POE maximum voltage?

[dave parker-3]

Hello

I have what I'm guessing is a really easy to answer question:

Is 59.2vDC an unacceptably high voltage to send through a POE injector
to a net4526?

I've salvaged a bank of lithium batteries and charger from an electric
scooter, and while I'm suspecting that there are enough amp hours there
to run the board for "a very long time" without charging, I'd like to
use those amp hours for other things, so I'd like to use the charger
while the board is in operation. The charger's logic  appears to have
voltage top out at around 59.2v, and maintenance is around 56v.  The
former scares me a bit.  Will the board tolerate that?  Is there
something I should add to the circuit to protect the board while the
charger is operating?  The cat5 run from the injector to the board is in
the 5-8' range.

I've tried finding a concise answer to this question with some extensive
googling to no avail aside from two documents that mention "absolute
maxium voltage = 68vDC.  That's not enough to make me feel secure about
my magic smoke, hence... I ask :)

Thanks in advance,

Dave Parker
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[dave parker-3]

I should mention that the battery bank itself is nominally 48vDC.

Dave Parker wrote:

> Hello
>
> I have what I'm guessing is a really easy to answer question:
>
> Is 59.2vDC an unacceptably high voltage to send through a POE injector
> to a net4526?
>
> I've salvaged a bank of lithium batteries and charger from an electric
> scooter, and while I'm suspecting that there are enough amp hours there
> to run the board for "a very long time" without charging, I'd like to
> use those amp hours for other things, so I'd like to use the charger
> while the board is in operation. The charger's logic  appears to have
> voltage top out at around 59.2v, and maintenance is around 56v.  The
> former scares me a bit.  Will the board tolerate that?  Is there
> something I should add to the circuit to protect the board while the
> charger is operating?  The cat5 run from the injector to the board is in
> the 5-8' range.
>
> I've tried finding a concise answer to this question with some extensive
> googling to no avail aside from two documents that mention "absolute
> maxium voltage = 68vDC.  That's not enough to make me feel secure about
> my magic smoke, hence... I ask :)
>
> Thanks in advance,
>
> Dave Parker
>
>  

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[Paul Bartell]

sorry i forgot to cc the list:

---------- Forwarded message ----------
From: Paul Bartell <paul.bartell@...>
Date: Mar 27, 2007 7:33 AM
Subject: Re: [Soekris] POE maximum voltage?
To: Dave Parker <daveparker01@...>


you might consider a voltage regulator to put between the battery (i
dont know if they exist in 48v) and the poe injector.

On 3/27/07, Dave Parker <daveparker01@...> wrote:

> I should mention that the battery bank itself is nominally 48vDC.
>
> Dave Parker wrote:
> > Hello
> >
> > I have what I'm guessing is a really easy to answer question:
> >
> > Is 59.2vDC an unacceptably high voltage to send through a POE injector
> > to a net4526?
> >
> > I've salvaged a bank of lithium batteries and charger from an electric
> > scooter, and while I'm suspecting that there are enough amp hours there
> > to run the board for "a very long time" without charging, I'd like to
> > use those amp hours for other things, so I'd like to use the charger
> > while the board is in operation. The charger's logic  appears to have
> > voltage top out at around 59.2v, and maintenance is around 56v.  The
> > former scares me a bit.  Will the board tolerate that?  Is there
> > something I should add to the circuit to protect the board while the
> > charger is operating?  The cat5 run from the injector to the board is in
> > the 5-8' range.
> >
> > I've tried finding a concise answer to this question with some extensive
> > googling to no avail aside from two documents that mention "absolute
> > maxium voltage = 68vDC.  That's not enough to make me feel secure about
> > my magic smoke, hence... I ask :)
> >
> > Thanks in advance,
> >
> > Dave Parker
> >
> >
>
> _______________________________________________
> Soekris-tech mailing list
> Soekris-tech@...
> http://lists.soekris.com/mailman/listinfo/soekris-tech
>

--
"If you are savvy and smart about the choices you make in life, The
sky is not the limit!"
Mark Shuttleworth


--
"If you are savvy and smart about the choices you make in life, The
sky is not the limit!"
Mark Shuttleworth
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[dave parker-3]

I guess I was being overly optimistic a bit on the "really easy to
answer" part; two people have recommended that I add some sort of
regulation to the voltage to keep it below 56vDC.

I'm kind of (not just kind of) out of my league on this, but I've been
thinking then that the circuit described in the "Simple Voltage
Stabilizer" section of this page:
http://en.wikipedia.org/wiki/Voltage_stabiliser might do the trick? My
understanding is that it would "regulate" voltage only in as much as it
would keep it from exceeding a reference voltage, which I would probably
select as 54vDC to be safe.

Do people from Soekris read this list periodically? I was kind of hoping
for an "official position" on the topic. Minus that, I guess I'll have
to see if I can build one of those circuits.

Dave Parker wrote:

> I should mention that the battery bank itself is nominally 48vDC.
>
> Dave Parker wrote:
>  
>> Hello
>>
>> I have what I'm guessing is a really easy to answer question:
>>
>> Is 59.2vDC an unacceptably high voltage to send through a POE injector
>> to a net4526?
>>
>> I've salvaged a bank of lithium batteries and charger from an electric
>> scooter, and while I'm suspecting that there are enough amp hours there
>> to run the board for "a very long time" without charging, I'd like to
>> use those amp hours for other things, so I'd like to use the charger
>> while the board is in operation. The charger's logic  appears to have
>> voltage top out at around 59.2v, and maintenance is around 56v.  The
>> former scares me a bit.  Will the board tolerate that?  Is there
>> something I should add to the circuit to protect the board while the
>> charger is operating?  The cat5 run from the injector to the board is in
>> the 5-8' range.
>>
>> I've tried finding a concise answer to this question with some extensive
>> googling to no avail aside from two documents that mention "absolute
>> maxium voltage = 68vDC.  That's not enough to make me feel secure about
>> my magic smoke, hence... I ask :)
>>
>> Thanks in advance,
>>
>> Dave Parker
>>
>>  
>>    
>
>
>  

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[Frank Cole]

Hi Dave,

        There actually is an easy answer: DC to DC converter.

        And yes, above 48v on PoE is generally bad even though it might work on
some systems.

Frank

Dave Parker wrote:

> Hello
>
> I have what I'm guessing is a really easy to answer question:
>
> Is 59.2vDC an unacceptably high voltage to send through a POE injector
> to a net4526?
>
> I've salvaged a bank of lithium batteries and charger from an electric
> scooter, and while I'm suspecting that there are enough amp hours there
> to run the board for "a very long time" without charging, I'd like to
> use those amp hours for other things, so I'd like to use the charger
> while the board is in operation. The charger's logic  appears to have
> voltage top out at around 59.2v, and maintenance is around 56v.  The
> former scares me a bit.  Will the board tolerate that?  Is there
> something I should add to the circuit to protect the board while the
> charger is operating?  The cat5 run from the injector to the board is in
> the 5-8' range.
>
> I've tried finding a concise answer to this question with some extensive
> googling to no avail aside from two documents that mention "absolute
> maxium voltage = 68vDC.  That's not enough to make me feel secure about
> my magic smoke, hence... I ask :)
>
> Thanks in advance,
>
> Dave Parker
> _______________________________________________
> Soekris-tech mailing list
> Soekris-tech@...
> http://lists.soekris.com/mailman/listinfo/soekris-tech
>

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[Randall Nortman-5]

On Tue, Mar 27, 2007 at 07:35:10PM -0700, Dave Parker wrote:

> I guess I was being overly optimistic a bit on the "really easy to
> answer" part; two people have recommended that I add some sort of
> regulation to the voltage to keep it below 56vDC.
>
> I'm kind of (not just kind of) out of my league on this, but I've been
> thinking then that the circuit described in the "Simple Voltage
> Stabilizer" section of this page:
> http://en.wikipedia.org/wiki/Voltage_stabiliser might do the trick? My
> understanding is that it would "regulate" voltage only in as much as it
> would keep it from exceeding a reference voltage, which I would probably
> select as 54vDC to be safe.

I don't know any more than you do about what voltage the Soekris can
tolerate, but I can tell you that the circuits on that page are all
extraordinarily inefficient.  They will dissipate the excess power
in the form of heat.  This might be OK for a line-powered system, but
you're talking about battery power, so I suspect you won't want to be
wasting power like that.

Somebody else mentioned a DC-DC converter, which is in fact a
switching power supply, and that will certainly do the job more
efficiently.  You might find they are a little expensive, though, and
not available at your local Radio Shack.  DigiKey sells a bewildering
array of them.  (Emphasis on "bewildering".)  You will likely pay $20
or more, depending on how much power you need.

You might also see if you can just take a battery or two out of the
battery pack.  It will have multiple lithium cells connected in
series to produce a voltage that high.  If you take some cells off the
stack, the voltage will be lower.  However, the charger is likely
designed to charge to a particular voltage, though some chargers are
smart can adapt to different voltages.  (I suspect that is *not* the
case, as it would be added expense in the charger for no benefit in
the scooter application.)

>
> Do people from Soekris read this list periodically? I was kind of hoping
> for an "official position" on the topic. Minus that, I guess I'll have
> to see if I can build one of those circuits.
>
> Dave Parker wrote:
> > I should mention that the battery bank itself is nominally 48vDC.
> >
> > Dave Parker wrote:
> >  
> >> Hello
> >>
> >> I have what I'm guessing is a really easy to answer question:
> >>
> >> Is 59.2vDC an unacceptably high voltage to send through a POE injector
> >> to a net4526?
> >>
> >> I've salvaged a bank of lithium batteries and charger from an electric
> >> scooter, and while I'm suspecting that there are enough amp hours there
> >> to run the board for "a very long time" without charging, I'd like to
> >> use those amp hours for other things, so I'd like to use the charger
> >> while the board is in operation. The charger's logic  appears to have
> >> voltage top out at around 59.2v, and maintenance is around 56v.  The
> >> former scares me a bit.  Will the board tolerate that?  Is there
> >> something I should add to the circuit to protect the board while the
> >> charger is operating?  The cat5 run from the injector to the board is in
> >> the 5-8' range.
> >>
> >> I've tried finding a concise answer to this question with some extensive
> >> googling to no avail aside from two documents that mention "absolute
> >> maxium voltage = 68vDC.  That's not enough to make me feel secure about
> >> my magic smoke, hence... I ask :)
> >>
> >> Thanks in advance,
> >>
> >> Dave Parker
> >>
> >>  
> >>    
> >
> >
> >  
>
> _______________________________________________
> Soekris-tech mailing list
> Soekris-tech@...
> http://lists.soekris.com/mailman/listinfo/soekris-tech

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[Bodo Meissner]

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