Battery Fuel Gauge IC for single Celll Ni-Mh

[datta]

Could any of you suggest a simple Battery Fuel Gauge IC for single cell Ni-Mh battery.
Or could it be done by some other means?

Thanks in advance,
Datta

 

[audioguru]

A Ni-MH cell is 1.4V to 1.5V when fully charged and is still charging.
The voltage quickly drops to about 1.25V depending on how much current. Then its voltage slowly drops to 1.1V then drops quicker.
A voltmeter will not tell you how much charge remains. You need brains to calculate it.

 

[#12]

I can't answer your question, but I can possibly add some understanding.

The problem with designing a NiMH fuel gauge is that those batteries hold a rather steady voltage from 90% full to 20% full. You might do something that calls 1.26V or higher "90%-100%", then 1.25 to 1.22 = 89% to 20% full. The last 20% is when the cell drops from 1.25 to 1.0 volts. Or, you could call anything over 1.24 volts "safe" and start an alarm at 1.2 volts. These are rather crude methods, but they might be sufficient for you.

Another way would involve integrating the current that has been used, but the self discharge rate of the cell would interfere with that, especially in the first 24 hours or if you let the battery sit unused for days at a time.

It is not easy to make a really good fuel gauge for a NiMH battery. and I don't know of a chip to do the job. At best, I can suggest making a less than wonderful gauge.

As usual, anyone else who can contribute is welcome.

 

[audioguru]

A few times I took a flashlight with Ni-MH battery cells up a ladder in the dark. It worked perfectly for a while then dimmed very quickly and I was lucky to see my way down.
The discharge voltage is not linear.

 

[datta]

Thanks for the clarifications. what about bq2060a?

 

[audioguru]

what about bq2060a?

The BQ2060A is a nice battery "gas guage" IC. It measures the battery voltage and calculates its remaining charge then communicates to a controller IC using serial data. It needs a supply voltage much higher than a single Ni-MH cell.

 

[datta]

thanks..anyway we are using boost converter since we are using only a single cell ni-mh for the rest of the circuitry. so we are thinking of giving the output of the boost converter to the supply of the fuel gauge ic. is this feasible? will it result in any complication?

 

[audioguru]

Did you find a voltage boost converter that works when the battery cell is only 0.9V? Will its output be too high when the battery cell is 1.5V?

 

[datta]

Guru,

I am not very sure on this. But ppl in my team were discussign that there are boost converts that accepts as low as 0.8 V. will post the part number on monday