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Discussion Starter · #1 · (Edited)
First, you shouldn't drain batteries below 50% as it kills their life cycle.

When you gang batteries together they are either done in series or parallel.
Ohm's Law says when you hook them up in series current stays the same & when hooked up in parallel voltage stays the same. When you jump a vehicle off with another vehicle you are hooking the jumper cables up in parallel.

When you hook batteries up - to + you are increasing the voltage but the amperage stays the same. This is where some get confused so want to explain this further.
If you have a 12VDC battery 200amp you have 200amp available & can actually draw that 200amp at once like for a high power arc welder.
If you have two 6VDC 200amp batteries you can hook them up that you have 12VDC & can draw no more then 200amp at a time. But there is 200amp available to use.

HH

I did not mean draw 200amps all at once but draw 200amps before batteries were dead.
 

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More info

here is a video link from trojan on battery technologies .


[ame]http://www.youtube.com/watch?feature=player_embedded&v=B0f4t1hn-Wo[/ame]
 

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More info

here is a link from trojan on health of battery.


[ame]http://www.youtube.com/watch?feature=player_embedded&v=DgiII0OnAZg[/ame]
 

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More info

here is a link from trojan on maintenance .

[ame]http://www.youtube.com/watch?v=SAjmpwPCN_A&feature=related[/ame]
 

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here is system in use with all day testing. HuntingHawk please tell me that this system would run more than 4-5 lights for only 7-10 hours?

[ame]http://www.youtube.com/watch?v=45kTlFfvp2E&feature=related[/ame]
 

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Discussion Starter · #7 ·
21amps times 10 hours would be 210amp/hours which would be about 50% draw on the batteries. 225AH would be 50% exactly. But that is exactly why you want to use as much 12VDC items as possible. Same power draw on 12VDC versus 120VAC would give atleast ten times as many hours.

Plus you'll notice the inverter itself uses 2.5amps so over 10 hours that's 25AH draw in addition to what the lights had drawn. Depending on ambient temperature, that can actually be higher if its warm as second fan will kick on or fan go to a higher speed inside the inverter.

HH
 

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Discussion Starter · #8 ·
I think only on my very best day have I seen 225AH from my solar panels. 180AH is more common on a good day. That is 520watts of solar panels.

And think about this. The inverter not drawing power, just on standby, will draw about 2.5amps. That is 60AH over 24 hours & you haven't even run anything. I've had rainy days that I haven't even got that much from my panels.
 

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Ohm's Law says when you hook them up in series current stays the same & when hooked up in parallel voltage stays the same. When you jump a vehicle off with another vehicle you are hooking the jumper cables up in parallel.

When you hook batteries up - to + you are increasing the voltage but the amperage stays the same. This is where some get confused so want to explain this further.
If you have a 12VDC battery 200amp you have 200amp available & can actually draw that 200amp at once like for a high power arc welder.
If you have two 6VDC 200amp batteries you can hook them up that you have 12VDC & can draw no more then 200amp at a time. But there is 400amp available to use.

HH
1
Ohm's law says nothing bout batteries. sorry, it does not.

2 And when you put a number of batteries in series, it has no bearing on max amperage. If you take regular 12 v batteries and you chain em in serial to feed an arc welder, all you will do is fry your batteries.

More batteries only gives you more amp hours.. not more amps you can draw off the circuit.

We've had this discussion before : you gotta use the correct terminology if you want to discuss electrical things. If you don't , it just won't make sense.

If you couple 2 6volt/200 Amp/hour batteries, you will NOT be able to draw
400 [email protected] , it does not work that way.
 

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The analogy with water can be applied again to explain how battery voltage, current and capacity works.


a 6 volt battery is like a 6 feet tube of water placed vertically
At the bottom of the tube you will have 2.46 psi

If you place 10 of those tubes, parallel side by side.. coupled at the top, and at the bottom.
Then at the bottom of those tubes you will still have 2.46 psi . no change.

That's how batteries in parallel work.


now, if you take those tubes and you place them on top of eachother.
Then the lenght will become 60 feet.
At the bottom you will now have 24.6 psi.

This is serial.


We have not touched electrical resistance, and electrical capacity or volume delivered with this setup. This is just the analogy that explains "voltage".

To say that the law of Ohm (resistance) has anything to do with this, is as such incorrect and irrelevant


Now to add capacity to the same analogy, amp-hour, becomes volume.
You can have a low capacity battery, which would be represented by a 6 feet tube with a 1 inch diameter.
You can have a medium capacity battery, which would be represented by a 6 feet tube that has a 1 foot diameter or a high capacity battery.. which is 3 feet in diameter.
They all have the same voltage.. but the bigger they are, the more capacity/amp hour they have.


So what is their max current then (amps) ?
Well that depends on the smallest point where electricity flows.
Now we are talking the law of Ohm
But practically, in terms of batteries, they really do not have high internal resistance.
So they can theoretically provide very high Amps..

I say theoretically, because in practice, it depends on how they were manufactured.
Car batteries can, for short amount of time provide very high amps..for cranking.
but they were only designed to provide those amps for a very short time.
In a car , they could never reach their design limit because they would be drained before they get to hot from the high cranking amps.
But if you load them in series, they will have to take the total current from the chain.
In serie Battery 1 will have to take the current he delivers, and the current deliverd from Battery 2 , 3 and 4 combined..
In parallel, Battery 1 would only have to take the current he delivers, battery 2 only takes the current 2 delivers, etc etc

And that could increase the stress on the components well beyond their design spec.

So if you combine 6 volt batteries to get the required voltage for your Arc welder, well you'll get the voltage, and assuming you have enough Amphours in those batteries, it could make the arc welder work..And assuming you used thick electrical cables to combine em..
The batteries would fry because you exceed their maximum rated current (amps, not amp-hour)

In reality, few batteries come with a listed "max amps", so you would not know how much current you can draw from a number of batteries , coupled in series.

The Amp hour rating is irrelevant when you need "max amps"


In practice, coupling them in series to get a higher voltage for continuous load is only done in low voltage, low amperage applications.. Like the TV remote or an RC car.
 

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Discussion Starter · #11 ·
Ohm's Law is about how changing either E, I, or R affects the others. So how you hook up batteries changes E or I so the others will be affected also.

So ohms law does apply.
HH
 

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More batteries only gives you more amp hours.. not more amps you can draw off the circuit.
This is only partially correct. You are making the assumption that the batteries are wired in series, when making this assertion. I believe HH was talking about bussing them in parallel to achieve higher current. He could have worded it better, but it is, in fact, possible to buss together deep cycle batteries in parallel and, provided the cabling and terminals are correctly sized and the batteries properly over current protected, you can weld directly off the batteries (I know, because I have done it, not that I recommend it, if you have other alternatives). I don't believe he was talking about connecting batteries in series to achieve a high enough voltage to power a welding machine, as very few welding machines operate off high voltage DC.

Using your metaphor of vertical water tubes, this is akin to taking several of your putative 6ft tubes, sizing them all at 6" in diameter, and teeing them individually into an 18" diameter tube. As long as there is 6ft of water in the vertical tubes, you will have 2.46psi. But the flow will be that of the 18" tube, at 2.46psi (minus friction, of course). Metaphorically, this is akin to higher current for the circuit.

In practice, coupling them in series to get a higher voltage for continuous load is only done in low voltage, low amperage applications.. Like the TV remote or an RC car.
I don't know the basis by which you are making this statement. I can cite many examples of high voltage, high current applications that do exactly this.

1: My own home runs off a 24VDC battery bank, bussed up from 6VDC batteries wired in series. Each of those 6VDC batteries is comprised of 3 2.1VDC cell internally wired in series. Thus, in this instance, we have a dozen 2.1VDC batteries wired in series to produce 225Ah of current at 24VDC. Hardly a flashlight or a toy.

2: I worked for a firm that manufactured remote power stations for oil and gas pipelines. We used diesel generators to charge battery banks that supplied UPS power for the pipelines' valve stations. The largest battery bank I built was comprised of 160 Absolyte 3-100G33 battery modules. These consist of 3 cells each rated at 1600Ah. Each module can be wired in series or parallel, as each cell has its own terminals. We bussed them in a series/parallel combination to 110VDC nominal. We had to break the battery into four discrete sections, because we couldn't get a circuit breaker big enough to handle the entire battery bank to fit into the shipping container the battery bank was built into. Each of the sections was connected to its circuit breaker by 4x 120mm^2 cables (2 positive, 2 negative). Each section of the battery was protected by a 400A circuit breaker.

The battery fed a 3 phase, 400VAC inverter that supplied standby power for the valve station.

As such, we had a battery bank that was rated for 12,800Ah at 110VDC, and could output 1,600A continuously, if it had to. This was done by series stringing 60 2.1VDC cells and bussing 8 of them in parallel.

The entire battery bank weighed ~125,000lbs, and half the batteries had to be removed in order to move the container, as a 40' ISO container is only rated for 75,000lbs, and even that exceeds what we were able to get a permit to move on the highway from the factory to the port.
 

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Batteries have an internal impedance, that increases (mostly R, linearly) as batteries are connected in series, it drops when batteries are connected in parallel. In very high current applications this can be significant.
This is where the "tube of water" analogy breaks down somewhat.
Maximum energy transfer is possible if the impedance of the load matches the battery combination's impedance.
 

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This is only partially correct. You are making the assumption that the batteries are wired in series,
Well it was not an assumption, i clearly said
"And when you put a number of batteries in series... "

And it was in response to HH's comment
Ohm's Law says when you hook them up in series current stays the same & when hooked up in parallel voltage stays the same. SNIP

When you hook batteries up - to + you are increasing the voltage but the amperage stays the same. SNIP

My main point was the incorrect use of "amps" when HH is busy talking about "amp hours"..

If you have a 12VDC battery 200amp you have 200amp available & can actually draw that 200amp at once like for a high power arc welder.
If you have two 6VDC 200amp batteries you can hook them up that you have 12VDC & can draw no more then 200amp at a time. But there is 200amp available to use.

HH

I did not mean draw 200amps all at once but draw 200amps before batteries were dead.

I'm sure you'll agree with me, that for batteries, the "200" is referring to amp hours, not amps.
And if you couple 2 batteries with 200 amp hours in series, that you cannot draw more amperage from the system.. you only get more voltage..
when you get higher voltage, you automatically decrease the maximum current your system can take.

Let's say 1 battery can take 30 Amperes draw at 6 Volt
When you put 2 of those in series.
It will only be able to take 15 Amperes at 12 Volt.. Anything more will be over the design spec of that battery
The amp hours available will double... though..


to get more amps, you indicated correctly, you'de wire em parallel.
2 times 6 volt rated at 30 amps..
in parallel, will allow you to draw 60 ampere at 6 volt.. and each battery will simply deliver 30 ampere...

The amount of Ampere hours will double as well, but that wold only give you more "time" load were to stay at 30 ampere.. at 60 ampere the batteries will be drained just as quickly as a 30 ampere load on a single battery..




when making this assertion. I believe HH was talking about bussing them in parallel to achieve higher current. He could have worded it better, but it is, in fact, possible to buss together deep cycle batteries in parallel and, provided the cabling and terminals are correctly sized and the batteries properly over current protected, you can weld directly off the batteries (I know, because I have done it, not that I recommend it, if you have other alternatives). I don't believe he was talking about connecting batteries in series to achieve a high enough voltage to power a welding machine, as very few welding machines operate off high voltage DC.

No, he was talking serial..

Using your metaphor of vertical water tubes, this is akin to taking several of your putative 6ft tubes, sizing them all at 6" in diameter, and teeing them individually into an 18" diameter tube. As long as there is 6ft of water in the vertical tubes, you will have 2.46psi. But the flow will be that of the 18" tube, at 2.46psi (minus friction, of course). Metaphorically, this is akin to higher current for the circuit.
In my initial analogy, i did not discuss current.. in terms of water, if the tube is there, and no water flows.. there is no current. at all.
there is just pressure.. Just like in a battery bank.. if nothing draws a load, there is no current..
That was the analogy i made.




I don't know the basis by which you are making this statement. I can cite many examples of high voltage, high current applications that do exactly this.

1: My own home runs off a 24VDC battery bank, bussed up from 6VDC batteries wired in series. Each of those 6VDC batteries is comprised of 3 2.1VDC cell internally wired in series. Thus, in this instance, we have a dozen 2.1VDC batteries wired in series to produce 225Ah of current at 24VDC. Hardly a flashlight or a toy.

2: I worked for a firm that manufactured remote power stations for oil and gas pipelines. We used diesel generators to charge battery banks that supplied UPS power for the pipelines' valve stations. The largest battery bank I built was comprised of 160 Absolyte 3-100G33 battery modules. These consist of 3 cells each rated at 1600Ah. Each module can be wired in series or parallel, as each cell has its own terminals. We bussed them in a series/parallel combination to 110VDC nominal. We had to break the battery into four discrete sections, because we couldn't get a circuit breaker big enough to handle the entire battery bank to fit into the shipping container the battery bank was built into. Each of the sections was connected to its circuit breaker by 4x 120mm^2 cables (2 positive, 2 negative). Each section of the battery was protected by a 400A circuit breaker.

The battery fed a 3 phase, 400VAC inverter that supplied standby power for the valve station.

As such, we had a battery bank that was rated for 12,800Ah at 110VDC, and could output 1,600A continuously, if it had to. This was done by series stringing 60 2.1VDC cells and bussing 8 of them in parallel.

The entire battery bank weighed ~125,000lbs, and half the batteries had to be removed in order to move the container, as a 40' ISO container is only rated for 75,000lbs, and even that exceeds what we were able to get a permit to move on the highway from the factory to the port.
Well i based it on regular , off the shell use of batteries.
So regular AA batteries, car batteries, boat batteries.


I ignored that for instance car batteries have internally coupled cells because that's something you get "as is"..
If they build em that way, i asume they are properly designed to handle the load of that kidn of serial connection.

The big bank you mention, sounds like fun, probably comparable to Submarine battery banks..
But as you also indicated.. those aren't regular off the shelf, car batteries..

And i'm not really basing my stuff on anything more then "not having seen anything that would indicate other wise". So if there is anything otherwise, then i will learn from it.

The big setup you mentioned, i suppose those are batteries designed for such application.. They aren't regular batteries that i can buy in a car parts store or are they?
I assume those are batteries that are specced and built with internals to take such higher currents caused by serial connections... right?
 

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Batteries have an internal impedance, that increases (mostly R, linearly) as batteries are connected in series, it drops when batteries are connected in parallel. In very high current applications this can be significant.
This is where the "tube of water" analogy breaks down somewhat.
Maximum energy transfer is possible if the impedance of the load matches the battery combination's impedance.


I agree.. but in the case of batteries, it's not that important because the internal resistance is next to nothing, typically 0.003 ohms or something..
It's not enough become a factor.. Hence why mentioning the Law of Ohm is not appropriate to discuss voltage behaviour of coupled batteries.

Internal Resistance of the individual batteries stays the same..
The only thing that changes is the voltage..

And if the voltage increases. automatically one has to take into account that the maximum load (amps not amphours) must be reduced to avoid going past the internal design specification of the individual batteries.
Unless off course they were designed for it in the first place.. as shown in the above example by Lemmy.
 

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I'm going to have to disagree with you about HH's comments and let it go at that. I took something quite different from what he wrote, and it wasn't inconsistent with my own experience. I definitely think he could have worded it better, but…

The big setup you mentioned, i suppose those are batteries designed for such application.. They aren't regular batteries that i can buy in a car parts store or are they?
You can order them off the internet as a consumer. Nothing special about them. They're just a big AGM battery. The only thing needed is a big, fat wallet.

http://www.solarelectricsupply.com/Batteries/GNB-Absolyte-IIP/index.html

My own house batteries were bought off the shelf from a brick and mortar store. I walked in with $700 and walked out with the batteries. They're Trojan T105s. Used for scissor lifts, floor scrubbers, etc.

Yes, most people don't consider them consumer items, because most people live on the grid. People who live off grid know better.
 

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And if the voltage increases. automatically one has to take into account that the maximum load (amps not amphours) must be reduced to avoid going past the internal design specification of the individual batteries.
Unless off course they were designed for it in the first place.. as shown in the above example by Lemmy.
Yes. You're totally right here. One must know the rated current, as opposed to the rated capacity, when designing a system. Current is a measurement in Amps. Capacity is rated in Amp Hours. They are not the same thing, and it is nearly impossible to find batteries have a continuous current rating on the nameplate. One generally needs to contact the manufacturer's engineering department for this information.
 

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You do have to be careful when talking about batteries and amps... The manufacturers don't make it easy for us since they use different
methods to rate batteries.

You will see several different types of ratings that have the word "amp" in them but they are apples vs. oranges.

Batteries that are intended for engine starting, ie typical car batteries, will often be rated in "cold cranking amps" or CCA. This is a measure of how many amps of current the battery can provide right now for a high load, and is used because it's an indicator of that battery's intended use, which is turning a big starter motor and a big engine.

Deep cycle batteries, such as RV/marine or golf cart types, will typically be rated in "amp-hours" which is a better measure of that use. It is a measure of how many amps that battery can provide over a period of time for extended use before the battery will drain down below a certain voltage. That voltage is very low, usually something like 10 volts, which is absolutely dead flat for use.

200 amp-hour battery: 2 amps for 100 hours, 20 amps for 10 hours, 100 amps for 2 hours. Etc...

Some battery manufacturers will put both ratings on their batteries. Some will use a different measure such as "reserve capacity" which is really hard to compare since they are often calculated differently.

If you wire batteries in parallel, the voltage stays the same but amp-hours add up. If you wire them in series, voltage adds up but amp-hours remain the same.

Then of course there's series/parallel, a combination. For example, you have 4 batteries that are 6 volt 200 amp-hour golf cart types. If you wire them into two pairs, each pair in series, you now have 2 banks that will provide 200 amp-hours at 12 volts. (Series, volts add up and amp-hours remain the same.) Then if you wire those two banks together in parallel, you end up with one battery bank that will provide 400 amp-hours at 12 volts. (Wiring the two banks in parallel, volts remain the same but amp-hours add up.) This would be a typical setup for 4, 6 volt batteries.
 

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One reason manufacturers are reluctant to post continuous current ratings is because that rating is going to change dramatically with the internal temperature of the battery. And since the internal temperature is going to be influenced by a combination of the load on the battery and the ambient temperature, the answer is always "it depends."

If your load fluctuates, causing an inconsistent internal temperature, so does your current rating. If your ambient temperature fluctuates, so does your current rating. As such, there are too many variables at stake for a manufacturer to ever put a continuous current rating on the nameplate.

You generally need to be able to communicate your average constant load and be able to assure a consistent ambient temperature to a manufacturer before they will even begin to talk with you about constant current ratings.
 
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