Variable speed hoover tank vacuums

[Cybrvanr]

I have "repaired" numerous Hoover tank vacuums for people lately that have a speed control and power switch on the end of the hose. Inside the plastic body of the vacuum, beside the motor's fan assembly is a SCR voltage regulator just like one sees in a wall dimmer to a light fixture. Apparently, nobody told the Hoover electrical engineers that dimmers don't work on motor (inductive) loads very well. Time and time again, these voltage regulators go up in smoke. The voltage regulator has three wires going to them, power in, power out, and a control lead. The control lead goes to the hose, where the same lines exist, power in, to drive the power brush bar, and a ground, along with the aforementioned control wire. The control wire goes to a simple slide potientometer on the end of the hose, and a on/off switch, basically sending a variable amount of power back to the regulator to signal the desired amount of voltage requested to run the motor.

What I have found out is that many users like to leave the vacuum plugged in with the master switch on the vacuum's body turned on, but then the rocker switch on the hose turned off. They'll leave it like this for extended times. Basically, all this does is put full bias on the voltage regulator chip's control line cutting it off. Now, Hoover was at least a little smart, and mounted the voltage regulator on the side of the fan housing, so the airflow would keep it cool. The problem is that when someone allows the vacuum to sit at idle like this, the voltage regulator chip gets hot, but there's no airflow to keep it cooled off (since the motor is not spinning) Eventually, the user is suprised when the regulator chip finally shorts out, and the vacuum starts up at full speed at an inopportune time, and they can only turn it off with the rear switch. Frequently, they will continue to use the vacuum cleaner in this state until the voltage regulator completely burns out, suprising them again when the vacuum quits and emits a puff of smoke!

Now, most people that have these rarely ever run the vacuums at less than full throttle, so they really don't need the speed control, but they do like the convenience of having the on-hose switch to turn them off. Many ties I "repair" these vacuums by just disconnecting the control line, and by-passing the voltage regulator. When this is done, the user must turn the vacuum off at the body. Today, however, I rigged one a little differently. I bought a 120 volt relay, and installed it in place of the voltage regulator. I wired the control lead from the hose control to the coil of the relay, and then connected the motor to the switch side of the relay. Now, the user can turn the vacuum on and off with the hose-mounted rocker switch, but they cannot vary the speed, which they didn't use anyways. This is a much cheaper fix, than buying the $50 voltage regulator from Hoover...one of the things I may eventually try is repairing one of these by disassembling a $5 light dimmer from the hardware store with the same SCR voltage regulator chip! That is about the same price as the relay...although the relay idea is perhaps the most reliable way!

 

[hoover1060]

which model

are you working on?
The old Dimension 1000 cansiters?

 

[maytagbear]

That sounds like my

Windtunnel canister. Is it?

Lawrence/Maytagbear

 

[tolivac]

The "SCR Voltage Regulator" like found in lamp dimmers is a Triac-its a device like an SCR-a Thyrister-the main difference is the Triac is a Full Wave device-It passes both "sides" of the AC waveform.The SCR only passes one side-hence the SCR acts as a variable half wave rectifier.The Triac can feed AC loads--such as motors,Flourescent and HID lamp ballasts,and even some transformers.The Triac or SCR will work into Universal motors--like whats in the Hoover cleaner.Now--if we want to control the speed of a motor where speed is critical-such as a woodworkers router-a feedback circuit is used with the SCR or Triac.That will help compensate for a motor under load-the router bit cutting into the wood as opposed to the router running no load.The feedback circuit will measure the current draw of the motor-light under no load-but increases when the router is cutting the wood.then the feedback circuit changes the bias on the varister device to compensate the motor speed.Another way to think of a triac is two SCRS's connected-"back to back"Have seen this done in an FM transmitter to do a few things-The devices were connected to the primary of the plate transfomrers-it varies the voltage from the transmitter poower supply to th RF power amp tubes-thus variying their output.You can set the desired power out-say a 25Kw transmitter and you need to run it at 22Kw.You can set the circuit to that level.when you start the transmitter-the SCR's connected back to back as a triac (one pair per phase)"ramps up" the voltage to the stages.The feedback circuit for the transmitter voltage reg circuit is also tied into the VSWR circuit-monitors the nature of the load the TX is running into.If the antenna is iced up-the load changes-and a non regulated transmitter would be tripped off air.In this one the transmitter puts out enough power to stay on the air but not present a dangerous load to the RF amps.