Fridge Advice - Weird space to fill
- Thread starter iggi
- Start date
Mwilliamshs
Explorer
Please explain.
Mwilliamshs
Explorer
Danby DCR044A2BDD-3 4.4 cubic foot dorm fridge Energy Star Rated 115v AC
vs
TruckFridge TF130 4.6 cubic foot mobile fridge 12v DC
Most comparable models I found in a quick search.
TF130 is intensely documented here and thesamba, etc. Amp draw is widely accepted as 2 amps when running. There are common mods to lower this number with different fans, controllers, etc.
Danby is described by their tech support and BestBuy as 4 amps starting and 1 amp running. Let's say 2 amps for an average number.
How often they'll each in run in the same installation is hard to say. Let's assume it's equal since installation methods, cabinetry, environmental factors, etc vary so widely.
So, 2 amps @ 13v DC = 26 watts
And 2 amps @ 120v AC = 240 watts
To get that AC we need an inverter. The best ones are about 95% efficient. So 240 is now 252 watts. Inverters peak efficiency is typically about 30% load. A high-quality, pure sine wave (a must for efficiency if no other reason) inverter rated for 750 watt output (continuous, not peak) is a couple hundred bucks. You might say so what, I'll use for other things, and that's fine, but for transparency you'll have to account for the loss of refrigeration or the reduction of inverter efficiency at higher loads. The inverter is a necessary component in this system by the way. Wherever in the world you are, that expensive and hard to find (go ahead, google it) electronic part is essential. For the DC fridge, there are fewer parts and no fancy electronic gizmos at all (if you can succinctly explain how an inverter works, feel free to disregard this part).
So, $200 4.4 cu. ft. dorm fridge plus ~$200 inverter = 250 watts
Or
$700 4.6 cu ft TruckFridge = 26 watts
The more/better insulation argument is a wash IMO. The truckfridge goes inside a cabinet. The fridge is already insulated but if you want more insulation, insulate the cabinet. Simple. The dorm fridge however, is insulated but is also free-standing and needs to be because it rejects condenser heat through its metal skin. They all do this now. So not only is there no reasonable way to improve the dorm fridge's insulation, it also requires air circulation over its skin which in effect means it needs more space.
luthj
Engineer In Residence
Energy star is kinda a joke though. I will admit the small 120v fridge category is awash with inefficient crap in the USA. Europe has much better options. I will try to find my notes, but a top tier dorm sized fridge on a inverter (switched by thermostat to reduce standby power), was about the same as a isotherm of the same volume using the BD50 compressor. The dorm fridges compressor was a bit larger than needed, so it ran a max of 30% duty cycle, even in hot weather.
billiebob
Well-known member
I've been looking for coments on the Dometic CRX series. Glad to see you like yours, I'm looking at the CRX80.
I'm definitely not a fan of the kits but they might give the OP the flexibility he needs.
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luthj
Engineer In Residence
I was looking at swapping a 12V compressor onto a small fridge. Its actually quite simple. You need to rent/borrow a vacuum pump, and the pill port adapter. You need a digital scale to measure with, and a 12oz can of 134A. Buy or find a 12V compressor. Desolder the old compressor, and solder the new one in. Connect the thermostat to the compressor control terminals. Evacuate the lines for a few hours. Then recharge by weight.
Mwilliamshs
Explorer
Yes Energy Star ratings are dubious. That's why I included every other specification.
So you'll buy a fridge and ship it from Europe? $$$
And need a Euro-spec inverter to get 240v AC @ 50 hz from 12v DC $$
A very expensive inverter, that will be difficult to replace when it dies and that won't be usable by any other appliances.
Or will you also carry a travel adapter for your laptop charger? $
We've gone from Paddy saying AC is more efficient, even with inverter inefficiencies, to Luthj (love your sprinter 4wd project btw) saying with exotic appliances AC is about the same.
Where's paddy?
Mwilliamshs
Explorer
That DC fridge at less than 30 watts is gonna be TOUGH to beat by anything on an inverter. A 240v Euro fridge at a ludicrously low number like 0.25 amps (more like an LED lamp than fridge) is still 60 watts without considering a very good inverter will lose 5%.
63 is a LOT more than 26.
63 is a LOT more than 26.
shade
Well-known member
I agree, in that it's important to consider the entire system, as you did when considering a typical dorm fridge's need for ventilation space around the exterior cabinet.
As an example, when I was shopping for a 12V fridge, I ended up with an Indel B model, partly because it used the same Danfoss compressor as much more expensive brands, like National Luna. Even with the same compressor, the Indel B was less efficient due to the superior insulation offered by National Luna. It wasn't enough of a difference for me to justify the significant premium, but it did make a noticeable difference in power consumption.
iggi
Ian
@luthj @Mwilliamshs Thanks for all the excellent info!!
Mwilliamshs
Explorer
Explaining this to the little woman and found her response enlightening.
"So the AC fridge would need more than 2 solar panels and the DC fridge takes less than 1?"
She's referring to 100 watt solar panels. She's hazy on how it all works together but the way she sees through to watts vs watts is a great illustration of the differences here.
"So the AC fridge would need more than 2 solar panels and the DC fridge takes less than 1?"
She's referring to 100 watt solar panels. She's hazy on how it all works together but the way she sees through to watts vs watts is a great illustration of the differences here.
5spd97
Member
I just installed a 100 amp/hr Lithium iron phosphate battery and went on a 10 day camping trip with no hookups. The battery powers the 45l Truck Fridge, a 10" fan which runs all night, a few lights, and charges all of our devices. After 7 days the battery was still at 12.6 volts whch is close to what my two old FLA 95 amp/hr batteries started out at fully charged. I have 200 watts of solar but I park in the shade so I'm lucky to see 1 amp/hr at best. I keep the fridge at about 40F and we were camping above 5,000 ft so the ambient temps were pretty comfortable, thus less demand on the fridge. I ran the generator for about an hr just to test my new converter/charger but I probably could have done the whole 10 days w/o the generator.
Mwilliamshs
Explorer
Lot of holes in the story but I'll try to get some numbers from it. Have to assume 6 entire days and nights since 7 days is kinda vague.
At 12.6v your lithium iron phosphate battery is between 50 and 60% charged so you'd gotten roughly 50ah out of it at that point plus whatever you'd put back. Between solar and the generator, assuming those are your only means of charging, you probably added about 55ah. 1a x 6 hours a day x 6 days is 36ah plus at least 20a in that hour of generator use assuming even a very small charger/converter and likely much more given the rapid charging capabilities of your battery.
So at first glance it would seem you used about 100ah in 7 days.
BUT
Popular camping fans like the Maxxair 6-in-1 and the Fantastic Endless Breeze pull 2-3amps so in an 8 hour night that's roughly 20ah x 6 nights is 120ah.
A 45L TruckFridge eluded me but I found 51L and 41L portable models and a 49L fixed unit on their website. They all appear to draw at least 1amp over the course of an hour in moderate climates when used conservatively as reviewed on Teardrops and Tiny trailers, this site, etc. So 6 days x 24 hours = 144 hours x 1 amp = 144ah.
Add charging devices and lights at say 5ah a night x 6 nights = 30ah.
That's 294ah of use. From a 100ah battery that's roughly 50% charged. Guessing you charge from your alternator while driving or your solar works a lot better than you think or...?
5spd97
Member
Oh man, now your gonna make me get into the details, haha. First of all I'm not trying to spoof anybody; whatever my loads, temps, solar input, etc, works out to be; my point was that we managed to camp like we typically do 6 or so times a year, only this time I wasnt constantly screwing with the batteries and generator. LiFePo4 batteries are real pricey but I'm stoked about their performance.
As to the details. 7 days is 7 days. We set up at about 4:30 on a Friday afternoon and I waited until about the same time the next Friday afternoon before I ran the generator for about an hour. The converter/charger is 45 amp/hr but that is kind of immaterial to the 7day discussion.
My house battery is not connected to the alternator.
We use a large combination of independent lighting methods so as to minimize the draw on the house battery. That will change as I get comfortable with the new battery. We use solar Luci lights, $3 solar landscape lights, AA cell battery led lights, and two 10" long rechargeable led lights from the clearance rack at Walmart.
Our 12v fan is a 10" O2cool ordered from Walmart and runs off of D cells, a built in rechargeable battery, and AC/DC. It defaults to AC/DC if its plugged in, then to rechargeable, then alkaline D cells. I have no idea of its current draw but its no where close to 2amp/hrs.
I was wrong about our fridge because I was going from memory which apparently ain't great. It's a TruckFridge TB41A. We open it a couple of times in the morning and afternoon. I've never timed how much it runs but I would guess 15-20 minutes an hour and it appears to draw 3-4 amps when running.
We charge our two Ipads, phones, flashlights, led reading lights, etc, off of a brick initially and then recharge the brick from the house battery. We have no cell or wifi signal so the phones and Ipads are off or in airplane mode most of the time.
I quit worrying about the solar panel output during warm weather camping because shade is more important, but I've got it so I let it contribute what it can. I have an Mppt controller and can usually depend on 0.5 amp from sunup to sundown with periods of 1 - 1.5 amp from time to time. Who knows, it may have brief periods of 10 amps.
A typical trip with the two 95 amp/hr FLA batteries would go like this: after about 48hrs the first battery would be down to about 50% so I would switch batteries and put it on the charger for about two hrs. We try to minimize generator run time because it annoys everyone including us, therefore the battery would get some bulk charging, maybe a little absorption, and no float. It would probably be at 80-90% charge at the end of the two hrs. The other battery was weaker so it would only make it a day before I'd switch back to the first battery. Basically I was running the generator for two hours every day. Granted both batteries were 5 years old so they were beyond their primes.
Now to the lithium battery. Fully charged it started at 14.4 volts. The biggest voltage drop that I noted from day to day was 0.2v. So 0.2 x 7 days = 1.4 volts. 14.4 - 1.4 = 13.0. I think lithium discharge is fairly linear so the reading of 12.6 at the end of 7 days seems reasonable. The lithium can be discharged nearly 100% without damage and I can recharge at 45 amp/hr so I wont even need a spare gas can if I decide to bring the generator.
I'll conclude by saying that if your assumptions and math dont support my statements then you're using the wrong assumptions. Obviously the solar was contributing more than I thought or the fridge is using less power, but at any rate we camped for a week running the setup that I have described without any auxiliary power. On top of that after running the generator for an hour on Friday afternoon, we never ran it again and we broke camp on Monday morning. I just went out an looked at it and the panel shows 13.2v.
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