In physics, where you have a set up of resistors in parallel in a circuit, the effective resistance is the reciprocal of the sum of the reciprocal of each individual resistance.
What about batteries / cells arranged in parallel? What is the effective voltage?
It’s been a while and I’m most likely wrong here, but I beleive in general batteries in parallel will have the same voltage but the amps go up, whereas batteries in series will have their voltages added.
You are not generally supposed to put two voltage sources (e.g. batteries) in parallel, unless they have the same voltage. You will short the circuit and apply an infinite current between the two if they have any difference. I believe in theory the larger voltage would be the one to appear as the effective voltage but behavior would be unpredictable (and dangerous). If the two sources are exactly the same, the voltage of one individually would be the effective voltage, and their currents would be summed to form the effective current.
** Joey P** is correct. The voltage will be the same as having one battery, but you will have a higher current available to use.
Andrew
In electronics, to say that two things are in parallel by definition means that they have the same voltage. I suppose practically speaking putting batteries in parallel could increase the current (or more likely, allow a larger current. As an analogy, better tires allow you to go faster, but the don’t actually make you go faster), but from a theoretical standpoint the current depends only on the voltage and the resistance. The main effect is to increase the life of the batteries.
Does it? Resistors of different value can be used in parallel without violating the meaning of the word.
Batteries (or cells rather) in parallel just means that their positive and negative terminals are all commonly connected.
Well, yes, it does. The two resistors will have the same voltage across them.
If you are talking ideal batteries, two of them in parallel will have the same voltage as just one, as already stated by others.
Actual batteries have internal resistance so when a load is connected, there will be a voltage drop. With two batteries in parallel there will be smaller drop. So you could say that when current is flowing, two batteries in parallel has a slightly higher voltage than one battery. The difference may be negligible - it depends on the current and type of battery.
I don’t think that is terribly relevant; Parallel refers to the physical configuration.
I can’t see what your difficulty is, Mangetout.
If two elements are in parallel, then by the definition of parallel, which refers to the physical configuration, and also to things like Kirchoff’s Voltage Law, the voltage across them will be the same.
You can connect a 9 V battery and a 1.5 V battery in parallel. The voltage across them will be the same. It will be somewhere between 1.5 V and 9 V, depending on the internal resistances of the two batteries.
Neither battery will last very long, and it’s not a good idea, but what The Ryan said about the voltage being the same is perfectly correct.
I wouldn’t say that “parallel” means physical configuration. After all, I can connect two batteries in parallel, when the two batteries are actually sitting at right angles to each other. Maybe I wouldn’t go so far as to say that the definition of parallel is that they’re at the same voltage, but it’s not far off the mark.
common terminals regarding positive and negative charge
could be taken as parallel
as opposed to uncommon in series…?
I think I may have misunderstood Th Ryan’s post; it seemed to me that he was saying that two batteries of different native voltage could not be truly considered connected in parallel because they were not alike; on re-reading though, it seems more likely that he was stating they could not fail to output different voltages by virtue of the fact that they are connected by like terminals and that the voltage measured across any points on the pair of connections would be the same.
My apologies for the confusion.
DougC touched on the real problem with connecting batteries in parallel. Nominally, they have the same voltage, but in reality, small variations exist. Because, as pointed out, parallel elements “strive” to be equal in voltage, the higher voltage cell will discharge a bit to equalize. Time causes the voltage of all batteries to drop and chemistry variations mean that the two batts will not age at equal rates. Essentially, both batteries will adjust voltages back and forth until each is dead. This will happen MUCH faster than the natural chem related discharge itself.
brendan
good evening.
most conventional fire alarm devices connected to a fire alarm control panel operate at 24 vdc. the back up batteries for the control panel are usually two 12 vdc batteries hooked up in series.