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Battery Banks and Capacitance

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Battery Banks and Capacitance

Post by Soapbox » Thursday, 04 February 2010, 9:41 AM

Well I'm at the stage where I will be adding a couple of more batterys in the rear to raise my capacitance of available power.
Can some one please explain how I can figure out the reserve. Specificaly Amp hours in reserve. I'm realy cornfused do I add up all of the batteries ah for a total of how many amp hours? 55 ah + 55 ah = 110 ah?

I have 3 yellow top batterys to use. The only battery which will fit in a Honda Fit is a D51R which happens to be 38 AH; however, I also have 2 d34 which are 55ah.

Front 38
Rear 55
Rear 55
Total ?




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Re: Battery Banks and Capacitance

Post by drdx » Thursday, 04 February 2010, 10:12 AM

Since they're in parrallel, I'd think you'd just add them, but I do know that in most multiple battery situations it is advised to use the same model battery. I'm not sure if that matters or not.

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Re: Battery Banks and Capacitance

Post by Soapbox » Thursday, 04 February 2010, 10:30 AM

I believe you are correct about using the same. But here is my reasoning. If under the hood the engine motor replacemend calls for a D51 which is 38 amp hours this would take into account all of the potiential draw from the Stock electrical demands. Now the ECM (electronic control module) isn't capable of determining extras we all love therefore the end user must account for additional capacitance. Adding the same 38 amp hour batteries would take 2/3rds more to equate to the same amp hours as adding 2 55 amp hr battteries. Moreover, in a bank we are talking a ballenced system just because one glass or battery is full doesn't mean the other glasses or batteries won't fill up with the extra reserve. I think it is of more importance that batteies are closer ballenced in age vrs the size of the glass. But I may be wrong that's why I am Cornfused.

My additional draw calculates out to be 87 amps average with peaks of 160 amps.
On my car the accessories are fused rated @ 80 amps at the battery (i've never seen a car like this but the only two things which are directly connected to the battery are the alt and the starter fuseable links yes but not like this).
I'll look up some calculations and post up if someone else doesn't. but I have read and I still only vaguely understand.



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Re: Battery Banks and Capacitance

Post by drdx » Thursday, 04 February 2010, 10:42 AM

Well, you're talking amp hours. That's a little different than the cold cranking amperage. Amp hours, to me, more relates to long constant draw situations. You have an alternator and multiple batteries. If your demand is intermittant, the system has the ability to cushion the blow of bigger draws and catch up. If it is a radio that you are transmitting on, the draw only kicks in when you're transmitting and using that high draw item. Unless you plan on parking with no charging taking place, then I don't see how the amp hours applies. If you're talking with the motor running, it is different. Also, the alternator is going to charge different based on rpm. Even if it is a big alternator, at idle, it will only charge some of its real rating. Once you're above 1000 rpm's or so it will pick up most likely.

So let's say you have 200 amp hrs of batteries. That doesn't mean you have 200 amps plus the alternator on tap. Look at the CCA, factor in the average alt. output, be conservative, and you'll do fine. Use THICK wire on high draw items, don't run unnecessary items, like a stereo that is on but the volume is down, or driving lights. It all adds up.

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Re: Battery Banks and Capacitance

Post by Soapbox » Thursday, 04 February 2010, 12:30 PM

I have 1 run of 1/0 guage 15' long rated @ 500 amps but fused @ 240 amps. For Gounds I have done the flowing Battery to body, Battery to Engine, Battery to Frame all in 1/0 guage. On the bank I have each battery grounded @ a common point to body and frame with 1' sections of 1/0. It's a small car so I don't want to add any more weight than I have to.

With throwing in the CCA you've realy put another stick in the mud. I assume a the simple replacement of the stock wet battery to the AGM is an definate upgrade. I would have to look at the numbers.

So the answer to the origional question is: I can add the amp hours is yes for a total?




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Re: Battery Banks and Capacitance

Post by shooter » Thursday, 04 February 2010, 12:40 PM

i know it is kinda off topic but , dont forget good fuse holders and fuses . car fires going down the road can be deadly .

good luck and enjoy



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Re: Battery Banks and Capacitance

Post by drdx » Thursday, 04 February 2010, 13:41 PM

I think you can, but then again consider that your RESERVE hours, and probably not an indicator for your all out draw available as far as amperage on short demand. Worst case, you are erring on the safe side.

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Re: Battery Banks and Capacitance

Post by 'Doc » Thursday, 04 February 2010, 23:49 PM

Yes, you can add the capacities of the batteries for a total. Just remember that you alternator is going to have to run considerably longer/harder to keep everything charged to capacity. And with those AGM batteries, the output of that alternator had better be at least 14.4 volts to keep the @#$ things charged. The typical 13.5 volts ain't gonna do it. (Working on my second 'red top' battery. Get the 'yellow top' if you possibly can! They handle larger/deeper draws better. Wish I had known that to start with.) Wouldn't seem like 1 measly volt would make any difference but it certainly does.
It's also a good idea to keep all of the connected batteries the same size. Some times you can't but 'close' does count. The 'weaker' one of the bunch will really get a workout.
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Re: Battery Banks and Capacitance

Post by Soapbox » Monday, 08 February 2010, 8:03 AM

Yellowtops it is...err they are 3 of them only difference is the one under the hood is group 51 and the other are group 34. I checked alt out put and at idle it is 14.5. Due to the fact the honda's alt is controlled by the ecu the lowest I sould see is at idle. So I have 148 amp hours available.



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Re: Battery Banks and Capacitance

Post by executioner » Wednesday, 10 March 2010, 15:30 PM

Soapbox wrote:Yellowtops it is...err they are 3 of them only difference is the one under the hood is group 51 and the other are group 34. I checked alt out put and at idle it is 14.5. Due to the fact the honda's alt is controlled by the ecu the lowest I sould see is at idle. So I have 148 amp hours available.
Yes you have 148 amp hours ava. Thoery is you can pull 148 amps of load for one hour sortof, or 74 amps of load for 2 hours
sortof. That amp hour ava. to use will dischage the batts to about 10 volts or so. Thats to low for most 12 volt devices.

Why are you needing to use amp/hrs, what are you trying to fig out.



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Re: Battery Banks and Capacitance

Post by Soapbox » Thursday, 11 March 2010, 8:17 AM

The foundation of a good electrical system to me is the formost consideration when designing both a efficent and stable system. I will be drawing approximately 160 amps off the system and don't want to do dammage to my equiptment. Approximately 1500 watts.



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Re: Battery Banks and Capacitance

Post by 'Doc » Thursday, 11 March 2010, 8:28 AM

Considering how you would have to go about it, an amplifier used on a base is a time when using a tube amplifier seems like a real good idea. The power supply isn't nearly as difficult/cumbersome to manage. Just plug the thing into the wall outlet. Certainly won't be a 'wal-wart', but beats a hundred pounds of batteries.
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Re: Battery Banks and Capacitance

Post by drdx » Thursday, 11 March 2010, 9:06 AM

I think you're right on the money on the amp draw approximation. Just remember to factor in the draw of the radio (5 amps or so for a cb, more for a hi power one) and the driver if you have one. It's not like you'll be drawing that 160 amps constant. You're not transmitting constantly, and when you are, depending on the deadkey and peak draw, max draw is not a constant, so you should be fine. The batteries, especially in your case, act as a nice buffer for that brute force draw of a large amp.

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