Switch power supply

You_are_a_cunt · February 11, 2016

Figured this would be one of the places to post this, rather than Hobby Electronics.

tl;dr version:

got a free switch that I need to use. Requires 7.5VDC/1.0A but I only have 5/12/15V wall plugs. Is it safe/wise to use a 12VDC/1.0A plug on the switch?

detailed version:

Moving next week (WOOOOO!) and whoever decided to run the ethernet cable from the main router to the other room didn't think about redundancy or people needing more than one rj45 plug. Since the ISP-provided router gets the sweet sweet gigabit via fiber optic, I can't use my firewall/gateway/switch and it's loud, hot and far too big to keep running in my room. Or anywhere in the house, for that matter (where I live now it's sitting on the floor on the balcony, where nobody can hear it. And I don't have a balcony where I'm moving). A colleague had an unmanaged 8-port switch that he gave to me but he doesn't have the supply for it anymore. Since it's a janky 7.5V/1.0A input switch, I'm in a bit of a pickle since I don't have anything within a couple of volts that is either powerful enough to use while undervolting, or safe enough while overvolting. Best I have is 12VDC/1.0A from a router I scrapped a couple years ago. And the plug fits snuggly into the switch.

It doesn't sit right with me to use that 12V supply, although I know it works (sacrificed some old electronics to the gods of electricity that it doesn't blow the caps in the switch and managed to confirm that the switch works properly, even with a non-spec supply). The one thing that got me slightly worried is that I accidentally noticed it getting slightly warm around the plug after only a few minutes of usage.

I'm no electronics noobie, but I'm no guru either (and I can't get a hold of my dad on the phone since he's abroad on some oddball project). I know the dangers of overvolting and using non-spec supplies on electronic equipment.

Now, the question is: has anyone done this before? Would it be safe? Am I better off waiting another couple weeks or so until I'm settled in and have the time to source the parts I need to make a proper voltage step-down module or can I just keep using the 12V supply without the switch setting the apartment ablaze?

The switch is a TrendNet TE100-S88Eplus

I'd normally just use a router and just slap it into the network as an AP, but I'm out of routers and I don't really need an extra wireless SSID or AP for that matter.

Need the 8-port since I'll be running at least 2 PCs, a laptop, a smart TV, a server, a PS3 and the occasional extra PC or laptop when I'm working on client builds and such.

EmeraldFlame · February 11, 2016

You will fry the switch. You're pushing 60% higher voltage than it is designed to run on, and I highly doubt that it has that much leeway on it's voltage acceptance. You could probably get away with 10% one way or the other, but not 60%.

Just grab a cheap power brick, if you can't find a 7.5V 1A one, you can grab a universal on like this: http://www.amazon.com/ZOZO-Universal-Regulated-Replacement-Electronic/dp/B015PXUHYA/ref=sr_1_4?ie=UTF8&qid=1455202124&sr=8-4&keywords=universal+ac+adapter

You_are_a_cunt · February 11, 2016

11 minutes ago, EmeraldFlame said:

Just grab a cheap power brick, if you can't find a 7.5V 1A one, you can grab a universal on like this: http://www.amazon.com/ZOZO-Universal-Regulated-Replacement-Electronic/dp/B015PXUHYA/ref=sr_1_4?ie=UTF8&qid=1455202124&sr=8-4&keywords=universal+ac+adapter

Amazon shipping takes at least 2 weeks and I'm better off just making an in-line voltage regulator on my 12V supply

Since writing this I talked to my dad about it and he pointed me to the LM7808 IC that, paired with a couple of caps and a heatsink (so I don't fry the IC), will step the voltage down to 8V which will be just fine.

The LM7808 is like $0.25 and I have the caps I need already, and a variety of heatsinks I can chose from. Shouldn't take more than 5 minutes to set everything up

EmeraldFlame · February 11, 2016

Yup that will work absolutely fine too, I went the amazon route because I typically attempt to avoid recommending electrical and soldering work on here because it's hard to gauge people's abilities in that.

You_are_a_cunt · February 11, 2016

1 hour ago, EmeraldFlame said:

Yup that will work absolutely fine too, I went the amazon route because I typically attempt to avoid recommending electrical and soldering work on here because it's hard to gauge people's abilities in that.

As I mentioned in my original post, I'm far from being a greenhorn, but there are billions of parts I don't know about that would make my life far easier. I'll move over to Hobby Electronics with a tutorial tomorrow when I assemble the regulator.