โJan-30-2021 09:45 AM
โJan-30-2021 08:08 PM
โJan-30-2021 06:00 PM
theoldwizard1 wrote:NRALIFR wrote:
Yeah, that would have to be a very special inverter to produce 3-phase AC from 12v DC. The curiosity in me wonders how they do it.
CORRECTION ! Some models now use brushless DC motors instead of three phase !
Quick review of how a single phase inverter works. You will be sorry you asked ! I was an EE !)
"High frequency" inverters "switch" the incoming DC ON and OFF at 40KHz-10-KHz. This "square wave" AC is the sent to one of more transformers (high frequency transformers are smaller than low frequency transformers) and the resultant voltage is >180V peak-to-peak AC. This then converted (rectified) back to high voltage DC (>150V DC). A separate circuit makes a "synthetic" 60 Hz sine wave. This sine wave is sent to a Class-D amplifier that is powered by the +150VDC.
"Low frequency" inverters skip the step up stage and rectification stages. They still synthesize a 60 Hz sine wave and send it to a Class-D amplifier that use 12VDC. The AC output has to have enough power to drive a VERY BIG transformer that steps it up to 120VAC.
For 3 phase, you do it 3 times, making sure each of the synthesized 60Hz reference sine waves is exactly 120ยฐ out of phase with its predecessor.NRALIFR wrote:
This is a screen grab of the DC unit thatโs supposed to be for my fridge. 12V 7.5A 90W
I donโt see anything that I can identify as a dedicated power conditioning device, so I assume itโs inside the sealed can???
Nope. It is not in the picture.
Danfoss is one of the few manufacturers of DC powered refrigeration compressors. Note the box on the side. That is where the magic happens !NRALIFR wrote:
So, from a power efficiency standpoint, which would be the better way to go? AC conversion kit, or DC?
My GUESS is that the DC conversion would be a bit more efficient. 3 phase motors are always more efficient than single phase.
Last, I will through in inverter manufacturers are making a TON OF PROFIT these days. The actual cost of parts between a modified-sine wave inverter and a pure sine wave inverter is probably <$50 maybe even <$25. The most expensive part inside these things is the transformer (lots of copper and steel).
For some reason the low frequency inverters (you know they are low frequency because they weigh a TON) seem to be more "durable" but I don't know why.
โJan-30-2021 05:45 PM
NRALIFR wrote:
Yeah, that would have to be a very special inverter to produce 3-phase AC from 12v DC. The curiosity in me wonders how they do it.
NRALIFR wrote:
This is a screen grab of the DC unit thatโs supposed to be for my fridge. 12V 7.5A 90W
I donโt see anything that I can identify as a dedicated power conditioning device, so I assume itโs inside the sealed can???
NRALIFR wrote:
So, from a power efficiency standpoint, which would be the better way to go? AC conversion kit, or DC?
โJan-30-2021 05:10 PM
โJan-30-2021 04:58 PM
โJan-30-2021 04:18 PM
โJan-30-2021 03:34 PM
NRALIFR wrote:What are the wattage specs? Does the DC version actually have a DC compressor or is there an included inverter? If it does have an inverter is it 3-phase or single phase? I think a 3-phase inverter driven by DC would be very efficient.
So, from a power efficiency standpoint, which would be the better way to go? AC conversion kit, or DC?
:):)
โJan-30-2021 02:39 PM
โJan-30-2021 02:20 PM
NRALIFR wrote:
Yeah, that would have to be a very special inverter to produce 3-phase AC from 12v DC. The curiosity in me wonders how they do it. Iโm familiar with rotary and static AC phase converters, but not DC.
โJan-30-2021 01:42 PM
theoldwizard1 wrote:rdhetrick wrote:
Because the conversion isn't an absorption refer - it's a compressor similar to a household refer.NRALIFR wrote:
Thatโs probably what I would recommend. No DC-AC conversion loss.
Every 12/24VDC compressor refrigerator actually INCLUDES its own inverter ! The incoming DC voltage is converted to 3 phase AC and sent to the compressor motor. 3 phase is used because it is a much more efficient way of powering a motor.
Just to be clear, this "built in" inverter is specially designed just for this application. The AC output voltage does not have to "match" any "standard". It can be whatever voltage the inverter and motor designers choose ! Also, many (most ?) of these inverter are variable frequency meaning that the compressor motor itself runs at different speeds as the required.
If I lost you, a DC compressor refrigerator is likely more efficient than a straight up residential AC refrigerator powered by a separate inverter.
โJan-30-2021 01:35 PM
โJan-30-2021 01:18 PM
โJan-30-2021 12:47 PM
woodtrucker wrote:
We are on shore power almost always except for traveling. Would the truck charge battery enough to keep the 12VDC unit cooling while on the road?
โJan-30-2021 12:39 PM
rdhetrick wrote:
Because the conversion isn't an absorption refer - it's a compressor similar to a household refer.
NRALIFR wrote:
Thatโs probably what I would recommend. No DC-AC conversion loss.
โJan-30-2021 12:15 PM
enblethen wrote:
Why convert is my question!