Here’s an interesting situation - through my own incompetance, (or enthusiasm) I let the cells in my 1600maH 4S LIPO battery that I have built inside my home made portable HF amplifier, run down far too far before connecting an external power source.
When I got the amp home and wanted to charge the LIPO, the balanced charger only sees and reports cells 1 & 2 (3 and 4 have disappeared)! There is no bloating or other damage apparent on the battery. I suspect cell 3 has given up the ghost completely and when the charger gets to cell 3 and sees nothing, it simply says this is a 2 cell battery and goes back to charge cell one.
Something to watch out for - don’t let cells totally discharge!
A well known effect of Li-Po’s. I lost a number of new cells that I bought and left in storage for over a year before I could tackle the project I was working on. They were still in their original dispatch packaging and had only the charge that had been installed at the time of manufacture which of course had diminished below a recovery point. You live and learn.
4S LiPO when fully charged will output voltage in excess of what many rigs support. Switchable series dropping diodes are the usual solution. In my battery packs, I have battery protection circuits that protect against over-charge, short-circuit, over-discharge, and include balance charging. Boards are available on Ebay. I also top off the charge on unused batteries every 6-12 months and date-code them by writing on white electrical tape homebrew stickers.
My go-to battery is LiFePO4 4S2P 6Ah Bioenno Power BLF-1206W which has a BPM standard. Great for all day+ QRP and even short periods of 100W QRO. I’m not affiliated with Bioenno, I’m just a satisfied customer.
This battery is being used with my homebuilt amplifier, whose transistors would work best with 24-28 volts on them. Going up from 12/13.8 to 16 - 17 volts is not a worry but does bring a worthwhile gain in amplification.
Got one of those LED things that sit in the balance lead of the battery.
Can monitor the cells and set alarm if voltage reaches set low point, alarm will sound.
Now found out how to do that at last
Perhaps the balanced charger is reporting a reduced number of cells because of the output terminal voltage is too low.
Although its not a good idea to flatten a LiPo pack to 0.00v it can withstand this punishment on a few occasions throughout the lifetime of the pack. To determine if your pack has open circuit cells connect it across a current controlled PSU ~500mA(maximum) and adj the supply voltage until hopefully some current is drawn. This will confirm the battery is OK and proves the series cell connections are intact.
Continue with this method until the battery reaches within its operational voltage range. Transfer back to the balanced charger to finish the recovery.
I actually just ordered a replacement, for €18, it’s better to have a new reliable solution and Karl, I also ordered for another €2,30 a battery alarm. I already have two of these but they only go up to 3S, this new one is for 4S LIPOs. The question is whether I’ll hear the alarm while operating with headphones on and the alarm board inside the amps case. Next Saturday I’ll be operating with an external 4S LIPO on the amp however having an internal one (albeit a lower capacity) is very convenient.
Yes Jonathan - the old NiCd NiMh trick, but don’t think it’ll work fully for Li-Po’s? I’ve tried this method in the early days of Li-Po’s without success - specifically achieving a half decent capacity in the odd one that was resuscitated.
Are you trying to be funny Richard, as per usual ?
Yes, I have manged to successfully restore a Zippy 8000mAH from a near 0v state, it was certainly well below the individual cell voltage sufficiently to be rejected by my balanced charger. I never said I was conforming with the manufactures advice, I try something and if it works and is reasonably safe IMO I will merely suggest what I have done.
If you current limit and monitor the packs temperature whilst trying this, I cannot see any danger.
Don’t you mean on the web ?
As with anything in this hobby, YMMV, its anything but factual. Especially on here !
One of the issues, Richard, is that the charger manufacturers try their hardest to stop people killing themselves.
The potential for Lithium based cells to catch fire when mistreated is well known. In the amateur radio world we treat our packs gently but the RC boys hammer the bejesus out of them. Such high discharge and demands for fast charging will be more likely to push cells to their failure modes quicker than our use. Over discharged cells are more likely to have been abused and hence, more likely to be damaged and a fire risk. It seems a very sensible idea to make chargers refuse to charge cells which have an under spec voltage.
If (big if) you know what you are doing and take measures to manage the risk, it is worth trying this to see if you can reboot the cell. Whether it will recover to be viable long term is unknown. Some cells will come back almost as good as new and some will remain completely tatered.
Well the replacement LIPO got it’s first test today on the summit with the low voltage alarm fitted. The alarm went off a LOT earlier than I expected and even when I turned off the 40m amp, the alarm kept sounding - I had suspected this might happen and so had a screwdriver ready to take the amp apart and remove the alarm from the (internal) LIPO cell and connected my backup external 4S hard case LIPO, to continue the activation.
On getting home I checked how far the cells had gone down - Cell 3 was still at 56%, Cell 4 at 48% but Cells 1 & 2 were at 0% (Zero). The only thing that could have drained the first two cells at a different rate to cells 3 & 4 is the alarm itself (which I have had connected internally in the box with its LEDs running for the last 2 days).
The amplifier is powered from the propper output leads from the LIPO, so it cannot have caused the drain of just two cells.
By the way after getting the new LIPO 3 days agao I fully charged it - all 4 cells were showing 100% charge.
Moral of the story, so far - beware the alarm plugs! I’ll try to see if I can bring the charging connector outside of the box, which will make it possible to only attach the alarm during an activation and also allow charging of the LIPO without having to take the case apart.
Of course this could also be simply a faulty LIPO - I’m recharging it at present and then I’ll see how it behaves on the next activation.