Who's crazy? (changing 1.5A supply for 5A)

[FourFootMedia]

Got a couple of network switches in a "local" cabinet on an office floor at work which are currently running off 12V 1.5A power bricks (wall warts, whatever you like to call them), these are annoying as when plugged into the power distribution panel in the cabinet they take up 3 sockets.

So I propose using some in-line power supplies (like a laptop) so they don't obscure sockets. We have 2 x 12V 5A supplies kicking round the office perfect for the job, right?

However, my colleague is going crazy saying changing the 1.5A supplies for 5A switching supplies is nuts as 5A is higher than 1.5A and will cause the switches to fry.

If I'm not mistaken, this won't be a problem as the devices will only draw what they need (i.e. <1.5A)... correct?

Thanks

 

[electronicsuk]

You are right, your colleague is wrong. As long as the power supply can supply equal to or greater than the current demand of the equipment and the supply voltage is correct, everything should be fine. It may be worth adding some 1.5A inline fuses to protect the equipment in case of a fault, though.

 

[FourFootMedia]

Point noted. However I'm pretty sure they're internally fused, I'll double check tomorrow.
Thanks

 

[JohnD]

I used to work at a company that had some funny equipment. I pulled one of the cabinets out of the skip once, and found it had (say) a 6A MCB feeding a dozen ultra-fast-blow 1A cartidge fuse holders, one per device, all on the same DIN rail. I suppose they were quite a bit cheaper when you have a lot of them, and also a lot narrower so there might have been 20 or so per row in a 20" cabinet.

If one of the devices ever had a bad overcurrent fault, it might have tripped the MCB as well as its fuse, but the MCB could quickly be reset, and it's easier to see tripped MCB than a blown fuse. I suppose the same approach as having 50 13A sockets on an RFC with a 32A MCB.

For some reason I've forgotten, the internal carcase was wired with Blue for the fused live.

 

[bernardgreen]

As long as the power supply can supply equal to or greater than the current demand of the equipment and the supply voltage is correct, everything should be fine.

One thing to check is that the power supply you select does not require a MINIMUM current load to work properly.

 

[toasty]

One thing to check is that the power supply you select does not require a MINIMUM current load to work properly.

And of course that the polarity is the same on both

 

[TicklyT]

I used to work at a company that had some funny equipment. I pulled one of the cabinets out of the skip once, and found it had (say) a 6A MCB feeding a dozen ultra-fast-blow 1A cartidge fuse holders, one per device, all on the same DIN rail. I suppose they were quite a bit cheaper when you have a lot of them, and also a lot narrower so there might have been 20 or so per row in a 20" cabinet.

If one of the devices ever had a bad overcurrent fault, it might have tripped the MCB as well as its fuse, but the MCB could quickly be reset, and it's easier to see tripped MCB than a blown fuse. I suppose the same approach as having 50 13A sockets on an RFC with a 32A MCB.

For some reason I've forgotten, the internal carcase was wired with Blue for the fused live.

That sounds like a standard TEP 1E rack designed for telephone exchanges. An MCB on the DC power feed to the rack supplies a power and alarm monitoring unit, then a selection of DIN mounted 40mm cartridge fuses on the monitoring unit output to each card nest. The equipment is all positive earth, the blue wiring identifying -50 Volts DC.

Each piece of equipment designed for the racks has a power monitoring facility capable of identifying an individual fuse failure that can be linked back via the power monitoring unit to a central point, possibly at a different site.

Sometimes these racks are mounted in cabinets resembling a standard 19" cabinet, with a mains power unit in the bottom for the 50V DC supplies, for use at customers' sites.

 

[Space cat]

One thing to check is that the power supply you select does not require a MINIMUM current load to work properly.

So you measure the off-load voltage. If this shows correct, there is no minimum load requirement.

And of course that the polarity is the same on both

You can check for correct polarity at the same time.

 

[LiamPope]

...and of course that if the original power supplies give a dc output, your proposed substitutes are not in fact 12V ac.

 

[FourFootMedia]

One thing to check is that the power supply you select does not require a MINIMUM current load to work properly.

Nope, no minimum. All working fine now.