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Author Topic: How to setup a deep cycle battery for power outage  (Read 6234 times)
K9FTB
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Posts: 26




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« on: May 03, 2001, 08:47:07 PM »

Hi fellow hams - I'm interested in using a deep cycle marine battery (12 volts) as a backup for my VHF / UHF radio's at home. Other than using an AC battery charger, does anyone have ideas on how to permanently setup the deep cycle battery to remain fully charged, and always ready in case of a power failure? I'd prefer to have the supply voltage to the radios switch automatically during a power failure (something like a 12V relay?).

Not sure of how to best take care of the battery or what equipment might be necessary to avoid overcharging the battery.

Ideas or other alternatives would be welcome.
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K3UOD
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Posts: 145




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« Reply #1 on: May 04, 2001, 10:56:56 AM »

This is a good topic.

I just use a gel cell with a Sears "on board" battery maintainer.  This keeps the battery charged up but I have to switch power sources manually (buy disconnecting and re connecting the wires.

There is a simple way to accomplish what you want to do.  Ship's gyro compasses use this setup to keep the gyro spinning when the ship's generators go down.  Just find two rectifier diodes with sufficient forward current to supply your rig.  Connect the diodes in series between the positive terminal of your power supply and the positive input of the rig.  Connect the negative terminals of the power supply, battery and rig together.  Then connect the positive terminal of the battery to the junction between the two rectifiers.  If the current draw is high you may need to mount the diodes on a heat sink.

Whenever the power supply is energized, it'll feed current to both the rig and the battery.  If the battery's charge is low this can be a lot of current so if you want to transmit while the battery is charging you'll need a pretty big supply.  Asuming that the power supply is big enough to feed the rig and charge the battery at the same time, the system will switch automatically.

The voltage at the rig will be battery voltage minus the drop across the diode.  Most rigs won't mind.

With this set-up you can have several battery/diode combinations in parallel.  The diodes prevent circulating currents from occuring between batteries with different voltages.  If you only use one battery, you can just connect the battery across the rig and charge the battery via a diode (which keeps the battery from discharging through the power supply when the supply is turned off).

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K9MRK
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Posts: 11




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« Reply #2 on: May 04, 2001, 01:40:53 PM »


K3UOD's suggestions sound like the way to go to me.
A sealed gellcell is a lot safer than having a lead
acid battery sitting around the shack and their appear
to be some fairly high capacity ones out there now.

If you do however wish to use a deep-cycle lead-acid
I'd like to make a couple points. Any lead-acid
battery being charged gives off hydrogen. Even at
low charging currents the bubble stick to the plates
until you bump it or whatever. One spark is all it
takes. I had a car battery explode as I removed a
charger clip. Getting sulfuric acid out of your eyes
is no fun. So another vote for the gell cell.

Also many of the "so-called" deep-cycle batteries
out there today are the dual-purpose (also starting)
batteries. They don't stand up to complete discharge
use as do the real deep-cycle batteries. The "charge
maintainer" low-current charger is a must. The auto
battery chargers (even with a deep-cycle setting)
fry them in short order. I was replacing batteries on
my boat every other season before I figured that out.
The last one has gone 5 years with no apparent
degradation.

73,
Mark - K9MRK

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KB2SMS
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Posts: 19




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« Reply #3 on: May 04, 2001, 07:06:25 PM »

"Hi fellow hams - I'm interested in using a deep cycle marine battery (12 volts) as a backup for my VHF / UHF radio's at home. Other than using an AC battery charger, does anyone have ideas on how to permanently setup the deep cycle battery to remain fully charged, and always ready in case of a power failure?"

  How many amp hours is the battery? You could use solar panel(s) and a charge controller but the cost may be high depending on what size amp hour battery(ies) you use. The new Concourde batteries are made to be used INSIDE, VERY LITTLE hydrogen outgassing. Check them out at: http://www.solar-electric.com/

  A 75 watts panel puts out 4.5 amps so in 5 hours you could replace 22.5 amps back into the battery. I plan on starting out with a 100 Ah Concourde, I already have the panel.

73,
Tom - KB2SMS
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K3UOD
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Posts: 145




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« Reply #4 on: May 07, 2001, 08:23:56 AM »

That's a great alternative power site Tom.  I've been toying with the idea of a solar powered ham shack for years.  The drawback is the cost of the initial setup and replacement batteries.  Of course, you would only need a minimum system to run a VHF-UHF rig.

As a practical note, a small gasoline powered generator is only a fraction of the cost of an equivalent solar system.  They are more portable and easier to set up.  Many of them have 12VDC outputs for battery charging.  Many "never used" generators are available at a good price from people who bought them due to the Y2K scare.

I installed a GenTran transfer switch so I can easily connect my generator (a Coleman 5KW unit) to the house wiring.  Square-D makes a cheaper switch but it didn't have enough circuits for my needs.  My generator panel is set up to power the refrigerator, freezer, well pump (240VAC required, otherwise I could've gotten away with a much smaller generator), most of the house lights, and a few outlets.

I didn't hard-wire the ham shack to the generator panel because it didn't have enough circuits but it's easy enough to run an extension cord out the window to the generator.

I always keep 10 gal. of gas on hand (in a shed, never in the house).  That's enough to run the generator at full output for 16 hours.  However, I only need to run it a few hours a day to recharge batteries, fill the water jugs and keep the refrigerator and freezer cold.  
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K7LA
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« Reply #5 on: May 13, 2001, 10:14:58 PM »

K9MRK is correct about using true deep cycle batteries and not dual purpose ones.  You can tell the dual purpose batteries because they are labeled with Marine Cranking Amps (MCA) ratings. Wal-Mart carries deep cycle batteries at a reasonable price.  Good luck on your project.
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WB2WIK
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« Reply #6 on: May 17, 2001, 06:21:04 PM »

Good subject.

Not sure why anyone would go to the extreme of using a switch (relay or solid-state), or worry about battery outgassing, when these issues are already dealt with (for the past century or so) in the telecommunications industry, who runs all Central Office equipment on battery power, all the time, 24/7.

Just run your equipment on battery power all the time, with an automatic charger across the battery.  The charger should have the ability to rapdily charge if needed, i.e., 50A or more, then trickle down to a float when a high charge rate is not needed.  No switch required, if the AC mains fails, you're automatically on battery power and when the AC comes back on line, the battery will recharge.

I've done this for years at remote sites (repeaters, remote bases, etc.) with no ill effects at all, and normally enjoy rather long battery life (5+ years) unless the environment is extremely hot.

Since outgassing is always a concern, I always place the batteries outside the shack, usually just plain outside, period!  It's hard to start an explosion from hydrogen outgassing when the battery is surrounded by an infinite supply of air.  Remember that lead acid batteries don't like being stored or used while resting on anything even slightly conductive (such as earth, cement, etc) and it is always best to store or use them resting on a good insulator such as ABS plastic -- the reason that in your automobile, it is almost certain that the battery is not just sitting on a metal shelf or tray, but an insulator.  A wooden pallet or equivalent will also suffice.  

73 de Steve WB2WIK/6
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K3UOD
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Posts: 145




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« Reply #7 on: May 18, 2001, 03:03:49 PM »

Steve,  
What you describe is what I consider to be the ideal setup, and what I intend to do whenever I get around to buying a good automatic charger.  (Been thinking about it for 20 years now.)

However; I'm not so sure about your caution on not setting a battery on a conductive surface.  I've heard this since I was a kid back in the '50s, but I've never heard a reasonable explaination of why.  My father still will never set a battery on a concrete floor without a board under it.  I've never bothered (except when he was around) and I've never seen a battery discharge from sitting on a floor.

Maby when batteries had rubber cases this was a problem; but I can't see how setting a plastic cased battery on a conductive surface could hurt anything.  Granted, my newer GM vehicles have plastic battery trays, but all of my older vehicles have unpainted steel trays.  The batteries on the steel trays always lasted until the warranties were up.

I suspect that this has more to do with protecting the floor than the battery.
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WB2WIK
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Posts: 20595




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« Reply #8 on: May 18, 2001, 05:01:19 PM »

K3UOD:  Ya know, I felt the same way (about the batteries and storage/use on nonconductive surfaces) and could not for the life of me figure why an obviously insulated battery case requires an additional layer of insulation beneath it.  However, I became a "believer" (like your Dad) when I worked for Bell Communications Research and went to a few seminars on lead acid battery technology, which apparently has not changed much in a long time.

The cases are not as non-conductive as you might think.  They are typically polypropylene which is a good thermal insulator but not the greatest electrically.  If you have a sensitive millivoltmeter, wet the bottom of the battery case and touch probes to the two wet spots (one roughly under each terminal), you'll measure a potential difference on the outside surface of the battery!  (Try it, I did.)  Hmmmmm.

Another test, which we witnessed (in a videotape) during one of the seminars, was to take two identical PbH2SO4 batteries that start out "new," measure specific gravity of each and record them, then place one on a cement floor and the other one on an insulator, and come back every 30 days to re-measure.  The one stored on the cement floor starts dropping off even within the first 30 days, while the one sitting on an insulator will maintain specific gravity almost without change for the first 30 days.  It's interesting.

If you visit any place that is serious about storage batteries and running important equipment from it, such as telephone central offices which use 48 V battery banks (24 x 2V cells that are absolutely huge, probably >1000 times the capacity of a car battery), it is obvious they never let the cells sit on cement, they are always insulated from the floor -- to this day.  

I never delved very deeply into the subject and could still learn a lot about it.  My curiosity being mildly piqued by this discussion, I'll do some research and let you know what I find out.  It's been many years since those Bellcore seminars...

P.S. I'm surprised about the "metal shelf" comment.  I've had a lot of cars and can't recall any of them that placed the battery on a metal shelf that didn't have a piece of polystyrene or something in between, as supplied by the factory.

73!

Steve WB2WIK/6

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WB2WIK
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« Reply #9 on: May 18, 2001, 05:21:01 PM »

K3UOD:  Well, I tried (today), but too late.

I called the Society of Automotive Engineers (SAE)'s council on land, mobile and air batteries and charging systems, but they happen to be back east and by the time I called, they were closed.

However, I won't forget to call them back next week!  If you'd like to give them a call, I'll bet somebody there can shed light on this "insulating the battery" issue.  I just read a report from their annual convention in 1999 which addresses accelerated life testing of wet-cell storage batteries, and in one method, they actually immerse the batteries being tested in very hot water (150 degrees F) during testing, to heat the batteries up and make them die faster.  I'd guess that's not a good idea, then!

Their phone number (in Pennsylvania) is 724-776-4841.

Keep in touch, I'll let you know what I find out.

73 Steve WB2WIK/6
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K3UOD
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Posts: 145




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« Reply #10 on: May 21, 2001, 08:18:54 AM »

Thanks for the education Steve.  Great responses.

I guess that since a vehicle's battery is usually re-charged each time you drive, the battery shelf material isn't that important.  But, your post explains why a vehicle left sitting for a long time will have a dead battery (though internal leakage is another explaination).

I have to try the experiment of looking for potential differences on the bottom of a battery.  I happen to have a spare in my garage.

I've seen the battery bank at our local telephone switching center.  Twenty four glass vats, about 10 gallons each, filled with lead plates and potassium hypochlorate solution.  The engineer who conducted the tour said that the bank could run the entire switching center, including lighting and computers, for 24 hours.  They use a motor-generator to convert 48VDC to 120 VAC,  not very efficient but much cheaper than a solid state inverter.
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KB9YNB
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« Reply #11 on: September 20, 2001, 02:08:42 PM »

Well, I heard that the reason a lead-acid battery discharges when sitting on a concrete floor was that the THERMAL conductivity of the floor being different than the THERMAL conductivity of the surrounding air causes a difference in temperature between the bottom and top of the battery.  The temperature difference causes a convection FLUID current in the electrolyte, and thus a leakage ELECTRICAL current within the battery.

I'm an EE, not a CHEMIST, so I'm just going by what I heard.

Guess what else I heard?     Sheep.  (say it out loud if you don't get it.)

Could I please have change for my 2 cents!

KB9YNB
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N4ZOU
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Posts: 340




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« Reply #12 on: October 01, 2001, 05:04:15 PM »

Batterys don't like the cold so don't sit them on concrete or any thermal drawing surface. You don't need a large automatic battery charger unless your going to transmit 24 hours a day, 7 days a week as if you were in  repeter operation. A small 1 Amp  charger will work fine for normal operation of an amateur station. Most receivers draw less current than this in receive so 1 amp would slowly charge the battery even if the transceiver were on receive all the time. The battery would also last longer with a slow charge. No automatic controls to fail and burn up your battery eather. You can even make your own charger from a 12 volt transformer and a single diode. Lead acid batterys like a small amount of AC ripple in the charge current as this keeps the plates clean. Also add a fuse just to be safe. The battery will work like a huge capacitor and keep the ripple noise out of your receiver.  
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AL7KC
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« Reply #13 on: November 15, 2001, 11:52:15 AM »

I will concur with K9MRK's remarks, as I had a battery explode in the shack a couple of years ago.  Fortunately, I was not there when it happened.  However, some of my gear will forever show the acid markings.  If you do go with wet lead-acid, definitely get a plastic battery box.  These are readily available, marketed especially for boaters.  As for the charger, there's several auto-float trickle chargers commercially available for less than $30.  Easy to find in the motorcycle marketplace for keeping the batteries from croaking over the winter in places that have a non-riding season. Also seen at battery shop up here.  One brand is the Battery Tender Jr (12 volt Charger/Maintainer.)
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WB6MLI
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« Reply #14 on: May 31, 2002, 11:40:15 AM »

I too find solar the way to go on this. I am out here in SCE land, and who knows when California is going to get it right. My habits tend to favor Friday night and Weekend operating. I typically run about 100W out SSB or 50W out CW on a TS-180s for a few hours on those days. I use a Uni-Solar 32 watt panel and a Morning Star 10 amp SunSaver controller. The controller has a low voltage disconnect output, but I do not use the radio on that. The radio has its own fused direct connection to the battery. The controller tolerates the lower voltage on the battery during Xmit. The battery is a Sears Marine battery - 27 series I think. I do not use AC at all, (except for lighting). I've been doing this for three months now, and haven't had a dead battery. The other application is the garage door opener, which was in use for about a year before the radio (using an inverter of course). I use the 10 amp controller, because I expect to be adding another panel before Field Day. After Field Day, I think I will have enough juice for the Garage Door and the Radio! I have serious thoughts about an AGM battery, filling the wet battery every so often is a pain, as is managing the ventilation. I do visit the www.solar-electric.com site a lot! (The refrigerator is next!).
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