I am going to be helping a friend convert a bus (like "the

I apologize in advance for the TL;DR nature of this.

I have purchased three of the following
http://www.usplastic.com/catalog/item.aspx?itemid=35999&catid=459
(which are also the op pic) for use as the reservoirs in the system.

All three will be linked together, with the openings arranged so that they are at the top and bottom. The top will function as the points from which they will be pressurized and vented in the cases that the vehicle does not have electric or the reservoirs are being filled. The bottom will function as both the outflow and the points they will be filled from. The reservoirs will have a valve that can shut off the reservoir from the rest of the system so that if the vehicle has a water hookup it can run off that without the reservoirs being pressurized to the psi of the hookup.

The reservoirs will be placed inside the actual bus space, as close to the roof as possible, with adequate support (support going to the floor, and space taken up by the supports used either for other systems or turned into cabinets/storage so that space isn't wasted.) The main reason for this is that, while the bus will be guaranteed to have heating (through electric if there is a hookup, otherwise wood or propane), it cannot be guaranteed to have electric at all times and so if the drums were placed either on the roof or under the bus they would be susceptible to freezing.

The system would be arranged so that the reservoirs are the highest point that will be filled with water, and all the rest of the piping and the faucet and the hose hookup could be drained completely without power, with or without the reservoirs being including in the draining.

The actual pipe I am not sure of yet; I am vacillating between either pex (which would require insulation or another method of shielding them from UV) or schedule 40 PVC, with some brass fittings and portions (for the parts that go outside, or valves that will be repeatedly opened or closed--for pex all would be brass.) If pex, I will probably go with pipe insulation because I have a bunch from some recent demo work, but it is a bit large diameter for the purpose. It's not the split type pipe insulation.

The pros of pex in this situation are that it will be less of a pain to install, and is rated to a higher psi than schedule 40 PVC (which will be somewhat relevant later in the post) and if it does freeze will not crack (the drums are made of HDPE too, so should be the same, but not 100% sure) PVC does not require the pipe insulation, and would be easier to use larger pipe diameters as they are carried in big box stores and wouldn't need the insulation, so a 2" pipe would not take up as much space as 2" pex + insulation. PVC will also be significantly cheaper to use for larger diameter valves.

The reason for the larger diameter pipe is that it will provide better flow for the faucet and hose hookup this will be servicing in the event that there is no electric to run the system. I am, however, not sure how much of a difference the larger diameter pipe will make in this scenario.

Can anyone here with experience with unpressurized systems weigh in on the difference it will make?

As for the method of pressurizing the system: I am planning on using compressed air to pressurize the system rather than a water pump. The reason for this is that it seems like it will be cheaper, easier to install, and the compressor will not be prone to breakage the same way a pump would (because of debris, pumping air, etc.)

The system would be as follows: the small pancake compressor (which can pump to max 110 psi) is hooked to a regulator
https://www.freshwatersystems.com/p-11211-norgren-r91w2ak040-non-relieving-waterair-pressure-regulator-14-fpt.aspx
which regulates the psi down to 12, a short section of pipe connects that to another regulator which regulates it down to between 5-10psi (haven't decided yet) and in between the two regulators is a 15psi pressure relief valve. The second regulator is probably unnecessary but is there in case the first regulator fails, and the pressure relief valve is there as an indicator of the regulator failing. This then connects to the drums through the linked top opening. There will also be a second 10-15psi (not sure yet) pressure relief valve directly hooked to the reservoirs, past any regulators.

Is it better for the life of the compressor to compress to a higher shutoff when it kicks on, and kick on less often, or to compress to a lower shutoff when it kicks on, but kick on more often?

The drums themselves are rated to 100 kPa, which converts to just slightly over 14.5 psi. According to several posts online, similar HDPE drums can apparently handle more than that, some even reported up to 30psi, but I figured it would be best to have them operate under their limits, and from what people have posted online 5-10psi should be sufficient for use.

Can anyone that has used low pressure systems in the past weigh in? Is that enough for a decent usable flow, or is it going to be a pain to use?

Also lemme note that there are only three fixtures, the sink faucet in a utility sink, a hose faucet outside of the vehicle, and a faucet or connection for the most common campground hookup (even if this is the same as the hose faucet, so that the hose faucet can be used while the system is connected to a tap.)

The only part specifically bought for this so far are the three drums, so the project is not married to this design if it turns out to not be optimal.

Thanks for reading, will be checking back often and updating when my friend gets the actual bus here and we start work on this.

Just buy a ShurFlo 12v pump with 60psi switch for RV water supply like everyone else. You can mount the tanks anywhere and they won't need to be pressurized.

>>1026470
Those seem neat, and are about $40 cheaper than the compressor I was looking at. Since they're DC, how would you wire them in a system with an inverter /charger planned? From my reading it sounds like the inverter/charger needs to be the very first thing after the batteries. Do you have a converter before the pump? (I have never worked on an RV, as you can probably tell.)
Do those (or similarly priced pumps) have auto shutoff for if they are on and no water is getting used, or if the water runs out?
>You can mount the tanks anywhere
They're mounted in the bus because he spends winters in the PNW and has to worry about freezing, and can't guarantee he will have electric for a reservoir heating element, even with the batteries, but will definitely have heat inside the bus.

>>1026501
Also forgot to mention: he lives in the schoolbus for most of the year.

>>1026470
>>1026501
Actually looks like there are ac pumps that are similarly priced like this one
https://www.amazon.com/SHURflo-Industrial-Pump-Model-2088-594-154/dp/B0001FAA5Y#productDescription_secondary_view_div_1469193976909
So I'm assuming it would just be easiest to go with one of those in that case. And thermal overload protection would be what I'm wanting then?

Checked before when I read your post, but looked like ac pumps were more expensive than dc (like $200+), missed it cause cause on phone now and phone browsing is a pain.

>>1026520
Found another that is actually for potable water, ac, and better priced
http://www.pplmotorhomes.com/parts/cfp/plumbing-fresh/water-pumps-shurflo-revolution/86-8398.htm?utm_source=google&utm_medium=partsshopping&utm_campaign=partsfeed&jt=1&jap=1o2&js=1&jsid=36859&jcpid=8a8ae4cd48005458014820e2e0170ec4&jkId=gcp:se_36859:pp_55181564064:ag_15211804824:cp_194253624:n_g:d_m:cr_52737673584&gclid=CNjyl5uth84CFQyNaQodzCUCkA
However its still drawing about 5 amps more than the air compressors I was looking at, which is to be expected since the pumps are moving the water much faster. I think I will go with the pump, even if it means more amps, since its probably quieter too.

>>1026501

Not that anon, but you run 12v appliances straight from the battery (fused). You should be minimising anything that needs an inverter to run.

>>1026501
>Since they're DC, how would you wire them in a system with an inverter /charger planned?
You don't.
>>1026602
>Not that anon, but you run 12v appliances straight from the battery (fused).
This

Pic related is a shurflo pump sitting on top of a 55gal drum in the back room of a cabin.
The pickup tube is a length of 3/8" copper pipe that reaches to within one inch of the bottom of the drum.
The output of the pump goes through the filter to the plumbing of the cabin.
When a faucet is opened, the pressure drops causing the pump to come on in an attempt to maintain the pressure.
When the faucet is closed, the pressure quickly (seconds) builds up in the plumbing and the pump shuts off.
A $5 battery maintainer (~1A) keeps the battery charged.

File: IMG_20160722_142647157.jpg (374KB, 1280x720px) Image search: [Google]

374KB, 1280x720px

>>1026674
dropped pic

>>1026602
>>1026674
Okay so its a separate dc circuit with its own battery that gets charged by the main system if I'm understanding it correctly. That makes sense. Having the charger on a switch would be okay?

Thanks so much for helping me guys.

Any recommendations for a reliable inverter/charger? I don't mind spending more if its worth it, but don't want to spend for the very very best if its not significantly better than the second best. If that makes sense.


Planned inputs are shore power (from rv park or generator) converter from bus, and in the future he might want to add solar. Shore power will be 50amp, possibly with conversion plug to accommodate 30amp or 12amp. From what I understand that all gets handled at the inverter/charger, with breaker box only treating the line from inverter/charger as main, rather than 3-mode switch like how backup generators are handled for homes. Is that correct?

second the shurflo or similar. pancake compressors are loud as hell anyway.

>>1026453
>helping a friend convert a bus
>>1026454
>purchased three of the following
>>1026455
>method of shielding them from UV
>>1026456
>I am planning on using compressed air to pressurize the system
>>1026501
>Since they're DC, how would you wire them in a system with an inverter /charger planned?
>>1026520
>looks like there are ac pumps that are similarly priced
You're just 'lost' and have no idea of what you're attempting to do.
>>1026556
>Found another that is actually for potable water, ac, and better priced
This is what the guy is trying to get you to buy.
>>1026902
>a separate dc circuit with its own battery that gets charged by the main system
It gets charged by the bus alternator. There are dual battery diodes for setting this up.
You really should go look at some actual RVs. What you want to do is not new. Enough people have done it to find the best ways to do it.
>2" plumbing
>pipes insulated to protect from from UV
>round drums
>round drums overhead
>round drums overhead and pressurized
>appliances that only run on ac power
Your ideas are all shit ideas that could have been avoided just by finding out how an RV works.

>>1026934
>helping a friend convert a bus
>purchased three of the following
I'm not sure what the problem with either of these are.

>method of shielding them from UV
>pipes insulated to protect from from UV
Pex needs to be shielded from UV or it will fail. And in a fairly short time span. Most windshields block UV but side windows do not. I am assuming the bus side windows do not, so the pex would be exposed to UV. I realize that you do not need a thick layer of insulation to block UV, and taping the pipe (or painting, if cheap paint would actually stick to polyethylene) would work fine but I have a bunch of free pipe insulation.

>2" plumbing
It matters if the system is unpowered and not using a backup manual pump. As stated, I am not sure how much it actually affects flow or if it is a negligible amount, which is why I brought it up.

>round drums
>round drums overhead
I understand the concerns regarding failure, but I don't see how overhead failure would be much different from failure on the floor while in a bus (obviously different in a house attic vs crawl space.) This is done to save usable space. We may go with manual pump backups and keep them on the floor.

>I am planning on using compressed air to pressurize the system
>round drums overhead and pressurized
I have read about similar things being done, and the psi the drums would have been pressurized to would have been about half of their rated working pressure. I said that I was very open to other methods.

>This is what the guy is trying to get you to buy.
It's ac though, doesn't he want me to buy dc?

>You're just 'lost' and have no idea of what you're attempting to do.
I did some research online and believed I had come to the correct conclusion, but since this is something I have not done before and realized I could have come to a faulty conclusion I made this thread.

>>1026934
>>1026944
>It gets charged by the bus alternator. There are dual battery diodes for setting this up.
So the alternator charges both the battery bank for the inverter and the battery for the pump?
>appliances that only run on ac power
I don't understand. Why is this bad? Are there reasonably priced DC air conditioners and small chest freezers?

>You really should go look at some actual RVs. What you want to do is not new. Enough people have done it to find the best ways to do it.
I will do when I get a chance to see one in person.

>Your ideas are all shit ideas that could have been avoided just by finding out how an RV works.
I figured as much, since I 've never worked on an RV or even with DC. I did research online what I wanted to do, but I don't think I knew enough to effectively research. For instance, when searching "water pump potable" everything that came up was ungodly expensive or didn't meet the potable requirement (eg irrigation pumps.) When I searched with "shur flo" after that anon replied it was much more reasonable.

Thanks for taking the time to reply and try to help me. I appreciate it.

>>1026944
>>helping a friend convert a bus
>>purchased three of the following
>I'm not sure what the problem with either of these are.
Someone who knows what they are doing should be helping.
Those are ROUND drums. They waste space in rectangular environment

>>1026944
>>method of shielding them from UV
>>pipes insulated to protect from from UV
>Pex needs to be shielded from UV or it will fail.
Are they going to placed on the floor or along the walls of the bus?.
They should be behind/inside cabinets to protect them from everything.

>>1026944
>>2" plumbing
>It matters if the system is unpowered
It's vehicle. You shouldn't have considered un-powered in the first place.

>>1026944
>>round drums
>>round drums overhead
>I understand the concerns regarding failure,
Round drums waste space.
An extra 400 pounds that have to be supported for no reason. If the support fails there are 400 pounds of drums and water crashing down.
Overhead should be used for cabinetry for storage of small items, clothing, food, etc.
Lay the drums flat. Put a bed over the drums so he's not sleeping on the floor. Look for areas under the bus that containers could be fitted into.

>>1026944
>>I am planning on using compressed air to pressurize the system
>>round drums overhead and pressurized
>I have read about similar things being done,
Any leak that develops in the plumbing will be below the water line and result in the loss of all water into the bus. (you can't shut off the compressed air in the tanks)
The pump should be on a switch near the faucet and turned off during extended periods of non use. Turned on it's instantly ready for use. If it runs for more than a second when turned on and no valve is open, there is a leak. Turn it off and find the leak.

>>1026944
>>This is what the guy is trying to get you to buy.
>It's ac though, doesn't he want me to buy dc?
>it's ac though...
In the description of the followed link: This on-demand 12 volt DC pump is designed for all travel trailers, fifth wheel, campers, and motorhomes. The pump is high flow delivering 3 gallons per minute, with pressure up to 55 psi. It’s constructed to be reliable, low noise, and reduced cycling.

>>1026945
>So the alternator charges both the battery bank for the inverter and the battery for the pump?
Yes.

>>1026945
>>appliances that only run on ac power
>I don't understand. Why is this bad? Are there reasonably priced DC air conditioners and small chest freezers?
Air conditioners use a shit-ton of power. When driving, use the bus air-conditioner. When parked, use campground power to run an AC air conditioner mounted on the back or overhead. If parked without utility power, suffer with just 12v fans or get a small generator. You can't carry enough batteries to power an inverter to run an air-conditioner for any reasonable length of time.

There are refrigerators and freezers designed for RV use that run on ac/dc/propane. You'll need propane for cooking anyway.

When running on DC they do use a bit of power and will run the AUX battery down within a day or two. While driving it won't matter, the alternator is charging the AUX battery continuously.

>>1026987
Do not use an ac/dc/propane "ammonia cycle" fridge on dc. These things are power hogs and will drain a battery down very quickly. The dc setting is for travelling when propane is required to be shut off, and AC is not available. The vehicle's alternator will be powering the fridge at this point. If you want a DC fridge, find one with a Danfoss compressor. Cost is comparable to a new propane fridge

>>1026453
Like has already been stated in this thread: you want a DC pump. Anything that can be purchaced that runs off dc is cheaper long term in conversion/efficiency/inverter sizing costs. Also, square water tanks under the bed. They cost a bit more, but waste less space. It's a short bus, your "friend" is already limited in space. You also do not need 50a hookup for something that small. Only real loads might be a microwave and tv. Everything else should run off of dc or gas

>>1026982
>Someone who knows what they are doing should be helping.
Unfortunately for him, I'm all that's available. :-(
I do know what I'm doing when it comes to stuff in houses, and have the tools necessary for this project, even if I come off as clueless in this thread (which I am; I've never camped in an RV or even thought about them until this project.)
>Those are ROUND drums. They waste space in rectangular environment
I realize this, but couldn't find any rectangular ones that were explicitly potable safe (some are HDPE but are listed as not meeting FDA resin requirements or not suitable for foods) more than 5gal capacity and less than 275gal capacity. I liked the idea of rectangular ones better too, but this was the best I could find.

>Are they going to placed on the floor or along the walls of the bus?.
>They should be behind/inside cabinets to protect them from everything.
Walls.
They will be behind cabinets and other such structures wherever possible, but the whole thing will not have cabinets throughout so I can't guarantee that it will always be hidden behind them. There's also the issue of them being easy to access to diagnose and service while on the road without having to remove things to access them. My friend will have to fix anything that pops up on the road.

>It's vehicle. You shouldn't have considered un-powered in the first place.
This is a design constraint that his lifestyle places upon the project. In a best case scenario he would always have power, but it can't be guaranteed.

>Round drums waste space.
I agree with you, but they're the best available.

>>1026982
>>1027000
>An extra 400 pounds that have to be supported for no reason. If the support fails there are 400 pounds of drums and water crashing down.
I would ensure that the supports were adequate if we went with overhead. I do see your point, though.
>Overhead should be used for cabinetry for storage of small items, clothing, food, etc.
I agree with this, and we will put such cabinetry in definitely regardless of where the drums end up. We will plan out the whole layout before starting to install anything so space will be as efficient as possible.
>Lay the drums flat. Put a bed over the drums so he's not sleeping on the floor.
He already wants a bunk or loft, but if they go on the floor we will definitely make use of the space above them.
>Look for areas under the bus that containers could be fitted into.
There are such areas, and they would be a really efficient place to store water, but with the potentially no electricity requirement that would leave them open to freezing.

>Any leak that develops in the plumbing will be below the water line and result in the loss of all water into the bus. (you can't shut off the compressed air in the tanks)
I'm already going with the pump rather than the compressor, but this is a valid point I hadn't thought about--I had planned a valve shutoff to the compressor and a shutoff from the tanks, but in the former the tanks would still be pressurized even if not connected to the compressor and in the latter it would stop a leak in the plumbing past the drums but not a leak on the drums themselves. I suppose that could be guarded against with draining catch pans but that would be a huge unnecessary hassle. Good catch.

>The pump should be on a switch near the faucet and turned off during extended periods of non use. Turned on it's instantly ready for use. If it runs for more than a second when turned on and no valve is open, there is a leak. Turn it off and find the leak.
Will do and good point.

>>1026987
>In the description of the followed link:
Well I feel retarded now. I have no idea why I thought that pump was AC.

>Yes.
Awesome. That's what will be done then.

>Air conditioners use a shit-ton of power. When driving, use the bus air-conditioner. When parked, use campground power to run an AC air conditioner mounted on the back or overhead. If parked without utility power, suffer with just 12v fans or get a small generator. You can't carry enough batteries to power an inverter to run an air-conditioner for any reasonable length of time.
That is what was planned, and I already bought him a generator he's using now. From my reading though it sounded like the generator should still go through the batteries like campground power and not directly power the ac, since it will both power the batteries and run the ac that way (unless that's what you meant.)

>There are refrigerators and freezers designed for RV use that run on ac/dc/propane. You'll need propane for cooking anyway.
>When running on DC they do use a bit of power and will run the AUX battery down within a day or two. While driving it won't matter, the alternator is charging the AUX battery continuously.
We were going to put in propane, but I don't know if he wanted to have it be a main thing for powering stuff. Will run it by him.
For the freezer we were going to use one of those mechanisms that turn the chest freezer into a fridge and plug between the freezer and the outlet and just forgo a separate fridge entirely.
Will definitely look into those types of chest freezers.

Thank you for your exhaustive reply, it's very helpful and brings up things I hadn't considered at all.

>>1026990
Would you recommend a normal ac freezer then, or just not using the dc when not driving, or something else?
Will look into a freezer with a danfoss compressor.

>>1026992
Don't worry, we'll be going with a dc pump. I feel silly for entertaining the compressed air idea at all now.

I'll look again and if I can find some square tanks that are potable safe and similar capacity, I'll buy those instead.

The 50 amp is not so much because it needs a 50 amp by itself, but my reading made it sound like some campsites only have a 50 amp or a 30 amp but no 12 amp hookup, and a 50 amp regardless of your actual power needs allows you to use all three via conversion plugs converting down from 50 amp.

Thanks for your help.

>>1026990
Also thanks as well, forgot in other post.

>>1027000
>I realize this, but couldn't find any rectangular ones that were explicitly potable safe (some are HDPE but are listed as not meeting FDA resin requirements or not suitable for foods) more than 5gal capacity and less than 275gal capacity. I liked the idea of rectangular ones better too, but this was the best I could find.
>>1027010
>I'll look again and if I can find some square tanks that are potable safe and similar capacity, I'll buy those instead.
Of course now I google "square hdpe drum potable" and this comes up as first result:
http://m.plastic-mart.com/product/913/55-gallon-portable-utility-tanks-sp0055-mm
Not sure what I was searching the first time around, but I did look through all of uline and usplastics without finding a square one that met requirements before.

>>1027005
The difference between ac/dc/propane and straight ac or straight dc, is that the combo fridges use the ammonia cycle which is power hungry. Basically it uses a large heater or propane to heat ammonia to a gas, using latent heat of vaporization to cool the fridge. A dc compressor fridge obviously uses a much more efficient compressor

I'm the guy who is giving you all the grief, You've been a real sport about it and very generous in your acceptance of the advice. Thanks for not getting butthurt about it. I really do want it to turn out well for you and for the guy you're helping.

>>1027005
>Would you recommend a normal ac freezer then, or just not using the dc when not driving, or something else?
>>1026506

I don't know what size the freezer is but it runs off AC (with it's charger) or off 12VDC and even has it's own internal battery which will last at least eight hours.

With a matching connector wired to the AUX battery in the bus it would run significantly longer without and AC power.

>>1027107
Ah. I talked to him and while we will be installing propane to cook and as a backup heating system, he wants to keep as much as possible on electric (so long as reasonably efficient) since he is planning on solar and a gas generator being his main power sources, and gas for the generator is more ubiquitous than propane. I'm not actually helping with the solar part, except so far as making sure anything we add won't conflict with it when he adds it later.

>>1027152
No worries. If I didn't want my ideas mercilessly picked apart, I wouldn't have made a thread on /diy/. I'd rather be told I'm an idiot with dumb ideas, have it explained why those ideas are dumb, and then build it correctly than have my ass kissed and then build something stupid.

I saw that thread, and something like that seems like what we'd want. The only reason we were aiming for AC for the freezer is to do this:
http://newlifeonahomestead.com/convert-chest-freezer-to-fridge-solar/
TL;DR device plugs into outlet, plug freezer into device, temp sensor from device goes in freezer, device restricts freezer running based upon freezer temp.

>>1027152
>>1027322
PROS:
-Uses less energy than normal freezer or fridge (probably not less than a DC chest freezer though)
-More efficient than normal fridge or freezer when opened
-Can switch between fridge or freezer easily
-If no power, chest freezer becomes regular unpowered ice chest
-Can use top of chest freezer to set things on or as countertop when not opening or closing
-I can buy a decent small chest freezer at Sam's Club for $70-90.
CONS:
-I don't think they have such devices for DC chest freezers
-Have to stack food in fridge/freezer on top of each other
-Condensation collects in bottom of chest freezer when used as a fridge, have to wipe out about once a week with towel
-Can't have both fridge and freezer at the same time

A lot of those pros apply to any chest freezer, not just AC chest freezers running as fridges, but being able to turn the freezer into a fridge is a huge plus. I don't think they have such devices for DC chest freezers, but will check after this post (on phone atm, so if I switch to another tab it will eat this post.) If there are devices for DC chest freezers then we'll probably go with DC, if not then if the difference for DC chest freezers compared to AC chest freezers is really that large then we may actually get one DC chest freezer and compare running an AC chest freezer as a fridge to a DC fridge, and get the better of the two options for use as fridge.

>>1027324
DC. It is expensive, but you can find them used from time to time, and the cost of the unit is offset by the requirements of battery and inverter upgrades required for a cheapy ac chest.
http://www.backwoodssolar.com/sundanzer-8cf-refrigerator

>>1028276
It looks like there are not any devices (called "external thermostats" apparently) for DC freezers, and he only has room really for one unit (chest freezer or fridge) so being able to switch as needed is crucial. He was also planning on putting in as many batteries for AC inverter as possible already, limited by weight and space rather than cost, so it wouldn't be costing more in materials. Logic on that is the more batteries he has, the less he has to drain them and the longer they will last, and the more "free energy" he can take with him from hookups and he wont have to run the generator as often.


Since a 5.0 cu ft AC chest freezer only has a 1.69 amp draw, we will probably go with that or a more efficient AC chest freezer if we can find one of similar size and good cost:increased efficiency ratio.

The chest freezer and the AC unit should be the only major appliances that will need AC. For the run time of the AC all he really is shooting for is enough battery capacity to run it overnight from full charge without going to less than 40% or having to run the generator, as he (and the people around him) would prefer he doesn't run the generator during sleeping hours. Charging with it the next day is fine. Very preliminary planned batteries for use in all systems in next post

>>1028802
Planned batteries are
https://www.amazon.com/Optima-Batteries-8016-103-BlueTop-Starting/dp/B00075OSCO
Batteries are 55 ah. Planning 8-12 of them depending upon what else gets put in and planned layout. That 8-12 is only for inverter, will have additional batteries for DC systems as needed. Also read about proper wiring, so will be doing that: equal lengths 4 ga wire to positive and negative terminuses, the inverter is wired to those two terminuses.

Also in case
>and the longer they will last
was unclear, I mean last longer as in the life of the batteries.

>>1028802
>>1028276
Actually, wait. It looks like some DC freezers have a coarse adjustment screw that is not hard to access but still less convenient than the regular thermostat, that effects the regular thermostat. So you once you set you have 0-40F instead of -40-0F like the factory settings, and that's basically what would be wanted and would forgo the need for an external thermostat. So a DC freezer that can be adjusted to that it is then.