Ok, stupid question time. Can someone please explain exactly what an APU is and does. I have gleaned that it is an auxilary power unit but cant figure out exactly how it works. Batteries? Separate motor? They also sound very expensive. Probaably why very few co.'s offer them? I also was wondering about providing your own generator for power( I have a few of those from my contracting days). I only saw one other thread even mention this option. When you stop laughing, info would be appreciated. Thanks
An APU is a second, smaller diesel engine (one or two cylinders) used to produce electrical power and heat or cool the cab while the driver is sleeping. They are expesive but the cost can be recouped in 1-2 years in money saved in maintainance to the main engine, and fuel consumption, all while producing less harmfull emissions. The average APU uses .1-.2 gallons per hours of use compared to the 1+ gallons per hour used by most engines when idled to produce the same benefits and services. Over time this amounts to huge fuel savings and extended time between service on the main engine. There are different APUs on the market with different options but most will tie into the coolant systems of the truck to supply engine pre-heating in cold climates. These use of these systems are on the rise because of increasingly more restrictive engine idleing regulations being passed in cities around the country.
My experience on Cummins (400hp) is that I use about 0.5 gal/hr at 550 rpms, and 0.7 gal/hr at 700 rpms idling...when some APU's say 0.2 gal/hr---not too significant if 0.5 gal/hr idling-----but I guess they leave you alone at 5 min max idling areas?!
Cool, I never seen specs on Cummins idleing consumption. I remember Detroits and CATs using much more than that. I used to drive and old Pete COE w/ Detroit that used over 1 gal/hour idleing, drove a KW COE w/ Cummins 350 that did a lot better but didn't remember numbers on it.
LB, thanks for the info., is this second engine mounted on the cat walk? And if anti-idle seems to be the wave of the future, will this force co.'s to install them? It seems like a great piece of equip. if you own or lease. Can you get one installed on a new truck from the dealer? Thanks again.
Detroits I drove idled at about 900 rpms, so closer to 1 gal/hr...Yep But idling at 550 rpms for long periods over time is not suppose to be good for the engine...why I'll kick it up to 700 overnight! But co.s like mine who turn them over for resale at 5 yrs or 500-600K miles dont really care about engine wear & tear!!
Most are mounted in a tool box type setup hanging off the side of the frame on the curb side in front of the drive axle. Dealers offer them more and more on new trucks or you can have one financed in on a used truck purchase. Most companies seem to be waiting to see which one will be the most reliable before they invest in them or that have a few test trucks to try them out. I am already planning on getting one when I eventually go O/O but by then they will probably be standard equipment.
Well I just got done doing some testing on my 14L Detroit and she burns between 0.4-0.5 GPH at 550 RPM. I do remember reading about idling that low was bad, but can't remember why. For now, no APU for me unless the prices and install times come down.
Idling that low is bad because the oil pressure drops below a minimum amount needed to keep the rings pressurized. This is what I remember a mechanic telling me.
