Timer switch

[JBR]

Hi,

I'm thinking of buying one of these:

http://www.amazon.co.uk/Electronic-Wall-Switch-Timer-Day/dp/B0018S13PO

The spec. says that the minimum load must be 40W resistive or 17W fluorescent (and not suitable for LEDs).

I want to use it for seven 10W fluorescent outdoor lamps (wired in parallel, of course). Am I right in assuming that this would equate to 70W, and that the timer switch would be suitable?

Thanks.

 

[Taylortwocities]

If I remember my maths properly, 70 is bigger than 17. So that should be OK.

 

[JBR]

If I remember my maths properly, 70 is bigger than 17. So that should be OK.

Thank you. I had actually arrived at that computation myself, believe it or not!

The thing is that I don't understand the electronic components of these fluorescent lamps and their function. The manufacturers' statement that the item is suitable for minimum 40W resistive load, yet minimum 17W in the case of fluorescents, made me wonder whether there is some characteristic of these low power things that makes them behave differently. Yes, logically 7 x 10W would equal 70W, but I had to ask to make sure.

I do realise that resistors are a completely different thing, but the concept that series resistors are additive and parallel resistors reduce the total resistance made me wonder whether there may be some comparison. But don't shoot me down! It would be a miracle if you could reduce power consumption by adding MORE lamps to a circuit, of course.

 

[JohnW2]

If I remember my maths properly, 70 is bigger than 17. So that should be OK.

Although 70 is bigger than 17, if one thinks about the mechanism, of the potential problem when this sort of product is used with CFLs (or LEDs, come to that), I'm not convinced that it's necessarily going to be 'OK' just because the total CFL load is >17W - could it be that (although I don't recall ever having seen this stated) one has to have at least one individual CFL >17W to be sure of no problems? In the context which interest us, CFLs almost certainly do not behave just like simple resistors, the values of which can be combined 'in the usual way' when several are in parallel.

As you will see from what I've about to write to JBR, it seems that several people have had problems when using this timing to control CFL loads with a total appreciably above 17W - which may give some support to what I suggest above.

Kind Regards, John

 

[JohnW2]

If I remember my maths properly, 70 is bigger than 17. So that should be OK.

Thank you. I had actually arrived at that computation myself, believe it or not!

Although 70 is larger than 17, I don't think that necessarily means that you would definitely be problem free (see my post to TTC). Have you read the reviews of this timer in the Amazon link you have provided? Several people seem to have had problems with Energy Saving (Compact Fluorescent) lamps (CFLs) flashing when meant to be switched off, when the total CFL load was appreciably greater than 17W. This 'lamps flashing when off' is a known potential problem with products of this type, and there are some possible solutions when it happens.

Kind Regards, John

 

[JBR]

Thank you, John.

Yes, I have read reviews on Amazon by other purchasers of this item, which is precisely why I sought your professional advice.

I have now, in fact, ordered one of these, so I shall find out for myself soon enough. If there is a problem, I have a couple of options: I could replace one of the fluorescent lamps with tungsten, or I could (if the worst came to the worst) replace the timer switch with a conventional switch - I will have wasted £20 and some of my valuable time, so it could be worse!

You suggested that there are 'some possible solutions', so I'd be grateful if you could advise me of any you can think of.

 

[JohnW2]

Thank you, John. Yes, I have read reviews on Amazon by other purchasers of this item, which is precisely why I sought your professional advice. ... I have now, in fact, ordered one of these, so I shall find out for myself soon enough. If there is a problem, I have a couple of options: I could replace one of the fluorescent lamps with tungsten, or I could (if the worst came to the worst) replace the timer switch with a conventional switch - I will have wasted £20 and some of my valuable time, so it could be worse!

Fair enough.

You suggested that there are 'some possible solutions', so I'd be grateful if you could advise me of any you can think of.

Particularly since TTC only wrote it (in another thread) this morning, I wouldn't want to be accused of plagiarism, so I'll just refer you to:

Fit one of these across the live and neutral of one of the light fittings. http://www.maplin.co.uk/p/contact-suppressor-rg22y
Do't forget to sleeve the leads to the component. Works 99% of the time.

Kind Regards, John

 

[JBR]

Particularly since TTC only wrote it (in another thread) this morning, I wouldn't want to be accused of plagiarism, so I'll just refer you to:

Fit one of these across the live and neutral of one of the light fittings. http://www.maplin.co.uk/p/contact-suppressor-rg22y
Do't forget to sleeve the leads to the component. Works 99% of the time.

Kind Regards, John

Thank you again. I'm sure that would be within my capabilities, although I don't pretend to know what 'dv' and 'dt' are. Difference in voltage/time?

Anyway, if things don't work properly I'll happily give it a try. I can see no polarity markings. Would it matter which way round they are attached? I understand that this can be important with capacitors.

 

[JohnW2]

Thank you again. I'm sure that would be within my capabilities, although I don't pretend to know what 'dv' and 'dt' are. Difference in voltage/time?

You know more than you think! dv/dt is the rate of change of voltage of time - i.e. a change in voltage divided by the time during which the change occurred.

Anyway, if things don't work properly I'll happily give it a try. I can see no polarity markings. Would it matter which way round they are attached? I understand that this can be important with capacitors.

Nope. Either way around. Quite apart from the fact that involves a type of capacitor which is 'non-polarised' (can go either way around), we're talking about alternating voltage which changes polarity 100 time a second - so if you got it 'right' at one point in time, it would be 'wrong'10 milliseconds later

Maybe you won't need it.

Kind Regards, John

 

[ban-all-sheds]

ATEOTD, any timer, or sensor, switch which replaces a normal light switch will have to power its electronics, or charge the battery which powers them, by having current pass through the load when it is "off". (Except any which harvest power from ambient EMR fields.)

That current is very small, and will not produce any detectable activity in an incandescent lamp. But it is common for it to cause flickering/flashing/glowing in non-incandescent ones.

 

[JohnW2]

ATEOTD, any timer, or sensor, switch which replaces a normal light switch will have to power its electronics, or charge the battery which powers them, by having current pass through the load when it is "off". (Except any which harvest power from ambient EMR fields.) ... That current is very small, and will not produce any detectable activity in an incandescent lamp. But it is common for it to cause flickering/flashing/glowing in non-incandescent ones.

Indeed so - as you say, it's inevitable that there will be such a current, which may result in those phenomena. However, even in the absence of such a device using the load as a path to neutral, 'induced voltage' can sometimes produce such effects in non-incandescent lamps which are 'switched off'.

Kind Regards, John

 

[ban-all-sheds]

Absolutely.

 

[JBR]

Thanks gentlemen.

ATEOTD (I had to google that!), hopefully I won't need to mess about with a suppressor. Even if I can't avoid a bit of flickering, it may not be visible outdoors in daylight and I presume that the current drawn isn't going to double my electricity bills!

Re. the picture above, yes I've seen similar pictures before. We could build houses directly under power lines and enjoy free lighting!

 

[JohnW2]

ATEOTD (I had to google that!), hopefully I won't need to mess about with a suppressor. Even if I can't avoid a bit of flickering, it may not be visible outdoors in daylight and I presume that the current drawn isn't going to double my electricity bills!

Indeed. As I said, maybe you won't need it (the suppressor). In any event, even if you did, it would not help your electricity bills - the tiny current (totally irrelevant as far as bills concerned) would still flow - but through the suppressor rather than the lamps, so the only difference would be that the lamps wouldn't flicker when 'off'.

Kind Regards, John

 

[JBR]

Am I right in assuming that I would need to add the suppressor to only one lamp fitting?