RV Electricity – Start me up … Generators and rooftop air conditioners

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Dear Readers,

I saw a lot of cool stuff at the Hershey RV show last month, and the manufacturers are sending me demo gear to try out. Pretty cool, as I love setting up experiments, gathering empirical data and coming to meaningful engineering conclusions. I don’t do guesses – I do science. 

Here’s a topic that I’ve pondered for years but never had a good reason to look at more deeply than a howdy-do: hard (or soft) start capacitors for air conditioners. Briefly, rooftop air conditioners on RVs draw a LOT of peak current when the compressor kicks in. This starting current can be many times the average draw compared to when the compressor is actually running. That’s generally not a problem when you’re plugged into pedestal power because the PoCo (Power Company) can supply enough peak current to literally melt all your wiring in a flash. (And yes, I’m using the word “literally” properly in this context.) But generators are a different story entirely. 

Now, the real problem is when you’re using a small generator like a Honda EU2000i to run your RV’s rooftop air conditioner. While 2,000 watts (actually, 1,800 watt continuous) is plenty of power while the compressor is running, the surge current supplied by the starting capacitor generally causes the generator to trip due to the peak current. There have been a number of possible solutions offered as hard-start, soft-start, and whatever-start capacitors. However, the engineers at Micro-Air have designed something called the EasyStart™ which has definite possibilities. A discussion with their engineering group divulged how it works internally.

Basically the EasyStart has a smart chopper circuit which “learns” the peak current your compressor needs to operate and then adjusts the start current based on what your generator can supply. It learns over the first few starting cycles which tunes EasyStart to your particular air conditioner. This is how it determines how to control the amount of peak current it can supply to the compressor without tripping the generator. And voila, even a Honda EU2000i should be able to start a 15,000 BTU air conditioner at sea-level reliably without the need for a second companion or larger generator. 

This technology could also useful in campgrounds with only 30-amps of pedestal power that might have trouble starting your air conditioner. And it’s potentially a great addition to solar inverter/battery technology being used to run a smaller air conditioner. For air conditioners with less than 9,000 BTU capacity, there’s another smaller model EasyStart.

Cost is affordable at $299. Installation seems simple enough with just a four wires to connect, and the design looks like it should work. However, I can’t qualify this just yet until I do a few experiments, gather empirical data, etc. 

So Micro-Air has already sent me a demo EasyStart unit, Dometic says they can send me a 15,000 BTU air conditioner, and Honda will loan me an EU2000i. (I already have an EX1000 and an EU3000iS in my shop, but no EU2000i.) See the graph from Micro-Air with a comparison of peak starting current of a 15K BTU air-conditioner with (red line) and without (blue line) the EasyStart technology.

As I said, the technology looks very promising. So once I get all the demo gear in place I’ll run some starting experiments with a digital storage oscilloscope so we can see exactly what it’s doing and how well it works. 

Yes, I do have too much fun. Stay tuned for a followup article on compressor soft-starting technology. It will likely be a few months before everything arrives and I can set up the test, so please be patient. Good science isn’t quick – it’s thorough.   

Let’s play safe out there….

 

Mike Sokol is an electrical and professional sound expert with 40 years in the industry. Visit NoShockZone.org for more electrical safety tips. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

##RVT868

 

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Steve
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Steve

Mike,
I am not sure if you have covered this, but there are several after market systems to help the amp draw on compressor start up from the one you covered to basic add-on capacitors. Could you review the simple add-on capacitor which are much less expensive.

Also, have you ever seen a timer unit that puts a 5-10 second delay on starting the circulation fan, which adds to the initial start up amp draw? If you delay this 4-5 amp start-up draw a few seconds, it can only make the overall draw lower. Thanks

Mike Sokol
Editor

UPDATE: Dometic will be shipping me a 15k BTU air-conditioner this week for testing, which I’ll primarily use for the soft-start demonstration using Easy-Start. But then I’m going into destructive testing where I keep lowering the AC voltage down below 100 volts and monitor the compressor overheating. Yes, they know I might burn this up and are happy to send me a demo unit as long as I supply them with my data. At some point I’m going to need a big shipping-container in my back yard since there’s some upcoming projects that could actually explode, and I’m not doing… Read more »

Michael Sturtz
Guest
Michael Sturtz

We have a QD 6000 that won’t start our dual 13.5k Dometic ACs. As you probably know the QD6000 is an inverter generator. It stays running but the protection system trips not the breaker. It has a dual pole single throw breaker. It in theory should be able to start both ACs with power to spare. I’m wondering if I install two easy start capacitor units one on each AC if that would help. Some of the issue may be related to the time it takes for the generator to spin up to full throttle. It usually runs at a… Read more »

Mike Sokol
Editor

Michael,
Yes I think that installing a SoftStart unit on each air conditioner would do the trick. You should contact tech support at Micro-Air and tell them I sent you.

John
Guest
John

I have had and used the Easy Start for about 9 months. It just works great. Although the Honda 2k on eco mode will start the 15k btu Dometic AC most of the time, if there is a lot of humidity or at an altitude of 3k ft or more, it seems to struggle a bit. On the whole, this was a very good purchase and when on a 30amp connection, I can add a few more watts to the mix and not drop the load.

Mike Sokol
Editor

I have a really good feeling about the EasyStart technology. I’m still waiting on my demo 15K btu air conditioner from Dometic, but as soon as it arrives I’m ready to begin that experiment. Should be interesting.

Rory
Guest
Rory

Mike, I recently had fast start kits installed on my roof AC’s. I have found that they don’t require that sudden burst of power when the compressor kick in. I wonder why these “kits” are not standard equipment on RV roof AC’s. Will these be offered by manufacturers at least as an option in the future. My has eased my mind re: what appliances or electrical gadgets I have up and running when I turn on the AC.

Mike Sokol
Editor

It would make a lot of sense for RV rooftop air conditioner manufacturers to offer the EasyStart technology as an option, especially since it can allow the generator to be significantly smaller. Once I gather more information demonstrating how well this works, I’m sure that Micro-Air would be interested in producing an OEM version. as well.

Scott Rossell
Member
Scott Rossell

I’m currently able to run a 5,000 BTU window style air conditioner off my WEN 56125i inverter generator. It’s a minimal 1,000 watt/1,250 peak generator. Very small and quiet. BUT, it’s not just ANY air conditioner. It has a very high Energy Star rating of 12.2. Previous efforts with a different model with a rating of only 9.7 failed instantly. I’m also able to run this same air conditioner on my battery bank alone. It’s an 8-battery bank with approximately 1,200 amp hours total.

Irv
Guest
Irv

Mike, I had an Easy Start and it worked great on a Honda EU2000i but had it removed with a refund from Easy Start because moisture got inside and shorted it out in the following scenario: We drove from NC to AZ in November mostly on I-40 which has lots of elevation changes. Most of the trip was in rain, drizzle, fog. My guess is that the unit is waterproof when at a fixed elevation but not when it undergoes rapid elevation and temperature changes. (Up to 8000 feet) The case may have been “water proof” but it wasn’t humid… Read more »

Mike Sokol
Editor

Interesting. I’ll pass this onto their engineering department.

Chuck MacMahon
Guest
Chuck MacMahon

Hi Mike,
The soft start for an AC compressor will indeed be a wonderful thing. Couple of questions for your tests, With the Honda 2000i in Eco Mode will the generator be able to sufficiently increase speed to handle the start load? Can 2 Honda 2000’s in parallel operate 2 AC’s? Currently my AC requires 2 Honda 2000’s at full speed to run a single 15,000 AC. Lots of noise and fuel.

John T
Guest
John T

Do you wire this into the AC unit, or into the electrical supply at the circuit breaker?

Mike Sokol
Guest
Mike Sokol

This wires into the air conditioner’s starting capacitor circuit. Looks simple enough for any good RV tech or electrician to do.

DAVE TELENKO
Guest
DAVE TELENKO

Very KOOL, pun intened!! To add to the surge issue with the ac’s. Lets say that your ac is running just fine & oops your honda runs out of gas. Now you have another issue along with the surge is the compressor has now pumped up to the pressure required to give you the cooling! I would think it would be difficult for the 2k gen with soft start to start the ac again! I actually don’t have any knowledge of this happening, just thought I would mention it.

So whats going on with the refrigerator testing?
Dave

Wolfe
Guest
Wolfe

I believe compressors are made to bleed off that pressure after a couple minutes. This is the theory behind the delay built into power monitors — keeping the compressor from restarting under pressure.

Mike Sokol
Guest
Mike Sokol

Yes, there’s a bleed valve and a 5 minute restart time delay in the EasyStart. No problemo…

Mike Sokol
Guest
Mike Sokol

First refrigerator arrives Monday…

Tommy Molnar
Guest
Tommy Molnar

Now THIS, is “news I can use” (as the saying goes). We don’t often yearn for the A/C, but there are those times. I do have a generator that can handle the A/C, but it’s big and cumbersome (and HEAVY) and I don’t really want to haul it long distances. I have a couple Champion 2000 watt gensets but again, I don’t want to take up that much space (or haul that much weight). I’ve been reading about these “Easy Starts” for some time now. They seem like a gift from heaven. You know, too good to be true. But… Read more »

Mike Sokol
Editor

FYI: Dometic marketing contacted me yesterday to ask what air conditioner I want for a test, so I’m ordering a 15,000 BTU unit with a heat pump. I’ll use it for both my SoftStart test as well as monitoring the compressor current when pedestal voltage drops below 100 volts. Lots of fun in store….

Randy
Guest
Randy

Will this type unit work for my Keurig coffee maker the same way? I have a 2000w inverter, but it trips when the start up/water heats up. If so, I’m in! Much cheaper than installing larger inverter!
LMK, Thanks!

Mike Sokol
Editor

Randy, sorry no. Resistive heating elements draw pretty much continuous amperage when they’re turned on. AC motors driving compressors have a secondary “starting” winding with a capacitor that gives the motor a big JOLT on startup. The EasyStart works by modulating this starting surge to only what the compressor needs to start up. No such luck with your coffee maker or hair dryer.

Scott Rossell
Member
Scott Rossell

I’ve been using an inline 80 farad capacitor in my mobile power system for over three years in order to use my Keurig coffee maker. It cost me $90, is about the size of an inverter, and works flawlessly to power that dead short water box of caffeinated goodness. Admittedly, 80 farads may be overkill. I initially tried a 5 farad canister style capacitor at half the price, but it wasn’t enough to get the job done. So I went all-in on the 80 and it’s been great. In fact, I would never even consider building another mobile power system… Read more »

Mike Sokol
Guest
Mike Sokol

Not sure how an in-line capacitor will help except that your phase shifting the current and creating a 6-dB/octave single-pole low-pass filter. I’ll calculate the reactance later to see how this works.

Scott Rossell
Member
Scott Rossell

I have no idea what ANY of that means, but if I can provide any further data on my end, I’m happy to help. What I do know is that without it, the coffee maker pulls too much power and the inverter shuts down, but with it, that doesn’t happen. Also, I have to run it on the modified sine 3,000 watt inverter because the pure sine makes a horrible sound when I use it with the coffee maker. It still works, but the sound is very disturbing; a kind of rumbling buzz – almost sci-fi sounding actually. Very loud.… Read more »

steve roland
Guest
steve roland

I can already tell you it works great. My Honda 2000 will easily start and run my 15k BTU A/C. I got the bare bones circuit board, purchased a cap and wired it in. Much less expensive.

Wolfe
Guest
Wolfe

Where did you get the circuit board? I’d be very interested if the price wasn’t as much as a cheapie 4K genny. I’ve been pondering rigging up massive super-capacitors, but a smarter controller would probably overcome ‘grunt’ at some pricepoint.

Curt
Guest
Curt

Hi Mike, in the photo of the Easy Start in your hand, has the weatherproof connector let go of the cable covering? It looks like I see the conductors showing.

Mike Sokol
Editor

Closer inspection shows that the wires in the connector are sealed and there’s a short length of heat shrink tubing capturing a snake-skin braided cover. Looks totally watertight as assembled to me, but I’ll ask their engineering department to be sure.