Genuine SkyRC iMAX B6 mini overcharging issue for NiM especially

[ro0ter]

Hello all,

I do have a problem with my most recent charger - iMAX B6 mini.

The problem is so annoying that every NiMH cell charging / repeaking / etc stops with "overTemperature" error.. measured 53*C with vellman multimeter (iMAX overtemp set to 50*C).

I then started to charge the battery... it stated 1.34V and later on when I put it into my Liitokala charger, I see 1.48V...

I instantly measured the output of the iMAX charger and i noticed about 0.15V at 1.5V... Here`s a link with every check:
        https://photos.app.goo.gl/dY9mRTNn52L3MRJt6

It seems the charger has an offset of -0.20V at 0.20V which gradually decreases as the voltage grows:

• -0.09V @ 0.09V - reads 0.00V (probably software-limited)
• -0.19V @ 0.19V - reads 0.00V (probably software-limited)
• -0.20V @ 0.39V - reads 0.19V
• -0.20V @ 0.50V - reads 0.30V
• -0.18V @ 1.00V - etc
• -0.15V @ 1.50V
• -0.13V @ 2.00V
• -0.06V @ 3.30V
• -0.03V @ 4.20V
• -0.02V @ 5.00V
• -0.03V @ 6.00V
• -0.03V @ 10.00V

I`ll make a better measurement in the afternoon, at every 0.25V...

I had not tested individual cell voltage readings, but I hope to be able to also do that.

Anyone has any idea what might cause this and how can it be fixed? (either hardware or by calibration). I will try to perform a calibration with a 25.2 voltage source and 6 identical resistors in series (eventually also in parallel to try and avoid resistance manufacturing error / tolerance). I`ll probably buy 30 pieces of 680-ohm, 1% resistors and solder them 5p6s (or.. I`ll see what 1% resistors they have)... that will end to 136ohm, it will eat up to 300mA and dissipate about 103mW/5 resistors. Should that be ok?

Anyway, I haven`t opened the charger so far and I hope I won`t find dragons inside.. anyone has any schematics or advice on what might cause this or how can it be fixed?

Thank you!

[Psi]

Just out of interest, is this a legit iMAX B6 mini or one of the many 3rd party copies?

[ro0ter]

Just out of interest, is this a legit iMAX B6 mini or one of the many 3rd party copies?

It`s a genuine as far as I think, this is the purchase link: https://www.aliexpress.com/item/Genuine-SKYRC-iMAX-B6-Mini-60W-Professional-Balance-Charger-Discharger-For-RC-Battery-Charging-Re-peak/32655009726.html (referrals removed). Correct me if I am wrong.

[Armadillo]

That is because your nimh battery is already terminally old and internally leak hence the delta V detection cannot detect steady voltage rise terminating voltage.

Not that the battery cannot be used, just that it cannot retain the power for long time anymore.

Set overtemp to 45 and terminate as alternative OR Change Battery.

[ro0ter]

That is because your nimh battery is already terminally old and internally leak hence the delta V detection cannot detect steady voltage rise terminating voltage.

Not that the battery cannot be used, just that it cannot retain the power for long time anymore.

Set overtemp to 45 and terminate as alternative OR Change Battery.

The battery is a 2400mAh which proves to have 1835mA in a Liitokala NOR test... so NOT dead..

The charger does the same with any NiMH battery.. either if it`s a charge or a re-peak..

How about the error-offset in measuring mode? :| any opinion on that? Thanks!

[wraper]

Just out of interest, is this a legit iMAX B6 mini or one of the many 3rd party copies?

It`s a genuine as far as I think, this is the purchase link: https://www.aliexpress.com/item/Genuine-SKYRC-iMAX-B6-Mini-60W-Professional-Balance-Charger-Discharger-For-RC-Battery-Charging-Re-peak/32655009726.html (referrals removed). Correct me if I am wrong.

Most of "genuine" IMAX are counterfeit. Have you scratched holographic sticker and verified code on IMAX website?
https://www.skyrc.com/antifake/public/

[Armadillo]

Firstly, Are you sure in the imax manual, it tells you the method to use it to measure voltage? What voltage? RMS, average, or PEAK? It passes through LIPO balancer stage etc......

Secondly, I don't trust your power supply and the meter reading unless those are calibrated by a precision voltage reference calibrator recently.

If it charges the battery, then should be OK right for the price?

[ro0ter]

Just out of interest, is this a legit iMAX B6 mini or one of the many 3rd party copies?

It`s a genuine as far as I think, this is the purchase link: https://www.aliexpress.com/item/Genuine-SKYRC-iMAX-B6-Mini-60W-Professional-Balance-Charger-Discharger-For-RC-Battery-Charging-Re-peak/32655009726.html (referrals removed). Correct me if I am wrong.

Most of "genuine" IMAX are counterfeit. Have you scratched holographic sticker and verified code on IMAX website?
https://www.skyrc.com/antifake/public/

Hi wrapper,

I am using a different API/webpage section of skyrc: http://verify.skyrc.com/index.php?code=613162853118

I had checked this code twice, first time this morning (scanning the QR code with my phone, after scratching the label) when I got the green mark, second time now (when I got an exclamation mark, 2 times checked, still me; I expect the counter to go up as many visitors of the forum will click the link).

Were you not able to see the google photos share link in the initial post? I have there screenshots with the successful validation, plus photos with unscratched + scratched label.

[ro0ter]

Firstly, Are you sure in the imax manual, it tells you the method to use it to measure voltage? What voltage? RMS, average, or PEAK? It passes through LIPO balancer stage etc......

Secondly, I don't trust your power supply and the meter reading unless those are calibrated by a precision voltage reference calibrator recently.

If it charges the battery, then should be OK right for the price?

The imax manual is very thin on all aspects.. it states it measures the battery voltage. There are no clarifications about any stages etc. Can this voltage offset be caused by some charging circuitry/component? I find it very odd since the nimh batteries end up in over-temp every time... measuring the battery voltage while it is being charged shows the same offset..

My multimeter might have a 0.01~-0.02 volts offset, but I am positive that it measures correctly. It has not been calibrated lately (like in the past 10+ years), but if you really need this, I can drop by a friend this week and have him test my mini-supply and my voltmeter.. anyway.. this is not the scope of the discussion, but I respect your point and I am willing to confirm my multimeter`s calibration.

My small PSU is from R&D (as seen here ). I`ll say it`s quite stable... maybe I should add an output filter, I am considering that since I purchased it.

I had tested with 2 multimeters (no-name and velleman dvm890) and they both show about same reading, way different than the charger`s reading.. you can see the respective photo in the google photos album shared in the first post. I would trust the velleman, not the uni-t m890g...

[Armadillo]

The answer is so obvious;

Any site that dare not put on its Trademark LOGO is fake, like the Red and Black Logo.

[Armadillo]

Give the Charger, fake or real, a little respect by using a proper Power Supply because the interaction of switchmode with another cheap switchmode is anyone guess.  Use proper Power Supply Designed for battery Charging.

Also, lower down your charge peak current e.g. limit so that the detection circuit can detect the terminating voltage.
For smaller nimh, lower down even still to 1/10 C or 2/10C current limit.

Many faces similar issue, but opted fast charge like 1C, by using temperature as limit terminating charge instead.

Fake or Real, all the same, except software programming in the most part and not from SkyRC.

Firstly, Are you sure in the imax manual, it tells you the method to use it to measure voltage? What voltage? RMS, average, or PEAK? It passes through LIPO balancer stage etc......

Secondly, I don't trust your power supply and the meter reading unless those are calibrated by a precision voltage reference calibrator recently.

If it charges the battery, then should be OK right for the price?

The imax manual is very thin on all aspects.. it states it measures the battery voltage. There are no clarifications about any stages etc. Can this voltage offset be caused by some charging circuitry/component? I find it very odd since the nimh batteries end up in over-temp every time... measuring the battery voltage while it is being charged shows the same offset..

My multimeter might have a 0.01~-0.02 volts offset, but I am positive that it measures correctly. It has not been calibrated lately (like in the past 10+ years), but if you really need this, I can drop by a friend this week and have him test my mini-supply and my voltmeter.. anyway.. this is not the scope of the discussion, but I respect your point and I am willing to confirm my multimeter`s calibration.

I had tested with 2 multimeters (no-name and velleman dvm890) and they both show about same reading, way different than the charger`s reading.. you can see the respective photo in the google photos album shared in the first post. I would trust the velleman, not the uni-t m890g...

[ro0ter]

Again, I`m puzzled by the big voltage difference.

I agree that a cheapo smps near an other smps doesn`t do good.. I had however checked it with the ACASIS 12v adapter (the one in the 8th review, attached photo to this message as well), with the original SKYRC power adapter and with a more beefy psu - https://www.aliexpress.com/item/12V-24V-Power-Adapter-Supply-2A-4A-5A-6A-AC100-240V-Plug-Transformer-AU-UK-EU/32659669505.html

Ignoring the PSU, I see the voltage measuring difference on all nimh batteries, the more discharged the battery, the bigger the difference...

Thanks all for all your input, will dismantle the charger and see what lies inside.. I had also looked over the internet, it seems I don`t have a clone (just performed firmware upgrade).. it costed me $45 together with its skyrc adapter. I don`t remember the box anyway, will serach for it, maybe it`s not thrown yet. will post more photos later or tomorrow, however the scope of this thread is not to validate the authenticity of the charger.

purchased july 2018, only discovered the problem yesterday.. I would say it correctly charges and "almost" entirely balances lipo packs (that`s the scope), but since 2 of my my liitokala ports were toasted (ordered new 8205A), I needed a fast way to charge 3 nimh batteries at once..

I also asked the chinese, this is his reply:
The product is normal, the voltage difference is within reasonable error

Call me dumb, but if 10% (0.15v at 1.5v) is reasonable error.. better call me a priest!

[wraper]

Were you not able to see the google photos share link in the initial post? I have there screenshots with the successful validation, plus photos with unscratched + scratched label.

Do you expect everyone go to external link and scroll page to the bottom when you even did not say that you verified it?

[ro0ter]

I`m sorry.. I didn`t mean that.. it`s just that usually I check everything before posting.

However, I`m not really sure that I have a genuine unit now, after Armadillo`s and your replies 

The forum didn`t let me upload all the photos.. and I might have a bug report here, who should I contact about this (e.g. uploading photos you get to the 2mb post limit, you get an error that you are over-limit, but you are not told that part of the photos were uploaded then you shrink and compress the photos, all of them are under 800k and you try to upload them.. again over-2mb-size-limit - and that`s because part of the initial large photos were uploaded)?

I am really grateful for your time and for your help, be assured my intention is not to point fingers nor to argue with anyone

Again, sorry for any impression that I might had left.. And now I almost believe that I purchased a fake unit, considering your and Armadillo`s comments.. I`ll ask the seller.

[Armadillo]

The reason why I am not really interested with "Voltage" accuracy is, [many share the same]

Charger is for charging battery with an automatic means to terminate the charge to ease user burden of monitoring it.
It Charges base on  the amount of "Charge Capacity" that is put into the battery, resulting in the battery displaying its "OWN" chemical voltage, and Ultimately the battery when use, the voltage will dip gradually anyway.

Maybe check that the Threshold is properly set.

But also  your pursue of voltage accuracy is nothing wrong and most likely achievable. Happy Hunting.

[wraper]

B6 mini can be calibrated although it's not apparent if zero offset is calibrated as well during process. https://www.skyrc.com/index.php?route=information/blogger&blogger_id=190

[ro0ter]

Now these last two posts are really useful. BIG THANK YOU Armadillo and wraper!

I did see the nimh sensitivity in the manual but I ignored it since I had no clue what it did... now it makes sense . If I can`t accurately calibrate it (if the zeroing-error does not dissapear), I`ll tamper with the sensitivity setting.

I searched a lot for the imax b6 mini voltage measuring error, but I found nothing useful...

I might try the calibration with my 6s pack if it doesn`t require all cells to be 4.20v sharp..

The rcgroups forum link is excellent, I see that some other users have the voltage offset issue (mine is smaller, charger doesn`t blow/swell lipo packs). I`ll try to calibrate both balance and main. I really trust my vellman

Also, funny that I have HW version 1.0....... (or the mini never had a v2?)

[Armadillo]

4.2v Sharp? Really?
Mine after juicing are never equal. 

[ro0ter]

NiMH sensitivity adjustment did not help...... Also, cannot calibrate at all...

There are times and times.. if I start the charger connected to microUSB it sometimes measures accuretly.

Some acquaintance of mine just confirmed that he also has an offset (although 0.06V @ 1.39V - iMAX reads 1.39, actual voltage is 1.45)