LiPo battery PCB connector suggestion

[Nikos A.]

Hi everyone,

I design a low power PCB that is very constrained in height. The PCB will be supplied by a small LiPo battery and I am looking for connector solutions. Most of the times LiPo batteries are shipped with this JST connectors but they are very bulky for my application. The max. height of the battery connector must no exceed 2mm

Do you have any asuggestions?

[beanflying]

What sort of current? JST (or mainly clones) makes the 2.5mm XH R/C type but they alone have a huge range with much lower pitches and smaller form factors

[Nikos A.]

What sort of current?

Thank you for your answer beanflying. Just a few mA max. continuous current (2-5mA)

[beanflying]

There is the JST-PH also in common use for the smaller R/C gear with 20-60mAH 1S packs but it's still 2mm pitch and over rated for your current and still bigger than you might want. You could try Mouser/Digikey etc and use their parametric search for 0.5 - 1mm pitch connectors.

You might do better to consider running a flexible flat ribbon and matching connector from the mobile phone sized gear if you are really pushed for space. Not something I have had to source so hope someone else steps in with some pointers.

[MarkR42]

JST-RCY is typical on smaller RC battery packs, it's a wire-wire connector and can handle several amps. It seems unnecessarily big for some applications.

I used a JST-SH (3 way) connector on a recent project, they are 1mm pitch and very small. I got a company to crimp some leads for me, there is no way I could crimp something that tiny by hand, not even for prototypes.

[Miti]

I’ve seen many boards at work, and I also designed few, with solder pads only. Unless it needs to be disconnected often, I don’t see the need for a connector.
On the other hand, if it is mass produced, it adds a hand solder step, which could be expensive.

[Nikos A.]

Hi Miti, I agree with you. My initial prototype was designed with solder pads only. Every time I was attempting to solder the battery terminal I had to be very careful to not short out the battery. I know that most of these LiPo batteries a coming with an integrated protection circuit. Do you know what kind of protection they provide? I know that they provide under-voltage protection but they protect against short circuits as well?

[Siwastaja]

Why do you need to ask? Just look at the datasheet. If the cell is crappy/no name enough not to even have a datasheet, how could you trust it having an important protection feature just by guesstimating some similar products having it?

Not all cells have any kind of protection circuitry, not even the UVP you talk about. You need to verify the actual specs on per-product basis.

[Miti]

Hi Miti, I agree with you. My initial prototype was designed with solder pads only. Every time I was attempting to solder the battery terminal I had to be very careful to not short out the battery. I know that most of these LiPo batteries a coming with an integrated protection circuit. Do you know what kind of protection they provide? I know that they provide under-voltage protection but they protect against short circuits as well?

I can’t speak about all the batteries that you can buy out there, but all some of the ones that I used were fully protected to short circuit, meaning that the battery is disconnected from the output. In some cases I used the protection to solder it without worrying that a flying wire touches the wrong component. I shorted the wires briefly, I soldered them, then the first charge restores the battery connection. Another method is, place a heat shrink tube on one wire so only one is exposed at any time. It’s easier to keep your eyes and fingers on one wire at a time.

[Siwastaja]

If the cell definitely and demonstrably has an UVP circuit, then it's very likely (but not guaranteed) the same protection chip implements short circuit protection based on the Vds (Rds_on) measurement of the back-to-back MOSFET switch.

I would still avoid shorting the cells no matter what.

[Miti]

Hi Miti, I agree with you. My initial prototype was designed with solder pads only. Every time I was attempting to solder the battery terminal I had to be very careful to not short out the battery. I know that most of these LiPo batteries a coming with an integrated protection circuit. Do you know what kind of protection they provide? I know that they provide under-voltage protection but they protect against short circuits as well?

I can’t speak about all the batteries that you can buy out there, but all the ones that I used were fully protected to short circuit, meaning that the battery is disconnected from the output. In some cases I used the protection to solder it without worrying that a flying wire touches the wrong component. I shorted the wires briefly, I soldered them, then the first charge restores the battery connection. Another method is, place a heat shrink tube on one wire so only one is exposed at any time. It’s easier to keep your eyes and fingers on one wire at a time.

Strike that! I just tested 4 models of LiPo pouch type with protection that I have around, and they all recovered after the short is gone and IF they are not connected to any board. One of the 4 models which is soldered to a very low power board though, does not recover, meaning that the current capability in protection mode is very low and, probably, even charging the capacitors on the board is too much. The one that didn't recover must be an isolated case, or maybe I assumed it doesn't recover because it didn't recover in circuit, I don't remember the whole context.  So better use the second method, isolate the wires.

[Nikos A.]

Thank you for your input guys  It seems that I will proceed with the solder pads approach taking into account short circuit precautions

[beanflying]

Depending on your local supplier you should be able to buy pre tabbed LiPos without BMS (preferable and add your own if you can afford the discharge). While the BMS current draw is negligible if you are using small cells it is still a consideration. So consider fitting it externally or DIY something that only checks when your circuit/device is powered.

This sort of thing for the cell (my local) https://www.master-instruments.com.au/products/65516/LP852040.html with the flat tabs within reason tough to short out.