Test/Review of Charger Opus BT-C700

[size=+3]Charger Opus BT-C700[/size]





This is a compact 4 channel analyzing charger from Opus.




I got the charger in a cardboard box.



The box contains the charger, a power supply and a manual.



The charger has a barrel connector for 12V power input.



As all analyzing charger it has a display and a couple of buttons.



When powered on the charger briefly shows the version number of the software.



Selftest during powerup shows all the text on the display.



When working the display looks like this, the DISPLAY button can be used to select what to show (v/h/mA/mAh).
The MODE button is used to select mode for one or for all slots, it is also possible to change mode later on.
The CURRENT button will step between the possible currents.




The charger uses a AA/AAA two level slot. Notice the metal strips touching the side of the battery, this is probably connected to a temperature sensor.







[size=+2]Measurements[/size]

• When not powered it will discharge the battery with 0.4mA
• Charge will restart charging after power loss, or battery insertion.

[size=+2]Charge[/size]

The charge mode can select between 200, 300, 400, 500, 700 and 1000, default is 400mA. The 1000mA is only available in slot #1 and #4 and only when slot #2 and #3 is empty.



The charger reduces current when the battery is nearly finished, this keeps the heat down, but makes it more difficult to terminate correctly. This charger is smart enough to terminate correctly even at the lower current.
Display shows 2027mAh in 3:20





The same with the 3 other slots, all have nice terminations.
Display shows 2049mAh, 2020mA, 2030mA in 3:28, 3:18, 3:23



Even at 200mA current the charger do a nice termination.
Display shows 1849mAh in 9:27



With 400mA the current is high enough to see the increased temperature when the cell is full.
Display shows 2052mAh in 5:53



The charger is rated to do 1A, but it is at the limit.
Display shows 2078mAh in 2:29



The charger needs some time to reconize a full cell, but it is smart enough to do it at low current.
Display shows 190mAh in 0:22



This XX is also fully charged.
Display shows 2076mAh in 2:52



Same with the Pro.
Display shows 2623mAh in 3:07



For some reason the 1A charge current is slightly lower here, but the cell is perfectly charged.
Display shows 2553mAh in 3:15



The AAA is no surprise, also perfectly charged.
Display shows 790mAh in 2:00



With four cells the maximum charge current is 700mA and it is handled fine (Remember my temperature sensor is not mounted on the same cell as the V/A sensors).
Display shows 1944mAh, 2091mAh, 2032mAh, 2091mAh in 3:06, 3:21, 3:15, 3:20



The charger uses below 1A from 12V.



M1: 43,6°C, M2: 47,4°C, M3: 48,3°C, M4: 44,4°C, M5: 51,5°C, M6: 32,6°C, HS1: 58,9°C

With the compact size the temperature is a bit high at full charge current.



M1: 42,1°C, M2: 46,1°C, M3: 46,2°C, M4: 42,5°C, M5: 50,6°C, HS1: 69,2°C



The charger is a bit slow to start, because it is waiting some seconds for user input.



Charge current is regulated with pwm.



Here I have selected maximum charge current, but due to my sense equipment (0.1ohm resistor in series with battery) the charge cannot reach full current.



Trickle charge is done with a current spikes each 30 second.



The spike is 0.0003 second long.



[size=+2]Discharge[/size]

The discharge mode can select between 100, 200, 300, 400 and 500mA, default is 300mA



The discharge is to somewhere between 0.8 and 0.9 volt.
Display shows 1855mAh in 3:44



A 100mA discharge takes a lot of time.
Display shows 1931mAh in 19:23



Discharging four cells at once will heat the charger.
Display shows 1895mAH, 1980mAh, 1977mAh, 1980mAh in 3:39, 3:59, 3:50. 3:59



M1: 38,7°C, M2: 41,5°C, M3: 42,1°C, M4: 39,2°C, M5: 50,5°C, M6: 34,1°C, HS1: 54,2°C
Discharge do also generate some heat, but not as much as charging.



Discharge is also done with pwm, above curve is lowest current.



Highest discharge current.



[size=+2]Discharge Refresh[/size]

This function will cycle the cell a couple of times, it finish with a charged cell.



Display shows 1904mAh in 2:30



[size=+2]Charge Test[/size]

This function will charge the battery, discharge the battery and then charge it again. The display will show the discharge capacity and time.



Looks like two nice charge curves with the discharge between.
Display shows 1948mAh in 2:28



[size=+2]Quick test[/size]

This function measures the internal resistance of the battery, this is an indication of how well the battery performs (Lower value is better).




First line shows the reading when I just put the battery in the charger.
The second line shows the reading when connected to my test equipment, but without extra resistance.
+10, +40 and +100 means I have added that much resistance (Tolerance is only a few mOhm), the result is supposed to show these values.
All tests are done with the same battery.

The charger gets wrong result frequently when I am using my test rig. I suspect that my test rig is affecting the charger.




Replacing the wrong result with the value from an adjacent column makes the result look very good.



The charger load the battery a bit before doing the actual measurement.



Testing the mains power supply with 2500 volt and 5000 volt between mains and low volt side, did not show any safety problems.



[size=+2]Conclusion[/size]

This is a compact analyzing charger and this means it will run a bit on the warm side when using full current. The charge algorithm is a bit special with the lower charge current when the battery is nearly full, but it works well and do keep the final temperature lower.

All functions works as expected, the user interface is easy to use and it was not early or late on a single termination, this makes it a good NiMH charger.



[size=+3]Notes[/size]

The charger was supplied by gearbest for a review.
I have tested two copies of this charger, the first one was faulty and would not terminate when using lower charge currents!

Here is an explanation on how I did the above charge curves: How do I test a charger

Thanks for review

Question, I dont see a slot button, how do I change the say Display on one of the slots?

hammerjoe said:

Question, I dont see a slot button, how do I change the say Display on one of the slots?

Click to expand...

I do not remember if you can change for a single slot or you always has the same display for all slots.

Hjk,

In your opinion does this charger do anything that is hurtful to batteries as in shorter lifespan?
I am just asking for curiosity because of it algorithm to drop the current towards the end which as a result sees to result in a drop in voltage as well.

I wish the default current was 500mA instead of 400mA.
Its interesting to see that it also drops the current to half even at 400mA. Why do it because of heating concerns if when the 700mA current is selected it drops to 350, so charging at 400 all the way wouldnt matter that much right?

Btw HJK if I may ask you how can you determine the charger terminated right when the battery is full or how do you the battery is completely full?

hammerjoe said:

In your opinion does this charger do anything that is hurtful to batteries as in shorter lifespan?

Click to expand...

I would say the opposite, keeping the temperature low will improve the lifespan a bit.

hammerjoe said:

Btw HJK if I may ask you how can you determine the charger terminated right when the battery is full or how do you the battery is completely full?

Click to expand...

I do generally look at the temperature track, when the temperature increase the cell is basically full. You might stuff a bit more energy into the cell by charging a some more, but it is minor.

You can read a bit more about termination here: http://lygte-info.dk/info/batteryChargingNiMH UK.html

When I was shopping for a 18650 charger, I end up getting the Opus BT-C3400 because photos of the Opus BT-C700 looks exactly like my LaCrosse BC700 and the same UI - looking like LaCrosse is a rebranded Opus. For familiarity, I got the BT-C3400 a few months ago. The BT-C3400 (now on my desk) looks just like an oversize BC700 (sitting next to it).

Looking at this review, the BT-C700 looks very different now and have some behavioral differences. If the new BT-C700 works as well as my old BC700, most users would be quite pleased with it.

yeah lol ill stick with my C9000 for nimh/nicads

To what temperature is it safe to charge nimh before it starts damaging them?

I have this sensor probe shop.lacrossetechnology.com.au/La Crosse Technology/tx25u-la-crosse-temperature-sensor.html
http://shop.lacrossetechnology.com.au/La Crosse Technology/tx25u-la-crosse-temperature-sensor.html
I don't know how accurate it is but when i was charging 4 amazon AA blacks i stuck it under battery 4 and charging at 700mah it read 38c.
The charger dropped the current down to 350mah and the temp drop to 35c to finally settle to 33c.

Is 38c bad? I mean the batteries felt hot. Not hot that cant touch them but hot.
I don't think i will charge 4 batteries with 1000mah with this charger.

hammerjoe said:

Is 38c bad? I mean the batteries felt hot. Not hot that cant touch them but hot.

Click to expand...

Specifications says 40C ambient, i.e. the batteries are allowed to be hotter than that.

I have been using this charger for the past couple days and the charger is terminating too soon with one of the fairly new 2400mah rayovacs nimh. It has had maybe 50 charges.

Twice now doing a charge/test at 700ma the bt-c700 terminates at about 1900-2000mah.
Its the same sympton I have with the Opus bt-c3100 v2.1 but those were on brand new amazon blacks and brand new duracell ion batteries.

The voltage on the charger reads 1.41V... isnt it too low? Why would it terminate so soon?

The third battery in the charger is consistently getting lower values with this charger. I have it testing on the bt-c3100 right now.

I get the same result in slot#1 and charging at 700 or 500mah so I am guessing the charger is working fine.
The charger is not terminating on voltage because the battery reads 1.41V/

Is it because the charger is detecting a dv/dt? I will have to chek the battery resistance. Maybe the battery is heating up.

Thank you HKJ for the test/review. After read your post, I brought this charger.
May I post the instruction for anyone that plan to buy BT-C700.

Opus BT-C700 v2.1

- Independent settings by insert one battery at a time.
- Change all slots mode by hold down MODE button for 2 sec.
- Charge current : 200, 300, 400 (default), 500, 700, 1000mA
- Discharge current : 100, 200, 300 (default), 400, 500, 500mA
- If batteries only insert at slot 1 and/or 4, the max charing current is 1000mA. Otherwise 700mA.
- Heat down by reduces the charging current 50% when the voltage reach 1.475v.
- Two battery temperature sensors. Cut off at 60c.
- Two onboard temperature sensors. Cut off at 77c.
- Backlight timeout is 30 sec.

CHARGE Mode
The mAh is the accumulated charging capacity.

DISCHARGE Mode
Discharge to 0.9v. The mAh is the accumulated discharging capacity.

DISCHARGE-REFRESH Mode
Discharge-charge 3 times. The mAh is the last cycle accumulated discharging capacity.

CHARGE-TEST Mode
Charge-discharge-charge. The mAh is the accumulated discharging capacity.
[Bug!] Not realtime update, show only when discharging finished.

QUICK-TEST Mode
Test the internal battery resistance (milliohms) for 10 sec.
[Bug!] Couldn't change mode later by re-insert battery method.

It look like that have only 2 battery thermal sensors and 2 onboard thermal sensors.

I scanned the manual instruction. I think the battery thermal sensor has only 2, not 4.