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What incandescent lamp wattage to buy for PSU troubleshooting ?

R1S8k

Jul 28, 2018
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Hi,

I'm working on troubleshooting Dell 275W PSUs for work PCs, I didn't know that LED lamp won't work. And our local market is almost out of stock of incandescent lamps.

So I want to order from online stores, but don't know what wattage rating to choose.

Any idea of what to choose, and what equation I have to apply to know what is the proper wattage to buy ?
 

kellys_eye

Jun 25, 2010
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What's wrong with ordering proper resistors and making a 'known' load?
 

R1S8k

Jul 28, 2018
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A lamp is good for me, as when there's a short, the lamp will light up and prevent an explosion.
 

Martaine2005

May 12, 2015
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Sounds like the OP wants to make a current limiter.
I have two 100W bulbs in parallel and individually switched. Normally only require 100W but sometimes swap one for a 60W.
Each DUT (device under test) requires a certain current to switch on. If 60W doesn’t allow the DUT to turn on with limited current, try a 100W. Some current hungry devices require both 100W bulbs (200W) before it will switch on with the limited current through the bulbs.

Martin
 

R1S8k

Jul 28, 2018
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So you want to put this lamp in series with the input power connection?
Yes, exactly.

I've done it before, but didn't know actually wattage importance. I used an arbitrary incandescent lamp.

Recently, I used an LED lamp, and the test didn't work as expected, then I used a working Dell PSU, and it didn't start up.
 

R1S8k

Jul 28, 2018
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Some current hungry devices

Martin
Yes, that my concern now, how to know what wattage is suitable to the PSU I'm working on ?

So, as I'm working with Dell 275W PSU, how to calculate the proper lamp to put in series with the connection ?

I think I have to know the starting current for the PSU.

For the lamp it's easy to know the current, so if I'm using a 100W lamp, then, i = 100W/240V = 416mA.
 

crutschow

May 7, 2021
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Yes, that my concern now, how to know what wattage is suitable to the PSU I'm working on ?
Assuming the PSU takes 200W, then its normal operating current is about 200W/240V = .83A, so the bulb would have to be quite large to carry that amount of current without significant voltage drop (likely at least 500W of incandescent bulbs).
 

R1S8k

Jul 28, 2018
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I found a manual for OptiPlex PC, and found this:
dell275w_current.PNG

So I guess the idle current is 2.5A.

But when the testing the PSU, and not connecting it to the motherboard which means the test at "no load", I think the current should be lower than 2.5A.
 

bertus

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Nov 8, 2019
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Hello,

The 275 Watts would only be reached at full load.
With a lower load, the power will be less.
You can test the powersupply with about 10 % load.
That way a smaller bulb would do.

Bertus
 

Bluejets

Oct 5, 2014
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Any idea of what to choose,

I use a 150W incandescent flood lamp as a series test lamp for many things including your switch mode power supplies.
First photo is the 150W flood lamp.
....if you want more current try a 275W bathroom IR heat lamp.
Although the first would normally be sufficient....all you are looking for is a degree of current limiting.

Mount in an appropriate insulated ES lampholder (usually vertically to disperse any heat...also they are "bright")
Lampholders from the 3 in 1 bathroom fittings are also ceramic but should be available from you local electrical supplies store.
(centre post active ....just conventional)

Lampholders also come in floodlight fittings but be sure it is ceramic lampholder inside....most newer ones are molded plastic.
 

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kellys_eye

Jun 25, 2010
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Some basic static test measurements would be the better testing method - checking for obvious shorts. A straightforward MCB with a low rating (say 2-5A) would cover for dead shorts you might have missed.

There are some good tutorials on Youtube and documented for following a SMPS repair technique.

My preference is for an isolated variable AC power source with current limiting. If you intend doing this type of repair on a regular basis then some better test equipment would be preferable.

The old 'bulb limiter' has its place but, imho, not for SMPS serving work (I use a bulb limiter when testing/working on antique valve radios!)
 

Delta Prime

Jul 29, 2020
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Playing devil's advocate here! Why could you not use a 10 Watt 250 Volt incandescent light bulb
with no load . No calculations would be needed for a direct short on the switch mode power supply 10 watts 250 volt incandescent bulb will light up and prevent your circuit breaker from tripping .
If you are troubleshooting what the power supply unit is powering then that's a different story which has already been stated.
I use Uncle Fester in series


photo_1685787214269.png


Like this!!

1684430580872_1685787748965.png
 
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Delta Prime

Jul 29, 2020
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You might also find info on this SPMS repair page
Under the series light bulb trick.
Everything requires some percentage of a loaded output based on the manufacturer's specifications.
The devil's advocate light bulb 10 watt 250 volt with no load on the output will light up indicating a direct short & will basically tell you nothing! except it is shorted! Also will not cause undue stress and household circuits by not tripping the breaker. A 10 watt light bulb is being frugal. But if that's all you got... it will work.
 

ramussons

Jun 10, 2014
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Hi,

I'm working on troubleshooting Dell 275W PSUs for work PCs, I didn't know that LED lamp won't work. And our local market is almost out of stock of incandescent lamps.

So I want to order from online stores, but don't know what wattage rating to choose.

Any idea of what to choose, and what equation I have to apply to know what is the proper wattage to buy ?
If you are not doing a Load Test, 60 Watts is fine.

I use this while troubleshooting a wide variety of equipment. This morning it was a uWave oven (the control board).

I suggest you order 100 Watt bulbs, use them in series / parallel depending on requirement.
 

R1S8k

Jul 28, 2018
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Hi,

I purchased couple Edison lamps from aliexpress @60W.

edison_lamp60w4w_aliexpress.PNG

Then I connected it in series with this working Dell PSU, and I shorted the green pin with the black one so that PSU launches.

But the PSU didn't launch and the lamp is flickering slowly; like, 1 flicker every 1 second.

20231213_165337.jpg

I measured the impedance of the PSU and the lamp, the PSU is 1M ohms and the lamp is 178 ohms. So what is the explanation of this action ? I doubted that the seller shipped me a 60W lamp.
 

Delta Prime

Jul 29, 2020
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If you use an incandescent light bulb not an "LED light bulb" on the output of a power supply for a load then you must realize the low cold resistance results in an inrush current spike and can trigger over current protection circuits in the power supply unit under test.
 

bertus

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Nov 8, 2019
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Hello,

You likely bought a ledlamp with a brightness of about an 60 Watt incandescent lamp.
The power will be around 6 Watts.

Bertus
 
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