Solar Zip

[Azimov]

I've posted this in another thread, but decided to start a string just for this mod as the other string is getting lost in the noise. This project started after I read several posts of people trying to solarize a Zip Zap or Bit CharG. This mod will work on either or any of the clones for that matter.
First, lets start with some numbers. The stock Zip battery supplies 100mA @ 1.2VDC. Now, common sense would tell you that all you need to do is supply these numbers via a solar cell and whoosh, your off running a solar car. Not so grasshopper. The fact is, solar cells are very different from batteries. You can see a detailed explanation of why this is over here.
http://tinyrc.com/forums/showthread....&threadid=1698
I'll have to repeat a few things here that are in that other thread for the sake of convenience so bear with me. I did some initial testing and found that 2VDC @ 300mA is the bare minimum needed to get a Zip moving under solar power alone. And I would suggest going higher if at all possible. This is where we run into a problem. Most solar cells out there don't supply these ratings on their own unless they are really huge. We need a solar array (that is a multiple of cells hooked together) to reach these numbers. And, most importantly, they need to be as small and light as possible. I used special cells from a surplussed NASA satellite program, but these are very hard to come by. A quick search on the web found these cells, which are comperable to what I used.
http://www.solar-world.com/SuperCell...tovoltaics.htm
The .5VDC @ 400mA will do the trick nicely. Still a little pricy, but if you are serious about doing this mod, you will have to pay the piper. You will need at least 4 of these hooked in series. That is, positive to negative, positive to negative on and on just like batteries in a flashlight. This will give you 2VDC @ 400mA, plenty for our needs. You'll need to brush up on your soldering skills as well. But, you should do that anyways . Once you have your array together, much like the shingles on a roof, open up the PCB cover, remove the stock battery and solder the positive lead from your solar cell array to the positive lead of the battery terminal. Do likewise for the negative lead. Attach the array to the PCB cover and reassemble.

[Azimov]

And, here is what you get.

[Azimov]

Test the car under a halogen lamp or full sunlight to make sure all is functional. If you haven't done so, put the blue gears and blue motor in the car. A solar application seems to do much better with these low power motors. If you notice the car has paper clip bumpers to protect the very fragile cells. That's one of the trade offs for using these ultra light solar cells, they are very thin and brittle. You could crush one in your hand like a saltine cracker, so precautions to protect them are mandatory. It would be a shame to run your new solar project into a lawnchair leg on the patio and shatter your expensive solar array! You could laminate the cells to a thin strip of sheet styrene plastic as well to strengthen them up a bit. The bumpers are soldered together and are super glued to the front and back of the chassis. They have about 1/8th of an inch of clearance around the solar array and aren't attached to the solar cells at all. This bumper system could be made out of left over plastic model parts trees or swizzle sticks, or maybe even plastic toothpicks to make construction easier. The idea is to protect the cells in any way possible.

[flatlander_14]

nice work azimov how well does it work indoors if its bright inside? or can it run on plain ceiling lights at all? lol nice addition with the spoiler, i had to laugh when i saw that how exactly did you attach the bumpers all around it?


edit: ignore the last question, we posted the same time but your's went through first

[Azimov]

Now for some results. The car performs very well in full sun and partial shade. As a matter of fact, in full noon day sun, it screams like a dual cell mod. That is, it would if it wasn't using the blue gears and blue motor . These restrict the top end a bit, but the power is definately there. Moreover, these solar cells are so light that the car is lighter than with the body and stock battery! Now, you could take that cute little rear spoiler off and replace it with a 5th cell hooked in series with the others and you would get 2.5VDC @400mA using cells from the link I supplied. This would allow you to upgrade to the green or even turbo motor And possibly green or red gears. I initially tested this car with the red gears and red turbo motor, but found that it didn't have enough power to turn the back wheels in slightly overcast conditions. The blue on blue works best for overall performance. Besides, what are you gonna do with all those blue motors clanging around in your parts box anyway?

[sessiz10]

Excellent job azimov.

[Azimov]

A couple of last thoughts here. One way to make your solar Zip more versatile would be to include a buffer cap. This should be in the 1F range and hooks directly to the positive and negative battery terminals the same as the solar array. This buffer cap will fit into the body cavity of the car and will add almost no weight to the project. The reason for this is that sometimes your car may run under a chair or the branches of a potted plant and find itself in a shady spot. With only the solar cell for power, it's dead as a doornail and you have to go fetch it. With the buffer cap, the car will feed off the capacitor for a second or two allowing you to get back into the sun. A diode should be placed on the negative rail to ensure that the buffer caps power doesn't feed back into the solar array. But, to be honest, I'm not sure this is needed. I've built many solar projects this way without the diode and have never had a feedback problem. But, the experts recommend one. Your car will behave a bit differently with this cap installed however. You will need to place the car in full sun for a minute or two until this cap fills up. Then, the car will behave normally as it sips juice from over the top of the cap while the cap remains full. When you hit a shady spot the solar output drops and the car runs off the cap until you get back into full sun.

[Azimov]

To sum it all up, you need at least 2VDC @ 300mA to get the car to run directly from solar power. It doesn't matter how you accomplish this as weight of the solar array is the only other factor. These numbers are the absolute minimum. Seriously, you will just be wasting time and money if you ignore these specs. The link I provided contains the only solar cells I know of that will accomplish this. Be very very careful as you build the array. I crushed one of my cells with the tip of my soldering iron while soldering the cells together. They are that brittle. But, they are so small and light that you will be amazed. That's about it. If you have any questions, please post them here and I'll do my best to answer. Good luck! And remember, you are attempting something fairly difficult and expensive here. But, the reward of watching your creation zip around your patio or garage slab without a battery is well worth the effort.
And then, there's that Mad Max end of the world, apocalyptic time in the near future when there are no batteries or companies called Everready anymore and all the kids are saddened that their toys don't work. You can just pull your solarized Zip out of your dusty raggedy Jinco jeans and blow em all away.

[Azimov]

how well does it work indoors if its bright inside? or can it run on plain ceiling lights at all?

Nope, won't work inside at all. Full sun and just slightly overcast conditions are the only way it will go. There just isn't enough light produced indoors to pull it off. Now, you could set up a little course indoors that is lit with a couple of those 500 watt halogen work lamps and the car would probably work. I use them all the time when testing solar ideas indoors or when it's dark out and I'm on a late night building marathon.

[Namuna]

Off to Bit Science...

[actofgod]

Nice writeup, Azimov! I've got a couple questions for ya:

1) Would a car with the mosfet mod be able to use fewer solar cells to get the wheels turning? Perhaps 3 instead of 4?

2) I'm thinking of doing a "hybrid" bit I'd like it to run off a battery while the battery is getting charged by one or two solar cells mounted on a stock body's hood and/or roof. I'd need a diode for that I guess, but what kind? Would it still be safe to charge up the battery with DC current with the diode and solar array attached, or would I always have to charge with sunlight? Depending on current draw, using just a couple cells to charge probably wouldn't last indefinitely, but it would greatly extend runtimes, and you could just let it idle for a few minutes to recharge some. The only problem I see is that you need enough voltage to charge the 1.2v battery, and these cells are only 0.5v each. Looks like you'd need three of them; I'd like to get that number down to two. Gotta find another cell with at least 0.75v and hopefully still have sufficient current.

BTW, can you edit that link in your first post? It's not working for me.

[Azimov]

1) Would a car with the mosfet mod be able to use fewer solar cells to get the wheels turning? Perhaps 3 instead of 4?

Very possibly. One of the limitations of these PCB's is the transisters that eat up a bit of juice that could be flowing to the drive motor. Replacing them with mosfets would mean more can flow to the motor, hence less is needed originally to achieve the same effect.

I'd need a diode for that I guess, but what kind?

Any run of the mill diode will work. In the situation you mention, charging a battery while having the cell on top, it would be mandatory. You don't want to run the risk of overcharging the battery while the car sits in the sun motionless. A buffer cap won't suffer from this, but a battery would.

I'd like to get that number down to two.

You could try wiring a voltage pump in there. This would take come of the current and turn it into more voltage. I'm not sure how far you would get robbing Peter to pay Paul, but it may be a way to lessen the number of solar cells.

BTW, can you edit that link in your first post? It's not working for me.

Ok, try this one.
http://www.solar-world.com/SuperCell...tovoltaics.htm

[flatlander_14]

i hate to steer this thread in another direction but....

would it be possible to make a solar peak charger? this would be really effective for us people who run with button cells. i know it would need multiple solar panels to get over 3.6v in my case, but what else is needed in the circuit to not blow up the batteries?(ive done it once, i dont want a repeat of history ) from my guess, could i just wire in that buffer cap you were speaking of?

[Azimov]

would it be possible to make a solar peak charger? this would be really effective for us people who run with button cells. i know it would need multiple solar panels to get over 3.6v in my case, but what else is needed in the circuit to not blow up the batteries?

Very much so I would think. All you would need would be the peak charging circuitry and instead of a seperate wall transformer to supply the juice you could use a large solar cell hooked to a voltage regulator to keep the voltage at safe levels. Solar cell size isn't a factor here since it's not being lugged around by the car. I have some panels that are 6" square that I got from allelectronics.com that were really cheap, like 5 bucks or so, and they are rated at 9VDC @ several hundred mA. I've tested them in full sun and they can actually produce over 11VDC. They are big, heavy glass, but very sturdy and powerful. Something like this hooked to the peak charger through a voltage regulator would work if you match the voltage and current output to the peak charger's timing as it corilates to the batteries that you are trying to charge. The peak chargers that require a seperate power source are fairly cheap as well.

[Azimov]

Just found out that the cells that Radio Shack sells are rated at .55VDC @ 300mA. So, 4 of them would successfully solarize a Zip.