By Mike Sokol
Since I published my initial peak starting current data last month comparing SoftStartRV technology to stock starting capacitors, I’ve had hundreds of questions about how well it works. In fact, I just wrote about this in
So let’s get those pesky questions out of the way first. Yes, I did gather this data myself. Yes, SoftStartRV seems to work exactly as advertised. No, a $10 hard-start capacitor is not the same thing at all.
But I wasn’t particularly happy with only being able to create a rough peak current graph showing the differences since my Fluke and Southwire recording meters would only sample the data 5 times a second.
Now that’s plenty fast enough if you want to monitor how much power something uses over a period of minutes or hours. But I needed to see down into the millisecond range (1/1000 of a second) to know how this product really works. And I simply couldn’t afford the $100,000 piece of test gear that can capture thousands of pieces of data in a fraction of a second.
So I invented my own High Rate Data Logger (which I’ve named HRDL, pronounced “hurdle,” like “turtle” but much quicker!) out of spare parts I had laying around in my shop. Yup, I built a $100,000 data logger out of $200 in parts plus an old laptop computer. Really, I did.
With HRDL I can now capture up to 192,000 data points per second at an accuracy approaching 1 part per million. More on how I did this and my plans for future analysis of all sorts of RV electricity things in my Sunday RVelectricity Newsletter coming tomorrow. But today I’m going to show you the basics of exactly what’s going on inside of a SoftStartRV box that allow you to start a rooftop air conditioner with a 2,000 watt inverter generator. So hold onto your seats, ladies and gentlemen, this is going to be a wild ride.
Note these are the actual curves generated from my own test data last week, not some graph drawn up by an artist with a sharpie. As my earlier 5-sample/second data graph hinted at, the factory capacitor works by drawing a lot of current for a short period of time, while the SoftStartRV unit works by drawing less than half that current for twice as long. But in my new graph there are thousands of samples to draw the curve more accurately.
This technology does two things for you. First, since the peak startup current is much less with the SoftStartRV technology, you can use a much smaller generator to run it (my Honda 2200is works great on a 15k Penguin II). Second, there’s much less of a “hammer” when the compressor starts up. As you can see from the yellow graph line, the SoftStartRV spins up your compressor up to speed gently over 1/3 of a second, while the stock factory capacitor puts the hammer down for less than 1/6 of a second with a much steeper rise time in current at the beginning of the compressor starting cycle.
There’s also a third possibility that this more gentle starting current from the SoftStartRV may help increase the life of your air conditioner compressor. I can’t be sure of that without a few thousand hours of testing, but I certainly don’t see any way for the SoftStartRV to harm your compressor.
So what else can I see with my new HRDL meter? Well, in the next higher resolution graph the red line shows that the stock starting capacitor has a 20-amp rebound current with a little wiggle at 30 Hz. Yes, underneath the top line you can see the actual sine waves in the background which form the 60 Hz AC current. And I believe that rebound wiggle in the graph after startup is probably a pressure wave in the Freon gas as it’s being compressed 30 times a second by the 1,800 RPM motor. Sort of like ringing a bell, but in this case it’s Freon coolant in a gasified state as is collapses into a liquid.
Yup, HRDL is accurate enough to hear the echo from Freon bubbles collapsing inside of the compressor, plus a whole lot of other things too cool for school (as we used to say). Want to know more about how I accomplished this data grab and my future plans for HRDL? Read my Sunday RVelectricity newsletter tomorrow for details.
And find out more about where you can purchase a SoftStartRV unit HERE.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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