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J1772 120v varying PWM solar charging

I have a few year old Prius plug in and I want to add power to the battery bank via solar panels on top of my car port when it's parked all day

I plan to use as small as possible, yet still adequate, charge inverter (thinking a 1500w pure sine like this one on Amazon coupled with a J1772 120v adapter similar to this one, and approx. 1000w of panels that will output approx. 18v (they come with their own solar charge controller).

According to this site:

"Level 1 Charging

This is the slow charging route that uses a standard 120 volt power outlet. Electric cars sometimes have the option of designating either a flow rate of 8 or 12 amps…The difference between 8 and 12 amps is the higher amperage rating will charge your car faster. 8 amps is like a trickle charger you can plan on three miles per hour." ( [Note: my Prius has option select either 8 or 12 amps]

The 200w panel (5 of them) I'm looking at specs are: Output power / Amp / hour = “16.12 amp”

and the WindyNation VertaMax Pure Sine Wave 1500w Inverter says will "convert battery power to 115 - 120 VAC household power"

and I found on this site re: the Prius plug-in specifically:

Bob answered about a year ago

The 120 volt chargers draw about 12 amps. maximum. A standard 15 amp circuit should be fine. 20 amp even better. The circuit should be for the charger ONLY as the current draw is pretty near the maximum of a 15 amp circuit.

Joe answered 5 months ago

Don't know about previous years, but I just got a 2017 and under vehicle settings/ charge settings you can choose 8 amp or max amp charging. I had my circuit breaker trip twice, switched to 8 amps and the problem is fixed (

I'd prefer to just 'trickle' (again I'll be at work all day so not in a hurry) directly from the panels through the 1500w inverter thru the J1772 120v adapter plugged into the car J1772 port to the onboard batts so save overall cost as much as possible.

Naturally I definitely don't want to damage my onboard bank, so my question is: if the amount of power produced from the panels while plugged in during the day ever falls below 8 amps (for example, the weather turns very cloudy) will it just not 'transfer' that charge/do anything?


Another member answered: "This EVSE will expect a AC power supply of 120V 12A as a minimum because thats how much current it's telling the car to take from the inverter. I suspect your inverter will shutdown with an over current warning when you drop below 12A from your solar system.

What you really need is a EVSE that varies it's output as the input power varies. This is easy to do technically (you just vary the PWM "pilot signal" as the solar power varies) and I would begin your search by asking the question on the OpenEVSE forum (here). For reference the J1772 standard supports charging down to 6A 

Does this ring a bell with anyone on here? = a J1772 120v adapter I can plug into the 1500w inverter that has this "vary the PWM "pilot signal" as the solar power varies" please? Thanks for any help!!:)

OpenEVSE supports charging down to 6A. It can be set via push button, serial, WiFi or MQTT. OpenEVSE can also dynamicly adjust current to match solar output via MQTT.


Christopher, thank you much for replying. Sorry I'm not much of a 'techie' when it comes to the lingo - I just Googled MQTT and found "is a "lightweight" messaging protocol, which enables the publishing of data from Emoncms, as well as subscribing to data from other connected devices" I'm hoping to avoid it requiring that much 'hands on' input - I'm hoping it can be 'pre-programmed' such that <6A it [ideally] does nothing, but if that could be harmful, then <6A those amps go to small 2nd batt bank, and programmed so whenever >6A it lets that pwr go thru to charge the onboard pack - is that hopefully possible, please?
Christopher, Is this something OpenEVSE can help me with pls?

Unfortunately, what you are trying to do is going to be very technical especially if your setup is not grid connected. It is likely the EV will not respond well if it it attempting to pull a certain amount of power and it is not available.

You will need to setup a system to monitor the generation and send the data to the charging station. We recommend OpenEnergyMonitor EmonPi. You will also need some battery capacity to handle rapid changes in output as changes in charge current can take up to 30 seconds.

The Data from the energy monitoring setup will need to be sent to a MQTT Server, the EmonPi has one built in.

OpenEVSE WiFi will need to subscribe to the data on the MQTT Server and setup to use PV divert Mode.

Check our your Solar PV Divert mode here to get a start.

Here is a discussion of a few similar projects...

Hi Christopher thanks for replying. Since posting I've found a few companies that make automatic/programmable DC Power Supply Module/Regulator, and I've messaged them to see if they one that can be programmed to only 'switch on' at 120v DC and 8A minimum, and turn 'off'/switch if ever falls below 120v and/or 8A - this shouldn't impact parts downstream from the module? I haven't heard back - do you know of any such a module by chance, please? I think this could be my most straightforward solution? Please let me know, thanks! :) - Mike

The vehicle will draw AC power downstream from the inverter. The DC voltages and current from the panels will be different than the AC voltages and current.

The vehicle will likely not respond well to a sudden disconnection of power. The vehicle expects to get signals from the pilot line to start/stop and change current.

Christopher, thanks again those are good points I'll research more & let u know thx have a good weekend:)

Hi Mike,

I think an off the shelf solution for you may be based on the type of charge controller you buy for your solar system. The Midnite Classic has a variety of programmable relays built into it. Some turn on at a certain Battery state of charge (say 95%) and then turn off at another battery state of charge(say 85%). Other charge controllers may have similar functions. Using this type of system you could have a relay between the battery and the Open EVSE switching 120 VAC. When the battery is sufficiently full the relay would close and you car would charge at the selected Amps. When the battery charge diminished to the the lower level the relay would open and the car would stop charging. Crydom makes a nice selection of relays that the output from the Midnite Classic turns on and off easily.


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