Quote:
Originally Posted by Blacktree
This is an interesting project. But there are a couple things you may need to consider.
First of all, 250 Watts won't be enough to completely replace the alternator. But you probably know that. You might need 4-5 times that much Wattage, depending on your car's power requirements.
Also, while reducing the load on the alternator sounds good in theory, there is a downside. The alternator has a "sweet spot" where it's most efficient. If it goes out of that zone, its efficiency drops. So ironically, giving the alternator a helping hand might actually waste power. Personally, I wouldn't bother unless the alternator is being overloaded.
The exact numbers may differ from one unit to the next. But I read a scientific paper where the alternator they tested was most efficient at 30-40% of its max load, spinning at 2000-2500 RPM (that's alternator RPM, not engine RPM).
Instead of "helping" the alternator, maybe you could turn it off when it isn't needed. Sort of like pulse and glide. I think some modern cars do that already.
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Great info, thanks! With everything turned on, my car's power consumption is around 65 amps and 250 watts is only around 18 amps at 14 volts, so that definitely wouldn't be nearly enough to entirely replace the alternator under all conditions. But for how I drive and my typical consumption of around 10 amps, that should be plenty for almost all conditions. As little as I drive, just the 50 watt panel may end up being plenty since I can count on one hand the amount of trips I have taken in the last several years long enough that significantly draining my 74 amp hour battery would be a possibility.
Interesting, I didn't know alternators have an efficiency curve but it makes total sense. My alternator is rated at 105 amps since the engine was from an Acura TSX, so it definitely has a very easy life powering my Civic with all LED lighting and comparatively very few electronics. I'm likely going to wire it to a switch on the dash so I can turn it on if needed such as for the very occasional road trip and keep it off the rest of time except when engine braking. Completely removing it is not an option on this engine because the same belt also drives the water pump.