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I want to power my Mikrotik HEX POE switch which accepts up to 57V DC through a DIY UPS.

I want to build it from a MeanWell ADD-155C which haa battery connector (CH3 aka B+\B-) and four 12V CSB UPS12460 batteries and connect the Mikrotik to CH1\COM.

enter image description here

My questions are:

  1. Is it OK to use this schematic?
  2. Which voltage should I adjust on B+\B-? According to the battery documentation, there is Float charging voltage characteristic which is 13.5..13.8V. Does this mean I should set it to four times (54.0..55.2) this?
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  • \$\begingroup\$ @SolarMike On chematic, 12v is "nominal" battery voltage, aka "marketing". HEX POE accepts 12-57V range, but at 48-57V is preferred to make POE function correctly. Maybe I totally misunderstand something? \$\endgroup\$
    – filimonic
    Commented Apr 26, 2022 at 12:01
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    \$\begingroup\$ placing multiple "fuse" in series tends to be a bad idea. \$\endgroup\$
    – Abel
    Commented Apr 26, 2022 at 12:09
  • \$\begingroup\$ CH1 is output channel and it is rated 48-58V as for MW ADD-155C docs, set by variable resistor. It powers Mikrotik, with input rated 12-57V, so I assume everything is fine when using without battery connected as an AC\DC converter. CH3 aka B+\B- is battery Input\output, and it is regulated with the same varistor as CH1. As I understand, when AC is connected, ADD-155C will power (charge) battery until B+\B- voltage equals CH1 voltage. When AC is disconnected, ADD-155C will power CH1 directly from battery. CH2 is 5V internally regulated, and let's leave it NC. \$\endgroup\$
    – filimonic
    Commented Apr 26, 2022 at 12:14
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    \$\begingroup\$ make sure you don't accidentally have a unit for A instead of C. C model does appear to be intended for your uses and they may mean well, but with an adj range of 48-58 V, your unit should not be leaving the factory set for anything outside that range. \$\endgroup\$
    – Abel
    Commented Apr 26, 2022 at 12:31

1 Answer 1

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Looks legit... to an extent.

Considerations:

  1. You need a single fuse. More fuses are not better at all.

  2. Your terminal numbers of the ADD-155C are off. The load should be connected to 7 and 8, batteries to 5 and 6. Double-check before connecting.

  3. Considering the questions you are asking, I profoundly advice you to ask for a competent help for the practical implementation of your setup in order not to get a life-treatening electric shock.

  4. 57V is a deadly. Don't check yourself, get my word for granted (or check the related regulations in your area, chances are you need to be a certified electrician in order to mess with it). If you are not constrained by very, very long cables, consider going to 24V instead. 24V (it will be 28V, actually) is safe to touch. Still unpleasant, but safe. Mikrotik devices (as well as a lot of other POE-powered stuff) are happy with 24V and 24V is good for at least 40-50m CAT-5E cable. You will need only 2 batteries and you will have to use ADD-155B instead.

  5. Your floating voltage calculation is right. Aim for the lower limit, unless you have frequent outages and the batteries fail to recharge between them.

Most Mikrotik devices have a power voltage monitoring. You can even script some automation - e.g. send mail or play a sound when the voltage goes too low (say, 10V per 12V battery).


p.s. where did you get HEX POE? I need one right now and it is out of stock everywhere.

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  • \$\begingroup\$ Thanks. Sorry, my HEX POE was bought 10 months ago. \$\endgroup\$
    – filimonic
    Commented Apr 26, 2022 at 13:48
  • \$\begingroup\$ Could multiple fuses be useful if one is physically near each battery, to guard against short-circuiting one battery? \$\endgroup\$ Commented Apr 26, 2022 at 14:54
  • \$\begingroup\$ Batteries should be installed in a way that it is geometrically impossible to short and secured in their places. On the other hand, fuses introduce their own resistance and contact resistances and are points of failure themselves. What's worse, the added resistance may prevent a single fuse from, eeer, fusing when something goes wrong. \$\endgroup\$
    – fraxinus
    Commented Apr 26, 2022 at 15:06

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