Solar Panel Mod charger

Hey thanks for the late reply, but still a reply...
You can see my installation on the following link:
Prius Solar Cell as battery charger
Let's see how it works.

 

I love it, especially that I'm not the only solar charging Prius out there. Interestingly, my Prius is also blue just like yours, but lacks the special wheels.

In your write-up where you mention, "I read max current accepted by the battery to avoid damage is 4.5 Amperes", I've seen that as well, but it is not an actual limitation of the battery. Even the Prius's built-in charging system will charge the battery as fast as it will take a charge (up to 90 amps) at 13.5 volts, or higher for a short de-sulfating period. The key thing to limit for the life of the battery is the voltage.

One thing that would be great to know about the MPPT you finally chose, is what voltages it uses to maintain the battery. Next time you have a sunny day, if you could leave a volt-meter on the battery without the car taking power (no dome light, key fob far away, doors locked, etc), and record the voltages that would be really nice to know. What I would expect to see is ~15V coming from the panel into the MPPT, and between 13.2 and 13.5 volts on the battery. If the MPPT maintains the battery voltage above 13.5V, that would concern me, especially in summer. The MPPT may be smart enough to use a higher voltage for 10 minutes or so, but I would be surprised if that is the case, besides this function is already accomplished by the built-in Prius charge system.

I'm also curious, though it depends mostly on the sun and temperature, what is the maximum current you are able to produce with the MPPT. For my car, I did this test with the headlights on to create drain.

So to recap, it would be great to know voltage in, voltage at battery, and current under full sun of the SunGuard SG-4 MPPT.

By the way, one thing I mean to add to the input (solar panel side) of my charger, is a large storage cap. I believe this would improve charge current and ventilation performance, since both of these loads are modulated and not "smooth".

-Michael

 

But SunGuard is a PWM not MPPT. It switches on and off rapidly to keep the voltage down. Is this good for the electronics while the car is ON/READY? May be a more complete solution is to use a relay to cut off the solar charger when the car is on.

 

As long as the solar charger never holds the battery above a safe voltage, everything is fine. Regardless of how the charger converts the solar power (MPPT vs PWM vs Buck Converter) there would be negligible ripple.

Also, while the vehicle is in READY, the Prius holds the battery voltage above what the charge controller should be putting out, in effect isolating the solar charger. Personally I would not mind some extra power injected into my car while driving, but my best case scenario of ~35W would still be a drop in the bucket.

 

During my first test with good sun, I got 13.5 v, an little more than 2.8 amperes, with everything off on the car.

Nexus 7 ?

 

How does it affect the solar ventilation? Will it pull most of the current from the fan?

Nexus 7 ?

 

Really good project and good presentation by Michael. Thank you!

I have two questions:
1. Is it safe? What happens with the Hydrogen that releases from the battery while charging? During battery charging, oxygen and hydrogen are released after a cell has achieved approximately 95 % of its charge, during boost charging or overcharging. As far as I know, you should charge a battery in vented area. Hydrogen is very flammable, and can explode even at very low concentrations. Most flammmable gases only explode when there is a narrow range between the amount of air and amount of gas in the mixture. With hydrogen, however, the range is huge, and so from a very small concentration of hydrogen to a very large one any hydrogen and air mixture is potentially explosive. I understand that in some point, the solar vent will start and blow the build up Hydrogen out, but what if not? What if there is not enough sun to trigger it, but enough to charge. If the mix is strong enough, any spark, from electrical motor or electrostatic discharge, will cause a big bang. Can this be an issue?

2. How do you know if the battery life is over? Or, what if the water evaporates and the battery become dry due to prolong charging?

I'm still considering to do the mod, but just wanted to be sure if it is safe. I have a dash camera that I want to run 24/7 for security reasons. It drains around 400mA and is enough to flatten the battery over the weekend. It use to work for 4 days without charging, but now the battery is 2 years old and it doesn't have the capacity any longer. It only goes less than 48 hours.

By the way, "MORNINGSTAR SUNGUARD 4.5A 12V" charger is over $60 in AU.

 

Is it safe?... well I am using it since last year, and I have not exploded yet... lol.... just think how much hydrogen could be released by the small battery. For other pv controllers you need to refill with water on the battery, with this one you don't have too.

 

If you follow the link to the blog where I am explaining the mod, and my analysis of it, you will see that after about 5 minutes charging the battery, it goes to a "maintaining state" where it does not need to supply current to the battery, there is where the vent start spinning.
I did a Design Of Experiment trying to understand how much it is affected the charger to reduce the internal temperature of the car... so I introduce variables as sunshade, slightly open moonroof, and charger working, in all different combinations; in summary the sunshade was the most effective way to prevent higher temperatures inside the car, like for 10 Celcius, meanwhile the vent or open moon roof only around 2 celcius... So, really don't expect so much of the vent. There is not a significant difference using the charger or not to reduce the temperature inside the car... come back later and may be I have already posted the DOE with the results.

 

Regarding safety, there are three factors that I believe make this redundantly safe: #1, if the voltage is set and maintained properly and an AGM battery is used per the Prius design spec, there will be a very slow creation of hydrogen which is internally recombined in the battery to make zero hydrogen release. #2, if for some reason hydrogen is released, there is a vent tube which vents it outside of the car., and #3 hydrogen is incredibly talented at escaping due to its small molecular size and being much lighter than air, and would most likely never reach explosive ratios from a car battery even if destroyed/dried the battery through overcharging. Keep in mind, the Prius will put the charge voltage much higher than the trickle voltage for a period every time when you power on the vehicle, so Toyota also felt it was safe to charge an AGM battery inside the cabin. It would be considerably less safe to charge a conventional lead acid battery in this way, especially if the charge voltage were not correctly for the temperature, or the charging circuit malfunctioned, but point #3 above would probably still save you.

"2. How do you know if the battery life is over? Or, what if the water evaporates and the battery become dry due to prolong charging?"
The biggest sign that your battery is going bad is that if you put the car in ON without touching the brake to put it in READY, it wont take long before there is not enough power to put the car into ready. Likewise, if not in READY, and you listen to the radio for 45 minutes and your car later won't go into READY, you have a dying battery.

For anyone considering the mod, please just use an inexpensive "Buck Regulator". In hindsight, having used this solution now every day for however long, the buck regulator is the way to go, especially for its predictability and cooperation with the cabin blower. If you are concerned about the affect of constant trickle charging or are in a very hot area, just put the trickle voltage slightly lower, for instance 13.0 V.

Regarding using this mod to offset a high drain during the night such as a dash cam, this mod will help significantly, but you will still greatly shorten the life of your battery if there is something (like a 24h dash cam) cycling the battery each night. If you were to go the dash-cam route anyway, set the trickle charge voltage as high as the battery manufacture allows (at the max temperature your battery will every be) to maximize the life of the battery under this very stressful situation. Sulfation and loss of plates will still eventually kill your battery though.

 

As a follow-up, I added a 25V filter cap to the input of my buck converter. This improved charging and fan performance significantly. The output of my buck converter is self-limited mostly by the temperature of the buck converter, and seems to cap out right around 2.8 Amps as well, with plenty of power left for the ventilation system. By the way, 2.8 A is plenty for charge keeping or recovering a partially discharged battery.

 

The effectiveness of the vent or cracked open windows depends a lot on the outside air temperature. In Seattle, near the Puget Sound (essentially the Pacific Ocean), the summer air is pretty cool, but cars still get really hot in the sun. The vent system (or cracked windows) help a lot in this scenario.

 

An easier place to connect to the solar panel is at the bottom of the rear passenger door frame. Remove the plastic molding, it pops right off and you will see the cable harness. Remove the black plastic shield. There are about ten wires in the harness, of which several are 16 or 18 gauge. The rest are smaller gauge. Locate the larger green wire. That is the solar panel output. Photos and more details are here: Hacking the solar? | Page 7 | PriusChat.
John

 

Hi guys,
I just bought a Prius III 2011 with solar panel wnd was surprised about the limited use. Obviously you want to charge at least the 12 V battery with its many users in off-mode. That then needs not to be done by the engine and give a little bit of extra mileage.
The main tasks seems to be to find the green wire coming from the panel, presumably below the left rear door, connect a strong new wire to it and run it to the battery compartment. Any advice on how to best do that?
There I intend to connect a Solara SR 85 TL which is supposed to intelligently charge 12 V batteries. Costs about 35 Euros. Anything else I should consider?
Thanks for help, this is my first Prius.

 

congrats and welcome!

this has not been done to my recollection, all the best in your missionary work, maybe you'll be able to help others!
please post a write up with picks when you are finished.

 

Hi everyone, I signed up a user account specifically for this issue!
I agree with the person above who said this is insulting to put all that engineering and cost into the car by adding the solar panel and having it do nothing but run the air flow fan.
The solar panel was actually the reason I purchased my prius over a few others at the lot. While walking around the car, I just happened to notice the roof was different, and looked closer to see a solar panel integrated into the roof line! So Cool! I figured this car must be more efficient than the others , so I eliminated those cars and decided on thus one immediately . Not until looking through these forums did i find out the solar panel is virtually useless.
And that's been bugging me the whole time I've had thus car . I actually got a "dead battery" for simply leaving the accessory on and charging my phone and a camera battery for about 15 minutes, early on.
Since then, I've had a love /hate attitude to this car. I do a LOT of parking and sitting , while using a phone , camera, handheld radio.... all if which I akways simply plugging into the 12v accessory outlet while the car was off if they needed charging .
Having to leave the car "on" the whole time now , with the engine starting up every 30 mins, sort of defeats all the goid mileage claims of this car.
And that especially irks me , knowing I have a very expensive solar panel a few inches away that could easily recharge all of these devices.
There doesn't seem to be much interest in this situation other than the few people on here, a few years ago.
Has there been any updates , or new ideas how to get some better use out of the panel? I'd be happy to just get a 12v outlet or two from it.

 

I paid $30k for a 65w solar panel?!

I agree, it's a bit gimmicky but I never get a heat wave when its 111° and I open the car doors. Plus car camping is slightly better.

This might work for you.

 

welcome!

not that i recall seeing. i hope you have better luck than rfkiel above.

all the best!

 

You need to read the owners manual that tells you what the solar panel is for.
It ONLY runs a fan to circulate outside from the front of the car, through the car and out the back.
Which is supposed to keep the hotter air from heating the car. So when you open the door you are not hit with
a wave of 125 degree or hotter air!
It does NOT supply power to any outlets. I guess if you really wanted to you could rewire it to do that.
That is why you are draining your 12v battery.

 

Yes, I know that, hence my question. I just explained that I didn't know that *at the time of purchase* and was wondering if anyone has made any modifications to allow the solar panel to charge the small battery , power a 12v outlet , or anything else . In this day of cell phones and ipads, I just find it odd that almost nobody has complained that the car needs to be "on" to use the 12v outlets, particularly when the solar panel easily powers a small fan .
If it was easy to do, i'd literally rather cut the power wire to the fan and run it to an aftermarket outlet .