Solid State relay

[ericmark]

I while ago I had some problems as the solid state relay was protected by an MCB and it transpired they are too slow and one needs semi-conductor fuses.

Same job also a problem with E-stop had to fit second E-stop contactor as can use semi-conductors.

And these also ran heaters.

 

[Iggifer]

no its not......it has a control voltage of 3 - 30 vdc and a 10 amp max load..... how did you come up with that?

Unless I'm being particularly dense are you sure you searched for the right PN on RS? As the one I linked is:

Depth 44.5mm
Height 27mm
Length 58.2mm
Maximum Control Voltage 240 V
Maximum Load Current 50 A
Maximum Load Voltage 520 V rms
Minimum Load Current 5 mA
Mounting Type Screw Mount
Output Device Triac
Switching Type Zero crossing

http://uk.rs-online.com/web/p/solid-state-relays/1718948/
http://docs-europe.electrocomponents.com/webdocs/0114/0900766b80114479.pdf

I will gladly stand corrected if I'm reading it wrong[/quote]

 

[bhm1712]

no its not......it has a control voltage of 3 - 30 vdc and a 10 amp max load..... how did you come up with that?

Unless I'm being particularly dense are you sure you searched for the right PN on RS? As the one I linked is:

Depth 44.5mm
Height 27mm
Length 58.2mm
Maximum Control Voltage 240 V
Maximum Load Current 50 A
Maximum Load Voltage 520 V rms
Minimum Load Current 5 mA
Mounting Type Screw Mount
Output Device Triac
Switching Type Zero crossing

http://uk.rs-online.com/web/p/solid-state-relays/1718948/
http://docs-europe.electrocomponents.com/webdocs/0114/0900766b80114479.pdf

I will gladly stand corrected if I'm reading it wrong

[/quote]

No its me being dense and looking at the photo rather than the spec

 

[bhm1712]

Surely the way it is written means that it is only 'guaranteed' to work between 27.6V and 195.5V.

No, as said already

24-230v plus or minus 15% is not 27.6v and 195.5v

+/- 15% means that the device will operate within 15% either side of the expressed voltages..... its a mathematical form of expressing standard deviation/tolerance. It would be no different when a machinist gets an engineering drawing from a designer to make something on a milling machine. The drawing may state measurements in millimeters +/- 0.05mm. So this means that the final dimensions of the workpiece can be 0.05mm over or under the spec, but will be within the tolerance. Its the same with the control voltage on our relays - the control voltage is stated as requiring to be 24-240v +/- 15% so the control voltage can be 15% under the minimum stated and 15% over the maximum stated. As a bonus, it will also work with any voltage between those 2 figures....

 

[Iggifer]

No its me being dense and looking at the photo rather than the spec

oh good. I felt rather silly for a minute

 

[Aragorn84]

when a machinist is given a drawing, a measurement would state for instance 10mm +/- 1mm

That could also be represented as 9-11mm as a range.

But would it say 9.5mm-10.5mm +/- 0.5mm?

Dont think so.


John isnt suggesting he doesnt understand a mathematical deviation, hes saying that using both a deviation AND a range is nonsensical.

 

[bhm1712]

No i dont think its nonsensical at all.

Its completely different to saying 9.5-10.5mm +/- 0.5mm. My analogy of a engineering drawing was just to try and explain something. A designer wouldnt want 2 alleged identical items to measure completely different because the machinist decided to make one 9.5mm and the other one 10.5mm, but the tolerance is required as none CNC machining will not be 100% accurate. The designer is saying he wants the work piece measurements to end up within 0.5mm of the stated dimensions, as obviously they have decided that within 0.5mm will not detract from the quality or operation of the piece.

The relay is a multi control voltage relay meaning it can be used on a wide range of control systems from 24 volts to 230 volt control systems. Almost like a 'one size fits all control systems' relay. The manufacturer is not trying to say that they expect somebody to have a control system which fluctuates between 24 and 230 volts. That would be nonsensical. Its not necessary from a consumers point of view to buy something which has such a large range, but means flexibility is massive - have one of these in stock and you can pretty much use it anywhere. From the manufacturers point of view that means it will be a money maker.

The +/- 15 % is there to explain that although the stated range is 24-230v the relay will work on voltages 15% less or 15% more than the stated range. This caters for control systems where the PSU when under load is only delivering say 22.5v, or if the single phase voltage is not strictly 230v. For example, in the factory i work which generates its own power, the voltage on a single phase can be anywhere between 225-250 volts depending on what time of day it is, or what machinery is in use in the factory. If the relay was strictly 24-230 volts then it would not work in the majority of electrical systems in the country.

Im pretty sure that all electrical control equipment has a tolerance like this but not all manufacturers will state that. Many control systems are not actually running the exact voltage at which the equipment is stated to require. If they didnt work this way, then everybody would have a hard time getting anything to work for any decent period of time after comissioning of a system was complete.

 

[r.bartlett]

no its not......it has a control voltage of 3 - 30 vdc and a 10 amp max load..... how did you come up with that?

Unless I'm being particularly dense are you sure you searched for the right PN on RS? As the one I linked is:

Depth 44.5mm
Height 27mm
Length 58.2mm
Maximum Control Voltage 240 V
Maximum Load Current 50 A
Maximum Load Voltage 520 V rms
Minimum Load Current 5 mA
Mounting Type Screw Mount
Output Device Triac
Switching Type Zero crossing

http://uk.rs-online.com/web/p/solid-state-relays/1718948/
http://docs-europe.electrocomponents.com/webdocs/0114/0900766b80114479.pdf

I will gladly stand corrected if I'm reading it wrong

[/quote]

no stock in UK being quoted 7 weeks for delivery!

Went for the one you suggest c/w a heat sink to suit

here's hoping

Thanks very much

Richard

 

[bhm1712]

hope it serves you well. If youd have given us a bit more detail we might have been able to narrow it down more for you and save a bit of cash. Good luck with it.

 

[ricicle]

Same job also a problem with E-stop had to fit second E-stop contactor as can't use semi-conductors.

And these also ran heaters.

 

[JohnW2]

Surely the way it is written means that it is only 'guaranteed' to work between 27.6V and 195.5V.

No, as said already ... 24-230v plus or minus 15% is not 27.6v and 195.5v

True, but we are trying to make some sense of the way they've expressed it. It can be argued that one could be excused for assuming that "24V - 230V ±15%" meant:
"The lowest controlled voltage guaranteed to work is 24V ±15% and the highest voltage at which it is guaranteed to work (satisfactorily) is 230V ±15%."
...which would lead to EFLI's interpretation that it is only guaranteed to work with control voltages between 27.6V and 195.5V.

+/- 15% means that the device will operate within 15% either side of the expressed voltages.....

That's another interpretation. It's probably the one which, in context, makes the most sense, but that doesn't make it a satisfactory (or unambiguous) mathematical practice.

its a mathematical form of expressing standard deviation/tolerance. It would be no different when a machinist gets an engineering drawing from a designer to make something on a milling machine. The drawing may state measurements in millimeters +/- 0.05mm. So this means that the final dimensions of the workpiece can be 0.05mm over or under the spec, but will be within the tolerance.

As I keep saying, a spec may be expressed as a range of acceptable values OR as a nominal value plus an acceptable tolerance around that nominal value - but if you try to do both at once, you simply add confusion and ambiguity...

... it would be conventional for a drawing to say that the acceptable final dimension of a part is "4mm ± 0.05mm" - which is clear and unambiguous. One could alternatively say that the acceptable final dimension was "3.95mm - 4.05mm" - which is equally clear and unambiguous. However, what one earth would one make of, say, "3.96mm - 4.04mm ±20%"? .. and, more to the point, why on earth would anyone use such a contorted and ambiguous method of expressing something which could be expressed clearly in either of the ways mentioned above?

Its the same with the control voltage on our relays - the control voltage is stated as requiring to be 24-240v +/- 15% so the control voltage can be 15% under the minimum stated and 15% over the maximum stated. As a bonus, it will also work with any voltage between those 2 figures....

I understand what you're saying, but it still doesn't make any mathematical (or other) sense. If the spec says that the relay is guaranteed to work at 15% under 24V (i.e. 20.4V), at 15% above 230V (i.e. 264.5V), or at any voltage in between, then why not just say that it is guaranteed to work between 20.4V and 264.5V? How do voltages between 20.4 and 24V, or between 230V and 264.5V, differ from those between 24V and 230V, if it is guaranteed to work at any of those voltages?

Kind Regards, John

 

[JohnW2]

For example, in the factory i work which generates its own power, the voltage on a single phase can be anywhere between 225-250 volts depending on what time of day it is, or what machinery is in use in the factory. If the relay was strictly 24-230 volts then it would not work in the majority of electrical systems in the country.

Indeed - which is why one needs a relay speced to operate with voltages in the range of voltages which may exist - but why say it will work up to 230V±15% when what you mean is that it will work up to 264.5V? Why not, for example, 200V±32.25% ?

Im pretty sure that all electrical control equipment has a tolerance like this but not all manufacturers will state that.

If you look at a properly written spec for such a component it will merely indicate the acceptable range of control voltages. Absolutely noithing is gained by specifying a narrower range and then qualifying it with a "± figure".

Kind Regards, John

 

[bhm1712]

why not just say that it is guaranteed to work between 20.4V and 264.5V? How do voltages between 20.4 and 24V, or between 230V and 264.5V, differ from those between 24V and 230V, if it is guaranteed to work at any of those voltages?

Well the only difference is potential difference...... 3.6v at the lower end and 34.5v at the top end! its still voltage!

I concede from this point onwards! i cant explain it anymore than i have. For me personally its straight forward, and ive never come across anybody else who ive worked with who has questioned it either.. all i am interested in when im replacing a SSR is 1)is it suitable for the load, 2) is the control voltage of the SSR going to work on my control system.

Thats it.

I agree that you coud interpret it differently, but as an electrician/controls engineer your training and experience should dictate how to interpret it.

 

[EFLImpudence]

We understand what you are saying and if that is what it means when dealing with these devices we cannot argue.

All we are saying is - in English and mathematics that's not what it says.

A bit like 'volt-free' contacts.

 

[JohnW2]

We understand what you are saying and if that is what it means when dealing with these devices we cannot argue. All we are saying is - in English and mathematics that's not what it says. A bit like 'volt-free' contacts.

Exactly.

Kind Regards, John