DC glory

[mlow]

Hi guys,

I've recently discovered the benefits to running sites purely on DC, and am now looking to design a template for powering all of our on-grid sites with a pair of 12V AGM batteries in series. The theoretical run time you can achieve running off just a couple of small AGM batteries is quite impressive. A big beefy liebert 1KVA $1k UPS would power a medium sized site (consuming under 100W) for under 2 hours.

Here's what I'm currently thinking..
For small sites with 3 Rocket APs (worst-case 10 watts each), a AirFiber-X backhaul (worst-case 15 watts), a WS-250-DC and mikrotik router (worst-case 20 watts combined), a total power consumption 65W, I could get 20 hours of run time if the grid goes out with the following equipment:

• 2x 12v 55AH AGM battery in series for 55AH @ 24V (for a total of approx. 1320 watt-hours) ($320 CDN)
• 1x DROK 600W 12-60V input 12-80V output DC-DC converter for regulated 48v to power WS-250-DC. It's good to power up to 240W with 24V input, more than we'll ever draw at a site. (not sure what conversion efficiency will be) ($40 CDN)
• 1x NOCO G7200 24v battery charger/maintainer/reconditioner ($110 CDN)

For a total of $470 CDN and (1320 watt-hours / 65 watts) = 20.3 hours run time, this approach is far better than running off of any AC UPS I've found so far.

Just thought I'd share why I'm excited for fully DC sites in our nework. 20 hours is long enough in most cases for the grid to come back on, and we could probably squeeze more time out of the batteries and the 12v input converter. For larger sites, we could use higher-capacity batteries, with the goal of reaching a minimum 24-hours runtime when the grid goes off.

If you guys have any other suggestions, I'd love to hear them :)

[sirhc]

Hi guys,

[*]1x DROK 600W 12-60V input 12-80V output DC-DC converter for regulated 48v to power WS-250-DC. It's good to power up to 240W with

This NOT needed and in fact you do not want to use it.

The WS-12-250-DC unit will accept 9-60V DC input and still power 24V and 48V devices.

The WS-12-DC unit needs conditioned 48V but the WS-12-250-DC does all the conditioning for you and you always want to hook the WS-12-250-DC directly to the battery bank and the WS-12-250-DC will provide 250 watts of power with 24V input.

These are 2 different models:
WS-12-DC expects 48V +/- conditioned input

WS-12-250-DC is a smart DC power supply that will work on 9-60V DC input and report on battery health.

The WS-12-250-DC will monitor and report your battery voltage so why clogg things up with a converter now the switch can not act and report on battery voltage dropping.

[mlow]

The reason I chose to get the converter and the "dumb dc" switch was mostly the $60 savings and the size difference in the switch (though the converter will take up its own space). I imagined that the WS-12-250-DC "smart DC" switch would have a conversion efficiency quite close to that of the DROK converter. If it's massively more efficient, I'll probably reconsider. Still, I plan to get a DROK converter to do some efficiency tests (and cuz I want one for my bench).

The price increase for the extra voltage range seemed hard to justify for me..

[sirhc]

The other advantage of the SMART DC is the ability to shed ports to save battery based on battery level. Also the SMART DC give you the ability to shut down and wake up ports based on time.

Yes the efficacy of the SMART DC is darn good, better then most other devices.

Also the smart DC will send alerts based on battery levels and allow you to run the batteries down further in an emergency. If you hook the (2) 12V batteries in series to get 24V the SMART unit will operate down to 9V which is 4.5V per battery which is much lower of a DOD than any other device will allow.

[mlow]

Those are things I hadn't considered.. would need a separate networked voltmeter when using the converter in order to monitor the bank voltage. Hopefully I never have to bring the batteries anywhere near 6V per, which is what the converter would allow for.. but cool that we could run it off some 9v alkalines from the hardware store in an emergency

Thanks for the info sirhc,
Have you guys done any tests to see what the efficiency of conversion is running at different loads with different voltage inputs? I could more closely calculate runtime with that info.

[sirhc]

READ THIS POST viewtopic.php?f=6&t=619&hilit=100+watts&start=30#p6582

[mlow]

Thank you!

[rockhead]

If NOCO battery charger is one they sell at Canadian Tire I'd sleep better with a Samlex America charger, they are brilliant. I've got one site 'at the end of the line' for power that the landlord warned me they had fried many UPS's. It has been hassle free for five plus years.

[mlow]

Thanks for the tip, we have a 24V Samlex charger at a fully off-grid site, and no complaints. Though it's only been in use for a year now.

[maxbb]

I have a WS-12-250-DC that just arrived for beta test. I want to deploy on most of our towers. What configuration are people using using for battery/ps combo on dc units?