Some have received this charger and found, like HKJ’s test shows, that the voltage display (at least for LiIon cells) is 0.05V too high. The result is that charging stops at appr. 4.15V.
This is easily fixed as the case can be opened by 4 screws.
Hold the charger with the display against yourself (south) and rotate so the backside comes up. Inside, the PCB is fixed by 2 screws (DO NOT UNSCREW!). 1/4” south of the LEFT screw you find two resistors R63 (01B=1k) and R64(302=3k).
Simply solder a small resistor, 68KOhm across R63.
FIXED!
EDIT: Here is a picture of the mod (top, middle) 68kOhm across R63.
The correction of the end voltage will change inverse proportional with the resistor if the correction is small as here. But only one value will make the OPUS display true voltage.
My offset was initially 0.052V and a 68K (5%) resistor was exactly right. The OPUS stopped after the fix at 4.204V and showed exactly the same voltage as my Fluke meter i.e. no voltage error after the fix.
Enthusiasts could try using a potentiometer or try to change R64 instead (add a resistor, around 39 Ohm in series - is more difficult!).
EDIT:
I have now also tried NiMh charging (1A) after the fix. The voltage readout is nearly correct (max 0.006V off in my case) so that is OK.
Charging stopped at 1.52V (and my Eneloop was too hot for my liking, not going to use this on my precious Eneloops). It was an old cell from 2006-05 and the heat could be due to high internal resistance.
Dang, looks good!!! Did you do some reverse engineering yourself to figure this one out? I gotta see if I have a 68K - probably do in 0805, not sure - are they 0805's or 0603's?
Ohh - would a smaller value than 68K produce a higher charge voltage? Don't think I'd need to go higher though anyways.
Yes, I had to look inside and figure it out
I found also the current determining resistors but those have to wait.
And yes, the correction of the end voltage will change inverse proportional with the resistor if the jump is not too large. But only one value will make the voltage display true voltage.
0805 I think. I used a leaded 1/16W resistor.
No sorry, was only kidding. I looked at it last night, before you posted, but my look was pretty darn useless. Still @work now, will check out your note this evening. Looks easy enough to follow your info. Thanks!!! Really appreciate this! I'll see if I can post a marked up pic, depends if I got the resistor on hand. I don't have any leaded resistors, but we might here at work...
Edit: Oh boy, not good. Think my C100 is dead - display comes up scrambled. I don't think it's related to the attempted resistor mod. I removed the resistor and it's still dead. I didn't verify the charger before making the attempt - I'm thinking it was dead from me possibly taking it apart when I first got it. I don't see anything wrong, but the display operation is a mystery to me. Wonder if I lost a part of something. On the backside of the PCB there's a row of contact points that I don't understand the purpose of.
Sorry to hear that. Of the same reason I did’nt touched the two screws that hold the PCB because it can be difficult to place the zebrastrip (a rubber bar with carbon rings that makes connection). Sorry I did’nt mention that!. Beware of dust but don’ t rub or touch the carbon rings. Help can be Googled with search words faulty error zebrastrip.
Good luck!
It seems like the bottom has ventilation holes but the top has none. During discharge the heat from the resistor is trapped in the case and heats the cell. Would making some holes at the indicated location help cool the case and the battery during discharge? Note that the discharge resistor is on the right, almost right under the 3 holes I drew at that point.
Think I have them, but my charger is dead anyways. It's that finicky connector for the display that I messed up somehow, and just can't get it working. Forgot the name/type of connector, but it's common in old calculators where everything has to align perfect, no pins, etc.
They are called elastomeric connectors. They are extremely sensitive to re-use. Sometimes they work, sometimes not. I think the oils from your hands screw them up. Not sure though. Sorry yours got messed up.
I swore I’d never buy anything from Gearbest again. But since they’re the only one’s who have it, I took a chance and ordered one. for $12 and change, I’m not going to be too picky. I’ll mod it if I have to.
Well guys, I found a problem with mine other than under charging a little. The USB output on mine outputs 3.86 volts with no load on a freshly charged Panasonic unprotected 3400mAh 18650 which I know is good. When I load it up with a 250 millivolt load, the output drops to less than 3 volts. The display on the Opus shows 4.17 volts loaded or unloaded. I’ve very disappointed. I sent a message to GearBest. Let’s see how they handle it.
Did you do some reverse engineering yourself to figure this one out? I gotta see if I have a 68K - probably do in 0805, not sure - are they 0805's or 0603's?
. I'll do some googl'ing as you suggested.