Battery Backup for repeaters

[K9EKG]

Hi everyone! I have a Relm Desktop repeater which operates on AC power mains, with no attached means for battery backup.  I need to find out what kind of battery backup setup would be feasible for my system.  It is a 25 watt model (50% duty cycle) and has a small group of users.  I would like it when the power goes out that I could still communicate with my wife and friends over the machine in a short period of time to coordinate activities.  As is may be, most all of the users on my machine are Firefighters, EMS and Police personnel, so we do quite a bit of coordination on my machine for things.  It was suggested that one of those UPC UPS stations like for computers would keep us on the air for up to 30 minutes, which might buy enough time to hook up a generator.  There is no listing for the consumption of my machine other than it uses 105 watts.  I can't even find the amperage level it consumes and even using Ohm's Law I cant find enough numbers to complete the equation.  If anyone has built a VHF/UHF repeater, I'd love to hear what you do for battery backup.

Thanks in advance

73

Chris, K9EKG

[KC7YRN]

Power is voltage times current. That should get you started.

Then there's power factor to think about, which you can measure with a $50 gadget from C. Crane or which you can ignore in favor of experimentation. Borrow a friend's computer UPS, start your regular practice net, pull the plug and see how long you run.

You'll want one of the big ones, of course, since the normal sizes are only big enough to keep the computer running while you frantically save all your files and do an orderly shutdown.

[KE4SKY]

For a 25w voice repeater I'd get a BCI Group 27 deep cycle gel or AGM battery, such as an Exide Prevailer or Johnson Controls Dynasty high-rate series UPS backup and box it with a Schumacher 1.5 amp automatic battery maintainer which you can get at any marine or RV store.  This is generally adequate to power a repeater remote receiver link site or packet digi for about 48 hours independent of the AC mains during power outages.

A good working rule of thumb which will keep you out of trouble most of the time is to plan one amp-hour of battery capacity for each watt of transmitter output, for each 12-hour operational period. This assumes an operating duty cycle of 20-25%  If your repeater isn't keyed up from somebody sitting on their mic or running it down with long-winded rag chews you should be good for a couple of days.

[KC7YRN]

Ed,

For a repeater like this guy's, which is AC-only, what kind of inverter would you use? Is the repeater likely to be able to live with a square wave or modified square wave coming in?

What voltage is it likely to be internally on the DC side of the repeater's power supply? Could a 12V system be spliced in?

Fred

[KI6LO]

One thing that I would suggest is that if the repeater is mounted in an environment that would expose any battery devices to extreme cold (less than 40 degF) for any duration, be careful for using gel cell batteries. In my experience, gel cells fall off very rapidly in cold climates when not insulated from exposure.

For your situation, I would research a quality true sine wave inverter with a suitable battery bank to power it with a charger system to keep the batteries up to snuff. Run the charger fulltime, draw power from the inverter / batteries to power the repeater. This way the system is isolated from the AC line continously so dropouts are not even noticed. The system could even be controlled via a set of voltage monitors and relays to switch off when the DC power drops to a preset level and back on when DC levels are up again (after AC is reapplied and batteries are charged). This can be accomplished without the use of computer interfacing or with it, but using a computer complicates the system and power requirements.

Good Luck,

Gene KI6LO

[KC8VWM]

Disconnect the internal battery of the UPS and connect the leads to an external marine trolling motor battery.

The UPS circuit will ensure the battery is at full capacity at all times and you will have extended operating time from a marine battery.

When purchasing a marine battery pay no attention to "cranking amps" ratings.  You are looking for longevity and that is rated in "amp hours or AH"
It is for this reason I recommend a "trolling" marine battery.

You might even consider connecting a solar panel for when "all else fails". I have much experience in solar energy distribution systems. Please indicate if I can be of any further assistance.

73
Charles - KC8VWM


 

[KC8VWM]

I seemed to have missed the most important point.

Not only will the UPS circuit ensure the battery is charged at full capacity at all times automatically, but, you will also notice that you will need no additional inverter, or AC switching system when the power goes out. UPS backups have all this circuitry already built in.

A UPS seamlessly keep you on the air automatically without any user intervention required. This is useful for repeaters that are not attended to on an individual 24/7 basis at a remote repeater site location.

The marine battery suggested for modification is much larger in capacity than the original battery that is supplied with the UPS thus, provides for much longer operational time. It is also possible to combine batteries in a bank arrangement creating a reservoir of energy supply for your equipment from a single UPS.

This is a very cost effective alternative to AC switches, external inverter systems that are many more times expensive than cheap computer UPS backups.

Modified UPS backup systems as suggested also provide very clean AC sine waves as they are initially intended for sensitive computer equipment. They switch from AC to DC power sources without any spikes or negative effects on the equipment.

73

Charles - KC8VWM

[KC8VWM]

Another battery I would highly recommend is the same ones they use in floor washing machines. These riding floor cleaning machines are what they clean grocery store chain floors with on any given night shift.  

They contain batteries that have excellent AH ratings.
Golf cart (non gel cel) batteries are also very good.

I have used gel cel batteries in the past with my solar electric systems and found that they can be very problematic. Once they lose power below a certain voltage they can no longer be recharged. Once a gel cell battery is depleted you can basically kiss it goodbye as there is no going back to 13.8 volts ever again.

I lost several of them this way and they are not cheap to replace. They might not spill and not freeze in colder climates but if they dont recover from a discharge and supply electric power in times of need, what good are they anyways?

I reverted back to the basics and now I stick with acid type batteries. At least if they freeze, they will thaw out and provide power.

73
KC8VWM

[KI6LO]

>......At least if they freeze, they will thaw out and provide power.......

My experience is if the freeze, write 'em off and replace since they won't be 100% after that.

Gene KI6LO

[KG6AMW]

Take a look at Power Sonic Batteries.  The make an excellent AGM battery. (http://www.power-sonic.com)

KG6AMW

[K1CJS]

""Disconnect the internal battery of the UPS and connect the leads to an external marine trolling motor battery.
The UPS circuit will ensure the battery is at full capacity at all times and you will have extended operating time from a marine battery.""

Forgive me if I'm wrong, but the continuous running of a small UPS to provide power in this manner would possibly cause the ups to fry itself--there is no fan in these units to draw off excess heat.  They are made to operate for just the few minutes it would take to shut down your computer.

Again, if you're speaking of a larger unit that has this feature, fine!  But those smaller units just won't fill the bill.

[KE4SKY]

I'm not familiar with the Relm desktop, but our club used to have a couple of similar Ritrons, which used an AC supply, but the equipment itself ran on 13.8VDC and just used the AC to power a transformer.  It may be a simple matter to connect it to an external battery and some models did have a "fail to battery" mode on them.

[K9KJM]

I agree with KE4SKY.
 All of the little repeaters like this that I have seen really run on 12 volts DC and just have a small built in AC supply. Dig into the repeater and see where to supply the 12 volts, And run it directly from
the Marine deep cycle battery.
A fully automatic 10 amp charger that drops to no charge when the battery is fully charged is needed.
(I use Schumacher)
We have been doing this for many years at remote repeater sites with great results.
The KISS formula (Keep it simple........)
Running a UPS to provide AC to run the AC power supply inside the repeater that again converts it to 12 volts is just two wasted steps..........

[K3DWW]

I have a repeater with a 40 watt transmitter and a 25 watt link transceiver in a county-owned building that has an auto-start (well, usually (c:) motor generator. After much fiddling with batteries and much trouble with chargers and inverters I took the easy out and installed a big APC UPS. Works great, keeping the repeater and link up thru the several minute interval til the generator stabilizes. 73, K3DWW