Current and Voltage sources in series and parallel respectively

[vineel567]

Hi All,

I am new to electronics and eevblog forum, I have a question from basic electronics.
1. What are the consequences of connecting current sources in series in a circuit
2. What are the consequences of connecting voltage sources in parallel in a circuit.

I found some references
http://web.cecs.pdx.edu/~prasads/BasicLaws.pdf
https://filebox.ece.vt.edu/~LiaB/Lectures/Ch_4/Slides/Voltages%20Sources%20and%20Current%20Sources.pdf
But interestingly one contradicts the other.
Please can someone explain what happens when above arrangement is used in a circuit and Is it desirable to use the sources in the above said configuration?

Thanks in advance.

[alm]

These documents agree that voltage sources in parallel (or current sources in series) is a bad idea, although less bad if they have the same voltage. An ideal 2V source will provide 2V no matter what. The same applies to an ideal 3V source. If you connect these in parallel with ideal wires which have zero resistance, than there is somehow a 1V drop across that ideal wire connecting them.

Real voltage and current sources have finite output impedances (think of it as a resistor in series with an ideal voltage source that limits their maximum current). So if you connect real voltage sources in parallel current will flow and voltage will drop over these 'resistors' to equalize the voltage. This could generate heat and may not be healthy for the source, though.

[sub]

For ideal

[vineel567]

Thanks alm,

So Ideally there is nothing wrong in connecting two equal voltage(ideal) sources in parallel.
The only undesirable situation arises when two voltage sources(non ideal) with different voltages are connected. And that too these non ideal voltage sources will have some internal resistance which will come into picture to balance the both voltage drops. Please correct me if am wrong. Thanks

[awallin]

So Ideally there is nothing wrong in connecting two equal voltage(ideal) sources in parallel.

There is also nothing gained by connecting two equal ideal voltage sources in parallel 
In practice you might connect two batteries in parallel to get more current to your load.

[alm]

And that too these non ideal voltage sources will have some internal resistance which will come into picture to balance the both voltage drops.

Yes, but whether the voltage sources will survive this balancing is a different matter. I would expect that connecting a fully charged 12 V car battery and 24 V truck battery in parallel would kill at least one battery, for example. Two AA cells of the same capacity/chemistry/charge level in parallel is generally fine, even though the voltage will be slightly different.

[vineel567]

Thanks alot awallin, alm, got it.

[Nerull]

There are a few applications where this is done. It's not uncommon to find car batteries connected in a mixed parallel/series fashion in small electric vehicles. The LM317 datasheets from a few manufacturers show application notes hooking them in parallel. My HP3615 supports both series and parallel operation. The world will not end if you connect two voltage sources in parallel, but there are precautions you must take.

What happens when you connect two voltage sources in series, assuming both are 'floating', is you add the voltages. Almost every handheld battery powered device is powered by multiple batteries in series.

[vineel567]

Thank you

[rolycat]

Almost every handheld battery powered device is powered by multiple batteries in series.

While that used to be the case, the combination of lithium and lithium-ion cells which supply 3V or 3.7V respectively with modern low voltage circuits is rapidly changing that convention. Also, many LED torches and other gadgets are powered from a single 1.5V battery using a boost converter to produce the higher voltage required.

Finally, many portable devices are powered by a single 9V battery containing six cells in series (as recently illustrated by Dave's dissection video). "Battery" is a generic term for a device containing one or more cells.