'4 button chargers' BUG
 

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.

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.

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.

@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.

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.

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.

Those that are checking the cell voltages, are you using a calibrated meter?

@Andy - dont think so mate, just a reliable one that Ive had for a while now. Seems to do the job well, but not sure about calibration.
You reckon that could cause alot of probs?

Can you define what you classify as a "4 button charger"?

I posted something along these lines in a thread a couple of days ago, all my info's here:

http://www.oople.com/forums/showthread.php?t=93876

Seems quite a common issue from what I gather. Have you tried reconnecting the battery back to the charger after charging to see what it then reads?

A "4 button charger" are those standard design of multi-type (Ni-XX, Li-XX) chargers that are everywhere now.
Ansmann xMove 2.0
Core UDC
iMax B6
Turnigy
Team Orion
etc
etc

...although in fairness, the Team Orion and Turnigy Im hearing good things about. The Turnigy has little variable resistors so you can fine tune the calibration so its exactly right. I gotta love that idea.

Sorry Poopers, hadnt seen that before I started this thread. You're right, it definately does seem common.
Ive reconnected the battery, and it still shows as 4.2v per cell, so it isnt an inconsistency (which is a good thing that it isnt).

Hoewver, Id love to get a side by side comparison of the tolerances of each brand of charger, so maybe people could charge up a set of cells, test the voltages in each one after balance charging, and then post their results on here.

I'll start:

CHARGER: Ansmann xMove 2.0
APPROX. COST: £50
CELL 1, END VOLTAGE: 4.14v
CELL 2, END VOLTAGE: 4.15v

0.06v is quite a small voltage, and a meter could quite easily be out by that amount. Try measuring a voltage with a couple of different meters, and see the difference.

I'm not saying your meter is out, but worth checking against another.

@Andy-AJ: Good idea mate. I'll measure the cells on some other voltmeters at next club race event (Wed 29th) Cheers for the headsup :)

For the measurement you're looking to perform you need quite an accurate meter, you're looking for 0.06 in 8.4 volts or a 0.7% variation.

For example this : http://www.maplin.co.uk/ut60e-true-r...nterface-46458

Has a best DC voltage accuracy of 0.8%, which is more than you're looking for!

you have to bear in mind all of those are cheaper versions, my bantam is spot on against my multimeter ( yup its calibrated for my work)

You're right Mark, I think this is something that I am learning.
My Etronix transmitter and my cheap 4 button charger look great on paper - they have all the same features as the big guys for a fraction of the cost, so you might be forgiven for thinking "why on earth would I want to spend more"

I think the reality is that you are paying for precision, for well made, well specced components and in the case of our chargers - calibration and reliability that is spot on.

p.s. if you dont mind me asking. What price is your bantam charger? Do you think its worth the higher cost compared to these cheapers 4 button chargers?
Thnx :)

mine were from a sponsor but i belive there around the £100 mark. personally as long as they undercharge by that much its ok, its if they over charge i would be concerned about.

You are asking a lot of something that is mass-produced and lands on your doormat for only £50. It has managed to balance your cells to within 0.24% and to reach the voltage limit within 1.5% when the measurement device only has an accuracy of 0.8%.

With all of that, you will also be within 0.5% of the voltage of every other competitor, and have well looked after cells able to last a full season. And when we had NiMh cells... :wtf:

I have one of these chargers. It is very reassuring to know that it is roughly right, and not precisely wrong. ;)

If you want a Bantam for half price, I have one that will be going on the For Sale board soon. Excellent condition, with leads, in box. The Core UAC-50 that replaced it (needed the higher charging rate, nothing wrong with the Bantam) seems to me to be identical in performance, but way less robust in its plastic case - the Bantam is metal. HTH :)

Carnim, I would carry on using your charger and Radio gear without worrying. As has been mentioned already, you are not over charging your cells, and providing you are not having any interference issue's, your Tx and RX are doing their job. Why spend money that you don't have to, save it for spare's. It's very easy in this hobby to get carried away with the hype of the latest and more expensive equipment, making you faster.