As where I live has had power outages this past year, and I would like to keep my network going (NBN Wireless unit, Mikrotik Router and the other router on another power circuit in the shed). Each unit uses 24V supply and I have CAT6A cabling with fibre and CAT6A cabling to the shed (50M away). I’ve also got passive PoE lightning arresting units on each side of the network link to the shed (redundant link).
Goal 1: To have resiliency in place whereby if one power circuit cuts out then the other will be able to provide power to keep the network up, and vice-versa.
Goal 2: to include a battery at each DC distribution box to enable power to come from that if total blackout occurs from electricity provider.
Goal 3: attach a surplus solar panel at the shed to provide power to the battery at that DC distribution box. which would in-turn lengthen the battery life when we have another multi-day power outage.
Power usage is 23W router, 12W router, 16W NBN Wireless
I have originally considered having multiple 24VDC inputs each with an in-line fuse and a Diode to prevent going back out where it came. These are connected through a bus-bar which then has 24VDC going out to each item of network equipment (fuse and diode covering each output).
Now I’m not sure if I need a DC-DC converter on each end of the long run between the shed/house or if a solar battery regulator would take care of that given that I would like to in time upgrade to having solar as an input and a battery on each end.
Yes, I am working my way to piggy-backing this DC solution to other remote telemetry applications thus why I’m not doing the easiest option of using some AC UPS’s to provide 2hrs power to the equipment.
And yes looking at starlink in the future and going the 12v option means much less power usage than running through an inverter.
Before I start building, I’d love some feedback on anything I might have missed.
This week I’ll measure the voltage drop between the house and the shed for 24VDC supply.
Thanks in advance.
Hi David
Yes. To run parallel supplies the diode is essential. The fuse is optional but not a bad idea but if one equipment goes bad to blow the fuse at this point all fuses are likely to blow in turn leaving you with nothing. See next part for solution.
Each 24V source should be capable of taking the WHOLE load.Unless the sources are EXACTLY balanced you will find the highest voltage will try to supply everything until an equilibrium is reached.
Diodes are not necessary at this point (they will do nothing except be another 0.7V (approx) voltage drop but it is here that you want the fuse or circuit breaker. So if one equipment goes bad only the one fuse will blow and the rest will stay up. Contrary to what some think a fuse DOES NOT protect the equipment. The equipment is faulty and that is why the fuse blows. The fuse or circuit breaker protects THE SUPPLY TO THAT EQUIPMENT. This applies to all uses of a fuse.
You will need a cable run of sufficient size to cater for the load at the end. You will get SOME voltage drop (that is Physics) but you need to decide what is acceptable. A converter is only going to add to your load. It would have to be able to supply the load current and by the time you factor in something like 85% efficiency means the supply is supplying the missing 15% I think you would be behind. Better off with a heavy cable.
There is a reason the power grid distribution is many thousands of volts. Less “I^2R” or heat loss.
As for solar. You will not be able to charge both batteries with the one solar system because of the presence of the battery isolating diodes. There is no reason you should not charge one or both batteries with their own private solar panel. Keep everything on the battery side of the diode and treat the whole thing (battery and solar system) as one 24V source.
Each diode will have to carry the total load as there will be no indication of what the load sharing is at any one time unload you fit meters. I would strongly recommend power schottky devices here.
I would also recommend using “Solar” batteries which are designed for this sort of thing. DO NOT use automotive batteries at either end. They will fail in a short time. Use deep cycle units that are built for float charging.
Do this under full load. Don’t forget that if the voltage happens to be too low the equipment may not be fully functional and the drop you measure will be meaningless. If this happens you might have to measure the resistance of the cable and calculate the expected drop. This will be difficult just with a DMM as the DMM lead resistance will be a factor. You would need a 4 wire resistance measuring system or pass a known current through the cable and measure the drop then calculate the resistance. Anyway if you have to do all this it probably means the cable is too small.
Cheers Bob
Add on.
A low voltage shut down device on each 24V source will save a battery over discharging and damage (read destruction).
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My NBN drops out after approx. 20 minutes after a power outage.
Hi Peter
If it is locally powered (at your place) and has a back up battery it is probably running out of grunt. I don’t think these batteries are very large and this could be normal.
Cheers Bob
Hey Peter,
From what I could find, it seems like NBN expects their batteries to keep running after a power outage for around 5 hours.
Battery back-up information | nbn.
It may be worthwhile looking into replacing this battery or otherwise diagnosing why its only lasting 20 minutes as its expected to last a fair bit longer than that. Maybe even looking at a higher capacity option?
Hope this helps.
Sam
Talk with your NBN provider, as there maybe warranty over the faulty battery.
additionally it might be their responsibility to remedy because it was initially supplied with the NBN service
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Sorry guys,
I neglected to mention I have NBN over copper 
, but it works great for us.
It’s the box on the street than only lasts approx. 20 mins. 
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Hi Peter
Well that does make a difference. Not much you are going to be able to do about that except complain bitterly to the correct ears. That is if you can get those ears to listen. They may suffer from selective deafness.
Cheers Bob
After that little fiasco I wonder how 
David61301 is getting on with his project.
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