# Extra batteries + cap for carputer...opinions?



## WuNgUn (Feb 9, 2008)

Some of you know, I'm running a carPC setup, which in almost any case, draws more power than any single headunit out there!

Power needs to be supplied to the mainboard, HDD, DVD drives, water pump (yeah, it's liquid cooled), front monitor (and/or rear 22" monitor), USB devices (GPS, Griffin Powermate, OBD-II reader, FM reciever, HVAC controler/servos, etc...) and on top of that, a pair of Tru T4.65's bridged (200W X 2), and a Alpine MRP-F550 for the 10" Aurasound sub and center channel...

I was thinking 'The big Three' upgrade, a smallish 5 Farad cap and (I think I have room for) a pair of smallish motorcycle batteries (19 to 25 Amp/Hrs.)
The reason for the extra batteries is because me and the wife go to the drive-in quite often and do a lot of camping in the summer months, so the extra storage would be nice...
I also use a 15 Watt solar panel when we camp to replace the juice I used overnight with the music 

Just to be sure, the batteries have to be in parallel, right? Run the 4 gauge to the trunk, thru + on one battery, then thru + on the second battery, then the cap, then the distribution block?
The grounds on the extra batteries can both go straight to ground on the chassis?

Thanks!


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## starboy869 (Dec 16, 2006)

HI,

I think motorcycle batteries are 6v. You would need to wire them in series to get the 12v. However you'll be limited on the ampere. I would find a small 12v battery instead.


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## OldOneEye (Jun 16, 2005)

Not sure its going to be that easy. Your are going to have to isolate your main battery from the extra batteries. Not sure if the Motorcycle batteries you speak of are designed to be discharged fully (possible) and recharged. Maybe more of a wheelchair/golf car battery is more appropriate (designed to get cycled without much detriment to the battery itself).

Juan


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## Whiterabbit (May 26, 2006)

series or parallel. There are benefits and disadvantages to both.

you can run 12 volt batteries in parallel. Each battery added increases reserve charge and current capacity. ESR also decreases. But if any individual cell fails it will be a parasitic drain on all other batteries it is connected to and toast them all. Drain rate is shared between all batteries which will promote overall battery life.

You can run batteries in series to 12 volts. 2 volt batteries are very common for this, and also 6, 4, and even 1.2 cells (I was REALLY interested in those 1.2 volt cells). They can be stacked to achieve 12 volts. The advantage is since cell failure doesnt dump the whole line. When you read 10 volts, you know one of your 2 volt batteries has failed. replace and good to go. ESR is additive resulting in very slow current response. much worse than deep cycle. May not be a problem if your capacitor is big and fast enough (keep in mind carbon "super" caps will operate slower than a typical cylindrical cap).

finding large capacity low voltage batteries isnt easy.

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Note hybrid cars operate on hundreds of volts and ultra high capacity. This is done by combining series and parallel circuits. you will see the advantages and disadvantages of both system types.
But can be very effective.
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A neat concept is the idea of using D-cell batteries (I'm not even kidding). The best D-cells are very robust, are made from high end materials, have superior battery life, and can have reserve charges as high as 10,000 mAh. ten are wired in series to reach 12 volts @ 10 Ah. Then ten banks of these are wired in parallel to achieve 100 Ah of charge at 12 volts for a bank cell count of 100 D cell batteries. The resulting charge is time and a half that of a yellowtop at a fraction of the weight and VERY VERY highly installable anywhere in the car (how many configurations can YOU think of to stack 100 D cells?)

The option is very very expensive. If I could have found the cells for $2 a piece, I would have had no second thoughts about this option. Typical prices can be above $7.

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Above all else, two things need to happen. Your batteries require acid venting NO MATTER WHAT. Even sealed batteries can swell and explode when exposed to extreme voltages. Even worse than a standard open lead acid battery which will simply vent hydrogen without pressurizing. I recommend air tight containers (minus the acid vent) for non sealed batteries, and minimum gravity fed acid drains for SLA batteries.

Second, your batteries need an absolute minimum of overvoltage protection to prevent hydrogen production and heating from happening to begin with. The easiest way to do this is with an SCR and fuse to create a "crowbar circuit". Google that, you'll pull plenty of schematics. I used a circuit breaker which increased the cost of my overall circuit to $10 instead of <$5.

You will need an isolation relay if you plan to drain the rear batteries dead without killing the whole car. 3 cars died last year at marv's bbq, and mine was one of them. One was lucky enough to be able to start after some idling, one car needed a jumpstart, and my car didnt even feel it because the battery under the hood was untouched by the stereo.

Chad suggested the best method for relay isolation. Tie it to the fuel pump. isolation will be there no matter what unless the car is running. I recommend sourcing solid state relay(s) because RV automotive battery isolation relays are noisy as all heck.

Optional but I recommend is isolating each battery in the secondary array in a parallel circuit from undervoltage conditions. This will disconnect any battery from an array that drops too low in voltage for a long period of time so if one cell fails, it doesnt drag the whole array down. turning the car on should attempt to recharge the suspect battery. The best way to do this? I never figured that out.


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## WuNgUn (Feb 9, 2008)

Okay then...so I guess I'll just keep the single car battery 
Phew!!


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## Whiterabbit (May 26, 2006)

for your perusal also

http://www.batteryuniversity.com/


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## OldOneEye (Jun 16, 2005)

If _I_ was going to do it, and my car had an old battery any way, I would try to fit two smaller hawker/stinger/scosche/etc. type of batteries under the hood with an isolator. (heck, you might not even need it.. read on). I also have a nice gadget that is an adjustable turn off circuit based on voltage (PAC makes it). If you know what you are doing, you just tell it to kill shut down your system at a predetermined voltage, that way you can still start the car. Since the batteries are the same age, no need really to isolate them (and if they are next to each other, no need to run a fuse between the two).

Depends on the car really. If I had a full size truck, i would be getting the biggest batteries I could fit, go get an extra battery tray from a Diesel truck (on the diesels they have an option of a second battery since they take quite a bit of juice to crank over), and away we go.

Not sure what you have room for, but the next car will probably just have the biggest battery that will fit and a safeguard to keep me from getting stranded.

Juan


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## WuNgUn (Feb 9, 2008)

The power supply for the PC has a sensor to detect low voltage (11V I think), and it'll shut itself off when it hits that low...
But that isn't any good at the drive-in!

What's the easiest way to increase capacity when adding an extra battery?


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## RedGTiVR6 (Jun 26, 2007)

WuNgUn said:


> Some of you know, I'm running a carPC setup, which in almost any case, draws more power than any single headunit out there!


How do you come up with that? Most of the PSUs have fuses of between 10a and 20a....most head units have at least that big of a fuse. Now, if you're running a heavy duty carPC then yes...it will draw more power...

I just want to make sure that people aren't mislead in thinking that a CarPC requires a lot more power than a regular HU.


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## Abaddon (Aug 28, 2007)

RedGTiVR6 said:


> How do you come up with that? Most of the PSUs have fuses of between 10a and 20a....most head units have at least that big of a fuse. Now, if you're running a heavy duty carPC then yes...it will draw more power...
> 
> I just want to make sure that people aren't mislead in thinking that a CarPC requires a lot more power than a regular HU.


Well, wouldn't that be because of the amplifier on the Head Unit? And since almost everyone on here doesn't use the on board amp on their HU...  

I have no problem believing that a CarPC takes more current then a standard HU (without the amp powering speakers).


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## RedGTiVR6 (Jun 26, 2007)

without the on board amplifier, sure. I just with there was a little more clarification in the original post. While most people who post here might not use built in power, you would be surprised how many people just read forums and don't contribute.


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## Megalomaniac (Feb 12, 2007)

WuNgUn said:


> Some of you know, I'm running a carPC setup, which in almost any case, draws more power than any single headunit out there!
> 
> Power needs to be supplied to the mainboard, HDD, DVD drives, water pump (yeah, it's liquid cooled), front monitor (and/or rear 22" monitor), USB devices (GPS, Griffin Powermate, OBD-II reader, FM reciever, HVAC controler/servos, etc...) and on top of that, a pair of Tru T4.65's bridged (200W X 2), and a Alpine MRP-F550 for the 10" Aurasound sub and center channel...
> 
> ...


man you will pulling a lot of constant draw lol. if you are trying to get the most out of it while the car is off, you need more reserve power, so start filling that trunk with batteries. or add more solar panels(btw where did you get yours?)? also if you do add batteries you will need to upgrade your alternator to keep up the demand to keep them charged.

btw if you cold upgrade 1/0awg that be cool, you'll have a faster recover time when charging them


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## WuNgUn (Feb 9, 2008)

Is there anything wrong with adding a couple of smaller 12v batteries into the 1/0AWG from the main battery up front, in parallel, then to the ditrobution block?
Then ground each individually? No muss, no fuss...


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## OldOneEye (Jun 16, 2005)

Voltage follows the path of least resistance so a hodge podge of batteries isn't going to help. Now, two of the same exact battery (same age, etc.) would be fine (it acts like one battery really), anything else (mix and match) is asking for problem.

Juan


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## WuNgUn (Feb 9, 2008)

OldOneEye said:


> Voltage follows the path of least resistance so a hodge podge of batteries isn't going to help. Now, two of the same exact battery (same age, etc.) would be fine (it acts like one battery really), anything else (mix and match) is asking for problem.
> 
> Juan


If they are arranged in parallel, the voltage stays the same, correct? Unlike series...
Is this STILL going to cause issues?
I don't have room more a similar battery like the one under the hood, so what is my next best option?

I was also thinking about adding an extra battery to the car for camping/drive-in only...not a permanent battery. Something I can 'plug' in when needed, and unplug when I don't...
Maybe route the solar panel (or two) into a charge regulator for these as well? This would be good for camping...


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