[SOLVED] 3S LiPo Balance Charge Port & Connection Detection

[Zaprooder]

Hi all,

I'd like to say thank you firstly. I'm pretty green to all of this and signed up to get some help with what I'm doing. There are a few aspects to my project that I am struggling with and have previously posted two threads asked for help. The replies I have gotten have been very useful, informative and helpful. I'm sorry I keep posting begging for assistance, I'm not really at a stage where I think I could be useful or give advice to others, but hopefully one day I'll get there and be able to contribute with positive advice.

So back to the point of my post. My project is powered by a semi-permanent 3S LiPo pack, meaning it's meant to be left inside the device enclosure and be in-line charged. Eventually replaced at the end of its life cycle. I want to put a four terminal connector on the case which can be plugged into a balance charger, this connector is obviously internally wired to the LiPo pack's balance charge port. All this seems simple enough in theory but I've run into a bit a paradox. I'd like to have a symbol appear on the device's LCD display to indicate the charger is plugged in. This is a bit of a problem as I'm having a hard time figuring out how to detect it. The four terminals for the balance charger are directly connected to the nodes on the battery cells, so I can't simply have a voltage detector on one of them to detect it as it would be on all the time. I could use a terminal plug with a mechanical cut-off, like a headphone jack socket with 4 connections on it (like the ones used on cell phones for the combined headphones and microphone), but with that I feel there is danger of things connecting to the wrong place when the plug is inserted and removed, plus, I was told to always assume all Users are idiots, so some clown may think it's a headphone jack and plug some in, which wouldn't have a happy ending. So far my only option I can come up with is to have the standard balance charger port on the outside so there's no confusion as to what it is and just not bother with the detection of the charging status, but I REALLY REALLY want the charging status on the display. Is there any trick or tip I could use to detect the presence of the charging current?

Many thanks,
Z

 

[KlausST]

Hi,

maybe you can use a low ohmic shunt (or FET) in series with the charge+ line.

If the charger is active, then you will see a voltage drop acrosse the shunt. You can use a comparator with an appropriate threshold to get true logic levels.

Klaus

 

[Zaprooder]

Thanks Klaus. I had to do a bit of Googlong and Wikipediaing to make sure I understood what you were saying, but hopefully I've grasped it. IS this the kind of thing you mean (picture attached). I tried to simulate a LiPo charging supply. It usually supplies about 0.1V above what the battery charge is. I'm not sure if the shunt would interfere with the charge operation though, LiPo cells have a pretty low internal resistance. Anyway hopefully I've understood the basic concept.
**broken link removed**

 

[KlausST]

Hi,

Yes, this was the idea.

Some hints to the schematic:
* the 10mOhm will not be a problem for the charging circuit. Often a CI CU charging is done and with the CU charging the current continously decreases and therefore the voltage across the shunt decreases.

It´s hard to find the LM607 datasheet. But i see it is a low offset OPAMP. The low offset is important. But you use it as a comparator. Some OPAMPS don´t like this.
I´d improve on a defined threshold level. Now with this - not feedbacked circuit - any offset voltage inthe OPAMP tends to give erroneous output.
Also, if you want to input the information to a ucontroller, then i´d use a schmitt-trigger or a positive feedback comparator for sharp edges in logic levels.



btw: yo can do the sense in the GND line as well....

I try to modify your schematic and post it.


Klaus