battery – Experimental Engineering

Posted on March 14, 2018 by The Engineer — Leave a comment

First Alert CO-FA-9B Carbon Monoxide Alarm Teardown

Here’s another domestic CO Alarm, this one a cheaper build than the FireAngel ones usually use, these don’t have a display with the current CO PPM reading, just a couple of LEDs for status & Alarm.

This alarm also doesn’t have the 10-year lithium cell for power, taking AA cells instead. The alarm does have the usual low battery alert bleeps common with smoke alarms though, so you’ll get a fair reminder to replace them.

Not much at all on the inside. The CO sensor cell is the same one as used in the FireAngel alarms, I have never managed to find who manufactures these sensors, or a datasheet for them unfortunately.

The top of the single sided PCB has the transformer for driving the Piezo sounder, the LEDs & the test button.

All the magic happens on the bottom of the PCB. The controlling microcontroller is on the top right, with the sensor front end on the top left.

The microcontroller used here is a Microchip PIC16F677. I’ve not managed to find datasheets for the front end components, but these will just be a low-noise op-amp & it’s ancillaries. There will also be a reference voltage regulator. The terminals on these sensors are made of conductive plastic, probably loaded with carbon.

The expiry date is handily on a label on the back of the sensor, the Piezo sounder is just underneath in it’s sound chamber.

Posted on September 12, 2017 by The Engineer — 2 Comments

103RS GPS Tracker Teardown

I thought it was time to add a bit of security to the gear I take camping, so this GPS tracker unit was sourced from eBay. This is a Rewire Security 103RS, a slightly customised version of the common Chinese TK103 GPS tracker.

The small module has all it’s power connections on one end of the unit, on a Molex multi-way block. The white connector is for a piezo-shock sensor – this interfaces with the alarm functionality of the unit. There’s an indicator LED for both the GPS & GSM status, and a switch for the backup battery.

The other end has the antenna connections, microphone connection for the monitor function, along with the SIM & SD card slots.

Once the end panel is removed, the PCB just slides out of the aluminium extruded casing. It’s pretty heavily packed with components in here. A switching regulator deals with the 12v input from the vehicle battery, and is protected by a polyfuse on the right. The GSM module is hiding under the Li-Po backup cell, unfortunately the sticky pad used to secure this wouldn’t come off without damaging something. The pigtails for both the GPS & GSM antennas are permanently soldered to the board here.

The bottom of the PCB has the GPS module, and mainly input protection & bypassing components. There is a FNK4421 Dual P-Channel MOSFET here as well, probably used for switching the external relay or alarm siren. The SIM socket for the GSM modem is located here in the corner.

Posted on August 19, 2017August 17, 2017 by The Engineer — Leave a comment

EpEver Tracer 4210A MPPT Solar Charge Controller Teardown

Here’s the solar charge controller to go with the MT50 from the last post. This is the 40A version of the EpEver Tracer A series, the 4210A. This unit is large, and very heavy. Most of this weight comes from the enormous heatsink which doubles as the mounting plate for all the other components, and the large inductors that are going to be required for the DC-DC conversion that MPPT requires.

The front panel has a basic LCD, which shows various stats, such as PV Volts & Amps, and battery bank Volts & Amps. The pair of buttons are used to navigate the basic menu to configure some options, along with switching the load terminals ON/OFF.

There’s a specs label on the top, with a slight difference here vs the manual, which states the max. PV volts as 92v.

Removing 4 machine screws from the bottom of the unit allows the top to come off. Like the MT50 remote panel, this unit also has moulded-in brass thread inserts in the plastic parts. The PCB in here is heavily comformal coated, which stops me from reading the laser-etched numbers on the semiconductor devices, so there will be few details there.

Here’s the bottom section of the main PCB, with the enormous screw terminals, which will easily take cables up to about 16mm². The RJ-45 jack which hosts the unit’s RS-485 bus is to the right, and a smaller 2-pin connector on the left sorts out the battery temperature sensor.
The DC output MOSFET switches are hiding just behind the right-hand terminals, there’s a pair of them in this unit to handle the output current. Some beefy diodes polarity-protect both the battery & PV inputs.

Moving up the board shows two 35A automotive blade fuses soldered into the board – these would be a real pain to replace if they ever blew, however with the electronic load current protection built into this unit, it’s an unlikely situation, unless something went hideously wrong. The main switching devices for the DC-DC converter are hidden – they’re clamped to the heatsink with the bars at right angles in the photo, I’m not going to dig any deeper into this just for those though – they’re just TO220 devices.
Under a load of thermal gunk on the right are 4 current shunt resistors, and the amplifiers for reading their values. These 1206-size SMD resistors looked a bit small for the power rating to me, but they’re heatsinked in operation to a small heatsink mounted in the top cover.

The upper section of the PCB hosts the main microcontroller, and the connections over to the front panel LCD & buttons. Couldn’t really get much info from these chips, due to the conformal coating.

Right at the top of the unit are these toroidal inductors, potted into aluminium housings. The copper windings of these is very heavy – at least 2.5mm². They’re electrically in parallel, the 20A version would only have a single inductor.

This small heatsink sits inside the top cover, and provides some cooling to the current shunts.

Not much to say for the display board, there’s going to be nothing here apart from an I²C LCD driver & the pair of front panel buttons, so I won’t bother removing this from the case.