Charging NiMh battery pack with BQ2004 - new thread

[farukh037]

Hi.
I'm trying to charge a 18V/3Ah NiMh battery (15 cells x 1.2V) with the BQ2004E component.
So I have studied the BQ2004 datasheet and their switch-mode developpement system to adapt it to my specific case.
I tied TM1&TM2 to GND for selecting a C/4 charge. My Rsns is a 300mΩ/5W (Icharge = 0.225/0.3 = 0.75A = 3000/4).
I tied INH and VSEL to Vcc for choosing a PVD termination. I selected the number of cells with N = (780/120 + 1)*2 = 15 cells.
A 10kΩ NTC thermistor is placed on the TEMP connector.
So here is my circuit. View attachment 39643

It seems to work, when I connect my DC Alim (30V/6A) it goes in "Fast-charge pending" mode for any seconds, then goes in "Fast-charge" mode. But the "Charge complete" mode comes very early (about 5-10 minutes whatever it's initial charge). I've no more that 18.6V at the terminals of battery after charging.
I'm very newbie and don't know how to find where could be the problem.
Can you see anything wrong on my circuit and could you help me to make tests to highlight the issue ?

Thanks very much for your help

Hi Anard,

I am also sufferring from the same problem. i want to charge NiMH and Nicd battery of 9.8Ah and 4.4Ah respectively. Both are of 10 number of cells.

 

[farukh037]

Hi.
I haven't solved my premature charge interruption and don't know more where to search.
If you have some ways to solve it, I'm still interested…

I also noticed that when pluged without battery, the charger does the same : it indicates first "waiting for conditions" for some seconds, then "charging" for about 1 to 5 minutes, whereupon it indicates "end of charge".
According to datasheet, it should turn off the 2 leds when no battery is connected. Maybe it could be a way to search.

this issue comes when i select 12 cell by selecting RB1 as 200k and RB2 as 40K.

 

[farukh037]

Did you calculate RB1 and RB2 correctly? They should divide the battery voltage by a factor of 7.5 since it is expecting Vbat to be the voltage across 2 cells.

I don't see anything in the datasheet about what kind of thermistor to use and what values for RT1 and RT2. How did you come up with these?

Bob

Dear Bobk,
Hope you are good!

i have seen that you have a great knowledge about the IC BQ2004. Kindly help me on the issue.

Regards!

 

[farukh037]

?
When you select 12 cells and connect a 10-cells battery, or when no battery is connected ?

with no battery. I am selecting 10 cells by selecting RB1 as 200K and RB2 as 50K for my 10 cell NiMh Battery. i am using -delta voltage termination. current flowing is OK. but the termination is not constant.

 

[farukh037]

I designed a battery charger with BQ2004H for 10 cells Nimh battery 10AH. I found the charger will always stop fast-charge before it's completely charged and the time seems shifts in the table in datasheet. For example, I set TM1 and TM2 as low/low, fast charge safety time should be 650min, but it always stopped/ terminate before the battery is fully charged. Anyone can give me an idea about it?

a) Charge rate : C/8

b)Termination: -ΔV method and C/8

c) Auto discharge and Temperature termination are not using.

 

[farukh037]

I think you might be on to something. If the inductor is far smaller and lighter, it probably has a lower max current. If it is not sufficient for the charging current, it might be saturating, causing a large ripple in the voltage, which might trigger the deltaV condition.

Bob

Dear Bobk,
Thanks for your response.

inductor with a value of 110uH of 3.9A is used with 10uF of Capacitor with ground. i am using these value with the reference to evaluation board of BQ2004E/H. Circuit diagram is attached here with.

Regards.

 

[farukh037]

In evaluation board, 100uH inductor is using with 10uF capacitor. i think it is not a big difference.

 

[farukh037]

when disabling the voltage termination mode by connecting VSEL pin to GND or VSS, IC take complete time (650 min) to charge the battery pack. otherwise by leaving VSEL as floating (negative delta voltage termination) IC terminates the fast charge within 10-30 mins.

 

[BobK]

I think your charging rate is too slow for delta-V termination. This is normally used at C/2 to C charging rates.

Bob

 

[farukh037]

I think your charging rate is too slow for delta-V termination. This is normally used at C/2 to C charging rates.

Bob

Capacity of battery is 10 Ah. Should I charge it with 5A current for C/2 charge rate. I think its too much.

 

[BobK]

No, that is fine for a fast charge.

Bob

 

[farukh037]

Hi Guys,
My problem of Early Termination is resolved. My charger is working perfect now. The problem was that i was using an unregulated VCC for charging IC, replacing this unregulated switching base IC with Linear regulator IC "L78L05" has resolve my issue.