recovered a lipo cell having 1.45volts - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-22-2014, 12:02 PM   #1
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I am: michael o
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recovered a lipo cell having 1.45volts

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I don't have a lot of experience with lipos so this may not be useful information to others..... but I recently bought a bunch of 2s/1350mah/30c ThunderPower lipos on this forum that were advertised as new (but I understood had likely been on the shelf for "a while").... three of the packs were fine but the fourth had one cell at 3.85v and the other at 1.45v.

btw, good communication with the seller and he and I agreed I would try to bring the cell back to life and discuss so more; no complaints in this area

Online I found a LONG thread on rehabilitating Makita 18volt lithium battery packs (I'm aware that some r/c have been scrounging A123/LiFe04 cells from similar packs)....

... and within that thread was a long post by "Firedog91902", an r/cer, which included the following paragraphs:

"If the cell voltage below 2.5 v, the charger won't start the charge. If the low voltage is caused by an internal short, it's toast. More likely the cell was stored with an external load and it might still recover. Here's a safe method to find out. Connect a small Ni-MH cell (1.2 v) to the cell (positive to positive) and see if the voltage starts to recover. The internal resistance of the NI-MH cell will prevent very high current if the Li cell is internally shorted, but if the voltage doesn't start up in a few seconds it's bad. If the Li cell charges to 1 volt, switch to 2 Ni-MH cells in series. If it reaches 2 volts the charger should now work and charge the cell.

2. Store the charged cell 24 hours to see if the open circuit voltage drops below 4 v. If it does there is likely an internal short or other problem and the cell won't hold a charge.

3. Connect a 2 ohm resistor capable of 2 amps to the cell and note the voltage after 60 seconds. If it stays above 3.7 v it will probably work fine in a tool battery. If it's less, use it in a flashlight or other low drain device."

I used individual 2amp NiCad cells, first one alone, then two in series, then three in series ... and each brought up the voltage on the low cell, eventually up to around 3.5 volts... and at that point my Icharger 308duo accepted the pack for charging; I ran it thru three cycles; the cells balanced, internal Ir reasonable at around 5 and the pack voltage did not collapse when put under sustained load with an old Ace R/C expanded scale voltmeter.

comments/cautions welcome

Newmarket, Ontario
MAAC 15048

Last edited by michaely; 08-22-2014 at 12:13 PM.
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Old 08-23-2014, 07:08 AM   #2
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Re: recovered a lipo cell having 1.45volts

Do you really want to bring down a plane or heli that cost you hundreds of dollars and countless hours because you played around with a $6.00 battery?

Discharge it, cut the leads, get another one and go back to flying.
... Luke 6:38
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Old 08-23-2014, 04:07 PM   #3
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Re: recovered a lipo cell having 1.45volts

Good post Michealy!

That supports my experience with run down lipos exactly! I have done it successfully several times with only one failure so far. I had a pack that only 3 cells of the 4 recovered so I cut off the bad one and now run it as a 3 cell pack. Instead of using NiMh cells to charge them I just put my charger on the NiCad setting with the lowest amp out put it will go to, watch the voltage and when it comes up to the pack's nominal voltage I switch it back to Lipo setting.

Now I appreciate what deaconFlyer has said as being the best thing to do in a perfect world but...

#1 those batteries retail out here for around $30.

#2 Those are park flier/foamy batteries and not powering a overly expensive plane.

#3 In a remote area like I live you don't just walk across the street for a replacement! The nearest LHS is 4 to 6 hours away or 10 days to 2 weeks by mail!
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Old 08-28-2014, 12:26 PM   #4
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Re: recovered a lipo cell having 1.45volts

Meh, I've recovered several Lipos- either for myself or friends.

In all cases, its never a risk if you practice safe battery use, namely check the battery before each flight. And not just overall voltage either, but use a checker that lists each battery's voltage. You can spot a dying cell in a pack long before it becomes a problem. Since I do this with every battery I have in my collection before every flight, salvaged or not, this is a matter of routine, but helps me identify a potential problem before it manifests itself.

Second, fly with a battery alarm (or telemetry). That way if one cell drops below min (I use 3.5 as my min for most batteries) the alarm goes off if you have a bum cell that drops to below min not long after take off

Third, a revitalized battery should be flagged as such (I use colored tape on the packs). This is to remind me to keep an eye on it. Over time, the revived cell will lose capacity faster than the other cells in the pack. I have noticed this occurs about a year after the salvage if you tend to use it a lot. You will see this when you balance charge. The bum cell will be lower than the others when you start the balance charge. It will also still be balancing after the other cells in the pack have reached max voltage. That is when you will know that pack is near the end of its life. But as I said, you see this about a year later. So if you manage to get another year from what may have been a throw-way pack, that not a bad salvage in my books
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Old 08-28-2014, 04:27 PM   #5
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Re: recovered a lipo cell having 1.45volts

I also have recovered a few lipos by zapping them as nimh on my charger for a few seconds, after which the charger would recognize them as a lipo.

I don't trust those batteries though and I mark them as 'suspicious' to ensure they only go into cheap foamies from then on.

One that really hurt though was a 4S 4000 Zippy. I used a pair of them in series for my 52" flying wing. I know that battery was never stressed but it still dropped a cell.
I don't have any other planes that can use that batt so I just still use it on the wing as a nose weight paired up with a good one for shorter flights.
My death spirals are a thing of the past. I just fly faster now.
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