'4 button chargers' BUG

[Cardnim]

Has anyone actually measured their individual cell voltages AFTER a balance charge.
It seems that all these "4 button chargers" that are everywhere at the minute and basically are all the same - it seems they have a wide tolerance within them as to what they think is "fully" charged.

I have an Ansmann xMove 2.0 which is great and hasnt missed a beat, except I just measured my individual saddle packs which came off the charger - supposedly fully balance charged at 4.2v each (thats what it showed on the LCD display).
However, what they are ACTUALLY sitting at is 4.14 and 4.15

Now this isnt too bad, as its UNDER the 4.2v limit, but it means Im not getting all the juice out of my batteries.
More worringly, is if my charger had been even 0.1 OVER that limit (eg. 4.21v) this could be dangerous and at very least definately lessens the life of my batteries.

Anyone else either tried this, or willing to try it?
Would be really interesting to try a side by side comparison of different brands and makes.

I know how to fix it, as the charger uses a resistor array to suck volts out of the higher cell(s) when balance charging, and it is these resistors which are cheap and not giving a true Ohms rating.
I can replace them with high accuracy resistors once I work out their values.

[bigred5765]

i think under load when your driving it, the lipo will drop way below that any way, and as your not running them flat you'll see no advantage doing it, as long as there not over 8.4 i wouldn't worry about it.

[_sleigh_]

You'll more than likely find you have a high resistance joint/connector in the balance lead setup. It's a common issue with all these types of charger and will probably develop into a total fault in balance charging in the near future.

Check all of the balance leads and replace if they're suspect. You could try borrowing a set off someone else to confirm.

[Cardnim]

@bigred - youre right of course mate, I doubt I would notice any difference and its not dangerous as its below the 8.4v lipo limit. However, it is somewhat worrying that a different charger may be charging OVER this 4.2v cell limit - and that is both damaging and potentially dangerous.

@Sleigh - no mate, this is a genuine problem with all these 4 button chargers. Its been well documented elsewhere on the Internet (hence what got me to test mine). Nout to do with the balancer leads and/or board; its to do with the cheaper components used within them.

Again, its not a crisis, but I would recommend people take the 10 seconds to pop their charged cells onto a good voltmeter just to see what the true picutre is - I certainly feel safer knowing that my charger tolerance is stopping BEFORE 4.2v and not after.

[MattW]

Yeah there is a fair amount of variation - and it's down to component tollerances I suspect. I wouldn't even want to bet that a lot of them are the same on every charge.

A lot of people tried to tell me that when we changed to LiPo it was ok, as would only need a cheap charger - there was no advantage to buying an expensive one. Well - not true!

Buying an expensive charger doens't guarentee it will be better, as I have seen it posted that some very expensive gear from a popular make isn't accurate either - but i think it does improve your chances. For example, I use a GM/Groupner UDC40 - £250 new. However it charges my LiPos arurately every time, and the cut off voltage is adjustable in the unlikely event of any issues.

That said, there are of course many examples of decent gear available at a decent price - for example, I'm sure I saw a thread of poeple commending the Core RC UAC50 on here a couple of days ago.

[ianjoyner]

I think checking your cells frequently with a meter is good advice.

I've also seen no reason to balance charge unless they're out for some reason (which probably indicates a fault with the pack anyway).

The only time my cells have gone out of balance is following a balance lead problem. I've done hundreds of cycles on packs without ever balance charging, in my experience the cells just don't drift apart. As soon as anything is connected to that middle pin you risk them going out of balance (even if they're supposedly being balance charged), so I avoid even connecting the balance lead... but I check them regularly.