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Old 30th Dec 2016, 9:46 pm   #21
The Philpott
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Default Re: Vintage Christmas Tree lights

Simultaneous posting but along same lines!
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Old 30th Dec 2016, 11:15 pm   #22
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Default Re: Vintage Christmas Tree lights

Quote:
Originally Posted by nontechnicalian View Post
Most started off at 2.5A and then quickly went down to between
0.6 and 1.0A. There were 3 above 1.0A
Arent those currents a bit high if you're running a 20V lamp on 12/14V ?
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Old 31st Dec 2016, 12:02 am   #23
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Default Re: Vintage Christmas Tree lights

Yes. What sort of power supply? Can we see a pic of it at some point? AC or DC?

(Avometer is set at AC current)
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Old 31st Dec 2016, 1:16 pm   #24
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Default Re: Vintage Christmas Tree lights

Quote:
Originally Posted by The Philpott View Post
Now you see what i mean by measuring voltage (across) things and amps/current (through) things
Apologies, I didn't realise that I should still be testing the voltage as well as the current. I read:

'A more sophisticated test is to obtain say 15 MES batten holders and screw these to a piece of board. Wire them in series, insert the lamps and connect to the mains, Then measure the voltage across each lamp'

and thought that since I was only measuring one bulb unconnected to the others in a string, it was pointless measuring the voltage.

I chose to use the Avometer, because it is a 12V (more like 14V) AC supply that I have, rather than a DC transformer and my little yellow multimeter doesn't measure AC current (only DC). I can however repeat the test using the multimeter to test the voltage across the bulb (see I'm getting there!) as well as the Avometer in series again.

Thanks again for your help and guidance with this.
Ian
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Old 31st Dec 2016, 2:04 pm   #25
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Default Re: Vintage Christmas Tree lights

No problem, definitely getting there. If all the bulbs are closely matched then attention turns to

-the actual wiring and bulb holders which are a bit elderly, (corrosion/fraying?)
-spikes in the mains supply due to other nearby appliances switching on and off or an iffy distribution board/block,

Then i start to run out of ideas..
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Old 2nd Jan 2017, 12:53 pm   #26
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Default Re: Woolworths Christmas Tree Light Repair.

Morning and a happy New Year to you all!

I did the tests for voltage (and I also measured each bulb for resistance)
The majority of voltages were 13.3 v with a range of 12.7 -13.5 volts.
Resistances ranged from 3.4 to 12.5 with a mean of around 7.
As I said in my previous post: 'Most started off at 2.5A and then quickly went down to between 0.6 and 1.0A. There were 3 above 1.0A'.

Can I infer from this that all the bulbs are okay?

If I were to select the best bulbs, what am I looking for? -Am I looking for those with a high initial current, which then went to 1.3A, or am I wanting the ones that started off at 1.3 and went down to 0.6A?
In terms of voltage, do I want to keep the ones with the higher or lower voltage? -Ditto for resistance.

Ian
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Old 2nd Jan 2017, 3:38 pm   #27
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Default Re: Woolworths Christmas Tree Light Repair.

The variation in resistance looks significant, provided all measurements taken using the same meter*

I would try to use those that are closest in resistance, the variance shouldn't be much more than 10 or 20%. The difference between 3.4 and 12.5 ohms indicates to me that this is where the problem lies.

I don't think the Voltage measurements have shown up anything of significance.

(* when measuring and comparing resistance of lamps, particularly small ones, resistance should be measured using the same meter {and meter setting} for all the lamps. This is because the results can be slightly increased by the meter heating up the filaments during testing.)

Last edited by The Philpott; 2nd Jan 2017 at 3:39 pm. Reason: i can't spell
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Old 2nd Jan 2017, 8:40 pm   #28
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Default Re: Woolworths Christmas Tree Light Repair.

Something is not right here, the O/P refers to the current drawn by the lamps as being in the range from 0.6 amp up to 1 amp.
This seems very improbable.
Series wired sets of 12 lamps almost always use lamps each rated at 20 volts and 3 watts. That implies a running current at rated voltage of 0.15 amps.
With the lamp under run at about 13 volts the current should be less, about 0.12 amp.
The reported running currents are thus several times greater than expected.

A lamp that draws an amp at 13 volts would probably be about 1.3 amps at 20 volts or over 25* watts which is most improbable*.

So what is going on ?
Defective meter ?

*I have seen series Christmas lights of such wattages, usually home made by use of vehicle lamps in series. I have never seen MES Christmas lamps of such wattages.
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Old 2nd Jan 2017, 9:37 pm   #29
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Default Re: Woolworths Christmas Tree Light Repair.

There are 16 lights in this set Broadgage. Does that explain things?
Unfortunately I can't repeat the test with the other meter as it doesn't measure AC current.
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Old 2nd Jan 2017, 9:51 pm   #30
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Default Re: Woolworths Christmas Tree Light Repair.

The only way you'd be able to measure the voltage across individual lamps is to connect them in series. That would mean they'd all draw the same current, so the measured voltages might not be realistic unless the lamps all have the same voltage and power rating.

I'd rely on COLD resistance readings.
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Old 3rd Jan 2017, 12:31 am   #31
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Default Re: Woolworths Christmas Tree Light Repair.

Re odd current readings.. Is the rotary switch on the avometer out of phase with the cam plate..? The current readings are indeed odd..
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Old 3rd Jan 2017, 2:32 am   #32
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Default Re: Woolworths Christmas Tree Light Repair.

I have an ancient set bought by my mum sometime in the 1960's. there are 12 lamps(20 volts?) and they work every year so far. Lately I have taken to running them via a lamp limiter to ameliorate any start up surge, and (hopefully) prolong their life.
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Old 5th Jan 2017, 12:49 am   #33
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Default Re: Woolworths Christmas Tree Light Repair.

Time to put this seasonal post to bed I think!

I have learned many things, -so thank you as a group for that.

Since I invested in a dimmer switch (the one I gave a link to in an earlier post), I have not lost any lights and I find that even at the half way point the lights are bright enough.

I've attached a pic to show you.

Thanks again and all the best to you in 2017.

Ian
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