Dual DC in on mini

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Dual DC in on mini

Fri Nov 03, 2017 11:01 pm

What happen if we connect two independent DC inputs to the mini's barell connector and POE in.
Which one will power the device and what is the logistic behind it.

We have several Mtik powerbox pro's and we power them with two independent dc inputs, barrell and POE in.
The powerbox takes the input with higher voltage. Works great as a redundant power, however there is no way to find out which one of the ports is currently on, nor the incoming current.

Cheers, Pavel

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Re: Dual DC in on mini

Mon Nov 06, 2017 10:43 am

DC power in is protected by a single flyback diode, and both polarities use wired-AND logic with the outputs of the POE input's bridge rectifiers.

Powering via both at once is not a recommended method. I can, however, tell you that I've tried it briefly in the lab without breaking anything,
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Re: Dual DC in on mini

Mon Nov 06, 2017 1:12 pm

I wanted very much to do this. I have a MINI out in a storage shelter that does not have reliable AC mains power but it does have PoE via a 300 foot buried CAT5 run. The long run has a voltage drop at high wattage that was alerting on low voltage for the 48V kit. I could power it with a brick from local AC power but as it is unreliable, would want the PoE power as a backup. I asked Dave if I could use both PoE and barrel at the same time but he would not endorse it and did not give a reason.

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Re: Dual DC in on mini

Mon Nov 06, 2017 1:48 pm

So the official answer is NOT RECOMMENDED, not responsible for damage of any kind resulting from this.
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Re: Dual DC in on mini

Mon Nov 06, 2017 2:56 pm

I think the reason is that if POE DC+ in were to become sufficiently more positive with respect to DC+ in (barrel connector) for any reason, sparks can and will emit from your device and could possibly render it nonfunctional.. Just a theory, though, I may do some testing later in the week on this.

Dave will probably have input once he gets his crazy canadian internet working.
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Re: Dual DC in on mini

Mon Nov 06, 2017 2:59 pm

This is not recommended as you are bonding 2 separate DC power sources together and there is no protection circuits in place to protect each power source from the other.

In units that have redundant power supplies there are circuits between the power sources to prevent them from affecting each other and in the event something happens to one that it does not short out and the other power supply heats things up and POOF or worse.
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Re: Dual DC in on mini

Mon May 03, 2021 6:38 pm

The WS-6-MINI remains one of my favorite small switches for microPoPs.

If you are doing a design revision on this product, it would be very useful to allow dual power input like the MikroTik products do (I think they have a rectifier on both inputs). I have to repair a line feeding a WS-6-MINI this week, and if I could plug it in to a second power source, I could keep it powered and rely on secondary network paths so no customers go down. I connected a secondary power on a MikroTik this past week for re-working a power supply, and it kept everything working while I repaired a system.

Thank you, Chris

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