KB Electronics 8811007 Solid State Variable Speed AC Electric Motor Control, 6.0 Max amp, 115V, # K177-1006

This review is for the KBWC-13K solid state speed control. I purchased this controller with intent of modifying it so the fan of my Magic Heat unit would run slower and be less noisy when the woodstove fire was producing less heat. The Magic Heat uses a simple (on/off) thermostat controlled 1/200 hp single speed shaded pole fan motor to circulate heat into the room. So my next step after receiving the KBWC-13K was to disassemble it to see what I was working with. The attached photo illustrates the few components that are inside. Overall the components, assembly and soldering are of very good quality. The only oddity is the small trimmer potentiometer (black circular part with blue center located in middle front of the picture) which is wedged up against the larger control knob potentiometer leads. There's no real problem here; just not a typical component mounting. I suspect the trimmer is located in this manner to prevent heavy handed screwdriver users from damaging the trimmer. Overall I am very pleased with the construction/quality of this product.There are three minor design “features” to keep in mind with this speed controller given it was originally developed back in the 1960's. Most users probably won't notice these; but should be aware of them. The first requires understanding that the two potentiometers are set up in parallel. The circuit triggers on whichever potentiometer is set to a lower resistance. So, if the trimmer is set so the motor has a high minimum speed, then there's very little usable speed adjustment range from the control knob and vice versa. The second is that the circuit has control setting hysteresis. This can be observed if you dial the speed of a motor down to a very slow steady rpm and then disconnect the power to the circuit (as happens with the thermostat switch of the Magic Heat). When power is reapplied, the fan may struggle to start, if it does at all. If there was no hysteresis, the fan would spin back up to the original slow rpm setting. The third is the circuit's asymmetrical triggering of the triac. This can sometimes be heard as a repetitive, very low volume, loud-soft, HUM-hum-HUM-hum sound. This noise is often louder when working with old, poorly mounted, or cheaply made motors. I can usually identify this sound when I'm in an adjacent room where the low frequency of this noise comes through over the fan airflow noise. There's a ten page Teccor Electronics application note AN1003 on the web that provides a more technical understanding of this type of speed control.The entire controller operates at AC line voltages so disassembly and modification should only be done by a person educated/trained in AC power circuits/electronics. Here I'm suggesting an alternative use for the KBWC-13K; not a detailed modification process with essential safety considerations.The KBWC-13K potentiometers are configured as two-terminal components (center terminal, the “wiper”, is connected to one of the end terminals). This means I can easily replace the trimmer potentiometer with a two terminal negative temperature coefficient (NTC) thermistor. With a suitable NTC in place of the trimmer, the motor rpm will hold a steady slow speed at room temperature and increase the motor rpm with increasing temperatures up to the full motor speed at some desired high temperature. The control knob potentiometer is now used like the original trimmer to increase the minimum motor speed if it happens to be too slow at the desired low temperature. Another similar modification back in the 1970's/1980's was using a photocell in place of the trimmer which makes the fan speed up with increasing light levels. Keep in mind that these are low cost, simplistic controllers; the performance can vary significantly from one installation to another.After the modified controller was connected into the Magic Heat circuit, I decided to measure the fan current consumption. While the shaded pole fan was performing very well with the controller from minimum to maximum speed; measurements showed the fan was only 10% efficient at full speed and only slightly better at reduced speeds. Shaded pole motors under 1/15-1/20 hp are known to have very low efficiency which is what prompted me to test the current consumption. A Permanent Split Capacitor (PSC) motor usually has about double the efficiency of a similar hp shaded pole motor. So I modified the Magic Heat to use a PSC motor. However, the PSC motor was surprisingly noisy and sluggish when starting at low speed settings. An on-line search revealed that for a PSC motor, only the main (“run”) winding should be controlled by a phase type speed controller while the auxiliary (“start”; one with the capacitor) winding should bypass the speed control so it always has full AC power. The common two wire installation of the speed control has it wired in series with the motor so the motors' run and start windings are in parallel and powered by the controller simultaneously. This alternate approach makes the motor a 3-wire configuration, eliminating use of the built-in on/off switch of the speed controller (which I wasn't using anyway), and requires a separate on/off power switch (Magic Heat thermostat covers that). Having full voltage on the start winding, regardless of the speed controller setting on the run winding, provides full power for motor starting at all speed control settings. This modification reduces the slow speed operating noise (to a point) and increases motor efficiency at reduced speeds. In my installation, the 3-wire PSC motor configuration operates at a full speed efficiency of 33% and increases to a high of 53% at the minimum speed. Again, this is a modification that should only be performed by an electrician.Final note. If plan on buying 3 or more controllers; find a seller that reduces the selling price for buying multiple units vs a flat rate per unit. Sellers that adjust the built-in shipping costs according to the weight of your purchase may save you some money for multiple units. The single unit pricing of this Amazon seller is reasonable for a one or two unit purchase.

I'm a licensed engineer.I have an attic-style fan that I installed to circulate warm air from my utility room to the living spaces rather than letting that heat it escape through the attic by conduction.To accomplish this, I set the fan up with a thermostat control to turn on above 90F, which keeps the utility room pleasantly warm and dry while also re-circulating the excess heat.The problem was that the fan was way too fast and too loud in the adjacent living spaces when it kicked on. I needed something to slow down the fan, which was a low wattage AC fan with a permanent capacitor across the line (little round guy on the power cord going to the motor).You can't use a dimer switch for this sort of application because it will burn up, and many fan controllers intended for ceiling fans won't work either because they have fixed detents for replicating industry standard speeds at low/medium/high.By contrast, this controller uses a solid-state component called a Triac to give you much more precise continuous control over the fan speed. Using this controller, I was able to lower the fan to a much slower speed than the standardized fan controls, allowing me to get the right balance of comfortable warm airflow and quiet noise levels.When doing this, it is important to realize that AC motors can stall if the voltage is lowered too much, and that they will burn up in place if they stall with power on. These motors need the airflow to keep themselves cool while running.This control has a fine adjustment for setting for the minimum fan speed, which prevents someone from accidentally stalling the motor with the knob alone. This minimum speed adjustment was essential for me to achieve the desired effect in my home while preventing the fan from lowering below stall speed.Overall, this controller allowed me to fine-tune my attic-style fan safely and make my home much more comfortable in the winter while saving me money on heating bills and reducing the heat level in my utility room.

Easy to install, works good, but would have preferred for lower rpm on low.