[j-nsp] MX80 Power

[Christopher E. Brown]

On 3/29/12 9:05 AM, Kevin Wormington wrote:
> Curious if anyone has used one AC and one DC power supply in an MX80?  Yes, I know the docs say it's not supported but we all know how that goes.
> 
> Thanks,
> 
> Kevin

The big issue is not will the device support it, but why devices
generally don't, and often actively prevent this.


The issue is potential differences between the systems, attempting to
equalize through your device, or a person.  This includes not just
normal operation, but failure and event (device fail, lightning, infra
damage) handling.


It is possible to design a combined AC/DC power system for this, but it
is not simple or easy, technical or regulatory wise.

It is possible to design isolated input power supplies for devices.

It is possible to design the devices to maintain approp internal
isolation to take advantage of this.

It is possible to do all of this at the same time, and in theory meet
all of the require safety regs.

Possibly != easy or cheap.  Most folks will accept the increase in
equipment cost.

Most folks will simple hook up the gear if it will allow it, without
regard to the special requirments for install or power systems build out.


That places the gear makers in an interesting position.

They could make the gear to do it, but it would cost more.

It would only be safe and not risk gear damage if it was coupled with
proper install and AC/DC power systems design.


I have seen plenty of devices running one AC and one DC supply, even
though it was always a "DO NOT TO IT" item for that device.  I have seen
more than a few damaged, and more than a few safety issues.

It is why many gear makers add additional restrictions, like gear
refusing to power up if both AC and DC supplies are inserted.

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Christopher E. Brown   <chris.brown at acsalaska.net>   desk (907) 550-8393
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IP Engineer - ACS
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