Can an AC Power inverter successfully power an arduino PWM load?

I’d like to make a PWM diversion load controller with an arduino Mega 2560. The standard frequencies are 490 and 980 hz. If the PWM diversion load of about 1KW is powered by a 2.8 kw 120v pure sinewave inverter (Outback 2812), will the inverter have problems with the PWM nature of the load? I ask because the inverter has had problems with a Watlow Din A Mite controller using a single cycle variable time base scheme - the CFL lights would flicker because the output voltages was 10 volts different between on and off cycles. See the waveform in the file below.

Can anyone offer an opinion if the PWM load can be successfully powered from an inverter?

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PWM and AC don’t really mix. Normal incandescent light dimmers use phase control, which is something like PWM synchronized to the AC line frequency. They normally are built with TRIACs, which don’t turn-off 'till the AC goes through a zero-crossing.

You probably could build an AC PWM dimmer with MOSFETs, but you’d need at least 2 MOSFETs and a bit more circuitry because MOSFETs don’t work with AC. But, a CFL doesn’t respond linearly to voltage changes like an incandescent filament.

Normal CFLs are not dimmable. There is a ballast circuit in the base that expects full line-voltage. There are dimmable CFLs, but I think they need a special dimmer. There are also dimmable fluorescent fixtures (that use normal fluorescent tubes), and these have a special high-voltage ballast circuit controlled by a 0-10VDC dimming-control voltage.

single cycle variable time base scheme

I’ve never seen that before. It looks like a regular incandescent lamp might flicker at low levels too, because of the time between voltage pulses.

Thanks for the reply, Doug.

I see my question was not clear. The 1KW load to be controlled by PWM and powered by the inverter is a water heater element. I'm not building a dimmer. The flickering CLFs was a byproduct of the bad interaction of the single cycle variable time base scheme on the inverter 120vac output.

I'd like to make a PWM diversion load controller

That implies the current is diverted into a dummy load when not going through your load. Is that what you mean?

Zero crossing point switching is important for reducing any RFI ( radio frequency interference ) so it needs to be synchronised with your AC supply.

This single cycle variable time base scheme is mostly used for heating control, not for lightning or motor control. As stated it avoids RFI and heater objects have a very long time constant so the flicker doesn't matter

Zero cycle switching works well for loads with a long thermal time constant, such as heaters, but Im not sure I understand what PWM has to do with this. Zero cycle switching takes place at the frequency of whatever the mains is , usually 50 or 60 hz , and has to be syncronised with the zero crossing points of the mains voltage. You could make a zero cycle switcher fairly easily with an Arduino, but it wont be using PWM.

turgo: I'd like to make a PWM diversion load controller with an arduino Mega 2560. The standard frequencies are 490 and 980 hz. If the PWM diversion load of about 1KW is powered by a 2.8 kw 120v pure sinewave inverter (Outback 2812), will the inverter have problems with the PWM nature of the load? I ask because the inverter has had problems with a Watlow Din A Mite controller using a single cycle variable time base scheme - the CFL lights would flicker because the output voltages was 10 volts different between on and off cycles. See the waveform in the file below.

Can anyone offer an opinion if the PWM load can be successfully powered from an inverter?

Let's step back and help me determine what your current setup is now ... You have an Outback 2812 2.8KW Pure Sine Wave inverter. You have a 1 KW Water Heater, the Diversion Load. You tried inserting a Watlow Din A Mite controller between the Outback Inverter and the Diversion Load. But the Watlow used a "weird" variably timed single cycle method to control the output. This cause flicking in the lights. Am I correct, so far?

So, you want to replace the Watlow Din A Mite controller with an Arduino running PWM Software. The PWM will pulse at 490 Hz or 980 Hz. This Arduino will be connected between the Outback AC output and the Diversion Load. Now, you want to now know if the Outback Inverter can properly drive a PWM type Diversion Load. First, did you contact OUTBACK regarding a PWM type Diversion Load on their Inverter? Second, Yes I do think the Outback Inverter can support the PWM Load.

May I ask why PWM? Is there a need for 10%, 25%, 50%, 75%, 100% type of loading scheme on the inverter? Are you diverting the Power after your Batteries are fully charged?

These guys are quite good regarding Outback Inverters! I think an (ex) Outback Employee hangs here ... http://www.wind-sun.com/ForumVB/forum.php

some really smart guys here too ... http://www.thebackshed.com/

This is an Arduino forum so my answer is "YES the Ardudino will work". But that is not the answer you are looking for. You really have an OUTBACK Inverter question so you really need OUTBACK support. I prefer you do not use 490 Hz , too slow. My gut tells me, "Yes the Outback could drive a 980hz PWM type Diversion Load" At 980 Hz / 60 Hz = only 16 PWM pulses per AC Cycle (maybe not enough pulses per sine wave?) I prefer to see a HIGHER PWM frequency, like around 2,000 Hz or more! But with software you can always modify PWM code later, IF the CPU is fast enough. But you ain't changing the WIDTH of the Pulses very often, right? So the PWM is doing ALL the work and CPU is only changing the Width quite infrequently, right?

No, I do not think you need to sync to zero-crossing either - that makes it much easier.

PWM and AC for as Resistive Diversion Load will "mix" just fine.

Let us know what you find out . Good Luck ...

Thanks, mrsummitville!

I'll follow those forum links. You have understood my question exactly correctly.

You ask,

May I ask why PWM? Is there a need for 10%, 25%, 50%, 75%, 100% type of loading scheme on the inverter? Are you diverting the Power after your Batteries are fully charged?

Yes, there is a need for many power output steps, to maintain a constant battery charging voltage while accommodating large changes in power consumed by household use. When batteries are fully charged, then all power not consumed must be diverted.

Could you not use a zero crossing detector and use the arduino to control the no of cycles of ac passed to the heater ? Ie at 60 hz you would be able to chose between 1 and 120 half cycles to be passed to the heater each second. Google on burst fire controller. Its a modification of what you already have but using half cycles rather than full ones which will have a higher frequency component.