Exchange linear pot for digital potentiometer

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Hi all,

 

I would like to control two 48V DC motors (500W) from electric scooter with my Arduino.

I've bought two pwm controllers from ebay and they work excellent. Issue is that controllers have pot on them (10k linear) and I need to replace that with digital one so I can drive it from Arduino.

I've bought MCP41010 (10k digital) and connected it via SPI, it all works great for one motor. Problems arise when I want to control two motors and connect both digital pots to Arduino. It doesn't work, precisly it burns pots :(

Pwm controllers are DC6-90V and pot on them is (5V, 0-5V, 0).

Setup is following:

Arduino is powering and controlling over SPI MCP41010. Motors are connected to PWM controller and controller pot terminals are connected to MCP41010. Controller is powered with batteries (48V).

Schematic:

http://picpaste.com/pics/kontroller-K4o3hFUi.1421686913.png

If I connect only one POT and motor controller all works fine, if I connect two, they burn out :( ?

PS:

Controller pictures:

http://pastebin.com/RpUpWKfk

 

Could using parallel connection for powering both controllers be problem?

 

Anyone has a clue?

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Hi,

 

Are the two controllers driven from completely independent batteries?  If so, they will be floating and the only common path will be via the two digital pots which are each referenced to the same ground on the Arduino.  Previously the analogue pots would float with the batteries.

 

You either need to have a common reference for the controllers which is the 0v of the digital pots using straps between the batteries supplying the two controllers or you need to electrically isolate the inputs of the digital pots and let the digital pots float with each controller.

 

David      

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There are some digital pots (not a lot; somewhat rare IME) that are "true" digital pots that indeed vary the resistance across output pins, that don't need to be referenced to an apps "common" ground and supply voltages and such.  I'd have to dig out past apps where we have used them.  See if you can find some.

 

A possible example:

MCP41HVX1 http://ww1.microchip.com/downloa...

 

Another?

AD5260/AD5262 http://www.analog.com/static/imp...

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Mon. Jan 19, 2015 - 08:54 PM
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I am thinking the same as flippers, youre pulling power  through the pots or have a ground loop

Keith Vasilakes

Firmware engineer

Minnesota

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Pots will "burn up" for only three reasons:

 

1. Too much voltage, end to end, on the pot. The spec sheet will tell you what the limit for this is.

 

2. Too much wiper current. This can happen if the lode resistance is too small and the tap (wiper) is set somewhere on the upper end of the pot.

 

3. Inappropriate voltage differences between the logic input and the analog pins. Again, the spec sheet will tell you the limits.

 

There are a few other things that can be done to hurt a digital pot, but these are the main ones.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Thanks guys for helping out.

 

First to answer about batteries. As picture presents, controllers run from batteries (both controllers) and arduino in this case runs from it's own power source (USB).

 

After researching around I also think that ground loop is what is killing it and one thing I should think of and got hint on was - isolator.

 

Just puting isolator between arduino and digital pot and running pot from 5v already present on the terminals would probably solve it completly, what do you think?

 

Once again thank you all for helping out!

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Of course there could be a much easier and cheaper solution. 

 

Is there any reason that the batteries need to float?  If not, then (presuming the motor controller ground is referenced to -ve of 48V battery) strap -ve of each 48v battery with a thick wire to a central Star earth point and also connect the Arduino 0v to this point.  You also might want to consider deriving your 5v for the Arduino from one of the 48v batteries.

 

David