Year: 2010
Make: AirFlow
Model: SuperTruck
Engine Size: ISX
Refrigerant Type: R134a
Country of Origin: United States
Gentlemen -
I am converting a belt-driven Sanden A/C Compressor to a 12 volt battery powered Sanden compressor.
The new electric compressor is under the bunk of the sleeper unit, whereas the belt-driven one was mounted on the diesel engine.
It is a dual evaporator system with the second one in the sleeper unit.
I would like to relocate a "T" fitting from near the forward expansion valve on the firewall, to near the expansion valve under the bunk, where the 12 volt compressor is located.
These "T" fittings are on the Suction low-pressure side.
The OEM config is the top image, the proposed re-design is the lower pic.
Can anyone see any problems or issues with the proposed re-configuration?
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Comments or questions will be entertained.
Thanks in advance.
Edited: Sun June 20, 2010 at 10:47 PM by Shepherd777
I don't think there is any real issue with where the T is located. Just wondering if the 12v "no idle" system compressor is equivalent in displacement and function (variable vs fixed) as the belt driven unit. I would discuss this with Sanden.
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Just a little confused on the return of the sleeper evaporator unit, but guess that I am not an expert. That tee in either the upper or lower drawing feeds both the compressor suction and the sleeper evaporator, is that suppose to be different? Its functionally still the same, and since this is a schematic type drawing the actual physically layout would be laid out differently, but still functionally the same.
See this Manual explains the advantages of the electrical system, states the motor can draw as great as 220 amps, but really doesn't tell where you are getting this power from. A bank of submarine type batteries?
How come they don't tell you how many amps it draws while running? That must be one big alternator.
Nick:
That manual has a few contradictions, but the numbers are close to right. They claim 15nm @ 2000 rpm. 4.21 hp or so.
745w / hp, so @100% eff. = 3136w The chart claims efficiency in the 90th percentile, so a probable draw of 3484w
At a very conservative 14.7v that would be 237a. At a battery voltage of 12.9 the current skyrockets to 270a.
But then thay recomend a 200a circuit breaker. 1+1=3 at this point. Perhaps the little scroll is not loading the motor beyond 180a in operation, but there is no way to say from that sheet.
I don't know how long (or how well) the scroll from a Honda Civic will cool a sleeper equipped class 8 truck, but perhaps we will know after he completes this install. Looks like the max cooling available is 15k btu/h on a cool day, and perhaps less than 10k btu/h with higher ambients.
Bob:
After years of flogging banks of group 31 AGM batteries, I can say this will be hard on alternators. With a dozen batteries in the bank & a 7.5kW load it was not as bad as this install. Figure 85ah per battery without killing them. That is 340ah for the bank pictured. At 170 amps, that is two hours of operation. That 170a load would need to include the cabin fan(s), as well as a suitable condensor fan for engine off operation.
The "drive off" load is awful. Not only do you need 170a to keep the compressor cooling as you drive, but you need another 120a to charge the battery bank back up. We beat up some alternators more than a little bit. A Niehoff C716 solved the charging problem, but it was not a cheap unit.
Keep us informed on your progress.
B.
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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
Shepherd,
Motor and alternator manufactures typically don't show efficiency curves that are real life. Those 90% dubious efficiency data points are at low ambient temps (approx 70 deg F) which are not real life. The motor cooling intake should not be the sleeper evaporative outlet air and exhaust should not dump into the sleeper, to avoid counter-productive A/C COP.
But, it may be productive to A/C the batteries as is sometimes done with Hybrid green vehicles.
I worked on a "Pony Pac" no-idle sleeper A/C WITH 2 COMPS AND ONE CONDENSER. It would keep HeCat happy cleaning up the comp dumps.
An interesting design is the Civic Hybrid with a 2 scroll compressors inside one housing. One belt driven and one with a high voltage electric motor so that they both draw oil from the same sump.
I wonder why OMEGA uses the TR90 instead of the TRSA50 with a built in oil separator which can run higher rpm with a smaller cheaper motor? The TRSA05 can survive with a low total A/C system oil circulation ratio (OCR) of about 1.5% while the TR90 needs 5 % or more.
I would be looking at a 24 v sleeper system with a 24 Volt HumVee alternator
Cordially,
hotrodac
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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod
Edited: Mon June 21, 2010 at 2:10 PM by ice-n-tropics
Certainly the current would be far less if operated well under the 40,000 BTH/Hr specification, my motor does very well with a 15.5K unit cooling 1,500 CF, and it certainly doesn't run 100% of the time. With 4 ea 100 AH batteries, feel you should be okay, especially if you sleep at night without that bright sun. How many CF are you cooling? Would be nice if Omega would show a curve of input current versus BTH/Hr. capacity.
Your batteries would last longer if you could somehow control the charge rate, a 300 amp alternator would tend to charge them very quickly, charging each battery at a 20 amp rate should have them fully charged in less then six hour if bone dead.
Oh, nice looking dog by the way. Does your dog travel with you?
Like Ice said, it's really hard to keep the oil flowing right with dual evaporators, and the scroll compressor doesn't like either too little or too much oil. Mostly for that reason, I'd split it into two independent systems. Electric for the sleeper bunk and conventional engine driven for the dash vents. When sleeping, you'd want all available battery power cooling the sleeper. While driving it's inefficient and needless to convert power to electric and back again. Fit a new condenser for the sleeper system somewhere on the outside such as the back wall of the cab. It doesn't need ram air since it would have full time electric fans. Also it'd be worth going 24 volts, but that may be moot since you already bought the 12 volt version.
Edited: Mon June 21, 2010 at 2:02 PM by mk378
Bob,
For max A/C cooldown in the cab and sleeper there should not be much exhaust of occupant air, therefore operate in the max. recirculation mode.
12 volt motor cooling air should not exhaust back into the cab or sleeper or sleeper evaporator air inlet.
If there is a natural flow through ventilation/leaks of enough air to cool the motor and exhaust it out of the vehicle then the motor will not heat the interior air.
The typical class 8 truck has roughly about 22000 to 24000 BTU dash air and 12000 btu+ of auxiliary sleeper A/C air.
You might consider a air separation curtain between the cab and sleeper to optimize the limited battery stored energy.
JMHO: The presentation claims of eliminating parasitic engine losses for a belt driven comp won' fly in my book. You are about 30 to 40% less efficient in the mobil mode with the battery powered compressor verses a conventional belt driven compressor.
Engine compartment alternator is only 70 to 80% efficient at actual operating temp. The A/C comp motor will also run hotter than the chart. Have a look at the Sanden hybrid scroll for the Honda Hybrid for the optimum solution.
hotrodac
-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod
Edited: Mon June 21, 2010 at 6:52 PM by ice-n-tropics
Efficiency probably comes into play by not having to run that big diesel engine all night like many truckers do. But do agree, some of it is lost by getting taking the compressor off engine for the main cab cooling. Not sure about the alternator, past ones were only about 50% efficient, but can't see a great deal of improvement there, then the battery charging and discharging inefficient, at least another 15%, and the motor inefficiency anywhere form 10 to 30%. adds up. Probably 40-50% overall if lucky, but measurements would confirm that.
Then the replacement cost of the batteries as they won't last forever, even lower if they are fully discharged over night. I also wondered why the entire system was replaced when only the sleeper was in question. Also wonder about winter time, probably more so in Wisconsin, typically, even in the summer, night temperatures are in the 60's. But those long cold winter nights.
Bob,
Alternator power input is in direct proportion to alternator output. If battery is charged and loads are low then alternator does not put out 300 amps as you claim.
2 cents: Loss of fuel mileage because of poor grasp of energy for electrical efficiency (non belt A/C comp) verses belt drive on the road will cause you guys to lose your face. If you don't read me, perhaps you guys need to ask some smarts, e. g., Bohica (short and quick) or Nick (if you have some time).
hotrodac
-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod
Edited: Mon June 21, 2010 at 9:38 PM by ice-n-tropics
Bob:
With only Omega's page to work from, it is hard to say what size fuse is appropriate. There is no way to make the horsepower they claim on even the recommended 200a fuse.
The statement about NOT installing a contactor from Omega makes me think there is some sort of control circuit (pile of mosfets) under that rear cover. The nearly flat torque curve & constant 2000 rpm supports this theory.
Tex (Ice-n-Tropics) is closely tied to the compressor business, perhaps he can tell us how much horsepower the trash90 can soak up @ a fixed 2000 rpm. That will give a more complete answer on the current draw issues.
As for the "T" fitting, it is always a design issue. Oil return in dual (or very long) systems can be frustrating to say the least. Personally I favor the oil separator approach, I have had good luck on 40 foot motorhome systems with it. A couple of added parts, but the compressor goes the distance.
It does look like you may be short on capacity. The Omega chart says 10 to 15 k btu/h @ 2000 rpm. Tex says more that twice that is typical.
You had not mentioned the 40SI & isolators when I started typing that post. Plan right now for more alternator, or carry a spare. Two 40SI's can be mounted & sistered, perhaps even on top of each other with an idler or two...
The isolator will be a real nice 200w heat source, so keep it well ventilated.
Tying the 40 SI sensing circuit to one bank of batteries as most isolators do will work, but... The sensing wire should be tied to the cranking batteries. If it is tied to the badly depleted AGM's, it will cook the cranking batteries. A 125a charge rate to those 4 G31's will be fine. We do 450a on 12 G31's without issue.
If you plan to build more than one of these I would seriously look at going to 28v, or even the "42v" systems once proposed for passenger vehicles. Reduced current, smaller wire, etc. - since you plan to run everything off of the alternator. Delphi did a lot of work on 42v, but it got pushed aside with the 300v hybrid stuff. Plenty of that technology got all the way to a producible part. Even 28v would be an improvement.
B.
-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.
I assume since this thread started off with a tee placement, this system hasn't even been run yet, we learned this is a diesel truck that already has bank of batteries just to start it, an electrical compressor replaced the conventional compressor that may place an additional 220 amp load on the system, and a bank of four more batteries have been added that in all probability will completely discharge that bank of four additional batteries.
Try repeating the above statement ten times in a role.
In terms of electrical loads on the alternator, the battery or many batteries in this case are the scavengers and will eat up everything left over that alternator can deliver. In a semi or complete discharge state, everything the alternator can deliver. An alternator is current limiting device, and it does this by limiting the strength of the magnetic field from the rotor, actually due to cost restrains, to the point where magnetic saturation has already been past further decreasing the efficiency of the alternator. And by choosing the wire size in the stator such that its impedance will cause internal voltage drops limiting the output voltage.
You can actually short the output of an alternator, or should be able to without hurting it. It will deliver its full output current, but into a short circuit, 0V times any current is 0 watts, so essentially its delivering 0 power. In this state, takes very little power to rotate the alternator.
For the typical alternator at rated voltage and current, it consumes just as much power as it can deliver, those suckers get hot, like 200*C hot. Good example of this was with the introduction of the CS-130 105 amp alternator that replaced the 63 amp 10SI, the former was smalled than the conservative designed 10SI, actually its key to higher output current was the installation of fans to keep it from turning red. To further conserve on cost, only 90 amp diodes were used and for the most part, would survive. A worse case scenario was a guy leaving his car at an airport for three weeks where all that standby current would drain the battery and discharge it approximately 50%. Angry after being treated like crap at the airport, starts his engine, switches on the AC forcing the radiator fans to turn on plus another 27 load from the blower, revs his engine to over 3,000 rpm to get the hell out of there, his half dead battery with an already 70 amp load on the system consumes the other remaining 35 amps, exceeds the diode rating, and the blow apart.
But hey, with the one year warranty, as long as more profit was shown by using the cheaper diodes as opposed to warranty cost, leave it, the bottom line is making money.
In the case of this 40ST, certainly would like to get my hands on it, retired now, with a rated output of 300 amps, a nominal truck load of 40 amps, an additional 220 amps to run that electric AC, that only leaves 40 amps left over to charge two large banks of batteries. Bohica makes a good point about adding a second alternator, will will need it. If diode isolation is used, the setpoint of the alternator will have to be increased to compensate for the diode drops or proper charge levels will never be maintained. But this can be compensated for someone if the alternator has an external voltage sense pin, but for which battery stack? Flip a coin.
Yet another factor in particular with trucks, a battle I could never win was the use of non-temperature compensated voltage regulators, a truck in Mexico would only need 13.3 volts to fully charge the batteries, but that same truck in a run up to Canada would need 15.5 V to fully charge the batteries that led to battery freezing and warranty repairs for the battery division. Hell with it, just leave it.
Realize that this post just started off by moving a tee for oil circulation problems that are developing into what I consider, major electrical problems as well. Feel you would solve both problems by sticking with the conventional system for the cab and just using the electrical for the sleeper. Like a window type unit with the fan blowing the hot air outside of the unit, a lever for recir or external air, and a thermostat, plus gaining an additional 200 amps to charge those batteries.
Batteries have another characteristic, they can discharge a hell of a lot more current without damage than what you can charge them with, and the charging rate is strictly determined by the output of the alternator. With an isolated alternator, if you used a 50 amp alternator would charge at a 50 amp rate, with a 300 alternator at a 300 amp rate, the later may well cook those batteries.
But lets see what happens after you fire it up.
Pal 2xo,
After a trip around the Cape, Nick went on record that the electric powered comp should be used only for no-idle sleeper with belt drive for mobil mode. What say you?
Do you think that Bob's electric driven over the road comp is an acceptable application for a revolutionary optimum fuel mileage prototype Class 8 truck? Or does it need to be scrapped before it drags this project down into the scrap heap.
TR90 @ 2000 crpm = approx 2.7 KW depending on pressures.
hotrodac
-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod
Edited: Tue June 22, 2010 at 10:19 AM by ice-n-tropics
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