Electronics > Power/Renewable Energy/EV's

Wanted, MPPT inverter that will keep running and just lower AC output voltage.

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Seekonk:
I'll put my PV water heater against your scrap pipes any day. $20 for electronics, #300 for a KW of panels, and a free water heater someone gave me because the plastic cold water down tube broke off. And mine only operates on excess solar normally wasted with 70% of my panels shaded at any one time. It would be absolutely impossible to heat with solar thermal at my location.

This is a 1KW control made from a $10 ebay inverter board.

Psi:
Yeah, I've been thinking about the best approach for my application.

Best plan for me is to buy a generic 1.5kW 48V to 230V inverter.
That way i can actually power 230V stuff in an emergency during the day.

Then for water heater thing, just rectify it and PWM into the current 3kW element at like 1khz and smooth out draw with some caps.  Max duty is going to be around 50% to max out panels but that's fine.

Saves me having to do much work other than making something to PWM the element with feedback to keep panel voltage at max power voltage. (and low current loop through thermostat).

No need to change water cylinder element or anything.
and inverter is off the shelf
and pwm + filter for 1kw shouldnt be that hard.

NiHaoMike:
You don't actually need AC, just a non continuous current for the thermostats to be happy. How about a boost stage and then a fixed 100Hz or so PWM to interrupt the current? The boost stage operates at whatever duty cycle it needs to in order to stay at MPP, unless the output voltage is already at the 300V or so limit.

Psi:

--- Quote from: NiHaoMike on June 07, 2023, 02:44:50 am ---You don't actually need AC, just a non continuous current for the thermostats to be happy. How about a boost stage and then a fixed 100Hz or so PWM to interrupt the current? The boost stage operates at whatever duty cycle it needs to in order to stay at MPP, unless the output voltage is already at the 300V or so limit.

--- End quote ---

DIY DCDC boost stage would work well, but would then need to spend time actually designing, building and testing one.   I kinda want to get a proper 230V inverter anyway, just so i have the option to run things from the panels

So it's easier to just use a off-the-shelf inverter, rectify then filtered PWM so it can drive the 3kW element with 1kW and not freak out the inverter.  But that creates the need to separate out the connection to the thermostat so it doesn't have to switch full DC load. But it needs a MCU anyway to do the PWM so pretty easy to add an extra input. Probably do more than one temp cutout just for safety. 

I guess it could be inverter and the two stage pwm, first pwm does mpp and runs at like 1khz,  2nd pwm runs at 50hz with no filtering. Then the thermostat would be happy and wouldnt have to do any rewiring of the cylinder.

Ed.Kloonk:
Then just use the triac method. I cheated and used that common arduino ebay light dimmer module with zero cross detection and substituted the 8A triac with the BTA41-600B Triac 600V 40A remoted on a giant bit of aluminium. Snubber builtin is iffy but circuit worked with 4.8kw element, 2000w inverter (that is really max 1500w   >:( ).

Just looked the 1.8kw element was fed about 4kwh @1kw today. The inverter can and does power computers and whatnot up to 400w sometimes as well so the waveform isn't -too- bad. Apparently. :-\

 :-+

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