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richinuk
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Advice / thoughts on my DC UPS design please

Sun Oct 26, 2014 7:10 am

Hi all,

I've been trying to put together a battery backup for our mains powered AP's. I'm by no-means an expert on this topic, so would welcome any feedback on my proposed solution.
UPS design.png
I've attempted doing this with a solar charge controller connected to a DC power supply, but found it didn't work too well. I've also attempted with the Tycon SCPOE, but found it had issues powering more than 1 x RB device at power-on.

So in essence, the battery is permanently connected to an AGM battery charger (CTEK MXS 5) which has multiple charge phases. The load is directly connected to the battery terminals through a regulated 24v DC/DC converter. I intend to put some form of low voltage disconnect between the battery and the DC-DC converter and possibly a RB912 before the DC/DC for battery monitoring purposes.

I have this running on the bench and seems to be working well, but unsure about running the load directly off the battery. Plus other stuff I'm overlooking!

Feedback welcome.

Thanks.
Richard
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jarda
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Re: Advice / thoughts on my DC UPS design please

Sun Oct 26, 2014 8:04 am

Looks correct but I would go with two batteries in series with 24v charger and without converter. There are also meanwell power supplies that do all the job with batteries connected.
 
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Re: Advice / thoughts on my DC UPS design please

Sun Oct 26, 2014 3:17 pm

A much easier solution with less components and battery failover is to use Meanwell SMPS
http://www.meanwell.com/webapp/product/ ... prod=AD-55
or
http://www.meanwell.com/webapp/product/ ... rod=AD-155
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richinuk
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Re: Advice / thoughts on my DC UPS design please

Mon Oct 27, 2014 12:31 am

Hey jarda/roadie, thanks for the meanwell reference. Have you used these devices and have any experience to share? I couldn't find any details about how they charge the batteries looking at their data sheets. Most chargers I've reviewed are at least 3 stage chargers with various protection against charging bad batteries etc. In the absence of such protection would the battery fuse be sufficient?

Thanks,
Rich
 
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Re: Advice / thoughts on my DC UPS design please

Mon Oct 27, 2014 2:02 pm

Hey jarda/roadie, thanks for the meanwell reference. Have you used these devices and have any experience to share? I couldn't find any details about how they charge the batteries looking at their data sheets. Most chargers I've reviewed are at least 3 stage chargers with various protection against charging bad batteries etc. In the absence of such protection would the battery fuse be sufficient?

Thanks,
Rich
I use Meanwell AD- 155 with 2 X 12V 110Ah batteries deep cycle leisure batteries, the float charge has to be carefully selected as cutout for Mikrotik is 28.3volts, so we use 27.2Volts, the charge current is i think about 500mA and once batteries fall below 19.2 volts total the unit disconnects the supply to Mikrotik, this to prevent batteries from being fully
discharged,

At other sites we use a battery bank 4 X 12V 110aH (24V - 220Ah) batteries deep cycle leisure batteries, which power the equipment direct and use a float charger to keep the battery bank charged, this way we have the cleanest DC supply to the equipment and has worked flawlessly for several years

Some very good info I received on this topic back in 2010?

http://forum.mikrotik.com/viewtopic.php ... deep+cycle

http://en.wikipedia.org/wiki/Float_voltage
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richinuk
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Re: Advice / thoughts on my DC UPS design please

Tue Oct 28, 2014 1:47 am

Hi n21roadie. Nice write up. I like the approach of using a float charger - the meanwell looks good but I don't feel that it has the right capabilities to charge batteries from flat.

What float charger are you using? I'm using a ctek one right now. Fantastic device but I'm thinking its too smart and the 1.2a load of my ap's may be confusing its logic! Over the past 24 hrs the battery voltage has dropped to 12.5v very gradually despite around 1.2a coming from the charger.

Rich
 
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Re: Advice / thoughts on my DC UPS design please

Sat Nov 08, 2014 6:34 am

Hi Roadie / Jarda,

Thanks to your advice, I've had some success building my DC UPS in a compact form factor - exactly what I was hoping to achieve.
IMG_9051.JPG
IMG_9053.JPG
IMG_9054.JPG
This is all mounted on a backplate for a 300x300x150mm box.

The 1A circuit breaker will be replaced with a 2.5A (I just had the 1A to hand). I also will be adding a termination block with inbuilt switch between the PSU and the batteries so I can disconnect them. There's a 15A fuse between the PSU and the batteries, and another 15A between the PSU and the load. This is powering a RB260GSP and a RB912G-2HPnD. The RB260GSP will power the AP antennas and backhaul. The 2x9AH batteries will be upgraded to 12AH, although the 9AH configuration currently gives me around 16 hours of runtime of the before the batteries drop below 10.5v each (switch+2 SXT's).

Now to go do some load testing :)

Cheers guys,
Rich
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Re: Advice / thoughts on my DC UPS design please

Sat Nov 08, 2014 1:34 pm

I also recommend the AD-155B, i've been using it for almost two years now and never had a blackout because of it. Takes care of the charging of the bateries pretty well (or at least I think so).
I'm running it with 4 12V 120Ah gel batteries, on a tower with around 15 wireless devices (sxt-s, 911-s etc) and 2 rb2011 and the tested uptime without power is well beyond 12 hours (after 12h the mains power was resored :D). I measured the total 24V load to be around 2.8A. If there is a power-failure-protected site in my network, that's the one :D.
Referring to your setup, I also recommend using 2x12v series batteries power supply for mikrotik installations because it minimizes the losses through the POE cables and increases the efficiency.
I think the up-converter only lowers your efficiency there, as you can connect everything pretty safe between 10 and 28v, without further conversion losses.

Before the AD155B setup, i was using an APC UPS (running at 24v - 2x110Ah batteries) that powered a laptop power supply that was taking care of all mikrotik devices. I was doing that because that was before the RB2011-s. Instead, there was a cisco 3524 which needed 220v. Looking back at the electricity bills before we moved to the 24V setup, the power consumption was triple than now and the battery uptime was maximum 4 hours, using the same number of wireless devices.

An uptime test with a 12v setup and 24v setup (using the same number of batteries, but connected in series or parallel) would be interesting in your case.
 
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 10, 2014 8:33 am

Nice solution and pretty much battery run time. Congratulations. Will it have some casing?
 
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 10, 2014 11:30 am

Yep. Enclosed in a Bud Industries SNB box - 300x300mm. This one's 200mm deep, but it's designed to fit in the 150mm one to make it more aesthetic!
IMG_2382.jpg
I still need to fit the cable glands etc. Need to test heat. Currently there's no ventilation on the box, so it'll need some testing.

Rich
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 10, 2014 11:36 am

Nice solution and pretty much battery run time. Congratulations. Will it have some casing?
It currently has 2 x 12v 9Ah batteries. I'm doing a drain test and it's been running for 13 hours now with 2 x SXT, RB260GSP and a RB912 (as pictured). Batteries at 22.9v so still some way to go yet.

Rich
 
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 10, 2014 7:37 pm

Nice. No need for bigger batteries I guess.
 
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 10, 2014 8:04 pm

DId you manage to get it solar powered or does it pull power from mains? It would be really cool to set up nodes without plugging in to any main lines. You could set up a tower anywhere.
 
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Re: Advice / thoughts on my DC UPS design please

Tue Nov 11, 2014 8:51 am

You would need wind/solar combination at least and it should be really overkilling otherwise you can easily come out of battery. It would be expensive as the batteries would be aging faster and also bigger batteries would be needed.
 
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Re: Advice / thoughts on my DC UPS design please

Tue Nov 11, 2014 9:46 am

Nice. No need for bigger batteries I guess.
Yep, verdict in - 16.5hrs. I'll still upgrade to the 12AHr ones I think - the case has the space and it'll give me probably another 5 hours or so.
DId you manage to get it solar powered or does it pull power from mains? It would be really cool to set up nodes without plugging in to any main lines. You could set up a tower anywhere.
So initially I intended to use a solar charge controller and instead of a solar/wind power input I was going to use a 15v DC power supply (charging 12v batteries). The idea was that I could replace the 15v PSU with solar / wind power and the rest of the design stays the same. There are many guys doing exactly this type of setup for remote locations (with solar/wind). This almost worked except for two issues that were becoming a pain (and expensive) to resolve for a trial-and-error novice (mostly around the choice of PSU)! I had the Meanwell recommended and that has worked a charm, but completely changed the design.

But if you're looking for a solar / wind setup, yep this will work, but as Jarda says you'll need to spend a bit on batteries. The system will continually charge / discharge (day/night) thus cycling the batteries. The batteries should last for a couple thousand cycles as long as you budget for only using the top 20% of the battery (so I am told!). Others say 50%. Be prepared to spend a bit as the panels are also quite pricey.

Rich
 
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 09, 2015 11:57 am

Hey jarda/roadie, thanks for the meanwell reference. Have you used these devices and have any experience to share? I couldn't find any details about how they charge the batteries looking at their data sheets. Most chargers I've reviewed are at least 3 stage chargers with various protection against charging bad batteries etc. In the absence of such protection would the battery fuse be sufficient?

Thanks,
Rich
I use Meanwell AD- 155 with 2 X 12V 110Ah batteries deep cycle leisure batteries, the float charge has to be carefully selected as cutout for Mikrotik is 28.3volts, so we use 27.2Volts, the charge current is i think about 500mA and once batteries fall below 19.2 volts total the unit disconnects the supply to Mikrotik, this to prevent batteries from being fully
discharged,

At other sites we use a battery bank 4 X 12V 110aH (24V - 220Ah) batteries deep cycle leisure batteries, which power the equipment direct and use a float charger to keep the battery bank charged, this way we have the cleanest DC supply to the equipment and has worked flawlessly for several years

Some very good info I received on this topic back in 2010?

http://forum.mikrotik.com/viewtopic.php ... deep+cycle

http://en.wikipedia.org/wiki/Float_voltage
Hello n21roadie

Maybe this is a little bit old post, but i wanted to ask. Is the charging current of AD-155B enought for 2x110Ah??
If no. What are you using to charge the batteries?
What about PSC100B http://www.meanwell.com/mw_search/PSC-1 ... 0-spec.pdf
It has 1.25A charge current. What batteries can i connect with this current?

Thanks for sharing
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 09, 2015 2:39 pm


Hello n21roadie

Maybe this is a little bit old post, but i wanted to ask. Is the charging current of AD-155B enought for 2x110Ah??
If no. What are you using to charge the batteries?
What about PSC100B http://www.meanwell.com/mw_search/PSC-1 ... 0-spec.pdf
It has 1.25A charge current. What batteries can i connect with this current?

Thanks for sharing
Hi,

I am informed that battery cell damage can occur if using a charger which has a charge rate in excess of 20% of a battery current rating ( example 110Ah max charger is 22Ah!)

So it is not how many batteries you can connect but how long it takes to re-charge ?

The AD-155 series has a battery charge function and while it is very low, this is only a problem if you are encountering regular AC power outages, it may take the AD-155B many days to fully recharge the 2 X 110Ah batteries,

Another consideration is the cut off voltage of 20V (+/- 1v), this to prevent batteries from being fully discharged, so I am looking at 15% DC voltage drop before cut off !

For me I may upgrade to
http://www.meanwell.com/webapp/product/ ... od=PSC-160
Which will give 2A recharge
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 09, 2015 2:56 pm

N21roadie, thanks for the response.

I think that the charging current must have a low level too. Let's assume a charging current of 0.00001A. I don't think it will charge a let's say 60Ah/hour battery even for 10 years.

How are things going with the AD-155B and the two 2*110Ah batteries?
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Re: Advice / thoughts on my DC UPS design please

Mon Nov 09, 2015 4:16 pm

N21roadie, thanks for the response.

I think that the charging current must have a low level too. Let's assume a charging current of 0.00001A. I don't think it will charge a let's say 60Ah/hour battery even for 10 years.

How are things going with the AD-155B and the two 2*110Ah batteries?
There is now 4 X 110Ah batteries series/parallel for 24V @ 220Ah?

Since I started using Meanwell over 2 years, it has worked flawlessly and use them for almost all my sites,

Over a year ago I reckon, a nearby lighting strike sent high AC voltage to one site which blew the AC side of the PSU but yet it had switched over to the batteries so no interruption to service from that site!
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Re: Advice / thoughts on my DC UPS design please

Fri Dec 18, 2015 2:12 am

FWIW, I've been using the PSC-60B-C on smaller systems (9ahr) and it is working well (~4 months now). Not the 110+ah you're asking about, but just thought I'd mention that I've tried the PSC range with success.

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