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Old 08-21-2019, 08:16 PM   #71
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Thanks for the reply's guys - possibly the worst thing to happen to smaller RV's is the addition of 15K BTU ac units. For the most part on a 25 ft C or B+ 13,5k BTU is fine to cool the coach.

Ok getting to my reason - with 13 btu you are free to plug into any 15-20 amp receptacle at your friends house and run your AC without popping a breaker. In fact, I've been doing it for over 30 years.

Anyhow my LTV Wonder has a 15.5 BTU Dometic and it draws around 18-20 amps, so even with the inverter / charger off, it still heats up the beakers and they open. This last week was my 4th location and I ended up using the generator to keep cool.

Ok the magic question is what the lowest current AC unit on the market? I found some 13.5 which only draw 12 amps which would be plenty safe. I don't mind going to 13.5 since I'm upgrading the RV with a lithium system and that would add another 20% of run time.

Not interested in 12 volt AC units since it requires massive cables and a total re-route of wiring. Any input would be appreciated.

Thanks Mike
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Old 08-23-2019, 09:40 PM   #72
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Originally Posted by LA-Hodag2 View Post
The Quiet 12v rooftop A/C is listed at $2749 on the ARV site. I believe that price includes installation since they say the price is based on replacing an exiting unit.

I will post here when I get more info from Advanced RV.
Correction to my earlier post. I spoke with Advanced RV and learned that the Quiet AC on their site is 110 volt, not 12. They are still testing 12v roof airs, but have not yet found one that they feel comfortable selling.
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Old 08-23-2019, 09:55 PM   #73
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Originally Posted by Idleup View Post
Thanks for the reply's guys - possibly the worst thing to happen to smaller RV's is the addition of 15K BTU ac units. For the most part on a 25 ft C or B+ 13,5k BTU is fine to cool the coach.

Ok getting to my reason - with 13 btu you are free to plug into any 15-20 amp receptacle at your friends house and run your AC without popping a breaker. In fact, I've been doing it for over 30 years.

Anyhow my LTV Wonder has a 15.5 BTU Dometic and it draws around 18-20 amps, so even with the inverter / charger off, it still heats up the beakers and they open. This last week was my 4th location and I ended up using the generator to keep cool.

Ok the magic question is what the lowest current AC unit on the market? I found some 13.5 which only draw 12 amps which would be plenty safe. I don't mind going to 13.5 since I'm upgrading the RV with a lithium system and that would add another 20% of run time.

Not interested in 12 volt AC units since it requires massive cables and a total re-route of wiring. Any input would be appreciated.

Thanks Mike
thats some high amps
my 15k btu machs only pull 11 to 12 running on high fan with compressor


off topic but my trade magazine on all electric vehicles found a loss of 50% range when environmental systems were used, (a/c and heat) but we never see this in the ads or other sources. even the tesla with huge range dropped to below 65% range with a/c or heat.

big problem to solve for folks like us that live in north east texas...102 in summer and cold winters.
this has stopped me form buying a pure electric like tesla
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Old 08-24-2019, 08:39 AM   #74
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In my first searches it appears as if the Colman Mach 10 is the most quiet and has a wonderful Bluetooth control so it can be adjusted while you're in bed!


Another pluss it only draws around 11 amps - big advantage for lithium owners.
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Old 08-24-2019, 09:25 AM   #75
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Anyhow my LTV Wonder has a 15.5 BTU Dometic and it draws around 18-20 amps, so even with the inverter / charger off, it still heats up the beakers and they open. This last week was my 4th location and I ended up using the generator to keep cool.

Ok the magic question is what the lowest current AC unit on the market? I found some 13.5 which only draw 12 amps which would be plenty safe. I don't mind going to 13.5 since I'm upgrading the RV with a lithium system and that would add another 20% of run time.
That’s a bit high for a 15kBTU unit, but Dometic’s installation manual shows 15.5-16.0A for their High Cap models, one of which converts from 4392W of cooling to a shade under 15kBTU/hr (one of the Penguin II units). The lowest total rated current draw other than the 11kBTU units are not much different than the 15k units, with 12.5A compressors and 3.5A blowers for 16A total. Or so they’re rated, at least. But some of the High Cap units, have lower rated current numbers.

https://www.dometic.com/assets/59/01...1.pdf?att=true (slide down to the big chart)

Don’t forget that reduced voltage at the pedestal, plus voltage drop in all the wiring up to the A/C unit will result in an increase in current draw, as will a weak run capacitor, and possibly dirty coils. Replacing with a new unit may not make much difference if the voltage is the issue. If it were me, I’d take voltage readings at the unit’s terminal strip while running steady-state under load before spending any coin on a replacement. But I like to know exactly what I’m dealing with before making a move.
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Old 08-24-2019, 11:23 AM   #76
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Thanks for the reply's - for the most part, I never have problems plugged into a campground. However, I often plug in friends homes / business and for decades never had a problem, that is until they started installing 15 BTU units, which pushes the amperage too close to a 20 amp breaker.



Upgrading to 15K units is a major mistake since a 13K can cool a 25-30 ft coach with no problem. In addition to being a problem plugging into homes, the 15K units pushes the capacity of the generators too hard as well.

The only solution is to dump my domestic 15K and install another 13K unit and get my draw down to 10-12 amps. While I'm at it, I'll install a Bluetooth unit so the unit can be adjusted while I'm in bed.

Regards - Mike
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Old 08-24-2019, 03:52 PM   #77
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Just wondering if an Easy-Start unit: https://www.microair.net/collections...nt=30176048267 would help with the power demand (at least the starting part) if you're using lower amperage sources....it claims to reduce the noise a bit as well?
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Old 08-25-2019, 07:44 AM   #78
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Just wondering if an Easy-Start unit: https://www.microair.net/collections...nt=30176048267 would help with the power demand (at least the starting part) if you're using lower amperage sources....it claims to reduce the noise a bit as well?

Thanks for the reply - I feel it has to do with the unit - some of the older compressors have difficulty starting since the line voltage dips so far, however most newer AC units start softly with some barely audible when the pump is running.

As I mentioned in my earlier post 15k btu has made it worse for everyone since they not only take more amperage to run, they take more to start so this is why we now have so many problems.

Basically, the soft start is nothing other than a capacitor that stores voltage to help the compressor get turning than the line voltage takes over. Most every AC unit's fan motor uses a capacitor to start since fans unlike compressors, don't have a starting winding to help them get going.


Regards - Mike
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Old 08-25-2019, 10:46 AM   #79
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Basically, the soft start is nothing other than a capacitor that stores voltage to help the compressor get turning than the line voltage takes over. Most every AC unit's fan motor uses a capacitor to start since fans unlike compressors, don't have a starting winding to help them get going.
Softstarters like the Microair are not "just a capacitor" they ramp up voltage using a computer controlled switching power supply slowly and cut the startup current way down. They allow a full size RV air conditioner to be started off a small 2000 watt inverter generator like a Honda 2000.

You also seem to be confused about the difference between a run capacitor and start capacitor, the compressor will have a start capacitor, it might not have a run capacitor depending on design, it might have both, the fan motor only has a run capacitor typically. You can get a larger "hard start" starting capacitor for the compressor. The fan needs no start capacitor as it does not require large starting torque unlike the compressor.

You must be confusing a hard start capacitor with a soft-starter, watch this video to fully explain, hard start capacitors can actually increase start surge as demonstrated:

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Old 08-25-2019, 11:13 AM   #80
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thats some high amps
my 15k btu machs only pull 11 to 12 running on high fan with compressor
Must be high voltage or mild outdoors temps, as both voltage goes down or outdoors temps go up amp draw will increase.

Coleman specs 2025 "desert" running watts which would be 18 amps at 110v and 16 amps at 125v. This is why the a/c breaker and wiring is rated for 20 amps. I have seen over 16 amps regularly on mine in FL summer heat and out in the Utah Desert.

The mach 15 standard watt draw under more "normal" conditions is 1560, to get down to 12 amps you would need 125v input. So you either have very high input voltage or are running it under very mild outdoor conditions to see 11 amps.
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Old 08-25-2019, 11:20 AM   #81
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Just to expand on jharrell's post above, single-phase motors use two windings or winding sets, including simple split-phase motors (no capacitors), and cap-start (start capacitor only) and cap-start, cap-run (start and run capacitors). And there are some other variants, like permanent split-capacitor (common in A/C fans) and shaded-pole (very small second run winding, common in table fans and such very small motors).

The capacitor is there to delay the peak of the current wave form in the second winding compared to the first or primary winding(s). If there was only one winding, the motor wouldn't 'know' which way to turn. Like a kid's push pedal car - with the pedals at the top and bottom, which way does it turn, and how strong can it turn with the pedals at or near the top and bottom. So a second winding is added that's magnetically as far out of phase with the first winding by as much as is practical.

In order for the two windings to not both pulse N or S at the same time, the current is delayed by the capacitor that's in series with the second winding, so there's a sequence in time between the A winding and the B winding, which is often just a start winding that's cut out after the motor starts. It tells the motor which way to turn, and provides additional starting torque because it is another winding, sequenced like chasing lights on an amusement ride.

A cap-start, cap-run motor doesn't cut out the B winding or the run capacitor, but it does cut out the start capacitor, since too much capacitance will take the sequencing from where it's good for a stopped and slow turning rotor to where it's too much and will actually work against you. What's good for slow speed is not good for rated speed.

Split-phase motors, which don't use capacitors, have a start winding but sequence the magnetic poles just through the differing impedance and inductance of the two windings. The effect is much smaller than a cap-start motor, with much weaker starting torque, but for the drum and fan in a clothes dryer (for instance), it's all that's needed.

Shaded-pole motors are similar, but the B winding is tiny, giving just enough sequence to tell the motor which way to turn. It's always in the circuit. That's why table fans take so long to get to speed - weak starting, but strong enough, and cheap to make. A very small capacitor is sometimes used these days to allow an even small, cheaper motor, with lower current draw overall, turning them into a sort of permanent split-capacitor (PSC) motor.

Since the current is reversing every 1/120 second on a 60Hz AC system, the capacitors can't store energy for later use. They just delay the current and therefore magnetic peaks in the B winding of the motor, sort of like adding a second set of pedals to the pedal car, clocked 90 degrees from the main pedals.

Three-phase motors, on the other hand, don't need a capacitor. The magnetic pulses just chase each other around the stator, 120 degrees of out phase with each other, just like the current in the poles. It literally has a smooth set of magnetics that are rotating around with the rotor trying to keep up. And since the sum of the current between all three phase conductors is always a constant, they're very very smooth. Unlike the heartbeat-like ba-bump ba-bump of a single-phase motor with two windings and some way to sequence the pulses, including use of one or more capacitor.
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Old 08-25-2019, 11:45 AM   #82
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Just to expand on jharrell's post above, single-phase motors use two windings or winding sets, including simple split-phase motors (no capacitors), and cap-start (start capacitor only) and cap-start, cap-run (start and run capacitors). And there are some other variants, like permanent split-capacitor (common in A/C fans) and shaded-pole (very small second run winding, common in table fans and such very small motors).
Also to make another point compressor motors haven't changed alot over the years they all require 4-7 times the starting current of their run current, the Coleman mach 15 is rated at 70 amps locked rotor. This is for a split second but its very difficult for a small generator or inverter to provide, if it can't the motor will stall and continue to pull LRA and stall generator or overload inverter. This is why a generator needs to be oversized to start an a/c but not run it and why a true soft-starter can help.

This very large surge will also cause a dip in incoming voltage. This is why I installed the Micro-air in my RV, My 3000w Magnum inverter is wired inline to power the entire rig. The Magnum will transfer over to invertering if it senses a single cycle of voltage below its set threshold. Sometimes my Mach 15 startup would cause a voltage sag low enough (80v) to cause the Magnum to disconnect shore and attempt to start the a/c itself leading to inverter overload even though my Surgeguard sees nothing below 102v because its sampling rate is much lower.

The Micro-air solved that issue completely and now allows me to run the a/c off the inverter if I desire, everything is much smoother now on a/c startup.

No one has come out with a RV inverter a/c with variable speed compressor in the US yet, Dometic has the Harrier overseas perhaps at some point we will get them over here, they have no need for a soft starter as it does a soft ramp on its own.
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Old 08-25-2019, 05:17 PM   #83
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Thanks for the replies - I suggest that if anyone is going to find fault with a post, to first research it more thoroughly, to avoid errors.

As I mentioned earlier, the primary reason owners are having problems with their AC units starting, is because RV manufacturers have in error, upgraded most coaches from 13.5k BTU units to more power demanding 15.5k BTU units, drawing 17+ amps on a system with only 20 amp breakers. Making matters worse, these coaches generally have smaller generators which struggle to keep up to the demands of these larger AC units.

Regretfully, many owners who are having this problem have “fallen victim" to paying up to $300+ for these so-called soft or easy compressor start devices worth at best $25-50 when a simple $9.00 kick-start capacitor, will offer better results for starting the compressor, here's why:

Unlike these “over-priced” start modules, which merely limit maximum amperage peaks and manipulate your “same low voltage”, "Start Capacitors" actually store “real current & amperage” to increase the motors torque when starting, so they don’t depend on line and generator voltage to supply the extra amperage needed to start the compressor.

Regardless of any patch or fix to start the compressor, you’re still confronted with a AC unit that draws to much amperage for the average 30 amp RV with 20 amp breakers leaving almost no room to run other items and charging.

Regretfully, the only real fix is to replace the unit with a smaller 13.5k BTU (10-12 amps) and lower you systems amperage. For the most part, a 13.5 K unit with proper voltage will cool just as efficiently as a 15K btu unit will running on low voltage.

Regards - Mike


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Old 08-25-2019, 09:36 PM   #84
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Regretfully, many owners who are having this problem have “fallen victim" to paying up to $300+ for these so-called soft or easy compressor start devices worth at best $25-50 when a simple $9.00 kick-start capacitor, will offer better results for starting the compressor, here's why:

Unlike these “over-priced” start modules, which merely limit maximum amperage peaks and manipulate your “same low voltage”, "Start Capacitors" actually store “real current & amperage” to increase the motors torque when starting so they don’t depend on line and generator voltage to supply the extra amperage needed to start the compressor.
Thank you for the reply, but complete wrong, I also suggest one understands motor capacitors and soft starters to avoid errors as so many have been posted in this thread and elseware.

All voltage and current comes from the generator or line, the start capacitor controls how much goes through the start winding and when, it does not supply it , in fact it can increase the amount of peak startup surge by allowing more current through the start winding, the larger the start capacitor the more current will be pulled through the start winding.

The video I posted goes through the trouble of measuring the difference to prove it.

"So called" soft starters are real devices (https://en.wikipedia.org/wiki/Motor_soft_starter) used in various applications that actually do lower starting current and you will not find one for $50-25 dollars. Hard start capacitors pull more current through the secondary winding to increase starting torque, that is their purpose, they are cheap for a reason.

If your compressor has an issue and is taking too long to start, the a hard start can get it going faster by drawing more current to increase torque and stress. A true soft starter allow for a very long slow ramp up of current and torque greatly lowering peak current and stress on the device.

30 amps is more than sufficient to run a 15k btu a/c and everything else and provides additional cooling over a 13.5k. A soft start is not necessary with a standard 30 amp generator. Where it shines is with smaller generators that cannot start either a 15k or 13.5k btu a/c or if you are attempting to run and a/c off batteries through a modest inverter or as I am running the whole coach through the inverter and trying to reduce voltage sag by lowering peak inrush.

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For the most part, a 13.5 K unit with proper voltage will cool just as efficiently as a 15K btu unit will running on low voltage.
Again that is not how a a/c works. Voltage will not effect cooling output, the unit will simply pull more current to maintain compressor and fan speed. The 15k unit will put out 15k and the 13.5 will put out 13.5 or they trip a breaker and don't.

Smaller a/c's will have smaller starting amps and run amps obviously and a soft starter will reduce start surge on them as well.
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