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I am trying to connect Feyree smart EV charger with Dynamic Load Balancing to DTSU666 smart meter via RS485.

Dynamic Load Balancing is a function of EV charger that lets you dynamically change charger output depending on reading from your energy meter (home consumption) to limit total consumption to a set current.

The only issue is selectable current range on EV charger is 20-100 A. I want to use this setup with solar panels so it can limit charging current depending on solar power in a way that total power output from my house (on bidirectional energy meter) is balanced to 0 A (no power pulled from grid and no power going to the grid, all excess power going to EV charger).

This means I would need to set DLB current on charger to 0 A so it could balance out nicely, but like I said the settable range is from 20 A to 100 A.

What's the easiest way to add constant value to the RS485 message on the fly? Can I put MKR 485 Shield between charger and meter and code it to simply add 20 A to the reading from meter? then I would set limit current on EV charger to 20 A and it could balance out and work as I intend?

Greenonline
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Martin
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1 Answers1

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Sounds like you want to do, what is effectively, a "man-in-the-middle" attack.

However, to do that, surely you would need two MAX3157 devices (and thus two MKR 485 shields)? One talking to the charger and one talking to the meter, with the Arduino "injecting" the "20A" message into messages from the meter to the charger. Yes, it sounds possible.

However, if you tried to use two MKR 485 shields (assuming that they are stackable), you will quickly discover that both shields use D6 and D7 for TX and RX - you can not configure this using jumpers or from software. So there would be a conflict - you wouldn't be able to address the shields independently. Therefore, a design using the MKR 485 doesn't seem possible. You need to think of something else.

Maybe you could design a custom PCB, or breadboard, using two MAX 3157 ICs (and not the MKR 485 shields), that you can enable and address independently, using additional digital pins for the addressing. Alternatively, use one shield in conjunction with an additional custom circuit for the other MAX 3157.

Greenonline
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