Hello from Dometic Marine - Makers of Cruisair and Marine Air Systems Brand Air Conditioning and Refrigeration Systems.
We've been monitoring this thread and decided to join the forum to lend some expertise and to help everyone out. We have reviewed the forum rules and regulations regarding commercial interests, and we hope that this post in no way offends or violates anything. All we want is for everyone to have the facts. The new SmartStart is a revolutionary new product that is unlike any other soft starter or hard start add-on in the industry. It is very important to understand how it differs so you can make the right choices for your individual situations.
Important information about the dangers of Portable Gasoline Generators
Before we begin, it is important to clearly state that Dometic does not condone the use of portable gasoline generators for any marine application since both the US Coast Guard and the ABYC strongly caution against it. Portable gasoline generators are not properly marinized and they present life-threatening risks and dangers, including carbon monoxide poisoning and risk of explosion since they are typically not ignition protected. For more information, please refer to the USCG bulletins on this topic available online at
http://www.uscgboating.org/assets/pdf/recalls/bscscan68a.pdf and
http://www.uscgboating.org/assets/pdf/recalls/BSC74.pdf. Also, please refer to the ABYC document TH-22 (
http://www.abycinc.org/th-22.pdf) where they discuss the use of portable generators on boats.
Test Setup and Equipment
In order to provide you with the most accurate information, Dometic obtained a Honda EU2000i generator and a Supco SPP6E Super Boost for side-by-side testing with the new Dometic SmartStart. Both the Honda and Supco products are very good, and by no means was this study conducted in order to put down either one. This study is meant to help everyone better understand how the SmartStart is different and where and why it can solve the problems discussed in this thread where other products cannot.
The current surge caused when an air conditioner compressor starts up is very short in duration, typically 150-300 milliseconds. Hand-held clamp-on current meters typically cannot measure this surge accurately because they typically display an averaged reading about once per second. As a result, the reading obtained with a clamp-on meter is always much lower than what has actually occurred. For our SmartStart development which started over one year ago, we at Dometic developed a custom and very specialized piece of test equipment to accurately capture and measure the start surge accurately. This specialized equipment along with an oscilloscope was to carry out the following study. Below is a photo of the test setup which conducted outdoors so we could run the Honda generator. We used a Cruisair model STQ16-R410A Turbo self-contained 16,000 BTU air conditioner for most of the testing.
Technical Differences between the Dometic SmartStart and the Supco SPP6E (Class E Super Boost)
The Supco SPP6E Super Boost device consists of a 88-106MFD start capacitor connected in series with an electronically-controlled, solid-state potential relay. Using voltage sensing, it connects the start capacitor in parallel to the air conditioners run capacitor during the start up. As the voltage across the run capacitor (Run winding to Start winding) increases during the start, the device switches out the start capacitor at a preset level or after a timeout period expires. This sequence partially mimics the behavior of a full hard-start kit (start cap with a mechanical start relay) but not exactly. A true potential start relay has its coil connected across the compressor Common and the Start winding. The voltage behavior between these two compressor terminals is a little more predicable during a start-up. As a result, a true start relay can accomplish a more reliable disengagement of the start capacitor. Nevertheless, the Supco Super Boost does provide a good portion of the benefit of a true hard-start kit and reduced cost. Based on our measurements (shown below), the Super Boost provided a startup current surge reduction of about 20-25%.
The new Dometic SmartStart is completely different. The SmartStart uses a microprocessor to provide real-time control of the applied voltage and current to the Start winding and Run winding independently. The voltage applied to the start winding is also shifted in phase by an internal start capacitor. The application of voltage is so precise that each half alternation of the applied AC power is individually handled by the microprocessor. Then, using back EMF detection, the SmartStart determines when the motor's rotor actually begins to rotate. The SmartStart then accelerates the rotor until it has achieved full speed. Then, at a very precise moment when the current waveform passes through zero, the SmartStart seamlessly bypasses its internal control devices with relays to connect the Run winding directly with L2 and disconnecting from the Start winding.
The SmartStart's intelligence then even goes beyond this. Using the information it gathers from each start, it actually "learns" from what happened during one startup to determine what to use on its next startup. So, immediately after installing and using it on for the very first time, the SmartStart may take up to 10 startups for it to optimize itself to the absolute lowest possible starting current. After that, it continues to fine tune its startup behavior from start to start, up or down, depending on age of the compressor, environmental conditions, and voltage.
The result of this microprocessor-controlled automation and recursive learning is the absolutely lowest possible startup current required for each individual compressor and SmartStart combination. For all models of the SmartStart, the average start-up current reduction achieved is 65%.
Test Results
Two sets of tests were run: One on utility power and one on generator power. The Honda EU2000i has an "ECO" switch that allows for economy mode operation. This economy mode of course results in the generator running at a lower throttle setting to save fuel. However, there is a trade-off. When ECO mode is turned ON, the generator cannot respond quite as quickly to rapid changes in load current. Under certain test conditions, the compressor start surge on generator power caused the generator's output voltage to drop drastically and to become erratic when the compressor start faltered, and also caused the generator's maximum output current to be clamped. So, in order to accurately quantify what each hardware configuration would do, accurate start current data was captured using utility power. Later in the generator tests, instantaneous voltage fluctuation was also measured. In the end, both current surge and voltage drop do matter since voltage drop can dramatically and sometimes detrimentally affect other equipment that may be operating on the same generator.
Analysis
The Honda EU2000i is quite a potent little device. Regardless of the start component configuration, it was able to start the 16000 BTU system reliably when the ECO mode was turned off. When the ECO mode was turned on, however, the generator had trouble with the standard configuration and with the Supco SPP6E installed. The Supco Super Boost did help, but the resulting voltage drop to around 67V (46%) was problematic in that it did sometimes reset the digital controls. Other equipment running off the same generator would have also been affected.
The SmartStart made a dramatic difference. With the ECO switch turned on, the generator was able to tolerate the 18 amp start surge with only about a 20% drop in voltage. With the ECO switch turned off, the generator didn't even flinch (i.e. no measurable voltage drop).
Summary
As was cited elsewhere in this thread, the Honda EU2000i can support a 16,000 BTU air conditioner without any added hardware. But as our testing showed, this would only work if the ECO mode was turned off. Adding the Supco SPP6E provides a marginal improvement, but for our specific test with the 16000 BTU system, it could not guarantee a reliable start-up if the generator was operating in ECO mode. Beyond this, if other equipment is already loading the generator (e.g. sea water pump), that will further reduce the available amperage for the compressor start-up. Adding the Dometic SmartStart provides a dramatic improvement, provides a reliable start under almost all conditions, and will allow the generator to be run in ECO mode, which will certainly reduce fuel consumption.
Dometic is very happy to contribute to this forum; however, we cannot guarantee that someone will always have the opportunity to monitor it at all times. We will do our best to return to this thread in the coming days to answer any follow-up questions. In the future, others from Dometic may use this user ID to answer other questions on this forum.
Thank you for your continued interest and support.
Thank you.
M. Giovanetti
Director of Technology
Dometic Marine Corporation
