Another bus nut and I are having a big disagreement over the amp hours in a set of batteries wired in series versus parallel. I know this has been explained before but can someone out there please, once again, set the record straight?
If you have one 12 volt Lifeline AGM, rated at say, 250 amp hours, and you wired two of them in series to feed a 24 volt inverter, has your available amp hours increased to 500 amp hours, or does it remain 250?
I said it remains 250 amp hours and would only increase if the batteries are in parallel. He thinks I'm dead wrong.
Thanks in advance for helping set the record straight.
Mike in GA
Two 250amp/hr batteries in series will make a 24v 250amp/hour battery bank. Two 250amp/hr batteries in parrallel will make a 12v 500amp/hour battery bank. Good Luck, TomC
You can't think about volts or amps in isolation. Gotta multiply them together to know your available power.
Mike,
Think of it this way, when you connect two batteries together you double either amps or voltage.
Mike, you are dead right and your friend is the one who is wrong.
This is the reason I do not like to use amp-hours to discuss battery bank capacity. A much better measure is watt-hours, which is the same unit used to measure household electric consumption. Those two battery banks would have exactly the same number of watt-hours, but the one with twice the voltage will have half the amp-hours.
-Sean
http://OurOdyssey.BlogSpot.com (http://ourodyssey.blogspot.com)
Yeah, I was thinking that that "Bump-Bump-Bump" sound that I heard coming through my computer was Sean smacking his head against a cinderblock wall ....
The sooner we make this stuff easy, the sooner the crooks can't take advantage of the unwitting?
I like watt-hours as a standard for busnut use as well.
happy coaching!
buswarrior
I've always used watt hours and converted it to amp hours for posting purposes. Isn't that funny...
Breian
Thanks everyone. Now I'm going to go collect on my bet!
Mike in GA
OK so what is the difference between running in a series versus parallel?
Kevin
Quote from: Kevinmc5 on February 17, 2012, 04:00:41 PMOK so what is the difference between running in a series versus parallel? Kevin
Kevin, series is red cable from starter to + on battery 1, then a "jumper" between - on battery 1 and + on battery 2; and the - on battery 2 to the black cable to the starter (or ground). If you have two 12V, 250 Amp/Hr batteries connected this way, you get 24V, 250 Amp/Hr.
Parallel, is a jumper between + on both batteries and a jumper between the - on both batteries; then the red cable to the starter connects to the + pair and the black cable to the starter connects to the - pair. If you have two 12V, 250 Amp/Hr batteries connected this way, you get 12V, 500 Amp/Hr.
So, of you want to double the voltage, you go series; if you want to double your amps/"current"/"capacity but keep the same voltage as the batteries, you go parallel.
I pray to S/He that is holy that this is a correctly presented half a$$ed truth by this heretical busnut....
I am so sorry in advance for what I might be doing wrong here...
This is where amp hours are a problem, and watt-hours are better.
Hang in there, audience, let's see if this helps?
Here are two mathematical truths, not mine, I'm just a parrot:
watt = amp x volt and amp = watt / volt
So, using the example of 12 volt batteries rated at 250 amp-hours, let's play around adding them together.
one 12v 250 Ah battery is worth 12v x 250Ah = 3000 Wh
So, if one battery is worth 3000 Wh, adding another should give us 6000 Wh, shouldn't it? SHOULDN'T IT???
So, working the math backwards, 6000 Wh at 12 v would be hooked up in parallel and give me 500 Ah.
But if we connect two in a series string, two of the little 3000 Wh plastic cases of mysterious yet miraculous energy, the 6000 Wh at 24 volts now, gives me an answer of 250Ah?!?!?
Of great confusion and frustration, using amp-hours, for some insane reason, I don't know about you, but when we end up with an answer like this, I am reminded of what it was that put an end to my mathematical and physics schooling.
Perhaps it may be over right here in an internet spectacle yet again?
The watt-hours measurements are making sense, add a battery, get more juice, measured in "watts" for short, regardless of voltage, where using the amp-hour standard seems to make no sense, in that it stays the same for the two examples. I've no time left to waste on the pleasantries of the scholarly establishment.
We are busnuts, hair is receding and graying, and we just need to build a battery bank to support our house systems with as much intelligence as we have left.
This is the double speak that the crooks will try to mess with our heads. Or we confuse ourselves with.
Would that be the crooks in our own heads?
Work in watt-hours, and things make a little more sense for us bus driver types.
And then we can talk about the long term health of the batteries, not using up more than half of that 3000 Wh per each battery... so, now I need twice as many of the little darlings....
ok, I will stop now. Tell me if I need to delete my account.
happy coaching!
buswarrior
Well, you got the math right!
The reason I use watts to figure things out is they represent power - actually doing something. They are independent of voltage, amps, AC or DC. They are just what you can do with what you have. For example, if you want to figure how long you can run a refrigerator from a battery with an inverter, you just figure how much power it needs - Kilowatt-hours per year- usually on a sticker on the side of the box. You convert that to watts per hour through your inverter, and that's how much battery you need to run the thing for an hour. The final step is to convert that to what your actual battery bank is - volts and amp-hours - so you know how many of the heavy nasty things you need to buy...
Brian