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Low Power Electric Pressure Cookers – a discussion of silicon controlled rectifiers?

15th July 2021

By Dr. Simon Batchelor (Gamos Ltd.)

In April 2020, we circulated a working paper among the MECS team for comment. The paper was made to communicate a basic concept and share with research partners the possibility that while we work towards enabling lower power family sized EPC appliances direct from the manufacturers, there may be ways researchers could pilot and prototype systems by using SCR voltage regulators. The information contained has proven useful for partners and collaborators and we now wish to place it on our website for wider use.  (June 2021)

The paper considers the use of silicon controlled rectifier (SCR) voltage regulators as a mechanism for reducing the power consumption of an individual electric pressure cooker (EPC) appliance. 

The investigation began as exploration of any mechanisms for creating a low power appliance from a commercially available appliance. In the paper we consider whether modifications can be made to the ‘delivery’ of the electricity such that a commercially available EPC behaves as though it were a lower power appliance. It seems to us that SCR regulators may have some potential.

Key Research Question:- Can auxiliary/additional devices, placed between plug and appliance, convert a ‘higher power’ EPC to a ‘lower power’ EPC without modifying the commercially available EPC and without compromising any of its inherent safety systems?

The SCR is within a good price range, and experiments to date suggest they make the EPC behave as a low power appliance.  However, these preliminary experiments do not answer important other questions:-

Does the use of the SCR2 compromise the efficacy of the thermal cut outs and digital control features of the appliance? Our understanding is that the thermal cutouts are a combination of mechanical and digital processes.  The mechanical processes should not be disrupted by the SCR and while we assume that the digital processes are operating at a rectified low voltage (5V DC?) we have not tested to see if they are affected.

Does the SCR work with all inverters? The reaction of the SCR to the pure sine wave inverter is not what we expected.  We thought if anything such a sensitive shift in power would occur in the cheaper inverter.  We will conduct further work to understand what is happening – or another researcher is welcome to try a combination of inverters and SCRs to explore this further. Please send us your conclusions.

What is the effect of the SCR on the battery chemistry? The current is being controlled in miliseconds, pulsing between being on an off. Does this intermittent high current draw reduce the life of the battery significantly, and could smoothing capacitors between the inverter and the battery mitigate this?

Is the SCR significantly affected by ambient temperature?  Our systems are potentially working in hot climates.  Many devices can overheat and this is a concern for energy storage. SCR1 dissipates heat via a (PC) fan (although it may be important to note that the heat is minimal (3 degrees measured), however SCR2 uses a heat sink to dissipate heat and that rises to 55 degrees by end of cooking. If this is working in a hot environment will its components have a lower lifetime?

What is the lifetime of the SCR?  Like all appliances and devices, we are unsure of the full lifetime of the product.  There is no reason to believe that the SCR will fail any sooner than most PCB circuits, but this has not been tested and will need to be assessed as part of any route to scale.