PWM on resistance load causes flicker on LED lights

[ClassicCrazy]

I have two Classics in Follow Me mode. I am using the AUX two of the follow Classic in Waste Not to PWM an AC resistance heating element in water heater.
The AC is provided by an Outback 3500 watt inverter.
I am using a SSR for the PWM to heater coil. I was told that perhaps there is a voltage spike being caused by the ssr turning on and off which is messing with the Outback regulation that may be what is causing LED light to flicker.
And that a capacitor across the AC terminals of SSR may help.
I found a capacitor from a well pump controller and put one across the SSR but that did not stop the LED light flickering .
Does anyone have any thoughts on this ?

Larry

[Rob Linschoten]

A common problem, I'm afraid. Can you give us the specs on the SSR?  If it is SCR - based, you are going to see a bit of a messed up AC sine wave. Not the Outback's fault.

RobL.

[ClassicCrazy]

A common problem, I'm afraid. Can you give us the specs on the SSR?  If it is SCR - based, you are going to see a bit of a messed up AC sine wave. Not the Outback's fault.

RobL.

Initially I was using a cheapy ebay Fotek, but today I tried a maybe fake Omron and a real older salvaged made in usa Idec. They all seem to have same results.
I just found this info on SSR's - I am going to study it tonight. https://www.huimultd.com/INFORMATION/Solid-State-Relays-Intro/
Larry

[boB]

Hard to say what is happening.   An AC SSR is typically a TRIAC and turns off on the AC zero-crossing which is good.

Usually, the turn ON is also on a zero crossing but not necessarily.

A resistor should be fairly easy on things, especially on an OB FX inverter output ?

Maybe the Aux 2 is set for DC PWM for Clipper use ?  That will change how the PWM works in other modes like Waste Not too as I remember.

Go to the Clipper setting and see if it is set for AC clipper.  If so, good.  AC mode runs at around 500 Hz which should be good for AC PWM.

boB

[ClassicCrazy]

Hard to say what is happening.   An AC SSR is typically a TRIAC and turns off on the AC zero-crossing which is good.

Usually, the turn ON is also on a zero crossing but not necessarily.

A resistor should be fairly easy on things, especially on an OB FX inverter output ?

Maybe the Aux 2 is set for DC PWM for Clipper use ?  That will change how the PWM works in other modes like Waste Not too as I remember.

Go to the Clipper setting and see if it is set for AC clipper.  If so, good.  AC mode runs at around 500 Hz which should be good for AC PWM.

boB

yes Clipper was set for AC and 150v . I turned it down to 120v  in case that makes any difference. 

Larry

[Rob Linschoten]

Sorry, I was asking for actual model numbers. You might be using a SCR instead of a TRIAC.

I use neither, in the past I have gone with a MOSFET. The first two are still locked to line frequency. It is my understanding the MOSFET will actually run at the AUX frequency regardless of the status of the sine wave. Basically the same idea as inverter output stage topology.

I did discover that some 120V dimmable LEDs are a lot more sensitive to AC line noise (i.e. generator output), as are the cheaper in-wall dimmer switches.

Not an engineer, just learned the hard way.

[ClassicCrazy]

Sorry, I was asking for actual model numbers. You might be using a SCR instead of a TRIAC.

I use neither, in the past I have gone with a MOSFET. The first two are still locked to line frequency. It is my understanding the MOSFET will actually run at the AUX frequency regardless of the status of the sine wave. Basically the same idea as inverter output stage topology.

I did discover that some 120V dimmable LEDs are a lot more sensitive to AC line noise (i.e. generator output), as are the cheaper in-wall dimmer switches.

Not an engineer, just learned the hard way.

Thanks for the info .
Big Clive did a tear down and made schematic for the SSR that I am using.
https://youtu.be/DxEhxjvifyY
Yeah maybe it is just the drivers on those LED lights that cause that.
I don't notice any flicker  on my LED computer  monitor .
Larry

[boB]

You certainly can and should use a MOSFET or IGBT for many different things.  Especially to clip DC but AC will work with them too (at least with added diode or two FETs back to back).  Higher frequency could be nice and smooth but if the frequency is too high, then a FET will get hot.  A few hundred Hz would be OK.  Did that years ago in discrete form as a Clipper.

Fast switching can also cause EMI and high voltage spikes that have to be snubbed pretty heavily...  Due to inductance.  That's why I prefer zero cross switching when possible.  Snubbing is kind of unavoidable for DC clipping though for the same function, but  with the lack of nicer higher frequency averaging instead of a more bumpy lower frequency thumps.  Thanks for inertia,  I find that most turbines I played with take the TRIAC pretty well.  Maybe not all of them ?  Can't remember.

MidNite used to use Teledyne SSRs...  Both 3 phase TRIAC 600V and 75A, 600V  (I think)  IGBT based SSRs.  Both were tough as nails.  Then they started to charge something like $300  for one of those so we made our own.  Maybe they didn't want to make them anymore ?

But there is the (now) Sensata owned Crydom which has been very good in the past.  I think Teledyne is great but just too expensive if you can still get them.    I haven't looked although we still make Clippers.

You can also, sometimes, short the turbine windings without load resistors, but load resistors make things smoother too, usually.

I am really glad that some people are still using small wind power !    "Small wind" meaning anything less than 100kW  I understand.

boB

[ClassicCrazy]

I am looking for  decent quality SSR. There are so many fake copies on the market that you need to look really carefully .
The one that Big Clive tore down was supposed to be 25 amp but only had a 13 amp part in it.
Larry

[boB]

I am looking for  decent quality SSR. There are so many fake copies on the market that you need to look really carefully .
The one that Big Clive tore down was supposed to be 25 amp but only had a 13 amp part in it.
Larry

Yeah, Crydom may be one of the only ones that you might want to trust these days ?

boB

[kitestrings]

We've also had very good luck with Teledyne relays - on much smaller scale than MS I'm sure.  For DC, I really like the ones from VB Controls.  They are US made (VA IIRC).

They all are famously overrated.  I've come up with an algorithm for sizing them, however, that I'm happy to share.  Take the manufacturer's rated switching current of the device and divide by two; by three is better still ;>]

[ClassicCrazy]

I am looking for  decent quality SSR. There are so many fake copies on the market that you need to look really carefully .
The one that Big Clive tore down was supposed to be 25 amp but only had a 13 amp part in it.
Larry

Yeah, Crydom may be one of the only ones that you might want to trust these days ?

boB

Not sure about the Crydom either- when you see brand new Crydom relays shipped from China for 1/4 the price of one shipped from Digikey for same thing - makes you think something is fishy there !  I ordered a Crydom from someone on ebay who has some new old stock and seems to be legit. Plus it is a model relay that the fakes wouldn't bother to copy ( has a bit different style lug on it. ) I had to study Crydom data sheets to discern the differences in similar models . For instance there is a d2425-10.  The -10 signifies that it is not zero crossing and instant on - so I passed on that one. The one I ordered d2435T - the T refers to the connection point on it ( hexed ) .
Larry
Larry

[ClassicCrazy]

We've also had very good luck with Teledyne relays - on much smaller scale than MS I'm sure.  For DC, I really like the ones from VB Controls.  They are US made (VA IIRC).

They all are famously overrated.  I've come up with an algorithm for sizing them, however, that I'm happy to share.  Take the manufacturer's rated switching current of the device and divide by two; by three is better still ;>]

I think your sizing advice is good !

Larry

[ClassicCrazy]

I made a video of the PWM causing disturbance to LED light and the noise from the Outback inverter.
https://youtu.be/nZk_FuNzjes
Larry

[boB]

I made a video of the PWM causing disturbance to LED light and the noise from the Outback inverter.
https://youtu.be/nZk_FuNzjes
Larry

Nice video example !   Damn that OB FX regulation !   

Are your Solid State Relays zero cross turn-on  or  anywhere in the AC cycle turn-on ?