Soshine SC-S2, Li-Ion Charger.

Well at last my Soshine SC-S2 Charger has arrived ... It just happened that I had two Ultrafire 2400mAh protected 18650 cells that were discharged to exactly 3.8 volts to test the charger with.

I first checked to see if the charger had voltage present with no cells inserted ... It did and the voltages were 4.22V on the left hand slot and 4.23 on the right hand slot ... I put the cells in and started the charging process ... Eventually after 4 hours, the right hand slot showed blue, so the cell was removed and the voltage was 4.18 Volts ... after another 15 minutes, the left hand slot showed blue and the cells voltage was the same at 4.18 Volts.

The charger is supposed to be a fast-charger, though I don't think that I would class it as such ... The instructions say 2.9 hours for a 2400mAh and 3.5 hours for a 2800mAh but I don't know what voltage they started at in their charging sequence ... I monitored the charging voltage and it seemed to come up quickly for the first two hours then the last part of the charge took about the same length of time ... As far as I could tell, the last hour or so was not a fixed voltage (CV), it just gradually built up to the point where the blue LED came on.

Towards the end of the charge, I put my Avo 8 in series with one of the batteries to check the current ... It wasn't registering much on the 10 Amp range, so I switched to a lower range ... The Blue LED lit, so I went back to the 10 Amp range and the Red LED came back on ... It seems that the charger is very sensitive to any small extra resistance in series with the battery ... So, I can't check whether the charger actually switches the charging current off when the blue LED comes on.

During the first part of the charge, the charger reached 115 degrees F in one area and the cells reached 94F ... These temperatures dropped considerably during the last part of the charging process.

The charger seems to be well made, though as yet I haven't compared its function to my Trustfire TR-001 ... I will do a side by side comparison test in the next week or so, just to see which charger is quicker ... I suspect that they will be very similar in their charging times ... I will do the test from the same 3.8 volts as todays quick check ... I just wish that I could check the charging current with my Avo 8 ... I might try it with one of the DMMs to see if that will work better.
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To measure charge current :

I put the 18650 battery in tail first and then use the MM to complete the circuit without actually putting the 18650 in all the way .

old4570 said:

To measure charge current :

I put the 18650 battery in tail first and then use the MM to complete the circuit without actually putting the 18650 in all the way .

Click to expand...

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I have made a sort of three ply insert out of a central plastic membrane sandwiched between two pieces of sticky backed aluminium foil ... The insert goes between the positive end of the cell and the charger contact with the cell fully inserted ... The ammeter makes the connection between the two metal foils.

The problem seems to be that the charger can see the extra resistance of the ammeter when it is on ranges that are more sensitive than the ten amp range ... The charger Red LED shows that the battery is being charged OK when the Avo model 8 is on the ten amp range ... The moment that I try to go to the one amp or 200 milliamp ranges (or lower) the charger Blue LED comes on to say that the battery is charged ... When I go back to the ten amp range the red LED comes back on.

I think that it is due to the slightly higher resistance of the lower current ranges when the ten amp (shunt) is removed ... I don't know if you can understand my explanation.

I will try my method with the higher charge rate at the beginning of the charge just to see if it works.
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No I understand ....

The little insert U use may be the cause of the resistance , or more correctly adding to it ...

I was thinking of doing something similar , but then I started thinking if there would be much added resistance ..

I went to the trouble of buying 2 1A amp meters , and then possibly making a sort of more permanent measuring system to read the charge rate for the entire charging cycle ...

Im going to have to buy one of those 18650 cradles and some gator clips so as to monitor the charge rate I think ...

I will be ordering the Soshine charger shortly , I look forward to you confirming if it shuts off on completion .

old4570 said:

No I understand ....

The little insert U use may be the cause of the resistance , or more correctly adding to it ...

I was thinking of doing something similar , but then I started thinking if there would be much added resistance ..

I went to the trouble of buying 2 1A amp meters , and then possibly making a sort of more permanent measuring system to read the charge rate for the entire charging cycle ...

Im going to have to buy one of those 18650 cradles and some gator clips so as to monitor the charge rate I think ...

I will be ordering the Soshine charger shortly , I look forward to you confirming if it shuts off on completion .

Click to expand...

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The sticky-backed aluminium sheet is quite thick and is what I originally used for bodies/weight on trout flies ... I checked the DMM on ohms and the lead resistance was 0.3 ohms ... I put one of my 3 ply inserts in circuit and the resistance went up by 0.1 ohms.

I put the Avo 8 on the 10 amp range and measured its resistance using the DMM and it was a virtual short circuit ... I could only see the lead resistance ... However with the ammeter on the 1 amp range, the resistance went up by 0.4 ohms ... The 100 milliamp range measured 4.0 ohms and the 10 milliamp range measured 40 ohms ... So even using the one amp range puts an extra 0.4 ohms in circuit ... The Avos leads together are about 0.1 ohms when measured on the DMM ... So using the one amp range on the Avo would put a total of 0.5 ohms in series with the battery ... I don't know how badly this extra resistance affects the results, but certainly it makes the charger change from red to blue LED ... Whatever voltage drop that occurs across the ammeter (during charging) would reduce the actual voltage across the cell ... Once the charger voltage across the cell and the extra resistance adds up to 4.18 volts or more, the charger LEDs turn to blue ... As such, I can't see a way of accurately checking that the current shuts off when the LEDs go to blue as the 100 milliamp range puts the extra 4.0 ohms into the circuit ... I need to do more research on this ... I will try checking on the ten milliamp range just to see if there is any current flow at all when the LEDs turn blue ... Due to the extra 40 ohms resistance the readings won't be accurate, but I should hopefully be able to see if the current drops to zero.

The only other way I can think of is to leave the cells in the charger after the LEDs go to blue and see if the cell voltage goes up above the 4.18 volts that I measured earlier to about 4.22 volts which was the open circuit voltage of the charger.

I hope this sort of makes sense.

Any other suggestions please.
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Hey march. The easiest non EE way to tell if the SC-S2 is trickle charging after the LED turns blue, is to do as you suggested.

You need a cell that charges up to your 4.18 Volts. Most cells, unless they're really really new, will drop in voltage after 20 minutes, by 0.01 or more. So, if you have a cell that charges up to 4.18 volts, and 20 minutes after removing from the charger reads 4.17 Volts, put this cell in the charger and wait for the LED to turn blue. Let it remain on the charger for an additional 20 minutes. Then, take the cell out and measure the voltage. If the cell reads 4.17 Volts, or less, the charger is shutting down and not trickle charging. If the cell reads 4.18 volts, the charger is trickle charging.

Don't make things anymore complicated than necessary!

Dave

https://www.candlepowerforums.com/posts/3304227#post3304227

I like to check :

old4570 said:

https://www.candlepowerforums.com/posts/3304227#post3304227
I like to check :

Click to expand...

Nothing wrong with that. I was just suggesting an easy way to tell if a charger trickle charges, or not.

A lot of folks think that because their cells come off the charger at 4.20 Volts after leaving them on the charger after it indicates the charge is completed, that their charger doesn't trickle charge. In fact though, this usually means it does.

Dave

march.brown said:

As far as I could tell, the last hour or so was not a fixed voltage (CV), it just gradually built up to the point where the blue LED came on.
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Click to expand...

So they lied when they said it was using the CC/CV algorithm, just like their other chargers. I wouldn't trust anything else they say either.

old4570 said:

I like to check :

Click to expand...

That is not going to work with chargers where you can put in a new cell to charge it (without cycling the power).

The LED turns blue when the charging current falls below approximately 30mA in the CV stage but the Soshine SC-S2 does not stop charging.

I bought 3 of these chargers some time ago but did not yet complete all the measurements and modifications that I had planned to do.

The chargers came in blister packs that I could only open with a knife.
Package contents: charger, wall wart with 12VDC output and12V car adapter cable.


Specification and instructions


Two of the chargers came with a 12V 1.2A wall wart, the third with a 12V 1.5A wall wart.

The specification on the charger label differs from that on the instruction sheet or the Soshine website.

The two charging bays are long enough for all of my 18650s.


I did some measurements with an Agilent 66332A, a PSU that can act as current sink.




I set the current limit to 5A and increased the voltage in small steps:

The Soshine SC-S2 is protected against short circuits but it does not have a low current precharge stage for deep discharged batteries.
The current in the CC stage is approximately 1A.
The off-load voltage of all 6 channels of my 3 units is a bit too high: between 4.240V and 4.254V

Enlarged view of the voltage range above 3.5V

The #3 Soshine is already modified to 4.20V off load voltage

The opened charger


The other side of the PCB


I don't understand the whole curcuit but each channel seems to be controlled by a MC34063 buck converter.
The HK324 quad operational amplifier could be used for current control and LED charging indicators.


The voltage is set with the R13, R2 voltage divider at pin 5 of the MC34063 for channel 1 and R30, R19 for channel 2.
The MC34063 has an internal voltage reference of 1.25V.
The theoretical output voltage is
Vout = 1.25V (1 + R13/R2) = 1.25V (1 + 24k/10k) = 1.25V * 3.4 = 4.25V
The real value can differ quite a lot since the voltage reference only has a 2% accuracy and the resistors used for then voltage divider will add some more inaccuacy.

An easy way to adjust the voltage is to put high ohm resistors parallel to the resistors.
A 10M resistor parallel to R13 will reduce the output voltage by approx. 7mV.
A 10M resistor parallel to R2 will increase the voltage by approx. 3mV.

To reduce the voltage from 4.25V to 4.2V a 1.3M or 1.5M resistor parallel to R13 is needed.

I simply soldered the additional resistors on top of the voltage divider resistors.

My preliminary rating:

+ two completely independent charging curcuits
+ 1A current in CC stage
+ CC/CV charging algorithm (although not perfect due to high output resistance)
+ wall wart type power supply (no dangerous voltage inside the charger - makes modifications easy and safe)
+ protection against short curcuit and reversed batteries


- voltage a bit too high
- does not stop charging when indicator turns blue
- DC connector plug a bit too loose in socket
- no precharge stage for deep discharged battries
- no safety timer
- no temperature control
- lid and sliding contacts flimsy
- springs at sliding contacts a bit weak
- wrong specification on the charger label

Done some more checking and the charger is definitely trickle charging ... I still get weird results on the different ranges of the Avo 8 though ... The trickle current is showing 4.0mA on the 100mA range and 0.8mA on the 10mA range ... I get different current readings with the DMMs, but it still shows that the charger doesn't switch off when the blue LED comes on ... I will just have to remove the cells when the blue LEDs come on ... At least I know that the cell voltages are then 4.18 for both channels ... If I leave them a few extra minutes inadvertantly, with this low trickle current, I will have to put up with perhaps a shorter cell life ... Three years or so instead of four.

My charger is almost identical to the pictures that "Tohuwabohu" posted ... My ac adaptor says input 100-240V , 50-60Hz 0.4A , Output 12V 1.5A , Model No.ACTM-09.

The charger label says input DC 12V 1200mA , Output DC 4.2 Volts plus or minus 0.05 , 1000mA X 2.

My charger on first glance looks exactly like the pictures other than a few differences in the printed labels ... It also came in a sealed plastic blister pack.

I will not bother with the mods to reduce the open circuit charger voltage , I will just take care with my charging techniques and watch for the blue lights ... I mean the blue lights on the charger not on the Fire-Engines (hopefully).

Tohuwabohu, thanks for the graphs and the pictures they are very informative .. You obviously have some very sophisticated test equipment ... I am waiting for delivery of a five volt reference so I can check both my cheap DMMs, at least then I will be able to remove the cells off charge at an accurately measured 4.2 volts or whatever lower point that I decide.

I'm giving up on all the charger current measurements in favour of a simple life ... In future, I will just remove the cells when the blue lights come on ... I will still religiously check the battery volts though.
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Just looked at this graph in more detail and it looks as though the Soshine unmodified is still charging at about 400mA when the voltage is 4.18 V.

My chargers blue LEDs come on when my cells are up to 4.18 volts ... You said that your Soshine LEDs turn blue when the current drops to below approximately 30mA ... This is where the graph says that the voltage is about 4.24 to 4.25 volts ... The modified charger seems to be pushing out about 180mA when it gets up to the 4.18 volts point.

I am probably interpreting the graph wrongly, as I don't have experience with the Agilent unit.

I will check my Soshine again with a partially discharged battery to see if my blue LED comes in at a different voltage this time.

march.brown said:

Just looked at this graph in more detail and it looks as though the Soshine unmodified is still charging at about 400mA when the voltage is 4.18 V.

Click to expand...

@ march.brown

All these beautifully colored lines but black and brown (PSU and Pila) show the properties of chargers, which don't keep to the CC/CV directions exactly. Thus your observation is true.


@ Tohuwabohu

A very surprising idea to show current over voltage instead of the usual way to show current and/or voltage over time. So quite a different aspect - current at (even very) low voltage becomes visible.

Interesting to see the foldback in voltage of the Pila in your graph, it really (probably solely) cuts off the current completely. You find this behaviour as well in the familiar sort of graph of a Pila I happen to have at hand.




May be that helps others to understand your unusual graph more easily.

Wulf

Wulf,
thanks for the explanation. I'm sure it will help others to understand the graphs.
It is easier and faster to do this type of measurement than to monitor voltage and current when charging a battery.
When I have done some more measurements on the Soshine I will start a thread in the Messerforum and we can discuss it there.

The Pila charger is indeed very special, I have never before seen a charger with a negative output impedance.
The Pila does completely stop charging when the charging current drops below 70mA and the resting voltage of the battery is high enough.
When the resting voltage is below 4.08V it will go into a sort of error mode (red LED on, green LED off) and continue to charge with very low current.
This can happen when the contact are dirty or the battery resistence is too high.

march.brown,
in the CV stage the Soshine does not push a current into the battery.
It is a constant voltage source with an output impedance of approx. 180 milliohm.
The current is a result of the voltage difference between the off-load voltage of the charger, the resting voltage of the battery and the sum of the resistences of charger, battery contacts and internal resistence of the battery.
When you put an amperemeter in the curcuit you increase the resistence and thus decrease the charging current.

The Agilent 66332A that I used as an electronic load has a very low impedance when it is in constant voltage mode - much lower than the internal resistence of a 18650 lithium ion battery.
This will lead to higher currents at the same voltage.

Tohuwabohu said:

Enlarged view of the voltage range above 3.5V

The #3 Soshine is already modified to 4.20V off load voltage

Click to expand...

With the modified Soshine charger (green line) the current drops to zero by the time the voltage reaches 4.20 V. This seems to mean it would take a nearly infinite time to fully charge a cell since the voltage will asymptotically approach 4.20 V but never reach it.

I wonder if the original preset voltage of 4.25 V was deliberately set slightly high like that in order to allow charging to 4.20 V to complete in a reasonable time...?

Mr Happy,
of course you are right, a battery in the modified charger will never reach 4.20V.
But I prefer to have a charger that will never charge beyond 4.2V over one that will charge up to 4.25V when the batteries are left in the charger too long.
The battery voltage will be lower than 4.2V when I remove them form the charger as soon as the indicator turns to blue but that's ok for me.

Excellent posts by Tohuwabohu, also the comments from Meterman which helped me better understand the graphs. :thumbsup: You guys are way ahead of most of us and are better equipped, when it comes to testing and explaining the results of these tests.

march.brown said:

... I get different current readings with the DMMs, but it still shows that the charger doesn't switch off when the blue LED comes on ... I will just have to remove the cells when the blue LEDs come on ... At least I know that the cell voltages are then 4.18 for both channels ... If I leave them a few extra minutes inadvertantly, with this low trickle current, I will have to put up with perhaps a shorter cell life ... Three years or so instead of four.

Click to expand...

Leaving cells on charge after the charge should have been terminated, for a short time, is probably not a big issue with this charger. The danger is forgetting to remove the cells, and leaving them to trickle for long periods. The big problem with trickle charging beyond a fully charged state, isn't so much the shortening of cell life, but the danger of the plating out of metallic lithium. From B.U.'s Charging Lithium-ion batteries page:

[FONT=Verdana, Arial, Helvetica, sans-serif]No trickle charge is applied because lithium-ion is unable to absorb overcharge. A continuous trickle charge above 4.05V/cell would causes plating of metallic lithium that could lead to instabilities and compromise safety.[/FONT]

Click to expand...

I don't think most Li-Ion users are aware of this. Most are more concerned with how trickle charging, or overcharging Li-Ion cells, shortens cell life. To me anyway, the plating out of metallic lithium is a bigger concern. The effect is cumulative, is irreversible, and the cells become unstable. The more a cell is subjected to trickle, or overcharging, the more likely a "venting with flame" incident could occur.

Cells with metallic lithium present, can "vent with flame" at any time, when they become unstable. It could happen while, charging, in use, in your pocket, or stored in your dresser drawer. This is an event that is not limited to occurring while charging.

Dave

Good evening everyone, I have just carried out a "top-up" charge on another Ultrafire 2400mAh protected cell ... My two DMMs read slightly different, for example this 18650 cell read 4.03V on one meter and 4.02 on the other ... Through this particular test the difference between the two readings was 10 millivolts with occasional flickers to 20 millivolts before settling to the lower difference ... When my five volt reference arrives, I will know which one is the more accurate meter and I will be able to correct both their readings.

At 1424hrs , the top-up charge started and the charger applied 4.18 volts to the cell.
At 1450hrs , the voltage was 4.21 volts.
At 1500hrs , the voltage was 4.22 volts.
At 1515hrs , the voltage was 4.23 volts.
At 1530hrs , the voltage was 4.23 volts and the blue LED came on ... I assume that this was the time when the current dropped to below 30 milliamps.
The higher of the two meters is quoted in the above figures.

I removed the cell and checked the voltage immediately ... It was 4.18 on one meter and 4.19 on the other meter... That was at 1530hrs.
At 2000hrs the reading was 4.17 and 4.18 volts.

The battery didn't heat up, so I never took its temperature.

To bring the cell up from 4.03 volts to 4.19 volts took 66 minutes.

I think I can live with this charger OK, assuming that I don't leave it trickle charging on the "blue" for too long ... I also think that the manufacturers charging times for 18650 cells are rather optimistic if you want to attain the full 4.20 volts.
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Am I understanding correctly ?

old4570 said:

Am I understanding correctly ?

Click to expand...

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R13 and R30 was quoted.