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Can you charge a LiPo through its balance lead?

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FilmBuff01/08/2019 10:32:16
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I have a Pulsar Pro electric glider that requires the nose cone (complete with motor, battery ESC etc) to be slid of each time you want access to the large 3S 4200 mAH battery.

Then you have to disconnect it from the ESC (due to a connector arming configuration) before it can be charged - using a bullet to Deans converter. Quite a faff.

I use a balance lead extender into the wing pylon so I can check the status of the battery - and was wondering if I could slow charge the battery in situ via the balance lead.

The Pulsar is so good that I have only charged the flight battery once. After three flying sessions and around three hours of flying the battery is still showing 80% charge.

Paul Marsh01/08/2019 10:47:01
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Yes I do charge through the balance lead using the charger. Only slow charge so ok I Use this:
Overlander RC3S

Edited By Paul Marsh on 01/08/2019 10:55:32

Martin Harris01/08/2019 10:51:08
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Technically yes, if you have a charger which will allow it but it's not good practice to leave a battery connected (unless your "arming configuration" takes care of this?) both on safety and battery life grounds. Charging a LiPo in situ has always been discouraged as it increases the risk of fire during charging - although few of us will have been unlucky enough to have a charging fire, there have been reports of such over the years.

Bob Cotsford01/08/2019 10:51:14
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The (usually!) red and black outer wires of the balance plug will be connected across the pack and those wires should be rated for at least 2A so a 0.5C charge aught be ok. Considering that similar wire is often used for switches on high power servo setups, SBus chains and the like quoted as being good for two or three times that much you might think it would be ok for a 1C (4A+) charge, but I'd have concerns running that sort of current through sucxh small guage wires for extended periods. The other question is whether you would be happy if there were a charge problem resulting in a blown cell or burnt wiring and it took out the plane too.

There is a reason most of us charge LiPos out of the model.

edit: the charger Paul links to above looks to have a maximum charge current of 1.5A which would be fine through the balance lead for a 3 hour charge.

Edited By Bob Cotsford on 01/08/2019 10:56:00

Paul Marsh01/08/2019 11:18:09
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Usually, I take a whole box of charged Lipos to a fly- in and have enough to fly all weekend, without needed to charge them, then plug all the batts into these chargers = charges them slow not to damage them and is easier. Problem is that you have to plug the balance port and the output leads if charging through a normal charger, which adds a stage to do and undo.

FilmBuff01/08/2019 11:26:11
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Thanks guys. I'm aware of the issues with in situ charging but I'm thinking a 0.5A - 1.0A charge through the balance lead would not be harmful?

FilmBuff01/08/2019 11:31:14
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Posted by Martin Harris on 01/08/2019 10:51:08:

Technically yes, if you have a charger which will allow it but it's not good practice to leave a battery connected (unless your "arming configuration" takes care of this?) both on safety and battery life grounds. Charging a LiPo in situ has always been discouraged as it increases the risk of fire during charging - although few of us will have been unlucky enough to have a charging fire, there have been reports of such over the years.

The battery will be fully disconnected from the ESC - but it will be in situ.

So I'm thinking 0.5A to 1.0A through the balance lead will not be harmful?

Edited By FilmBuff on 01/08/2019 11:31:49

Dickw01/08/2019 12:16:06
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Posted by FilmBuff on 01/08/2019 11:26:11:

Thanks guys. I'm aware of the issues with in situ charging but I'm thinking a 0.5A - 1.0A charge through the balance lead would not be harmful?

I charge the 2s Lipo rx battery on some of my models in situ via the balance lead using an adapter lead to my regular charger (adapter - the main charge leads are connected to the outer conductors on the balancer plug). I only use this setup on 2s batteries because with the main charge current passing through the outers on the balance plug the balancing would be problematic for more than 2s. However with a charger designed for balance lead charging that shouldn't be a problem.

Provided you keep the current low and you are happy with the normal charging risks, what you propose should work.

Dick

Edited By Dickw on 01/08/2019 12:16:36

Edited By Dickw on 01/08/2019 12:16:55

Frank Skilbeck01/08/2019 13:01:40
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I have an e-flite charger that charges 3s and 4s batteries through the balance lead at upto 3 amps. (it's the one that came with the original Habu EDF I think).

FlyinFlynn01/08/2019 15:37:45
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this Hobbyking DC-4S balance charger is designed to charge and balance 2s, 3s or 4s li-pos from a 9 to 16Vdc source, I have used a couple of these chargers for years. There is also a variant out there that does LI-ions too but sadly not from hobbyking.

Ben B01/08/2019 16:11:19
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Charging via a balance lead is fine. I have a couple of lipos charging this way as we speak. Only issue with charging in situ is if the cell puffs (can't get it out) or bursts into flames....

Boots01/08/2019 18:51:34
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i assumed you can ONLY charge through the balance lead, that is its purpose, if you charge from the power leads an unbalanced charge is sure to occur.

Bob Cotsford01/08/2019 22:16:00
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Not quite, the balance leads do what they say on the tin. They are primarily for relatively low current balancing. The main battery leads are sized for the high charge currents used for LiPos, not such an issue for low capacity packs but when charge currents go up above a couple of amps it's a bit much for the size of wire used on balance leads.

Most balance chargers put the initial bulk of the charge in at a high current through the thick battery leads, monitoring the voltage of each cell by means of the balance leads. If/when the charger detects a difference between cellsnear the end of the charge it can balance the individual cells via the balance lead by either discharging the higher voltage cell or boosting those at a lower voltage (depending on the design of the charger). This balancing act is carried out at a hundred or two milliamps, again depending on the individual chargers abilities.

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