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Old 05-06-2012, 01:29 AM   #1
catdsnny
 
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Default Aux battery setup

Anyone have a recommendation for aux battery setup to use with inverter? From what I have read, the best way is to mount a second battery under the hood and hook it to the charging circuit with a relay kit so it's isolated from the starting battery. There seem to be alot of these kits out there - any recommendations/experiences to share? Just purchased a 2011 2500 van and I need an entertainment setup for the kids, so I'm thinking around 1500W for TV, Xbox, laptops and the like.
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Old 05-06-2012, 02:42 AM   #2
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Default Re: Aux battery setup

You will not have enough space under the hood for the size of battery bank you will require run the electronics you mention.

An educated guess is that you will require a minimum of 30A DC to run the stuff.
A single standard sized battery (90-100aH) will give you about 35-45aH of energy...

Your kids will be whining after about 75 minutes.









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Last edited by OrioN; 05-06-2012 at 02:45 AM.
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Old 05-06-2012, 03:16 AM   #3
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Default Re: Aux battery setup

Just an FYI, 1500 watts from 120 vac is ~12.5 amps, run that load of of 12 volts, and it is a whopping 125 amps, not including wiring ns inverter loses. Add those in,, and it might be 150 amps.

A 450 ah battery bank (2 t-105 6 volt golf cart batteries) would be drawn to 50% in less than two hours. Not to mention, a 125+ amp draw is going to force the inverter into low voltage shut down quite quickly.

So, s we say in the off grid solar world, do a REAL load calc, both size and duration. Then figure your charge regimen.

Consider reading the following links,

http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Bat...of%20Batteries

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Old 05-06-2012, 04:42 AM   #4
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Default Re: Aux battery setup

Quote:
so I'm thinking around 1500W for TV, Xbox, laptops and the like.
Given those loads, did you perhaps mean 150 (not 1500) watts?
If you can restrict yourself to one or two loads (one TV *or* two laptops *or* an Xbox-with-TV) at a time, you are probably looking at 300 watts.
P=IE (power= current times voltage)... 300w / 12v = 25 amps
A size 31 battery is about 100 AH, so it will handle that load for about two hours (i.e. 50AH drain) before starting to dip lower than you'd like it.

As Icarus says: do a REAL assessment of your loads, and the duration you want for them.
THAT will dictate the size (in amp-hours) of your required installation. (and the impact on your wallet)

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Old 05-06-2012, 04:35 PM   #5
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Default Re: Aux battery setup

On the wattage calc, I wanted some room to grow, perhaps add a microwave. The XBOX is about 180w, TV is another 300w, Wii is 20w, couple laptops, DVD player, iPad charger, Mifi, etc probably add to 35w, so I'm over 500w right there. I was thinking of possibly a small microwave like 900w, so thats where my 1500w came from.

From what I have read on the auxiliary battery systems, the circuit is connected to the main battery and charging circuit while the engine is running, therefore, as long as the van is on the battery should not deplete, assuming that the alternator can handle the draw. So I'm confused about the "running out of power" in 2 hours statement - does this assume that the engine is not on? I'm only going to use this gear while traveling; its not like a camper setup. Are there higher output alternators recommended for this sort of usage?

Thanks,
Shaun
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Old 05-06-2012, 04:47 PM   #6
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Default Re: Aux battery setup

If you at only going to run this stuff while. In motion, why add a second battery at all?

If you really are going to run 1500 watts(~125 amp/12vdc) the stock alternator should probably handle it. That said, there are larger alternators out there. I might also suggest using lower draw equipment. For example what current flat screen draws 300 watts that will fit in a van? They make flat screens that are native 12 vdc so you don't have inverter loses. You are also not likely to run every thing at once,, especially the video stuff and the micro wave.

One might also ask (rhetorically/editorially) why do the kids need all this stuff for a road trip? What's the matter with looking out the window and seeing some of the real world now and again? We certainly have become a plugged in, scream centered society!

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Old 05-06-2012, 05:04 PM   #7
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Default Re: Aux battery setup

From a few of the posts I read, there were suggestions that it's better to run your gear off an auxiliary battery because it might cycle the starting battery too much and reduce the life. I guess there is also the possibility that the total draw might exceed the alternator and deplete the battery. Anyway, I felt like it was the safest thing to do. The stock Sprinter alternator appears to be 90A x 12v = 1080W, so it looks like I need to replace that anyway. The battery disconnect systems I've found so far seem to go to 150A. They have alternators for the Sprinter up to 260A (!). With the loss from inverter and cabling I'm thinking 200A might be ok. So if anyone can recommend a system they have used in that range the info would be appreciated.

Unfortunately looking out the window only keeps them occupied for so long. We make a yearly trip from NY to FL with 5 kids, aged 2 years to 9 years. All these gadgets make it alot easier on everyone.
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Old 05-06-2012, 05:26 PM   #8
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Default

Well... Now we get to the bottom of things...

1) the stock alternator is 220a so you do not need to upgrade

2) a deep cylce battery of 85-100 ah will get you through the occassional need when not running the engine but... FOR LOW WATTAGE USE...

3) ... 750W microwave will not run off said battery without destroying it... Physics..technology...

4) your engine should or can not be idled for excessive time unless you have high idle option/feature... Do a search on this forum for issues.
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Old 05-06-2012, 05:29 PM   #9
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Default Re: Aux battery setup

I have a 2011 cargo Sprinter. This is my third Sprinter. I also had a 2002 and a 2006. I ordered the factory auxiliary battery system on all three. I over 500,000 miles on my 2002 and over 650,000 miles on my 2006. I never had a reliability issue with the isolator on any of my vans. I have had to replace the batteries in time but never the isolators. I think the factory system is the best. Even though it is expensive in the long run I saved money over aftermarket systems. Several of my friends went that route and all of them has to replace their isolators at least once a year.
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Old 05-06-2012, 05:37 PM   #10
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Default Re: Aux battery setup

One choice if you will only need 120 volt power while driving is to power an inverter from the Sprinter 12 volt electrical system. See " orton DIY - vehicle inverter installation".

Your comment about wanting a microwave tells me you also want power available without the engine running. That would require a house battery and inverter since Sprinters do not like to be idled. Be aware that a microwave watt rating is not what they draw. The watt rating is cooking watts not the power required to operate the microwave. I have found the watt rating on the nameplate is also lower than actual draw. A "Watt-o-meter" should be used to check the actual wattage a microwave draws. I had to use a "600 watt" microwave to be able to run a microwave on my 1000 watt house inverter.
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