Snow plow prep package question – page 4 – ford truck enthusiasts forums electricity and circuits

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… Also, I have to make an assumption about the alternators because I don’t have the two in front of me. Higher output alternators generally are more robust throughout, larger bearings, better cooling, etc.I would be willing to challenge this type of assumption. Let me give you a little background …

What proof do you have that a larger output alternator is "more robust"? I seriously doubt you have the specs on the build sheet for the alternator. Don’t assume that because they upsized some portion of it, that they also agreed to increase reliability requirements. In fact, it’s HIGHLY likely that all the durability/reliability specs were left intact. For example, if they spec’d bearings for 2500 hours of use at with a confidence interval of 95% for the smaller alternator, they likely used that exact same spec for the larger alternator. Just because the bearing is larger, does not mean it’s "more robust"; that is a very loose term. It may handle a larger load because it’s bearing surfaces are larger, but that also means it has a larger load to support. Component fatigue reliability is driven by specifications and statistical processes and/or mathematical modeling, not some arbitrary measurement of a bearing size. IOW, if they spec’d the smaller alternator for 2500 hours at 95%, they probably spec’d the larger one for the same failure limits. This is VERY COMMON in most all industrial and manufacturing engineering practices.

Why does a larger alternator have a larger bearing? Because it has to support a larger load. Why does a larger alternator have more cooling capacity? Because it generates more heat. But none of that means it will last longer. Component reliability is driven by a compromise between costs and desired longevity; a target is set for the desired life-cycle, and then things are tuned to meet that spec.

I would be willing to challenge this type of assumption….What proof do you have that a larger output alternator is "more robust"? I seriously doubt you have the specs on the build sheet for the alternator. Don’t assume that because they upsized some portion of it, that they also agreed to increase reliability requirements. In fact, it’s HIGHLY likely that all the durability/reliability specs were left intact.Dnewton3, you are absolutely correct. While I love having more alternator output even if I never use it, there is nothing special about the higher amperage alternators. The highest output alternator arrangement you can get is what I mentioned in my earlier post…377A from two alternators. One is a 157A and the other is a 220A. If you have been around Ford for awhile, you’ll realize the standard alternator on the 2011-2016 gas Super Duty was a 157A unit. And the standard alternator on the F-150 from 2011-2014 and maybe beyond was a 220A unit. So when you order the highest output alternators on a Super Duty, you are actually just getting two "base" alternators. I know Ford offers a 240A unit, but I highly doubt the specs are anything different. Ford used to offer a much higher quality Leece-Neville alternators on their medium-duty trucks, not sure if they do anymore.

There is much more to an alternator to just the max amp rating it states. More critically, how many amps are being put out at idle or even mid range RPM? How many amps when hot vs cold? Many people mistakenly think they get the max amp rating all the time. Some alternators (not Ford) have ducting for cool air from the air dam of the car to the alternator for superior cooling. Beyond that, some offer full liquid cooling using the engine’s cooling system. I’ve had vehicles with both…an Audi with a Bosch 150A alt (air-cooled) and a Land Rover with a Bosch 170A liquid cooled.

The varied output of an alternator makes a good argument for wanting more amps. Ford’s latest electric "supplemental cabin heating" offered on diesels draws 150A of current. Combine that with the possibility of heated front and rear seats, heated steering wheel, lighting, audio system, and standard heater blower motor plus rear window defrost running simultaneously and it is clear why high amperage is needed. The glow plugs and DEF tank heater also draw very large amounts of current. The upfitters, should everything be connected at max current, can draw up to 180A if everything was operated simultaneously.

Ok, so in the example of my truck, SPP got me the 67A (332 amps) vs 67D (220 amps) option. My point is that if my current draw is 200 amps (just an example, and obviously it varies over time), then the 67D package is running at 91% of its rated load, while the 67A option is running at 60% of its rated load. Any electrical device that I know of will last longer when it is operated at a lower % load. That’s my point. Without data in front of us, it’s hard to say for sure what is going to be the best option, I’m just saying I went for overengineering on the alternator. Now, this is not a thing I chose to do randomly. I have had many alternator related issues in the past and in cases I have upgraded alternators (and cables, etc.) myself on other vehicles. I figure at worst I wasted a couple hundred dollars on the option.My understanding is that the 332A system is a diesel truck with dual alternators. However, I’m unaware of the ratings of these alternators individually. One problem dual alternators causes is that when one fails, the other supplies all the amperage (hastening its demise) yet the charging system fault warning (red battery light) stays off. I would imagine a device running at less than full demand would generate less heat, which might improve longevity.

My point is that all systems and components are designed with a life-cycle and duty-cycle in mind. Getting "more" amp capacity does NOT mean you’re getting longer life by design. Often, it’s not even linear, but more of a parabolic life-cycle degradation. Reliability specs that include confidence intervals for same failure-mode analysis are key here.

I also am not, by any means, saying the SPP package and it’s contents are bad to have. There are situations that make this package a very smart choice for many folks. But getting because it makes you feel more manly because it’s perceived to be more heavy-duty is an ill-conceived notion. If folks like the taller right height, and the stiff ride, then by all means spend the money that make you happy! For me, because I know I have no intent of a plow or other heavy item on the front, AND I have no intent add electrical load, the SPP is a waste of money for me. Having those higher-rate springs and the bigger load alternators will NOT make the trust last longer in a "normal" situation. They will, however, assure the truck performs as desired in higher-load situations.

But getting because it makes you feel more manly because it’s perceived to be more heavy-duty is an ill-conceived notionI don’t think anyone said the snow plow package made them feel more manly. I already said I got it because I feel like I like how the stiffer springs level the truck slightly and they will also support a heavy aftermarket bumper and possibly winch. I drove it before I bought it, and I had no issues with ride even at the 60/80 psig inflation. The dual alternators will do a much better job of supporting winch, lights, heated seats, air compressor, etc… I think the single large alternator would be fine also, but it’s hard to judge exactly what I might be running off all the upfitters and I wanted more safety margin. Hell, I guess you could pick apart my choice of a engine, or trim level, or whatever. People don’t normally lift trucks only after measuring and calculating exactly what they need to clear. My truck is overkill for my current needs. I’m ok with that. I hope you can be.