Banana connectors are quite ubiquitous in the electronics world, and rightly so: they are versatile, inexpensive, and easy to terminate. However early on into my electronics engineering journey I discovered there are some bad apples bananas to lookout for.
Bad Bananas
Bad banana plugs have a loose sleeve which is meant to allow the plug to rotate when mated with a socket.
Here's what they look like:
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| Image from Digi-Key Part Number 501-1200-ND |
Unfortunately corrosion and wear-and-tear degrades the conductivity between this sleeve and the body of the plug. This can cause erroneous measurements of the circuit. For example hobby RC battery chargers typically use banana connectors for the output port. In some modes, this port does the double duty of supplying charging current and measuring battery voltage. The high resistance of the rotation sleeve can cause a higher voltage measurement which causes a premature termination of the charging.
While the the best course of action, in my opinion, is to avoid these bad bananas, it is possible to improve the conductivity between the sleeve and the body of the plug. This is achieved by adding solder to the joint. See this image for an example:
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| Solder has been added to these banana plugs at the tip end of the sleeve. |
A few hints to execute this:
- Only solder one end of the sleeve.
- Add the smallest amount of solder.
- Use flux to help the solder wick into the joint.
Good Bananas
Soldering bad bananas can be a quick and easy remedy for most applications. But if you have the liberty to choose your banana plugs, I recommend choosing other kinds:
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| The "split banana peel" type (left) are typically inexpensive. The "cross split" type (middle, right) also provides excellent electrical contact. |
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