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Old 05-13-2021, 09:36 AM   #21 (permalink)
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Never tried, BUT, a bolt on electric hot water heater controller can be had for $20 and is decently adjustable from about 100f, and should handle the switching loads

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Old 05-13-2021, 04:49 PM   #22 (permalink)
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If the goal is extending the duration of leaving your alternator off, perhaps money spent on providing additional energy would be better?

It's one of those situations where you've created a "solution" that requires more solutions.
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Old 05-13-2021, 05:36 PM   #23 (permalink)
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If the goal is extending the duration of leaving your alternator off, perhaps money spent on providing additional energy would be better?

It's one of those situations where you've created a "solution" that requires more solutions.
My goal is to reduce the overall power use for slightly improved MPG when the alternator is on and more range/less battery drain when it is off. Not running the fans when they aren't needed would go a long way towards saving battery power. I'm not particularly concerned about running my battery dead as I have an Optima Yellowtop and I don't usually drive far enough from home for that to be a concern, but using less of the battery's capacity will save a few cents on my power bill and should help to prolong its life, which is a big consideration when a comparable replacement AGM deep cycle battery is nearly $300. My battery is going on 8 years old and I hope to not have to replace it for a while.

Adding a secondary battery would also add significant weight and take up more space in my trunk, so reducing power consumption is a better solution than adding more batteries even ignoring cost.
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Old 05-13-2021, 06:12 PM   #24 (permalink)
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I believe there is a way to rebuild an alternator to be far more efficient, fyi. I would think the easiest way to reduce electrical load is to just unplug one of the fans, no?
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Old 05-13-2021, 06:28 PM   #25 (permalink)
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I believe there is a way to rebuild an alternator to be far more efficient, fyi. I would think the easiest way to reduce electrical load is to just unplug one of the fans, no?
Thanks for letting me know, I never heard of that. I just know that alternators are generally only about 50% efficient. Do you have a link to any information on that?

Unplugging one of the fans wouldn't work, I live in the south and we see 100+ degree days here. The engine cools fine with 1 fan, but the AC doesn't work well at idle and low speeds with only half of the condenser getting cooled off and the compressor drags the idle down noticeably more than with 2 fans. The extra power the compressor draws from the higher head pressure would almost certainly outweigh any efficiency benefit from the power savings as the compressor uses much more power than the fans.
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Old 05-14-2021, 01:51 AM   #26 (permalink)
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I wonder how you could make an alternator more efficient...

I'm trying to remember how they usually work. If I remember correctly the voltage regulator shunts current through the rotor which cause an alternating current in the stator (or is it vise versa?) In any case, if you could use thicker wire without reducing the number of windings, that would help.

Now if the rotor's current is controlled by means of resistance you could instead control current by means of pulse width modulation instead to help increase efficiency. A permanent magnet rotor could be even more efficient, but then you'd have to think of another way of controlling voltage and current.

The rectifier is another point of energy loss. Using more efficient diodes may help. But more efficient diodes may not tolerate as much current. So lowering max current may be necessary.

Lowering voltage can also help by not charging the battery up to the point that it's self-discharge also raises. Although in theory your alternator could be more efficient if it ran at higher voltages/less current (more turns) and feed a higher voltage battery. Of course then there'd be DC to DC losses from the higher voltage down to 12V unless you completely rewired everything to use the higher voltage, including modding the ECU and any other place where voltage is stepped down for use in electronic chips and also your have to build your own ignition coils. But all this would probably not be worth the trouble.

Also, I don't remember if the rotor is wye wound or delta wound. A wye wound rotor would be more efficient, but the voltage and current would be different without changes in wire thickness, length and number of turns.

Another area of loss is the housing and rotor construction. You want them (or at least the housing) to be made out of very thing lamanates that are electrically isolated from each other made of an iron alloy with a very low hysteresis.

Of course if you have a lot of stop and go traffic, maybe making the alternator come on only while decelerating would help.
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Old 05-14-2021, 04:08 AM   #27 (permalink)
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https://ecomodder.com/forum/showthre...tor-38719.html

There have been several threads over the years
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Old 05-14-2021, 11:32 AM   #28 (permalink)
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Thanks, that is an interesting idea. As concerned as manufacturers supposedly are about fuel efficiency, I wonder why they don't use higher efficiency alternators such as permanent magnet. There must be a reason, I just don't know what it is. Perhaps they wouldn't be reliable in such a harsh environment or something. I remember reading that there are ways to build alternators with 80-90% efficiency, but their downsides such as reduced output and reduced reliability in harsh conditions make them unsuitable for automotive use. I'm sure cost has something to do with it also, but there must be another reason.
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Old 05-14-2021, 12:55 PM   #29 (permalink)
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If an alternator drags down the fuel economy by 10%, half of which is inefficiency, if you made it 99.9% efficient then you'd only increase overall efficiency by about 5%.

I do question whether alternator technology really hasn't improved over several decades. Are modern alternators really only 50% efficient?

As far as the battery goes the lead acid battery is tried and tested. You can make a lithium battery work. But now it needs thermal management, both cooling and heating, plus electrical management because they need to be balanced and if you leave your lights on you don't want a lithium ion battery discharged below it's threshold. Not to mention lithium ion can't be used in a 12V system, so you'd have to use another voltage and you couldn't use common 12V parts.
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Old 05-14-2021, 01:06 PM   #30 (permalink)
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Thanks for letting me know, I never heard of that. I just know that alternators are generally only about 50% efficient. Do you have a link to any information on that?

Unplugging one of the fans wouldn't work, I live in the south and we see 100+ degree days here. The engine cools fine with 1 fan, but the AC doesn't work well at idle and low speeds with only half of the condenser getting cooled off and the compressor drags the idle down noticeably more than with 2 fans. The extra power the compressor draws from the higher head pressure would almost certainly outweigh any efficiency benefit from the power savings as the compressor uses much more power than the fans.
'Improving Alternator Efficiency Measurably Reduces Fuel Costs', by Mike Bradfield, MSME, Remy Inc. ( DELCO REMY ), 2008
* starting with fuel to the engine at 100%
* the engine is 40% efficient
* the serpentine belt/pulley is 98% efficient
* the alternator is 55% efficient
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From AMCA / ASHRAE:
* the electric radiator fan motor is 92% efficient
* The airfoil shaped cooling fan is 90% efficient
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From the gas tank to the air actually moved by the electric fan, total efficiency is 17.3 % ( 82.7% of all the energy is lost )
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If the fan is running at all, at 40-mph or above, something's wrong.

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