Kitz ADSL Broadband Information
adsl spacer  
Support this site
Home Broadband ISPs Tech Routers Wiki Forum
 
     
   Compare ISP   Rate your ISP
   Glossary   Glossary
 
Please login or register.

Login with username, password and session length
Advanced search  

News:

Pages: [1] 2

Author Topic: 12V 2A vs 1.5A power adapter  (Read 629 times)

digitalnemesis

  • Reg Member
  • ***
  • Posts: 382
12V 2A vs 1.5A power adapter
« on: October 17, 2020, 08:24:27 PM »

What are the consequences of using a 12V 1.5A instead of a 12V 2A adapter on a router?
Logged

CarlT

  • Kitizen
  • ****
  • Posts: 1697
  • Software Defined WAN deployment engineer
Re: 12V 2A vs 1.5A power adapter
« Reply #1 on: October 17, 2020, 09:33:50 PM »

If the router ever draws more than 18 watts bad things may happen.
Logged
WiFi: Nighthawk® AX12 RAX120
Routing: pfSense VM
Switching: Mikrotik 2* CRS305-1G-4S-IN, 1 * CRS309-1G-8S+; various cheap and cheerful TP-Link/Netgear
Exchange: Wakefield
ISP: BT Full Fibre 900. Zen Full Fibre 900.

broadstairs

  • Kitizen
  • ****
  • Posts: 3350
Re: 12V 2A vs 1.5A power adapter
« Reply #2 on: October 17, 2020, 10:28:15 PM »

Certainly if using a Zyxel router bad things WILL happen, those with 5ghz wifi need 2A. I speak from experience.

Stuart
Logged
ISP:TalkTalk Connection:FTTC Cab:ECI Router:Netgear D6220

Alex Atkin UK

  • Kitizen
  • ****
  • Posts: 1652
    • My Broadband History
Re: 12V 2A vs 1.5A power adapter
« Reply #3 on: October 17, 2020, 11:02:06 PM »

Personally I would guesstimate that you can lose say 200mA per USB 2.0 port not occupied, 400mA per USB 3.0 port.

I've certainly managed to use a TP-Link WDR3600 on only 1A PoE adapter when it came with a 1.5A PSU which I accounted to the fact it has two USB 2.0 ports that need power if used.  For reference when sat idle acting as a switch only (theoretically WiFi is on but I'm not seeing the SSIDs so I think OpenWRT is being funny and its not broadcasting) its pulling only 5.3W using the PoE adapter I have it on, a dummy CPU load pushed it to 6W.

There are really no guarantees though and using an under-rated PSU potentially if its a badly made PSU you could fry it if you overload it.
Logged
INTAKE (ECI) Zen: Home Hub 5A OpenWrt Plusnet: VMG-3925-B10B Three 4G: Hauwei B535-232 Router: pfSense (i5-7200U) WiFi: Ubiquiti nanoHD
Thinkbroadbamd Quality Monitors

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 30804
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: 12V 2A vs 1.5A power adapter
« Reply #4 on: October 17, 2020, 11:29:53 PM »

The most likely scenario is that as the load drawn from the PSU increases, the output voltage will sag from the specified 12V DC.

Dependant upon how deep is the sag, you may well find that the modem/router will re-boot. And then continue in a perpetual re-boot cycle. That will definitely make the DLM process unhappy.
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: 12V 2A vs 1.5A power adapter
« Reply #5 on: October 18, 2020, 12:11:39 AM »

What Burakkucat said; the modem-router will get more and more unreliable and will crash more and more often the lower the voltage droops. The voltage droops could be of very short duration.
« Last Edit: October 18, 2020, 01:23:14 AM by Weaver »
Logged

Alex Atkin UK

  • Kitizen
  • ****
  • Posts: 1652
    • My Broadband History
Re: 12V 2A vs 1.5A power adapter
« Reply #6 on: October 18, 2020, 01:17:28 AM »

I'd personally risk in bridge/modem mode (its unlikely to go over 500mA), but not in full router mode where the load will be much more higher.
Logged
INTAKE (ECI) Zen: Home Hub 5A OpenWrt Plusnet: VMG-3925-B10B Three 4G: Hauwei B535-232 Router: pfSense (i5-7200U) WiFi: Ubiquiti nanoHD
Thinkbroadbamd Quality Monitors

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: 12V 2A vs 1.5A power adapter
« Reply #7 on: October 18, 2020, 01:52:08 AM »

I’m not following Alex’s reasoning,  :) but then I’ve never looked into such a thing so what do I know. I do recall that debugging such problems, especially short spikes is awkward and fixing them cures a lot of bizarre faults.
Logged

Alex Atkin UK

  • Kitizen
  • ****
  • Posts: 1652
    • My Broadband History
Re: 12V 2A vs 1.5A power adapter
« Reply #8 on: October 18, 2020, 03:30:14 PM »

I’m not following Alex’s reasoning,  :) but then I’ve never looked into such a thing so what do I know.

Manufacturer PSUs should always be rated higher than the maximum current the device will ever need.  If you're only using a subset of the hardware, it will NEVER hit that current requirement.

eg If it has two USB ports you'll never use, thats 5W that will never be drawn from the PSU.  Not using the WiFi might save another 5W.

Is it recommended, no, but there are situations (my own where PoE to 12V adapters outputting 1A are common and 2A are much more rare/expensive) where its a worthwhile compromise.

That said, if you're talking about powering from the mains, just get the right PSU, they are neither rare nor expensive.  But as a temporary stop-gap while waiting for a replacement, again it doable.
« Last Edit: October 18, 2020, 03:32:43 PM by Alex Atkin UK »
Logged
INTAKE (ECI) Zen: Home Hub 5A OpenWrt Plusnet: VMG-3925-B10B Three 4G: Hauwei B535-232 Router: pfSense (i5-7200U) WiFi: Ubiquiti nanoHD
Thinkbroadbamd Quality Monitors

sevenlayermuddle

  • Helpful
  • Addicted Kitizen
  • *
  • Posts: 5190
Re: 12V 2A vs 1.5A power adapter
« Reply #9 on: October 18, 2020, 06:22:51 PM »

There is also the fact that some PSUs are tightly regulated, and some are not.

A regulated Power brick rated at 12V 1A can be expected to provide 12V, at up to 1A.  It’ll probably work at a bit more than that but will be over-stressed and likely fail prematurely

An unregulated brick with similar rating is expected to produce 12V when the current drawn is exactly 1A, with different voltages at different currents.  Should the current drawn exceed rated current, the voltage would drop below rated voltage.   Probably worse, should you draw less current the voltage may rise, with a likelihood of damage to connected equipment.

Personally, I always do my absolute best to obtain original replacement parts when Power bricks fail.  Just too many variables.  And in the nightmare (but not inconceivable) scenario where one such variable leads to catastrophic failure involving smoke and flames, home insurers may fall back on the fact that the user manual probably warned against using anything other than original parts. :(
Logged

Alex Atkin UK

  • Kitizen
  • ****
  • Posts: 1652
    • My Broadband History
Re: 12V 2A vs 1.5A power adapter
« Reply #10 on: October 18, 2020, 08:29:12 PM »

Its pretty rare to find an unregulated PSU these days as all devices are variable load so tend to use switching PSUs that can more efficiently deliver this capability.  But yeah, definitely not a good idea to use a random PSU if you do not know if its regulated or not, although if its from another network appliance it will be.
Logged
INTAKE (ECI) Zen: Home Hub 5A OpenWrt Plusnet: VMG-3925-B10B Three 4G: Hauwei B535-232 Router: pfSense (i5-7200U) WiFi: Ubiquiti nanoHD
Thinkbroadbamd Quality Monitors

sevenlayermuddle

  • Helpful
  • Addicted Kitizen
  • *
  • Posts: 5190
Re: 12V 2A vs 1.5A power adapter
« Reply #11 on: October 18, 2020, 09:27:43 PM »

Its pretty rare to find an unregulated PSU these days

I disagree, unregulated PSU bricks are quite common.   Random example... the PSU brick for my Openreach-branded ECI FTTC Modem rates itself as 12V 1A.    I have just measured the open circuit voltage, it is ~15V.   Let's hope I don't get punished by DLM for conducting that little experiment. :D

The exception is probably 5V USB bricks, which need to conform to a fairly tight voltage range in order to call themselves "USB".

Does it matter?  Well that depends on the device to which it is attached, and whether the designers were briefed to make it work with unregulated PSUs, or whether they were assured of a regulated power supply.  That may be sometimes be documented in device specifications if you are lucky - but don't recall if I have ever seen it on consumer grade documents.

Edit, PS.  Interesting discussion in following link as to whether “switch mode” equates to (closely) regulated.  Hint... no, it does not.

https://electronics.stackexchange.com/questions/57654/switch-mode-power-supply-and-output-voltage-range-unregulated
« Last Edit: October 18, 2020, 10:04:29 PM by sevenlayermuddle »
Logged

Alex Atkin UK

  • Kitizen
  • ****
  • Posts: 1652
    • My Broadband History
Re: 12V 2A vs 1.5A power adapter
« Reply #12 on: October 18, 2020, 10:16:31 PM »

I disagree, unregulated PSU bricks are quite common.   Random example... the PSU brick for my Openreach-branded ECI FTTC Modem rates itself as 12V 1A.    I have just measured the open circuit voltage, it is ~15V.

I do not believe that's "technically" unregulated, as switching PSUs by their nature are regulated (and plain unregulated PSUs are big heavy bricks due to needing hefty transformers), just how close they stick to their target can vary a little.  However they are designed for a minimum amount of load, so testing unloaded is pointless.

I put mine on a self powered LCD meter and it came out at 14v, so with even that tiny load its bringing it down into range.
« Last Edit: October 18, 2020, 10:33:12 PM by Alex Atkin UK »
Logged
INTAKE (ECI) Zen: Home Hub 5A OpenWrt Plusnet: VMG-3925-B10B Three 4G: Hauwei B535-232 Router: pfSense (i5-7200U) WiFi: Ubiquiti nanoHD
Thinkbroadbamd Quality Monitors

Weaver

  • Addicted Kitizen
  • *****
  • Posts: 9114
  • Retd sw dev; A&A; 4 × 7km ADSL2; IPv6; Firebrick
Re: 12V 2A vs 1.5A power adapter
« Reply #13 on: October 18, 2020, 10:19:34 PM »

I didn’t know about the preponderance of unregulated PSUs. Good to know. Rather frightening.
Logged

sevenlayermuddle

  • Helpful
  • Addicted Kitizen
  • *
  • Posts: 5190
Re: 12V 2A vs 1.5A power adapter
« Reply #14 on: October 18, 2020, 10:59:26 PM »

@Alex,    You seem to be making the mistake of equating “linear == unregulated”, and equating “switch mode == regulated”.

A traditional supply with a big heavy mains transformer, can be very closely regulated - just stick a voltage regulator on the output, or even just a zener diode.   Its voltage will be regulated, just not likely to be very efficient.
 
A switching supply is likely to be much more efficient, but there is nothing in the definition of “switch mode” to mandate that it is closely regulated.

There is nothing “pointless” about testing O/C voltages.  Lots of devices consume only tiny currents, nano Amps if not micro Amps when idle or in “sleep mode” yet their supply decoupling capacitors will still be charged to the full voltage...  Not a problem if they are designed for it, but a problem if they are not.

Moreover, my “open circuit” measurement was of course a little white lie as my DVM itself drew a small current so not really open circuit.  I think input impedance is 10Mohm, iirc.
Logged
Pages: [1] 2
 

anything