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11-27-2024, 01:51 PM
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#71
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Senior Member
Join Date: Sep 2017
Location: Northern California
Posts: 1,617
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Quote:
Originally Posted by medarwin
Not true. This is a brushless 12v DC motor that powers the compressor. Fun Fact: Typical RV inverters "lose" 10-15% of the energy during conversion from 12v DC to 120 AC. In fact, converting any form of energy results in loss. Which is why it's stupid to generate electricity from natural gas/coal to power electric cars.
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Sorry, it is true. The Danfoss (now Secor) and similar refrigerant compressors are simple multi-phase brushless motors. A brushless motor requires an inverter to function. The rotor has permanent magnets on it. The stator has three (or a multiple of three) electromagnets powered by a three-phase inverter. The AC output of the inverter generates a rotating field via the stator electromagnets. The rotating field pulls on the rotor permanent magnets and thereby creates rotation.
So, yes, all "DC brushless" motors have an inverter.
See the details on this link (or many others). Scroll down to "control by inverter."
https://www.renesas.com/en/support/e...2-inverter-pmw
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11-27-2024, 02:10 PM
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#72
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Senior Member
Join Date: Jun 2010
Location: Browns Mills, NJ.
Posts: 250
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So all of those brushless motors for drills and hand tools and the brushless motors for remote control cars have inverters?
__________________
Rick and Dianne, dogs Mikki and Athos
2003 Winnebago Journey 36 DL
Recently retired and now broke
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11-27-2024, 02:20 PM
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#73
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Senior Member
Join Date: Sep 2017
Location: Northern California
Posts: 1,617
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Quote:
Originally Posted by rickf
So all of those brushless motors for drills and hand tools and the brushless motors for remote control cars have inverters?
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They do. With modern electronics, the inverter is quite small, but it's there somewhere. In a typical brushless computer fan, it's a small annular circuit board about 1/8" thick and an inch in diameter. In a drill, it might be part of the trigger mechanism (i.e., attached to it or in the same casing). Maybe only a cubic inch in the case of a drill motor. In some small motors its literally built into the motor casing.
Here's an image of a typical 12V brushless fridge setup using a Secor compressor. This one is in the current Novakool RFU-9000 fridge. The inverter is the box to the left of the compressor (about 2" wide, 5" tall, and about 5" deep).
Also interesting (to me at least) is that the unit shown in this image is adjustable speed. It comes from the factory set to a speed that will handle most RV fridge situations (about 2500 RPM). If it's installed in a smaller fridge, the speed will be set lower. In the unit I have, I replaced the speed control resistor with a potentiometer. This allows me to adjust the speed from 1500 RPM to 3000 RPM. Setting the speed down to 1500 RPM reduces the fridge energy usage by about 30% (and the fridge runs a bit quieter). Doing this also limits cooling capacity so would not be suitable for a 100F ambient.
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11-27-2024, 03:19 PM
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#74
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Senior Member
Join Date: Jun 2010
Location: Browns Mills, NJ.
Posts: 250
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Interesting, I was using brushless motors in RC cars 30 years ago. Somehow I don't think they had circuit boards that small back then. But, I am not an electrical engineer so I have no idea. What I am looking for is a fridge that draws very little power and gets cold. It seems from the reports on here that is happening. I know ARB came out with those car coolers that would also heat many years ago, I am thinking they used this technology since they were very efficient.
__________________
Rick and Dianne, dogs Mikki and Athos
2003 Winnebago Journey 36 DL
Recently retired and now broke
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11-27-2024, 04:00 PM
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#75
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Senior Member
Join Date: Mar 2014
Posts: 214
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Quote:
Originally Posted by hclarkx
They do. With modern electronics, the inverter is quite small, but it's there somewhere. ......
Here's an image of a typical 12V brushless fridge setup using a Secor compressor. This one is in the current Novakool RFU-9000 fridge. The inverter is the box to the left of the compressor (about 2" wide, 5" tall, and about 5" deep).
.......
Also interesting (to me at least) is that the unit shown in this image is adjustable speed. ........
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Ok....so I see from your signature you have a 12v Refrigerator.....why not a residential refrigerator with an inverter to supply 120v ??
and what comment, if any, do you have on the 12v refrigerator offerings available ( I have the furrion and so far so good---but many people are reporting failures)?
Which 12v refrigerator do you have and why that model??
(nice pics on your site btw !!)
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11-29-2024, 04:37 PM
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#76
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Senior Member
Join Date: Jun 2017
Posts: 199
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Quote:
Originally Posted by patch-y
Darwin.... what is the latest on your refrigerator project? Did you get the Dutchaire? If yes how do you like it?
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Well, all finished except installing 2 new fans in the top of the old fridge roof vent which I will control with a switch on the wall above the dinette for extra hot ambient temps. I removed the large speaker under the old fridge on the old panel and put in a new panel to hold the 12v breakers, sniffer and two new 3.25 speakers. I didn't have to buy any trim, I re-purposed the wood door panels from the old NoCold for trim. The whole deal cost less than $3K. That includes fridge at $2725, $153 for the solar panels (200W) and charge controller, $15 for 60' of 10 gauge wire and fuse holders, $8 for bags of 30A and 15A blade fuses for fridge and controller, $11 for fans, $11 for roll insulation and $12 for 2x4s. Mounting the panels used about $17 for Dicor and stainless screws. I used some leftover shelves from my kitchen build and a 2 x 4 piece of leftover birch plywood for the base. Total, $2952
I'm pretty happy with it, the fridge is huge as is the freezer and the ice maker makes ice very quickly. The fridge is very quiet also. We've had some lower than normal temps here in SE coastal NC so I need to wait for a couple of sunny days and daytime 70-ish weather to get good data on battery consumption vs solar generation in "normal" use. I was able to do everything myself except get the old box out the door and the new box in. I paid my neighbor 20 bucks for that help so add that to the $2852
I am going to try and add some pictures here. Hopefully the link will open.
https://www.dropbox.com/scl/fo/kaz4y...it7d6b82f&dl=0
I would certainly recommend the Dutch Aire HVAC units. I stayed away from the 110 AC comp unit to avoid the 10-15% loss converting 12v DC to 110 AC. YMMV.
Darwin
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11-29-2024, 04:53 PM
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#77
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Senior Member
Join Date: Mar 2014
Posts: 214
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Quote:
Originally Posted by medarwin
Well, all finished-------
I'm pretty happy with it, the fridge is huge as is the freezer and the ice maker makes ice very quickly. The fridge is very quiet also. -------
I am going to try and add some pictures here. Hopefully the link will open.
I would certainly recommend the Dutch Aire HVAC units. ----
Darwin
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Congrats...nice job!!!........thanks for those great pics....keep us posted over the next few weeks..... nice looking refrigerator....
Patchy
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12-03-2024, 03:35 PM
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#78
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Senior Member
Join Date: Sep 2017
Location: Northern California
Posts: 1,617
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Quote:
Originally Posted by rickf
Interesting, I was using brushless motors in RC cars 30 years ago. Somehow I don't think they had circuit boards that small back then. But, I am not an electrical engineer so I have no idea. What I am looking for is a fridge that draws very little power and gets cold. It seems from the reports on here that is happening. I know ARB came out with those car coolers that would also heat many years ago, I am thinking they used this technology since they were very efficient.
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The earliest car coolers/heaters that I recall (could hold a six-pack, nothing more) were thermocouple technology. Two dissimilar metals held together with DC applied. DC in one direction caused cooling, in the other it was heating.
You may be confusing slip rings with brushless. Slip ring motors are sometimes called brushless. The slip rings provide dc to electromagnets on the rotor and last a long time compared to a commutator. A true brushless motor (no slip rings or commutator)" uses permanent magnets on the rotor. The RC cars I recall had three wires from the motor to the little control box. Those had permanent magnet rotors and three wires were needed to carry three-phase AC from the little matchbox sized control module to the motor stator. The inverter and speed control were in that little matchbox sized box. I still have a couple of those in the garage that the grandkids play with now and then.
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12-03-2024, 04:10 PM
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#79
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Senior Member
Join Date: Sep 2017
Location: Northern California
Posts: 1,617
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Quote:
Originally Posted by patch-y
Ok....so I see from your signature you have a 12v Refrigerator.....why not a residential refrigerator with an inverter to supply 120v ??
and what comment, if any, do you have on the 12v refrigerator offerings available ( I have the furrion and so far so good---but many people are reporting failures)?
Which 12v refrigerator do you have and why that model??
(nice pics on your site btw !!)
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My RV is not very large; 30' with kitchen (and fridge) on the rear wall. So I was limited space and weight-wise. And the DC fridge I got slid right in place of the Dometic 6.8 cuft propane unit (and upped my capacity to 9.1 cu ft).
Back when I went to a DC fridge, there was only one mfgr with many years of experience, mostly on small boats, and a stellar reputation. That was Novakool. I have the Novakool RFU9000 (single compressor, 9.1 cu ft, 2.5 cu ft freezer, freezer below, fridge on top, weighs 115 lbs).
The Novakool is ultra simple. At least the RFU9000 is. Not much to go wrong. Uses the Secor 35 compressor. Has lots of insulation.
The model I got uses inside air for the condenser which was important to me for several reasons. This allowed me to add 2" of R-13.1 foam insulation on both sides and the rear and 6" on top to reduce energy use. Also, I mostly camp at altitude and in cooler months so having the condenser discharge heat inside the RV was a nice feature. With all of this I could turn the compressor at lower speed to get 15% more efficiency and quieter operation.
My only quibble with Novakool was not being totally up front about how they get the higher energy efficiency. They do this in part by not running a 0 degree freezer. In the fine print the freezer runs 20F below the fridge. I wasn't happy when I discovered this. I partially fixed this by adding a small fan in the freezer that runs when the compressor is running and extracts extra "cool" from the evap plate in the freezer. This and running the fridge at 36F. It's still not a 0F freezer, but stays below 15F, usually around 10F. Always around or below 10F if I have room for 2" of foam behind the freezer door .. which I usually do because anything placed there tends to fall out when the door is opened.
The insulation I added favored the fridge more than the freezer, so that was partly behind the not so cold freezer. I was barely getting their 20F difference before adding the fan and other mods.
BTW, there is a model just above the RFU9000 that has dual compressors. I would get that if I had it to do over. Slightly heavier but the fridge and freezer have independent controls so the freezer can be set at 0F if desired. I think other of their models are available with this feature.
The Novakool units are (or at least were) made in British Columbia.
If you call them on the phone, an engineer answers (or did when I last talked to them).
Re other questions .... the optimized compressor and inverter in a DC fridge are far more efficient than a 120V inverter and 120V fridge. We are avid boondockers so efficiency is important.
I've noted the fairly frequent issues with other brands. I expect none of those problems with the Novakool. And none so far in the 7+ years I've had it (beyond fiddling with freezer temp). The old style thermostat and a Danfoss/Secor compressor leave little to fail.
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12-04-2024, 01:28 PM
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#80
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Member
Monaco Owners Club
Join Date: Nov 2023
Posts: 52
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Quote:
Originally Posted by hclarkx
They do. With modern electronics, the inverter is quite small, but it's there somewhere. In a typical brushless computer fan, it's a small annular circuit board about 1/8" thick and an inch in diameter. In a drill, it might be part of the trigger mechanism (i.e., attached to it or in the same casing). Maybe only a cubic inch in the case of a drill motor. In some small motors its literally built into the motor casing.
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While calling all brushless motor controllers inverters is technically correct, it's slightly misleading to non-electronic savvy people.
Most people are going to think of an "Inverter" as the common device that both boosts input voltage and converts DC to AC - for example 12v DC inverter that both boosts and converts 12v DC to 120v AC.
A brushless motor controller does not typically (but could if the designer desired) boost the input voltage, it typically will only convert DC to AC.
To be an inverter, the Dc to Ac conversion is all that's necessary and requires few electronic components.
__________________
01 Monaco Knight 36r 8.3 ISC
07 Chrysler Aspen Ltd 5.7 Hemi // 05 JGC Ltd 5.7 Hemi SASed rock crawler // 04 JGC 4.7L
09 Kaw Concours 14 // 13 Wildcat X // 20 Husqvarna FC 250
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12-05-2024, 12:46 PM
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#81
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Junior Member
Join Date: Nov 2003
Posts: 5
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Norcold 12V AWESOME
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