Contrary to drawing number 2, batteries are never wired in parallel. The reason is that batteries have slightly different voltages and capacities, and wiring them in parallel as shown would cause a lot of current to flow from the stronger batteries to the weaker ones, wasting energy and quite possibly damaging the batteries.
Link to the article
http://www.straightdope.com/columns/read/2951/
And they are quite often wired in parallel, and no, it doesn’t hurt them.
Sorry Civiltongue, I concur with bdgr, but will add this: Batteries can be wired in parallel for more amps… however, if a battery in the lineup in #2 is below charge of the other batteries, it will simply be charged by the other batteries, and the entire output will be reduced, because power was expended to charge the battery. Nothing will get hurt, unless you are talking about a wet cell lead acid battery that has a dead cell… then all others may discharge into that short, and likely cause a fire. Sometimes, stacks of series connected batteries are connected in parallel to other stacked series batteries.
civiltongue: Don’t get out much do you, tech-wise?
I repair electronics as a hobby and have seen parallel batteries so many times you wouldn’t believe it. The most common example I run into nowadays are the cells in laptop batteries. (I’ll take out the dead ones and replace them to semi-revive the pack.) Usually grouped into 2-3 in parallel. In order to provide enough amp-hours you need something like 8-12 cells. Putting them all in series would give an “interesting” voltage compared to the needs of the computer.
Yes, the fact that one cell going south hurts the cells it’s linked to which in turn makes the whole battery prematurely fail is a problem. But the manufacturers are more than happy to sell you a brand new battery. Gotta make money somewhere.
I’m sure the car-mod people will be by shortly.
One of the most difficult concepts of electricity for the lay-person involves the differences between voltage, current, power and energy. The article furthers the issue by using the verbiage “6 volts of power.”
Shame on author for perpetuating ignorance.
Batteries are often wired in parallel. An example nearly everyone is familiar with is jump starting a car. Diesel powered pickup trucks typically have two starting batteries wired in parallel…and then there are those that think a car needs several kilowatts of audio power and the ability to leap off level ground.
Things CAN more easily go wrong with such a connection though. Especially when it is single cells wired in parallel. (NOT the case in automotive applications) In many battery types it is possible for a cell to fail shorted. If it is part of a parallel battery, Then the other cells may discharge at high current through the bad cell, heating it to very high temperature. In some cases the failed cell may violently rupture (“mild” explosion) due to steam pressure, or may start a fire.
It is good practice to protect each cell in such a construction with a temperature or over-current fusing device in order to prevent fire.
This can still happen when multi-cell batteries are paralleled, but is far less likely, as all the cells in a given series string would need to fail shorted in a short enough time frame for the battery to have remained in service. In a series/parallel battery good cell(s) in a series string with a failed cell will be (over) charged at a high rate when their string mate goes TU. In some cases this may still be problematic, more likely if there are only a small number (2-3) cells in each string.
Still, if you need to place 6X 1.25V 2200mAh cells in series parallel to get a 3.75V at 4.4 Ah battery, you are better off doing it thus:
_
I I
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Rather than
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Even though in an ideal world the two constructions would be equivalent. Again:a fuse in each series string is good practice. Also, it is good practice to match the cells used. All new identical cells at the very least, better if from one manufacturing lot, and best if sorted by actual capacity testing prior to assembling the battery. In no case should different capacity, brand, model, history, or age of cells be paralleled. Yes, the custom car guys get away with it and live. I don’t endorse their taste in “music” either…and note they are paralleling 6 cell strings, not individual 2V cells.
When the voltage of the series strings makes it practical, diodes may be used to isolate each string from being back-fed by it’s mates, but special arrangements must then then be made to allow charging, and the battery might well experience catastrophic failure while in charging configuration. This option is represented by the “battery isolators” used between the starting and house batteries in some RVs.
Ok, my dyslexia kicks in all the time when remembering of how to wire batteries properly. When wiring in parallel for automotive use, I have always been told to make sure I have two brand new batteries manufactured at the same time so they are both equal and brandy-new. How necessary is this? If you have a one year old battery, do you really need to go out and buy two brand new batteries to run them properly in parallel?
A friend of mine lives “off the grid” using solar power. He has a large shed full of batteries (about 3 weeks worth of no sun power). They naturally are wired in parallel. He gets them as salvage from phone companies. They are obviously not new. It works fine. They all will charge to an identical voltage. One that’s lower than the rest will suck up more charging current than the others, until it reaches the same voltage/charge level as the rest. NiCad or NiMH batteries won’t necessarily work that way, but lead-acid ones do. You don’t need new ones, or even the same model/capacity/brand. They just have to be nominally the same voltage (e.g. all 12v).
there are applications for battery banks to have cells both in parallel and series.
No.
The batteries will soon equalize themselves, with the weaker one sucking charge from the stronger one (or sucking more from the generator) until they are equal. So for the time that they are equalizing, you will have less charge available than if they were both brand new batteries. But that should only be a short time after you install them.
In fact, some would say you should NOT use 2 identical new batteries. Because they are likely to both wear out and fail at the same time, leaving you stranded with no working battery. Using a pair made up of a new battery & a used one will probably result in the used one failing first, leaving the new one still working enough for you to get home. (Actually, batteries age at different rates, so even 2 identical new batteries will probably wear out at different times.)
It’s not strictly necessary, but for a number of reasons, it’s best practice to have your batteries to have the same charge cycles. I prefer mine to from the same batch with the same manufacturing date, as batteries start to degrade from the moment they’re manufactured.
I just wired 8 6-volt gel acid batteries for 4 parallel banks of 2 each in series to provide 12v for an inverter system here in Haiti last weekend b/c 12v gel acid batteries are hard to get a hold of here. I prefer 12v gel acids but thems the breaks.
I’d just like to say that my space-time continuum tearing machine requires the batteries be inserted in an alternating pattern. Thanks.