New battery, 1 cell low - manual balance?

[PrivatePilot]

Greets all. New P3A owner but I have been into RC for about 3 decades including lots of past heli experience so the P3 was super easy to adjust to. Compared to a full 3D heli, the Phantom is childs play - I'm still amazed at the level of automation and the fact that I can simply take my eyes completely off of it and it hovers on it's own - as someone who was trained to NEVER take your eyes off your plane/heli/whatever for even a second (for fear of losing orientation), the P3 has had more of a learning curve "forgettting" training then learning anything.

Anyhow, my issue is with regards to a second battery I just bought from someone reasonably local on eBay. It arrived yesterday and was as advertised - genuine, low charge count (only 7), and in good physical condition.

But when I charged it up the first time I got the quick-flash on LED2 (or 3, I forget) - that code shows "Overcharge detected". I plugged it into my P3A and sure enough I got this:

I thought I'd go fly it (close to the ground) to discharge it fully and then recharge it, but same issue.

Anyhow, it recharged the exact same situation.

I set it to a 1-day auto discharge and have left it since (it should start the discharge tomorrow morning based on my understanding) and I'm curious if that will balance things?

If not is there a manual method of accessing the cell leads individually? I still have a few lipo balancers kicking around and I'm sure I could rig one up manual-like - I'm pretty handy with electronics.

Any advice appreciated. I did advise the seller and he is cooperating, but I would rather actually get it working vs returning it as I did get a good deal.

Thanks

 

[With The Birds]

Total capacity reported is significantly below rated and 300+mv imbalance on the low cell is very concerning. What charge level was on the pack when you received it?

Another observation- there is probably no good reason to have your critical level set above the 10% minimum, you are simply providing for a scenario where the AC may commwnce a forced auto land at an inconvenient moment.

I would upload the last flight log from that pack to phantomhelp log viewer to get a better feel of what is going on.

 

[PrivatePilot]

Thanks for the replies.

Total capacity reported is significantly below rated and 300+mv imbalance on the low cell is very concerning. What charge level was on the pack when you received it?

Unfortunately I didn't check the voltage/status before charging it the first time. It arrived in the mail, I didn't anticipate any problems, so I just plugged it into the charger and went to bed. It wasn't until the next morning that I woke up to the flashing code, plugged it in, and found the issue.

It should be auto-discharging now (it has been 24+ hours since I changed the setting to 1 day and then left it unplugged) so I'm hesitant to disturb it much at the moment as I have read that doing anything (even checking it's level) will reset the discharge countdown and it has to start all over again.

Are the 4 pins on the battery just telemetry/data between the battery and the P3, or are they actually individual cell taps where I could hookup one of my old Blinky balancers and attempt to manually balance that way, and then attempt a recharge and see if the battery recovers?

 

[With The Birds]

The battery had power and data connections only. The auto discharge to correct this issue is probably a waste of effort. Balancing occurs during charging by switching bleed resistors in and out of circuit to adjust the the power aplied to individual cells- during discharge they are just permanently switched on to the individual cells, no attempt is made to balance during discharge you only have to look at individual cells that have been through auto discharge to see this. I would return the pack if it was me and had the opportunity.

 

[PrivatePilot]

So, the seller very honestly refunded my purchase price. It's unclear if he wants me to return the battery or not, still sorting that out.

If he just tells me to keep it, I'm planning to open up the battery as a last ditch effort to get it fixed. Based on what I've seen online there IS a balance tap on the circuit board where I can connect my Blinky Balancer and get the higher voltage cells discharged down to a voltage that matches the one cell that's stuck low. I'm thinking that once they are in balance again the whole pack may then charge as intended back to full capacity. The reason it won't now seems to be the fault of the "smart" (or apparently, not so smart) circuitry that is detecting 3 of the cells are reaching the "overcharged" limit, while the last low cell's charge is being cut off as part of the ride coming to an end. It then becomes a vicious circle.

 

[PrivatePilot]

From what I understand of the Phantom charging system, the included charger is simply a glorified power supply. The work that would normally be done by a Lipo charger is done all internally inside the P3 battery, so using a fancy LiPo charger really offers no particular advantage.

 

[With The Birds]

yeah I just don't trust power supplies of this type have had a few for laptops overheat I do have one of the 3 battery chargers from amazon charges 3 at once in an hour but it has no display to see what's going on so Ill be adding a display to that thing. I have 10 batteries so when I need a few charged for a job on short notice I use that triple charger. I prefer to use a charger that will shut down as soon as it sees a problem and the glorified power supply wont do that

The battery will not charge if there is an issue with the supply- including over voltage.

 

[PrivatePilot]

I'm not sure you fully understand how the DJI batteries charge.

The only difference between using the DJI charger and your own LiPo charger is that your lipo charger will stay cooler. Aside from that, the battery makes all the decisions, not the charger. In the end you're not really any further ahead.

 

[PrivatePilot]

No, honestly, I still think you don't really understand it.

You are replacing an Apple (The DJI brick) with a fan cooled Apple (Your LiPo charger) in the end, that's it. Your LiPo charger is doing absolutely nothing more than DJI brick does - supplies voltage and amperage. The DJI battery accepts that input and then IT decides what to do with it, NOT the charger.

You are equating a regular LiPo to a DJI pack, but they are not the same thing. On a regular LiPo pack then yes, the LiPo charger is in control, but that's not the case for a DJI pack.

And I too have been around LiPo's since the beginning. I started with NiCad's actually, went through glow in both ground and aviation applications, NiMH briefly when it was a thing, and then LiPo. I've been in the RC world for many decades myself, thanks.

And I don't get what your fixation is with regards to the DJI charger heating up - I can't find any stories whatsoever of them being a fire hazard. The packs, sure...same as any LiPo can be, but the chargers, not so much.

Is a LiPo charger a viable option for charging? Absolutely - if my DJI brick buys the farm I have my 12 year old PolyCharge4 that I will immediately put back into service, but I know it won't really offer any benefits whatsoever over the brick, so I see no purpose to even dig it out of the basement at this point...UNLESS I end up opening this pack up to try to manually balance things and I need a proper LiPo charger once I've bypassed the DJI circuitry.