how do I connect 24v fridge to 48v battery?

[breaker1nine]

not sure what part i need because i dont know if i need the step up or step down version.  

24v dometic fridge lets say, connecting to my 48v lithium battery.  im looking for a voltage converter or regulator?  

I need the best efficiency too.  

could someone help me find the part i need to make it work.  

p.s.  no i dont want to use an inverter and go ac.  i want the best efficiency. and i cant find a 48v refridge to fit in my van.

thanks everyone who helps!

 

[Trebor English]

Do the math.  Some DC fridges that will run on 12 or 24 volts use less power on 12 volts.  If you are converting from 48 it migbt be slightly more efficient to go to 12 rather than 24.  

I would Google step down buck converter.

 

[tx2sturgis]

You need a DC to DC converter.

Or you can tap into the battery bank at 24 v (across 2 batteries) if you have 4, individual, 12v batteries in series.

 

[scottorious]

Do DC to DC converters draw power even if the appliance is off? That's a question I've wondered. I'm in the same boat. I have 48 volt batteries and I'm trying to figure out which direction to go. Up to AC or down to 24 volts. If you're set on going to DC, do you know if you want to go 12 volts or 24? Going to 12 volts means you might not need to buy 2 converters if you plan to have some things in 12 volts.

Here is a high current(15 amps continuous) converter to go from 48 to 12(You mentioned 24 but I wasn't sure if you currently own that dometic or if it can also do 12)
https://www.powerstream.com/dc48.htm

Maybe with that you can run the rest of your rig at 12 volts instead of having a 48 volt system, a 24 volt system and 12 volt system.

 

[breaker1nine]

Dometic CFX 40w fridge . Input voltage (AC) 120 V
Input frequency 50/60 Hz
Rated input power (AC) 60 W
Rated input power (DC) 60 W
Rated input current (AC) 0.72 A
Rated input current (DC) 7.0 A
Input voltage (DC) 12/24 V

Scott that powerstream link part was interesting. >88% efficiency at maximum load at maximum power output(272w). they dont mention how to figure out 60w of usage. i suck at math and appreciate the help here.

48v single battery is packing 3.4kWh in a foot by a foot cube weighing in at 75.5 lbs. I could get 24v lithium but they dont have the capacity of the 48v. I could get 2 and have the capacity but that would take up space i dont have to spare and weigh more wasting my fuel efficiency on the road. SO ya i will be on one single 48v battery to provide me with my space and capacity needs at the greatest efficiency.

I need the parasitic info on the dc to dc converter and compare it to just buying another dc to ac inverter to run the Dometic on just big enough to support the fridge. I already have a 48v ac inverter 600w for my computer that uses average 75-120w and will be using the laptop to charge all my stuff from it.

 

[tx2sturgis]

If the 24v device is OFF, then just turn off the DC-DC converter. 

But if you need power to it all the time, such as with the Dometic Fridge which has electronic controls, then you can't turn off the DC-DC converter.  

So now you need to figure efficiency losses AND parasitic losses. 

Many years ago the automotive industry was in debate about how to shed pounds for the latest round of EPA laws regarding efficiency and mpg ratings. 

One of the proposals was to change the automobile voltage standard to 36 volts, or more. This would mean that all the wiring harnesses could be much smaller gauge, and lighten the vehicle by maybe 50 or 100 pounds, since copper wiring is HEAVY. 

In the end, I think there was just TOO much 'resistance'...

 

[bonvanroulez]

Edit: Sorry, brain f**t.

 

[tx2sturgis]

I did some looking around at the specs for this Samlex unit. This one can provide 30 amps at 12 volts and that would give you a lot of spare capacity if needed. 

It is not cheap, but efficiency is rated at 85% and up, and the standby current is rated on the Samlex website at about 25 ma....which is very low.

Samlex makes good stuff, and I own and use a lot of it, but I have never tried one of their DC-DC converters.

https://www.amazon.com/Samlex-IDC-360C-12-Isolated-Converter-regulated/dp/B0073I1HR2

 

[John61CT]

Victron and MasterVolt also come to mind.

I also am very perplexed why anyone would try to use a high-voltage propulsion battery pack to power ordinary House loads.

Everything at 48V will be super expensive, and all you gain is a little savings in wire gauge.

Also without all the protective electronics and cooling systems originally included with that pack, it is very dangerously prone to thermal runaway, i.e. exploding into flames.

Out of the dozens of "lithium" chemistries, only LFP does not have that risk.

 

[Weight]

I would be very afraid to keep a re-purposed battery of that size in my van. And, I missed how you recharge this thing.

 

[ChetLazar]

The fridge start up surge is at least twice the normal running current.  The surge could be ten times the normal running current.  If you get a 48 volt to 12 / 24 converter that can't handle the starting surge the fridge could activate the low voltage shut down as it tries to start.  

The only way to tell is to try it.  The fridge surge has an amount of current and a duration.  Each device will vary.  The converter capacity to handle a particular amount will have a duration limit.  You don't know either the current surge amount or the duration.  It is not specified.  

One approach is to get a huge 48 to 12 converter.  A monster that could start a DT466 school bus diesel engine will start your fridge.  The down side with that is that efficiency at 2 amps will be lower on a 1000 amp converter.  

A 12 volt to 120 volt 60 hertz inverter can be expected to be about 80% efficient, some a little better.  Expect a similar efficiency.  Inside a 48 volt to 12 or 24 volt dc - dc converter you have basically the same stuff just in a different order.  An inverter starts with a rectifier/filter to make dc.  Then there is the switching, coils, and capacitors to change the voltage.  At that point the inverter puts out the ac.  A dc - dc converter has the rectifier/filter on the output end to make dc output from the switching, coils, and capicitors part.   A dc-dc buck converter combines some of the output rectifying with switching so there aren't totally separate parts on the schematic but the function is in there.  

The price of electronic stuff depends highly on sales volume.  Inverters for 12 to 120 (US, Canada) or 240 (everywhere else) have volume.  A 48 volt powered 12 or 24 volt power supply will not.

 

[John TF]

It would help us to help you if you gave model's devices being used ?
As an example , you say a Dometic 24v fridge , I did not know they made a 24vdc fridge , I thought there were only 12vdc in the 3 way units ?
And with no info about battery , can not even begin to help , some have inter-connects that you could change the voltage ?

 

[breaker1nine]

3 x https://www.altestore.com/store/sol...efficiency-solar-panels-p40891/#PAN330HITMONO
1 https://www.altestore.com/store/dee...-tech-lithium-batteries-p40602/#SIMPHI3_4-48V
1 https://www.altestore.com/store/cha...lexmax-60-mppt-solar-charge-controller-p6875/
1 https://www.altestore.com/store/inv...ure-sine-wave-inverters-p40496/#SAMPST-600-48
1 https://www.dometic.com/en-us/us/pr...-boxes/powered-boxes/dometic-cfx-40w-_-152176

that should be the info you needed people. I require power to make money in my skills or nomad is out for me. 48v is becuase of efficiency and capacity concerns. i will also have a 2000w inverter to handle appliances if I have to use it and will only be on as i need to use appliance. I guess I could just run the Dometic via the ac inverter. I would have to check the spike Chet was talkin about.

 

[scottorious]

Not to throw a kink into your plans but there's some good info about running a 120V freezer on an inverter and using a DC thermostat to trigger the inverter on and off. I haven't found a 48V thermostat though.

 

[John61CT]

OK my apologies for thinking this was just a recycled EV pack.

The AltE shop should be able to supply what you need, either a very high capacity 48-to12V DC-DC converter or a bunch of small ones, the rest run off mains power via inverter.

So much for efficiencies.

Personally, not for the OP but for others considering such an expensive LFP pack, best to stick with 12V unless you are doing propulsion or have an aircon unit or something else that specifically requires a higher voltage.

For exactly the reason demonstrated here, the thousands of excellent and inexpensive devices available at 12V are just not there at higher voltages, or cost many times more.


OP are you possibly within your exchange window with them to switch back to an all-12V system?

All the higher voltage buys you is lighter gauge copper for your wiring, which is not that big a savings in a mobile context.

 

[MrAlvinDude]

Would a DC-DC converter that charges a 12V battery be a way to go?

This way, the 12V battery would power the fridge when ever it was running, and the DC-DC converter just needs to continually charge the 12V battery at the average amperage needed over a time period, and does not need to be able to handle neither the 60W nor the motor start surges.

A rough estimate of the 0.665 kWh/24h turns out to be about 2.4A per hour @12V.

A 3-5 amp output DC-DC (down buck) converter might be cheaper/easier to find compared to  120W peak DC-DC converter.

Well, just a thought anyway.

 

[breaker1nine]

ahh something like this :  https://www.amazon.com/GOLF-CART-vo...4800&sr=8-14&keywords=48+to+12+volt+converter

 

[breaker1nine]

yes gsfish, 2k inverter for stuff like induction cooker or rice cooker or pressure cooker and only will be used in daytime with excess solar days to do some food prep like cooking down 4-8 cups of rice for storage, or cook down 8 chicken breasts or whatnot, that is unless i can camp out of my van, then i can cook via solar cooker device, which will be fun to start cooking that way, and using propane cooker.

there is no such thing as a single 3.4kWh battery that is 12v unless they are wired in series, and as for todays tech stands, that lithium isnt good with series but ok with parallel. My solar will be in parallel 3 panels pushing 330w each for total max in lab of 990w. that should be enough to charge my battery for the power i draw from it all day and night even on crappier days with less sun and many other factors. thats why i need such a large capacity of storage, unfortunatly 12v batteries that are lithium dont go up to 3.4kWh unless you go parallel, but then that would take up more space which i want to avoid. I only have the fridge to worry about on 12v. I dont have any 12v needs. I just want my computer to run with a bad day , all day and night without being charged. 48v was only option. I have a whole complete quote from the store I want to buy from and their experts put everything in I needed except the 48 to 12v converter which i think they didnt sell. their suggestion was to buy another inverter and use the ac connection from the fridge.
990w of solar on top of a chevy express cargo van regular size. I did measurments and looks possible, air vent will be that cool trick thru the licence plate I saw somewhere.

 

[tx2sturgis]

 air vent will be that cool trick thru the licence plate I saw somewhere.

lol....that would me mine...

 

[John61CT]

Note I'm not trying to argue against the OP here, so please feel free to ignore this, just FYI for others coming in via google afterwards looking at their options.

Cooking from electricity for a long time each day will use a lot of even very large solar array's output, no matter how much battery, using propane is much more sensible.

Computer gear runs at DC voltages natively, running off an inverter loses a lot of efficiency.

If you're spending thousands on an LFP system, you can get cells in all kinds of shapes and sizes, even the largest capacity 180AH only are say 7-8" tall on their side, they can sit stacked in any position

Letting the physical space you want to fit the batteries dictate what voltage you're going to run at makes no sense, to me. For a big expensive bank getting a steel box to hang under the chassis would not be expensive.

You do need to make sure you don't try to charge LFP in below-freezing temps.