Posted on Leave a comment

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

CO-FA-9B Alarm
CO-FA-9B Alarm

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.

Rear
Rear

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.

Internals
Internals

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.

PCB Top
PCB Top

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

PCB Bottom
PCB Bottom

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.

Circuitry Closeup
Circuitry Closeup

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.

Sensor Cell & Piezo Disc
Sensor Cell & Piezo Disc

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 Leave a comment

Quick Tool Review – Engineer PA-09 Crimping Pliers

For a while now I’ve been attaching terminals such as Molex KK Dupont, & JST PH to wire ends with a lot of patience & a very fine soldering iron, however this method takes a lot of time, and with terminals like Dupont types, the terminal won’t fit into the connector body properly unless it’s crimped correctly. Official tools from the likes of JST or Molex are hilariously expensive, (~£250 for the Molex KK tool), and each tool only does a single connector series, so these are out of the picture. The cheapest available tool (~£40) for these types of terminals is the Engineer PA-09:

Engineer PA-09
Engineer PA-09

These are simple crimping pliers, with no niceties like a ratchet mechanism, but nonetheless they work very well for the cost. The PA-09 can handle terminals from 1mm-1.9mm, there is another tool, the PA-21, which crimps terminals from 1.6mm-2.5mm. The fit & finish is good – proper steel (S55C high carbon steel according to Engineer), not the steel-plated-cheese that most cheap Chinese tools are fabricated from, the handles are solid & comfortable.

Handles
Handles

The rubber handles are press-fit onto the steel frame arms of the pliers, and don’t slip off readily.

Die Head
Die Head

The dies are well formed in the steel, and seem to be machined rather than stamped on a press, however the black oxide finish hides any machining marks. The smallest 1mm dies do seem to be a little fragile as they’re so small, so wouldn’t take much abuse without shearing off.

Crimped Molex KK Pin
Crimped Molex KK Pin

Here’s a Molex KK pin that’s been crimped with the PA-09. The insulation crimp has pierced the insulation slightly, but this isn’t much of a problem. The conductor crimp is nice & tight, and everything is small enough to fit correctly into the plastic connector body. The trick with these tools is getting a feel for when the crimp is done – squeeze too tightly & the contact deforms, not tightly enough & the wire will just pull out of the terminal. The official tools also crimp both the conductor & insulation at the same time, and they also hold the terminal in place while the wire is inserted. In these cheaper tools, the crimps are done separately, but they do hold on to the contact securely enough for the wire to be inserted properly with your spare hand.

Posted on Leave a comment

nb Tanya Louise Heating System – Oxide Sludge

I wrote a few weeks ago about replacing the hot water circulating pump on the boat with a new one, and mentioned that we’d been through several pumps over the years. After every replacement, autopsy of the pump has revealed the failure mode: the first pump failed due to old age & limited life of carbon brushes. The second failed due to thermal shock from an airlock in the system causing the boiler to go a bit nuts through lack of water flow. The ceramic rotor in this one just cracked.
The last pump though, was mechanically worn, the pump bearings nicely polished down just enough to cause the rotor to stick. This is caused by sediment in the system, which comes from corrosion in the various components of the system. Radiators & skin tanks are steel, engine block cast iron, back boiler stainless steel, Webasto heat exchanger aluminium, along with various bits of copper pipe & hose tying the system together.
The use of dissimilar metals in a system is not particularly advisable, but in the case of the boat, it’s unavoidable. The antifreeze in the water does have anti-corrosive additives, but we were still left with the problem of all the various oxides of iron floating around the system acting like an abrasive. To solve this problem without having to go to the trouble of doing a full system flush, we fitted a magnetic filter:

Mag Filter
Mag Filter

This is just an empty container, with a powerful NdFeB magnet inserted into the centre. As the water flows in a spiral around the magnetic core, aided by the offset pipe connections, the magnet pulls all the magnetic oxides out of the water. it’s fitted into the circuit at the last radiator, where it’s accessible for the mandatory maintenance.

Sludge
Sludge

Now the filter has been in about a month, I decided it would be a good time to see how much muck had been pulled out of the circuit. I was rather surprised to see a 1/2″ thick layer of sludge coating the magnetic core! The disgusting water in the bowl below was what drained out of the filter before the top was pulled. (The general colour of the water in the circuit isn’t this colour, I knocked some loose from the core of the filter while isolating it).

If all goes well, the level of sludge in the system will over time be reduced to a very low level, with the corrosion inhibitor helping things along. This should result in much fewer expensive pump replacements!