# batteries with different potential in parallel

Discussion in 'General Electronics Chat' started by sinlikenkuri, Oct 5, 2006.

1. ### sinlikenkuri Thread Starter New Member

Jul 31, 2006
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I'm just curious, what is the output of two batteries in parallel with different potential (say 9V and 1.5 V)?

Do you know any application of this ckt?

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2. ### Fahad khan New Member

Sep 26, 2006
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Its simply not allowed to connect two voltage sources in parallel.

3. ### n9352527 AAC Fanatic!

Oct 14, 2005
1,198
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The outputs are most probably heat, smoke and electrolyte, in that order

Seriously, it depends on the internal resistances of both of them (or the current capabilities). The one that has the largest current capability will win. And please don't verify this with an experiment

4. ### Fahad khan New Member

Sep 26, 2006
8
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It is simply not allowed to connect two voltage sources in parallel or two current sources in series.

5. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Hi,

The only application is to make an IR source for a reference to aid in night firing of mortars. They use two 9 volt batteries snapped together for the heat source.

6. ### sinlikenkuri Thread Starter New Member

Jul 31, 2006
7
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i asked this question because i'm stucked in circuit analysis during an interview. although i know a very large current will flow and may cause heat, the interviewer want to see any computations using every circuit analysis i learned from college. so what i did was to assume internal resistance values but there i am stucked again with the two diff potentials in parallel. anyways, thanks for all the inputs ;-)

7. ### Syed New Member

Dec 5, 2005
6
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I would say two 'different voltage sources'.

8. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
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Its not so much that doing so isn't allowed - its just that no good comes from doing so when the potentials don't match.

For equations:
1) try picking a wire size and length, or a trace size and length - calculate resistance therefrom
2) Using internal battery resitances and the conductor resistance, calculate current flow and the temperature rise per unit time - compare to heat dissapation rate
3) impress the interviewer with your ability to gage not only the time required for the copper to melt, but the ammount of light (if any) produced
4) further impress the interviewer by calculating battery temperatures after the wire pops - also calculate amp-hours remaining in each battery

I would have failed this interview. My people skills end when questions like this begin.