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Solar Panel Mod charger

Discussion in 'Gen III 2010+ Prius Accessories and Modifications' started by arkey, Dec 4, 2011.

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  1. arkey

    arkey New Member

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    Has anyone managed to use the solar panel of the prius other than just the air vent system? I usualy need to charge my mobile/ipad etc while parked (or driving).. is it possible with a simple modification or any after market accessories for that?
  2. arkey

    arkey New Member

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    Hmmm..:confused: It seems not many people interested in the solor panel mod.. has anyone got some technical details and diagrams of the solor panels on Prius? I just want to get a aux powerout from it..
    Jonnybegood likes this.
  3. cwerdna

    cwerdna Senior Member

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  4. SuperchargedMR2

    SuperchargedMR2 Diehard Rams Fan

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    I wish the solar panel also helped charge the battery pack. :)
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  5. Michael Cline

    Michael Cline New Member

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    I'm a new Prius owner as of today, "long-time listener first-time caller."

    There are a number of mods I "require" and charging the 12v system from the solar sunroof panel is top of the list. This feature is important to me for the following reasons:
    1. It should improve lifespan of the 12V battery, especially if left for prolonged times.
    2. It allows unlimited use of the car's radio and accessories, and power windows, without ever running the engine.
    3. It would be nice for camping to be able to charge/use things like laptops without running the engine or depleting the battery(s).
    4. Cooling is practical and nice, but it's just not right to have a 65W solar panel which does not produce usable power. Actually it is insulting.
    So far I've not found others who have posted plans, though many have requested the feature. I believe Toyota did not tie the solar to the 12v battery because it increases the complexity/risk when servicing the car that that the power is not completely disconnected, since the solar could power the system even after disconnecting the 12v battery. There is also mention of inability to isolate transmissions, heh heh.

    Note, having the Prius in the "Ready" position allows the traction battery to be used to charge the 12V system, producing up to around 90 amps, but also wastes a lot of power by running things you don't need and pretty quickly begins using some gas.

    I've researched that the panel puts out 22v nominal, 27 v max, and up to 6.3 amps. This is ideal for use with a charge controller into a 12V system such as "Genasun GV-4-Pb-12V, 4A MPPT controller for 12V Lead Acid Batteries". I have not _yet_ determined where to tap into the solar output. Additionally I need to determine how feasible it is to operate the fan and charger at the same time, albeit with less fan speed when charging. Having both greatly complicates the design since this means my mod has to play nice with what is already there and vice versa. A less solar-efficient and much cheaper alternative to the above MPPT is the $3 "LM2596 Buck DC-DC Adjustable Step Down Power Supply Module".

    If anyone has completed the mod, please share your findings! I'll follow up eventually if I make more progress on my own.

    -Michael
    wotcher likes this.
  6. Michael Cline

    Michael Cline New Member

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    It's ridiculously hard to find info about this, but here is some progress I've made so far and some bits and pieces to fill the information void. I'm using this thread to document my notes, for myself and others. Please comment or add additional info:

    observations:
    1. I've located the blower relay (aka solar ventilation relay) and understand its function: It switches between supplying either Ign or SolarOutput from the "A/C Vent Module" to the blower.
    2. The blower is surprisingly interesting. Despite having power, it receives instructions on how fast (if at all) to spin. I include this only as an interesting factoid.
    3. The "A/C Vent Module" is pretty finicky and slow to adjust to changing light conditions. It is also expensive to replace if something bad happens. It is also not active (and supplies no power) if the solar vent option is turned off. Therefore I will be drawing my power directly from the solar panel, not from this finicky expensive device's output.
    4. The "A/C Vent Module" is very inconveniently located left of the main blower assembly behind all sorts of things. I have not yet gotten access to the key wire which supplies the solar power to it.
    5. The solar cooling is a really neat feature at least here in Seattle where the air is cold, but the sun heats the car up. Cracking the windows is more effective, but less desirable.
    Next steps:
    1. Access the wire mentioned in note #4 above.
    2. Explore the current to voltage relationship under various lighting conditions both with the "A/C Vent Module" engaged and disengaged. Ideally I want to use both simultaneously with minimal impact to the blower, with additional charge power available when the Prius "vent" switch is turned off.
    3. Based on the above determine if an MPPT or cheap Buck regulator will be ideal for my project. I'm hoping to use a Buck regulator. The target voltage of the Buck regulator can be set more or less aggressive (from 12.9 to 13.5 volts) to balance charging versus fan cooling. The primary disadvantage of the Buck regulator is that it does not optimize the load for the solar panels, which means under a high load condition (such as running a laptop or charging a low battery, or under clouds) it may draw more current than the maximum power transfer amount for the solar panel, thereby extracting much less power, not to mention disabling/impacting the blower. Under low-load conditions the Buck should work great, just skimming what it needs to the keep the battery fresh and leaving the rest to cool the cabin! Disadvantages of the MPPT is less control, and it may be confused by the actions of the "A/C Vent Module" if run in parallel as I plan to use it. It is also more expensive.

    More to follow...
  7. WE0H

    WE0H ^^My garage queen^^

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    I picked up a 14v accessory jack today for my solar charger mod on my Prius. Just stumbled on your thread today :) My plan is a switch, acc jack and charge controller mounted in back to charge my battery's for my portable Amateur Radio equipment.

    Mike

    Mobile on my SGH-i717
  8. Michael Cline

    Michael Cline New Member

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    I've patched into the thick green wire (observation #4 in previous post) before it enters the "A/C Vent Module", this comes direct from the solar panel and even as the sun was going down had good no-load voltage. I had to remove the stereo to get to it which was unpleasant but not terrible, it all went back together just fine. I wish I had quieted the beeper while I was back there. There is probably an easier place to splice into the green wire, but I'm not aware of it...
  9. WE0H

    WE0H ^^My garage queen^^

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    Are the wiring diagrams in the 2010 service manual good for the 2012 car? I have been traveling and my car is back home so I can't take a look.

    Mike

    Mobile on my SGH-i717
  10. Michael Cline

    Michael Cline New Member

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    Here is some preliminary data based on observations, but not yet from an assembled system:
    1. The ventilation system triggers at about 20V, supplying about 16V to the blower. This requires pretty direct sunlight in Seattle.
    2. The ventilation system begins to work at about 1.2 amps, but is flakey and intermittent at this level. (It's not too sunny today)
    3. In semi-direct sun just enough to trigger the ventilation system, the voltage is pretty stable when drawing an amp or less, one amp dropping the voltage only a few 10th's of a volt.
    4. The Prius "A/C Vent Module" draws 10 mA (aka nothing) when disengaged by the dash switch, and 25 mA (still nothing) when engaged but not turning the blower. This is excellent news because it means you will never have to disengage it for the charger to work well in weak-sun conditions.
    5. In weak-sun conditions just shy of enough to trigger ventilation there is about 1.3 amps available to the battery for charging at 13.2 volts. The Buck regulator I'll use is current limited to 3A on the output, or 2.3 Amps drawn from the solar array at 20V. In the worst case scenario (low battery), this will dramatically increase the amount of sunlight needed to trigger the vent, giving priority to charging vs cooling, but in the standard case I think the two systems will be best friends.
    6. Because my regulator circuit is not MPPT, when combating a discharged battery on a bright cloudy day, the solar output will be pulled down from around 19V to about 14.5 volts, wasting 35% of the power and providing about 500 mA of charge current with 150 mA wasted due to poor tuning. Unfortunately we have a lot of these types of days in Seattle. On a bright sunny day it should be ~90% efficient providing a constant 3A until the target voltage is reached.
    7. The sun went away before I could determine how much the charger effects the trigger point of the ventilation system under "normal" conditions. I'll add a bypass switch for safety during servicing, and for when only ventilation is desired.
    metro-mike and ftl like this.
  11. Michael Cline

    Michael Cline New Member

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    My solar charger is completed and installed, and I love it. I'll post the design, sources of parts, features, specs, and pictures eventually.

    In the meantime here are some more observations (since this info is hard to come by and inconsistent from the various web sources).

    Aux battery (12 V system) power drain current of the 2010 Prius with keyless entry:
    1. Car off, locked, key fob far away, and having sat less than 1 minute: 400 mA
    2. Car off, locked, key fob far away, and having sat for more than a minute: 25 mA average (If key nearby, then variable from 150 mA to 2.5 amps including dome lights)
    3. Passenger door open, but dome lights off: 700 mA
    4. Driver's door recently opened, after breaks have finished pressurizing, with no dome lights: 1100 mA likely high due to searching for the key.
    5. While breaks are pressurizing: Did not measure, estimated in excess of 10A.
    6. Press the On button once, car is in standby with radio operating: ~5.5 Amps.
    7. Press the On button again, but no foot on the brake, car not in READY, radio on, navigation on, and windows enabled, blower set to minimum but not off: Initially 22 amps, quickly dropping to sustained 12.5 Amps. I didn't measure this for long since my meter was rated only up to 10 amps and I didn't want to blow the fuse. I was pretty happy it survived the 22 amp burst.
    -Michael
    dzhantim, genetiix, ftl and 2 others like this.
  12. MPGnutcase

    MPGnutcase Active Member

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    Wow keep us updated..........
  13. Michael Cline

    Michael Cline New Member

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    Here are the final plans for implementing the solar charger on the 2010-201x Prius, I speculate the wiring will be the same for any 3G model:

    Parts:
    1. Buck (Step Down) converter, available for $3-$12. Best to have a display which can show both input and output voltage such as this one which I used and had very fast shipping: (LM2596 BUCK STEP DOWN CONVERTER, WITH BLUE DISPLAY http://www.ebay.com/itm/1-PC-OF-A-DC-TO-DC-LM2596-BUCK-STEP-DOWN-CONVERTER-WITH-BLUE-DISPLAY-NEW/251259760601). Others (direct from China) will work just as well if you can wait that long but may not have the nice display.
    2. Heavy-duty switch to isolate the charging system, which is also useful for measuring charge current and calibrating the set voltage while the battery is disconnected. I have mine set to 13.10V (no load, measured at the battery with a DMM) and believe this to be an appropriate value. Use a DMM to verify the reading is correct. To maximize the life of the battery, I would not go above 13.15V float voltage.

    3. A wire leading from Bat to the charger. I strung this direct to the battery, and used this also to enable an always-on cigarette lighter plug. You can easily run the wire under the passenger side lower trim which pops out.

    4. 5A fuse on the Bat line unless you wire into an already fused circuit, 15A if you share this circuit with an always-on cig lighter like me.

    If you use a buck converter with display, the display will draw about 12 mA at all times including during the night. I decided this is insignificant and worth the ability to see system voltages at all times. Two alternatives are to use a buck converter without display which draws no current from the 12 system, or use a 6A Schottky diode between the charger and battery to isolate it. The latter will only run the display when solar power is present, but you will need to account for about .3V drop across the diode and as such will make accurately measuring 12v system voltage more tricky.
    Set up is pretty easy, I used the seat heater panel so as to modify as little of the car as possible, and mounted the buck converter with display there. You will need to pull the radio to tap into the Green wire running to the A/C Vent module, which is where the solar power comes from, and is the hardest step. You can buy click-on wire taps. Run this new tap wire to the input of your Buck Converter, and run the output of the Buck converter through a switch and fuse to the Battery or a Bat wire if you can find one. To set the output voltage, measure the output voltage (with A DMM) when the battery charger is not connected to the battery, aka charger switch OFF position, and set this ideally to 13.10V for very conservative floating of AGM batteries.
    You will find the charger gives about 2 to 3 amps charging current when you need it depending on sun and temperature of the solar panel, and charge state of the battery. It does surprisingly well on a cool bright cloudy day. The charger will take priority over the blower, but unless the battery is discharged there is essentially no degradation of blower performance. In other words both systems play very nicely together. If you actually pay close attention to the blower you will realize Toyota did not implement it very well and in many lighting conditions it doesn't work all that well even without the charger, but the charger does not make it much worse. Just sayin... ;(
    Enjoy the photos, and I hope the information I provided over the last week or so is useful. Having this circuit, especially with how many systems on the Prius draw power from the Aux battery when not in READY, I can't imagine not having this charger feature with voltage monitor.

    In the below photo you can see my implementation. The display can show either Bat voltage, or Solar input voltage, or alternate between both as I have mine set to do, and this switch is controlled by the little bamboo skewer button. The little hole is the output voltage adjustment, which I have set to 13.10V. The display is mounted where it does not shine in the driver's eyes, but can be monitored when interested.
    PriusSolar-0001.jpg

    In the second photo, be advised it was very difficult to get my panel to fit and I had to do some clever things, but the end product was great.
    PriusSolar-0002.jpg

    The third photo shows output on a sunny Seattle day with the headlamps on to pull the voltage down. In this case the solar panel was still putting out enough voltage to simultaneously run the blower, though the blower was off for the photo.
    PriusSolar-0003.jpg

    The below photo(from e-bay) shows the buck converter I used. Others will work just fine as well.
    BuckConverter.jpg
    Enjoy!
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  14. Michael Cline

    Michael Cline New Member

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    Replying to my own post, the drain current on my 2010 Prius now pulsates rapidly between 75 and 125 mA even when left for many minutes locked with the key fob nowhere near. As I wrote this post I could not figure our what could be causing it, since all my mods were all disconnected for the test... except for one: The Bluetooth sender for Torque App. FYI to those using these, you might want to check for current leakage or unplug it. (The Bluetooth sender was leaching the power during the night and stressing my semi-old battery)
  15. vallesj

    vallesj Junior Member

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    Did you found The issue? Solar panel generate variable voltage, so how the converter works since I think with variable inputs the output will be variable too.

    Sent from my Nexus 7 using Tapatalk
  16. vallesj

    vallesj Junior Member

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  17. sfv41901

    sfv41901 Blizzard Brigade #164

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    What are the chances this can be used to charge the traction battery?
  18. mrbigh

    mrbigh Prius Absolutum Dominium

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    NONE, the Prius PV panel has to little Volts and current output be be useful to replenish the HV pack
  19. vallesj

    vallesj Junior Member

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    I was thinking on regen brakes as individual dynamos on each tire, but the reality is that the electric motor is only one and it is tied to inverter and other controls. One option is to use a step up voltage converter, but it is not convenient, its complex, loses efficiency, and very small juice.

    Sent from my Nexus 7 using Tapatalk
  20. Michael Cline

    Michael Cline New Member

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    Sorry, I've been unresponsive for a time.

    I did find the power sucking issue, it was my Bluetooth sender for Torque App. You definitely need to keep that one unplugged when not in use because long-term it will cause discharge and premature failure of the battery!

    The Buck converter takes any voltage (up to 35V) and converts it efficiently down to whatever voltage you set as the target. The output voltage does not vary with the input voltage so this is ideal for floating a lead acid battery. The MPPT which you purchased should work more efficiently with your solar panel because it will dynamically adjust the load to prevent the solar voltage from falling off. The Buck converter at higher loads pulls the solar voltage down to about 14.5V, thereby wasting some energy. Either way it is only wasting a small amount of free energy.

    I was asked if this modification could be adapted to charge the traction battery:
    Practically speaking it would be very difficult, but more importantly it should not be done. You want to keep the traction battery as isolated as possible, so running wires in there and having various unexpected circuits energized to 200+ volts is a very bad idea. Also, this mod provides just enough power to maintain the 12V system, and would be a drop in the bucket for the traction battery. In fact if you use the stereo (5+ Amps) with the vehicle not in READY, my mod will not even create enough power to keep up with demand.

    Michael
    WE0H likes this.
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