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	Subject - 110vdc motor philgritsr2 i need to power a 110 vdc motor so i need some way to turn ac to dc can anyone help me please philgritsr2 Hi, I thought I would give some background on the motor,I have a tread mill that my Mom wants me to repair the main board is Fried all we need this thing to do is power up. I need to come up with a 110vdc power supply with 18amp max. draw and i will add something like a fan speed control pot. to change speed. I know this is asking a lot but can you help me come up with a plan for some kind of ac to dc adapter for this, My Mom just had heart surgery and the Dr. wants her to use it and money is tight. thank you so very much. Sincerely Phil JimmyDee Not going to work. The speed control on these things are not done the way one might think. The electronics are controlling a SCR. The SCR firing timing controls the voltage and speed of the motor. Sounds like a good idea but won't work. There may be something wrong with the motor that took out the controller. Jim philgritsr2 when I put some diodes inline and came up with 110 vdc the motor ran just way to fast and the doides got warm fast and I dont get any shorts to ground or any thing when i power it up whith a 12 volt car charger it ran good but no power when trying to walk on the tread mill please can some one give me anything to try please thanks phil philgritsr2 after looking further at the main board this is not the case as follows and is not SCR. see below The Silicon Controlled Rectifier (SCR) is simply a conventional rectifier controlled by a gate signal. The main circuit is a rectifier, however the application of a forward voltage is not enough for conduction. A gate signal controls the rectifier conduction. The schematic representation is: The rectifier circuit (anode-cathode) has a low forward resistance and a high reverse resistance. It is controlled from an off state (high resistance) to the on state (low resistance) by a signal applied to the third terminal, the gate. Once it is turned on it remains on even after removal of the gate signal, as long as a minimum current, the holding current, Ih, is maintained in the main or rectifier circuit. To turn off an SCR the anode-cathode current must be reduced to less than the holding current, Ih. The characteristic curve is as shown below. Notice the reverse characteristics are the same as discussed previously for the rectifier or diode, having a breakover voltage with its attending avalanche current; and a leakage current for voltages less than the breakover voltage. However, in the forward direction with open gate, the SCR remains essentially in an off condition (notice though that there is a small forward leakage) up until the forward breakover voltage is reached. At that point the curve snaps back to a typical forward rectifier characteristic. The application of a small forward gate voltage switches the SCR onto its standard diode forward characteristic for voltages less than the forward breakover voltage. Obviously, the SCR can also be switched by exceeding the forward breakover voltage, however this is usually considered a design limitation and switching is normally controlled with a gate voltage. One serious limitation of the SCR is the rate of rise of voltage with respect to time, dV/dt. A large rate of rise of circuit voltage can trigger an SCR into conduction. This is a circuit design concern. Most SCR applications are in power switching, phase control, chopper, and inverter circuits. Major considerations when ordering a SCR are: (a) Peak forward and reverse breakdown voltages (b) Maximum forward current (c) Gate trigger voltage and current (d) Minimum holding current,Ih (e) Power dissipation (f) Maximum dV/dt philgritsr2 can someone help me please please philgritsr2 has anyone got any ideas that might help me Thanks Phil Afterhrs Philgritsr2, First off, I have never came across a motor rated at 110VDC, in my experience, they have all been 90VDC or 180VDC. With the massive influx of off-shore products built to all different kinds of specifications, a 110VDC motor could exist, but I would make sure you know what you have. For a cheap DC drive I would look at E-BAY, I did a quick search a found they range from $25.00 to $125.00, Baldor, Control Techniques and Camco are all reputable maufacturers. IF YOU DECIDE TO ADAPT ONE OF THESE UNITS TO THE TREADMILL, MAKE SURE YOU HAVE SOME SORT POSITIVE CONTROL TO STOP IT ASAP. Most of these units have some sort of pull string that act as an EMERGENCY STOP device, do not overlook this small, but important detail! I would also have to agree with Jimmy Dee, it is possible that the motor could have taken out the control unit. DC motors have different characteristcs than A.C. motors when they fail. Most A.C. motors will reveal a fault instantly when power is applied, this is not alway true for a D.C. motor. Sometimes a D.C motor will run fine for a couple of minutes, then after it warms up, it will start to fail. Good Luck, Jerry