65W laptop supply in enclosure - safe to use?

[skotl]

I'm looking to modify the wire drive in a SIP 150 turbo (aka it has a fan) welder, which involves using a separate 20VDC supply to drive the wire spool motor.

I have a Dell 65W laptop power supply brick which claims to output 19.5V with a (presumably) max current of 3.33A
The motor expects 20V at a maximum of around 1.5 amps.

I'd plan to physically mount the laptop PSU in the base of the welder where it would be in the airflow from the cold-air fan. The PSU, as most laptop variants are, is a completely sealed device with no holes for airflow.

Do you think it will be comfortable in that environment, given that the fan will be blowing cold air over it? While the welder is on (30-60 minutes at a time) the PSU will be powered up permanently (the DC output to the motor will be switched).

Thanks

 

[SimonH2]

Don't see why that shouldn't work.
However, the spool motor is often driven from the welder output for a simple practical reason - so it runs faster when you crank up the output. In fact, I happen to have an old dusty hand drawn schematic of my old SIP Migmate lying around, and that is how it's powered.
Depending on your wiring, you may have to consider how you're going to control the feed speed.

 

[skotl]

Thanks Simon

I'm going to feed the PSU output through the existing speed controller circuitry - simply snip the current feed from the weld transformer.

 

[leezer3]

Our model railway club has done a similar thing without any ventilation other than a couple of grilles, so I don't think it'd be a problem per-se.

You'll find that even at full pelt, very little ventilation is needed, although the brick may get a tad warm.

 

[mfarrow]

I'm going to feed the PSU output through the existing speed controller circuitry - simply snip the current feed from the weld transformer.

Won't one be AC, and the other DC output?

 

[SimonH2]

The feed motor supply is taken after the rectifier. MIG welders are DC (and there'll be a big smoothing choke there as well).

I'm no welding expert (my welds usually look more reminiscent of seagull droppings), but I am curious to know what problem this is to solve. It has occurred to me that there might be a reason other than cost and expediency for running the feed motor from the main transformer - in that changes in current will affect voltage and hence feed speed, such as to create feedback that might regulate weld current a little.

 

[skotl]

The feed motor supply is taken after the rectifier. MIG welders are DC (and there'll be a big smoothing choke there as well).

I'm no welding expert (my welds usually look more reminiscent of seagull droppings), but I am curious to know what problem this is to solve. It has occurred to me that there might be a reason other than cost and expediency for running the feed motor from the main transformer - in that changes in current will affect voltage and hence feed speed, such as to create feedback that might regulate weld current a little.

DC indeed. This isn't a general problem with MIGs but is a specific problem with SIP / Cosmo Migmate and Topmig welders (google "sip wire drive problems"). The feed to the torch is fine but is too erratic for the motor drive, do the wire starts slowly then fluctuates as you weld. It can also stall quite easily.
So there are two mooted solutions; put a toroidal tranny and rectifier into the torch-switched feed into the motor (via the speed controller), or stick a switch-mode PSU into the chassis-switched live and put its DC output into the torch-switched feed.

The reason for having the switch-mode PSU permanently on (while the chassis switch is on) is that these PSUs don't like being constantly turned off and on. and have a long ramp-up / ramp-down.