The power supply (PSU) for my modem router (3com) and although under
warranty I am having problems getting 3com to provide a replacement.
The PSU is rated 12VDC 1000ma.  To solve the problem I have bought
what I thought was a suitable replacement with a nameplate rating
12VDC 1000ma.  I have measured the open circuit voltage of this
replacement as 16.8VDC which makes me very nervous.  The open circuit
voltage of a colleagues PSU (Belkin), also rated as 12VDC 1000ma, is
12.1VDC.

Can someone give me advice whether I can use the 'replacement' PSU
without fear of damage to the router?

I understand that PSUs come as 'regulated' and 'unregulated'  I assume
I have an 'unregulated' PSU and that the full load voltage is likely
to be 12VDC as rated. Does this make sense?

Edward W. Thompson  wrote:

> The power supply (PSU) for my modem router (3com) and although under
> warranty I am having problems getting 3com to provide a replacement.
> The PSU is rated 12VDC 1000ma.  To solve the problem I have bought
> what I thought was a suitable replacement with a nameplate rating
> 12VDC 1000ma.  I have measured the open circuit voltage of this
> replacement as 16.8VDC which makes me very nervous.  The open circuit
> voltage of a colleagues PSU (Belkin), also rated as 12VDC 1000ma, is
> 12.1VDC.
> 

His is probably a regulated one whereas yours is unregulated (as you
suggest below).


> Can someone give me advice whether I can use the 'replacement' PSU
> without fear of damage to the router?
> 

It'll probably be OK but I must admit I'm not sure that I'd risk it.
It depends how much the 3com router will cost to replace really.


> I understand that PSUs come as 'regulated' and 'unregulated'  I assume
> I have an 'unregulated' PSU and that the full load voltage is likely
> to be 12VDC as rated. Does this make sense?


Yes, sort of, but it depends how much power your router *actually*
takes whether it will load the PSU down to close to 12 volts.
Re-reading your post I've changed my mind, I think I probably would
risk it, I thought originally you said the 3com PSU was 100mA and the
replacement was 1000mA but in fact they're both the same.

The only issue is whether the 3-com PSU was regulated, if it was then
the router may not be too happy with an unregulated supply.

-- 
Chris Green

> Can someone give me advice whether I can use the 'replacement' PSU
> without fear of damage to the router?


No, you can use it only with fear of damage.


> I understand that PSUs come as 'regulated' and 'unregulated'  I assume
> I have an 'unregulated' PSU and that the full load voltage is likely
> to be 12VDC as rated. Does this make sense?


Yes. You really need a regulated one. However, if the 3Com router is of low
value to you and you want to risk it, it might work. On the other hand, it
might damage it. My guess is 60% works fine, 30% doesn't work, 10% causes
damage.

Christian.

In an earlier contribution to this discussion,
Edward W. Thompson   wrote:


> The power supply (PSU) for my modem router (3com) and although under
> warranty I am having problems getting 3com to provide a replacement.
> The PSU is rated 12VDC 1000ma.  To solve the problem I have bought
> what I thought was a suitable replacement with a nameplate rating
> 12VDC 1000ma.  I have measured the open circuit voltage of this
> replacement as 16.8VDC which makes me very nervous.  The open circuit
> voltage of a colleagues PSU (Belkin), also rated as 12VDC 1000ma, is
> 12.1VDC.
>
> Can someone give me advice whether I can use the 'replacement' PSU
> without fear of damage to the router?
>
> I understand that PSUs come as 'regulated' and 'unregulated'  I assume
> I have an 'unregulated' PSU and that the full load voltage is likely
> to be 12VDC as rated. Does this make sense?


As a matter of interest, what is wrong with your 3Com power supply? I also
have one with which I have a problem!

Ever since my ADSL line was upgraded from 512k to 1M, my 3Com wireless
router wouldn't work reliably - and gave up after being on for about 30
minutes. The symptons were that the noise margin would plummet, CRC errors
would go sky high, effective throughput would be less than dial-up - and
then it would refuse to synch altogether. 3Com replaced the router under
warranty - but the new one was exactly the same! [I have another, different
make, router and a PCI modem - both of which are ok - so I knew it wasn't
the line].

Then, I read in uk.telecom.broadband about factors affecting noise margin -
including noisy power supplies. I duly powered my router with an old power
supply which I had in my bits drawer - and the router works perfectly - with
a much higher noise margin than it *ever* reported when using the 3Com PSU.

The supply I'm using *is* regulated, and is rated at 1000mA. It gets quite
hot, so I imagine that it's running close to (or even above!) its limit.
Also, when it's been on for a few hours, the router's synch light goes into
a continuous fast blink - but it still works! The basic difference is that
my supply contains a tranformer plus rectifier - whereas the 3Com jobby is a
switched power supply - which is prone to generate a lot more electrical
noise. The 3Com supply is rated at 1.25 amps - but the router itself says 1A
max.

You could load your supply be connecting a couple of car sidelamp bulbs in
parallel to it. These are nominally 6w each - so 12w at 12v should draw 1A.
If the voltage when powering these bulbs is much closer to 12V, I think I'd
give it a go.
-- 
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In article ,
   Edward W. Thompson  wrote:

> The power supply (PSU) for my modem router (3com) and although under
> warranty I am having problems getting 3com to provide a replacement.
> The PSU is rated 12VDC 1000ma.  To solve the problem I have bought
> what I thought was a suitable replacement with a nameplate rating
> 12VDC 1000ma.  I have measured the open circuit voltage of this
> replacement as 16.8VDC which makes me very nervous.  The open circuit
> voltage of a colleagues PSU (Belkin), also rated as 12VDC 1000ma, is
> 12.1VDC.


Does the original say if it's regulated?


> Can someone give me advice whether I can use the 'replacement' PSU
> without fear of damage to the router?

> I understand that PSUs come as 'regulated' and 'unregulated'  I assume
> I have an 'unregulated' PSU and that the full load voltage is likely
> to be 12VDC as rated. Does this make sense?


If it's unregulated then the voltage under load will vary according to
that load.

The problem also is that if you use a regulated supply where a non
regulated type is needed, the regulator *inside* the device won't work
given that they need a slightly higher incoming voltage to operate
correctly. This may, or may not, matter.

-- 
*If a turtle doesn't have a shell, is he homeless or naked?

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

In an earlier contribution to this discussion,
Dave Plowman (News)   wrote:


>
> Does the original say if it's regulated?
>

If it's the same as mine, it's a switching power supply - which I presume is
regulated, by definition?

Mine gives 12.26v when no load is applied.
-- 
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In article , diy@privacy.net says...

> In an earlier contribution to this discussion,
> Dave Plowman (News)   wrote:
> 
> >
> > Does the original say if it's regulated?
> >
> If it's the same as mine, it's a switching power supply - which I presume is
> regulated, by definition?
> 
> Mine gives 12.26v when no load is applied.
> 

No-load voltage is pretty meaningless with switch-mode PSUs.

Set Square  wrote:

> In an earlier contribution to this discussion,
> Dave Plowman (News)   wrote:
> 
>>
>> Does the original say if it's regulated?
>>
> If it's the same as mine, it's a switching power supply - which I presume is
> regulated, by definition?


Not quite.
But adding regulation is almost free, and may actually stop it exploding when
no load is applied.
Unregulated SMPS are very uncommon.

Ian Stirling wrote:


> But adding regulation is almost free, and may actually stop it exploding when
> no load is applied.


It is not uncommon for SMPS to have a minimum load, below which they 
will shut down.


-- 
Cheers,

John.

/=================================================================\
|          Internode Ltd -  http://www.internode.co.uk            |
|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

On Tue, 6 Sep 2005 10:32:04 +0000 (UTC), Edward W. Thompson
 wrote:


>The power supply (PSU) for my modem router (3com) and although under
>warranty I am having problems getting 3com to provide a replacement.
>The PSU is rated 12VDC 1000ma.  To solve the problem I have bought
>what I thought was a suitable replacement with a nameplate rating
>12VDC 1000ma.  I have measured the open circuit voltage of this
>replacement as 16.8VDC which makes me very nervous.  The open circuit
>voltage of a colleagues PSU (Belkin), also rated as 12VDC 1000ma, is
>12.1VDC.
>
>Can someone give me advice whether I can use the 'replacement' PSU
>without fear of damage to the router?
>
>I understand that PSUs come as 'regulated' and 'unregulated'  I assume
>I have an 'unregulated' PSU and that the full load voltage is likely
>to be 12VDC as rated. Does this make sense?


Thanks very much for all your very useful comments.

With respect to 'Set Square' post, my 3com wireless ADSL router has
worked without problems although there seems to be a body of opinion
that it is not a 'good' product.  The problem with the PSU was it
simply failed, that is no output.

As a follow up, today I received an email from 3com to say they have
agreed to provide a new PSU.

The replacement PSU I have now found has a 'problem' in that the plug
does not fit the router, or any other device I have (3) with the same
OD socket.  From visual inspect it appears that the ID of the plug is
too small to allow the centre pin to enter.  

The source of the PSU advises this PSU is in common use with a range
of CCTV equipment that I find puzzling.  I was of the understanding
these plugs are standard in so much the OD of the plug determined the
ID for the centre pin, am I wrong here?

Edward W. Thompson  wrote:

> 
> The replacement PSU I have now found has a 'problem' in that the plug
> does not fit the router, or any other device I have (3) with the same
> OD socket.  From visual inspect it appears that the ID of the plug is
> too small to allow the centre pin to enter.  
> 
> The source of the PSU advises this PSU is in common use with a range
> of CCTV equipment that I find puzzling.  I was of the understanding
> these plugs are standard in so much the OD of the plug determined the
> ID for the centre pin, am I wrong here?


Obviously, yes!  :-)

I think there are three or even four different sizes for these
concentric power connectors and even the polarity is not consistent.

-- 
Chris Green

In an earlier contribution to this discussion,
usenet@isbd.co.uk   wrote:


> Edward W. Thompson  wrote:
>>
>> The replacement PSU I have now found has a 'problem' in that the plug
>> does not fit the router, or any other device I have (3) with the same
>> OD socket.  From visual inspect it appears that the ID of the plug is
>> too small to allow the centre pin to enter.
>>
>> The source of the PSU advises this PSU is in common use with a range
>> of CCTV equipment that I find puzzling.  I was of the understanding
>> these plugs are standard in so much the OD of the plug determined the
>> ID for the centre pin, am I wrong here?
>
> Obviously, yes!  :-)
>
> I think there are three or even four different sizes for these
> concentric power connectors and even the polarity is not consistent.


Yes, I've got several - all with the same OD but different ID's! If there
*is* any standard, maybe the different pin sizes are for different power
ratings - to ensure that you don't overload weedy supplies by connecting
them to high current consuming devices?
-- 
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

In message , usenet@isbd.co.uk writes

>Edward W. Thompson  wrote:
>>
>> The replacement PSU I have now found has a 'problem' in that the plug
>> does not fit the router, or any other device I have (3) with the same
>> OD socket.  From visual inspect it appears that the ID of the plug is
>> too small to allow the centre pin to enter.
>>
>> The source of the PSU advises this PSU is in common use with a range
>> of CCTV equipment that I find puzzling.  I was of the understanding
>> these plugs are standard in so much the OD of the plug determined the
>> ID for the centre pin, am I wrong here?
>
>Obviously, yes!  :-)
>
>I think there are three or even four different sizes for these
>concentric power connectors and even the polarity is not consistent.
>

I ended up buying a couple of adjustable PSUs from CPC which have 16 
plug-in end connectors. Even then, I repaired an electronic piano for 
someone last week and none of the connectors fit !

-- 
geoff

On Wed, 7 Sep 2005 06:31:37 +0000 (UTC), Edward W. Thompson
 wrote:


>On Tue, 6 Sep 2005 10:32:04 +0000 (UTC), Edward W. Thompson
> wrote:
>
>>The power supply (PSU) for my modem router (3com) and although under
>>warranty I am having problems getting 3com to provide a replacement.
>>The PSU is rated 12VDC 1000ma.  To solve the problem I have bought
>>what I thought was a suitable replacement with a nameplate rating
>>12VDC 1000ma.  I have measured the open circuit voltage of this
>>replacement as 16.8VDC which makes me very nervous.  The open circuit
>>voltage of a colleagues PSU (Belkin), also rated as 12VDC 1000ma, is
>>12.1VDC.
>>
>>Can someone give me advice whether I can use the 'replacement' PSU
>>without fear of damage to the router?
>>
>>I understand that PSUs come as 'regulated' and 'unregulated'  I assume
>>I have an 'unregulated' PSU and that the full load voltage is likely
>>to be 12VDC as rated. Does this make sense?
>
>Thanks very much for all your very useful comments.
>
>With respect to 'Set Square' post, my 3com wireless ADSL router has
>worked without problems although there seems to be a body of opinion
>that it is not a 'good' product.  The problem with the PSU was it
>simply failed, that is no output.
>
>As a follow up, today I received an email from 3com to say they have
>agreed to provide a new PSU.
>
>The replacement PSU I have now found has a 'problem' in that the plug
>does not fit the router, or any other device I have (3) with the same
>OD socket.  From visual inspect it appears that the ID of the plug is
>too small to allow the centre pin to enter.  
>
>The source of the PSU advises this PSU is in common use with a range
>of CCTV equipment that I find puzzling.  I was of the understanding
>these plugs are standard in so much the OD of the plug determined the
>ID for the centre pin, am I wrong here?


I have found, rather been told the answer to my question that being
the centre pin of the power receptacle fitted to a device requiring a
'regulated' power supply is made larger than one that will accept an
unregulated supply.

Ian Stirling  wrote:

> Set Square  wrote:
>> In an earlier contribution to this discussion,
>> Dave Plowman (News)   wrote:
>> 
>>>
>>> Does the original say if it's regulated?
>>>
>> If it's the same as mine, it's a switching power supply - which I presume is
>> regulated, by definition?
> 
> Not quite.
> But adding regulation is almost free, and may actually stop it exploding when
> no load is applied.
> Unregulated SMPS are very uncommon.


However, I've just found one that you can have for your very own!
http://www.ebuyer.com/customer/products/index.html?action=c2hvd19wcm9kdWN0X292ZXJ2aWV3&product_uid=86560

Nominally 5V, 0.7A.
http://www.mauve.plus.com/psu.jpeg


At no load, 6.2V, with 0.2V ripple.
At 10 ohms load, 3-4.5V.
Yes boys and girls, that's 1.5V ripple on a USB hub PSU.
There is no input filter capacitor...

On 14 Sep 2005 21:32:14 GMT, Ian Stirling 
scrawled:


>Nominally 5V, 0.7A.


Hmmm, on a 4 port USB hub?


>http://www.mauve.plus.com/psu.jpeg
>
>At no load, 6.2V, with 0.2V ripple.
>At 10 ohms load, 3-4.5V.
>Yes boys and girls, that's 1.5V ripple on a USB hub PSU.
>There is no input filter capacitor...


Ah, there's an LED missing, no wonder it's throwing a wobbly.
-- 
Stuart @ SJW Electrical

Please Reply to group

Lurch  wrote:

> On 14 Sep 2005 21:32:14 GMT, Ian Stirling 
> scrawled:
> 
>>Nominally 5V, 0.7A.
> 
> Hmmm, on a 4 port USB hub?

Yes.

> 
>>http://www.mauve.plus.com/psu.jpeg
>>
>>At no load, 6.2V, with 0.2V ripple.
>>At 10 ohms load, 3-4.5V.
>>Yes boys and girls, that's 1.5V ripple on a USB hub PSU.
>>There is no input filter capacitor...
> 
> Ah, there's an LED missing, no wonder it's throwing a wobbly.


I have doubts that an LED will fix it :)

On 14 Sep 2005 22:40:57 GMT, Ian Stirling 
scrawled:


>Lurch  wrote:
>> On 14 Sep 2005 21:32:14 GMT, Ian Stirling 
>> scrawled:
>> 
>>>Nominally 5V, 0.7A.
>> 
>> Hmmm, on a 4 port USB hub?
>
>Yes.
>

I thought the idea of a powered hub was that you got the full 500mA
available to each port to overcome problems that a motherboard may
have with supplying a full 2A just for the USB? If so, then that PSU
isn't suitable for a 2 port hub, let alone 4.

>> 
>>>http://www.mauve.plus.com/psu.jpeg
>>>
>>>At no load, 6.2V, with 0.2V ripple.
>>>At 10 ohms load, 3-4.5V.
>>>Yes boys and girls, that's 1.5V ripple on a USB hub PSU.
>>>There is no input filter capacitor...
>> 
>> Ah, there's an LED missing, no wonder it's throwing a wobbly.
>
>I have doubts that an LED will fix it :)


Always an optimist me, well, not really but just this once I was,
never mind......
-- 
Stuart @ SJW Electrical

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