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Old 05-31-2022, 02:20 PM   #1 (permalink)
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Solar panel, with no aero loss. what gain?

I have 2019 Tacoma, with 40% tonnue cover. details-

https://ecomodder.com/forum/showthre...oma-39148.html

This will allow me to mount a 100 watt panel and since I can flush mount in the cover there will be no aero penility , like others have experienced.

My plan is just hook it to the battery and the alternator should work less because the battery will always be fully charged and when there is a load, the alternator shouldn't be working at all as long as it see 13.8 volts at the battery.

If the panel can't keep up, then the altenator should kick in to keep the system at 13.8.

I plan on using a regular 12 volt socket mounted in the bed so the panel can easily be connected and disconected when I need to haul larger loads.

My math is I can get 400 watt/hours of power per day, which should cover the electrical needs my commute in the summer. I currently use about 15-17 amps of power while the car is running. Thats about 235 watts per hour and I'm in the car under 1 hour a day. So on sunny days, this panel "should" provide all my eletrical needs if the battery can store it. which is my main worry, how much will my factory 585 CCA Lead Acid battery store and will most of what the panel puts out go to waste?

What ideas do you guys have?

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Old 05-31-2022, 02:37 PM   #2 (permalink)
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You'll need to disconnect the panels when the truck isn't "on" or the batteries will cook. Either that, or get a charge controller.

Since the battery is always nearly fully charged, you'll get little benefit from the panels when the truck isn't on. Not only that, but a nearly full battery wastes more than half the energy while being topped up.

The truck may be able to serve all the electrical needs while driving if the HVAC and all lights are off. Otherwise. Even then, the alternator may still run.
My Acura has a base load of almost 200 watts with all accessories "off".

You're not going to measure any fuel economy benefits with this implementation. I think the only way you'd notice an improvement is to get a deep cycle battery and disable the alternator. You will want to keep an eye on voltage though and re-enable the alternator if it goes too low.
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Old 05-31-2022, 03:37 PM   #3 (permalink)
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Quote:
how much will ... most of what the panel puts out go to waste?
Underbody neon lighting.
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Old 05-31-2022, 03:49 PM   #4 (permalink)
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I will run a charge controller, I think other wise the panel could fry the entire electrical system. I left that out of my orginal post, in my mind that is implied any time you're dealing with a panel over 5-10 watts.

I need to figure out how to disable the alternator and do some A-B runs I guess to see how much MPG disconnnecting the alt is worth. I have a deep cycle battery I can throw in it for testing.
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Old 06-02-2022, 10:20 AM   #5 (permalink)
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so this my thinking now-

Solar panel> charge controller> 36AH lithium battery > 30amp DC to Dc 12 volt to 13.8 volt convertor> stock battery.

My thinking is the consant 13.8 volts to stock battery will keep the alternator from working. Leaves stock charging system in place as a back up.

there room under hood for charge controller battery and dc to dc convertor.

https://www.tacomaworld.com/threads/...thread.295653/

Cost panel and charge controller $110
Battery-150
dc to dc convertor -70
Brackets and wire about 100

total cost about 450 dollars

The lithium battery should supply electrical needs for the truck for about 1.5 hours .

Now, the trouble I have is the fuse for the alternator hard to remove, as it's bolted in and the fuse box has to be removed.

I can test if 13.8 volts to the battery keeps the altenator from producing current by putting a battery charger on the battery as the truck runs and use an amp clamp.

I did more reading and now believe peak loads may be over 30 amps when running the heater blower on high, but it's rare that I run it on high for more than a few minutes, I usually have it on low.
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Old 06-02-2022, 10:30 AM   #6 (permalink)
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If the alternator is spinning it will contribute to engine drag, even unloaded. @ 3mpg it isn't noticeable, but as you get higher in the distance per volume of fuel it becomes apparent. You may not ever see it, but your electrical system has a cold function so you may need to trick it even at 14.1v. I suggest a disconnect switch of some sort
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Old 06-02-2022, 02:39 PM   #7 (permalink)
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Quote:
Originally Posted by Piotrsko View Post
If the alternator is spinning it will contribute to engine drag, even unloaded. @ 3mpg it isn't noticeable, but as you get higher in the distance per volume of fuel it becomes apparent. You may not ever see it, but your electrical system has a cold function so you may need to trick it even at 14.1v. I suggest a disconnect switch of some sort


Yes, on most modern cars, the ECU raises the output voltage to 14.1-14.6 for a short period after starting, this to quickly replaced energy that was used to start the car.

Even though the battery is hit with this higher voltage, the current will be very low, because the starting battery will be fully charged from the lithium battery. The internal resistance on a fully charged battery is high, so the current flow will be low.
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Old 06-03-2022, 02:31 PM   #8 (permalink)
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I think first of all, on a non-electric or hybrid car, 100W panel might be too much. It's not enough to shut off the alternator completely for a long time, but it will quickly fill the battery.

If you just have solar panels laying around, I think an approach could be:
1. Replace the lead acid battery with a higher voltage and higher capacity lithium ion battery. The idea is that the alternator should not be able to charge the battery all the way to full, and it should not be applying excess voltage that would normally just create hydrogen and oxygen in a lead acid battery.

LiFePO4 is a bit problematic because its nominal voltage is a little lower. The usual lithium polymers will be around 50% charged at 14.8v at the alternator which IMO is about perfect. If you want something safer, you can use 6S lithium titanate which can charge up to 18V.

2. Limit the solar charging to 16V, I don't think car electronics are supposed to take much more than 16V.

3. If you can, limit the alternator charge voltage to 14V.

The result will be that you end up with a half full battery while driving, the solar panel charges the battery up to full if it's sitting outside, and you start off with a battery voltage high enough that the alternator won't be doing work.
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Old 06-03-2022, 06:24 PM   #9 (permalink)
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If you're going Lithium, you NEED LiFePO4. Lithium Titanate can work, but it's not optimal. Li ion is not at all optimal.

The thing is, you don't want or need to go over 15V with your charging system. 14V would be better.

LiFePO4 has a min voltage of around 2.8, a nominal voltage of 3.2, is fully charged around 3.6 and can handle up to 4V each. Put them in a pack of 4 in series and you get 11.2 min, 12.8 nom, 14.4 full, and 16V max, perfect for a 12V car system. Set your charge controller to around 14.5V and check the balance every month if you don't want to play around with a balancer.

But be aware, with the exception of Lithium Titanate, any Li battery will not like the cold or the heat.

As for Li Titanate, 5 cells isn't quite enough (11.5V nom/15V full), and 6 is too much (13.8V/18V full), although with 6 cells I guess you could keep them close to nominal voltage instead of full charged. But for a solar panel that tops off batteries so you can try to not use your alternator, you probably want to charge them up as much as possible. A fully charged LiFePO4 will stay at around 13V and fully charges with a normal Lead Acid battery charger that charges to 14.5V. Not only that, LiFePO4 is more energy dense. Li Titanate cells are close to Lead Acid in energy density. Having one that's half charged all the time would be like having a half sized Lead Acid battery.
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Old 06-05-2022, 06:54 PM   #10 (permalink)
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Lithium titanate is nowhere close to lead acid. It's the same as lithium iron phosphate per Ah just lower voltage. 6 in series will be 50% heavier. 14.4V on a 6S pack is 80% charge which is not that bad.

I know because I run a lithium titanate starter battery. It's 15lbs 5S 40Ah. The voltage curve is steeper than some images on the internet suggest.

I still think you can use a lithium polymer battery if temperature isn't a problem (I assume it's not if it sits in the back of the car). It will only cycle in a narrow range and will probably never be depleted.

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