OT. Battery quandry(sump pump) Need help

[Bernard Randall]

Totally false.

The only reason I mentioned the spark is that non electrical readers aren't necessarily aware of what is happening.

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

The big 'so what' is that the OPs concern was having sufficient capacity to 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,

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

[Wes Stewart]

[SNIP]

|If you need a more detailed discussion of parallel batteries have a look at |this link, |

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.

[RB]

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:

[Nova]

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)

[Bernard Randall]

The reference I made to cell shorts was that the term>

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

[Wes Stewart]

|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.

No, this thread began with:

|"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."

The OP simply wanted to know whether to connect a second battery in series or parallel. Many respondents before I gave him the correct answer.

Note that the OP simply wanted to increase the Ah capacity of his battery. He did not ask about redundancy, automatic changeover, or anything about unattended operation. Perhaps he should have, but he didn't seem to be concerned about it, so neither am I.

One respondent (probably repeating something he had read) gave out totally erroneous information thus:

Because the correct answer was given before I read the OP, I did not reply until the foregoing was posted. I offered a simple analogy in layman's terms of why this statement was incorrect and explained the operation of battery isolators in the same gentle terms.

Apparently itching to complicate things, you started off with:

|"It is not good practice to directly c "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 about such practice in either liquid or sealed battery systems....."

Your reference and I seem to agree.

I'm gonna go cut some wood now.

[Chipper Wood]

Wes, Actually I have used this configuration.... (Storage Batteries in parallel) Back when cars were still 6 volt. Living in a cold winter climate I decided to use two dissimilar 6 v. batteries in series to start my truck on cold winter mornings using some relays and solenoids, paralleling them when not starting, charging them together. Worked fine the first day. The next morning they were both almost completely drained. After checking and rechecking my circuits this continued until I added a switch to disconnect one battery from the charging system when idle and connecting it only while the truck was running. Walla ! solved the problem and worked great except when I forgot to flip the switch when parking overnight. I devoted some time and effort to find out why this had occurred and passed what information I gathered along. If you have real experience with this situation, I would be interested in your results. In theory, both theory and practice work. In practice theory doesn't always cooperate.

[Gothumbs]

I don't really think the original poster gives a crap about your past. He just wanted some information not what you once did.

[Wes Stewart]

|Wes, |Actually I have used this configuration.... (Storage Batteries in parallel) |Back when cars were still 6 volt. Living in a cold winter climate I decided |to use two dissimilar 6 v. batteries in series to start my truck on cold |winter mornings using some relays and solenoids, paralleling them when not |starting, charging them together. Worked fine the first day. The next |morning they were both almost completely drained. After checking and |rechecking my circuits this continued until I added a switch to disconnect |one battery from the charging system when idle and connecting it only while |the truck was running. Walla ! solved the problem and worked great except |when I forgot to flip the switch when parking overnight. I devoted some time |and effort to find out why this had occurred and passed what information I |gathered along. If you have real experience with this situation, I would be |interested in your results. In theory, both theory and practice work. In |practice theory doesn't always cooperate.

I understand what you were doing, but without seeing a schematic of the way you did it I cannot understand totally what the problem was. Are you sure that one of your solenoids/relays wasn't energized in the off (not running) condition.

Solenoids that handle the currents you were dealing with (particularly on a 6V system) draw considerable coil current and could discharge the batteries if left energized for long periods. If your added switch (the "cure") was also disconnecting this parasitic load, then that is the answer to your problem.

Otherwise, there is no reason why having two (or more) functional batteries in parallel will increase the self-discharge rate. My travel trailer used to sit for months at a time with two deep-cycle

12V batteries in parallel without charging. The trailer has a built-in charger of very poor design that didn't properly maintain the charge and also generated huge amounts of radio-frequency interference, so it was usually turned off. I have since designed and built a "smart" three step charger that is electrically quiet and can be connected indefinately.

I need to build another one to maintain the battery in my '99 Camaro, which goes dead while it is parked and we are traveling in the RV. There is apparently a substantial parasitic load from the ECM and anti-theft system that discharges the battery. After the last 3-month trip, I had to replace the battery.

Wes

[Rossco in Oshawa]

ROFLMAO at all the 'experts'...

...parallel batteries will not self discharge below the level of the lowest voltage battery... period. Unless of course you are applying a load to it/them and allow the discharge to continue until the battery capacity is depleted. We ar talking relatively good batteries here.

Typical non-cellular CO TELCO batteries are float charged at typically -54Vdc and 'equalize' charged at approximately -55.5Vdc -56Vdc. All the small 1.2 - 1.3Vdc cells add up to the appropriate voltage. They are monitored on a regular basis with an electrolyte check and are replaced if the electrolyte or the cell voltage tests below a certain point (varies per manufacturer). If you leave them without maintenance to sulphate/short/self discharge, whatever you wanna call it , they will self destruct and bring the overall voltage down to whatever the sum of the cell voltages are, minus the lost cell until the internal resistance of the defective battery causes more extensive problems in voltage level.

We are not talking TELCO batteries here...

Charging car batteries in parallel will work, with all things being approximately equal, with the main concern being that the current capacity of the charging equipment is adequate to charge the batteries at a trickle rate. You are doubling the current capacity of the batteries and if the battery charger design is good then no problem. It will take longer for the batteries to fully charge though. If the dead batteries try to charge at a rate higher than the charger is capable of providing on a steady basis, the voltage will drop the batteries will not charge and the charger will likely blow a fuse/pop a circuit breaker or whatever it does to protect itself when excessive current is drawn for any length of time.

In a battery series circuit, a defective cell (battery) will cause problems for the rest of the cells in the series. Unless you want the voltage to increase, do not put them in series. If you want higher current capacity, put them in parallel.

...just add me to the list of 'experts'

[Charlie Self]

Gothumbs does it again:

Who are you writing to? And why? If you don't like the thread, pass it by. If you think you're some kind of net cop, you're due for a big surprise.

Charlie Self "Don't let yesterday use up too much of today." Will Rogers

[CW]

Do you really believe that?

[CW]

Considering the disinformation being passed in this thread, I was going to say something but, Wes, you have a good handle on it.

[J. Clarke]

He's not looking for a solution for "a critical application", he's looking for a longer run time on a system that is working satisfactorily with a single battery. He's not dealing with a discharged or damaged battery, he's dealing with two batteries both of which will unless something malfunctions be fully charged and in equilibrium at the start of operation. Thus none of your concerns apply and I don't really understand why you're on about this.

[J. Clarke]

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.

[Wood Butcher]

And I got tired of scrolling my mouse wheel about half way down and gave up.

C'mon dude, learn to snip.

Art

[Bernard Randall]

The only person who knows if he is dealing with a critical application is the OP. The OP as in many of the posts on this and other NGs by the nature of his question is asking a basic question which shows either directly or indirectly that he does not know the full ramifications of his actions. Hopefully, through discussion, he will take the appropriate action depending on how critial he considers the application.

When dealing with batteries you are using an element which will ultimately fail, fact of life, depending on how it is used will affect how soon it will fail. However, battery powered equipment has many underlying potential problems, only a few of which were even touched on it the original thread. The bigest issue which was not discussed was what type of battery charger was being used. From the OP it appeared that the battery was being permanently float charged. Here I quote "A cheap, unregulated 'trickle' charger or manual two stage charger can overcharge a battery and destroy it". The full text of this can be seen at this link

mistakenly I try and look beyond the basic question posed, and if I see potential problems I try and bring them to the OPs notice, if he doesn't consider my viewpoint applies he just ignores it, isn't that one of the benefits of NGs?

Bernard R