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# Battery springs

## Battery springs

(OP)
I am working with the design of battery springs for a CR2 battery.

Does anyone knows where I can find relevent information about:

- materials and design guides for achieving the lowest contact resistance

- guidelines for design of battery compartments

Regards

-Lars

### RE: Battery springs

I had the chance to troubleshoot a fault batery spring design for a customerfew years ago.I had to re-design a replaceent spring to hold a battety against shocks too.

Please can you explaien what is a CR2 battery?
How much force you want from the spring?
What are the dimension constraint?
What are the environmental constraint?

### RE: Battery springs

(OP)
The following answers are for the negativ pole, where the spring permits the difference in legths of the batteries.

-Please can you explaien what is a CR2 battery? It is a battery with diameter 15.6 mm and length 27 mm

-How much force you want from the spring? for the smallest battery 0,5 kg (with a deflection of about 0,5 mm) and 1,0 kg with the a deflection of about 1.5 mm. The largest deflection will be about 2,2 mm when the battery is positioned in the wrong direction. These forces are suggested from a battery factory.

-What are the environmental constraint? they will be as for mobile phones.

Physical constrains:

-the diameter of the battery 15,6 mm

-in lenght about 5 mm from unbendt position to maximum deflection including support (plastic cabinet)

I´ve made some FE-analysis and the result in von Misses stress is about 1200 MPa in a bend radius of 1,5 mm and an arm about 6 mm, where the force is aplyed.

Regards

Lars Monroy

### RE: Battery springs

Lars Monroy, Are designing a flat beam spring? made of a sheet/strip material?

Which material did you check for the 1200MPa stress? As I recall they usually use SS AISI 301/302 full hard.

Did you considered using a conical helical spring?, they can be designed such thst the coils enters each other to receive a solid hight of the size of the wire diameter.

What do you mean 5mm length? Is it the space left between the negative side of the battery to the plastic cabinet, and if so is it for the longest battery?

### RE: Battery springs

Once the mechancial criteria are satisfied the surface finish will be critical in a battery appplication. By far the best results are with a thin gold alloy plating, not as expensive as you might think.

### RE: Battery springs

(OP)
The strip material used for FE was CuSn6.

The 5 mm is the length of the arm (part that bends)that bends.

I have considered the conical helical spring and it can be one posibility,but taking in consideration that the functionality of putting the battery in the compartment and taking it out has to be done in such a way that the the battery contacts both poles at the same time.

Using a helical spring the negativ pole is placed first and then the opposite pole is pushed until the battery is in place.

Regarding the gold plating it will a matter of measuring the contact resistance due to the force obtained by the spring and see how much the resistance can be lowered by using gold vs. Ni-Zn-plating.

### RE: Battery springs

try duracell.com/procell/design/batterycontact.asp and duracell.com/procell/design/cavity.asp

### RE: Battery springs

(OP)

-Lars

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