Brain Fart Time: Series/Parallel DC Theory

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480sparky

480sparky

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I'm having a hard time figuring this one out. It's far too late at night, but it's bugging me. Let's say I have three 2v batteries in series, I know I'll have 6 volts.

Series Parallel 1.jpg

But what happens if I reverse the middle battery? What happens to both my output voltage, as well as overall MaH output?

Series Parallel 2.jpg

Is my voltage now 2 volts, but I have a 3,000MaH capacity? Or something else?
 
480sparky said:
I'm having a hard time figuring this one out. It's far too late at night, but it's bugging me. Let's say I have three 2v batteries in series, I know I'll have 6 volts.

View attachment 22240

But what happens if I reverse the middle battery? What happens to both my output voltage, as well as overall MaH output?

View attachment 22241

Is my voltage now 2 volts, but I have a 3,000MaH capacity? Or something else?
Click to expand...

I think your voltage is now 2 volts but your capacity is only 1,000 mAH. Think of them as pumps with 1,000 gpm ratings at 100 psi. When you chain pumps you get a boost in pressure but not more output. You have 1,000 gpm at 200 psi fighting 1,000 gpm at 100 psi. The net will be 1,000 gpm at 100 psi.
 
480sparky said:
I'm having a hard time figuring this one out. It's far too late at night, but it's bugging me. Let's say I have three 2v batteries in series, I know I'll have 6 volts.

View attachment 22240

But what happens if I reverse the middle battery? What happens to both my output voltage, as well as overall MaH output?

View attachment 22241

Is my voltage now 2 volts, but I have a 3,000MaH capacity? Or something else?
Click to expand...

In your second example you do not have parallel batteries. You still have batteries in a series, but 2 are reversed and essentially cancel (and wear) each other out.

For them to be in parallel you'd need both the positive AND negative terminals connected together.
 
gadfly56 said:
I think your voltage is now 2 volts but your capacity is only 1,000 mAH. Think of them as pumps with 1,000 gpm ratings at 100 psi. When you chain pumps you get a boost in pressure but not more output. You have 1,000 gpm at 200 psi fighting 1,000 gpm at 100 psi. The net will be 1,000 gpm at 100 psi.
Click to expand...

So one battery or three.... it's 2v @ 1000MaH? In order to increase MaH output I'd have to go parallel + / -?
 
480sparky said:
So one battery or three.... it's 2v @ 1000MaH? In order to increase MaH output I'd have to go parallel + / -?
Click to expand...

Yes, tie all the +'s together and then all the -'s together. Now you'll have 2 volts and 3,000 mAh.
 
In addition to any other problems in the second circuit, note that the series current is flowing in the reverse direction through the reversed battery, charging or overcharging it. If the battery is rechargeable it could tolerate the overcharge if the current is low enough or it could be catastrophically destroyed by overcharging. The result depends on the battery chemistry. If the reversed battery is a primary battery, the consequences could vary from simply killing the battery, rendering it useless with high internal impedance or equally catastrophic as the worst case rechargeable battery. I know the original question was theoretical and hypothetical, but in the real world circuit there could be serious consequences.

DC generators might be more tolerant, or might simply not conduct at all in the reverse direction (as with an alternator-rectifier combination).
 
GoldDigger said:
DC generators might be more tolerant, or might simply not conduct at all in the reverse direction (as with an alternator-rectifier combination).
Click to expand...

That would be fun. The nearest I’ve had was three pumps all seemingly running. One had a failed non-return valve and had for some reason tripped on overload. I reset the O/L and didn’t expect what happened next, from going flat-out in reverse the motor tried to start, first time I’ve seen the motor windings hanging out of the air vents.
 
Voltages in series add.
In the first example, 2 volts + 2 volts + 2 volts = 6 volts.

But what I think you missed is that when you turn a battery around, it becomes a negative voltage. Nonetheless, the voltages in series still add.
Now, 2 volts + (-2 volts) + 2 volts = 2 volts.

This might be more intuitive is you drew your circuit diagram in a straight line (1-dimensional)
and put a co-ordinate axis beside it.
 
Tony S said:
That would be fun. The nearest I’ve had was three pumps all seemingly running. One had a failed non-return valve and had for some reason tripped on overload. I reset the O/L and didn’t expect what happened next, from going flat-out in reverse the motor tried to start, first time I’ve seen the motor windings hanging out of the air vents.
Click to expand...

I'd have paid money to see that! :D
 
drcampbell said:
Voltages in series add.
In the first example, 2 volts + 2 volts + 2 volts = 6 volts.

But what I think you missed is that when you turn a battery around, it becomes a negative voltage. Nonetheless, the voltages in series still add.
Now, 2 volts + (-2 volts) + 2 volts = 2 volts.
Click to expand...

Never mind
 
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