24 VDC roof air

[jjrbus]

It is just too hot out to do anything and my nap is over.  So I was doing a bit of surfing and came across this.  A 24 Volt DC RV air conditioner.

http://www.topleadercompressor.com/Products/2012/0611/16.html

Interesting possibilitys.    Jim

[fred heath]

If you only want to cool the bathroom. Small btu output. More for a truck cab than a mh coach.

[jjrbus]

2?

[Derek up North]

1 hour ago, fred heath said:

If you only want to cool the bathroom. Small btu output. More for a truck cab than a mh coach.

7850Btuh isn't that small.

[fred heath]

40 minutes ago, Derek up North said:

7850Btuh isn't that small.

That's for the 2300 watt unit. The 1400 watt unit only produces 4777 btu. Less than the 5k btu a/c you buy at WalMart for less than $100.00.

Now add the cost of the rooftop unit ($$$) along with two dedicated 12 volt batteries wired in series to accommodate the 24 volts required. And lets not forget our trucks run on 12 volt not 24. So you will need some type of converter to change 12 volt charge to 24 volt charge. And if that's not enough, you still need a place to locate all the extra batteries and related weight.

When all said and done, you get from 3 to 5 hours of cooling.

Like I said, good for a tractor cab or a bathroom.

[Derek up North]

Your bathroom is wired for 24v? 

[linda s]

There's a 12 volt one listed.  I like it. Wonder how much they cost. Bet it will run on a Honda 2000

http://www.topleadercompressor.com/Products/2013/1010/59.html

Linda S

[jjrbus]

I found a 24V on Ebay for $390.  Interesting the only vehicles I know of that run on 24V DC are buses. Most other vehicles are 12 volt that I know of?  I asked if they are available in 12 volt, so will see.   Without doing any figuring, the wires for 12V are going to have to be a large gauge with a big alternator.  

They are calling it 7000 BTU and I believe many early Toy's came with 7 and 8K units? 

http://www.ebay.com/itm/RV-Motorhome-Trailer-Roof-Top-Air-Conditioner-DL-1800-24v-7000-BTU-Cooling/262483526917?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D36866%26meid%3Da04c77091a3447c9879a122c842817c4%26pid%3D100033%26rk%3D1%26rkt%3D4%26sd%3D262483526917

[zero]

7 hours ago, linda s said:

There's a 12 volt one listed.  I like it. Wonder how much they cost. Bet it will run on a Honda 2000

http://www.toenpleadercompressor.com/Products/2013/1010/59.html

Linda S

How the heck would you run it on 12 volts with a 1600 watt Honda AC generator?   Specs say it needs 55 amps @ 12 volts to run, and that means around 150 amps @ 12 volts to start.   I guess you could get huge 150 amp rated converter and hook it to the Honda.  What would be the point?

[zero]

One added comment on the DC units. I don't see any advantage.  E.g., the smallest one is the DL1200 that has 4800 BTUs of cooling and needs 55 amps @ 12 volts to run.

A window unit from Home Depot with 5100 BTUs of cooling, made for 120 volts AC, will run on 40 amps @ 12 volts when hooked to an inverter.

[Maineah]

There are some new advancements in small AC units that use inverter technology to soft start and variable speed drive horizontal compressors making it possible to use smaller generators like a Honda. It is new technology but advancing rapidly being used now for homes in DC units up to 16,000 BTU boarder line solar power. I still think that battery powered AC units no matter what are going to be energy hogs that will require a fairly large battery bank and a good charging system. The 24 volt units were geared more so for sleeper boxes on large trucks as they all ready use 24 volt systems. The RV industry tried DC AC units and gave it up as a bad ideal on large motor homes but we may see them again in the very near future.

[zero]

As I understand it, inverter-AC units need the same power to get started as conventional AC units and it is that starting current that is the main issue with RVs. The advantage to an inverter-AC unit is it can be run steady all day, at a slow speed and low output.  Unlike a conventional AC unit that is either "on" or "off."  Panasonic uses the same "inverter" tech with their AC units as they do with their microwave ovens.  There is no overall savings in power use. It's more of a slow  & steady current draw, instead of a high-draw, medium-draw, - low-draw unit.  I don't use electric powered AC anywhere so can't say it's something I've ever cared about.  Inverter microwave, yes.  NOT to be confused with inverters we use in RVs to turn DC power into AC power.   A unit that turns DC into AC "inverts" the power to mimic a sine-wave for AC power. I.e. it makes it jump up and down, 60 times a second.  An inverter AC unit or microwave - has a little buzz box (pulse width modulation) that allows a normally "on", "off" device to become a variable speed or heat unit instead.

[Maineah]

They are using the inverter to ramp up the compressor slowly avoiding the heavy demand of starting a motor full speed this reduces the inrush of high current making start up current far lower They are also have horizontal scroll compressors that help reduce high head pressure problems.. Many are now using inverters to modulate temps by slowing the compressor instead cycling it at the same time slowing the condenser fan. The technology has come from the mini splits they are marvels of technology.most now are producing usable heat at !7*F. at a far lower energy cost. A good clue is the diminishing feed wire size.

[zero]

3 hours ago, Maineah said:

 A good clue is the diminishing feed wire size.

I'm not expert but I do know this.  Smaller wire does not have to mean better efficiency. Just means less starting current.  A slow start at low amps often in the end - equals a fast start with high amps.  Same reasoning why many high-draw appliances can be wired in 120 volts or 240 volts.  240 volts use smaller wire but no gain in efficiency.

[Totem]

 

LOL... all that just to justify not running a nice 2500 watt inverter genny (from any manufacture other than Honda), coupled with all of its expense, weight batteries, but hey the unicorn  sure is pretty.

or you could just get an EU3000...

 

 

Edited June 16, 2016 by Totem

[jjrbus]

Got an answer from the seller, they do not carry it in 12V.   I'm disappointed would be fun to play with! 

It is not because it is practical or the best way to do it,  it is because it it available.    

[Totem]

I once mused in this forum on trying to rig a bunch of batteries and run a rooftop unit off of a large power inverter; I am thinking that would be a better choice than a 12 volt truck AC that does 1400 BTU.

[jjrbus]

I used to run a 13.5K roof air off my battery bank with a Trace DR3624 inverter. 

[Donnie]

11 hours ago, jjrbus said:

I found a 24V on Ebay for $390.  Interesting the only vehicles I know of that run on 24V DC are buses. Most other vehicles are 12 volt that I know of?  I asked if they are available in 12 volt, so will see.   Without doing any figuring, the wires for 12V are going to have to be a large gauge with a big alternator.  

They are calling it 7000 BTU and I believe many early Toy's came with 7 and 8K units? 

http://www.ebay.com/itm/RV-Motorhome-Trailer-Roof-Top-Air-Conditioner-DL-1800-24v-7000-BTU-Cooling/262483526917?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D36866%26meid%3Da04c77091a3447c9879a122c842817c4%26pid%3D100033%26rk%3D1%26rkt%3D4%26sd%3D262483526917

You can get around the 12 / 24 volt fiasco by using a series-parallel  switch  . 2 of my busses had this set up..   2 12'2 or 4 6's...  4 6 volts may be a bit much for a Toyota............ just a thought...   Donie

Edited June 16, 2016 by Donnie

[zero]

13 hours ago, Donnie said:

You can get around the 12 / 24 volt fiasco by using a series-parallel  switch  . 2 of my busses had this set up..   2 12'2 or 4 6's...  4 6 volts may be a bit much for a Toyota............ just a thought...   Donie

Have you looked at the price of a high-amp series-parallel switch lately?   Pretty expensive and kind of negates the project since there is no gain to start with.  Those 12 volt and 24 volt DC air conditioner units use more power then a cheap unit bought at Walmart or Home Depot that runs on 120 volt alternating current.  But yes, you are certainly correct.   If someone really wants an AC unit that runs on 12 volts - hooking a cheap inverter is likely the most cost-effective way to do it.  In theory, if your motorhome has something like a 200 amp alternator, you could run it on 14 volts while the engine was running.  Not going to happen in any Toyota I know of. Not enough drive-belt to run any alternator over 70 amps that I know of.

Kind of off-the-point a bit, but have you ever seen the setup on a Chevy diesel K5 Blazer when the US military used it?  Talk about convoluted!   Uses 24 volts for something (like starting) and 12 volts for other things.  Runs dual alternators and dual batteries. One alternator for each battery and a small series-parallel switch for when 24 volts is wanted.  John Deere sort-of did the same on a few tractors, until some engineer at AC Delco dreamed up the 12-12-24 volt system with no chassis ground and NO switch.  System was part 12 volt neg-"ground", part 12 volt pos-"ground" and part 24 volt.  What a mess.  Came out in the mid 1960s and people are still pulling their hair our trying to figure it out, or make it work.  

[jjrbus]

Unlike us the gov can afford to do things like that! 

24V seems to be far more practical than 12V and I have never understood why it is not used in the auto industry?

[Totem]

15 hours ago, jjrbus said:

I used to run a 13.5K roof air off my battery bank with a Trace DR3624 inverter. 

just curious, how many batteries and type, and how long would it run without engine running? was this in a toy?

[jjrbus]

Not in a Toy, an MCI with a 24V 240 amp oil cooled alternator and 4 golf cart batteries.   There was no vehicle air and the most efficient way was to run roof air with the inverter.

The only time the AC ran off the batteries without the engine running  was when I did not pay attention,  the 4 batteries would run the air for 30 minutes or so.  When the AC shut off I would think oop's

[zero]

35 minutes ago, jjrbus said:

Unlike us the gov can afford to do things like that! 

24V seems to be far more practical than 12V and I have never understood why it is not used in the auto industry?

Because there was never a need for it.  6 volt systems presented problems with cold-starting and voltage drops.  Especially with diesels.   When 12 volt became pretty-much standard - there was no need.  Besides, in some ways, 24 volt systems are less reliable.  Wires are finer in starter and alternators and do not hold up well to vibration.   That all said, as I assume you know, 24 volts DC has been the operational standard in our military for a long time.  Since most cars and trucks have gas engines, and the distance from starter to battery is short, 12 volts, neg ground, has been the best compromise between performance, cost, and reliability.  In the 50s and early 60s, diesels often had 24 volt cranking systems to avoid voltage drop in tractors where the distance between batteries and starter was a lot longer then in a car or small truck.  Since then, 12 volt starter tech improved and eliminated the need for a 24 volt cranking system. I still have a 24 volt system on my Allis Chalmers HD6 bulldozer.

[Maineah]

20 hours ago, jdemaris said:

I'm not expert but I do know this.  Smaller wire does not have to mean better efficiency. Just means less starting current.  A slow start at low amps often in the end - equals a fast start with high amps.  Same reasoning why many high-draw appliances can be wired in 120 volts or 240 volts.  240 volts use smaller wire but no gain in efficiency.

No one wants to buy heaver wire than is needed unless they have money to burn. The new units use far less energy and by doing so they do not need a #8 wire to do what a #12 will.

 

7 minutes ago, jdemaris said:

Because there was never a need for it.  6 volt systems presented problems with cold-starting and voltage drops.  Especially with diesels.   When 12 volt became pretty-much standard - there was no need.  Besides, in some ways, 24 volt systems are less reliable.  Wires are finer in starter and alternators and do not hold up well to vibration.   That all said, as I assume you know, 24 volts DC has been the operational standard in our military for a long time.  Since most cars and trucks have gas engines, and the distance from starter to battery is short, 12 volts, neg ground, has been the best compromise between performance, cost, and reliability.  In the 50s and early 60s, diesels often had 24 volt cranking systems to avoid voltage drop in tractors where the distance between batteries and starter was a lot longer then in a car or small truck.  Since then, 12 volt starter tech improved and eliminated the need for a 24 volt cranking system. I still have a 24 volt system on my Allis Chalmers HD6 bulldozer.

It took the US a long time to realize that 6 volt systems were not cutting it. The British had 12 volt systems way back in the 30's and 40's First it saved them lot of copper and second it was far less prone to current loss from poor connections etc. The Germans are using very small wire in their vehicles carefully calculating distance to use the smallest gauge wire they can.I can see in the near future single runs of current carrying wire with fiber optic control and #20 wire running lights etc.

[jjrbus]

I knew that 24V used smaller wires, up to 6 times smaller.  Never did think of the smaller wires in a starter or alternator. 

[zero]

59 minutes ago, jjrbus said:

I knew that 24V used smaller wires, up to 6 times smaller.  Never did think of the smaller wires in a starter or alternator. 

Six times smaller?  No,  The figure is usually only 2 times smaller when switching from 12 volts to 24 volts.    I.e. a circuit with 12 volts and 10 gauge wire has an equal voltage drop to a circuit with 24 volts and 13 gauge wire.  10 gauge is exactly twice the size of 13 gauge wire.

[jjrbus]

39 minutes ago, jdemaris said:

Six times smaller?  No,  The figure is usually only 2 times smaller when switching from 12 volts to 24 volts.    I.e. a circuit with 12 volts and 10 gauge wire has an equal voltage drop to a circuit with 24 volts and 13 gauge wire.  10 gauge is exactly twice the size of 13 gauge wire.

I do not remember where I came up with the 6 times figure?  It was on the internet so must be true!

[86rader]

Interesting topic. I always thought that some sort of small DC unit to cool only the cabover section would be a good idea. I think I speak for most toyhome owners in that coach AC is used primarily for sleeping and that most of them are couples or singles. Insulate the area well, use an insulated reasonably air tight curtain and I see no reason why you couldn't cool the area with maybe 1000-1500 btus. I have one of those cheap 5K window units at home and it cools a small bedroom easily. A cabover compartment is a very small fraction of even a small bedroom's volume. Why use a 13.5K unit to cool the whole thing when you only need to cool the sleeping area.

As for charging a 24V bank, you could either go the inverter route or, with a bit of extra wiring and switching, you could conceivably charge the batteries in parallel and switch them to series during use. Of course this means you could not charge while using them.

If I ever get back into the toyhomeowner game (sold the Odyssey last year) I would look into it.

If you really did a good job insulating, I wonder how small you could go, BTUwise? Does anyone have any figures on how much heat a pair of resting adults generate?

 

 

 

[Derek up North]

27 minutes ago, 86rader said:

Does anyone have any figures on how much heat a pair of resting adults generate?

 

Sleeping:- 80w each

Seated quietly:- 120w.

http://www.wiley.com/legacy/wileychi/al_shemmeri/supp/powerpoints/chapter_5.pdf

[jjrbus]

7 hours ago, 86rader said:

Interesting topic. I always thought that some sort of small DC unit to cool only the cabover section would be a good idea. I think I speak for most toyhome owners in that coach AC is used primarily for sleeping and that most of them are couples or singles. Insulate the area well, use an insulated reasonably air tight curtain and I see no reason why you couldn't cool the area with maybe 1000-1500 btus. I have one of those cheap 5K window units at home and it cools a small bedroom easily. A cabover compartment is a very small fraction of even a small bedroom's volume. Why use a 13.5K unit to cool the whole thing when you only need to cool the sleeping area.

As for charging a 24V bank, you could either go the inverter route or, with a bit of extra wiring and switching, you could conceivably charge the batteries in parallel and switch them to series during use. Of course this means you could not charge while using them.

If I ever get back into the toyhomeowner game (sold the Odyssey last year) I would look into it.

If you really did a good job insulating, I wonder how small you could go, BTUwise? Does anyone have any figures on how much heat a pair of resting adults generate?

 

 

 

For me in FL the real downside to the Toy is insulation and single pane windows.   It barely has any insulation and the single pane windows are almost anti R value!  I would hazard a guess that 1 1/2" in walls that is 2 3/4" layers at angles to each other and 3 inch in ceiling with thermo windows would make a usable rig.  Thermopane windows are heavy so not a good option. I made 3/4" insulating foam covers for mine in the cab area

DC AC is likely not a good option but in dealing with people that think 20+ year old RV's are a good idea, so all bets are off.