#141996 - 07/29/08 03:50 AM
Back up 12v battery system
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Addict
Registered: 06/10/08
Posts: 601
Loc: Southern Cal
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I seem to be on a roll so let me throw this out there.
As I've written in other posts, I work as a medic on film/tv sets mostly in and around SoCal. Some of these locations are rather remote with very little in the way of amenities other than what we bring to them. I tend to work very long hours, sometimes for up to a week at a time with little movement of my vehicle and sometimes with very limited access to refuel on any sort of a regular basis.
I've been toying with the idea of putting together an extra 12v battery system to power some 12v accessories, ie, cell phone, laptop, portable dvd player, AA/AAA battery charger, etc. What I'm envisioning is a small solar panel, portable to take into account the movement of the sun, possibly a charge controller and a smallish sized deep cycle AGM battery, eg, Optima or the new ones that are rebadged Optima's on sale at Sears. This could also be used conceivably to jump start a car.
I've thought about doing a dual battery setup with an isolater on the car system but I don't have a lot of room under the hood and I'm liking the idea of making the whole thing portable.
Anyone have an opinion on why this wouldn't work? Given that I'll have to know the limits of power available and the ability of the solar cell to recharge.
I welcome any suggestions or criticisms. Well maybe not the criticisms too much...;^)
John E
_________________________
JohnE
"and all the lousy little poets
comin round
tryin' to sound like Charlie Manson"
The Future/Leonard Cohen
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#141999 - 07/29/08 04:01 AM
Re: Back up 12v battery system
[Re: JohnE]
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Product Tester
Pooh-Bah
Registered: 11/14/04
Posts: 1928
Loc: Mountains of CA
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Portable will be pretty bulky / heavy... even one battery. If it were me I'd do two batteries and store one in the trunk if there is not room under the hood. They make other batteries that are 1/2 the size of the optima and you can fit two of them or more under the hood where you can fit them  The two battery idea doubles your storage capacity so for the money it's the best bet. Add a solar charger and you should set. -Todd
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#142000 - 07/29/08 04:09 AM
Re: Back up 12v battery system
[Re: Todd W]
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Addict
Registered: 06/10/08
Posts: 601
Loc: Southern Cal
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Thanks Todd, I should have been more concise, I wasn't thinking of making the battery itself portable, more that the system, mainly the solar panel, would be. Instead of being wired into the electrical system of the car. What I'm envisioning is putting the battery into some sort of container with a wiring hookup for the panel and then some sort of output system.
You bring up a good point about battery size. Maybe (2) smaller batteries would make more sense.
John E
Edited by JohnE (07/29/08 04:10 AM)
_________________________
JohnE
"and all the lousy little poets
comin round
tryin' to sound like Charlie Manson"
The Future/Leonard Cohen
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#142005 - 07/29/08 04:18 AM
Re: Back up 12v battery system
[Re: JohnE]
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Veteran
Registered: 07/08/07
Posts: 1268
Loc: Northeastern Ontario, Canada
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Hi John,
I will start this reply by saying that I am not very knowledgable when it comes to electricity, so consider this information as real basic.
I have an Eliminator Powerbox 600amp that I bought at Canadian Tire, it provides both 120 volt AC and 12 volt DC portable power, and has a built-in light, booster cables and air compressor. It can be recharged off, 120 volt household current, 12 volt vehicle plug-in and with a solar panel. I use it regularly to boost vehicles, power lights/tools and inflate tires, it is very handy.
Here is a link, I an sure retailers in the USA sell something similar, http://www.canadiantire.ca/browse/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524443271701&FOLDER%3C%3Efolder_id=1408474396672502&bmUID=1217307644862
This link may not work, Google Canadian Tire Eliminator Power Box and you will find a selection of them.
There are also larger and smaller models available.
Mike
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#142017 - 07/29/08 11:42 AM
Re: Back up 12v battery system
[Re: KG2V]
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Rapscallion
Carpal Tunnel
Registered: 02/06/04
Posts: 4020
Loc: Anchorage AK
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You can monkey around with the circuits if you want, and eventually you will figure out all the design considerations, or you can go to a marine/rv center and see what they have, talk with their techs, and get exactly what you need. They may even build it for you.
Deep cycle batteries are not recommended for jumpstarting other vehicles, nor for starting your own vehicle. If you are going to use the car's existing chargins system to charge the secondary battery (highly recommended), then use a good quality automotive battery. Deep cycle batteries do not like a constant charge current either, so an auto battery is preferable for a solar panel charging system as well, unless you want to spend a lot of bucks for a regulating system.
If I were building a backup battery system for a vehicle, I would most likely wire the batteries in parallel using 12 or 10 gauge welding wire (properly fused), and have a cut-out switch so that I could go from one battery to the other but not both at the same time. This way I won't overload the alternator trying to charge two batteries at once, thus frying the alternator. I might build a little timer signalling device to remind me when one battery has charged and I can switch to charging the other. Then when I need to use battery power, I can go from one battery to the other as well. As far as the solar panel goes, just wire it with an accessory plug (cigarette lighter) and plug it into the jack on the dash to charge whichever battery needs it. The panel will never put out enough juice to have to worry about overloading the current. Even a big panel will only make about 15 to 20 watts peak.
I spent a good chunk of my life building and maintaining battery powered circuits, and the cheap way is to use car batteries and make as few changes to the existing circuitry as possible. Where I've had to use deep cycle systems, the cost has been significantly more.
_________________________
The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)
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#142021 - 07/29/08 12:58 PM
Re: Back up 12v battery system
[Re: benjammin]
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Old Hand
Registered: 02/08/08
Posts: 924
Loc: Toledo Ohio
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Harbor Tools has a 45 Watt solar Panel and charge controller, they sell it for $249.00 on sale right now for $189.00. It may fit what you need.
_________________________
You can run, but you'll only die tired.
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#142025 - 07/29/08 01:12 PM
Re: Back up 12v battery system
[Re: benjammin]
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Old Hand
Registered: 02/08/08
Posts: 924
Loc: Toledo Ohio
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You can monkey around with the circuits if you want, and eventually you will figure out all the design considerations, or you can go to a marine/rv center and see what they have, talk with their techs, and get exactly what you need. They may even build it for you.
Deep cycle batteries are not recommended for jumpstarting other vehicles, nor for starting your own vehicle. If you are going to use the car's existing chargins system to charge the secondary battery (highly recommended), then use a good quality automotive battery. Deep cycle batteries do not like a constant charge current either, so an auto battery is preferable for a solar panel charging system as well, unless you want to spend a lot of bucks for a regulating system.
If I were building a backup battery system for a vehicle, I would most likely wire the batteries in parallel using 12 or 10 gauge welding wire (properly fused), and have a cut-out switch so that I could go from one battery to the other but not both at the same time. This way I won't overload the alternator trying to charge two batteries at once, thus frying the alternator. I might build a little timer signalling device to remind me when one battery has charged and I can switch to charging the other. Then when I need to use battery power, I can go from one battery to the other as well. As far as the solar panel goes, just wire it with an accessory plug (cigarette lighter) and plug it into the jack on the dash to charge whichever battery needs it. The panel will never put out enough juice to have to worry about overloading the current. Even a big panel will only make about 15 to 20 watts peak.
I spent a good chunk of my life building and maintaining battery powered circuits, and the cheap way is to use car batteries and make as few changes to the existing circuitry as possible. Where I've had to use deep cycle systems, the cost has been significantly more. You are right that gel-cell batteries don’t like a high amperage charge, they are not the best choice to have if you are going to use the alternator to charge them. In an alternator tied system I would use 2 6-volt golf batteries tied in together. Yea the golf batteries are heavy, but they have a lot of reserve power, can handle a good amount of charge current and also handle a lower discharge that a starting battery can’t take. Car starting batteries don’t like to be deep cycled and in fact will be destroyed if you discharge them a lot like what happens with house batteries in a camper (and this is what is going to happen when you use the house battery to run computers, DVD players, chargers, inverters and the like) they are a very poor choice for house batteries in a camper. AGM batteries will work well with the charge rate from a solar panel. Starting batteries (a normal car battery) have thin plates and are made to deliver a lot of amps for a very short time, they are not made to have a constant drain on them like golf, gel-cells, AGM or deep cycle batteries are.
Edited by BobS (07/29/08 01:37 PM)
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You can run, but you'll only die tired.
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#142116 - 07/29/08 09:57 PM
Re: Back up 12v battery system
[Re: JohnE]
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Enthusiast
Registered: 08/23/05
Posts: 289
Loc: WI, MA, and NYC
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The main question which determines just about everything else hasn't been asked yet. Namely, how many amp-hours do you want this battery to have? I have a PowerPort 73A, which is an SLA 12V, 8AH battery that weighs 6lbs. It comes in a carrying case with three built in DC outlets and a charger. It's excellent for ham radio use and a wide variety of other applications.
Edited by Fitzoid (07/29/08 11:12 PM)
Edit Reason: corrected model number
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"When I read about the evils of drinking, I gave up reading." Henny Youngman
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#142117 - 07/29/08 10:10 PM
Re: Back up 12v battery system
[Re: Fitzoid]
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Addict
Registered: 06/10/08
Posts: 601
Loc: Southern Cal
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Thanks Fitzoid, I'm intrigued by the Powerport stuff. Wonder how hard it would be to recharge one of their battery systems with a solar cell?
I'll look into their system.
John E
_________________________
JohnE
"and all the lousy little poets
comin round
tryin' to sound like Charlie Manson"
The Future/Leonard Cohen
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#142124 - 07/29/08 10:46 PM
Re: Back up 12v battery system
[Re: JohnE]
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Enthusiast
Registered: 08/23/05
Posts: 289
Loc: WI, MA, and NYC
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There's no problem recharging them with solar panels, and they sell a bunch of them for that purpose. However, as opposed to their batteries, the panels are overpriced and you can do better elsewhere.
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"When I read about the evils of drinking, I gave up reading." Henny Youngman
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#142129 - 07/29/08 10:54 PM
Re: Back up 12v battery system
[Re: JohnE]
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Old Hand
Registered: 02/08/08
Posts: 924
Loc: Toledo Ohio
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How big a battery you need is important, but so is your charging system. And intended use.
Charge some batteries wrong and you will destroy them. A good example is an AGM battery, charge it fast with a high current you will boil the fluid and separate the jell from the fiberglass mat inside.
Use an auto starting battery in place of a deep cycle battery and it gets deep cycled a few times and you will destroy a battery.
There is a lot of things to take into account to get an off grid system to work right. It not as simple as just going to the store and buying a battery and then having a charger for it.
_________________________
You can run, but you'll only die tired.
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#142135 - 07/29/08 11:25 PM
Re: Back up 12v battery system
[Re: BobS]
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Enthusiast
Registered: 08/23/05
Posts: 289
Loc: WI, MA, and NYC
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Yup. Auto batteries are for cold cranking, namely, generating a lot of current for a short amount of time, e.g., 30 seconds, and then they need to be immediately recharged.
Deep cycle batteries are for extended usage between charges, and you can bring them down to 20% of capacity without damaging them. (Try that with a car battery.) You can get enormous capacities for deep cycle batteries for use on boats, RVs, solar powered homes, etc.
Sealed lead acid (SLA) batteries are very nice, as you can run them down, they hold their charge fairly well when not in use, you can trickle charge them so they're always ready to go, and they generally don't explode or leak.
There are lots of types of batteries and they all have unique performance characteristics, such as how long they hold a charge, number of recharge cycles, whether you can trickle charge them without damage (you can't do this to the Lion batteries), how fast you can safely charge them, whether they can be reconditioned, usable temperature ranges, etc., etc. Far more info to write about batteries than would fit here!
Companies like PowerPort will give you lots of information about how best to recharge their products.
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"When I read about the evils of drinking, I gave up reading." Henny Youngman
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#142184 - 07/30/08 04:03 AM
Re: Back up 12v battery system
[Re: Fitzoid]
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Addict
Registered: 02/02/03
Posts: 647
Loc: North Texas
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#142269 - 07/30/08 05:20 PM
Re: Back up 12v battery system
[Re: jshannon]
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Enthusiast
Registered: 03/28/06
Posts: 358
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How about just picking up a portable jumpstarter? http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=40615It's portable, 24Ah, already comes self contained with the necessary outlets, and no need to mess around with complicated charging systems, just charge it from your car cigarette lighter. Plus it comes with cables so you can jumpstart your car if your main battery dies. I have one wired up to one of my vehicles right now, so it's always topped off when the car is running. I was going to go the dual battery route also, but I did this in the meantime and it works well enough that I might just keep it like this. I think a solar system would be more trouble than it's worth. Even if you were to get one large enough to put out decent power, it wouldn't be portable anymore, and the smaller ones aren't always capable of recharging SLA batteries. A car alternator can recharge the battery in a fraction of the time that it would take the solar panel. Carry an extra 1 gallon gas tank and you have enough fuel to recharge your batteries for a really long time. Edit: I see that swampdonkey already brought up the idea.
Edited by ducktapeguy (07/30/08 05:24 PM)
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#142289 - 07/30/08 08:34 PM
Re: Back up 12v battery system
[Re: ducktapeguy]
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Old Hand
Registered: 02/08/08
Posts: 924
Loc: Toledo Ohio
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The problem with these portable jump starters is that they are notoriously unreliable. They usually are at least a year old (battery wise, The battery has been doing nothing for a year, not good) before they get on the store shelves, the jell cell batteries in them don’t like to be overcharged, the things generally don’t have a great charge controller in them so when you plug it in and leave it the battery gets too much voltage and the battery while showing a full charge doesn’t last very long.
I worked for a guy that owned a used car lot and had a lot of these things laying around that were not that old. It’s less expensive to just buy another jump box then it is to replace the battery in it.
If you are going to have a portable reserve battery, you should invest in a good adjustable charge controller and figure out the voltage charge limits for the type of battery you are using. Most people think this is not needed and just plug the battery into any available power source and call it good.
Portable battery power is about more then a battery, it’s a reserve system. The battery is only one part of that system. The charge controller is just about as important as the battery if you want it to work for a long time.
Edited by BobS (07/30/08 08:40 PM)
Edit Reason: Spelling
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You can run, but you'll only die tired.
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#142293 - 07/30/08 09:20 PM
Re: Back up 12v battery system
[Re: BobS]
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Enthusiast
Registered: 08/23/05
Posts: 289
Loc: WI, MA, and NYC
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+ 1. The car battery chargers that work through a DC lighter socket take forever, and you'll do much better off with the portable units that jump the battery directly. Then let the alternator do the charging as God intended... Also, batteries start to go bad once they leave the factory. That's why car and deep cycle batteries are dated and you shouldn't buy one older than 6 months. Even then, they are frequently on the way out. I bought a car battery with a CCA (cold crank amperage) of 800 at CostCo. Took it straight to one of those car care places that tested it at 500. Went straight back to CostCo. Either it was bad from the start, improperly stored, or they changed the date label. Take your pick. Edit: Oh, you were talking about a portable jump starter -- my mistake. They've actually saved me a couple of times. Buy one with a built in trickle charger; leave it plugged in. If you're going on a long trip, throw it in the car. Replace the battery (if possible) or the unit every few years. I wouldn't go off the beaten path without one.
Edited by Fitzoid (07/30/08 09:37 PM)
Edit Reason: See text
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"When I read about the evils of drinking, I gave up reading." Henny Youngman
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#142296 - 07/30/08 09:54 PM
Re: Back up 12v battery system
[Re: Fitzoid]
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Old Hand
Registered: 02/08/08
Posts: 924
Loc: Toledo Ohio
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I read someplace that all battery makers (Every one of them) lie about the amperage rating of the batteries they make. The best you can hope to get out of even the newest battery is 75% to 80% of its amp ratings.
As far as the trickle charge for the jump boxes if it doesn’t have a good controller to cut off the charge (and they don’t) it will overcharge the batteries. When a battery is fully charged, the charge needs to be turned off, even a small charge is too much.
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You can run, but you'll only die tired.
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#142305 - 07/31/08 12:07 AM
Re: Back up 12v battery system
[Re: BobS]
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Pooh-Bah
Registered: 09/01/07
Posts: 2432
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I read someplace that all battery makers (Every one of them) lie about the amperage rating of the batteries they make. The best you can hope to get out of even the newest battery is 75% to 80% of its amp ratings.
As far as the trickle charge for the jump boxes if it doesn’t have a good controller to cut off the charge (and they don’t) it will overcharge the batteries. When a battery is fully charged, the charge needs to be turned off, even a small charge is too much.
It is possible some fly-by-night battery retailers exaggerate the batteries true capacity. But there aren't very many battery manufacturers and all the big ones are on average pretty straight-up in their ratings. Verging on quite conservative for the premium producers. Generally, as long as you go with a reputable battery producer you will get what you pay for. Often more than their stats say. Some of the confusion is that people think batteries are like buckets, you get out what you put in. You never do. Even if you could you really wouldn't want to. Once the voltage on the battery drops your ability to get the energy out in a usable form comes to an end. The battery still had energy remaining but not enough to do anything with. Also, before the voltage drops below usable levels the battery is getting worn down. The lower you take the battery the fewer cycles you can get out of it. The rule of thumb is that only a third of the batteries capacity is usable if you want to get the maximum life out of the batteries. All the reputable battery manufacturers are quoting the accurate figures on what the batteries will do. it is up to you effectively use what you buy. One of the best manuals for setting up a system comes from the world of boating. Most libraries can hook you up with a copy of: "Boatowner's Mechanical and Electrical manual" by Nigel Calder. he has an in-depth discussion of various systems, batteries, chargers, and how to put them together to do what you want.
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#142307 - 07/31/08 12:27 AM
Re: Back up 12v battery system
[Re: Art_in_FL]
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Enthusiast
Registered: 08/23/05
Posts: 289
Loc: WI, MA, and NYC
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Yeah, I'd have to agree. Just about any auto supply store will give you a fairly detailed printout of a battery's characteristics for free. After returning my CostCo bargain, I bought a different cold crank 750A battery that tested slightly above specs.
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"When I read about the evils of drinking, I gave up reading." Henny Youngman
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