Imax B6

[trebor]

Help, My Imax B6 field charger is starting to play up. If I select 3cell Lipos and do a balanced charge it charges ok but will not finish off and play a tune like it used to. It shuts the charge down to 0.0 amps and the cells fluctuate around 4.19 to 4.2v but it will not complete. If I left it the timer would just shut off and it sits there doing nothing. Has anyone come across this before ? This is on all lipos which are in good condition, I charge Nimh function works fine and the alarm sounds off

[MattyB]

If all cells are at 4.19-4.2V/cell at shutdown it is finishing - that is fully charged for a std (non-HV) pack. Can't explain the absent alarm noise though!

Edited By MattyB on 28/06/2018 17:48:17

[trebor]

Its annoying, the battery goes on charge and then its time for a cuppa and a chat. If the alarm doesn't go off I forget it and end up waiting longer.

[Don Fry]

All my chargers do this to a pack occasionally. The pack seems fine. But I have started to notice the pack fails not too many charges later.

A first sign of failure.

Are all the packs from the same purchase?

Have you tried the charger on a 2s, or 4s pack.

Edited By Don Fry on 28/06/2018 18:10:59

[trebor]

Dont say that, I hope not all my batteries are on the way out I have 3 different batches and its my new ones as well. I have a GT charger somewhere, I shall run them all down and mains charge them next time.

[Don Fry]

Trevor, don't bank on my pronunciations. I know little about leccy things. But that's my take on the problem. You have a pack not balancing. Try a pack that does balance on another charger.

[Slickriff]

As far as I can make out a lot of the chargers with "6" in them are badge engineered from the same manufacturer. I have had the same thing happen on more than one (they will usually say full....but can be hours to do the last few mAh). It isn't the batteries in my case. In fact I have a couple of duo607 chargers where the batteries now register as full in the right period of time on the left hand connectors, but not on the right. Weird...but not a lot I can do about it. Realistically, when pressing the display and it is showing 4.20V per cell, and only a handful of mAh in half an hour then they are done. I know this as if I swap sides they register as full within a couple of minutes.

[Alan H]

I have seen this on several occasions, it only seems to happen on older packs and I am fairly sure it is the charger having difficulty in accurately balancing the pack. When this happens I manually stop the charger then check the cell voltages, provided the balance is reasonable I use them as normal and without any problems.

[Biggles' Elder Brother - Moderator]

I don't think there is anything wrong with your charger, I think the problem is in your batteries.

The most likely explanation is that you batteries a bit out of balance. Basically what is probably happening is the highest cell reaches 4.2V, although the lowest maybe at, say 4.1v. The charger then never sees a fully finished condition,...its aware that some cells ae below max, but there's little can do. It might try shoving 0.1A in there but it will almost immediately stop doing so because it runs the risk of overcharging the maximum cell. Catch 22!

A lot of folks think that "balanced chargers" actually balance the cells, this isn't really so. They really just monitor balance, they are not really capable of adjusting by singling out one cell for charging so as to bring it up to match the others.

So, what can you do? Well if the imbalance (examined cell-by-cell on a battery checker) is relatively small - less that 0.05v - you might want to just leave it alone for now. But if its bigger than that you can try the following:

1. Discharge the battery

2. Charge it to about 3/4 full. Check the balance.

3. Discharge the battery.

Repeat steps 2 and 3 above while the balance is improving. Sometimes this can bring a low cell gradually up to match the others. Sometimes its too slow a process to be practical.

The best solution probably lies in one of these. This does actively balance your battery. Use it with the battery approx 3/4 charged again. I think if you do this your charging finished alarm will re-appear again!

BEB

Edited By Biggles' Elder Brother - Moderator on 29/06/2018 11:45:52

[Don Fry]

Thank you for that BEB, but out of curiosity, what are the balance leads for, if the charger is not shoving power to the weak cell at the end of the charge process.

[Nigel R]

"A lot of folks think that "balanced chargers" actually balance the cells, this isn't really so. "

Erm. Actually. That really is so.

I have a balance charger, and it really does balance the cells.

On this particular one you can see the behaviour during balancing; the current pulses between a trickle output, and zero, about every 20 or 25 seconds. During that period it gives a short rest to the cells, about 4 seconds, in order to read the 'off charge' voltage, then uses that reading to apply a trickle charge to the low cells, whilst applying a similar discharge load to the high cells.

[Gary Manuel]

Posted by Biggles' Elder Brother - Moderator on 29/06/2018 11:43:58:

A lot of folks think that "balanced chargers" actually balance the cells, this isn't really so. They really just monitor balance, they are not really capable of adjusting by singling out one cell for charging so as to bring it up to match the others.

I thought this too and my batteries always finish up balanced after charging (Hobbyking Quattro and Accucell 6). I'd be interested to see your source of this information.

If the chargers don't actually balance the cells, they are breaking the trade descriptions act.

Edit - I realise that they cannot actually "charge" each cell separately - but they do charge them all, whilst loading individual cells via the balance lead until all are balanced - much the same as the battery balancer you linked to.

Edited By Gary Manuel on 29/06/2018 13:03:32

[Simon Chaddock]

trebor

The final elements of a balance charge are down to 1/100th of a volt. It only take a tiny bit of extra resistance on one balance wire circuit - either the pin connector into the charger but can be in the cell itself - for the charger to get confused. It charges to 4.20 on each cell, but the extra resistance means one cell is not actually at that voltage.

When the input cell voltages reach 4.2 the charger halts the charge to check the "static" cell volts but of course one cell promptly drops below the others so the charger starts charging again, however almost immediately all the cells return to 4.2 V again so it stops charging and checks again and so on until the timer cut in.

With the B6 showing the cell voltages wiggle the balance plug in the charger socket and see it the cell voltages settle down. If it makes no difference then it is likely one cell has a slightly higher internal resistance than the rest. This cannot be rectified and will only get worse as the LiPo gets used.

As long as the individual cell voltages are not more than, say, 0.02 V different when the battery balance charge rate drops to 0.1A you should be ok but sooner or later you will start to notice a drop in the usable capacity and/or maximum power.

If the LiPo starts to feel "squishy" then it is at the end of its life, at least as a flight battery!

[trebor]

Just re charged some Lipos on a GT charger and had no problem. I will try swapping over the balance leads and socket board to see what happens next time I go flying

[Biggles' Elder Brother - Moderator]

My source Gary is the experience of charging 1000's of batteries and observing what happens!

Yes, there are chargers out there that genuinely balance the battery and can address and charge cells individually - the Revolectric PowerLab 6 would be an example and it costs £200! As you say Gary the standard "B6 type" 4 button charger cannot charge a single cell in order to balance the battery. If you present it with a partially discharged, fully balanced, battery it will do a great job and usually produce a fully charged, fully balanced, battery. The balance lead connection is there to help it do this by monitoring the individual cell voltages and ensuring no individual cell goes over 4.2V.

But if you present it with a partially discharged, unbalanced, battery what it will give you back is a fairly highly charged (98% or so) unbalanced battery! So if it genuinely is a "balancing charger" in the sense most people think then it's pretty rubbish at it isn't it!? In practice it will never fully balance this battery, to a reasonable tolerance, in any reasonable time. This is what I mean when I say these chargers are not balancing chargers, they are chargers that monitor the balance whilst they charge - exclusively via the main plug.

BEB

Edited By Biggles' Elder Brother - Moderator on 29/06/2018 20:27:53

[Gary Manuel]

Thanks BEB.

I had assumed that you had read some fact based report based on how balance chargers work or studied their schematic diagrams by the way you presented your argument. So you agree that balance chargers do actually balance the batteries via the balance leads, but are not perfect at it, as a failing cell will always be troublesome to bring up to the same voltage as the other cells in the battery. That's pretty much how I perceived them and I can live with that.

[Biggles' Elder Brother - Moderator]

Posted by Gary Manuel on 29/06/2018 20:56:32:

Thanks BEB.

I had assumed that you had read some fact based report based on how balance chargers work or studied their schematic diagrams by the way you presented your argument. So you agree that balance chargers do actually balance the batteries via the balance leads, but are not perfect at it, as a failing cell will always be troublesome to bring up to the same voltage as the other cells in the battery. That's pretty much how I perceived them and I can live with that.

Sorry Gary, no I don't agree - well not entirely anyway! In my view they don't balance, they just maintain a pre-existing balance whilst charging. If that pre-existing balance isn't there they won't bring it about.

BEB

[Gary Manuel]

Well here's the schematic diagram of an Accucell 6 which is a pretty generic 4 button balance charger:

**LINK**

and here's a rather nice video of a charger strip down, which explains how all the various parts of the charger work - including processor controlled individual cell loading.

The bit you are interested in is 29 minutes in:

Edited By Gary Manuel on 29/06/2018 21:42:11

[Biggles' Elder Brother - Moderator]

But Gary, loading a cell is not charging a cell! Testing its charge state and ability to hold voltage will not balance it!

I suspect we may well be splitting hairs a bit here and are both seeing the seem thing but from a different starting point. Maybe we just have to agree to each have their own view on this.

BEB

[Bob Cotsford]

Sorry BEB, but I'm agreeing with Gary on this, almost every charger that I've owned has attempted to balance cells when that type of charge is selected. Most B6 clones claim a 100mA balance current, better chargers go up to 300mA as my current GT unit does.

The exception? The Hitec X4 that I bought following magazine reviews lauding it. It claims to be a balance charger and iirc claims to use a 300mA balance current. My experience is that it is a fraud.

It is the only exception though, everything else from B6 and clones through Turnigy dual units to GT quad all attempt to balance a pack. If they fail then it's because the pack has a cell with a high IR or there's a duff balance board..

[Gary Manuel]

Sorry BEB, but this is not hair splitting. The balance chargers are doing their job.

Looking at the schematic diagram I linked to, the balance current of the Accucell is controlled via a Darlington pair and limited by 6 x 120 ohm resistors in parallel = 20 ohms. This gives 4.2 / 20 = 210mA maximum balance current per cell. This is consistent with the typical specified balance currents Bob has quoted.

[PatMc]

As I understand it the higher voltage cell(s) are loaded whilst the lower voltage cell(s) continue to be charged thus balancing the battery. There are limits if a battery is well out of balance, the cells don't always end exactly in balance but in my experience the balance is generaly improved. Also if the cells are well out the charger will sometimes time out as a safety feature before the charge is complete but in these cases the battery is probably near the end of it's useful life.

A point to remember is that the voltage of each cell is monitored by a different sub circuits. If these individual circuits are not well calibrated the cells may be displayed as equal when they're not & one or more cell may be overcharged each time. I once lost several batteries to a badly calibrated charger due to this before I realised the cause.
Best check each cell voltage with a DVM against what the charger displays.

[Gary Manuel]

Posted by Biggles' Elder Brother - Moderator on 29/06/2018 22:10:39:

But Gary, loading a cell is not charging a cell! Testing its charge state and ability to hold voltage will not balance it!

Loading a cell discharges it - or charges it at a lesser rate by shunting some charging current away from it. Balancing is achieved by loading the HIGH voltage cells, giving the low voltage cells chance to catch up.

[Gary Manuel]

I agree with everything PatMc just said.

[Biggles' Elder Brother - Moderator]

We'll just have to agree to differ then Gary.

BEB