Backup power

[Beebe]

I just had an idea and I'm not sure if it will work... All our sites have mains power with an APC UPS for power backup. I realize it's inefficient to drive the power through an inverter to get it from the 24v DC that the batteries in the UPS output up to 110v AC, only to power the transformer that transforms back into 24v DC to drive a war board. Seems crazy to go through all that when it's the right power in the first place.

So what if I added some connectors directly onto the battery terminals to get 24v out directly from the battery straight into the WAR board?

Has anyone done this? Anything to look out for? What about when the batterys are being charged by the UPS, would I still get clean 24v dc out of it?

Thanks,
Roger

[kbldawg]

I think there a some folks doing this. I too have been wanting to optimize our power systems and agree, coming strait out of the batteries makes more sense to me than anything else. I looked at doing this a while back and got diverted.

There was some discussion about this on the ISP-Wireless list some time back.

You'll need


A Smart Charger so that the batteries are only charged when they need to be. This will prolong the life of your batteries and keep them topped off properly.
Some sort of protection between your batteries and your equipment. Not sure about this. I don't know if a simple in-line fuse is in order or something more extensive.
A vented battery enclosure.
Decent batteriesanything else?

A setup like this I bet would run close to a week without power.

[luke541]

I do pretty much exactly what you listed kbldawg.

I have 14 remote sites now that run off 4, 6v golf cart batteries "$180.00 each", more if you don't have a core to exchange.

One of the sites runs 4, 2 port wars for about 6 days before it draws down to about 9v and then everything shuts down within about 1 hour. I use 3, 45w solar array's to keep a site with 4 boards going without worry.

Clever thing a guy at a local radio shop showed me and I duplicated was an old pager with a relay attached to it that allows me to make a phone call and with the right code switch the site over to emergency power "a small 24v battery" that will keep things going long enough for me to get to the site. Pager service only 3.99 pretty inexpensive security blanket for fairly remote sites.

[nelson05]

Would you mind sharing a little more information about the equipment used and the approximate costs of your pager setup? Sounds like a very cool system!

[Beebe]

Can anyone confirm whether my idea will or will not work, to re-use the same UPS, but just take out the inverter and hook straight onto the batteries?

It'd save a bunch of money over just ripping out the UPS and building a battery setup on each tower. It seems like I already have everything I need, I'm just using it inefficiently.

I just don't know if hooking straight onto the batterys will be ok while the batterys are being charged.

Thanks,
Roger

[kbldawg]

Sorry for diverting the thread Beebe, I misread your post and was thinking you wanted insight into doing things the other way.

I'll shut up now.

[tog]

Theoretically that would work, Beebe, but it certainly is "hackish" and unsanctioned by APC. I've never done it so I can't say for sure whether it's advisable or not.

It could be a pretty nice setup, though, considering how evolved the battery monitoring/charging part of a normal SmartUPS is. If it can deal with the batteries "mysteriously" being drained without the load going through the UPS inverter circuitry... it really wouldn't be much different from our setups where we attach a smart charger and our load to the battery posts.

[Stratolinks]

The APC units have a smart batetry charger and monitoring circuit, but is it designed to work as a power supply? I don't know and I'm not sure I would trust it.

All our WRAP board sites have a 12 Gel battery directly connected to the loads (fused first) and have an Omron industrial DC power supply (switch mode regulated 13.8V at 5 Amps) connected to the battery via a blocking diode. Once it is connected we adjust the trimmer on the power supply to get a steady 13.75 volts at the battery. This provides a stady standby voltage to the gel battery to keep it charged and ready for any power outages. I don't have the info handy but a flooded battery requires a lower standby voltage or you will boil off all the water.

These Omron power supplies are made for control systems in factory environments that can have lots of AC line surges and sags and they keep the output very clean. 3 of our sites that have these supplies have been able to exceed the 500days of uptime. And yes Omron has 24 volt versions of these 200W DIN rail mount supplies too.

[Beebe]

Sorry for diverting the thread Beebe, I misread your post and was thinking you wanted insight into doing things the other way.

I'll shut up now.

Please don't - I appreciate any input and ideas, I'm just interested in saving some $$ too if it's possible without compromising results. It's going to take a while to get all the sites upgraded too, would be a lot quicker to 'hack' it if it works.

Thanks for your input everyone,
Roger

[palmczak]

read this thread.

http://forums.star-os.com/showthread.php?t=5536&highlight=battery

It is about solar but much applies.

I don't spend the extra for smart chargers since there is a voltage threshold that as long as you don't go above you won't ruin your batteries. (good power supplies like Astron or Iota allow you to adjust the output voltage) Since they are fully charged 99% of the time, it does not pay for smart charging (IMHO) I have several sites I maintain that have batteries 7-10yrs old that support 2 way radio gear. At 10 years we change them weather they test OK or not but most will sustain a load of 75-80% of rating.

I don't run any sites (except subscribers) from AC. Batteries do a fabulous job of keeping things running.

Depending on how many radios you have normal deep cycle batts will run a few WAR4's for several days if fully charged. Sams club or Costsco generally have good pricing.


Joe

[oscarBravo]

Can anyone confirm whether my idea will or will not work, to re-use the same UPS, but just take out the inverter and hook straight onto the batteries? It should. Most of our sites are powered by alarm power supplies, which float-charge 17Ah 12v lead-acid batteries at 13.6v. They have separate terminals for connecting the batteries and the load, but they're actually connected together.

I've hacked APC UPSs before, including hooking one up to two 110Ah deep-cycle RV batteries (via a circuit breaker in lieu of a fuse) to greatly extend runtime. Done carefully, it shouldn't pose any problems, but forget about your APC warranty.

[lonnie]

The 1,000 Watt APC units use 2x12V batteries for 24V, which is perfect for our CPE and Dual boards. The 48V Metro can use the AC power to drive a 48V POE.

[pwmaclean]

So, what are all the "northern" people using? it get's down to -40c here sometimes. and I dont have heated shacks at all the tower sites. would I still go with a deepcycle battery, charge controller and inverter?
Also, I dont want to have to switch over to battery. Can I just use the power off the battery and charge it at the same time?

[DrLove73]

You could always hire some Santa Clause elf's to run inside the hamster wheel filling the batteries and heating the units :p

[Stratolinks]

Absolutely. ALL our sites are directly powered from the battery. Then a properly set, current limited power supply is connected to the battery to charge it and run the equipment as long as mains power is on. When the AC power fails, the load simply sees a small drop in the supply voltage. When AC power returns, the battery voltage climbs back up to the set point. Make sure you use a gel type battery otherwise you will need a bigger charger in very cold weather. If you are using flooded batteries, you could place the batteries inside an insulated enclosure, and they would likely keep above freezing temperatures just with the small charge current. I don't recall the freezing point of battery acid, but is is rather low. If a flooded battery gets discharged too much in cold weather they will freeze.


So, what are all the "northern" people using? it get's down to -40c here sometimes. and I dont have heated shacks at all the tower sites. would I still go with a deepcycle battery, charge controller and inverter?
Also, I dont want to have to switch over to battery. Can I just use the power off the battery and charge it at the same time?

[mrmike]

If you have access to AC, wrap the batteries with some heat trace first, then some insulation.... toasty batteries are friendly batteries.

[Stratolinks]

While a battery's capacity increases as temperature rises, there are other factors that come into play as well. Well, let's clarify that a little further: with flooded (aka wet cell) batteries there are other factors, much less so with gel or AGM batteries.

With flooded batteries the off-gassing and evaporation increase quickly as temperature rises. With a constant voltage charge the battery will boil at temperatures in the low 30C range, even with a low charge current. Flooded batteries therefore must have battery temperature compensation built in the charge controller to prevent battery damage. I recall reading a very in depth article about batteries that suggested the best temperature to keep batteries at was, if I recall correctly, was between 3 and 5 C. Cool enough to be able to keep a full charge voltage without boiling away the acid, and warm enough to not worry about freezing. The article went into a lot of other technical details that I do not recall precisely. If I recall correctly the paper was put together by one of the well known US universities. If you want to look it up, and find it on the net feel free to correct any of my recollections.

Here are a few quick links that I found on the subject:
http://batteryuniversity.com
http://www.windsun.com (http://www.windsun.com/Batteries/Battery_FAQ.htm#Industrial%20deep%20cycle%20batter ies)

When discussing flooded batteries at a local industrial supplier the flooded battery they recommend was a quite large electric forklift battery. This battery is the same footprint as a group 27 automotive battery, but about 2.5 times taller, and is 6 Volt, and I think 400+AH rated (read this as BIG and HEAVY). This battery has the thickest plate material of any flooded battery and can handle deep discharge cycles quite well. The expected life in electric forklift use is 10 to 20 years with monthly maintenance. The maintenance is cleaning battery terminals and topping up the cells with distilled water. NEVER use bottled drinking water or tap water due to the other chemicals and minerals found in it. They highly recommend the use of a "hydration" cap to prevent the loss of the liquid from the batteries.

If you want to try the leading edge of short term backup power...
http://ept.dgtlpub.com/2008/2008-05-31/home.php?page_view=38
Take a look at the super capacitors in the upper right corner.

In my opinion, I would not use a flooded battery for a remote site that you don't want to visit regularly. I would recommend an AGM type battery with a good quality regulated charger. If you are in a northern climate, keeping the batteries warmed will increase their run time if ever needed, although it may not make a huge difference if the load is small enough. Flooded batteries could be used in locations where you have regular maintenance capability, but if you don't maintain them properly you WILL replace them much sooner than you would otherwise have to.

[pwmaclean]

Where would a dude get a 24v or 48v automatic trickle charger in north america (canada preferrably)?