OT. Battery quandry(sump pump) Need help

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I know this is off topic but I have gotton so much information here I hope to get an answer. I have an in line emergency battery powered sump pump that will run about 5-6 hrs on a full charge. I wish to connect a second battery to double the pumping time but I am not sure of the proper wiring. Option number 1, I can hook the positive termimals together and the negative together just like jumpstarting a car. Or option number 2, I can hook the positive pump lead to battery 1 positive, then battery1 negative to battery 2 positive, then pump negative lead to battery 2 negative. I don't know which way is better or if one way will give me 24 volts going to the pump which I sure don't want. Any help will be greatly recieved. Thank you all. Larri
--
larry in Cinci



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larry in cinci wrote:

Use Option 1. Hook in parallel for extended power. Positive to negative will double the voltage which you don't want (series).
Gary
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You want to hook them up in parallel.
scott
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larry in cinci wrote:

You want to connect the positive to the positive and the negative to the negative (in parallel). This will give the 12 volts with double the amp/hours. Connecting the other way would be in series and WOULD result in 24 volts.
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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Thanks for such quick responses. I thought one way was wrong and the other right but my begining electrical training is over 40 years ago and the mind gets cloudy. Larry

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Don't do it.... Storage batteries have an internal resistance factor that will discharge another battery connected in parallel unless they are exactly equal in every way. difficult to achieve even if they are new identical batteries. They will discharge each other. There is an isolator that is used in motor homes etc. that will solve this problem. It is 2 diodes that will allow current to flow out of each battery to a load (Your pump) only. It must have a current capacity large enough for the load intended. You will also require another isolator to charge them, Same idea, It will allow current to flow from the charger to the batteries only and not between them. Both isolators connected properly will allow normal function of double the battery capacity but prevent a cross connection between them. One battery connection can be commonly connected. There may be a combination unit available. Check with a RV. supply co.
--
Chipper Wood

useours, yours won't work
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Virtually all modern battery isolators are full bridge design and will have 4 terminals: batt 1, batt 2, load, and charger.
Art

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Chipper Wood wrote:

Telco's run multiple cells connected in series to make up a "string" of the required voltage. "Strings" are then paralleled to provide the required amp/hour rating desired. The battery strings, rectifiers and load all connect to a common buss. They do not use isolators. IIRC the cells we're now using were installed in 1973.
A typical installation is pictured on page 5 of the following:
http://power.tycoelectronics.com/pdf/round-cell-batteries.pdf
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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A roomful of telco batteries that last for decades, "only need water every 10-15 years" and cost kilobucks is a very different beast than two car batteries in a basement.
Larry -- this issue is known, understood, and -solved-. Use an isolator.
Max
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Max wrote:

What do you believe "this issue" to be? Geez. Put the batteries in parallel. Put them on a charger. They'll charge to the same voltage. Eventually they'll self-discharge but that won't happen any faster than it would if they were sitting on a shelf by themselves and with a trickle-charger on them it's irrelevant anyway.
And I doubt that the telco pays "kilobucks" for a 2-volt cell.

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--John
Reply to jclarke at ae tee tee global dot net
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Telcos typically use -48 volt batteries. The diode drop for a combining bridge is much less significant that when the battery stack is only 12 volts.
Even if Schotkey diodes are used the losses associated with the bridge on a 12 volt system are significant.
RB
Nova wrote:

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RB wrote:

Telco's use individual 2 volt cells connected in series to give the required voltage. 24V, 48V, and 130V "strings" are common. In my 35 years of telco work I've never seen a 48 volt battery in any power plant I've worked on. They don't use a combining bridge so the "diode drop" (whatever that is) does not apply.
-- Jack Novak A power certified telco technician Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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wrote:
|Don't do it.... Storage batteries have an internal resistance factor that |will discharge another battery connected in parallel unless they are exactly |equal in every way. difficult to achieve even if they are new identical |batteries. They will discharge each other. There is an isolator that is used |in motor homes etc. that will solve this problem. It is 2 diodes that will |allow current to flow out of each battery to a load (Your pump) only. It |must have a current capacity large enough for the load intended. You will |also require another isolator to charge them, Same idea, It will allow |current to flow from the charger to the batteries only and not between them. |Both isolators connected properly will allow normal function of double the |battery capacity but prevent a cross connection between them. One battery |connection can be commonly connected. There may be a combination unit |available. Check with a RV. supply co.
I've seen this same misinformation given in rec.outdoors.rv-travel several times. It is totally incorrect!
Battery isolators are used in RVs for only one purpose; to isolate the "house" battery from the "starting" battery such that running down the house batteries doesn't leave you stranded. *That* is the function of the isolator.
Lets me offer this simple analogy for parallel batteries, because they are nothing more than storage reservoirs for electrical energy. Consider two buckets (A & B) of water sitting on the floor with a pipe connecting them at the bottom. If you fill Bucket A, the level in B will rise right along with it. Likewise, if you remove water from either, the level of the opposite will drop the same amount. (The height of both above the floor will be equal; the principle of the water level)
Note that one bucket *does not* drain the other. Why on Earth should it? Where would the energy go?
To extend the analogy to the isolator case, consider that you want to water the garden with water from one bucket, but the other supplies drinking water and you don't want to run out of that. The connecting pipe is modified to include two one-way check valves. The water supply that fills the buckets connects to the check valves so that water can flow in, but not back to the supply. Water for the garden is taken from Bucket A, but the check valves prevent the backflow of water from Bucket B, thus preserving the drinking water supply.
The electrical equivalent of a check valve is a diode. Battery isolators are nothing more than two of them connected such that the charging system can fill (charge) both batteries simultaneously while preventing separate loads from draining both.
Connect the batteries in parallel (+ to +, - to -) and don't worry about it.
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<snip>
It is not good practice to directly connect batteries in parallel, as an earlier response stated batteries do have internal resistance and unless the batteries are exactly matched the higher charged battery will discharge to the level of the lower one. If you don't believe it do the Kirchoff analysis. In emergency situations batteries are connected in parallel, such as when jump starting a car, but as you will notice there is an ititial spark and heavy current flow from the donor battery trying to charge the dead one.
The analogy of the two water buckets doesn't hold water in this case because you overlook the connection between the individual cells of the batteries. One cell can becomes high resistance, quite common, in which case the capacity of that battery becomes virtually zero; or if a cell partially shorts, due to buckling of the plates or sediment shorting the plates, in which case the battery terminal voltage drops.
In professional installations the solution would be two batteries controlled by a differential relay so when the first battery drops to its rated discharge voltage it would be dropped from circuit and the second connected. In this application the diode isolators would probably be the best alternative.
Bernard R
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Correct, and in fact if the recipient battery is "dead enough", the stranded car won't start until that battery has built up some minimum level of charge. For this reason, it's of the utmost importance to start the donor car first, so that the energy needed to recharge the dead battery comes from the donor car's *alternator* instead of its battery -- lest you wind up with *two* cars needing a jump start.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
For a copy of my TrollFilter for NewsProxy/Nfilter, send email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response.
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Bernard Randall wrote:

<snip>
Do you think the spark may be caused by the fact that one of the batteries is dead?
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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On Fri, 7 May 2004 11:27:44 -0500, "Bernard Randall"
|
| |> wrote:|<snip> |> I've seen this same misinformation given in rec.outdoors.rv-travel |> several times. It is totally incorrect!|> |<snip> |> Lets me offer this simple analogy for parallel batteries, because they |> are nothing more than storage reservoirs for electrical energy. |> Consider two buckets (A & B) of water sitting on the floor with a pipe |> connecting them at the bottom. If you fill Bucket A, the level in B |> will rise right along with it. Likewise, if you remove water from |> either, the level of the opposite will drop the same amount. (The |> height of both above the floor will be equal; the principle of the |> water level)|> |> Note that one bucket *does not* drain the other. Why on Earth should |> it? Where would the energy go?|> | |<snip> |> Connect the batteries in parallel (+ to +, - to -) and don't worry |> about it.|> | |It is not good practice to directly connect batteries in parallel, as an |earlier response stated batteries do have internal resistance and unless the |batteries are exactly matched the higher charged battery will discharge to |the level of the lower one.
So what? Be an optimist, the battery with the lower terminal voltage has been *charged* to a high voltage. The total AH capacity remains the same except for the slight I^2R loss.
|If you don't believe it do the Kirchoff |analysis.
Oh please, I'm a retired EE, don't try to baffle me with big words.
|In emergency situations batteries are connected in parallel, such |as when jump starting a car, but as you will notice there is an ititial |spark and heavy current flow from the donor battery trying to charge the |dead one.
So what? *You* do a Kirchoff analysis and tell us why this surprises you. | |The analogy of the two water buckets doesn't hold water in this case because |you overlook the connection between the individual cells of the batteries.
That's why they're called "batteries", they are a collection of cells. I didn't overlook anything of the sort. But if this baffles you, change "batteries" to "single cells" and connect them in parallel. The charge/discharge analogy continues to "hold water."
|One cell can becomes high resistance, quite common, in which case the |capacity of that battery becomes virtually zero;
So what? If it has high internal series resistance, it becomes less of a voltage source and more of a current (limited) source. So it may not contribute to the load current, but it certainly doesn't detract from it either. The *high internal resistance* sure the hell isn't discharging anything, as was the misguided concern of the post to which I originally responded.
|or if a cell partially |shorts, due to buckling of the plates or sediment shorting the plates, in |which case the battery terminal voltage drops.
So what? A failure can occur in a stand alone battery too. I guess that means we shouldn't use batteries; they might fail afterall.
| |In professional installations the solution would be two batteries controlled |by a differential relay so when the first battery drops to its rated |discharge voltage it would be dropped from circuit and the second connected. |In this application the diode isolators would probably be the best |alternative.
There are millions of RVs running around (one of them parked outside my house) and who knows how many solar energy installations that are using many multiples of parallel connected batteries. Do failures ever occur? Sure, usually from abuse in the charge/discharge cycle, but *not* because there is something inherently wrong with parallel connections. See:
http://www.trojan-battery.com/technology_connection.htm
I stand by my earlier remarks.
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<snip>
necessarily aware of what is happening.

As an EE you sure have some funny ideas, it's a series parallel operation.

extend the run time of his emergency sump pump from 5-6 hours to 10-12 hours; with a straight parallel connection the user has litttle idea what is happening to his battery pack unless he routinely tests both batteries, but battery faults, either due to high resistance cells, or short circuited cells will drastically cut down the battery capacity. The best solution is to have a single battery pack of the required ampere/hour capacity and to routinely test it.
If you need a more detailed discussion of parallel batteries have a look at this link, http://www.amplepower.com/pwrnews/parallel /, it doesn't outright condem parallel connection, but it does show that the problem is not as clear as Wes would like us to believe and is very dependent on the type of batteries used.
Bernard R
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On Fri, 7 May 2004 17:39:33 -0500, "Bernard Randall"
[SNIP]
     |If you need a more detailed discussion of parallel batteries have a look at |this link, | http://www.amplepower.com/pwrnews/parallel /, it doesn't outright condem |parallel connection, but it does show that the problem is not as clear as |Wes would like us to believe and is very dependent on the type of batteries |used.
Thank you so much for providing this link, although I was already very aware of Ample Power's web site. You clearly read things differently than I. To save the other readers from digesting this, and to put you on point let's use *your* reference for further discussion.
Remember how you got your panties all bunched up about cell shorts?
Ample Power (your reference, remember) says:    
"It is our opinion based on reference 1 and 2 that disastrous cell shorts are not a major failure mechanism, and the consequences are, in any case, no more than what happens during equalization. Since the early 1960s when we designed our first battery charger, we have witnessed no dangerous situation that resulted from a cell short."
End Quote
And
Quote:      "Up to this point, we have attempted to define the scope of the issue, and examine the failure mechanisms and their consequences to parallel configurations. We find *nothing alarming* (emphasis added) about such practice in either liquid or sealed battery systems, as long as the batteries are properly instrumented and prudently cared for. We do favor sealed batteries over liquid batteries for parallel systems because of the consistency of cell chemistry, and the fact that we can't tamper with it accidentally. We don't promote an unlimited number of batteries in parallel. One limit is indicated by the answer to the shorted cell question that was asked above. There are other features of parallel systems that *are attractive* (emphasis added)."
End Quote
Earlier you said:
|It is not good practice to directly connect batteries in parallel, as an |earlier response stated batteries do have internal resistance and unless the |batteries are exactly matched the higher charged battery will discharge to |the level of the lower one.
To which I replied:
"So what? Be an optimist, the battery with the lower terminal voltage has been *charged* to a high voltage. The *total AH capacity remains the same except* (emphasis added) for the slight I^2R loss."
You replied:
|"Totally false."
But *your* reference says:
Quote:
"First, a parallel system allows more convenient sizes which yields a greater range of systems. For instance, a 100 Ah battery can be placed in parallel with a 200 Ah unit to obtain a total of 300 Ah. Charging proceeds as expected, with each battery receiving its share of the charge current, and *each reaching a full charge at the same time* (emphasis added). On discharge, each battery supplies current according to its relative capacity, and both batteries maintain the *same percent depth of discharge* (emphasis added)."
End Quote
As I said before, I stand by my remarks.
Connect the frigging batteries in parallel and stop fretting about it.
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wrote:

The reference I made to cell shorts was that the terminal voltage would be lower with a cell shorted, I said nothing of any fire damage. What is the result of this? Lower voltage and smaller capacity at the best, at the worst a cell where it isn't a dead short but inhibits the cell from properly charging but the internal resistance is sufficiently high to inhibit the required current flow. >

In the paragraph you quoted above I believe you will find that they are refering to two batteries of different a/h capacity, not a situation where either battery is in fault condition whether it be one cell is high resistance or shorted. In either of those cases their a/h capacity is totally unknown. Or are you claiming that you can predict the a/h capacity of a damaged cell??
This thread is discussing the situation as it applies to a sump system which appears from the supplied information to be unattended. You claim to be an EE, all the experienced engineers I have worked with don't look at situations through rose colored glasses as you appear to advocate. Anyone with an engineering background will have to take into account what happens in the fault condition of a critical piece of equipment. In this case the battery is one of those items. As I said in my initial post, and now expand, if it is a critical application I would use 2 batteries with separate chargers and a differential relay to auto change the batteries when the first reached its rated dischage voltage.
Bernard R
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