FitRV's lithium/alternator/inverter setup

[prfleming]

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.

[booster]

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.

[prfleming]

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...

[avanti]

Here is an interesting section from the 2015 Sprinter Bodybuilder's guide:

PTO.png

So, they limit the takeoff power to 11.4 hp.

[booster]

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.

[prfleming]

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...

[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.

[Boxster1971]

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.

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