use the TIC simulator provided by the manufacturer of the charging station to manage the power available for charging. There is no modification on the station which provide a TIC input, normaly connected to the counter of the house but don’t take in account the solar energy and the price (different between night and day).
Only the engineers who designed the charge controller can be certain if it is safe to automate a system in a way they did not design.
I highly recommend you ask the manufacturer about what you want to do with their gear.
It is surprisingly easy to accidentally automate out safety with DIY add on circuits.
@PaulHutch the parts used are the one of the manufacturer : HAGER XEV304 to command a station XEV101. I just want to replace the current transformer to give to the XEV304 the value that I want. It’s the XEV304 who communicate with the station. There is no risk with this method.
An other possibility is to communicate directly with the TIC protocol (standard) but precisely it’s not the solution I want to use.
I stand corrected regarding maximum current ratings for digital pots. The MCP41HV51-502E/ST that @Nathan_2268 referenced can in fact handle up to 25mA, as he stated. The trick with that part is that it requires a second supply of at least 10V to function properly.
Conceivably, one could desolder the 100k part which comes on the MIKROE-4110 and replace it with the 5k version. However, the wiper resistance can be as high as 200Ω, which would likely exclude it from usefulness, based on the resistance values you specified above.
Thanks a lot @David_1528 .
I will study that this weekend.
Have a nice weekend too.
