Watts over the Radio

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The potentiometer position is converted into a Watts value and transmitted over the radio link.
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[@engineereuler1762]

Man, you're an inspiration! I wish I had the same amount of time that you have or that what you are getting compensated for your videos is very high

[@andymouse]

Looking good...cheers.

[@JulianIlett]

cheers or cheese?

[@ndmusick11]

After you get the current sensor working on the solar panel "transmitter" side you could add a current sensor to the EVSE. Set it up so you can see what is going on at both sides.

[@pete3897]

I have a small suggestion to greatly reduce the RF transmissions - configure the transmitter to only send the bytes when the pot value has changed since last time. That way you'll only transmit when the pot is rotated rather than constantly. As easy as "if packet[0] != lastPacket[0] then" :)

[@lesliefranklin1870]

That would be great, except you wouldn't know for certain that the last packet was received. Perhaps, the receiver could reply with an acknowledgement packet?

[@pete3897]

@@lesliefranklin1870 To be fair, even with it constantly transmitting you still don't know if any packets were received, so that's a separate issue :) But yes, ack's had crossed my mind too. You cold also send perodic updates regardless of state change eg every 5 seconds and still be much less RF-intensive.

[@lesliefranklin1870]

@@pete3897 I agree it would be a good goal reducing unnecessary RF. I am in favor of positive feedback, even with automation, as it seems the direction Julian is headed. For that, it would necessitate an acknowledgement. Just my humble opinion. 😀

[@pete3897]

@@lesliefranklin1870 +1 for the acks. Show us the acks Julian

[@JulianIlett]

The ack payload is enabled, so I can send data from the 'receiver' back to the 'transmitter' to prove data is being transferred properly.

[@andersson.l.e]

Nice video as always. Interesting topic too.

[@zostay23]

The EVSE microcontroller should return the actual watts back to the input controller so you can see it hop up and down on those 16ish actual values. If you get a amp meter inserted into the circuit, it would be nice to send back the actual power being sent so you can get feedback. Oh, and regarding the 6A minimum, if you wanted to get fancy, you could integrate over the solar power inputs, wait until it accumulates enough to turn it on for 30s or so at 6A, so it'd be mostly off, but then push a charge every so often.

[@JulianIlett]

I may pass the actual charging power back in the ack payload. Bear in mind that the car's HV battery contactors will engage/disengage every time charging is started/stopped so you wouldn't want to do that too often.

[@zostay23]

@@JulianIlett This is true, though you could have the same problem during the day with the sun going in and out of clouds. If the goal is to say your car is entirely charged by solar another idea might be to accumulate charge into batteries and then use them as a buffer for the 6A level. In theory, the batteries wouldn't have to be real, you could just accumulate the charge from the stats in a variable and pretend you had the batteries and be almost as good even if you were drawing some of the power back from the grid. Anyway, then you just stop charging if the accumulator gets too low to avoid contactor wear.

[@TheEmbeddedHobbyist]

Would that be Dustin or David Watts? i can see them over wifi already🙂 your display should show the watt value that the car see's and not when the pot is sending, as your changing the watt's on the display but the watt's to the car as you say are changing in bigger steps. I think the information is what the car's doing and not what the pot is sending. or beter still display both.

[@JulianIlett]

Yes, I'll display both.

[@Globaltalentgt]

So beautiful

[@shehryarshaheen7115]

There should not be any delay between "right now " and the IDE display.

[@UpLateGeek]

I don't know why, but whenever I hear someone with an English accent say "watt", in my head it's "wot". It's the exact same sound, but for some weird reason it's spelled differently.

[@jacquesb5248]

brilliant!

[@dogastus]

Could do with a little hysteresis to stop the value jittering between two levels.

[@JohnBrown-cx3lv]

Have you considered a small PV cell facing the same way as your rooftop array, so that you could estimate the generation with no messy wireless stuff? Just an idea, as I was thinking about this sort of stuff a while back, and that was one idea I was considering.

[@ion337]

Cool stuff Julian! Have you considered securing the RF comms to complicate eavesdropping/replay attacks and harden the system from radio interference?

[@JulianIlett]

It's a very short range system - the hackers would be easy to locate.

[@randallneikirk6385]

Since map uses integer calculations you will not have intermediate problems but you do lose the end point as you noticed. Other websites recommend that you increase upper limit of the source by 1 to account for the loss in the calculation process.

[@JulianIlett]

Interesting, I'll give that a try.

[@jessoman]

This is phenomenal. I have been trying to figure out how to get excess solar in my off grid setup to go to the car and I'm thinking something custom like this might work. Do you think I could have a hall effect sensor on my (house battery) and one on my PV array and one CT clamp on the house and use an Arduino to find the "sweet spot" every 15 minutes to work out what charge rate I can have the car?

[@danielwilson2109]

hey Julian, as a fellow electrical enthusiast I was wondering. we see battery specs every where, 500 life cycles here 5000 for some lifepo4. how do we create a product that holds these manufacturers accountable? see what I mean? to have a minimum life cycle and also it would be of benefit to the manufacturers... thoughts?

[@alisoncarney1745]

ARE YOU GOING TO USE A CURRENT SHUNT CURRENT AS 60A SHUNT GIVES 75MA OR UP TO 5V OUT AND IF IN SERIES OF SOLAR PANEL OUT IT WILL SHOW CURRENT IN AND OUT ALL VALUES ARE APPROX LIKE TO SEE YOUR CODE AFTER YOU DO IT PLEASE LINK IT IN WHEN FINISHED THIS PART I WILL KEEP WATCHING

[@Fran55on]

Hi! I like to suggest to explore the possibility to use timer 1 to produce the 1kHz PW-modulated signal. As fare as I know timer 1 is 16 bit, an should allow for a higher resolution (aka more than 17 discrete values) of PWM.

[@JulianIlett]

I will do that if the coarse steps in the PWM signal prove to be a problem.

[@jeffmerlin2580]

Why is packet two uint16_t in an array? Seems like you never touch packet[1] 🙂

[@ncot_tech]

I noticed that too

[@JulianIlett]

It's old code. I was sending two floats (temperature and humidity), hence a two element array.

[@Andy-185]

0x11 discrete values 🙂

[@JulianIlett]

Indeed :)

[@petermciver9827]

Hi Julian. Interested to know how you will get a figure of watts from your solar system. Won’t you be needing to get a measure of “capability” rather than actual watts… before the load (car) comes on? Just wondering how you are planning to do that.

[@JulianIlett]

I have a DDS-238 in my fuse box measuring solar Watts. I'll be using the opto-isolated pulse output (1600 impressions per kiloWatt hour).

[@TheDefpom]

With the transmitter being in an ISM band you should try to minimize the duration of transmission to reduce the amount of radio interference it will be generating to other devices on the same band, some countries actually have legal limits on transmit duration for that reason as it’s a shared radio band, can you get away with it transmitting once every couple of seconds for example?

[@JulianIlett]

Once per second is probably enough.

[@rorymacleod8488]

You cant send WATTS over a radio , Nicola Tesla proved that !!

[@pete3897]

What is qi wireless charging?

[@JulianIlett]

The wireless charging systems for electric vehicles can transfer tens of kiloWatts over several inches of air gap.

[@David_11111]

Yay

[@robertmalsbury8477]

Hi Julian, what is the maximum distance between the transmitter and receiver to work?

[@JulianIlett]

From my tests in the garden, about 25 metres.

[@cmuller1441]

Instead of a pot, just use a rotary encoder...

[@piconano]

Why not put it at 10KW, and trick reality into charging the car faster?

[@JulianIlett]

I could also trick reality to eliminate all clouds above High Wycombe :)

[@piconano]

@@JulianIlett UK and clouds go together like two married people that hate each other :)

[@paranoiia8]

What? Watt!