Custom DC UPS, bypass AC-DC stage & Support Automatic safe shutdown

Home Tech Electronics & DIY Projects
81

Random video i came across

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82

That is rubbish. To charge the batteries and discharge there is more loss than running from AC

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83

I think in the video the guy is having massive blackouts, so to extend the run time of the PC on the batteries he skipped AC-DC computer PSU.

84

I found it. It’s Meanwell DRS-240-12.

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This one has all the features. 20A seems to be the max current. If you are running load of 10A, remaining 10A will be used for charging.

The charging current is also adjustable.

Has tons of features, can tell if load is running on battery or main power, custom charge curve (with external meanwell programmar) and stuff like that over ModBus/CanBus.

It has relay contacts that close and open ON following

  • AC Fail
  • DC Okay
  • Battery Low
  • Charger Fail

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With the sweet sweet price including importing to India.

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Totally unaffordable and way too industrial for us, back to DIY route.

2 Likes
85

Heisen, Inspired by this thread, I went ahead and completed a long pending set of projects which required somme minor DIY but minimal of “getting hands really dirty”

Most of the elements compiled below have been done after fair amount of research and validation and I won’t go into the deets right away but feel free to ask if needed..
Hopefully some of it may come in handy for others

Setup 1

  1. DC-DC : For my home server(s) : proxmox (20-25W) , NAS (20-25 W) and opnsense router (15-20W)

a) Stable max Load at 12V - approx 4A
b) Stable load at 19V (proxmox is a Lenovo p330) : 2A

Parts:

  1. Mean well 10A 12 V SMPS - 1500/-

  2. Industrial DC DC converters from genergy.in : 8-40V → 12V (10A) and 10-14V to 19V (6A) : Approx 3.5K

  3. 6AH 4S (12.8V) lifepo4 battery from robu: 1.5K

  4. low voltage cutoff module (XH-M609) : 200/-

  5. Blade fuse sockets, wiring and misc - 100/-

  • Meanwell unit is set to 14.2V output. I could have used a 15V SMPS set to 14.6-14.8V for 100% charge for the lifpo4 bms but I intentionally used this here as I had one spare and I don’t need 100% charge for this setup. 80-90% at 14.2V is more than enough
  • I intentionally did not add a relay changeover given the low loads and to minimize any chances of tripping

removing power at smps keeps the battery o/p stable at around 13.6-13.7V and a net draw of about 5-5.5A

Setup 2
This is for a unmanned house in another location where I need to keep a load balancer router, 2 ISP units (12v) plus 3X PoE APs and 3X PoE cameras (48V) plus a RPi and a network controller (5V) powered up . Max power failures are 1 hour but can have rare longer outages also.

setup is Same as above but with

  1. 15V Meanwell amps set to 14.6V for 100% charge (1500/-)
  2. 15AH lifepo4 pack (2.8K)
  3. 48 V and 5V DC DC SMPS (about 2K total)
  4. XH-M609, fuses and misc - 400/-

And since I was knee deep into it anyway, I decided to ask the lifepo4 supplier to send across 4x high star 100AH cells and a 100A Daly BMS with UART which will be used for an inverter when I can find the time

2 Likes
86

So around 1 hour runtime on this. Hopefully the power won’t be out any longer.

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Cost of 100ah cells and bms?
Also isnt JK ones better than daly?

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This one is for my current place where the max outage is 2 mins (dg backup)
Outages can be longer at the other place for which I got 15ah

Fwiw, it’s actually very straightforward to build own packs also.. although this time I chose to use prebuilt for the cylindricals (minimal price delta) and diy for the larger prismatic

1 Like