Fan motor size depends on the total airflow being delivered, the pressure developed, and the impeller's efficiency. Impeller efficiencies generally range from 40% to 65%. If we assume an average value of 60%, we can use the following formula to estimate the fan power requirement.
Fan power (hp) = airflow (cfm) x static pressure (in. water) � 3814
In our example, Fan power = 7325 cfm x 2.4 in. water � 3814 = 4.6 hp.

You can use the FANS or WINFANS (Windows version) computer programs available from the University of Minnesota Biosystems and Agricultural Engineering Department and some county Extension offices. The program is very user friendly and guides you through the fan selection process by asking some simple questions about your grain drying or storage bin. If you have access to the World Wide Web, the program can be downloaded from: www.bae.umn.edu/extens/harvest.html. The program allows you to select fans from a list of over 200 commercially available models and see if the selected models provide the desired airflow.
http://www.ladwp.com/energyadvisor/EA-35.html

Thanks calvo@nbnet.nb.ca for the info.

Problem : : We have a project that requires a micro timer relay device which would have a set of clean contacts to power an external device. It should run on 1.5 volts with minimal power requirements. It should have an adjustment screw to vary the time from 1 to 10 seconds. The contacts should remain open provided a signal is applied every 1 to 10 seconds depending on the setting. If current is not applied during the set time periods the contacts should close to trigger another device. The typical ice cube size off delay relays are a little large for our application. Can you suggest any supplier of a suitable timer really? We should consider using 9 v. if 1.5 is too stingy.............thanks.................James
Solution :

Although there may be some proprietary N.C. delay off small packaged 1.5v relay/timer devices out there, you'll be hard pressed to find one. The 1.5v criteria being the greatest barrier, and small package being the second. Newark Electronics (http://www.newark.com/) had a 1.5v Potter & Brumfield relay Newark # 50F9205, a while back. You can check their web site but can't search by relay specifications, so a call to them may be more productive. That relay was less than �" so you could piggy back a 555 time chip on it. Another good source of relays is Allied Electronics (http://www.alliedelec.com/default.asp).

Your best bet, is to home grow your own. Once you locate a relay (5 & 6 volt are plentiful at the two sources above), you can put the relay on one side of a printed circuit board. On the other side of the printed circuit board put a 555 timer. Add you precision potentiometer, and set it all inside a paraffin wax cube. You should be able to come up with a device 1" mini-ice cube. Your out-put requirements of the relay, you may be able to use I/O modules, TTL, or reed devices, making your package smaller.

Additional information: 5V ultra miniature by radio shack, 555 timer datasheet, 555 timer circuit, 12v supply, 5-9V relay.

Additional links to circuit that can be modified : headlight flasher.

Thanks xbolton@singnet.com.sg for the info.
Problem : We have a job where the installing contractor placed two air-cooled chillers too close together, the owners use one at a time but, due to expansion, the owner now uses both. As we predicted, when both are running there is a condition where the airflow is being short-cycled, now two fan motors are down. Our investigation found that the bearings i.e. one ball touched the stator thus causing the motor to blow, on telling the installing contractor (Japanese Firm - Takisha) he refuses to believe and instead still believes the motor should last 5 years. How can I reason with him that the temperature of the airflow should be around 110-120 degrees F. Would appreciate if you could help in putting forward a better argument.
Solution :Ambient Temperature and Ventilation has a direct bearing on the life of a given motor and when considering life expectancy. As a general rule of thumb each 10L C increase in total temperature over the maximum permissible to the motor insulation system halves its life. Bearing or gear lubricant life is halved for every 25L F (approx. 14L C) increase in temperature. Heat eventually causes deterioration of most lubricants and seals leading to leakage and increased friction. The motor temperature ratings are based on normal room ventilation. With the heat from another system, a condition of thermal runaway can occur, motors are not equipped with thermal protection. See N.E.C. Temperature Codes to help looking up the specs for your motors. Reliance Motors will back this up.

Thanks fred2341@aol.com for the info.
Problem : When 120vac power goes off to a machine or the plant, I need to determine if it has been off for two hours or more. Looking for an inexpensive ""off delay"" timer that uses battery power for timing or some other device having contact output."
Solution : The industrial solution: about $150
Use the normally closed contact of a relay and a red lion timer (battery powered). Cub3T
http://www.redlion-controls.com/products/timers.html#CUB3T.

Fun and Cheap: about $20
Go to radio shack and by a 556 timer and book, couple relays.
http://www.radioshack.com/

Expensive but deluxe: About $250
Calls you if the power goes out.
http://www.comforthouse.com/comfort/temal.html
or
http://www.visiplex.com/visiplex/vs1200.htm

Another possible solution: about $50
though the auto reset may trip you up. PowerAlert
http://www.efs.net/aliter/

Thanks Xcman2000@aol.com for the info.
Problem : Need a electronic rolling dice simulator. (i.e. lights in the pattern of a die blinking on and off)
Solution : Click on the word DICE to see a schematic and instructions using a DM74AS27N chips from Digikey Online (70 cents each.)

Thanks JArmstr301@aol.com for the info.
Problem : I recently encountered a communications problem while working for a client. The problem was erratic conveyor operation on a high speed conveyor attached to a Crisplant Sortation System. It seemed that the conveyor sections would stop as if someone had pulled an emergency stop cord. But the problem was never in the same place each time. What I found was bad communications on the Ethernet.
Solution : This was caused by a combination of bad SDS connectors and exceeding the minimum bend radius of the CAT5 cables. The connectors were changed from a plug type to a BNC connector and the wiring was changed to eliminate any bends with a radius of less than 1". This solved their problem.

Thanks charris709@aol.com for the info.
Problem : Hobart Mig Welding Machine with wire feeder. Even after the operator released the trigger of the gun the wire stayed hot.
Solution : Checked the SCR's and found that one of them was letting voltage bleed by. Replaced the SCR and fixed the problem.

Thanks SKelvin261@aol.com for the info.
Problem : What is the difference between Class A and Class B wiring? electrical power systems technology
Solution : Class B requirements are for residential use, and are more stringent than the Class A requirements for commercial use.

Thanks to Bill Brown for the info.

Problem :How do I wire up this strange motor?

Solution :The following describes how to deal with an AC/DC "universal" motor that has 4 unmarked wires coming out. Be sure you don't have some other motor, such as a 3-phase unit. The universal motor is called that because it can run on AC or DC. The first task is to determine which two wires go to the armature, get an ohmmeter and connect it to the wires until you find two that show some continuity. Rotate the shaft slowly by hand and note if the resistance changes as you turn it. If it does, you probably have the armature, and the fluctuations are due to the brushes making and breaking contact with the commutator. The other winding (field coil) should show a steady resistance.

Thank you Stuart@k-marsh.demon.co.uk for the info.

Problem :I know what a stepper motor is, but I am unsure of what a servo is. Is it simply a stepper motor with a gear box, or do they have regular dc motor inside.

Solution :Generally, a servo has a dc motor. It is used with some position measuring device (typically a potentiometer or shaft encoder) to form a closed loop positioning system. i.e. it compares where it is with where it wants to be, and drives the motor to reduce the error (ideally to 0) A stepper motor is usually used as an open loop device. A given no. of steps moves through a defined no. of degrees. You may want to drive it to an end stop containing a micro-switch to enable you to define your starting point.

Thank you APCC for the info.

Problem :What is power factor?

Solution :Power factor involves a relationship between two types of power: Working Power and Reactive Power. Working Power is measured in kilowatts (kW). It does the work for the system--providing the motion, heat, or whatever else is required. Reactive Power, measured in kilovolt-amperes-reactive (KVAR), doesn't.

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