Member #2972

Member Since: April 1, 2006

Country: United States

  • Perhaps they updated it since your reply, but the opamp is an LMV358, a rail-to-rail output version of the venerable LM358. It doesn't really matter though, as the output appears to be buffered by a transistor for logic level. The fact they didn't use an old LM393 is odd, as its faster (its an actual comparator, designed for open loop gain, not closed loop), has the same input specs, and can be powered by > 5V. Does the job though! As majority of window voltage events an arduino is likely to measure won't be ultra short.

  • Great little board, the chip is pretty stand alone, but as its an SOT23-6, it can't dissipate much heat so don't expect to get more than 300mA charge current out of it. It'll limit the current if it over-heats so the chip will only be damaged by over-voltage. Whilst you can of course connect your application circuit to the 'SYS OUT' - this is directly across the battery. So if your application draws more than say 30mA, it will never indicate 'end of charge' because it detects when the battery is full by when it stops drawing 7.5% of main charge current. When jumper is set to 500mA, it will average the charge current of 300mA, and 'cut off' during constant voltage phase when the battery AND application circuit draw less than 37.5mA. Not a project breaker, but if you're wondering why the LED never turns off with your circuit attached - that'll be why.

  • As many seem to have trouble with this, it is advisable with nay product to read the datasheet of the devices used, as well as check out the schematic. I've used this chip in commercial products, and it does what it says, but like most chargers, there are caveats. The absolute maximum voltage the charger chip can take is 13V, recommended max 12V - however - the charge current is fixed, there is no thermal cut-off as the pass element (MOSFET in this case) is external. So with 12V in, and say, a half dead battery, 3.6V, the voltage across the mosfet is 12-3.6 = 9.4V. With 1A charge, that will have to dissipate 9.4W in heat. Using a 5V supply? 1.4W. There is hardly any heatsink copper on that board so I think, mounted as it is, the FET can take 2W maximum before it dies of heat. Even with extensive copper pour, I don't see it getting past 4 watts. To be fair, sparkfun did recommend a 5v charger, but no mention of battery capacity. The timer capacitor will have to be changed to give a timeout of greater than the maximum time taken to charge a battery of its specific capacity. This is all in the datasheet, but not completely obvious. I would ask sparkfun to look at switching chargers, perhaps with dip-switch options to set charge current for those who wish to charge 1000mAh to 6Ah batteries, and be able to use between 5 and 15V without things somking.

No public wish lists :(