PTS Flowbench Forum

Hello guys!

I need to find some alternative components to the Bruce's Solid State Relay Contro Module kit.

I found here in Brazil, a lot of SSR's, with 3-32VDC inputs (for adjustment) and some with 470 Kohms input (to use with trimpots). They are at a very reasonable price.

But... a problem camed out:

It is pratically impossible to find 10 turn potentiometers with 470 Kohms resistance. The common around here are from 1K to 10K.
Even founding a 470kohms potentiometer, it would not be the perfect solution, once these circuito has no complete isolation from the fire line (220V) on the other side of the SSR.

Then I found on China suppliers some alternatives, at a good price range.
Like these ones:
LSA-H3P120YB
LSA-H2P120YB-F
KZLTD
SSR-80DA-W
SSR-100WA-H

They feature: isolated circuits from input lines and fire lines, numerous input types (for use with 10K trimpots and mA inputs from PID, Soft Start, Closed Loop output auto adjustment, and numerous Amper options.

But reading in internet (Brazilian texts), and also on the China suppliers SSRs ads, I could understand that SSRs are not the best way to control inductive loads, and if you want to use then you should use a very high security margin from 3 to 6 the amount of Ampers.

So, if I am going to run 8 Domel motors, from about 6A each, would be 48A, that going by the margin adviced, I would need a 240A SSR power regulator module.

It it really needed so much big margin?

Until 120A those modules are affordable, but more than that they are very expensive, as well as bringing the Bruce's SSR parts or even bringing the Crydom board from USA to use with some local SSR (Crydom Board).

Any way it is possible to use that China modules? Are they substitute (in function, not quality) for Bruce's / PTS' motor control parts?
Or are any other alternatives cheaper, safe (isolated input/control from the fire/power line) and better?

Those ultra cheap controllers that require a 470K potentiometer are definitely not suitable. The potentiometer will not be isolated from the mains, and it cannot be driven from an external dc control voltage. They are designed mainly for dimming lights and can have some pretty erratic control characteristics if you try to control an inductive motor load. Definitely not recommended.

I quickly looked through those Chinese controllers on your list, and all of them have either 0-5v or 0-10v isolated dc control inputs which will work fine with a 10K multiturn potentiometer. They probably all use back to back SCRs which are excellent for controlling inductive loads.
Read through the fine print, and if it says anything about SCRs or suitable for motor control or inductive loads, that would be a big plus.

Now the problem with a great many types of motor load, is that if you just switch on the power, there can often be a huge inrush current surge that can be multiples of the normal full load running current. That will require some derating of the controller, and three to six times is probably a reasonable figure.

Now if we use a soft start, or remember to turn the speed knob right down to zero before switching the main power switch on or off, we can avoid the huge power surge. You will need to do that anyway if you are going to be pulling close to the maximum current from your power board to avoid popping the fuse or circuit breaker. So you don't need to hugely oversize your power control module, but make sure the heatsink is very generous. If you can hold your finger onto it continuously without screaming, its probably fine.

Well, thank you Tony.

I will ask to the vendors about back-to-back SCR in their modules.

Some of the manufactures offers Soft Start feature, if the client asks for.
So in this Soft Start case, the margin could be smaller, like 2x the needed Amper rate?

I saw that Bruce used a 75A SSR for 8 motors, wich made me confuse if it is really needed so much margin in the Amper rating...

And just thinking here: those modules have a 5VCC output. It should not be so difficult to create some sort of Arduino PID module, controlling the SSR module via 20mA input.

With that, and the potentiometer connected to the Arduino, wich would verify at every start if the potentiometer is at zero position. If no, the potentiometer has to be turned down to zero in order to actually initiate the system and thus permiting the velocity to be increased once again by through the potentiometer.
Just an idea...

At the same time I am talking to some vendors in Brazil, if they can do something like those Chinese, at a close price range.

One of Bruce's flow bench pressure control modules has all of that including the soft start.

Soft start is excellent, because you can set your motor speed potentiometer manually up for 28 inches and then leave it alone, and just switch the main power to the bench on and off and the pressure comes right back to where it was set.

You don't really need any controller excess power rating with soft start, although if a vacuum motor ever blows up it might take out the controller too if its running right at the very edge. Cost comes into it obviously, but something a little bit bigger than really required is probably good insurance.

Tony wrote:One of Bruce's flow bench pressure control modules has all of that including the soft start.

The PID one? Or that SSR + Board + Potentiometer kit?

Any way, Bruce's components are the easiest way to go but it would be very expensive to bring it here to Brazil.

Tony wrote:Soft start is excellent, because you can set your motor speed potentiometer manually up for 28 inches and then leave it alone, and just switch the main power to the bench on and off and the pressure comes right back to where it was set.

You don't really need any controller excess power rating with soft start...

That way explained, with Soft Start feature I would have no need for example to crate some module like the one I was thinking, using Arduino?
If it is so, thats very good.

I think I can buy some chinese SSR SCR module rated for 120A (8 motors x 6 ampers = 48A) for something about R$290,00 wich is still expensive but not absurd. And no need for external 12-24v power supply.

I am talking to the vendors on AliExpress right now.

paulo_aa wrote:The PID one?

If you just get yourself a Chinese power module, heatsink, and a ten turn potentiometer, that will get you started.

Then eventually either Bruce's PID pressure controller box, or build your own home brew pressure controller.

Tony wrote:

paulo_aa wrote:The PID one?

If you just get yourself a Chinese power module, heatsink, and a ten turn potentiometer, that will get you started.

Then eventually either Bruce's PID pressure controller box, or build your own home brew pressure controller.

Tony designed the PTS PID and added support for various voltage outputs so it could be used with other than PTS SSR and added soft-start feature for that purpose. it is typically not activated by me when I build them as the PTS SSR already has that feature on the phase angle control. It's just a matter of flipping a DIP setting to turn on soft-start.

I over-rate my SSR because it cost me the same to buy a 50, 75 or 125 amp SSR. I only stock 75 (8 motor) or 125A (12 motor) now

For now, my chinese vendor is asking me how many time I want programmed in the Soft Start feature...
I just don't know what to answer. Wondering something about 30s or 45s...


Anyway...
I was looking more and, please tell me if I am correct:

I can buy the Crydom ECD board 25MW1-682-401 (https://www.ebay.com/itm/1-USED-25MW1-6 ... SwX61ZAlLx) and use it with any 125A SSR that I can find with 3-32VDC input?
This board is fost start?

These components (Crydom EDC Board and Crydom SSR 3-32VDC input are the one selled

I ask, because simple SSR are not that expensive arounde here. I can can get Crydom board here, it would be a better deal than bought some chinese power control module without any sure it it will run correctly...


Thank you two since now, for being patient with some cheap and dummy guy in electrics and electronics like me.

paulo_aa wrote:
I ask, because simple SSR are not that expensive arounde here. I can can get Crydom board here, it would be a better deal than bought some chinese power control module without any sure it it will run correctly...
.

Be very careful Paulo, most SSRs just switch things on and off, they are not capable of speed control. If it cheap its probably just the on/off type.

If is says "random fire" or "suitable for motor speed control" then it should be o/k. These speed control modules are a lot more complex inside, which is why they are always far more expensive.

Still think you would be a lot better off buying from Bruce.
Something that is cheap and ends up being of absolutely no use is not a bargain.

I have a whole bag of those controller boards!

I remove them from the SSR's I sell and install the Phase Angle Control module. I never could find any info on that controller board??

Maybe I should start selling these on eBay?? My bag is full and been wondering what I could do with them