General SWG questions

[bobfloyd]

Answers would no doubt be in the many other posts but I'm not having much luck finding exactly what I want to know...

Some questions...

1. The chlorinator output control knob - is this just a variable resistor? Cranking this to max lowers the resistance thus increasing the current through the chlorinator plates?
2. The chlorinator output meter - this is nothing more than just a calibrated ammeter?
3. If the chlorinator plates are old and the coating is worn down, thus the plates are not producing chlorine efficiently anymore, this won't have an impact on the current flow, thus, the output meter could still read 100% even though the chlorine output is not good?
4. There are 3 wires going to the cell, black, red, white. I presume the white is connected to a probe that checks for a closed circuit (I.e. Back to red or black) to ensure there is water in the cell housing?
5. The coating on the plates isn't a catalyst per se, it's actually slowly consumed by the chlorination process?
6. Without the coating, the titanium plates would still produce chlorine, but not as much? Somehow the coating stimulates more chlorine production?

Cheers,
Scott.

 

[ajw22]

What make and model SWG are you asking about?

Please put details of your pool in your signature. It gives all of us context to properly answer your questions.

 

[bobfloyd]

It's a CrystalClear RP3000 SC.

 

[Brad_C]

1. The chlorinator output control knob - is this just a variable resistor? Cranking this to max lowers the resistance thus increasing the current through the chlorinator plates?

In a manner of speaking, but not directly. ie it's not a rheostat, it just drives the electronics.

2. The chlorinator output meter - this is nothing more than just a calibrated ammeter?

Kinda, sorta. In general Cl output is proportional to the average cell current, but sometimes there are fudge factors applied by the electronics to manage things like duty cycle so you may not be seeing a direct coulomb count.

3. If the chlorinator plates are old and the coating is worn down, thus the plates are not producing chlorine efficiently anymore, this won't have an impact on the current flow, thus, the output meter could still read 100% even though the chlorine output is not good?

No. As the catalytic coatings are degraded the resistance of the cell to the water increases, so current flow and consequential Chlorine output falls. Same effect as the water gets colder. Most chlorinators have the ability to increase the voltage across the cell to compensate so you don't really start to notice until it's "mostly dead" and the chlorinator runs out of ergs.

4. There are 3 wires going to the cell, black, red, white. I presume the white is connected to a probe that checks for a closed circuit (I.e. Back to red or black) to ensure there is water in the cell housing?

Hard to say. Some do, some use a center tapped cell, some have electronics in the cell.

5. The coating on the plates isn't a catalyst per se, it's actually slowly consumed by the chlorination process?

No, it's a catalyst. Like any catalyst it is subject to degradation and poisoning. This is the ultimate limiter of cell life.

6. Without the coating, the titanium plates would still produce chlorine, but not as much? Somehow the coating stimulates more chlorine production?

I suppose in tiny amounts it's possible. My experience is pure titanium seems to tend more to plain electrolysis of the water so you get oxygen rather than Chlorine.

 

[bgpbucko]

I just replaced my SWG on Friday and opened up both to see what makes them tick.

1. The chlorinator output control knob - is this just a variable resistor? Cranking this to max lowers the resistance thus increasing the current through the chlorinator plates?

Not directly. The standard SWG circuit has the transformer secondary go through pairs of SCRs which are driven by a control board. The SCR output goes to the cell. The control knob adjusts the control algorithm on the control board which then adjusts the on-time of the SCRs. Hence varying the output power seems to just control how much of the AC cycle goes through the cell. It's essentially a glorified electronic dimmer.

2. The chlorinator output meter - this is nothing more than just a calibrated ammeter?

Yes, it measures cell current. My previous SWG measured electronically across a shunt and displayed the output on a LED bargraph. My new one has an analogue meter wired across the shunt.

3. If the chlorinator plates are old and the coating is worn down, thus the plates are not producing chlorine efficiently anymore, this won't have an impact on the current flow, thus, the output meter could still read 100% even though the chlorine output is not good?

I guess that depends on the chemistry of it all. But I imagine if the output meter reads 100%, then there is full current flow and the electrolysis is making _something_.

4. There are 3 wires going to the cell, black, red, white. I presume the white is connected to a probe that checks for a closed circuit (I.e. Back to red or black) to ensure there is water in the cell housing?

Yes, the white wire measures water flow/presence.

 

[bobfloyd]

Thanks guys.
Bgpbucko - so the output knob is controlling the scr gate voltage? My understanding of why an SCR is used in the first place is so that there is a means of controlling at what point the anode/cathode current may pass. So we're basically controlling the duty cycle? The chlorinator plates I presume receive a steady voltage but this is pulsed via the scr's ? The output meter is somehow taking an average current flow? Can you clarify what the shunt does?

Any idea guys how the reverse function works? What times when the reversing occurs (e.g. I can select every 4 hours or 8 hours).

I presume given there are 4 Scr's in the chlorinator, 2 of them are working away for say 8 hours while the other 2 sit there cold and patiently waiting for their turn?

Scott.

 

[Brad_C]

It honestly depends on the chlorinator. Mine has 2 triacs rather than scrs( effectively 4 scrs in back to back pairs) but the implementation is really device dependent as is the gate triggering logic. Reversal is just that though, it just reverses the effective polarity of the cell.

 

[bgpbucko]

Bgpbucko - so the output knob is controlling the scr gate voltage? My understanding of why an SCR is used in the first place is so that there is a means of controlling at what point the anode/cathode current may pass. So we're basically controlling the duty cycle? The chlorinator plates I presume receive a steady voltage but this is pulsed via the scr's ? The output meter is somehow taking an average current flow? Can you clarify what the shunt does?

The power that goes through the cell is actually rectified AC, straight off the transformer at usually 9V. Because of this, it's a rectified half sine wave at 50 (or 60)Hz. The SCRs are just switched diodes, turned on at varying parts of the sine wave cycle. If it turns on in the early part of the cycle, more energy goes through the cell. Whereas if it's switched on in the latter part of the cycle, less energy is sent through.

Two SCRs are used as generally the transformer is center tapped. One tap uses energy on one part of the AC cycle, the other tap has the inverse polarity and is used for the other half of the cycle. This also means that the chlorinator cell gets a chopped half sine wave through it, not steady DC voltage.

The output meter is just a regular old ammeter configuration - a shunt resistor in series with the load and a meter across the shunt which actually measures the voltage. The distance the pointer moves is the average current of the half-ac cycle, with the AC cycles damped by the spring.

Any idea guys how the reverse function works? What times when the reversing occurs (e.g. I can select every 4 hours or 8 hours).

I presume given there are 4 Scr's in the chlorinator, 2 of them are working away for say 8 hours while the other 2 sit there cold and patiently waiting for their turn?

As Brad_C says, the extra pair of SCRs is used to reverse the polarity. Essentially, the are wired in parallel but reverse with the other pair and switched during the reverse cycle.

 

[bobfloyd]

Hi. Ok, I think I understand.

I'm actually troubleshooting a problem where my meter is 100% in one direction but only 75% in the other. I was thinking the four SCRs are in a full wave controlled bridge rectifier configuration and therefore couldn't see how a faulty scr could cause this behaviour - but if it's using a centre tapped transformer and 2 controlled scrs then I understand that perhaps the pair responsible for the reverse direction could be causing the issue...
Maybe one is working and one isn't...I would have thought my meter would then read 50%.

Maybe I should just replace all 4 in one go.

Scott.

 

[Brad_C]

Sounds like you need to put a CRO on it and double check both the gate waveforms and volt drop across each SCR. On the other hand, if you actually have 4 SCRs then if it's a faulty SCR or two, the faulty ones will be running quite a bit hotter than the others.

Of course you can keep firing the "parts cannon" at it, but you'll save a lot of time and money by diagnosing it properly. Unless you get really, really lucky and replace faulty parts by pure luck.

 

[bgpbucko]

If you're getting different readings for different directions, I guess the easiest first step is to swap the cell cables, then see if it's the cable output DC polarity that changes it, or the cell DC polarity.

 

[Brad_C]

Just a random thought. Having recently upgraded my Chloromatic from a 16g/hr to a 24g/hr I was cruising the docs to see if there was anything I missed, and I spotted an Australian Patent number in the user manual, specifically : 684550.

A look in the Auspat website : Aus patent 684550 reveals the original patent for the two triac rectifier used in the Chloromatics complete with waveforms and explanations. So for anyone wondering how the cell current control and reversal works on these new-fangled synchronously rectified devices, this patent has a pretty good explanation.

This would also work similarly with a set of 4 back to back SCRs. Interesting, I had misinterpreted the opto triggering of the triacs on my unit. That or they modified as part of the "embodiment". Either way, next time I bust it open I'll have to scope the waveforms.

Translating that from 2 triacs to 4 SCR's. If you had a single SCR failure, enough salt in the pool and the cell was conductive enough, it would be entirely possible to see more than 50% on the duff side if there was plenty of conductivity and the unit was throttling back to maintain the rated output. As I stated earlier, the remaining triac for that side would be running hotter than the others. The dead one would be stone cold.