Community discussions

MikroTik App
 
User avatar
TomjNorthIdaho
Forum Guru
Forum Guru
Topic Author
Posts: 1492
Joined: Mon Oct 04, 2010 11:25 pm
Location: North Idaho
Contact:

idea for a mUPS version 2

Sat Apr 10, 2021 12:11 am

1'st ; The Mikrotik mUPS is a discontinued product.
In my opinion, the 700 mA power limitations was nowhere enough to power any NetPower device or any multi-port POE-out devices with multiple devices getting POE power from a single mUPS.

2'nd ; I would like to see a mUPS version 2 product that is low cost and has power enough capacity to power one or more NetPower16P devices under full maximum load.
The parts list is simple and low cost.
- An external 24 or 48 volt power supply
- A mUPS plastic case ( same case as was used with the now discontinued mUPS
- A new board in the original mUPS plastic enclosure case

I attached a simple schematic with this post.
There is no voltage regulator.
It has two diodes and one current limiter.
It will work with 12 or 24 or 36 or 48 Volt DC power supplies.
External 12-Volt batteries can be connected in series to provide 24 Volts ( or 36 or 48 Volts )
Each diode drops .7 Volts ( all diodes have a .3 or a .7 Volt drop )
When running on utility power, the output voltage is .7 volts less than the DC input voltage to the mUPS-version-2
The batteries will charge to .7 volts less than the DC input voltage
When running on battery power ( no utility power ), the voltage out will be .7 volts less than the battery.
Hence - a 24 Volt DC power supply connected to the mUPS-version-2:
- Utility AC power is available , the DC output voltage is 23.3 Volts
- Battery power only ( no utility power ) , the DC output voltage is 22.6 Volts.
* Using SNMP on your Mikrotik, you can graph and monitor the actual voltage on your mUPS-version-2 battery system.
(( FYI - with the original mUPS system, there was no method available to remotely detect and remotely measure the remaining battery voltage )))

This is my schematic for a new mUPS-version-2 board to go into the original mUPS plastic case:

EDIT: Note - multiple mUPS-version-2 devices can be connected to the same battery system ( unlike the original mUPS )
EDIT: The only power limitations are diode-load-capability, Utility Power Supply capability - amps -and- battery output amps capability
EDIT: The use of two diodes in the design provides reverse polarity protection ( battery and/or power supply )
You do not have the required permissions to view the files attached to this post.
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11383
Joined: Thu Mar 03, 2016 10:23 pm

Re: idea for a mUPS version 2

Sat Apr 10, 2021 1:01 pm

The simple design is guarantee for batteries to get destroyed sooner or later. Even if one uses very simple lead-acid batteries, there are a few problems:
  • when charged, a 12V lead-acid battery has voltage of around 13.7-13.9 Volts. Exact number depends on exact manufacturing process (e.g. normal vs. AGM) and battery temperature
  • if under-charged for prolonged periods of time, sulfatization of electrodes happens and in time period of a few months electrodes disintegrate (before tgat batteries loose much of capacity). Under-charged batteries are those with voltages below 13V when charging ends (charge maintenance mode with UPS-like usage)
  • if over-charged (over the voltage mentioned in first bullet), they start electrolysis of water which leads to loss of electrolyte (and destruction of electrodes). Same happens if charged with excessive current, which easily happens when batteries are depleted (voltage drops below 11V)
  • charge amount is proportional to idle voltage (varies almost linearly with battery voltages between 11V and 13.7 where short term overcharge to around 14.3V is tolerated)

Other battery chemistries (lithium, nickel) are even more susceptible to miss-charging procedures.

E.g. if two 12V lead-acid batteries are in series, and to ensure batteries are kept optimally charged, supply voltage would have to be exactly 28.3V (assuming 0.7V drop on diode) and I don't think many off-the-shelf power adapters are this precise. Next problem is PA current: it would have to be rated at current enough to simultaneously support full load of mUPS (e.g. 2A) and charging of fully depleted batteries (optimum max charging current is around 0.1C to minimize charging time while keeping service life as long as possible), say 0.7A for 7.2Ah batteries. Let's say PA would be high quality rated at 2.7A and that it would limit output power (instead of emiting smoke). But if mUPS load was minimum, almost full PA output would be used for charging batteries (too much!).
In addition it needs protection against depletion of batteries, discharging below "empty" voltage can cause dammage.

In short: mUPS needs to be more intelligent than required by your proposal.

What you propose might be a viable DIY solution, definitely not for an off-the-shelf device used by dumies (with regard to power supply and battery knowledge).

Who is online

Users browsing this forum: biomesh and 14 guests