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Author Topic: Powering a 12v 16w bulb  (Read 1183 times)

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Bashy

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Powering a 12v 16w bulb
« on: January 30, 2017, 09:35:33 AM »
what psu would power a 12v 16w bulb
I have this temp switch that works fine with a 5w bulb
But if I try a 16w bulb the relay clicks and clicks, but, if
I move the bulb a little then the relay will activate it

I thought it may have been the psu, I i bout a variable
One that goes up to 12v 2amp, I am at a loss, is it the
 temp switch or the psu that is struggling?

Offline broadstairs

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Re: Powering a 12v 16w bulb
« Reply #1 on: January 30, 2017, 10:14:03 AM »
I would suggest the heat from a 16W bulb assuming its a tungsten one is affecting the temperature switch, the PSU rated a 2amps should be fine.

Stuart

Bashy

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Re: Powering a 12v 16w bulb
« Reply #2 on: January 30, 2017, 10:51:22 AM »
Hi Stuart, deffo not the heat from it, the switch is housed in a separate box and the bulb is inside the Davis bucket

Offline broadstairs

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Re: Powering a 12v 16w bulb
« Reply #3 on: January 30, 2017, 11:19:16 AM »
Well perhaps the switch cannot cope with the extra current with 16w you have around 1.4 amps. What is the switch rated at? If not that then it could be the PSU and if you do replace it go for one which has a higher current rating.

Stuart

Bashy

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Re: Powering a 12v 16w bulb
« Reply #4 on: January 30, 2017, 11:40:47 AM »
The switch is one of [urlhttp://www.ebay.co.uk/itm/50-110-C-Digital-Heat-Cool-Temp-Thermostat-Temperature-Control-Switch-DC12V-New-/152003309559?hash=item23641a6ff7:g:noEAAOSwBLlVVHA~]these[/url], rated at 10amp  8O I have tried 3 different psu's and
i bought this latter one as its a 2amp at 12v. In theory, it should work, i can use 3 x 5w bulbs with no issues.

Perhaps a computer PS would be better, or will just have to forget the 16w and just use more of the 5w, shame though as i bought 10 x 16w lol

Offline weatherc

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Re: Powering a 12v 16w bulb
« Reply #5 on: January 30, 2017, 01:39:57 PM »
How tick is the cable between the PSU and the bulb/thermostat?
Thin cable/long distance = lots loss.

My own experince with 2 x 20w @ 12V heating-mats for my own rainpot, to thin cable on a 10 m distance caused voltage to drop to 8V  :lol:

Offline teal

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Re: Powering a 12v 16w bulb
« Reply #6 on: January 30, 2017, 01:48:16 PM »
  Hi, your power supply should be ok as a 16W bulb @ 12V = 1.3A ( watts divided by volts = amps), however is your power supply regulated,  that means will it give you 12 volts @ 1.3 amps, it may be that the  power supply voltage is dropping down when its under load. looking at the thermostat the relay should be ok for the 16w bulb, just check that you have wired it up correctly see UPLOAD, I think its the same thermostat that I have used on my heater here .

Offline teal

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Re: Powering a 12v 16w bulb
« Reply #7 on: January 30, 2017, 01:51:14 PM »
How tick is the cable between the PSU and the bulb/thermostat?
Thin cable/long distance = lots loss.

My own experince with 2 x 20w @ 12V heating-mats for my own rainpot, to thin cable on a 10 m distance caused voltage to drop to 8V  :lol:

  Hi, great minds think alike.

  teal.

Bashy

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Re: Powering a 12v 16w bulb
« Reply #8 on: January 30, 2017, 01:52:21 PM »
Hi guys, thanks, the cable I am using OS not much thicker than speaker cable, it was originally for a anti bark thing for outside, I will have to get the multi meter out and check out what is actually being given at yon end......

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Re: Powering a 12v 16w bulb
« Reply #9 on: January 30, 2017, 01:53:54 PM »
  Hi, you will have to check it when it is under load.

  teal.

Bashy

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Re: Powering a 12v 16w bulb
« Reply #10 on: January 30, 2017, 02:44:38 PM »
Damn you, ive just checked it not under load lol   #-o :oops: :roll: 12.5v @2a back in a mo....

Offline niko

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Re: Powering a 12v 16w bulb
« Reply #11 on: January 30, 2017, 02:46:30 PM »
The other thing is that bulbs are lower resistance when cold so they take a big gulp of (inrush) current when you first turn them on which may glitch the supply voltage. Anytime you have electronics fed from the same supply as a switched big load you need a decent sized capacitor across the supply to handle the initial surge of current.

Bashy

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Re: Powering a 12v 16w bulb
« Reply #12 on: January 30, 2017, 02:54:45 PM »
Ok, that just flew over my head but sounds important lol

Just checked under load

  5w   11.4v @2a
16w     9.7v @1-2a it was fluctuating between 1 and 2 amps

So, thats not enough to power the 16w, so it looks like i am gonna need a PC psu  :(
But, at least that should then power both fans in the shield and the 16w bulb, at the
minute i am, using 2 separate psu's
« Last Edit: January 30, 2017, 02:58:20 PM by Bashy »

Offline teal

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Re: Powering a 12v 16w bulb
« Reply #13 on: January 30, 2017, 04:05:28 PM »
 Where did you check the voltage at the end of the cable or at the power supply, it needs to checked at the end of the wires, near the thermostat  you could use one of these  say a 12v 3.2amp, some are water proof.

  teal.

Offline niko

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Re: Powering a 12v 16w bulb
« Reply #14 on: January 30, 2017, 04:10:14 PM »
5w   11.4v @2a

That can't be right  :?  A 12 volt 5 watt lamp should only be pulling less than 0.5 amps.

 

cumulus