Posted on Leave a comment

Covid-19 Lockdown Projects – Extracting Diesel Heater Exhaust Waste Heat

Since I fitted the new “8kW” diesel heater to the camping power trolley, it has occurred to me that there is a lot of energy in the exhaust gas stream that ordinarily would be wasted into the atmosphere. Since we’re all still on lockdown here in the UK, I figured it would be good to run an experiment to see if it was worth recovering this energy – in the form of heating water.

Heat Exchanger
Heat Exchanger

Some time ago, I stripped an old gas combi boiler, and recovered some parts – most important here the HDW plate heat exchanger. This large chunk of stainless steel is a stack of formed plates, brazed together, that usually would heat Domestic Hot Water. In this instance it’s being repurposed to transfer heat from exhaust gas to water.

Brazed Connections
Brazed Connections

These heat exchangers are mounted in the boiler via a plate with O-Ring seals on, so they don’t really have fittings – just holes in the end plate. Solving this problem was simple – braze on some copper fittings with 55% silver brazing rod. The 22mm is the exhaust side, while the 15mm is the water side.

First Test
First Test

Cobbling together some random hose & fittings, along with a small water pump allowed me to run a first test. At this point there is no lagging at all on the exhaust system from the heater, so it’s going to shed a lot of exhaust heat into the air before it even gets to the heat exchanger. However I was able to get around 600W of heat into 15L of water, heating it up nicely. The heat exchanger is plumbed contra-flow here – exhaust comes in via the stainless tube on the bottom right, and water comes in through the speedfit elbow on the top left.

Lagged Heat Exchanger
Lagged Heat Exchanger

After the temperature of the water tank hit a plateau at around 45°C, I decided to insulate everything the best I could with what I currently have. I’ve wrapped the heat exchanger with some recycled PET insulation here, just to hold the heat inside. I’m not concerned about the exhaust outlet being in contact with the fluff – this system is so effective at pulling the heat out of the exhaust that the gas exiting the far end is totally cold!

Unlagged Exhaust
Unlagged Exhaust

Now it was time to get the exhaust system under the trolley insulated. This is the system removed from the unit entirely. This is constructed from copper pipe, brazed onto standard silencers. Deadening the sound from the unit is important, as this gets used on campsites!

Fibreglass Tape Insulation
Fibreglass Tape Insulation

An hour & some itchiness later, the exhaust is completely covered in fibreglass insulation, secured in place with stainless steel ties.

Exhaust Hanger
Exhaust Hanger

The exhaust originally passed through a close-fitting hole in the frame rail which would obviously not work now due to the thickness of the insulation layer, so this was modified with a grinder. Since there was now no support for this end of the exhaust, a pair of drilled holes & some stainless steel wire form a nice hanger!

With all this insulation in place (including around the tank & pump), the rig is now able to easily hit 65°C within a short time, so there has definitely been an improvement. At this point, it’s clear that waste heat recovery is worthwhile, so I’ll be building a proper rig to capture this energy for reuse!

Posted on Leave a comment

R-134a Refrigerant Analyser Module Exploration

Main Board
Main Board

This unit recently appeared on eBay, as a spare part from a refrigerant charging machine, and I figured it would make a good explorational post. This unit analyses the purity of R-134a refrigerant gas, using an Infrared sensor cell, and communicates over RS-232.

The sensor cell itself is at the top right of the board, we’ll get to that later on. There’s a small diaphragm pump at the lower right, for purging the cell with air. The port with the red cap is the outlet, and the remaining open hose barb is the input of gas to be tested. This would connect to a flow regulator & solenoid valve that the board controls.

It’s pretty clear that this board has multiple applications from all the unpopulated components. There’s space for a keypad, indicator LEDs & an LCD on board, so maybe this can also be fitted to a handheld analyser?

Power Supply
Power Supply

From looking at the input circuitry, I can surmise that the input voltage is somewhere between 12-24v DC, as there is a 35v input electrolytic filter capacitor. There’s a couple of switching regulators which generate 5v & 3.3v rails for the board, with some input fusing.

Main Connector
Main Connector

There’s two serial links on this board, driven from the main microcontroller – the primary one is on the connector marked JMAIN, along with the power input & a couple of other unknown signals.

MSP430 Microcontroller
MSP430 Microcontroller

Over on the other side of the board is the brains of the operation – an MSP430 microcontroller, with an RS232 transceiver IC & another RS-232 port marked COM2. The remaining connector is a JTAG port for the micro.

Gas Analysis Cell
Gas Analysis Cell

Here’s the gas analyser cell itself, sandwiched under another board. There’s a temperature sensor on the side of the cell at the bottom, and even though there’s many pins on the header here, only a couple are actually used for the IR emitter.

IR Emitter
IR Emitter

Removing the screws from the top allows the board to be removed, which exposes the Mid-IR emitter component with an exposed element. This looks to be very fragile, so I won’t be messing with this much. From metering the connections, this appears to be driven at about 2v from the microcontroller.

Top Of Gas Cell
Top Of Gas Cell

The window into the gas cell looks to be made of something exotic – considering the IR application & the colour, this is probably Zinc Selenide.

Gas Test Cell
Gas Test Cell

Removing some more screws on the bottom exposes the bottom of the cell with another IR window, and an O-Ring where a pressure sensor sits.

Output Amplifiers
Output Amplifiers

There’s a couple of very accurate LT1884 Rail-To-Rail Precision Op-Amps next to the cell, most likely used to measure the output from the sensor itself.

Mid-IR Sensor & Pressure Sensor
Mid-IR Sensor & Pressure Sensor

Finally, there is a dual-window thermopile sensor, and a pressure sensor. I wasn’t able to get any information on either of these, but I did find some ranges of sensors for Mid-IR measurement operations, that mentions a wavelength around 10µm for R-134a spectroscopy.

I will try to get this module going & measuring some gases, if I can work out how to talk to it – I already know the serial lines so it’s just working out a command set. If anyone has any information on these, please do get in touch! A service manual for the refrigerant machine this came out of would be good!

Posted on Leave a comment

Tau-Volantis Storage Server – Upgrades Part 2

Tau-Volantis Server
Tau-Volantis Server

So, it’s time to finish off the upgrades to the core storage server on my network. Now a new motherboard, CPU & RAM have been obtained (MSI GA-X58-USB3), Core i7 950, 12GB), along with new SAS/SATA HBAs for the disk rack I can get everything fitted into place.

Dell H200 SAS RAID Card
Dell H200 SAS RAID Card

Proper branded LSI HBA cards are expensive so I went with the cheaper option & obtained a pair of Dell H200 RAID cards. These have custom firmware flashed to them, but luckily can be crossflashed to a standard LSI firmware to become an LSI9211-8i card – providing 8 lanes of either SAS or SATA connectivity on a pair of SFF-8087 ports. Flashing these cards was very simple, once I managed to work my way into the EFI shell on my main machine, which I was using to do the flashing. Find all the firmware files & required software here:

One thing I left out from the flashing was a BIOS – this means that the boot process is speeded up, but also means the system BIOS cannot see the disks connected to the cards, so they’re not bootable. This isn’t a problem however, as I never plan on booting from the data storage disk array.

Active Cooling
Active Cooling

The SAS2008 RoC (RAID on Chip) on these cards runs at around 8.5W thermal power, so some active cooling is required to keep temperatures within check. I have attached a 40mm fan to each card’s factory heatsink, using M3x25mm screws. Getting the screws to grab the heatsink was the tricky bit – I needed to crimp the outer corners of the fins together slightly, so when the screws are driven in, the gap is forced to expand, which grabs the threads. The fans will be connected to spare headers on the motherboard for speed monitoring.

GA-X58-USB3
GA-X58-USB3

It was a struggle finding a motherboard with the required number of high-lane-count PCIe slots. Even on modern motherboards, there aren’t many about within a reasonable price range that have more than a single x16 slot, and since I’m going with the new HBAs, a single slot is no longer enough. The motherboard I managed to obtain has a pair of x16 slots, and a x4 slot (x16 physical), along with a 3 x1 slots. The only downside is there’s no onboard graphics on this motherboard, so an external card will be required. Another cheapie from eBay sorted this issue out.

ATI Radeon HD3450
ATI Radeon HD3450

Since I need to use the x16 ports for the disk controllers, this card will have to go into the x4 slot.

Motherboard Installed
Motherboard Installed

Here the board has been installed into the new chassis, along with it’s IO shield. Both HBA cards are jacked into the x16 slots, with the SAS/SATA loom cables attached. I did have to grab longer cables – the originals I had were only 500mm, definitely not long enough to reach the ports on these cards, so 1m cables are used. The fans are plugged in with extensions to a pair of the headers on the motherboard, but the MB doesn’t seem to want to read RPM from those fans. Nevermind. While the fans are a little close to the adjacent cards, the heatsinks run just about warm to the touch, so there’s definitely enough airflow – not forgetting the trio of 120mm fans in the bulkhead just out of shot, creating a breeze right through the chassis.

Boot SSD
Boot SSD

Since the onboard SATA ports are in a better position, I was able to attach the boot SSD to the caddy properly, which helps tidy things up a bit. These slot into the 5-¾” bays on the front of the chassis, above the disk cage.

Loom Closeup
Loom Closeup

To take up the excess cable length, and tidy things up, the data loom to the disk cage is cable-tied to self-adhesive saddles on the side of the chassis. This arrangement also helps cooling air flow.

Server Overview
Server Overview

With the new components, and the cabling tied up, things inside the chassis look much cleaner. I’ve rationalised the power cabling to the disk backplanes down to a a pair of SATA power looms.