I appreciate this site that is allowing me to get an answer to a phenomena I am witnessing. I'm trying to series 5- D Cell Batteries. However I cannot make it completely through because the middle battery refuses to pass the voltage through. I can hold the wire from the negative post of the second battery to the positive post of the third battery and get 7.4 (plus or minus) on the multimeter. However, when I solder the wire in place the total voltage will disappear and only three batteries on one side will complete a circuit of 4.5 volts, while the other two batteries complete a circuit of 3.3 volts. I am baffled by this. Is my body (finger) touching the wire to the terminal acting as a capacitor allowing the voltage to series thru? It almost seems that the action of soldering is shorting out the whole series. Could someone shed some light on this?
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4$\begingroup$ You might be better asking on the Electrical Engineering Stack exchange $\endgroup$– John RennieCommented Apr 9, 2015 at 18:14
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2$\begingroup$ Are you soldering directly to a battery terminal? That would be difficult to do reliably. $\endgroup$– garypCommented Apr 9, 2015 at 18:55
2 Answers
If you are seeing 4.5 volts across three batteries and 3.3 volts across two others, then the join you think you made is not a join.
There is a common thing in electronics called a "cold solder joint". It usually happens when your solder is not quite hot enough when it touches the metallic surface - just the kind of thing that happens when you solder to a large piece of metal such as a battery.
Most likely, if you could just "unsolder" the wire, give the surface contact of the battery a good scratching with fine sand paper, let your iron get really hot and allow a small dab of solder to flow onto the battery with some solder flux, then you will get contact and the circuit will work as you expect.
As an aside, the way you formulate your problem suggests you could use a bit of a primer on batteries, voltage, current, shorting, capacitors, etc. I may expand this answer later if you would appreciate the additional info. For now, see if my suggestion explains your observation - and whether the proposed fix works.
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$\begingroup$ It's a valid comment on your part but I've soldered thousands of components. I pre-soldered the tip of the battery with a very hot iron (40w) so that I knew the solder would adhere and it would heat up the immediate area very quickly so as not to harm the interior of the battery. Then I tinned the end of the wire so I could attach it very quickly. I can touch the wire to the solder and get my full voltage. As soon as I 'sink' the wire tip into the solder with heat the voltage disappears. The 4.5 volts from the 3 batts in series simply will not join the 3.2 on the other side. $\endgroup$ Commented Apr 10, 2015 at 22:45
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$\begingroup$ Hmmmm. What happens if you switch the batteries around. In other words - right now you have a "bad" connection with 1-2 not connecting with 3-4-5. What if you made the connection 3-4-5-1-2 and measured from the top of 3 to the bottom of 2? $\endgroup$– FlorisCommented Apr 10, 2015 at 22:54
You should not sold components that aren't design to be solded. Most batteries have an antioxide surface treatment that make it bad for solding (I can tell for experience). Also, when solding, is the surface which has to reach certain temperature; and that is not recommended in general for batteries.
So, if it's a good solder, you may had damaged the battery, if you don't warm it enough, you may have a "cold solder joint" as @Floris said.
The correct use of D cell type batteries is with the appropiate battery holder, that you do can sold. Also, then you can check if there is a solding fail, or a battery fail.
