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  #1  
Old March 6th, 2012, 12:28 PM
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For those running a single large battery

Quick question for you guys out there running a single large battery (Odyssey, etc) for the truck rather than going with a dual system. Are you using a monitoring device to see how much charge is left in the battery (ie. when you need to crank the engine up and let it recharge)? I am looking to power a frige, rack and roof top lighting (which will be led), winch, laptop charging,... I like the idea of a simple 'big battery' design, but also like the idea of being able to monitor if it's getting a bit low from peripherals.

Thanks so much in advance!!

-Aaron
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  #2  
Old March 6th, 2012, 12:37 PM
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I don't run any sort of monitor and I've never had trouble with mine. I run a fridge, 2-meter radio, charge an iPhone and iPad, GPS, etc.

http://www.defendersource.com/forum/...ad.php?t=26830
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Old March 6th, 2012, 01:20 PM
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The best way to monitor the battery health is with a voltmeter. Digital voltmeters are easiest to read but are a bit more pricy than the needle type. Do not even consider the kind with crappy dials like the one below. Those are worthless; by the time the needle moves enough to tell you anything significant about your battery condition, guess what, it's too late!
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  #4  
Old March 6th, 2012, 01:26 PM
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We love Chris' write up, but I must point out what I consider to be safety deficiencies.
1. Soldered cable lugs. A huge no go in my book. Lugs should be at minimum hammer crimped with a punch, preferably with a real crimping tool. A soldered terminal, if it gets hot, can fall apart.
2. Unshielded positive battery terminals with wing nuts. Too much chance for metal to metal contact with the aluminum hold down clamps. A boot should guard the positive studs and cables. The wing nuts should be replaced with proper nuts and washers and tightened with a wrench.
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Old March 6th, 2012, 01:36 PM
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The major worry is that you will run the fridge, which is likely the major consumer of battery juice, to the point that the start battery is flat and you can't start the engine. This is the major argument for separate battery banks for start and accessories. If you must stay with a single then you have to calculate how long you will be off the charge source (alternator), how many amp hours you will draw during that time, and then buy a battery with enough reserve capacity, plus a significant safety margin, to be full enough to start the engine.
Figure out the total draw of all your stuff, multiply the amps by the number of minutes it will be in use, divide by sixty and that'll give you your total amp hour usage without recharging. Add another 50% for safety. Now you know how big a battery to buy. Buy your battery based on reserve capacity minutes. This is the number of minutes it can discharge at 25 amps and not go below 12V. The calculation for RC is RC/2 + 16 = AH, so a battery with a RC of 100 has an expected 66 AH delivery.

For example:
Fridge 8 amps x 480 minutes = 3840
Lights 5 amps x 480 minutes = 2900
Entertainment 15 amps x 120 minutes = 1800

Total of 8540/60 = 142 AH + 71 AH = 213AH needed.

If you go to the Trojan, Deka or Odyssey websites, you will find specs for the batteries in size weight, etc as well as reserve capacity minutes. Buy your battery based on this figure as well as whether it will fit.

If you do your calculations correctly and keep your usage to your planned levels there is no reason not to expect that you can safely run your accessories without worry.

I will also add that you don't necessarily need to split the charging if you add a second battery. Doubling the battery will more than double it's life expectancy ( they aren't discharging as deeply) and will double the useful RC.
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Old March 6th, 2012, 03:03 PM
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Chris & Bill, I was kind of hoping the two of you would chime in on this one - thanks!

Bill, so on Odyssey's site, they list the spec's for the 2150 as a 20hr nominal capacity (ah) at 100, and a reserve capacity of 205 minutes. How does this play out with your scenario above? Also, by saying that doubling the battery will double the useful RC, would you say that it's better to run two smaller size batteries in parallel than one larger size (assuming they are all of the same quality), or is it rather a moot point?

Again, thanks so much in advance - this is good stuff!

-Aaron
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  #7  
Old March 6th, 2012, 04:15 PM
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Aaron the G31/2150 has a RC rating of 205 minutes. Using the calculation above that gives you about 68 AH. If your total draw is less than that (including the safety margin I mentioned) then you are golden.

I can't reliably predict your use and needs as well as you can. Of course anything you can do to unload these tasks to another technology or means of delivery will help your power management. Do you HAVE to have a reefer or will an ice chest do? Can you use battery lamps, and not have entertainment from electronic devices? Your call. Just remember that it can be expensive to live "off grid" in a style to which you have become accustomed.
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Old March 6th, 2012, 06:34 PM
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Quote:
Originally Posted by o2batsea View Post
Do you HAVE to have a reefer or will an ice chest do? Can you use battery lamps, and not have entertainment from electronic devices? Your call. Just remember that it can be expensive to live "off grid" in a style to which you have become accustomed.
Oh, come on.

You can run an Engel fridge for several days and still start the vehicle off of that Odyssey. I take my truck to the desert all of the time; the fridge runs off the battery from the time I park (afternoon) until mid-morning the next day, after I've finished my hike or whatever. The truck starts right up like it had a fresh battery, every time.

Ben Little forgot to unplug his Engel and went on vacation. When he came back days later, the truck still started.
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Old March 6th, 2012, 06:35 PM
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Thanks Bill... going to do some homework based on the formulas above. At least it helps explain the math behind determining the best battery / setup.

Chris... now I'm really confused! :-/
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Old March 6th, 2012, 06:43 PM
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Quote:
Originally Posted by chris snell View Post
I run a fridge, 2-meter radio, charge an iPhone and iPad, GPS, etc.
Seriously? It's not a fucking Jeep!
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I am talking purely from an aesthetics standpoint.
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  #11  
Old March 6th, 2012, 06:50 PM
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Originally Posted by nuclearmonkey View Post
Thanks Bill... going to do some homework based on the formulas above. At least it helps explain the math behind determining the best battery / setup.

Chris... now I'm really confused! :-/
What I was trying to say is: don't sweat it. Running what you're running, you'll be fine. Unless you're planning on parking your truck for days without running it, a single big Odyssey will be all you need. I wouldn't waste the money on a voltage gauge and I wouldn't want the added clutter. If you're really paranoid, pick up a good 12V folding solar panel to throw on your roof while you're gone. You won't need it but if it gives you peace of mind, go for it.
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Old March 6th, 2012, 07:38 PM
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Keep in mind that the fridge turns off and on so you are not running it 24x7, if you keep it in the shade, run a cover and have items in it you will find that it will only turn on for a short amount of time then turn off.


I have had my engel plugged into my disco for days at a time without starting it running off 1 standard optima and the disco still started like nothing had changed.

The ARB that I have now will shut off if it detects a drop in the battery for even more protection.
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  #13  
Old March 6th, 2012, 08:41 PM
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Chris, take a deep breath. I don't have any clue what his fridge draws. Maybe not much, but whatever it is he has to figure it out. Of course he will likely be just fine with a set up similar to yours. A Group 31 deep cycle has a LOT of power. I have two Deka AGM 31 deep cycle as my house bank on the boat and I can run a 10K Btu window AC unit all night in the summer on them. I have them on their ends so they don't take up a lot of real estate either. When I finally install the onboard Air, they will still be able to power it.
Just want him to be aware and not guess at whether he needs X amount of battery. I ask those seemingly stupid questions because people just seem to think they can run whatever for however long they want and it won't drain the battery, or just have no idea what they can run. I was certainly not trying to imply that he should go all hobo.

I know how much I have in the batteries and how long they will last with everything running that I want to run. That's all I'm sayin.
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  #14  
Old March 7th, 2012, 01:30 AM
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Chris, your set up is very clean, tidy and well done but I would point out that the under seat battery box on a Defender is not the best location to be putting fuse blocks or smaller delicate electrical connections and so forth that are subject to corrosion or failure due to dirt ingress. It’s a harsh environment subject to moisture, dirt and depending on the type of battery, possibly corrosive vent gasses, etc. with effectively no through ventilation. Larger supply level fuses are about the most I would want to put in there if I really had to.

The best location is above the seat box at the bottom of the cubby or under the console if available, if not then in the center of the dash behind a cover or panel, under the hood as high as possible if no space inside or if all else fails the passenger seat box area whilst still not good is better as it is more water resistant and has no battery in it.

On a NAS truck the perfect location is at the bottom of the cubby (94/95) with a false floor to cover it if needs be or under the console (97). Its central and has easy access to most locations of the truck as well as easy access to get to the fuses if needed. Battery supply cables are relatively short and don’t have to run inside the truck any great distance. If you are sitting in water to the top of the seat box level then you have other problems to worry about than the fuse box anyway.

I know I commonly have water and dirt enter my battery box even living here in the ‘dry’ SW. Normally dry snow melt swollen creeks or the very rare mud hole are my main causes but in other areas, mud/water holes or deeper water crossings are much more common. Due to the venting requirements you shouldn’t attempt to seal an enclosed battery box so water and mud, etc. will enter.

Ian
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  #15  
Old March 7th, 2012, 08:17 AM
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Don't some Defenders have certain factory fuse panels and relays under the passenger seat compartment?
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  #16  
Old March 7th, 2012, 08:32 AM
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Chris runs carpet so I suspect he avoids water like the plague.

But I totally agree with Ian. I get a lot of dirt/mud in my battery box and I am sure my blue sea fuse panel doesn't like it. Jeff and I built a box to go under the tuffy to both raise it to a comfortable height but also give room for electronics. We never got around to making a second for me, but I think if you wheel your truck that really is the best place for electronics.
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Old March 7th, 2012, 08:48 AM
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So you should leave the cutout holes open in the battery compartment to allow for air flow? I tried filling in most of them because offroad down here more closely resembles swimming. As for the frige, I haven't picked up one yet, but am leaning towards Engel, ARB, National Luna...

Thanks!!
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Old March 7th, 2012, 09:14 AM
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I say you will never stop it coming in, but you make sure it can get out quickly. So low drain holes would be better than high ones.

But I just noticed you are from South Florida after your swimming comment. May I recommend putting your electronics on the ceiling and relocating your ECU there as well? I have seen this swimming first hand!
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Old March 7th, 2012, 09:33 AM
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Such naysayers. I've run my setup for three years now and it's still in fine shape. There is no corrosion on the Blue Sea Systems fuse boxes. These are marine-grade and designed for boats in salt water. The battery box itself will corrode away before they do and it's fine, too.

The battery hasn't moved a bit under the aluminum bars because it's clamped down tightly. I will concede on the crimping of the terminal ends. I've since started crimping all connections and need to go back and crimp those leads.
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Old March 7th, 2012, 10:19 AM
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I think this is a regional thing Chris. When was the last time you had a muddy waterline on the inside of your doors at the top of the seatbox level? Happens regularly here. In South Florida they have "trails" that keep your headlights under the water for longer than above and put their ECUs on the dash to allow them to do so.
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