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 > Electrical: DC AC Conversions - Efficiency

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road-runner

Oregon

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Posted: 09/12/17 06:18pm Link  |  Quote  |  Print  |  Notify Moderator

I took a look at the Danfoss web site and couldn't find any information that would help make a conclusion about AC vs. DC efficiency. Maybe somebody knows where to find this info?

I got the impression that the Danfoss compressors are variable speed, which suggests to me that the motors are non-60 Hz AC motors, further suggesting they are driven using a variable frequency inverter. Is this inverter powered by AC or DC? Does the 120 volt AC input simply get converted to 12 or 24 volt DC? Does the DC input get converted to 120 volt AC? Will using your own inverter be more or less efficient? Or is it something altogether different? Without knowing info like this, actual measurements with using different power sources will be the only way to find the efficiency information. Is this data already available, or is it waiting for somebody to figure it out?


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Bigg Al

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Posted: 09/12/17 06:21pm Link  |  Quote  |  Print  |  Notify Moderator

100 Amp Hours.


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BFL13

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Posted: 09/12/17 06:28pm Link  |  Quote  |  Print  |  Notify Moderator

How far is the fridge from the battery bank? You need short, fat wires for 12v but thin, long wires will do the 120. If the inverter is close to the battery bank, as is proper, you can locate the fridge anywhere to be run on 120. You might be having a big inverter anyway like that, so then why not use it to run the fridge too?

There is more to this than electrical efficiency. Generally, when RVing you don't give a rat about efficiency, as long as you can get it all done. The main thing is not to run out of battery at 3AM and get to the next recharge time mid-morning.

Practical considerations are what count when RVing. Running long, fat wires is not practical. Efficiency is way down the list of things to worry about. [emoticon]


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time2roll

Southern California

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Posted: 09/12/17 07:07pm Link  |  Quote  |  Print  |  Notify Moderator

TWH99 wrote:

I still need some clarity regarding Amp Hours when wiring batteries in series.

If I have two, 12 volt, 100 Amp hour batteries and I wire them in parallel I will have a battery bank of 12 Volts with 200 Amp Hours.

If I wire those same two 12V, 100 Amp hour batteries in series, I will have a 24 Volt battery bank. How many Amp hours will my 24 Volt battery bank have?


12v 200 amp/hours = 2400 watt hours (12 x 200)

24v 100 amp/hours = 2400 watt hours (24 x 100)

same energy, same weight, same foot print, same volume.

https://www.lithiumion-batteries.com/pro........teries/24v-100ah-lithium-ion-battery.php

http://lithionicsbattery.com/product/24v........e-case-with-internal-neverdie-bms-copy/?


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TWH99

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Posted: 09/12/17 08:33pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks TimetoRoll and Bigg Al,

My application is a Mobile 20 foot travel trailer that I will travel & l live in full time. I would like to run everything on battery, re-charged by solar Photo Voltaic cells. I will have a generator (Honda EU2000i) for back up. I will have a fixed, non-expandable physical space for the battery bank in the trailer. The wire run between battery bank and 3000 watt inverter will be less than a foot long and wires from solar panels to the battery will be relatively short also, but the longest less than 15 feet long.

1. Are these wiring lengths going to be helped significantly regarding resistance with the 24V system? I think I prefer the simplicity of a 12V battery bank for charging/operating the devices I have that can be plugged in to my 12 volt receptacles, and by-passing the inverter which uses power and produces heat.
2. I will run a 5K BTU window unit air conditioner that will have a start up surge of about 200 Amps (12 volt), will run with compressor on using about 40 Amps (12 volt). With 600 Amp hours of Lithium, 80% useable = 480 Amp Hours, I should be able to safely run the small Air conditioner for 8 hours. Will running approximately 500 watts continually for 8 hours through the Inverter be “hard” on it, shorten it’s life, increase energy consumption as it heats up.? Do I need to worry about any of this or is it only a concern when the constant load is much closer to the Inverters regular capacity. In my case if I had a high quality 3K Watt Inverter (3500 surge for 5 seconds) could I run it continuously at a 2000 or 2500 watt load for 8 hours without it skipping a beat or shortening it’s lifespan?
3. Recharging the 600 Amp hour battery pack. The Inverter/Charger combo unit says in it’s shortened spec sheet: Charger-125AC Efficiency – 88%. I’m guessing the efficiency relates to the Inverter and means for each 100 units of Battery power it draws it only converts 88 equivalent units to the device being powered…is that correct? What does the 125AC mean regarding the Charger? Does it mean it can pump in 125 Amp hours back into the battery each hour assuming the power supply can keep up with that? If not what does it mean 125AC.
4. As related to #3 above, if I am using a small Honda EU200i generator to recharge the battery bank (assume no PV solar panels working) and no draw on the battery bank, and the Amp hours on the battery has been drained down to 20% or 120 Amp Hrs, roughly how long will it take to charge the battery bank back up to 600 Amp Hours or what is the hourly rate of recharge in Amp Hours. I’m not sure what the relevant numbers are on the Honda spec sheet that relates to recharging a battery but one of these must be it. AC output – 120V 2000W max. (16.7A) 1600W rated (13.3A). and DC Output – 12V 96W (8A) and Receptacles 20A, 125V Duplex
5. Lastly, please confirm if this recharge calculation is correct for Solar Panels. A clean, properly angled, 100 watt panel, in 70 degree weather will be about 80% efficient during the peak hours equaling 80 watt charging rate per hour which equals 80W / 12V = 6.6 charging Amps per hour or 10 hours of full sun to put in 66 Amp hours into the battery bank.

Thanks to anyone who has stayed with me and is willing to answer some or all of my questions.
Tim

theoldwizard1

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Posted: 09/12/17 08:44pm Link  |  Quote  |  Print  |  Notify Moderator

TWH99 wrote:

I have heard other RV people say, if going with a large setup and starting from scratch (not up grading 12V) a 24V system is best. Is it as simple as increasing the volts (doubling it in this case) cuts the Amps consumed in half ...

The big win of higher voltage battery bank is less energy lost due to voltage drop (heating the wires) between the battery bank and the load. 24V is good, 48V is better, BUT other than inverters and a few other items, there are not many 24V/48V appliances.

TWH99 wrote:

I will be doing a Lithium Battery Bank. Is a 24V, 100 Amp lithium battery roughly the same price and physical dimensions and weight of a 12V 100 Amp lithium battery.

Twice the energy, so twice the cost.


TWH99 wrote:

Anything less expensive…like smaller gauge wire, less resistance with long wire runs due to higher voltage?

If you down size the wire much, you will have voltage drop issues again.

TWH99 wrote:

All things being equal, is their longevity or durability differences between a 12V and 24V system.

Not really, but I think that 24V inverters are built a bit more "robustly".

TWH99 wrote:

I’m guessing the reason for not upgrading from 12V to 24V is all the major components must be also be upgraded, thus there is not much from the old 12V system that is useable in the new 24V system.

They do sell 24VDC to 12VDC converters. If you are only going to be running lights (hopefully LEDs) and maybe a TV and a cell phone charger, this should be all that you need.

theoldwizard1

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Posted: 09/12/17 08:52pm Link  |  Quote  |  Print  |  Notify Moderator

TWH99 wrote:


My application is a Mobile 20 foot travel trailer that I will travel & l live in full time. I would like to run everything on battery, re-charged by solar Photo Voltaic cells. I will have a generator (Honda EU2000i) for back up. I will have a fixed, non-expandable physical space for the battery bank in the trailer. The wire run between battery bank and 3000 watt inverter will be less than a foot long and wires from solar panels to the battery will be relatively short also, but the longest less than 15 feet long.

Short wire runs from the battery bank to the inverter is a BIG WIN ! Stick with a 12V battery bank, but I would go UP one wire size just for peace of mind.

Depending on how many hours a day you are running in the A/C off of the battery bank will be the deciding factor on how many solar panels you will need. That and the "fixed, non-expandable physical space for the battery bank". You may only get a couple of hours (at best) of A/C usage after the sun goes down !

Check into getting a "soft start" for the A/C.


The restricted battery bank space is likely going to kill all of your plans.

* This post was edited 09/12/17 08:59pm by theoldwizard1 *

BFL13

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Posted: 09/12/17 09:18pm Link  |  Quote  |  Print  |  Notify Moderator

Sometimes you can carry extra batteries in the towing vehicle and jumper them to the trailer's batteries for more AH.

pianotuna

Regina, SK, Canada

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Posted: 09/12/17 09:27pm Link  |  Quote  |  Print  |  Notify Moderator

The most efficient way would be to run right from the battery bank.


Regards, Don
Full Time in a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

TWH99

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Posted: 09/12/17 10:29pm Link  |  Quote  |  Print  |  Notify Moderator

thanks for the comments theOldwizard1
"Check into getting a "soft start" for the A/C."
Yes, soft start is a good idea!
BFL13 - another good idea, stow extra batteries in tow vehicle. My batteries will be inside trailer so might be a hassle to "jump" them. They are so dang heavy I don't see myself moving them around. Would have to create a door on exterior of trailer to access the batteries. I think my biggest problem will be not having enough roof real estate for the solar panels. But this "plan" is still about 2 years out in the future so maybe there will be more compact options for solar panels then.
Piano tuna -yes, by passing the inverter for all 12v needs is the most efficient.

Another question: are the 3-way refrigerators, when used in the 12v mode, way less efficient (needs more watts to run) then the newer compressor refrigerators of equal size? I had heard that was the case but it was not quantified. If yes, More efficient by 10%, 50% or ?? anyone know?

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