Hacking the solar?

That is an interesting thread, thanks for pointing it out! Maybe someday I'll try one of these mods. I don't have a lot of need for charging external equipment, but maintaining the aux 12V battery sounds interesting. And if we do that, I suppose it would make that battery more useful for running equipment with the hybrid system off. Like charging other equipment (except this way, there's no guarantee you're not discharging it faster than charging).

 

At 13.5 volts and around 2.8 amperes on sunny days is good enough to connect many type of devices

Nexus 7 ?

 

Finally I have the time to make some graphic representation of the study I made checking currents and voltage using my battery charge controller. You can see the link here:
Prius Solar Cell as battery charger: Analyzing the performance of my battery charging controller

 

Now I have updated my blog with the Design of experiment for different options to decide what is better to reduce trapped heat inside your car.
Prius Solar Cell as battery charger: September 2014

 

Wow Sambra, you have done a great job collecting data and posting it for us. My Prius is often not used for a month or more and the battery is dead when i try to start it. This is a great solution. Thanks for doing all the work.

 

After that happens about twice, your battery is likely weakened and needs to be replaced.
To prevent that from happening, the best solution is to connect it to a small automatic battery tender type charger.
Standard 110V versions are readily available for about $35; solar ones might be available too, likely at a much greater cost.

 

Just completed my Prius solar connection to a charge controller. My installation differs from Sombra slightly. Instead of locating the solar wire in the ceiling, I located the wire as it passes through the bottom of the rear left passenger door frame. Photo 1, To do this, just remove a 3 ft section of the molding at the bottom door frame. Put your fingers under neath it and pull up. photo2, It comes right out. You will now see a black cable harness. Where another cable joins it, remove the black tape around the extra insulation and remove the insulation. There are about 10 wires in the harness. There are just a few of larger wires. Locate the green one, that is the solar wire. Using a wire connector, connect this to about ten feet of #16 or 18 wire. photo3, Fish the wire under the seat and into the rear compartment. Fish the wire along the lithium battery compartment, over to the 12v battery. I used a Sunguard solar controller just like the one Sombra used. photo4 Once you have all the parts together, it takes just one hour to complete the installation.
John

 

Here is a parts list for the job:
1. Sunguard 4.5 amp Controller ($37 on Amazon.)
2. Inline fuse with 10 amp fuse
3. Wire terminal connector kit (Walmart, $7.95)
4. #16 wire, 10 ft.
5. Black electrical tape
Connect the fuse between the battery + terminal and the charge controller + battery connection.

 

Wow. I never would have believed that the solar cell designed only to turn a little fan would have that much output, as documented in the blog posts linked above.

He did mention though that direct sunlight was critical so this solution won't work at all if the car is stored inside while not being used.....and maybe not well in cloudy areas too.

And finally, a battery that won't hold up for 4 weeks of non-use has lost some of it's capacity already and if it looks like this solar charging system is going to work for you, it will work much better if you start with a new battery. Even this might not keep the old one alive very long.

 

Good job!

 

I strongly recommend using a Buck Step-down Converter instead of the charge controller. The ones without display are the best implementation since the display draws power. Example product: "RioRand LM2596 DC-DC Buck Converter Step Down Module Power Supply Output 1.23V-30V"
Advantages of the Buck Converter are complete controllability and predictability, and plays really well with the fan. You can set your float/charge voltage as aggressively or conservatively as you like, I suggest 13.1. (The Prius charge system will handle de-sulfating, etc.). The buck converters are also dirt cheap @ around $2.50 each. Here are my original implementation instructions and notes: Solar Panel Mod charger | PriusChat

As a side note, if you get clever with one of the "display" buck converters, you can rig a switch to turn off or drive the display from the input to eliminate leakage current from the battery when parked in the dark.

SolarPriusGuy, excellent find regarding tapping the solar wire under the rear passenger door. Hitting that wire in the dash was the most complicated step of the upgrade when I first did this.

 

Here is a recap after completing the installation in December: Just returned from a six week trip while my solar powered Prius sat in the driveway. The 12v battery is fully charged and I had no start up problems. Of course, the car was outside with no obstructions to full sun for the panels.

 

I'd recommend maintaining the 12V battery with the solar panel, not trickle-charging it. If a reliable charging current can be derived from the solar panel, through a charge-controller circuit, it could alleviate the anxiety associated with the inevitable slow-drain on the 12V auxilliary battery.

I've gone into much detail on the subject of trickle-chargers vs. battery-maintainers in other threads. In either case, circuitry is required to limit the current being applied to a battery once it is fully-charged, otherwise the battery is sure to be damaged by over-charging.

 

Or you can use a source that isn't capable of providing enough current against a full charge to do any damage.

 

I think we're talking about enough current here to top-up a Prius battery. The easiest way is for the voltage to be controlled to deliver the right amount of current to give it a proper charge, although current-limiting is also an option. Such a controller should also monitor the charge level of the battery and deliver programmed charge cycles in response to monitoring. This is very similar to the way a battery-tender works. The simplest way is to set the maximum voltage to the level of a full-charge on the battery, but this can cause problems as the battery ages.

 

great job VallesJ, one thing.. Can you detail your use of the capacitor in your install
Thank you

 

What capacitor? Are you meaning the diode?


Nexus 7 ?

 

I must have read it somewhere else...someone used a super capacitor as a buffer for the solar panel for partially cloudy days. I have been researching this mod for many days..so too information overflow. Since you mentioned it..the diode size would be helpful.

Thank you

 

I did this mod the other day using the instructions a few posts up and the SunGuard controller from Amazon. I'm curious, I don't have a way to test/measure it but would the solar panel be enough (hypothetically, on a sunny day in the southwest) to safely use the car as a solar charger for a phone/tablet plugged in by using accessory mode? Or would that still run down the 12V battery pretty fast?

 

Got very inspired by Solarpriusguy and I decided to do the mod on my Prius 2011. Solarpriusguy was kind to make the photos of his mod available on the forum again which made it much easier. I used a Victron BlueSolar MPPT 75/10 Controller with Bluetooth (bought on eBay) so now I can monitor the charging on my mobile (works with both Android and iphone). It works great with enough power to keep both the battery charged and run the ventilation fan. See attached photos.

 

I second this and confirm it works as said.

I am using a Renogy 10A Wanderer
Controller purchased for $15