Bosch Professional GAA 18V-24 USB charging adapter 1600A00J61 1600A00J5W (WHL #49)
Something out of the ordinary for today, a brand new item, bought for disassembly and kind-of off-label use. A Bosch Professional USB charger which happens to have a 12V port also…
Contrary to my very first thought when I found this charger, it does NOT allow 18V batteries to be charged from USB or a 12V source. Maybe I should test that, but I doubt it. However, it does convert the other way – stick in a 18V power tool battery (ranging from 1.5Ah to 12Ah as of today) and get a USB charger with a lot of oomph, or a “heated jacked” power source with a lot of potential for baggy pockets. And after disassembly, it offers access to the battery contacts, allowing easy lab power supply charging of these 18V battery packs.
I bought this from a German office supplier (Böttcher) for 14.38€ plus shipping (which was omitted due to reaching some total value threshold). Some sell this for closer to 10€. Others charge you double or triple that. Which still is a steal for what’s inside…MSRP is 32€, traditionally way higher than street price, still way too cheap for the Bosch “Blue” brand.
That deep blue really pops with my lighting and colour temperature settings. Love it!
The back offers two standard USB ports (2.4A max combined) and a barrel connector in between, offering 12V at 1.2A max. Should be a 5.5×2.1mm port, but don’t bet your life on it, I’d rather check once again. However, that is easily interchangeable.
Now for the interesting part…
The battery contacts are a separate piece. Which is great, because for my intended secondary application, the entire thing might be too large, so once I remove the outer shell, I can stack it in a different way. Only thing that stops me from doing this is three screws (self tappers) and the friction fit. Some force later…
There’s a tiny PCB with LED and SMD push button behind the external “On” button area, which permanently enables power once activated. And there’s quite a sizeable main PCB connected to it! Remember, that thing is basically just a fancy power bank that works on power tool batteries.
Below the bottom heat transfer pad is a huge diode, probably reverse polarity protection. Might be to prevent charging the wrong way round…
And there’s another huge pad on the bottom, electrically insulating the thing from the contact block, but adding some heat sinking at the same time. There’s another two fat diodes and some ICs. Again, much more than expected.
So the main chippy probably is the XLsemi XL4013. Interesting choice, likely oversized. 4A, 180kHz fixed switching frequency, 8-36V buck regulator down to 1.25-32V.
Then there’s a ST224A, an LM224x quad op amp. Most likely doing some stuff for charging and discharging protection, maybe overcurrent protection as well. The main voltage reference probably is a tiny three-pin SOT-23 device that I haven’t seen yet. By the way: The entire main PCB is conformally coated and partially gunked with some kind of epoxy, so that’s great for building site ruggedness, but a little bit terrible for reading IC markings or reverse engineering the juicy bits.
The two SOIC-8 on the bottom are AO4407A 30V P-channel MOSFETs, easily identified by their 4-3-1 pinout (SSS-G-DDDD in pin order). So they switch the 5V supply high side, which is always nice for power supplies, but maybe not 100% necessary for an isolated power source like this. Even the USB metalwork isn’t connected to the USB GND/0V, they aren’t taking any chances with weird ground loops here, maybe there is a dual-port constellation of attached devices that will act weird when using low-side N-channel switching. Both channels seem to be identical and are current monitored via a 20mΩ low-side shunt.
And then there’s this “A825B 1703” 20-pin wide body SO chip next to the power button. That thing has to be a microcontroller, there’s no other chip that could be worthy of a “software version” label on the silk screen. Probably controls general power, monitors currents and voltages, has the important job to flash the LED when turned on, and also checks if the attached battery is acceptable. It doesn’t do anything when hooked up to bare 18V, it requires two different resistors to the negative side, likely one being temperature (NTC) and the other being a coding resistor for the capacity of the battery pack. If I’m not mistaken, it is 1KΩ and 6.2kΩ for the borrowed 2.0Ah pack that I was using, will revisit that with the bigger pack(s) that I’m going to buy. Still: I cannot find any details on this, I highly doubt it’s the avionics CAN thingy that pops up on a google search.
One last thing for this post: Power draw and voltage stability. This is how the charger regulates voltage over a full discharge of the battery pack, from 5x 4.2V = 21V down to about 3.2V per cell or 16V total:
Not sure about the general ups and downs, might have touched the unit on the big spike downwards. This is measured after like 1.5 to 2m of somewhat usable cable, I’d say it’s about 11.8 to 12.0V at the connector itself (which could be higher, given every gadget has some leads causing similar voltage losses).
It does get warm a bit, but certainly not “whack in a 7812” level hot. I’d need to perform a direct discharge test or have a known good battery to check conversion/discharge efficiency, this one is a 2.0Ah pack that was commercially used with a drill for unknown amounts of time. But clearly we’re getting more than 2.0Ah out of it, meaning the 18V->12V conversion works as intended. Also getting less than 3Ah, meaning there’s no hidden perpetuum mobile hidden under the yellow gunk 
Idle consumption is just 1.6mA with all ports powered. It starts at about 15mA, but that is, *drum roll*: The friggen LED. That thing seems to be powered directly from the battery and wastes the entire voltage minus 2.5V at ~13mA current. Until the micro decides to turn it off after a few seconds. And I thought this thing might drain the batteries in no time…
Fully-off consumption (that is: never turned on after inserting a battery) is below the detection range of any of my multimeters. Good job, Bosch, well done!
