Spring mod on a standard cell holder

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Joined
Dec 2, 2017
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Yesterday I saw this excellent thread by Watts-on secondlifestorage.com/t-Watts-on-s-SpringSlot-18650-Battery-Holder?highlight=Spring

I like to tinker for entertainment and don't have a 3D printer, so wanted to see if it would be possible to modify a standard cell holder to have some of that awesome spring clip action.

After taking a close look at the cell holders and a pack of plastic clothes pins, I decided to give it a try...

Edited to add photos using phone

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I made a jig out of wood scraps and finishing nails to hold the pieces in place.

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Found that plain scissors will cut the plastic just fine. The red circle shows where I put a small notch in the cell holder to locate the spring for assembly.


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Epoxy on the end of the cell holder. Add some weight to the clothes pin to hold it once it is in place.


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I used a dab of epoxy on the spring to the bottom of the cell holder


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Check for alignment and let it dry...

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After the epoxy dries, I will see what happens to the spring end when I make some cuts so it will open.
 

Korishan

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How do you know if his name is Will?
 

Chablism

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Like you have have no 3 D printer so Great idea

Sorry but I have a hard time to understand what has been done

Hard to see but this is a spring tab design so great starting point

Have you cut away the end wall of the spring holder

Best I can tell is yes so that end wall can pivot but what do you do with the tab spring on that side

Adding cloths pins for longer lever for short is end wall with
Leg of spring pinched between is great idea

If yes then how do you get electrical contact?

The 2.5 mm screw could hold this pivoting end wall assembly together but I did not see this detail

Tks for posting
 

Cherry67

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Korishan said:
How do you know if his name is Will?


And he is not "away" :D .

Nice idea, btw, have to look to understand its features.....
 
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Just using what I have and seeing how far I can get.


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My tester has an array of cells pretty close together and a vertical lever will be required for my setup.


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Here is the holder out of the wood jig. Starting to study how to make the incision so the end will move with the lever.


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Chablism

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Jan 27, 2018
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Since the tab springs are fully functional another approach to consider could be a vertical lever that just rotates and pushes the one end of battery up out of the holder

I have been considering to do what many electronics use which is a ribbon layed under the battery. Pull the ribbon and battery pops out
 
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Yes, one long (and strong) ribbon to pop out all the cells at once. If you have a tester with independent slots, it would take one ribbon per slot so one cell could be pulled without disturbing the others. Ribbon could be fastened with one of the cell holder mounting screws, just need a source for the ribbon.

I made the cut for the end of the cell holder and the spring tension took over. The cut is easy with a hacksaw blade, but it was difficult to complete the cut because the spring was in the way. I had to use a hot knife to complete the cut, but the spring force caused the end to move into the melting plastic, and that was a bit messy.

I would recommend cutting the end first. The vertical cut is easiest to make, just a few mm away from the end so the metal contact retainer is not affected. That allows the contact to stay on the end piece, but it will move when the lever moves.


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The epoxy on the bottom of the cell holder did not hold the spring so I will have to add some material on the sides and a screw to hold the spring coil properly.


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I need wider wood sticks. They are cheap. I will look for popsicles with wide sticks so I can get a treat as well.
 

Chablism

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Jan 27, 2018
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Yet anouther option is to take advantage of open bottom of holder

Fix one end of holder to a bottom board

Place a correctly sized shim block under holder on the other end

Install the battery carefully in holder

When done you push the entire holder down against the shim

Since holder can move down but battery can not. The battery pops out.



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Could open end of this tab spring holder help with the original mod
 
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Dec 2, 2017
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Thanks for the ideas. Look what I got in the past 24 hrs !


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So let's go through my revision number 2 build. I will be adding a wood "sled" for the cell holder. This will raise the cell holder to make room for the spring and to allow a single hole to pass both wires (+/-) since the solder tabs will be between the cell holder and the mounting surface.

Also there is considerable thought given to strength of the lever. In this revision, I will share lessons learned working with this type of clothes pin and spring and cell holder and a tight space requirement for my tester. This process may work for other types of parts, but the actual dimensions and strength of materials may require adjustments, so I will not be making or working from blueprints.


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Cut wood sticks to size, then stack several and drill them at the same time. Drilling may split the top and bottom pieces, so use a scrap on the bottom.
* I used a chop saw to cut the sticks because the knife was not easy enough for me.


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View of the bottom of the wood sled. I added a small crossmember for strength in the center. I am now using glue sticks and the hot glue gun instead of epoxy, much easier and quicker.

Tip: use a bead of hot glue between the wood and the cell holder, just be quick to assemble. Hold the pieces against the nails to locate evenly. Also add a bead of glue on the inside of the wood sticks where the hole is drilled this will help prevent splitting on the end with repeated and continual forces bottom the spring.


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Trial fit with lever and cell end but no spring.


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Added the spring and noticed some room for improvement on the lever piece. Here is a better way to make this part :


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To make the lever from one of the clothes pins, slice it with a sharp knife. The plastic may split if the knife is not cutting good.

The end of these clothes pins have a softer plastic for the grip. Use the knife and slice some of the grip material off to put under the cell contact tabs if your tabs are going flat.

I made several attempts to make the large hole for the spring saddle. I tried to cut a notch, then tried a drill, then tried to grind it and removal of material made the part weaker or caused a split. The best way is to use heat to make this area soft and push the material in using a screwdriver shaft. The cold screwdriver will shape the hot plastic and this makes a stronger piece than cutting material away.


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This is the first try with a cell using the first lever. Even though this lever does not have the spring saddle, it works well holding the cell. Once you try a spring action cell holder you may want to have some for your tester.

I will try to do this for all 32 slots on mine (eventually).

Family time now!!
 

Chablism

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Jan 27, 2018
Messages
177
Thanks for update

Would it be possible to repurpose a part of the laptop battery housing to replace the wood frame?
 
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Dec 2, 2017
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So I went through many different levers made from the clothes pin handles and they look like they may be too thick for my application, meaning the lever would hit the cell holder next to it and not have a full range of motion.

Here are the rev 2 levers from clothes pin parts.


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All of these have a saddle over or under the spring, but none of these are wide enough to hold the spring captive. These will work if you have space to move the lever on that end of the cell holder.

I would like to learn how to design a part for 3d printing, Here are a couple of levers using the jumbo sticks and these will fit the space constraint on my tester.


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The one that is mounted on the cell holder is just a stick glued to the end of the cell holder. The clothes pin spring is sandwiched between the end of the cell and the stick, surrounded by hot glue.

The smaller part is the one I would like to move forward with, it has a 90 degree bend on each side and should have holes to hold the spring captive.

Would anyone care to recommend some free drawing software that I could try to CAD this part for 3D printing?
 
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Chablis_m said:
Thanks for update

Would it be possible to repurpose a part of the laptop battery housing to replace the wood frame?

Hi Chablis,
The laptop battery case material is kind of thin and brittle. It may be possible if you can cut it without splitting.
 
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