Introduction: Magnetic Connectors for Batteries

Hi everyone,

Here is a small tutorial about useful and easy to make battery connectors. I recently started to use 18650 cells batteries from old laptops, and I wanted a quick and easy way to connect them. Connectors using magnets were the best option, but I had to figure out how to use them correctly.

UPDATE:Thank you all for your comments! I have added a new step at the end to answer the most relevant and recurrent questions!

Quick description:

One connector is made of 2 magnet that keep the electric wire between them. Then I used hot glue to protect, glue and insulate the connectors.

Advantages:

  • They are really easy to make
  • They are really easy to use
  • No soldering iron is required
  • They avoid short circuits as the connectors repel each other, and if they attract it is on the insulated parts (as both connectors free the same magnetic pole).
  • It takes 5 minutes to make (time for the hot glue to harden).

Step 1: Magnets + Wire

In the first step I just added the wire between 2 magnets.

Step 2: Plastic Support

I have put this on a transparent piece of plastic. I used this piece of plastic to melt the hot glue on it and detach it easily. So make sure the plastic is smooth enough (to detach the hot glue) and heat resistant (at least a minimum so it does not deform).

Then I have added a third magnet below the plastic to stick the magnets above to the same place when I am pouring the hot glue.

Step 3: Add the Hot Glue

To stick everything together and insulate the magnets, I proceeded as follow:

-I cut a small part of PVC tube (about 1 cm high, and 2 cm of diameter; it has the same diameter than the 18650 cells)

-Then cut the PCV ring so it is open

-I added the hot glue on the magnets using the PVC ring to maintain the hot glue. (Make sure you are in a well ventilated area)

-Wait few minutes the time for the hot glue to harden;

  • If it is not long enough the hot glue will be still liquid
  • If it is too long, the hot glue will stick very well to the PVC and plastic piece and it is hard to detach

-Then detach the hot glue

-And remove the PVC ring!

Step 4: Use It!

Now that it is done you can use it to connect easily any electronic device to your battery!

If you make the north pole magnets of all the connector pointing in the same direction, they will repel each other, that is useful if you don't want short circuit. And if you want them to connect, just make other connectors with the magnets upside down!

Step 5: Questions & Answers

In this step I answer some of the frequently asked and most relevant questions:

  • What is the resistance of the connectors?

As my multimeter was not accurate enough to measure the resistance of the connectors, I have used the four-terminal sensing technique, and measured the resistance of others connectors to have a comparison:

  1. One magnetic connector: R=50 milliOhms
  2. One magnetic connector soldered to the wire (see next question) : R=17milliOhms
  3. One wire of the same length than the 2 connectors above : R=17milliOhms

To finish, at this range the multimeter's wires resistance might influence the results given above, so the resistance could be even smaller.

As a conclusion I would say that the resistances of the connectors seem quite low to me. The connectors with one wire stuck between 2 magnets without soldering has the higher resistance with 50 milliOhms. Then the connectors soldered to the wire, and the wire alone have the same resistance of about 17 milliOhms.

  • Why not soldering the magnets to the wires directly?

I have tried before publishing this instructable, and here are the main reasons I did not solder my connectors:

  1. First I had some problems to solder the wire to the magnet, the tin did not stick to the wire correctly and flowed on the magnet. I have tried later with another magnet but I had no problems. So I think some magnet might be coated with some kind of product to protect them or whatever.
  2. The soldering iron is magnetic and it sticks to the magnet. So be prepared if you plan to solder a magnet!
  3. The heat of the soldering iron might demagnetised the magnets, if the soldering iron is in contact for a long time with the magnet.
  4. I think it was interesting to publish this article without the use of soldering iron

On the other hand, the resistance of these soldered connectors seems lower, so it is quite interesting as well!

To conclude I would say that both the sandwich technique (wire between the magnets without soldering) and the soldering techniques are useful depending of what you want to make. And to finish the hot glue (no matter which technique you have chose), is something I would recommend because it has 2 main properties:

  1. It insulates the magnets (and the magnets stick to everything that is ferro magnetic!)
  2. And it protect the wire end close to the magnet

  • Will the magnets drain the battery?

No the magnets will not drain the battery (unless you use them to short-circuit the battery!).

Comments

author
conundrum2142 made it! (author)2017-07-27

Great idea!

Its a shame some enterprising manufacturer can't make smart 18650s with NFC reading ability (so any smart phone can check a bare cell) and these magnetic connectors built in. Also it might cut the number of ecig/model/etc related accidents as people switch to the new safer connectors.

I would avoid soldering though and use spot welding, with 3D printed shroud that permits venting and mechanically shields the wires at both ends, and contains the NFC chip, cell protection etc.

Once made a pack of LiFePO4 (cheap and nasty) and it might have worked for years if the soldering process hadn't weakened all those cells.

author
PavanSP made it! (author)2016-06-06

Great tutorial. I will definitely make this one for myself and post some pictures.

To improve the design a little so we can prevent a short with battery polarity reversed, have the magnet with the positive end contact, a little recessed. This will allow only the protruding top (positive) end of the battery to make contact with it. When you try to touch it to the other end, the positive end of the wire contact might stick to the battery's negative end because of the magnetic pull, but will not make contact with it, preventing a short circuit.

author
lapenta made it! (author)lapenta2016-06-17

I made some using the battery itself as a mold. this way, the 2 connectors are different, and the positive one is a little recessed, as you said. So there is no way to connect it wrong.
To do them I taped the battery with masking tape, used a metal sheet from another battery (carcass) as a mold, bracing it to the taped battery and protuding it a little bit from the battery ends, placed the magnets and wire and then filled with hot glue.
It works very well, and looks neat.
now I'll do some with ogoo, it will last longer and be more flexible.

author
lrd made it! (author)2016-06-14

I have to build several little joule-thief robots and had to find a cheap way to attach the battery and your idea came to my rescue. I'm using just one thin magnet to each pole and two others to attach the battery to the robot body. It was not so professional as yours but it is working. Thanks.

joule.thief.man.png
author
DarrenO2 made it! (author)2016-06-13

How do you know when to remove, You said that too soon it will be liquid but too long the glue sticks to the plastic. is it seconds or minutes?

author
Matlek made it! (author)Matlek2016-06-14

I'd say you have to wait at least 2 or 3 minutes (but I guess it depends on your hot glue). The best thing is to try, if it is too liquid the glue will spread everywhere and you'll see it. And if you wait too long (lets say 10 minutes), it will work, but you might have some problems to detach the glue form the plastic! have a try, and let me know if it worked!

author
pikwitonei made it! (author)2016-06-06

This is so cool! It is such an original instructable that it redefines for me the number of options I now have available for connecting to a battery.

author
lapenta made it! (author)2016-06-06

Thanks pal, very nice idea. I've made some, but used less magnets, as I didn't have many of them. I used 2 for each connector. For the mold, I used the metal sheet that is used on the batteries: I disassembled them, cutted the top and bottom parts and filed the rough edges, than used some masking tape on the batterie to avoid the glue to stick to it.
Then I placed the "naked" connector (the 2 magnets and wire sandwich) on the batteries, inside the mold, that was protuding from the batterie's end and filled with hot glue. It became great. In my case the hot glue entered around the magnet, so mine became polarised.
Anyway, I just wanted to thank you and share my experience. I didn't clicked the "I made it" because it require pictures and I don't have any. Sorry for any english mistakes.

author
pablo.gazzara.9 made it! (author)2016-06-04

Its very good design for a charger, or a battery tester

author
baerht made it! (author)2016-06-04

Nicely done

author
jimbarbera made it! (author)2016-06-04

Ingenious! Elegant in its simplicity. I got lucky and found some Teflon tubing of the correct diameter. Slips right off. Silicone tubing would probably also work. If you need higher voltage, just use a single loose magnet to stick two or more batteries together.

author
yrralguthrie made it! (author)2016-06-02

Not sure why it makes any difference if the connectors touch. The only way they can touch would be if not connected to the battery. Then there is no problem with a short because there is no power. It's not going to create a short by connecting the power leads of a non-powered device.

author
garfnodie made it! (author)garfnodie2016-06-04

Better to be safe than sorry. What if someone who doesn't know what they are doing hooks it up backwards and but the power source on the bare wire end and not the magnet end, now you have a potential short, but at least you still got a built in fail safe with the repelling magnets.

author
MatthieuR made it! (author)MatthieuR2016-06-04

Except if bateries are in parrallel, in that case you'd short the other battery.

author

some of the gizmo boards you might use this neat trick might gave circuitry to charge the battery. In that case, shorting them together would be bad.

author
yrralguthrie made it! (author)yrralguthrie2016-06-03

If the gizmo boards you might use this neat trick have the power available to charge the battery, why do they need a battery? Only case I can see where that might happen is an actual battery charger.

author

I was thinking of the dual purpose boards a power bank.

I recently re-engineered something to make it rechargeable and battery powered. The guts of a power bank (with smaller batteries) was key. The "lipstick tube" style use a very simple, almost single IC solution.

author
TampaGeek made it! (author)2016-06-04

A very clever idea... I don't think I'd use it for making semi-permanent (long lasting) connections but for prototyping and testing I think this is quite an ingenious approach. I might try to coat or line the PVC ring with something to keep the glue from adhering to it... have to give that some thought. Overall, kudos to the author... quite imaginative and "out of the box" thinking.

author
Valvelifter made it! (author)2016-06-04

The best thing about Instructables is the number of ideas different projects give me for other applications. This is a classic example. I'm not sure of the merits of this idea but I can see useful applications.

author
tytower made it! (author)2016-05-27

So the wire is under the magnet before you pour the glue and then magically disappears in the next photos so what have you done with it ?

author
Matlek made it! (author)Matlek2016-05-30

Hello! The wire is always between 2 magnets. Then I add the hot glue to stick and cover everything. So there is one magnet invisible inside the hot glue, and another magnet visible with a part outside the hot glue to connect to the batteries! And the wire is still beween the magnets. Did it help?

author
yrralguthrie made it! (author)yrralguthrie2016-06-03

This is not really a bad idea, but a couple of caveats.

First hot melt is temporary and doesn't really hold well for long. Second gluing an electric connection together will work...sometime and likely not for long.

author
ElectroFrank made it! (author)ElectroFrank2016-06-03

Hot melt glue is very permanent (unless it gets very hot !)

The wire is held firmly between the magnets, the glue just stops it being pulled out. But soldered to the magnet would be better.

author
yrralguthrie made it! (author)yrralguthrie2016-06-03

No sir, hot glue is not even close to being permanent. In addition it can easily be removed by simple jarring. Hot glue is a craft glue, not made for permanent installations. And example: A CNC router I received recently had the controls on the front panel fixed with hot glue so they would not rotate. Did not work. Hot glue only works well if it can surround an object, it will not stick well to any surface I've tried. I've received many pieces of electronics with internal components hot glued together so they will not move. The glue simply does not stick well after it cools, unless the components are encapsulated.

author
tytower made it! (author)tytower2016-06-03

Yes got you now Thanks

author
randalosgood made it! (author)2016-05-30

$2.95 on Amazon for the same device

author
ElectroFrank made it! (author)ElectroFrank2016-06-03

£1.24 on Ebay for these. They used to cost much less from Maplin, but they don't seem to stock them now.

http://www.ebay.co.uk/itm/Magnetic-Electrical-Connector-Pair-/291330796346?hash=item43d4ab2b3a:g:gX0AAMXQatBSblNW

author
ElectroFrank made it! (author)ElectroFrank2016-06-03

Small magnetic connectors (I just discovered) are also used for jewelery making. Very cheap for a quantity, and the silver or gold plating will be very easy to solder to.

author
Matlek made it! (author)Matlek2016-05-30

Hi, I've checked on the internet before to do this but could not find suittable devices, do you have the link to compare? Anyway, this is much more fun when it is homemade, and for $2.95 I think I can make many of them ;)

author
LuKáŠB34 made it! (author)LuKáŠB342016-06-02

+ $5.95 shipping

author
srilyk made it! (author)srilyk2016-06-02

That looks like it's strictly for C or D cell batteries.

You can buy magnets from wish.com for really cheap (but the pictures often look like they're a lot larger, so make sure you've got a ruler/calipers handy when you're buying them)

author
yrralguthrie made it! (author)yrralguthrie2016-06-02

$8.90 you forgot the postage

author
gizmologist made it! (author)gizmologist2016-06-02

The author is using 18650 Li-Ion batteries. C and D size holders are everywhere; much easier to find than 18650 holders.

author
Laral made it! (author)Laral2016-06-02

Heh, you forgot to mention the $5.95 shipping! Ehhhhhhhhhh!

author
Laral made it! (author)2016-06-03

I think drawing current through a magnet is a bad idea. Magnets have resistance and are not ideal conductors. A better approach IMO would be to use stranded wire. You could strip a longish section, fan it out, and wrap it around ONE magnet, and twist it all together at the top face. That way the wire itself would be in contact with the battery terminals. You would get good pressure without the resistance of the magnets.

author
Laral made it! (author)2016-06-03

True, the holder would be the best way to go, especially given the high price of magnets these days. And the contact would be firmer without the resistance of two magnets added in. But what does this have to do with the author's ability to solder? Your rude comment is uncalled for and is, at best, a non sequitur. You have no evidence whatsoever to back your claim.

author
munish4u911ex made it! (author)2016-06-02

Can one be more discouraging than that? I think it's a really neat and usable idea. And just because the instructable presents a way that doesn't require you to solder, it does not mean the author doesn't know soldering.

author
bigfoot_tmn made it! (author)2016-06-02

Great idea! Quickly solve the problem and is almost free. Thank you!

author
chexin51 made it! (author)2016-06-02

Very good idea - maybe add the instruction at step 1 that you make a circle with the end of the wire that closely matches the diameter of the magnet for stability before adding the hot glue. I'm sure there are hundreds of others who are asking themselves " why didn't I think of this ? "

author
arvevans made it! (author)2016-06-02

Cute idea. Don't let the nay-sayers get you down. There are just jealous that they did not think of this first.

author
BrianM172 made it! (author)2016-06-02

Can you use these to sorta- use on other things? I want to measure the voltage of something, but the place where you put the wire on the voltmeter are just 2 metal stubs.... Can I put magnets on the other side of the stub and do this? If so, my life is gold...

author
MichaelG9 made it! (author)2016-06-02

AND USE IT?

How about the missing part where is gets connected to a USB plug?

There are more than 2 connections, and I assume connecting the wires to the correct polarity can be an issue?

Great up until the connecting part that is missing.

author
gizmologist made it! (author)gizmologist2016-06-02

The last two photos show it connected to a USB voltage regulator/converter. These batteries do not produce enough voltage singly to power through USB. Battery nominal voltage: 3.7V, USB voltage: 5V.

But this Instructable is about making connectors.

author
kaygarystudios made it! (author)kaygarystudios2016-06-02

Use red wire for positive and black for negative, that way you always know how to connect to whatever you need. I am sure that the picture was just an example for how he uses this.

Excellent idea, I have many arduino projects that this will work perfectly for.

author
gcai_fwb made it! (author)gcai_fwb2016-06-02

hey give matlek some slack the ible was about making the Magnetic Connector - not what it is connected to - I going to use them for a completely different connection than a USB connector

@matlek - Great idea and execution - kudos - simple ideas are always the best

author
Laral made it! (author)Laral2016-06-02

Quick search on usb pinouts - Google Search, 1st hit shows what you need:

USB.jpg (500×328)

USB.jpg
author
zappenfusen made it! (author)2016-06-02

$2.95 and $5.15 shipping. How's that for a deal?

author
gcai_fwb made it! (author)gcai_fwb2016-06-02

no deal there :)

author
hackbyte made it! (author)2016-06-02

Yeah, i love your instructable ..... I'm collecting these tiny lttle magnets (they seem to be a bit smaller) for a while from some stuff i need to refill most times twice a week.

I search every time to get this particular brand and packaging because of these small magnets....

Let me tell you, i already use them to adapt Micro (AAA) batteries for Mignon (AA) battery holders and such things.... And i always thought about how to make nice little on the fly contacts for batteries....

Now i know a really good, safe and durable looking method.

Thank you very much! ;)

Greetings from hamburg, germany,

hacky. ;)

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