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How do I charge a 2S lipo through the balance lead?

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Adrian Smith 114/08/2018 16:10:26
2151 forum posts
835 photos

p1050182.jpgI have this little Optipower Ultra Guard back up system which is on a 2S Lipo. the connections you can see are the balance lead to the battery and the lead to the RX. The item doesn't function properly and the guys from Midland Helicopters where I bought it from suggest the battery voltage may be a bit low and try charging it through the balance lead.

I don't think my charger will do this as apart from the balance connection, two banana plugs are used to charge any normal lipo.

I haven't seen a charger that will do this through the balance lead. Any ideas how I can get round this?


Edited By Adrian Smith 1 on 14/08/2018 16:11:11

J D 814/08/2018 16:26:07
1117 forum posts
65 photos

I have a balance lead charger that came with a Twister MEDIVAC helicopter.

Denis Watkins14/08/2018 16:27:53
3586 forum posts
166 photos

I don't understand this, but the blurb says it charges in flight?

It charges and balances from your lipo, which ensures you have back up every flight Adrian

Charging the 2C one time is logical if it was low

But you would think the intelligent board would take care of that

Disconnect the balance lead and put your tester on that small lipo

To see if it or one cell is low

Edited By Denis Watkins on 14/08/2018 16:42:26

Frank Skilbeck14/08/2018 16:48:38
4356 forum posts
101 photos

A lot of the simple chargers that come with the small ARTF planes only charge through the balance lead, you could ask your club members if anybody has got one (I've got a least two)

Something like this

Edited By Frank Skilbeck on 14/08/2018 16:50:02

Dickw14/08/2018 17:04:57
423 forum posts
71 photos
Posted by Adrian Smith 1 on 14/08/2018 16:10:26:


I don't think my charger will do this as apart from the balance connection, two banana plugs are used to charge any normal lipo.

I haven't seen a charger that will do this through the balance lead. Any ideas how I can get round this?

Edited By Adrian Smith 1 on 14/08/2018 16:11:11

If you are happy to do a bit of soldering it is easy to make up an adapter - I charge all of my 2s Rx Lipos regularly this way using my normal charger. See diagram attached.

I only use this method for 2s.


2s via balance leads.jpg

John Lee14/08/2018 17:21:52
616 forum posts
46 photos

I used one of the little ARTF chargers to top up mine originally, but when I ruined the battery by leaving it plugged in for weeks I replaced the battery with a HK one with a JST connector to charge through, at less than £4 it's cheaper than a charger.

Other thoughts are the battery should charge at up to 2c through the UltraGuard so have you tried plugging it in to your model's power source for a couple of hours & see if it charges? Also try the unit with a different charged 2 cell pack plugged in - any capacity will do for testing.

Adrian Smith 114/08/2018 17:49:54
2151 forum posts
835 photos


I must admit that is what I am doing now but using a spare RX + RX battery connected to the unit with a switch. The red light is flashing which indicates it's charging so I will leave for a few hours. I have another of these units and the voltage is 7.85V (2S) & 3.9V for one cell so that unit is ok. I am trying to get a reading voltagewise from the one I have the problem with, but I have not come up with anything sensible yet.


I like that little charger, not expensive either.


I suspect it is because of low cells. I think I haven't flown the aircraft often or long enough for it to build up a decent charge. We will see.

I will report back when I have some meaningful data or results.

Adrian Smith 114/08/2018 22:25:54
2151 forum posts
835 photos

After 3-4 hours trickle charging off a RX battery one cell is at 3.97V +/-, but reading on the outside on the +/- outside wire is 4.77V which is presumable the total for two cells. Not good.

Will have a look tomorrow.

Engine Doctor15/08/2018 09:06:56
2205 forum posts
20 photos

It does sound as if you battery has had it ! . You could try charging each cell one at a time through the balance lead . Please only do this if you are happy and understand the wiring of a multi cell LiPo.. You will need a normal extension lead . Take the outer cover off the socket end so that the pins are sticking out . Remove the signal wire and the pin. The pins Neg/- and Pos/+ are the same spacing as the balance lead pins . Fit connections on the other end so that the lead can be connected to you charger. . Set your charger to 1s and capacity of battery. . Plug other end with the pins sticking out into balance lead socket ,Connect to first cell starting from the Neg/- wire on balance socket so first wire is N/- and second wire is Pos/+ for first cell. When charged move along to the next cell, Neg/- will be the second wire ( that was used as the pos/+ for the first cell) and Pos/+ will be the third wire and so no Repeat until all cells are fully charged . Check voltage and individual cell voltage , then decide if battery is any good

If cells are too low and charger wont recognise them give them a short boost on the normal / NiMh side of the charger for a few minutes only. If Charger still refuses to recognise the cell then its had it and next stop after a full discharge is the bin. .

I generally find that once cells have been discharged so low that they need a boost on a normal charger to get charger to recognise them then the capacity is seriously diminished and they are only any good for low power applications .

Nigel R15/08/2018 10:03:48
2718 forum posts
445 photos

Sub 1V on a lipo cell is bin time IMHO.

Adrian Smith 115/08/2018 12:42:07
2151 forum posts
835 photos

I agree Nigel R. I have ordered two replacement lipos from Trex-Align this morning due to be delivered to me tomorrow. Hopefully, that will resolve the matter for the small cost involved. If not I guess the attached circuit board might be faulty, but that's a lot more money to replace .......

More later.question

Adrian Smith 116/08/2018 16:41:42
2151 forum posts
835 photos

So today I removed the shrink wrap on the circuit board and removed the original 2S lipo. The Voltage on the new lipo was showing 3.85v per cell, so all ok there. So I attached it to the circuit board and tested. I checked my new charger too by giving the battery a short charge.p1050183.jpg

As a matter of a test I re-checked the discarded lipo and the voltages for the 2 cells was 3.95v and 0.66v! As an experiment I put it on the charger and status light wouldn't light up so that's it for the original battery - complete US. I returned the Ultra-Guard unit to the aircraft and all now fires up correctly.

By the way the charger came from Etronix and the lipos from Trex-Align and both items came with in 24 hours. Good show all round.

Stuphedd16/08/2018 17:07:20
631 forum posts
327 photos

I dont know if this is any help but I fly a lot of 2S powered stuff and have made a simple lead to balance charge the little blighters from my normal "all cando " lipo charger

AS per DickW above

2S Lead

Edited By Pete Willbourn on 16/08/2018 17:08:43

Colin Carpenter16/08/2018 17:24:18
543 forum posts
35 photos

I have knocked up something similar for my Blade 2S Heli lipos. Colin

Adrian Smith 116/08/2018 17:45:16
2151 forum posts
835 photos

Nice work, Pete.

I took the easy option for a tenner though and bought the dedicated charger for 2/3S batteries using balance plug.

That said it's interesting to see how you chaps got round the problem. yes

Edited By Adrian Smith 1 on 16/08/2018 17:45:41

robert chamberlain16/11/2018 01:09:53
110 forum posts

I have a new 6 volt Rec system so wouldn't a 2 cell Life batt be too high? Also, my 5 cell nickel pack is OK at 6 volts but comes off the charger at 7 plus volts. All this OK to use?

Dave Hess16/11/2018 09:40:07
301 forum posts
18 photos

LiFePO4 will be fine, but be aware that it has different discharge characteristics from lipo. It charges to 3.65v per cell, which drops to 3.33v per cell and stays there throughout the discharge until it's nearly empty, when the voltage starts to go down rapidly, so checking it doesn't give you much idea of how much charge is left.

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