Question about 12v DC power supply.

[Ken from ontario]

I am in the process of building a Low Resistance Soldering(LRS) , all that's needed initially is a microwave transformer, an old soldering iron(to be dismantled and only use the gun's outer shell), some wire, foot pedal, anyhow, I skipped the microwave transformer all together and decided to go with a ready made 110V 50 Amp power supply.
The LRS assembly went very smoothly but the power supply has built-in fan that is constantly on and running when the unit is plugged in and that's what concerns me. the problem is: as soon as I start to solder, the fan stops running although the unit still continues to supply power ( I can still melt the lead and solder), I was wondering if this is supposed to happen ?
I read a lot of reviews on this power supply and it seems the fan is supposed to be always on.

On the power supply body there's a notice that goes like this:
This power supply has a built-in fan on/off control circuit.
Fan automatically works according to working temperature.

If that's the case then why it's running prior to soldering but it stops when under load? Bear in mind I am a novice working with electricity so it might be my ignorance that's getting the better of me but it makes more sense if the fan keeps on running especially when I'm using all the amperage the unit can produce , I never used the unit more that 30 seconds, maybe the fan sensor needs time to detect the excess heat and will eventually starts "Automatically"
So do you pros think something is wrong with the power supply or the fan sensor? do I need a bigger/better unit with higher output?

I can still return this unit if I have to, this is actually my second power supply,, the first one was a 30amp and much cheaper($31 CDN) this one I really like to keep because it feels more refined or should I say "robust" and twice the price of the older one.

I would appreciate your thoughts and welcome all your comments.

 

[kb58]

A wild guess would be that there is a thermal switch controlling the fan that is supposed to be wired "Normally Open", yet is wired "Normally Closed." Without seeing a schematic though, it's impossible to say for sure.

 

[Ken from ontario]

@kb58,
The fan runs continuously when the unit is connected to a low draw anything like IKEA halogen light bulb, it only stops when connected to a draw of (I'm guessing here) 12V but 40-50 amps .
Unfortunately I can't get to the schematic diagrams without breaking the seal .
Thanks for the reply.

 

[SLK001]

My guess is that when you are soldering, the voltage drops too low for the fan to run, since it is being powered by the output of the supply.

 

[Ken from ontario]

My guess is that when you are soldering, the voltage drops too low for the fan to run, since it is being powered by the output of the supply.

Actually what you described makes sense to me, I thought or expected the fan to run continuously just like all the reviewers complained about which lead me to believe no matter how much load I put on this power supply(within it's limits ) the fan should not stop at all, I am a bit disappointed that this is happening , I am beginning to think this unit is going to fail soon.

 

[markba633csi]

It really sounds like the unit was not designed correctly or not tested before shipping- one of the two
I would exchange it for another one or another brand altogether
Sure, you could run the fan wires out to another small supply but you shouldn't have to go to such lengths

 

[atunguyd]

My guess is that when you are soldering, the voltage drops too low for the fan to run, since it is being powered by the output of the supply.

I agree with this. Easy to confirm by putting a voltmeter across the Soldering iron and monitoring the voltage

Sent from my SM-S908E using Tapatalk

 

[markba633csi]

The output of the supply should be regulated to within a few percent at full load; if it's dropping enough for the fan to stop
then it's clearly malfunctioning or mis-adjusted and should be sent back
Of course if you are exceeding the rated current that's another matter...

 

[Ken from ontario]

The output of the supply should be regulated to within a few percent at full load; if it's dropping enough for the fan to stop
then it's clearly malfunctioning or mis-adjusted and should be sent back
Of course if you are exceeding the rated current that's another matter...

The manufacturer recommends not to exceed30amps continuously even though the power supply is rated for 50 amps, if I understand correctly, a short burst of low resistance soldering during of which the circuit is closed for about 30 seconds , the unit needs to supply the maximum amperage it can support which is 50 amps, maybe that is the cause of the fan shutting down.

 

[cathead]

Apparently the LRS supply circuit is put together with the microwave transformer with a low voltage
secondary on the transformer which would provide alternating current at low voltage. The 50 amp
supply you are using is of the SMPS (switching mode power supply)variety which is of course provides
direct current. Personally I would use the microwave transformer as the SMPS is quite a complicated
piece of electronics and likely will fail if overloaded just once. It is basically an oscillator circuit that
generates AC radio frequencies in the kilohertz range and transformered down and then rectified
to provide direct direct current again. The microwave transformer on the other hand has no electronics
and will only warm up with a heavy electrical load which wouldn't be too concerning. I use 120 volt ac
soldering irons and have not seen the need for trying to improve on their function. At times I will use
a Variac to power soldering irons to control the temperature.

In closing, having looked at the LRS page, it appears that it is used for soldering metal pieces together
rather than for electronic work. Maybe it has some useful application not particularly obvious to me.
I'm certainly not trying to pick apart your project but rather trying to understand it's usefulness.