[changzuki]

Originally Posted by BobS

CrazyJerry,
Wow, what a great part-by-part system analysis. Are you retired or just don't bother with sleep, anymore? If you don't mind, a couple of questions:
1. With an alternator cutoff switch, the alternator rotor is still engine-driven. Could a switch-driven clutch like the AC compressor clutch reduce the load on the belt even further (and the relays then could be replaced by a diode bank)? Would this be of advantage?
2. Have you seen Lasersaber on Youtube? He has replaced his car battery with 6 supercapacitors and a very small battery. With your minimal draw, you may be able to
get by with an even lighter setup than his, maybe 1/2 lb. If you haven't seen his video, Youtube the words "boost pack".
Looking forward to much more of your analysis.
BobS

Hi BobS - and thanks for your kind words... I don't sleep much anymore and quite a ways from retirement - which I don't believe will exist as we know it today, so this entire 12 year off-grid experiment is a challenge to constantly do more with less on all fronts. Knowledge is worth its weight in gold and so is the ability to think things through and take necessary risks to make x,y, or z work. I get lucky once in awhile and the inspiration from folks on ecomodder and other forums is fuel for me - we need more of this!...
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>>1. With an alternator cutoff switch, the alternator rotor is still engine-driven. Could a switch-driven clutch like the AC compressor clutch reduce the load on the belt even further (and the relays then could be replaced by a diode bank)? Would this be of advantage?
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---Excellent question! Let's take a look at this "piecemeal".
An AC compressor clutch (or variation of) would effectively disengage the spinning of the Alternator's rotor, but at the end of the day is there a gain or a loss? I don't know the actual energy difference between what it takes to spin just the unengaged AC clutch pulley at speed vs the no load spinning of the normal alternator setup at speed but there is likely a advantage going to the AC clutch setup as you've suggested in your question..
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RPMs being equal between the two (and I do realize there is typically a pulley diameter difference here), the alternator normally has a cooling fan which should consume some extra energy to spin it, the AC compressor lacks this so sticking with a no-load spinning only situation, the advantage should go to the compressor clutch setup.
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At some point though, one may want to use the alternator and here is where it may get interesting... In addition to the alternator draw (in creating field and output currents along with its normal spinning friction), we can add on the amps (current) draw of the magnetic compressor clutch... Depending on the clutch and figures used this can normally be 3-4 amps dc (possibly as high as 7amps on a 12 volt system – Nippendenso or the like brand). This translates to somewhere in the vicinity of 36-48 watts just to power that magnetic clutch - this is not a lot of juice as long as the clutch assembly is sound. If the magnetic clutch's is worn and the air gap becomes larger it will take more juice to engage it – and this can easily jump to a couple of hundred watts and blow a fuse. In this case a couple of hundred watts is roughly one-fourth the output of the 800 watt alternator used in the Centurion.. To give it a little perspective, the roughly 200 watts it would take just to power a sloppy air gap magnetic clutch, is more energy than the head/clearance/brake/dash lights, wiper motor and onboard four camera Centurion use...
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As far as an AC magnetic clutch itself is concerned: A typical car’s air conditioning compressor will need approx 4-5 hp to run at full load so its magnetic clutch assembly should be stout enough to handle the common alternator full load rating of just over one horsepower.
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So back to the question... If the electrical demands are not requested (say for the mid-morning Green Grand Prix Stage I fuel economy portion), then your suggestion of the magnetic clutch disconnect likely has some clout here. This portion of the event is 100+ miles so there could be some decent savings here of this type of alternator disengage.
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If on the other hand, the electrical demands are requested - Green Grand Prix at night in the rain, then we could add the additional energy needed by the magnetic clutch to the regular electrical demand and there would be an energy penalty above and beyond the normal alternator output. I do believe the roughly 36-48 watts may not seem like a lot, but on most cars you can hear an alternator whine a bit, or a pitch in rpms, when simply turning on a smaller load like a couple of 55 watt halogen headlights. On a smaller engine like Centurion's limited displacement 850cc engine, it's much easier to experience this extra load.
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With a lead acid battery: Would the 36-48 watts used to engage the magnetic clutch be more useful and use contribute to a higher mpg, if used instead, with the regular alternator setup to float charge the battery at roughly 13.4 volts - which uses less energy (amps) - than keeping the battery in its bulk charge voltage of 14.1 volts or so and at the same time possibly extend its lifespan? More food for thought.
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So, depending on the situation, this modification (or variation of it) has potential to reap some benefits especially over the car’s lifetime and just may be worth the effort to do.
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As an additional note: this modification would do away with the disconnect relays I had installed. When the magnetic clutch disengages the alternator it effectively stops it as though the car is shut-off, so the disconnect relays would not be necessary. In the same way, the diode bank that is suggested in the original question would also not be needed. The alternator by default has those built-in so the additional diode bank would not be necessary.
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Using a brushless permanent magnet alternator is an entirely different story, and, in this on-or-off charging scenario could be more efficient compared to the standard alternator which wastes a lot of energy just to create a magnetic field…Typical pole claw alternator is 50% efficient and CEN advertises about 70% efficiency on their alternators. PMA's typically are in the 90% efficiency range but are much more challenging to control for battery charging - but a carefully watched volt/amp meter should tell you when to disengage via a magnetic clutch ..)
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To incorporate a setup like this in Centurion would require a bit of creativity since free space within the engine bay is at a premium.
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Swapping spaces with the air filter may provide a solution though since the existing alternator space is pretty busy with the exhaust manifold, oil filter access, and steering box.
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I may have overlooked something but I'd love to hear others' thoughts on this, again I really like this question as it challenges any external load management (power steering pump, alternator, etc..) and opens up the door to think of other ways to accomplish the engagement of these loads, if, and when they are necessary... Additional discussion might also include battery longevity based on the chemistry when used in an on off system like this.
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>>>2. Have you seen Lasersaber on Youtube? He has replaced his car battery with 6 supercapacitors and a very small battery. With your minimal draw, you may be able to get by with an even lighter setup than his, maybe 1/2 lb. If you haven't seen his video, Youtube the words "boost pack".
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---Yes!!! Leaving myself open to criticism here, I am in the camp that supercapacitors have great potential for future electrical storage. As you mention, there is a weight savings here. If handled correctly they are safe and have the ability to last a long, long, time.. A couple of issues (that are becoming less over time) are: The management of higher voltages of the supercapacitors to be usable in say a standard 12 volt automotive application. For example, the ability to have a decent amount of usable electricity from them over a longer period of time - not just a short burst - say for a starter motor. Similar to lithium, multiple cells/capacitors need to be watched for balancing issues. The example you have given would actually be a pretty good setup as a booster pack for a small battery in something like Centurion since its power requirements are very, very low. I have not made it that far yet, but have had some excellent results with a small lithium battery.. My experiments with small lithium is from a desire to have a common battery storage platform for the house, Aurora trike, electric mower, Centurion, etc... Maybe when the lithium market fades, supercapacitors will be the answer. We'll see!
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~CrazyJerry