Solid State Relay - Need help!

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chiloschista
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Solid State Relay - Need help!

Post by chiloschista » Mon Nov 10, 2014 10:12 am

Hi ensemble,

as first post here I start with the need of some help with an issue related to Solid State Relay.

The machine is composed of:

- a CNC router/hot wire cutting combo
- a chopper board to control stepper motors and Z level probe (parallel port #1)
- a supply for wire heating
- a breakout board to control two Solid State Relays (parallel port #2, USB for 5V SSR supply)
- a Solid State Relay to control the wire heating (DC-DC)
- a Solid State Relay to control spindle on/off (DC-AC, 10A)
- a spindle (Kress, 4.8A)
- control wires are shielded and grounded

The machine works well and has several hours of work on its shoulders, both on milling or hot wire cutting.
Both control board seems to work properly.
The DC-DC SSR works well controlling wire heating
The DC-AC works well controlling a vacuum cleaner, even if I set the cleaner at partial power.
The spindle works well if I connect it directly to mains supply, at partial speed also.

The problem arise when I try to control the spindle with the SSR.
If I set the spindle at full speed, with the on board knob, it works well.
If I set the spindle at partial speed, revolution speed jumps a lot. Definitely not usable and even dangerous. The bit could break, ruining the piece or worst...
If I control the SSR with a LIPO 3S battery, there are no issues.
Voltage measured at control line with a multimeter is stable at around 4.2V.
(I should find the divider I built several years ago and check the control line feed with a PC sound card oscilloscope)

At this point I'm not sure if it is the spindle that creates so much electrical noise, to disturb so much the breakout board, or the line, or the SSR.
I tried adding capacitors on the control wire, SSR side, and on USB 5V line on breakout board side, with no noticeable improvement.
I tried feeding USB from a wall charger and even another mains supply, no changes.

I'm not sure which solution could be the better.
Using a FET, as suggested by Tilman (thanks!)?
Going for another SSR, maybe a phase controlled one?
Changing the breakout board and using a better shielded one?
Last one continuing with manual control ... (nooooo...)

In the case of the FET solution, should I create a filtered power feed, or just connect it to a suited power supply? A schematics would be helpful.

I'm becoming crazy with that and developments suffer from this waste of time :angry:

Any help will be really appreciated: thanks in advance!
Best regards,
Ric

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MikeB
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Re: Solid State Relay - Need help!

Post by MikeB » Mon Nov 10, 2014 10:20 am

I'm guessing a bit here, but it seems you may be using something like PWM to control the SSR that is switching AC. If this is the case, then you most likely need to synchronise the PWM to the AC frequency.

Mike.
ersky9x/er9x developer
The difficult we do immediately,
The impossible takes a little longer!

chiloschista
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Re: Solid State Relay - Need help!

Post by chiloschista » Mon Nov 10, 2014 2:05 pm

I guess not. I control the SSR through Mach3 with on/off functions (M3, M5). PWM is disabled.
And also, why it works with the vacuum cleaner?
Thanks for your answer!
Ric

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Kilrah
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Re: Solid State Relay - Need help!

Post by Kilrah » Mon Nov 10, 2014 2:25 pm

If the SSR is an AC model it likely uses some kind of PWM internally.
The spindle's speed regulator would also use PWM, and I wouldn't be surprised if the variations you see are due to interference between those 2 PWMs.

chiloschista
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Re: Solid State Relay - Need help!

Post by chiloschista » Mon Nov 10, 2014 3:20 pm

Ok, thanks.
So probably I would see the same issue if I feed the SSR by an external source, through a FET.
Is there a solution then?


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Kilrah
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Re: Solid State Relay - Need help!

Post by Kilrah » Mon Nov 10, 2014 4:20 pm

Removing the SSR... if you're switching DC then use a FET instead of it, if AC a good old mechanical relay would do the job...

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tilmanb
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Re: Solid State Relay - Need help!

Post by tilmanb » Mon Nov 10, 2014 7:44 pm

My first idea was that since the motor is inductive thee SSR might have issues with that.
But Ric had testes driving the SSR with a higher control voltage which seemed to make it work reliably.
Hence the idea that the inductiveness is perhaps not a problem and the idea to boost the control voltage with a FET.

A SSR should not have problems driving a pwm controlled load. It just can't switch itself at that frequency.

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tilmanb
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Re: Solid State Relay - Need help!

Post by tilmanb » Mon Nov 10, 2014 7:55 pm

Thinking of it. The motor speed control is probably some phase angle control. The inductive effects are of course higher with the stark rising edge at half load than the perfect if phase shifted sinus.

Ric, I would look for a SSR that is specifically made for inductive loads.
I don't think they would be much more expensive and your problems are probably all gone.

Alternatively. I suppose that spindle speed control probably does not have some proportional control input? If it had, you could perhaps hook that up directly to mach. Probably not a option, but would be nice.

chiloschista
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Re: Solid State Relay - Need help!

Post by chiloschista » Tue Nov 11, 2014 8:51 am

Thanks Tilman for your detailed analysis.
In the meantime I found this interesting document, which shows a better filtering solution than a simple capacitor.

I found this SSR also, which should be a random turn on, up to those instructions and if image is correct.

Do you have a better suggestion?

Thanks!
Ric

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tilmanb
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Re: Solid State Relay - Need help!

Post by tilmanb » Tue Nov 11, 2014 10:10 am

chiloschista wrote: I found this SSR also, which should be a random turn on, up to those instructions and if image is correct.
This is still the zero crossing type. You need one with P instead of a Z in the product code with his product family.

The Thyristor type random turn on ones are a bit more expensive. But ebay has some.
I suspect your chances are a whole lot better with one of those. Because they don't have those phase shift issues.
Once that is out of the picture we could still have issues with that motor speec controller. But one thing at the time I would say...

To visualise the problem. A zero crossing SSR is basically a TRIAC. Those can be ignited to become conductive, but when the voltage falls to zero they need to be re-ignited. So basically they need switching every time the voltage crosses zero volts. That is really simple and no big deal.
The problem is with inductive loads the phase of the current is shiftet to the phase of the voltage. The TRIAC switches at zero volt, but current is not at zero at hat time.

chiloschista
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Re: Solid State Relay - Need help!

Post by chiloschista » Tue Nov 11, 2014 10:39 am

Mhmm, the image shows a D-240A40P one, which should be a random turn on, isn't it?

Will search again ...

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