Building a Customized Lab Heater

By: Daniel A. Levenson

Lab heaters are ubiquitous in research labs. They can range from applications like a hot plate heating a beaker, to a heating element heating a whole chemical bath. I have found that in my experience there are no good heating options that can be used for multiple applications. Scientists are often reduced to haphazard solutions, like using a Sous Vide meant for heating food in plastic bags to heat chemical buckets. What if there were a simpler solution? One where the same heater could be used, just with a change of the accessories?

Figure 1. Sous Vide For 'Bucket Heating'

At its core, a lab heater is a power source, a controller and a switch that allows you to turn that power on and off. With that in mind, I managed to track down a damaged commercial "LabBrisk' one and look into the inner workings of it. In my experience its best to learn from others instead of immediately trying to reinvent the wheel.

Figure 2. Internal components of a commercial lab heater.

The microcontroller appears to take up the majority of the space in the heater, with a little space allocated for the solid state relay. With the addition of a switch, plugin for the power cable, thermocouple and outlet for the power it appeared to be an incredibly simple setup.

To begin I started by ordering the microcontroller and components such as the switch, outlet, 16 gauge wire, thermocouple outlet and extension cable. I picked up an anodized box from the local electronic shop as well as the heat shrink I needed for this project. Now it should be absolutely noted that 16 gauge wire is rated to a maximum of 18 amps, meaning that the choice of heating element could cause the wires to go out of spec. In this case I had obtained a simple 1500 watt boiler heater, then when used at the 120V my house outlet can output would only supply a maximum of 12.5 amps.

Equation 1. A = W/V

Where A = Amps

W = Watts

V = Volts

Keep in mind that during a heating application that the maximum output of power happens near the begging, before your heating element has gotten to full capacity.

The first step was to simply power up the components and get them to heat a heating element. This turned out to be more difficult then originally anticipated, as the sketch provided by the manufacturer did not adequately explain how to get the relay to be in the open position when the temperature had not reached the requisite temperature. If you find this odd, then you are not alone.

Figure 3. Wiring diagram for the heat controller

Figure 4. Measuring the voltage potential difference on the solid state relay.

Figure 5. First test of the heat controller with a collar type heater.

Next it was to get a case which could adequately house the components. In the commercial case, I noted that the case was a similar size to all of the components. I took care to measure the height of the relay attached to the heat sink. Although this solid state relay is rated to 40 amps, the most power I will be drawing from it is around 13.5 amps. This still goes over the 10amp recommendation requiring the use of a heat sink, so it required incorporation.

Figure 6. Measuring the height of the combined solid state relay and heat sink.

I was able to precure all all aluminum case from my local electronic shop with an overall height of at least 3.2 inches. The top surface of the heat sink still required sanding to to reduce the overall height so it could fit inside the box. Holes were then cut out in the appropriate areas for ease of access to a) temperature controller b) power adapter/switch c) output power and d) thermocouple.

Figure 7. Testing the placement of all internal components in the electrical box.

The heat sink was fixed to the bottom of the case using M4 bolts. Feet (18mm x 14mm x 4mm) were printed in PPS (polyphenylene sulfide (PPS)) which was selected due to its a) chemical resistance b) thermal stability and c) electrical insulating properties.

Figure 8. A 3d model of a 'foot' used to raise the box from its table top.

Figure 9. The final placement of the feet of the box and heat sink bolts.

Each M3 x 10mm bolt then had medium strength locktite and allowed to set. Due to this case being all metal, a ground cable was fixed to the back right bolt. This is done incase of an electrical short causing the case to become electrically charged/energized. The output was then soldered to the wires leading from the solid state relay before being bolted to the side of the case with M3 x 10mm bolts.

Figure 10. The female Amphenol Industrial Operations connector used to electrical output from the relay.

The male type connector (Amphenol Industrial Operations 97-3106A-10SL-4S) was then soldered to the connector and protected with heat shrink wrap.

Figure 11. Soldering the connections on the male Amphenol Industrial Operations connector.

The other end of the leads were then tinned for quick testing and placed into the heating element for testing. Once the unit was powered on, it was quickly apparent that the heating element was heating up quickly. With that confirmation, the next step was to make the extension cable that goes from the thermocouple to the the heat controller, using specialized cable. The crimping on this one required a specific 26 gauge crimp.

Figure 12. Testing the heat output following the addition of the Amphenol Industrial Operations Connectors.

Finally all the internal wires were trimmed to a smaller length and properly crimped with their prospective loop connectors and attached. Thermal paste was placed between the solid state relay and the heat break.

Figure 13. The final cleaned up internals of the laboratory heater.

Voila! We have our completed device!

Figure 14. The completed laboratory heater, ready for use.

This was an incredibly satisfying project to have completed. I think that it is important to note that there were some excellent lessons learned throughout this process.

Firstly when drilling the holes in the case. I used a Dremel equipped with a tungsten carbide bit. The bit used for shaping the holes got quickly gummed up quite quickly. Hydrochloric acid was excellent at cleaning it up, but it is important to note that the use of a lubricating oil could have stopped the issue in the first place.

Next, the placement of the controller was not ideal. Placing it in the bottom corner made it difficult to place the mounting bracket, as well as wire up all the necessary connections. In hindsight, it would be more ideal to place it somewhat in the center of the panel instead to leave plenty of room for it.

Finally, I learned that at certain gauges of wires it becomes no longer feasible to tin the wires. Tinning is done to solidify all the copper strands, to stop them from fraying by coating them in a layer of solder. At 16 gauge, I found that the heat required heat the wire sufficiently to have solder to melt on it also began to melt the protective coating on the wires themselves. It becomes imperative to use crimp on connectors instead, and to make sure they are used correctly to ensure firm electrical connections. Frayed wires can disconnect and touch the metal box, causing the box itself to become an electricution hazard. Grounding is one way to mitigate that, and ensuring all connections are done correctly is the other.

If you have made it this far, thank you for reading all the way to the end! Stay tuned for more projects and updates, and feel free to email with any questions.