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Old 04-24-2012, 4:40 PM
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Default Repeater emergency back-up battery

Hello all,

I have a Vertex VXR-7000 UHF Repeater operating on GMRS. I am wanting to install an emergency back-up battery for it.

Can i use any regular car battery? Or is there a certain type of battery i should use?


Thanks in advance for the help!
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Old 04-24-2012, 4:57 PM
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A car battery will work, but they are designed to provide a lot of current really quick, like for spinning a starter. They are not designed for doing long, slow, low level current draws, although they will work.
You may run into issues with the life span of the battery using it in that manner. If you've got a spare car battery sitting around, you can use that.

If you were going to be purchasing a new battery for your repeater, you'd want to look at either a gel cell type battery or a deep cycle battery. We've had good luck with the Optima deep cycle "blue top" batteries on some of our smaller systems. On some of our larger systems, we are using large gel cell batteries in parallel to give us the run time we need.

Make sure, no matter which battery you choose, that you look at the manufacturers suggested float voltage and adjust your repeater power supply (or whatever runs your system) to that voltage. Too high a voltage will damage your battery, too low will not charge it sufficiently.
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Old 04-24-2012, 5:04 PM
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Quote:
Originally Posted by WQOC472 View Post
Hello all,

I have a Vertex VXR-7000 UHF Repeater operating on GMRS. I am wanting to install an emergency back-up battery for it.

Can i use any regular car battery? Or is there a certain type of battery i should use?


Thanks in advance for the help!

I think part of the answer depends on what your planning on using to charge the battery and also on the exact type of battery you plan on using.

I have used a deep cycle marine battery for a number of repeater applications like yours. They seem to survive better than the common automotive battery. I also get the largest size I can. In most cases, it is the bus or truck type battery that takes two men and a boy to move. It is large and I think they call it a D8 size. They weigh in close to 100 pounds and are about 2 feet long.

The larger battery allows for several days operations of the repeater that is running 100 watts output. If your power is less, then it will last longer. Just remember that depending on the charger, it could take 2 to 5 days to bring the battery back to full charge.

Your charger should also have some sort of diode isolation so it is not tied directly to the radio power supply. This way you can use a maintenance type charger to recharge and maintain the battery and not boil it dry. These chargers are not cheap, but they work well.

You can take a look at KUSMAL for an idea on the chargers.

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Old 04-24-2012, 5:08 PM
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I will be using the internal charger within the VXR-7000 repeater to keep the battery topped off during normal operation in AC Mode.
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Old 04-24-2012, 5:20 PM
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Enersys SBS C11F are what we have started using at our sites. 4 of them will sit side by side inside a 19" equipment rack. You can order the SC11-U shelf for the 19" racks that hold them nicely.
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Old 04-24-2012, 5:30 PM
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There are several types of lead/acid batteries, some designed for service as engine starting batteries as mmckenna says. Others for low-maintenance requirements like gel-cells and depleted electrolytic. Then there are the type designed for deep cycle service like trolling motors and golf carts. Each has it's own advantages and disadvantages.

If your repeater is installed in an area that is hard to get too then some type of low-maintenance battery with a tightly controlled charger is what you need. If it is where you can get to it easily then a deep cycle battery might last longer. A car battery would be a poor third choice.

Because it will be a power source for hopefully short power outages, it will be in the circuit all the time. You will need to set your charger to the high end of the float voltage range, about 13.6 to 13.8 volts. Otherwise your battery won't be completely recharged after a power outage. But at that float voltage, you will have to add water from time to time. Car batteries are sealed so you can't add water to them, their service life is going to be pretty short. Low-maintenance batteries have the ability to recombine the hydrogen and oxygen to replace the water so their life will be reasonable long. Deep cycle batteries will last a very long time if taken care of properly. Minimize the number of charge/discharge cycles they are subjected to and keep the electrolytic level above the plates and you could get 20 years of service out of them.

There is another option on float voltage settings. Set the float voltage to the low end, around 13.2v. This will minimize gassing of the electrolytic and you will only have to add water about once a year. But you will need to visit the repeater after every power outage and crank up the voltage to the equalize range of 14.4v until the battery is completely recharged and then drop it back.
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Old 04-24-2012, 6:25 PM
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A good option would be golf cart batteries.
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Old 04-24-2012, 6:45 PM
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Will any of these work?

Walmart.com: EverStart Maxx Group Size 29 Marine Battery: Automotive

Walmart.com: EverStart Maxx Group Size 29 Marine Battery: Automotive
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Old 04-24-2012, 7:35 PM
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I would rate those better than a automotive starting battery, but below a gel cell type battery. They will work.

While it does say they are maintenance free, all that means is you can't add water to them. They can still off gas hydrogen when rapidly charged so ventilation is important.

To bad you weren't local. I've got our field techs out replacing batteries on our phone system. I've got 74 100 amp/hour gel cell batteries coming off line that still have some life left in them. The local amateur operators usually grab them. They would be perfect for repeater back up power.
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Old 04-24-2012, 8:57 PM
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1) You want to use a so-called "deep cycle" battery (or batteries; see below). My recommendation is the Group 31 sized 8G31DT made by East Penn. Note that gel cells can be installed in occupied spaces; flooded cell lead acid batteries should not be.

2) Your battery (or bank of batteries wired in parallel) should be sized in two ways: for max current draw and for max energy withdrawal before recharging.

3) Max current draw (in amps) should not exceed 5% of nominal battery rating in Amp-Hours. (The 8G31DT is rated at a nominal 96 AH.) So figure out what your average current draw is and multiply that by 20. If the result is <100 AH one 8G31DT; if between 100 and 200 AH, two batteries in parallel; and so forth. (The usual rule of thumb is to assume a 95-5-5 (squelched receive-unsquelched receive-transmit) duty cycle. So figure out system's current draw squelched and multiply by .95; figure out unsquelched current draw and multiply by .05; figure out current draw on transmit and multiply by .05; add all three values and multiply by 20. This is the minimum size of the required bank in AH.)

4) Max energy draw from the bank should not exceed 50% of nominal capacity before being recharged. Using the average draw calculated above and multiply by the number of hours the system has to run on batteries and then multiply by two. This is the minimum size of the required bank in AH.

5) Don't scrimp on the charger. You want a multiple stage charger that is also capable of true zero current float stage. I'd recommend a Tru-Charge, sized (in amps) at 15-25% of the resultant bank size (in AH).

6) When you install this type of power supply, the radio is connected to the batteries and works on 12VDC. Charger is also connected to the batteries and left on. While AC is available, batteries will remain at full charge and load will be carried by the charger.

7) For what it is worth, I run Quantar stations (100W) on two or three 8G31DT batteries. Since Quantar requires 110VAC, these batteries are wired to a device called Heart Interface, which combines a 50A charger, a 1 KW inverter, and a fast (<18 msec) transfer switch. Primary function is to keep the Quantars from rebooting while the generator starts, stabilizes, and accepts load, but design spec was to carry Quantar for two hours (long enough if generator fails to get DPW up to station with a skid mount genset). In tests, system has exceeded the design basis easily. Total cost under $1,400.

4) The
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Old 04-24-2012, 9:30 PM
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Quote:
Originally Posted by mmckenna View Post
Enersys SBS C11F are what we have started using at our sites. 4 of them will sit side by side inside a 19" equipment rack. You can order the SC11-U shelf for the 19" racks that hold them nicely.
Powersafe SBS 190F's are nice as well and have the same form factor as the C11's.
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Old 04-24-2012, 10:56 PM
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Quote:
Will any of these work?

Walmart.com: EverStart Maxx Group Size 29 Marine Battery: Automotive

Walmart.com: EverStart Maxx Group Size 29 Marine Battery: Automotive
In a word, NO! 2 quick points -

1) I had the group 29. Kept it up nice with a conditioning charger. It up and died for no good reason after 14 mos. Walmart weaseled on the warranty.

2) I work part-time at Walmart. My battery was hardly the only one to be flaky. We get a lot of 'em back.

The Everstart Maxx is a fine and cheap short term solution but I don't really think you'd find it reliable for long term repeater use.

My $0.02 - YMMV
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Old 04-25-2012, 9:40 PM
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If not done properly, there could be disastrous results (not my batteries, but it did yak acid on my gear).
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Old 04-25-2012, 10:29 PM
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A Wal-Mart battery is last the last battery you'll ever have to buy, I've never had one make through the free replacement period.
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Old 05-17-2012, 7:53 PM
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I've got a 100w Quantar that has two deep-cycle batteries (not Group 8 sized, but bigger than a normal battery) in series as the 24v battery back-up to keep it alive long enough for the genset to come online. The guy who used to maintain the site had two little motorcycle-sized batteries on it which were long since dead.

Luckily the power only drops at this site once or twice a summer during storms, so the Q's internal charging circuit so far has been able to maintain the new batteries. I definitely think this would not be the case if the batteries were used more often.
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Old 05-18-2012, 1:47 PM
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Luckily the power only drops at this site once or twice a summer during storms, so the Q's internal charging circuit so far has been able to maintain the new batteries. I definitely think this would not be the case if the batteries were used more often.
My site is about the same way, The last time we lost power was last April during some severe weather. But this repeater's primary use is for.... yes, severe weather. So... when the power goes out, we need it up and running!
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Old 05-19-2012, 1:49 PM
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You need to get the right battery for the application. Automotive batteries are intended for deep cycle loads that vehicles require on startup and won't be the best thing to put on a repeater. Check with a local battery deal for some Power Sonic batteries and put a few more in parallel to get the amount of time you want the repeater to run without power. Something like this would be best:

Power-Sonic PS-1270 12V/7AH Sealed Lead Acid Battery w/ F1 Terminal

My experience with Power Sonic batteries has been good and I would recommend them. My opinion is that nothing will last forever, so expect to replace any backup battery system every 3-5 years to keep it reliable.
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Old 05-19-2012, 7:58 PM
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You need to get the right battery for the application. Automotive batteries are intended for deep cycle loads that vehicles require on startup and won't be the best thing to put on a repeater. Check with a local battery deal for some Power Sonic batteries and put a few more in parallel to get the amount of time you want the repeater to run without power. Something like this would be best:

Power-Sonic PS-1270 12V/7AH Sealed Lead Acid Battery w/ F1 Terminal

My experience with Power Sonic batteries has been good and I would recommend them. My opinion is that nothing will last forever, so expect to replace any backup battery system every 3-5 years to keep it reliable.

Those are the same size used in most burglar alarm panels; definitely not enough Amp-hours to run a repeater (unless it never transmits) even if you put 5 in parallel. For $100 you could get a really decent deep cycle battery. (Not automotive)
Also if you ever get a chance, hold a Power-Sonic in one hand and a Yuasa battery of the same rating in the other and it will be obvious why the Yuasa will always last a few years longer even in a burglar alarm---and they price out about the same. They are both made in china though
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Old 05-20-2012, 12:19 PM
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Right...I just did a quick Google search for one so that they could see what the PowerSonic batteries look like. That is not intended to be an example of a model to use for sure...
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Old 05-20-2012, 11:01 PM
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Right...I just did a quick Google search for one so that they could see what the PowerSonic batteries look like. That is not intended to be an example of a model to use for sure...
I Didn't mean to jump on your back or anything, but I just bought a case of 8 Yuasa 7-12s last week and I noticed how heavy they were as compared to the Powersonics.
Usually they cost more than the powersonics, but ADI had them for $12.99 ea in case lots so I replaced 6 batteries in alarm panels that were showing battery failure & two for me. The Powersonics do not seem to last more than 3 years, but then again some of those sites can get kinda hot in the summer.
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