trikes and weight savings for higher fuel milage

[ghurd]

Heat.
Bio-D too complicated.
Maybe WVO.
With all the circumstances around here lately for the solder guy and myself, did not have time to do anything worth reporting.  The available time to tinker with WVO was used up with that dang timer.

And the wife threw out my two nearly full 64oz jugs of semi-new only-slightly-rancid-smelling oil 6 weeks ago.
Don't know what she was thinking!
G-

[Bruce S]

Heat.
Bio-D too complicated.
Maybe WVO.
With all the circumstances around here lately for the solder guy and myself, did not have time to do anything worth reporting.  The available time to tinker with WVO was used up with that dang timer.

And the wife threw out my two nearly full 64oz jugs of semi-new only-slightly-rancid-smelling oil 6 weeks ago.
Don't know what she was thinking!
G-

WVO, good way to go. save the stockings and strain the WVO through those to clean it. Good cheap cleaning, will be clean enough to blend with heating oil. 50/50 is what neighbor used as a test in his shed as a test to show his wife they could use that and still be warm, without the smell of mess.
Oil sat settling for 3 months so water was not a problem.
A cute quick and fairly clean strainer is funnel shaped old metal window screen then stockings, if HOT outside then big cheapest you can find coffee filter.
Pepa did his by long term settling in big plastic containers and it looked as good as any new bottle. NO smell either

 

[Bruce S]

If you need lots of power under 50cc, there are lots of choices that run on gasoline.  Here there is a 4.5 hp engine.   

http://www.rtfskymasters.com/home/rc-vehicles/hpi-baja-5b-ss-kit/ 

They may even make a turbo for these guys....  Kinda what we need for the supermileage car (higher compression).

I will not need that much power I don't think. Pretty cool way to jump into having a good high-performance engine 

The local shop that I purchase propane in bulk ( 90lbs at a time) has a shop that will convert my gasoline engines to single, dual or tri-fuel at cost for kit plus $35/hr so long as the engine is in good running order.

I want to get the frame sorted out, drive motor in place. I already know that the 550watter 48V isn't going to cut it and still be able to get going from a standing start.

Through rough calculations of what I have minus  body I'm looking at 400lbs. My 150cc scooter weighs in at 680lbs after taking off the extra "stuff" and it currently gets 92mpg using a "few modifications" once the warranty was out.
I can list those who are looking to purchase a scooter for fuel sipping
Even the 49ccs we modded work much better.

 

[ghurd]

My 150cc scooter weighs in at 680lbs after taking off the extra "stuff" and it currently gets 92mpg using a "few modifications" once the warranty was out.

This is probably an off topic twist, but...

A couple friends have those BIG Goldwing class bikes.  Those are like 1400cc now?
They are grown-up, so they don't drag race or drive them 125MPH.
They all claim to get about 60mpg "crusing around", whatever that means.
One guy kept track for like 3 years.  Half the time it has his wife on it.  Pretty sure he said 62 or 64 mpg.  It's a Kaw.

The 150cc is only 50% better than the ~1400cc?
Why?
Fairings?

Anyway.  What if someone took something like a 250cc Honda Rebel and added some fairings?  Maybe tweaked with better air cleaners and exhaust system?  Etc.
Any idea what MPG that would be?

G-

[taylorp035]

Based on your photo on page 1, 400 lbs is a lot of weight.  Our car this year will weigh only ~105 lbs.  Last year's used fiber glass, steel, and aluminum for the frame and it weighed 180 lbs.  Add another 50 lbs for the larger dimensions and extra lights and a proper seat + a bit more for a better transmission and you get ~ 250 lbs.  Using carbon fiber, you could cut 50+ pounds out of that number if you tried.  The power required will definitely need to be more than a 550 watt dc motor.  I would get a 1500 Watt brushless out runner (the bigger version of my starter motor).  Using a Castle ICE controller, it will not have any start up issues that plague most smaller brushless in-runner motors.  Plus, there will be no maintenance and they take tons of abuse (3 combat robots and a starter motor - all with little to no support by extra bearings).  RPM's should be useable (390 kv).  Plus, with the ICE controller, you will have data logging, which is super easy to use.  No load power use is very low (full speed on 12v is about 30 watts @ 5k rpm, as low as 2 watts at idle speed).

But you have a wattage limit of 749 watts     I got too excited there....   Well, nothing is labeled in watts (only on the data sheets), and I doubt the inspector will think that such a tiny motor could put out 1 hp (2" x 2").

If you double the wind resistance and the rolling resistance compared to last year's SMV, then you should get half the mpg's or about 300-400 mpg.  I guarantee that you could get over 200 mpg because there were several teams in year's past that have weighed ~500 lbs and no aerodynamics and have gotten 200 mpg.  The key is not to run the engine while you are coasting (the biggest breakthrough for SMV cars).  If you run the engine for the whole time, the best that you can do with a really good SMV car is ~200 mpg unless you have a special hit and miss engine.

So are your plans to go electric or stick with the 49 cc engine?  Starting an engine 1000's of times can be harsh on the starter if not built right.  Else you have to run with the engine on all of the time.  The batteries should prove less problematic too, as small engines love to stop working.  You would also have to change the oil every 20 hours or so.  And if you push the engine too hard, it could overheat in a contained environment.

[taylorp035]

In response to Ghurd's efficiency question, there are 3 main things that eat your power.

1) Air drag
2) Rolling Resistance
3) Transmission

and then there is the efficiency of the engine, which is linear to the mpg.

You can't change the transmission much, but a single stage belt or chain would be best.
Engine efficiency is probably a big factor between the 150cc and the 1400cc.  OHV is much better than L-head.
Air drag is probably a bit higher on the 1400 cc, but not by much.  Average speed is very important since mpg is related to velocity squared.
Rolling resistance is most likely close to the same, since the scooter will have lower pressure tires and a smaller diameter yet it weighs many pounds less.

So if the factor is only 2x between the scooter and the Goldwing, then I am not surprised. 


EDIT:

And for the golf ball approach, using bubble wrap will do this easily.  I did watch the mythbusters episode...  11% improvement.  That is amazing.  I wonder if it is any better.  We could test the theory out in our wind tunnel at school I guess.




EDIT 2:

If found some smarter people who had a good discussion about the golf ball effect.

http://www.physicsforums.com/archive/index.php/t-417914.html

In conclusion, most tests are inconclusive at best.  Another worth test came in at 2% in lowering the CD, which translates to a very low % increase in mpg, especially at low speeds.

[Bruce S]

G-
I"m the author of this so I'm okaying the drift since it does pertain to what I'm trying to do.
Rode a Honda Rebel 250cc while son was "over there" to keep it running and gas from gumming everything up, nice bike didn't like the fuel cutoff switch though, messy.
 
Always got 50+mpg easy.
Front fork had 7" rake, nothing radical just better riding. windshield added to keep bugs out of teeth  .
AND the engine is much better than the 150cc I have, even with the mods I've done.
Better carbs, better exhaust, better riding profile, better tires.
The 150cc has us sitting up like a billboard, and the engine is a piece of work:(. The exhaust is "interesting" looks designed to break, at cheap-o weld spots. Already rebuilt mine, gotta love the 90Amp welder , and is so closed inside the bike was choking on its own back-pressure.

The slight mods I've done and keep it legal allowed me to go from 75mpg to 92mpg city. I do take it up on the highway, but not often. 680lb doing 65 is not for the faint at heart. Bike screams down the highway, just too light for windy days, plus pushing 150cc beyond 55 is not good for that poor engine.
My trip down the upgrade path for the scooter, started when I wanted to understand why they said NO E-85, even NO E-50. Now I know why  .
It is now running E-50 and loving it, not sure how well it would hold up to E-85 though, time will tell how the head holds up to E-50, an engine head I can swap easily enough.

taylorp035 has most all the rest correct.
IT however is was vehicle of choice for pizza delivery around StL since the back rack can be easily extended to hold those cool keep hot boxes.


 

[ghurd]

You guys may have interest in something. 
I would have sworn it was on the cover of Pop Mech/Sci had in 1981 +/- 18 months, but a look on ebay says it was not on the cover, probably another publication?
Yellow 3-wheeler with fiberglass body.  2 in front, one in back.
Basically a 750cc Kaw(?) with front forks removed, VW Bug front end, connected together.  Side by side seating for 2.
Home-Brew.

They claimed 3/5ths the wind resistance of a man on a motorcycle.
Great article if anyone could find it.   
G-

[taylorp035]

A thought that I have had many times is by comparing these cars to a real full sized car.  If you take the numbers from my SMV and compared to a 30 mpg sedan, you are looking at about 10x more weight, 10x more air drag, 1.5x more efficient engine,  and 2x as much rolling resistance.

If you figure it out, the SMV car should get about 10x the mpg or 3000 mpg.

They claimed 3/5ths the wind resistance of a man on a motorcycle.

Hmm... sounds about right.  The drag coefficient for bicyclists has been studied in depth and I think the number is around 0.7 - 1.  This is about 2-3x higher than the bug.  The frontal area is roughly 2-3x bigger....  3/5 th could be achieved.

[Bruce S]

taylorp035
More likely to go electric / engine series hybrid. 
I want to keep it "real" in terms of real world driving and affordability.
We all know that pound for pound gas or Alky carries so much more power available that it is very hard to ignore.
So my idea is to hopefully make the most of both worlds.
I have available to me , large numbers of re-usable  18Vdc NiCd batt-packs. being that they are only rated at 1300ma it will take a large number of them to go to work and back. round trip being around 30miles daily.
There are some newer style batteries I'm being told about that are lead based, but with either higher density energy density or much faster recharge rates.
One is already being made available per order not one of those ready in 5 years kind of thing  . Energy density showing around 42wh/kg versus 35wh/kg for Lead-acid

Keeping things in perspective.
1Kwh=~3400btus, 1 US gal E-85 using a horribly inefficient ICE running 15% efficient = ~ 12000btus or 14000btus if I use LPG fuel. SO I figure if I use both to my advantage I can have a vehicle that will get me where I'm going and back without breaking the bank too.

isn't this fun
Bruce S
 

[Bruce S]

You guys may have interest in something. 
I would have sworn it was on the cover of Pop Mech/Sci had in 1981 +/- 18 months, but a look on ebay says it was not on the cover, probably another publication?
Yellow 3-wheeler with fiberglass body.  2 in front, one in back.
Basically a 750cc Kaw(?) with front forks removed, VW Bug front end, connected together.  Side by side seating for 2.
Home-Brew.

They claimed 3/5ths the wind resistance of a man on a motorcycle.
Great article if anyone could find it.   
G-

G- google books is a great place to find/read those. about 80% of them are up and completely readable even search-able.
I remember reading where this was done too.
There are plans all over the 'net to build these types using foam-core and 'glass.
Thanks

[taylorp035]

Good luck at getting 15%.  We will be getting 12% from ours.  Last year's setup ran at ~9.7% according to my calculations  EDIT: with the engine efficiency curve and 9-10 % according to the mpg and my excel calculator.

I see where you are going.  If you could take that 500watt motor you had and use it as a generator on the engine, then you could charge at ~ 300 watts nicely and still runs for miles with no electricity.  If my calculator isn't cheating me, I get 16.6 Wh per mile for your approximate setup.  That's well with in your storage capabilities with NICD packs.

[Bruce S]

Good luck at getting 15%.  We will be getting 12% from ours.  Last year's setup ran at ~9.7% according to my calculations  EDIT: with the engine efficiency curve and 9-10 % according to the mpg and my excel calculator.

I see where you are going.  If you could take that 500watt motor you had and use it as a generator on the engine, then you could charge at ~ 300 watts nicely and still runs for miles with no electricity.  If my calculator isn't cheating me, I get 16.6 Wh per mile for your approximate setup.  That's well with in your storage capabilities with NICD packs.

Thanks for the calcs.
On your SMV how much can you change? can you say change the fuel being used or must use the gasoline they provide?

[taylorp035]

Well, the fuel is iso-octane or 100 octane gas, which doesn't pre-ignite at all that I know of.  The stuff is very rare and about $200 / gallon before the gas prices went up.  They buy about 5 gallons for all of the cars, and we usually can get about a gallon at the end of the event.  Most of the engines will run on 93 octane.  There isn't really much more energy in the 100 octane gas (i need to look that up), so it has little to no value to anyone else.

EDIT: 

Isooctane:  125,969,466 J/gallon

But I am finding different numbers all over the internet.  In my calculator, I used 132,000,000

[Bruce S]

I should be posting this over in your post on your SMV.
I ask, mainly for research reasons and really don't want to muddy the waters of your current work.
I am still working on a test engine that I have that I can work with different fuels. Nothing more than a Horizontal B&S 3.5 pull start.
I know its running characteristics almost by sound. I have two carbs for it. One for everyday use ( E-10) one drilled and adjusted by me () to make use of Alky at any blend from E-10 to E95 ( need to stay legal). plus I have located the IMPCO kit to allow me to switch to propane.

Was curious if you could switch fuels if you wanted to. Sounds more like the fuel used is what they provide.
Thanks

[taylorp035]

Right, we have to use their fuel (and it is monitored very closely).  I'm not very good with engines, which shows you why we still don't have a final running engine yet.

For your use, the number of gallons that you will go through will be rather small @ 200 mpg, so switching carbs when you run out of your special blend shouldn't happen too often.

[Bruce S]

Right, we have to use their fuel (and it is monitored very closely).  I'm not very good with engines, which shows you why we still don't have a final running engine yet.

For your use, the number of gallons that you will go through will be rather small @ 200 mpg, so switching carbs when you run out of your special blend shouldn't happen too often.

I was a grease monkey long before internet was around or affordable, and was the major source of income until 6May1978.
I enjoy still working with all kinds too bad y'all aren't nearer to StL.
Iso-octane has an upper limit of compression what's your engine running at? probably better I go re-read your posts.

Cheers;
Bruce S
 

[taylorp035]

Stock, the engine is about 8:1 to 9:1.  We haven't made any formal measurements.  We are halfway done with a 14:1 50cc conversion (chromed sleeve too ).  I would hate to see that go to waste b/c that cost $800+.  Unfortunately, going smaller only increases the thermodynamic efficiency.  It still has about the same friction from everything else.

Next year we will build an OHV and will probably spec it out to be 18:1, but due to losses, it will end up at 14:1.  At 148cc, it would probably make 10hp I bet on iso.  Trying to transfer all that torque using spokes and a limited amount of grip will be tricky at best.  Might have to go 3-wd all electric in hub motors  .

[Norm]

neither said anything about the use of duct-tape instead of hot glue

LOL... I'm so used to seeing the ebike batteries covered in duct tape that I get suspicious if I don't see any!

And now a little...
a e r o d y n a m i c s

(it's even related to ground transportation!  How's that for getting back on track?)
http://www.evworld.com/article.cfm?storyid=870
http://ecomodder.com/forum/showthread.php/index-phil-knox-aerodynamics-seminars-mod-data-lists-7118.html

Zap: trying to horn in here and show you pics of my latest way of building battery paks...

step 1 is cutting around the top and bottom





Just like the way they look like they were never touched and how easy
it would be to wire them up in any configuration.
Norm.

[taylorp035]

Here is a good picture showing my frame rail set up.  Basically, the idea is to distribute the load where it is needed, hence I think thick body shells are pointless.  The lower "roll bar" prevents the whole car from twisting, so it is about 10 layers thick and 2.5" x 6" in cross section.  It doesn't need to be that thick, but after several additions, the layers added up.

Here a larger version of this pic:     http://i51.tinypic.com/vq654z.jpg


And I hope to see a cooled seat in your car too, Bruce.     I will make sure to get all of the kinks out of the system so other people can model their own systems.

[Bruce S]

Norm;
 That is pretty cool! I will give the freezer method a try too.
Thanks
Bruce S

[Bruce S]

taylorp035:
With regards to a cooling seat. I have a few of these bad boys left from building a cold top for the chef/wife.
Its fun to watch 8 of these frost over a SS top in minutes and how pretty the Chocolate looks while its being slathered out then cut.
Keeps canned beer nice & cool too. in fact will keep an entire 6-pack well chilled, just don't ask about the electric bill 

These are the sealed ones running 350w each.
 I used the heat pipes from old Dell Small Form Factor computers and 12V 2.65A squirrel cage type fans to exhaust the heated side into air-tube vents to the bottom of the SS table so no one would get heated up by the air. Also allowed the fins to remove more heat without worry of recirculating the heated air up towards the Peltiers.
For kicks, I used some old 12V18Ahr batteries in parallel to see if it could be portable. SURE no problem for a few minutes
ALL 8 running at the same time is over 200 Amps running full out.

   

[zap]

Thanks for the pictures Norm... it helps with the explanation.

I freeze them too to get the hot glue to let go but I don't freeze them for an hour.  I think Bruce has seen some anomalies with the packs after being frozen.

A whole different story...I think I might try a few packs at their default 18v to test yet another ebike
"Hi... I'm zap... and I'm a ebikeaholic"Sorry for the sidetrack Bruce.

[Bruce S]

Thanks for the pictures Norm... it helps with the explanation.

I freeze them too to get the hot glue to let go but I don't freeze them for an hour.  I think Bruce has seen some anomalies with the packs after being frozen.

A whole different story...I think I might try a few packs at their default 18v to test yet another ebike
"Hi... I'm zap... and I'm a ebikeaholic"Sorry for the sidetrack Bruce.

There is NO sidetrack, so no worries.
Norm's stuff is different in the freeze method he uses. The batteries are in parallel. I haven't tested that configuration yet BUT I will.

Norm. The freezer anomaly ZAP is talking about: Once the batt packs are built, 12Vdc @ 2.4 and above there exists a problem when they get frozen and allowed to be drawn down to less than 0.9V/cell and then recharged. Rich is testing larger sized packs too 7Ahr sized for the next trip (2012) to Philippines. I've had 1 20Ahr packs pop and a 3.9Ahr pack pop, but could not put 2-n-2 together until I started testing after we returned & some of the packs in Banaue were at 0.0V out of the shipping box. 
The packs you & I built both 2.6 & 3.9 sets are series parallel to bring the packs up to 12V then stacked for higher current.
I started testing packs here this past winter hoping to find the answer. I also reached out to a friend in Memphis to ask. He finally confirmed that we should NOT leave the coverings on packs built this way.
ALL of the cans in the packs should be allowed to touch so the heat build up can DISSIPATE across the pack as a whole. Otherwise they can pop like mine did. IT so far has been the middle packs of the stacks, which makes sense since that's where the heat will buildup.

I have a write up about this but was waiting until the Memphis builder to confirm or deny my thoughts.
SO once you build these 6V packs as units, let them sit measure the voltage or drain one set down to 5.0 volts then pop it in the freezer for an hour then recharge after being brought back up to room temp and SEE how they hold up.

Sorry, should've put this out sooner, but needed to make sure I wasn't seeing things that didn't exist.
   

[Norm]

Bruce, Now that I have a  WattsUp meter I plan on charging an 18 volt to 20..5 after
charging and a brief rest then hook it to a treadmill motor no load and noting how many watt hrs.
ituses before dropping to 18 volts. and comparing it to others in a control group.
If it isn't satisfactory isolate the problem or cell and try blowing the whiskers off with 12 volt
charger(16 volts) no sense putting one all together then finding out there is  bad cell/s.

My biggest concern is using these with an inverter so I can figure how many to use for x amount of
light.....a few led lights with a remote to turn  on a 24 watt CFL or 2 when needed. outside lights.
batteries charged by wind.....

Oh hey I gotta get back to my PedGen.....later !

[Bruce S]

Oh hey I gotta get back to my PedGen.....later !

Norm;
 When you get finished with your days ride 
I have a couple small inverters that I've tested these with in a 16Ahr configuration with them at14.4 to settle the voltage lag issue. I can run my 700 watt Microwave off the packs a few times. The inverter is a 900watt unit. I stole one of your ideas , I grabbed an old set of battery jumper cables 12ga twisted wire sets set up one side with hoop connector for inverter and bus-bar for connection to batt packs.
One thing I've been doing, building Ghurd dump controllers for each batt-pack so they can whatever charge they need.
NO windturbines here, not even allowed... YET:)
The 12Vdc packs can run the 100, 150 & 300 watt inverter with no known problems. I even have one of the cig-power plug cheapies from K-MART (100watt) and clamps to hold to battery terminals ( we use it to charge cameras, older cell-phones, etc)
With weather storming through StL right now  I would have to lock it down.

[Madscientist267]

I used the heat pipes from old Dell Small Form Factor computers and 12V 2.65A squirrel cage type fans

That reminds me - I think I'm gonna take you up on the offer for a heatpipe/blower for these peltiers...

And you say you have a 350W Peltier?

Steve

[Bruce S]

I used the heat pipes from old Dell Small Form Factor computers and 12V 2.65A squirrel cage type fans

That reminds me - I think I'm gonna take you up on the offer for a heatpipe/blower for these peltiers...

And you say you have a 350W Peltier?

Steve

Send me a PM with your mailing address I'll send one out. I'll send the biggest Heat pipe unit I can find ( similar to the pic I posted).
Not just 1 350 watter BUT bought 12 of them ! sent one out for testing, loaded 8 on a SS chill table and a few left to play around with.
They show 15.4Vdc max at  30.7A max but I drive them at 13.8Vdc and ran them flat out Wattsup meter showed a continuous draw of 29A.
  The table got cold quick 
The squirrel cage fans had heat coming out and were noisy, but I had them running flat out too. THAT was fun seeing the proof of concept working like is was supposed to, right up til the batteries started getting DEAD  .
I can send you the link if you wish, I'm not big on linking non-reviewed sites on here, and there is a minimum order.

With the fab abilities of your group, getting the heat piped away you should have NO problem.
Cheers;
Bruce S

[Madscientist267]

Holy crap dude thats a lot of juice. And I just saw how big they are too... whew... is that 2 1/2" square? heheh

I'm running a test right now with the 17.5 gallons of ice for the 5cu ft freezer, to see how bad the insulation/freon transfer losses are. Froze 7ea 2.5 gal water 'jugs' to <0F for about 2 weeks (they were stable ), then pulled the plug and started writing down the temps periodically. Currently been in phase change for 48H+ as of this morning, closer to 60H+ now.

Wondering if a single high wattage module would be the answer rather than several. Just seems like I'm never going to get the multi-module design flying thanks to some logistics problems (heat spreader being the main one). I have the ten 50W modules, and the three (125W I think?) from JW, but without the heat spreader, I'm kinda stuck.

I have a high current DC supply (modular SMPS) good for 60A @ 13.8V that may end up part of the picture here, at least for initial cooldown, if I don't just give in and use the compressor (if I could just start the thing with my inverter).

How well do they perform at lower input? Say in the 2-5V range? The idea is simple... cooling capacity IF I need it... otherwise throttle WAY back. If I can do the coleman on 9W, I should be able to get away with something in the 2-3x range for that (coleman ~2cu ft, freezer 5)... Something like 25W (+ the fan) sounds good to me. And no surges to deal with! YAY!

Also, how does the heatpipe sink handle those things at full power? Thats a LOT of heat even for a pipe design... 

Steve

[taylorp035]

For higher mileage, you can use a free wheel from a bicycle in the back or have a clutch and some nice bearings like this:





Spins for ever, unlike a normal bicycle.  The power sucked by the bearings and sprags adds up.

A lighter flywheel also helps, especially if you want to start the engine a bunch of times.  Else, don't bother.

Video of the rear axle:

http://www.youtube.com/watch?v=by4lR4Tb6Fw

[Bruce S]

Holy crap dude thats a lot of juice. And I just saw how big they are too... whew... is that 2 1/2" square? heheh

I'm running a test right now with the 17.5 gallons of ice for the 5cu ft freezer, to see how bad the insulation/freon transfer losses are. Froze 7ea 2.5 gal water 'jugs' to <0F for about 2 weeks (they were stable ), then pulled the plug and started writing down the temps periodically. Currently been in phase change for 48H+ as of this morning, closer to 60H+ now.

Wondering if a single high wattage module would be the answer rather than several. Just seems like I'm never going to get the multi-module design flying thanks to some logistics problems (heat spreader being the main one). I have the ten 50W modules, and the three (125W I think?) from JW, but without the heat spreader, I'm kinda stuck.

I have a high current DC supply (modular SMPS) good for 60A @ 13.8V that may end up part of the picture here, at least for initial cooldown, if I don't just give in and use the compressor (if I could just start the thing with my inverter).

How well do they perform at lower input? Say in the 2-5V range? The idea is simple... cooling capacity IF I need it... otherwise throttle WAY back. If I can do the coleman on 9W, I should be able to get away with something in the 2-3x range for that (coleman ~2cu ft, freezer 5)... Something like 25W (+ the fan) sounds good to me. And no surges to deal with! YAY!

Also, how does the heatpipe sink handle those things at full power? Thats a LOT of heat even for a pipe design... 

Steve

Steve;
 Sorry for not getting back sooner, saw this note and got onto other things.
These throttle back real nice though I never took them down to 5V lowest I played with was 9V and they were still cold, but left the fans at full throttle.
To be honest the multi-module in my original calcs worked out to be a better design rather than a real large single one.
Reason being the ability spread the work and cross-sectional work loads. Fancy name for overlapping cooling zones.
The heat pipes worked ok, I knew they would be hard pressed to keep up so I allowed the fans to run at full speed from initial switch on. The idea of getting to heat away by using tubes and forcing the heated air out was because standing there with all those fans blowing hot air was NOT my wife's idea of a fun time.
I forced the air to the very bottom of the table via the tubes and let the air dissipate. This caused a slight vacuum on the fins, which I believe aided in the cooling effect.
The vortex engineers tell me I'm mostly correct but could've done better, I asked them if they'd be nice enough to come show me:).
I have drafted a dorm sized fridge that has its compressor shot. I neighbor came over to salvage the freon for me.
My plan is to attach the chips to the sides instead of the top like yours. Bottom would be better, but then tops items would not be chilled fast enough.
With the chips on the sides Left & right, I can spread the work-load and allow the heat to rise. This design will also allow me to funnel the heat sides of the chips towards the back and make use of small vortexes for heat management.
BUT of course work and round-TUITs are piling up  most I may get done is the compressor removed and metal casing removed we'll see.
The rain has stopped in StL for now and a levee broke down home so everything may be on hold. A cousin was evacuated away from the Black-river area and its all hands on deck for moving her "stuff". Glad I put those AV tires on the Suburban. 
 

[taylorp035]

My experience with low voltage power on the TECs is that they are most efficient at the lower power levels (even near 5 watts on a 140w chip), but their possible delta T is very low.  In the case of the fridge, I doubt you can do very well on the low power levels.  my excel calculator suggests that 50-75% power may be the best bet, but there are a lot of factors to play with.

[Madscientist267]

I hear ya on the TUITs. I got a handful of them myself.

Lower power is definitely more efficient.

I've been playing with the coleman a bit more, and I'm zeroing in on a design for a buck converter regulated by a thermistor.

I have a tendency to stock it, run it out, then restock it completely again. This of course results in spikes in the heat load that the 5V supply takes forever to remove. It does fine at holding a decent temp (albeit a touch higher than at 12V), but full power is needed after the restocks. Or at least more power... I don't have it hooked up to a variable yet, so I don't have that kind of data... Soon...

I've managed to hit 32F at full power just this week, a delta of 38F. At 5V, delta is typically 30F. Of course, these numbers represent the ambient air vs inside air, so I don't know exactly what it measures at the chip.

Either way, not that much gain considering its 5+ times the power, but it's ability to pump heat is significantly better.

Steve