Weird issue with parallel Li Ion (need help with board design!)

[audiomodder]

Hey all-
So I have a very strange issue I need help with. It has to do with connecting 2 of these in parallel:
https://www.ebay.com/itm/10pcs-LiPol...53.m1438.l2649

They have a protection board for each of them, the DW01-P (attached).

I am using this to power a small audio / video device that consumes < 2A from the both of them (total). There was a lot of background noise / audio rippley distortion crap that went away only when I plugged in the USB charger (!)... OR, I found out, when I only have one battery connected. They are fighting each other in parallel (even though they balanced out a long time ago).

I think the li-ion PCBs are confusing each other and going into over discharge protect (ODP) mode and then back on ever few milliseconds. It's weird and I've never seen this before.

Any ideas on what I could do? Some kind of filter or balancer IC would be great.

[budm]

Re: Weird issue with parallel Li Ion (need help with board design!)

Do you have the scope to look for what kind of noise you are getting from the batteries and at the audio output?

[sam_sam_sam]

Re: Weird issue with parallel Li Ion (need help with board design!)

What happens when you only use one battery do you have the same problem

[sam_sam_sam]

Re: Weird issue with parallel Li Ion (need help with board design!)

Hey all-
So I have a very strange issue I need help with. It has to do with connecting 2 of these in parallel:

They have a protection board for each of them, the DW01-P (attached).

I am using this to power a small audio / video device that consumes < 2A from the both of them

Some time you can put the protection in parallel and it works but sometimes for some reason they will not work together

Have you ever solder on these types boards before it can be done but you have to VERY CAREFUL doing this

The first thing you need to make sure of is that you take your time and do not be in a hurry

There are two ways to do this

One is to take the protection boards off of both batteries ———->

PLEASE MAKE SURE that you have the the positive terminal of both batteries and the negative terminals of both batteries facing the same way BEFORE you solder the terminals together otherwise you are going to have very BIG mess on your hands if you not have this right and it will happen very very fast the battery pouchs will explode

I know I had it happen to me once a good thing they were very small batteries it could have been very very bad

Then use only one protection board

One very important note the positive terminal on these batteries is very easily broken off the part you can solder and the part of terminal that is left you cannot solder to them then you are out of luck

Unless you have a battery spot welder to weld a piece battery tabbing so you can solder it again

Second way to do this is take the protection board off of only one battery
But if you do it this way you need to get some heat shrink tubing that big enough to put the two batteries together before you start soldering them together

And really you should do this either way you choose to put the batteries together

I have put these types of batteries together in parallel with the protection boards sometimes it works with out any problems and sometimes it does not work

You can have the same type of problem if you put them in series they will power the device but you can not change the batteries

It all depends on what type of protection boards they are using

Or could be that the device does take more power than the protection board can give it if this is the case then you need to find a protection board that can handle the power this device needs

I know this because I have a NextBook tablet that I bought a replacement battery and it did not like the protection board that was on the replacement battery I had use the protection board off the old battery for it to work right

The problem was that it would not charge right and it would not turn ON unless you had the charger hook up to the tablet

[petehall347]

Re: Weird issue with parallel Li Ion (need help with board design!)

never used those cells i parallel . not something i would consider . if i was to i might think of resistor divider to balance them a little bit . no 2 things are exactly alike .

[Th3_uN1Qu3]

Re: Weird issue with parallel Li Ion (need help with board design!)

I agreee with sam_sam_sam - pull the protection board off one cell and only use one board for both parallel cells.

[gabiz_ro]

Re: Weird issue with parallel Li Ion (need help with board design!)

May or may be not OK
Protection board is designed for 1 cell.
In this case one with 1500mA
Over current protection may trigger at 2000mA

I am using this to power a small audio / video device that consumes < 2A from the both of them (total).

In that case may be at limit,a little increase of volume may result in increase current to 2A amd protection will switch off cell.

[audiomodder]

Re: Weird issue with parallel Li Ion (need help with board design!)

Thanks for the suggestions everyone.
As I am making this board for production, removing / modifying the Lipo PCB really isn't a good alternative at all. I plan to sell 100s of these.

I seem to have fixed the issue though. Not entirely sure how, but what I did was:
1) matched new connectors / cables for each battery (same length, too)
2) rebalanced both batteries (charged each separately
3) added much larger cap (470uf instead of 100uf) to audio board

So far, so good! Maybe the issue will turn up later when / if they unbalance...
Also, the circuit for the audio already has a nice LC filter, though adding another one couldn't hurt I guess. If I want to go really nuts, I could step up and use an LDO just for the audio board...yuck that is not a great solution. Let's just see where this goes in the meantime,

I scoped everything btw, but it was really hard to see the noise. the power rail is <100mV noise level, probably closer to 50mV. It looked really clean but obviously something was in the audible frequency range.

[petehall347]

Re: Weird issue with parallel Li Ion (need help with board design!)

maybe consider an over temperature cut out , just in case . i know very little about those cells but i do know they are a fire risk .

[kc8adu]

Re: Weird issue with parallel Li Ion (need help with board design!)

use 1 protection board rated to handle the load and parallel as many cells as you want to get the needed capacity.
multiple boards in parallel will always have quirks as they are never going to trip at the same current.