quad battery 24v system

I built a portable PC with DVR card and have the ability to use 4 security cameras and a 20" LCD monitor that runs on 12v.

If I cost up the amount of watts that the PC uses, it appears that there will be less current draw on a 24v supply than a 12v rail.

The security cameras are on 500' of Cat5e using 3 pairs, so effectively 18g, by supplying 24v down the cable, I can solve the voltage drop problem.

I need this rig to run for up to 8 -10 hours at a time, without starting my SUV.

The current will be fairly constant, but I do without having the LCD on most of the time and use the energy mgmt on the PC to keep things throttled down.

I do not know the EXACT constant watts required or AH rating, but pulling 400w on a 12v system will drain my main battery in no time, so that's not an option.

What I propose is a series\parallel 4 battery system that gives me the constant and sustained AH rating and the 24v benefits.

This will not be used every day and I do not anticipate the batteries every being completely depleted.

If I buy 4 car batteries and configure them in series\parallel, with a relay to charge them in 12v pairs when required, do you see any major flaws?

Do I HAVE TO USE the deep cycle Optima types?

Comments?

I know just enough to be dangerous. VERY dangerous.

Use ONE battery. Otherwise series is much better than parallel - ie 4x12 as a 48V system. Parallel causes problems.... Why do you want an AGM battery? An AGM battery will not deliver any more power than a wet cell, and wets of larger capacity are available. (A yellow top D31A (75AH) retails here for $550. I can get a electrically more robust 100AH (wet cell) for $220 (half the price in practice).   

series qty 2 = 24v

Parallel those x 2 = AH

Both together will give me 24v the wiring is simple.

I don't want to spend $600 when I can use less expensive batteries.

This isnt a high current setup, just long draw. I dont care if it's wet or dry for the amount of usage, but when I hear some color mentioned with the word top, I see $$$

300 - 500w from 12v is 14A and could be double that as the supplied voltage goes down.

At 24 I can not have to use 4g cable for everything.

I know just enough to be dangerous. VERY dangerous.

anonymous1 wrote: I don't want to spend $600 when I can use less expensive batteries.

So, again, why AGM? Four batteries cost the same irrespective of how you connect them.    However, how you connect them GREATLY influences their life.

anonymous1 wrote: Both together will give me 24v the wiring is simple.

But not the implementation. Why add the complexity of parallel batteries? Or will you not isolate them? If money & reliability is not an issue, GO FOR IT!. (I thought 2 in parallel was bad enough - but imagine losing THREE extra batteries when just ONE fails!) Besides, parallel is NOT simpler than series. (I assume your equipment is as low powered as it can be? And you have a suitable charger & regime?)     The rest is simple. IAW what you wrote, extend your 24V logic to 48V. Half the current yet again - hence one-SIXTEENTH the copper losses of 12 volts (else ~1/4 the cable size) - not to mention better battery efficiency and reserve time. And NO ISSUES regarding paralleling the batteries, and far less requirement to replace all FOUR batteries instead of just one. As to using Optima yellow... for starters, it seems more of a red application. But why AGM, let alone Optima??? (But I did ask.) If you want 24V, try to use TWO only batteries. Avoid paralleling. If current draw is the only issue, I'd rather have six 2V cells than four 12volt monoblocks! Are you missing the basics? Your "it appears that there will be less current draw on a 24v supply than a 12v rail" is pretty basic... Let me guess, it will be half the current. Correct? And 48V half again. Of course, the higher the (distribution) voltage, the more efficient it is. Plus the lower the battery discharge current, the greater the battery capacity (in AH) is. Hence why cars went 6V to 12V and will probably go to 42V, and why AC transmission is at VERY high voltage (it ain't just to zap mosquitoes and parachutists!)

ok thxI know just enough to be dangerous. VERY dangerous.

Glad someone remembered Ohms law, it's why trucks in Europe use 24 volts (apart from starting the engine).

For me it's a double win - the efficiencies from higher voltages, and the benefits of NOT paralleling batteries. Some still don't see the paralleling issues - maybe they should consider why trucks are 24V and vehicles may be going 42V etc. Is it because high current is an issue (it isn't for the x-kW audiophiles!), or because paralleling of batteries is an issue, or they just want to profit from everyone having to upgrade to 42V systems? (That last is tricky - who runs who? 42V will benefit equipment & audio OEMs and will kill certain aftermarkets... (about time too!)) Oh well, like I say - if I get 8 years from a single cheap battery, I'll get 16 years if I parallel two of them. (That's as logical as other claims isn't it?)

Of course I'm not apposed to a 12v system with 2 batteries in parallel as long as they can sustain the 10 hours of constant draw.

The issue would still be finding appropriate batteries that will not be over taxed, at least 75AH ratings.

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I know just enough to be dangerous. VERY dangerous.

LOL - series is still better. But 12V is easier. There are lots of batteries above 75AH. 4WDs etc typically use 100AH or more. As to overtaxing, we pay a 10% GST (Get Stuffed Tax). How much do you pay? BTW - I'm glad you changed your original reply - those "done all the time" statements go with early failures and non-alcoholic whines.     I try to answer rather than argue - see my reply to JMelton's comments that I provided no references etc. So I did (just a few), but he has yet to respond with his references. (Who say's paralleling is okay when not being used, or that the monitoring required is cheap and easy?) The last I heard that paralleling was okay was from some new gung-ho company rep that was (eventually) unable to offer any evidence; but he didn't think that paralleling batteries would double their failure rate (ie - self-collapse failure) - so you can imagine how she/he impressed me. If people answered my questions, I could answer better. You were the one that wanted cheapness yet mentioned Optima. WHY? yTF do you want an AGM, let alone an Optima? (No wonder you have problems with limited battery size!) If you think paralleling is acceptable, then do it. But if you think parallel does require some switching, then why not go series which doesn't require switching, nor load balancing etc? Monitoring series batteries is merely a voltmeter. And series equalisers are simpler too. I don't understand why you didn't parallel the 4 proposed batteries i the first place - the power draw is the same. (Excluding lower losses at higher voltages, and conversion losses.) Why the "each way" compromise? If going series, go the whole hog! The current from each battery is the same whether parallel or series (excluding parallel imbalances and failures), and more than four-folds the capacity of the 4-monoblock battery. Oh well, my attempt to educate is taken as an argument. Yet an argument is a 2-way discussion or counter points. Interesting. Both are failures.