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Automatic Alternators are also sometimes called a “flip-flop” relay. When two compressors are operated together it makes sense to balance the load between them to equalize wear and extend your maintenance interval. The automatic alternator will transfer the base load requirement back and forth between the two compressors.
For example, if the #1 compressor starts, pumps the system up to pressure and then stops, the next time system pressure falls the #2 compressor will start.
We can assist you in determining if an automatic alternator will be beneficial to you and provide installation service or assistance.
There can be many reasons why the incoming voltage to your compressor isn’t at the proper level. If the line voltage you’re getting is more than 5% off from the nameplate voltage of your equipment, motors run hotter, draw higher currents, deliver less power and wear down faster.
A common misconception is that it’s always OK to run a 230 volt motor on a 200 or 208 volt service. Some 230 volt motors even say “useable on 208 volt”. Whether or not this works depends on the actual load that is put on the motor and how often the motor is started. If the load draws less than nameplate horsepower and isn’t started too frequently, there’s usually no problem. If the load is greater than nameplate horsepower (like most compressors) and/or the motor starts frequently (like some compressors), low voltage will kill the motor.
Buck-Boost transformers are the most economical way to correct poor supply voltage because they don’t have to be big enough to take the full power load of the circuit. Give us a call for sizing and a price quote.
What do you do if you move to a new building and find out that the available electrical service is 208 volt and all of your equipment is 460 volt?
Installing your own distribution transformer may be a much more economical way to solve the problem than changing out motors and control components. Many distribution transformers are also “shielded” or “isolation” transformers. These serve to eliminate problems from “dirty” power that can damage sensitive electronic components downstream. Sizing is important for good performance - the experts at Cal can help!
For increased safety, most equipment will have a control circuit operating at a lower voltage than the drive motor. In compressors, we commonly see control voltages of 115 and 24.
The control circuit transformer will reduce line voltage to 115 or 24 volts (sometimes a machine will require both reduced voltages). They are usually protected with fuses on both the high (primary) and low (secondary) voltage sides. These are sized in terms of VA (Volt-Amps) or KVA (Kilovolt-Amps).
A motor starter is a device that’s used to start an electric motor. It consists of a contactor and an overload relay. A contactor is a heavy duty magnetically actuated switch that connects the motor to the line. The overload relay senses the current drawn by the motor and opens a switch to shut the motor down if the current is excessive.
The magnetic coil that closes the contactor is wired to the machine’s control circuit.
Motor starters are seen most on motors 3 hp and larger, or smaller motors that need to be remotely controlled. Smaller compressor motors may have temperature switches built in to their windings to shut down the motor if it becomes overloaded. These motors are stopped and started directly by the pressure switch. Starting larger motors directly with the pressure switch is not a good idea. The pressure switch contact points are not capable of carrying the high starting current and will quickly burn out. Motor starters are sized by the current they have to carry. They are also rated by horsepower and voltage. Contact us for sizing assistance and a price quote.
Phase Monitors are protective devices that can shut the compressor down if there’s a problem with the incoming power. There are different versions that can sense all or some of the following:
- Unbalanced voltage
- High Voltage
- Low Voltage
- Loss of a phase
- Phase reversal
Any one of these problems can cause serious and expensive damage to the compressor. In areas where the quality or consistency of incoming power is questionable, phase monitors are cheap insurance against an expensive failure.
A pressure switch (also used for vacuum and called a vacuum switch) consists of a switch mechanism that is connected to a bellows or diaphragm that reacts to system pressure. Some are adjustable and some are not. They are selected operating range and
differential. Operating range is the pressure limits in which the switch will work. Differential is the difference between the cut-in and cut-out pressures. A popular switch
found on many compressors will a range of 40 to 250 PSI and an adjustable differentia of 35 to 60 PSI. This means that the lowest pressure that the switch can be set to close at is 40 PSI, and the highest pressure it can be set to open at is 250 PSI. The differential that
is actually available to use varies with the pressure range you’re actually working in. As pressure increases, available differential increases as well. Some switches have
differentials as low as 5 PSI. The contact points in the switch are usually rated for the amount of current they can carry. Some switches are also horsepower rated.
When you replace a pressure switch it’s important to make sure the contacts are of the same configuration as the switch you have. Double Pole Single Throw (DPST) contacts are very common. These will have 4 terminal screws, two of which are labeled “Line” and two of which are labeled “Load” or “Motor”. Some pressure switches need to be able to signal whether they are open or closed. These commonly have contacts called Single Pole Double Throw (SPDT). There will be three terminals labeled “Common”, Normally Open” or “Normally Closed”. Cal Supply stocks a large selection of pressure switches for whatever you need.
A relay is a remotely operated (magnetically actuated) switch. Many compressors use them in their control circuits. They can also be used to signal a compressor fault to a remote location. They come in many operating voltages, contact configurations and mounting types. Cal Supply can provide replacements for existing units or assist you in new applications.
Time delay relays are very common on rotary screw compressors and pressure lubricated reciprocating compressors. These relays receive a control signal, wait for a pre-set time, and then operate a switch. In a rotary screw compressor they are most often used for “Auto Dual Control”, which prevents the machine from starting too often during periods of light load. In pressure lubricated reciprocating compressors that are equipped with a low oil pressure shutdown switch, they bypass the switch for a short period of time at startup to give the compressor’s oil pump time to build up pressure. These are available in many time ranges, operating voltages, operating modes, and contact configurations. On compressors with electronic controllers, any needed time delay functions are usually built into the controller.
Rotary screw compressors use temperature switches as safety shutdowns. Some machines use one, others use two or more. They’re there to shut the machine down before it overheats to the point where the oil will catch on fire. If there’s only one it will be located in the discharge pipe between the air end and the sump/ separator. A second switch would be located on the outlet of the sump/separator.
Water cooled reciprocating compressors often have temperature switches at the cooling water outlet and the compressed air outlet of each stage. If cooling water is lost, or the machine is run out of oil, these can often avert a catastrophic failure.
Lubricated reciprocating air compressors used with medical or breathing air systems have temperature switches installed on the compressed air outlet which will shut the machine down if the air temperature rises enough to create carbon monoxide by burning the oil.
Compressors with electronic controllers will often have temperature functions built in and use thermister probes as sensors.
If you need to add or replace a temperature switch, please give us a call.
Cal Supply offers a wide variety of Start/Stop pushbuttons, indicating lights, selector switches, replacement contact blocks, legend plates and application assistance. A worn out switch is often the cause of nuisance shutdowns.
