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If I were to get the 220 Alternator, should I expect it to have an impact on fuel economy?
;)PP
 

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No. There is a fuel loss due to the electricity produced but either alternator will eventually produce the same.
 

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Any difference in engine load for a given output would be due to the individual efficiencies of the alternators - not the size. Surprisingly, alternators are not very efficient energy converters. Without specific data on the each unit, it would be impossible to say which is more efficient. If there is a difference, it would probably be small and unlikely to make a significant difference in mpg.
 

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Just a half educated guess, but I think the only time it would make a noticeable difference is if you were using a lot of the added capacity over the stock alternator. If there are additional draws on the battery that are requiring the alternator to be engaged more often, then that energy has to come from somewhere. If it's being put into the battery, then it's not being put into the propulsion of the van.

Either way, the difference is probably going to be very minor compared to everything else that affects the MPG.
 

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I'd expect that a larger alternator may weigh a little more (a couple of pounds at most), may have more rotating friction, may have a larger fan for added cooling, and may be less efficient at lower current rates that may be typical during normal driving.

I'd also expect that even if all these "mays" applied to larger alternator (and I'm not sure they do), I will not notice the difference or be able to measure it.

I think that if someone installed a 300 to 400 Amp alternator so they could run a rear AC while driving (or some other steady high load like that) then it would show up as lower MPGs.

By the way, Ford Transit information includes how much power it takes to run different size alternators if I recall correctly. It may give some good insight on whether alternator sizes change engine load significantly. I'd personally go with largest alternator and not worry about fuel to power it.
 

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Both PM I have owned, the previous gas PM andthe current diesel PM, have the 220amp alternators. I also typically run a 1,200 watt heater in the back of the van. With the heater on there is no affect on mpg! The wind on the other hand has an affect on mpg!

I was very pleased with mpg on the gas as I am on the current diesel!
 

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It is this one from Menards hardware store, Dual Quartz Radiant Tower. It works great it has a low, 600 watts setting and a high 1200 watts setting. I always run it on 1200watts. Warms up the back really nice.
 

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Besides Adrian, what are you guys running that you need a 220 amps alternator? My Sprinter came with a 90 amps alternator and it was more than adequate for charging the starting battery and one extra bunk battery. When it went out (tthe alternator was still good, only the clutch in the pulley locked up) I replaced it with a 150 amps just because I could buy a 150 amps for less than I could a 90 amps.
 

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There may be another factor here. Alternators are notorious for producing almost no power at low speed and have to be belted up to an engine with a ratio that allows it to spin at a reasonable speed at idle and red line. Most are producing almost no amps at the 1800 rpm they run lots at. A larger one produces more output at these slow engine speeds. It is likely the 90 amp unit was turning faster so you got as much as the 220 amp one produces at those low rpms. This might explain the standard one being so much higher rated too. The cost is lifetime and a larger output slower turning alternator increases the likelyhood of long life. YMMV
 

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There may be another factor here. Alternators are notorious for producing almost no power at low speed and have to be belted up to an engine with a ratio that allows it to spin at a reasonable speed at idle and red line. Most are producing almost no amps at the 1800 rpm they run lots at. A larger one produces more output at these slow engine speeds. It is likely the 90 amp unit was turning faster so you got as much as the 220 amp one produces at those low rpms. This might explain the standard one being so much higher rated too. The cost is lifetime and a larger output slower turning alternator increases the likelyhood of long life. YMMV
RD for clarification,
The rpm is Alternator rpm not engine rpm the Alternator has a 2.5 to 1 or 3 to 1 pulley ratio so at 600 rpm engine idle the Alternator is turning at 1500 rpm and should put out 15amps for A 90amp alternator.
 

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Both PM I have owned, the previous gas PM andthe current diesel PM, have the 220amp alternators. I also typically run a 1,200 watt heater in the back of the van. With the heater on there is no affect on mpg! The wind on the other hand has an affect on mpg!

I was very pleased with mpg on the gas as I am on the current diesel!
Adrian, you may not be seeing a difference because it's smaller than typical variations between tanks, but I'm sure that running a 1200 watt heater or any other load has to decrease MPGs.

To produce that much current/power, an alternator requires at least 2 horsepower from engine. And since vans require around 50 HP to maintain speed on road (depending on load, speed, van size, etc it can change a lot), it suggest to me that 4 or 5 percent reduction in MPG is not only possible but likely. A drop of around .5 MPG wouldn't surprise me at all.

If it didn't increase fuel consumption, I'm sure OEMs would have started using electric heat instead of engine waste heat. It'd be cheaper to increase alternator size and add electric heaters (particularly at back of vans and minivans) than it is to add hoses, valves, dampers, etc...
 

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RD for clarification,
The rpm is Alternator rpm not engine rpm the Alternator has a 2.5 to 1 or 3 to 1 pulley ratio so at 600 rpm engine idle the Alternator is turning at 1500 rpm and should put out 15amps for A 90amp alternator.
Without the numbers I was saying that.... low output at low speed. What would the number be like for the 220 amp, about 30-35?
 

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Chance, you are probably correct on the slight drop in mpg.

Fuzzy, yes I have a second battery wired to main battery so the alternator charges the second battery and a 1,500 watt inverter. The inverter has a wattage draw display. Below 1,300 rpm the alternator does not charge much when running the heater at 1200 watts. The inverter display shows the battery Voltage dropping to below 11 volts. Around down I have the heater at low setting 600 watts and as I get on highway I turn the heater to high 1200 watts. The alternator charges and keeps everything running well. I run the heater when cold for entire 1000 mile trips. The heater is behind driver seat and I can adjust from low to high as I drive when getting on or off the highway.

I also have a small fridge that is always running a lamp and a tv in the van that my son often watches movies while driving. A 2000watt inverter would have been a better choice for everything I'm running. Although I have no issues a little room to spare would be more comforting. The digital display is nice to see so when plugging electrical components individually I am able to see how much wattage each item draws.
 

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The following alternator torque curve is from Ford Transit, but should be close to PM. At least it shows what a modern alternator of similar size is like.
 

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And this is current curve for same alternator. If we combine the two curves it's possible to estimate efficiency at full load. Efficiency should be similar to PM.

I wish I could figure out why I can't post two pictures on same post.
 

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Re the curves in the 2 posts above: I assume the RPMs on the horizontal axis are alternator RPMs. A question is what are the pulley sizes so the RPMs can be related to engine speeds. In the old days alternators were generally driven at twice engine RPMs but I have no idea about modern vehicles.
 

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Re the curves in the 2 posts above: I assume the RPMs on the horizontal axis are alternator RPMs. A question is what are the pulley sizes so the RPMs can be related to engine speeds. In the old days alternators were generally driven at twice engine RPMs but I have no idea about modern vehicles.
The Ford document, which is great in that it has a lot of details about a lot of things, lists the speed ratio at 2.7 for gasoline and 2.69 for Diesel engines. Difference may just be in rounding. The curves for Diesel engines show alternator spinning up to 15,000 RPM. Diesel engines can't even spin it that fast due to redline but it's good to know alternators can spin pretty fast.

What is most interesting to me is estimating roughly from curves at what RPMs the alternator is most efficient. Above 6000 or so it starts to drop off significantly.
 
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