Bonzo Moon Posted February 15 Share Posted February 15 I was testing an FPV tx the other day and like a fool forgot to disconnect the lipo until a while later. Put a meter on it and it read zero! Quite a recent 3s 800mA. I was not pleased. Checking cells I discovered that in fact it was only one cell that had gone to zero, two others were showing 3v + . I tried unsuccessfully to kick the zero cell into life by charging as NiCad, at NiMh, but it stubbornly stayed at zero. Reluctant to bin it I salvaged the 2 good cells and turned it into a 2s 800mA. Here's how Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted February 15 Share Posted February 15 Tell me about it, I also have a couple of 4s now 3s on my starter motors. 1 Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 13 minutes ago, Paul De Tourtoulon said: Tell me about it, I also have a couple of 4s now 3s on my starter motors. It's the way to go! I wonder how many people just bin them though? Quote Link to comment Share on other sites More sharing options...
Geoff S Posted February 15 Share Posted February 15 There's no real need to change the balance connector. You just plug it into the 3S socket and the charger will 'know' it's a 2S LiPo as all the balance connectors on a charger are wired together. 1 Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 13 minutes ago, Geoff S said: There's no real need to change the balance connector. You just plug it into the 3S socket and the charger will 'know' it's a 2S LiPo as all the balance connectors on a charger are wired together. Plugged into my charger and because one cell would not allow current to flow through it the power lead showed zero, charger said low battery, and didn't want to know? Quote Link to comment Share on other sites More sharing options...
Geoff S Posted February 15 Share Posted February 15 How does the charger 'know' you're plugged into the 3S or the 2S balance connector? Mine certainly doesn't and it displays individual cell voltages. Quote Link to comment Share on other sites More sharing options...
Phil Green Posted February 15 Share Posted February 15 (edited) Yep, several of my 2S batteries started out as 3S. I mostly use a blunt plastic tool rather than a Stanley knife. As Geoff says, theres no need to change the balance plug, just remove or insulate the 4th wire if its a 3S to 2S fix. Edited February 15 by Phil Green Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 4 minutes ago, Phil Green said: Yep, several of my 2S batteries started out as 3S. I mostly use a blunt plastic tool rather than a Stanley knife. As Geoff says, theres no need to change the balance plug, just remove or insulate the 4th wire if its a 3S to 2S fix. I was thinking after using the blade a plastic spatula would be safer! I just went very carefully 😉 Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 28 minutes ago, Geoff S said: How does the charger 'know' you're plugged into the 3S or the 2S balance connector? Mine certainly doesn't and it displays individual cell voltages. Good question. Mine has 5 slots for balancing leads. It certainly senses the voltage on the power lead to see if it's with acceptable parameters for the settings you have chosen. I doubt I can plug a 3s into the slot with one dead cell and tell it that it's a 2s. More importantly there was zero volts across the power lead, so it just said 'low voltage' and wouldn't work. My charger doesn't display individual voltages either? Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 8 minutes ago, Bonzo Moon said: just remove or insulate the 4th wire if its a 3S to 2S fix. might try that next time. Quote Link to comment Share on other sites More sharing options...
Jim Hearnden 1 Posted February 15 Share Posted February 15 That looks like the modern version of Bomb disposal to me 😉 1 Quote Link to comment Share on other sites More sharing options...
Paul De Tourtoulon Posted February 15 Share Posted February 15 Just unclips the battery balance wire on the dead cell and move the others along like they would be with one less cell. 2 Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 1 hour ago, Jim Hearnden 1 said: That looks like the modern version of Bomb disposal to me 😉 Like ITV Trigger Point? Quote Link to comment Share on other sites More sharing options...
Jim Hearnden 1 Posted February 15 Share Posted February 15 13 minutes ago, Bonzo Moon said: Like ITV Trigger Point? Danger UXB that are old enough to remember it! https://en.wikipedia.org/wiki/Danger_UXB 1 Quote Link to comment Share on other sites More sharing options...
Jason Channing Posted February 15 Share Posted February 15 Inside the pack the cells are still wired in series whether or not you disconnect the balance lead. Probably the daftest thing Ive read in a long time and the most dangerous. Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 (edited) 18 minutes ago, Jason Channing said: Inside the pack the cells are still wired in series whether or not you disconnect the balance lead. Probably the daftest thing Ive read in a long time and the most dangerous. Of course they're wired in series in the pack. I took the end one off the series, so it was two good ones in series. And the balance lead and power lead attachment points needed changing to suit a 2s not a 3s. I am a qualified electrical engineer too as it happens 😉 It's not daft and on other groups people are telling me they already do the same thing if there's one dead cell in a pack. Please tell me what's dangerous about it? Edited February 15 by Bonzo Moon 1 Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 22 minutes ago, Jim Hearnden 1 said: Danger UXB that are old enough to remember it! https://en.wikipedia.org/wiki/Danger_UXB Sadly I do remember. 😏 Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted February 15 Share Posted February 15 I'm afraid being a qualified electrical engineer doesn't necessarily mean everything is safe.... a club mate is a qualified electrical engineer and he often connects Lipos together via their power leads to 'give a jump start' to one exhibiting a poorly cell.... 1 Quote Link to comment Share on other sites More sharing options...
Jason Channing Posted February 15 Share Posted February 15 You never said you opened the pack up and resoldered the pack and bypassing the dead cell, you made it sound like you only removed the balance lead.Sounds like a pain to save a few pounds. Second thoughts Ill go with my original post, Having reread the posts, as the posts suggests just removing the balance lead, Quote Link to comment Share on other sites More sharing options...
JOHN MOSLEY 2 Posted February 15 Share Posted February 15 19 minutes ago, GrumpyGnome said: I'm afraid being a qualified electrical engineer doesn't necessarily mean everything is safe.... a club mate is a qualified electrical engineer and he often connects Lipos together via their power leads to 'give a jump start' to one exhibiting a poorly cell.... That's the guy we need there when you have a heart attack then.😇🤣 Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 7 hours ago, Jason Channing said: You never said you opened the pack up and resoldered the pack and bypassing the dead cell, you made it sound like you only removed the balance lead.Sounds like a pain in the arse to save a few pounds. You never said you opened the pack up and resoldered the pack and bypassing the dead cell, you made it sound like you only removed the balance lead.Sounds like a pain to save a few pounds. Did you actually watch the video? 😉 You can see I rebuilt and rewired the pack after removing the dead cell? Pain in the ass for some, but I enjoy messing with stuff and OK, it saves a couple of quid too. As I said, people are posting telling me they already do the same thing. My video was intended to be educational, but each to their own! Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted February 15 Share Posted February 15 As a matter of interest did you try and charge the one ‘dead’ cell. I’ve done that on a number of occasions, true it’s mainly been if I’ve had 1 cell that’s badly out of balance but I’ve also done it on an otherwise ‘dead’ cell. Even having done that the ‘repaired’ battery is consigned to desk duty. Quote Link to comment Share on other sites More sharing options...
Bonzo Moon Posted February 15 Author Share Posted February 15 16 minutes ago, Ron Gray said: As a matter of interest did you try and charge the one ‘dead’ cell. I’ve done that on a number of occasions, true it’s mainly been if I’ve had 1 cell that’s badly out of balance but I’ve also done it on an otherwise ‘dead’ cell. Even having done that the ‘repaired’ battery is consigned to desk duty. I saw online that once a lipo has gone as far as zero they cannot be revived. 3.65v is less than 10% but I've done it from the low 3v mark. Worth doing for a little bit of work to have a useable 2s 800mA I reckon. I don't like chucking stuff away! 1 Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted February 15 Share Posted February 15 1 hour ago, JOHN MOSLEY 2 said: That's the guy we need there when you have a heart attack then.😇🤣 Hoping to avoid that Mr M! Quote Link to comment Share on other sites More sharing options...
Phil Green Posted February 15 Share Posted February 15 (edited) 4 hours ago, Bonzo Moon said: Good question. Mine has 5 slots for balancing leads. It certainly senses the voltage on the power lead to see if it's with acceptable parameters for the settings you have chosen. I doubt I can plug a 3s into the slot with one dead cell and tell it that it's a 2s. More importantly there was zero volts across the power lead, so it just said 'low voltage' and wouldn't work. My charger doesn't display individual voltages either? Sorry no, me & Geoff were both talking about the resulting 2S battery having a 3S balance plug, the faulty cell is gone at that point 🙂 You treat the repaired 2S battery as any 2S, except the balance plug (which is now a 4-way with only3 wires connected) goes into the 3S balance port. The balance ports are simply commoned so the charger sees a 2S 👍 Edited February 15 by Phil Green 1 Quote Link to comment Share on other sites More sharing options...
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