How much power is enough?

By Barry Taft, Graco Technical Assistance

One question we get in our technical assistance group on a regular basis is, “How much power is required to operate our foam or polyurea proportioner?” There are many things to consider when planning for a generator or shore power supply.

This article is not intended to replace the expertise of a certified electrician. Please consult a certified electrician before purchasing or installing any generator. In addition, Graco has recently added guidelines and tips on choosing and setting up a generator in all proportioner manuals which can be downloaded from www.graco.com. Refer to manuals 312065 and 312062.

Generator under-sizing is all too common due to budget concerns, lack of understanding and misinformation. This mistake is not only jeopardizing the generator, but all equipment that is being powered by it. I can honestly say that no one has ever contacted me to let me know that too large a capacity generator has given the owner concern. I can share many stories where too small a power supply has damaged equipment – leading to costly repair and down time. That said, too much kilowatt capacity is better than not enough.

Before inquiring about a generator purchase, you need to calculate your power requirements. Make a list of all the items that you intend to incorporate into your trailer before you start your shop comparison. The total system requirements for Graco proportioners are listed in the operation manual under the model's description and/or in the technical data sections. In addition to the proportioner, consider the other electrical equipment requirements in a trailer operation. This can include air compressor, air dryer, fresh air panel, lights, various outlets for electrical agitators, power tools, etc. Heat and air conditioning is often overlooked. It is not for the operators, but for the materials. Chemicals with 245fa blowing agent must be stored below 90°F (32°C) to keep from off-gassing.

Generator sizing
• List system components using starting requirements, in watts
• Add-up watts required
• Multiply total watts by 1.25 = KVA (Kilovolt-ampere), use this number to size the generator

Proper system set up, start up and shut down procedures are critical to the operating equipment and generator. The order of the steps are important, follow them closely. Failure to do so will cause voltage fluctuations that can, over time, damage electronic equipment.

Start up
• Check fluid levels on generator (oil, coolant and fuel). Running out of fuel can cause severe damage to the generator and powered equipment. A 40 – 60 kW generator working at ¾ load can consume approximately 3 – 4 gallons per hour. Verify that there is enough fuel to complete each day's task.
• Ensure that the Reactor disconnect switch is in the off position
• Ensure main breaker on the generator is in the off position
• Check the oil in the air compressor
• Close the bleed valve on the compressor
• Start the generator and allow it to come to full operating temperature, at least five minutes
• Turn on the main breaker for the generator
• Engage the compressor starter and air dryer if included
• Turn on power to spray machine – refer to the equipment manual for proper operation

While running
• Use air compressors with constant speed head unloading. Direct in-line air compressor starting and stopping will draw high currents, as high as 9 times the full current load, causing massive voltage fluctuations across the system, damaging equipment.

Shut down
• Relieve spray machine system pressure and park the machine in accordance to the equipment operations manual
• Turn off power to the spray machine
• Turn off air compressor and dryer
• Open compressor bleed valve to relieve pressure and remove water from tank
• Turn off main breaker on generator
• Allow generator dwell time before shutting down per manufacturer's recommendations
• Plug into shore power if engine block heater and or trailer heater is required in colder weather