"simulating" a battery

**Curiosity** · 07-26-2010, 05:52 PM

It will only charge the battery when it has vUsb, and use the battery for power without. T is only used when charging, so you shouldn't need T connected when it's using the battery for power which is the only time you need it. If it's open, the only thing that may happen is the charger won't function properly. 5V may also damage it, so be carefull.

**nst6563** · 07-27-2010, 08:47 AM

So if T isn't really necessary...how would I go about simulating the battery being installed so the unit turns on without the battery? I tried measuring the resistance between the - and + terminals and there wasn't any (or it was so small that my meter wouldn't pick it up on the lowest setting).

from the datasheets I looked up on the mtk chipset, input voltage is from 3.3v-5v -/+ 5%

**Curiosity** · 07-27-2010, 02:53 PM

I wouldn't think that it uses the thermister to detect the battery, but a resistor would simulate it. 67k would be around abient, but anything around that should work, like 65 - 70 I'd think. It probably has a 100K range.

**nst6563** · 07-27-2010, 10:29 PM

Well, connecting T to ground via 67k resistor doesn't do anything. The power light goes green...but flashes very fast...I'd guess at a rate of around 5-10hz. It won't turn on though. I'm kind of at a loss...I thought for sure this was possible.

**OldSpark** · 07-28-2010, 01:06 AM

Try a 7.1k resistor (from the battery's 3rd connector to -ve).
Not sure how accurate that needs to be - a 56k paralleled with an 8.2k is 7.15k (<1% error).

As I understand it, the battery is equivalent to the common Nokia BL-5C (Li-ion; $10 upwards) and merely has a thermistor temp signal.

**nst6563** · 08-02-2010, 12:52 PM

I haven't had the time lately to test the resistor mentioned...but could it be that the battery thermal indicator is shutting the whole thing down? I did notice that when I leave the unit on the dash or the rear deck of the car and the sun's been out it won't start. However it doesn't seem to have that problem if I store it in the glovebox, and then plug it in before the pc powers up.

I have a Globaltop G33 bluetooth receiver as well that sits on the rear deck, it's black, and it doesn't have the issue of not turning on when it's hot. Different battery characteristics??

**Curiosity** · 08-02-2010, 08:53 PM

Have you checked the battery voltage when it's hot? I wouldn't think temp would be that big of a deal, but maybe it is. I was just checking all the batteries around here and they use a 10K thermister and read about 6-8K, so the thermister might be bad on that.

Try putting some tape over the T contact and see if the battery still works. Just as a test. Don't leave it there. If it still works, then you won't need to do anything with it.