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11-07-2017, 11:34 PM
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#121
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Bronze Member
Join Date: Dec 2016
Location: Minnesota
Posts: 40
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Wouldn't a wider belt with more friction handle more torque...with same tension?
An example is my previous coach had a DD 6V92 with double V belts to drive the alternator (300 amp Delco 40si). Same tension, 2 belts, twice the torque.
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11-08-2017, 12:08 AM
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#122
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Platinum Member
Join Date: Aug 2010
Location: Minnesota
Posts: 12,061
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There are two different, but related belt tensions. We are used to setting the static tension which is uniform around the belt and causes friction to grip the belt, but it is not the major tension that is causing side loads. When the belt is running, one side is pulling hard to turn the pulley, and the other side is essentially slack minus some of the static tension. The pull of the belt at the pulley circumference has to be opposed by the engine bearings and for 20 hp at a relatively small radius the force is going to be pretty large. Multi-vee, cogged, etc belts are just better ways to get the friction needed for the rotation to be able pull the high force on the belt to cause the tension that is transmitting the power.
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11-08-2017, 12:40 AM
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#123
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Bronze Member
Join Date: Dec 2016
Location: Minnesota
Posts: 40
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Yes, you have a point on the torque induced side load. The scary thing is you may not know if you are are toasting the front bearing until 50k miles or so...
Maybe MB has designed in some margin...
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11-08-2017, 01:00 AM
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#124
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Site Team
Join Date: Jul 2013
Posts: 5,343
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Here is an interesting section from the 2015 Sprinter Bodybuilder's guide:
PTO.png
So, they limit the takeoff power to 11.4 hp.
__________________
Now: 2022 Fully-custom buildout (Ford Transit EcoBoost AWD)
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)
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11-08-2017, 01:11 AM
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#125
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Platinum Member
Join Date: Aug 2010
Location: Minnesota
Posts: 12,061
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Good find, and not unexpected for sure. From the chart posted earlier from Volta, that would limit them to about 100 amps, so probably around 5500 watts. That kind of puts a kink in whole system, although it is still much better than anything else.
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11-08-2017, 02:17 AM
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#126
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Bronze Member
Join Date: Dec 2016
Location: Minnesota
Posts: 40
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Yes, that is the MB published spec. I'm thinking ARV has been in contact with MB, and getting the actual capability to work with. They for sure wouldn't offer warranty on something that would fail and cause warranty issues...
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11-08-2017, 02:41 AM
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#127
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Platinum Member
Join Date: Feb 2016
Location: Portland, Oregon
Posts: 3,145
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I would very much doubt Daimler Benz would change these, likely tested, maximum power limit numbers. Interesting that the 4 and 6 cylinders numbers are the same, perhaps the weak point is at crankshaft or front bearing.
I think Dodge is the only one offering direct PTO idled for fuel saving on 4 cylinders. If I remember correctly my Ford F350 4x4 had an optional PTO from the transfer case.
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11-09-2017, 06:20 PM
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#128
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Platinum Member
Join Date: Mar 2012
Location: Maryland
Posts: 1,191
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FitRV's lithium/alternator/inverter setup
Quote:
Originally Posted by GeorgeRa
I would very much doubt Daimler Benz would change these, likely tested, maximum power limit numbers. Interesting that the 4 and 6 cylinders numbers are the same, perhaps the weak point is at crankshaft or front bearing.
I think Dodge is the only one offering direct PTO idled for fuel saving on 4 cylinders. If I remember correctly my Ford F350 4x4 had an optional PTO from the transfer case.
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Agree that the limit published would not be changed by Daimler. This should be interesting to see how ARV will deal with exceeding the limit. They will probably just limit load form the 48V Volta generator to 8.5KW. There are transmission PTO options with higher outputs for Sprinters. They are just no offered in USA/Canada. Here is page from the European Sprinter builders guide that is about twice as long as the USA version. Problem is the Sprinter must be stationary to use the transmission PTO.
- - Mike
2012 Sprinter 3500 Extended converted B-Van by Airstream
__________________
2024 Airstream Interstate 19
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