This joins the radiometer and 4" prism as one of the basic sun toys that everyone should have. It's a fun design with a transparent case, exposed motor, different colored gears, and counter rotating crystals. It looks to be quite well made, and I was pleased to find that its large built-in suction cup does a good job. Up close you hear a little whirring sound (not objectionable) from the motor and high speed gear, but from across the room it runs silently. Its speed doesn't vary with the intensity of the light, it either runs or it doesn't run. Occasionally it will click for a few seconds as the shadow of the sun passes over it.
I saw one reviewer who said the single crystal unit worked fine, but the double unit was underpowered and would barely rotate in bright sunlight. I don't find that to be the case at all, mine rotates even when the sun is partial obscured by clouds. As I write, it is late on a winter afternoon in New England with the sun low in the sky at 60 degrees off perpendicular, and my double unit is still running. I experimented and found it would even run when the solar cells were illuminated from the back!
Minor negatives --- Compared to the one big bright solar spectrum a 4" prism will throw on the wall, the spectrums from this thing are pretty small and dim, though the compensation is that there are many of them and they sweep around the room. When the sun is at the right angle, you have to expect that some of these 'rainbows' are going to pass over your eye, so you get a little flash now and then. It's more complicated than a prism or radiometer, so it's probably not going to live as long.
For those interested technically its solar panel is 4 cm x 2.5 cm = 10^-3 m^2 and looks to be five (1/2 V) cells in series. Since the power of bright sunlight is 1,000 w/m^2, if inexpensive solar cells with efficiency in the 5% to 10% range are used, the output power available to drive the DC motor would be 50 to 100 mw, or 20 to 40 ma @ 2.5V.
update --- It's now nine months since I put this on a window using the vacuum sucker and it's never fallen off! Still works fine too.
update2 --- Well after two years, it's showing its age. One crystal broke off when it fell and the gears are now sticking. I just ordered a replacement.
More technical--- When my new one arrived, I took apart my old one to look at the motor, which still works. (I am a motor control engineer.) The motor is not a DC motor with brushes, which is good as brushes wear out. It is a brushless AC PM (permanent magnet) motor that a finger test shows will spin in either direction (at roughly 200 RPM). The 2.5V from the solar cell is converted to AC by a tiny circuit board mounted above the coil. The board's active component(s) is covered by glop, but it is probably a single IC clocked by an external crystal, which seems like overkill.
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How to repair Solar Powered Rainbow Maker
Three things predictably fail on Solar Rainbow Makers- the solar cell fails to produce enough power, the bevel gear that drives the prism shaft cracks, and the suction cup fails to hold. Fixes we found:1)Solar Cell-Found the original solar cell produces approximately 50mA @2volts in direct sunlight. Located a larger solar cell producing 130mA@2volts, but was a little larger.(https://www.amazon.com/dp/B07BLP238X?psc=1&ref=ppx_yo2ov_dt_b_product_details)Cut wires to existing cell, soldered wires to new cell. Glued new solar cell to old cell holder. New cell produces enough power to turn prism even on cloudy days and out of direct sun.2) Bevel Gear Crack-Repair posted online by something else, used thin wire twisted around base of bevel gear to close crack in gear and apply super glue. This works but you will need to slightly enlarge bevel gear shaft hole to prevent it from stretching and reopening crack when you place gear back on shaft. Very small drop of super glue on shaft to secure bevel gear on shaft after enlarging shaft hole. Alternative method is to heat shaft with butane lighter and slide bevel gear onto shaft while pinching to keep crack closed. Plastic bevel has low melting point and one must be careful not to get shaft too hot; get just hot enough so that gear will slide on shaft without stretching crack. When cooled gear will fuse to shaft.3) Removed suction cup and replaced with Velcro tape. Used small piece of matching Velcro on window muntins. We can't apply suction cups or velcro tape directly on our windows since we have installed solar film and either would damage it if attached. The solar film does not interfere with the solar cells.All these repair require disassembly of Rainbow Maker. The two long machine screws that go through the motor armature plates have tiny nuts on the back side. Be careful not to lose them! Only tool required is a tiny phillips head screw driver. Note-Will need soldering skills to attach old cell wire leads to new solar cell.I've probably spent way too much time repairing these but it has become a challenge and perhaps an obsession to fix them. It is satisfying to see one once broken and sitting in a drawer back spreading color.
Top reviews from the United States
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Reviewed in the United States on February 16, 2009
Style: DoubleVerified Purchase
This joins the radiometer and 4" prism as one of the basic sun toys that everyone should have. It's a fun design with a transparent case, exposed motor, different colored gears, and counter rotating crystals. It looks to be quite well made, and I was pleased to find that its large built-in suction cup does a good job. Up close you hear a little whirring sound (not objectionable) from the motor and high speed gear, but from across the room it runs silently. Its speed doesn't vary with the intensity of the light, it either runs or it doesn't run. Occasionally it will click for a few seconds as the shadow of the sun passes over it.
I saw one reviewer who said the single crystal unit worked fine, but the double unit was underpowered and would barely rotate in bright sunlight. I don't find that to be the case at all, mine rotates even when the sun is partial obscured by clouds. As I write, it is late on a winter afternoon in New England with the sun low in the sky at 60 degrees off perpendicular, and my double unit is still running. I experimented and found it would even run when the solar cells were illuminated from the back!
Minor negatives --- Compared to the one big bright solar spectrum a 4" prism will throw on the wall, the spectrums from this thing are pretty small and dim, though the compensation is that there are many of them and they sweep around the room. When the sun is at the right angle, you have to expect that some of these 'rainbows' are going to pass over your eye, so you get a little flash now and then. It's more complicated than a prism or radiometer, so it's probably not going to live as long.
For those interested technically its solar panel is 4 cm x 2.5 cm = 10^-3 m^2 and looks to be five (1/2 V) cells in series. Since the power of bright sunlight is 1,000 w/m^2, if inexpensive solar cells with efficiency in the 5% to 10% range are used, the output power available to drive the DC motor would be 50 to 100 mw, or 20 to 40 ma @ 2.5V.
update --- It's now nine months since I put this on a window using the vacuum sucker and it's never fallen off! Still works fine too.
update2 --- Well after two years, it's showing its age. One crystal broke off when it fell and the gears are now sticking. I just ordered a replacement.
More technical--- When my new one arrived, I took apart my old one to look at the motor, which still works. (I am a motor control engineer.) The motor is not a DC motor with brushes, which is good as brushes wear out. It is a brushless AC PM (permanent magnet) motor that a finger test shows will spin in either direction (at roughly 200 RPM). The 2.5V from the solar cell is converted to AC by a tiny circuit board mounted above the coil. The board's active component(s) is covered by glop, but it is probably a single IC clocked by an external crystal, which seems like overkill.
I saw one reviewer who said the single crystal unit worked fine, but the double unit was underpowered and would barely rotate in bright sunlight. I don't find that to be the case at all, mine rotates even when the sun is partial obscured by clouds. As I write, it is late on a winter afternoon in New England with the sun low in the sky at 60 degrees off perpendicular, and my double unit is still running. I experimented and found it would even run when the solar cells were illuminated from the back!
Minor negatives --- Compared to the one big bright solar spectrum a 4" prism will throw on the wall, the spectrums from this thing are pretty small and dim, though the compensation is that there are many of them and they sweep around the room. When the sun is at the right angle, you have to expect that some of these 'rainbows' are going to pass over your eye, so you get a little flash now and then. It's more complicated than a prism or radiometer, so it's probably not going to live as long.
For those interested technically its solar panel is 4 cm x 2.5 cm = 10^-3 m^2 and looks to be five (1/2 V) cells in series. Since the power of bright sunlight is 1,000 w/m^2, if inexpensive solar cells with efficiency in the 5% to 10% range are used, the output power available to drive the DC motor would be 50 to 100 mw, or 20 to 40 ma @ 2.5V.
update --- It's now nine months since I put this on a window using the vacuum sucker and it's never fallen off! Still works fine too.
update2 --- Well after two years, it's showing its age. One crystal broke off when it fell and the gears are now sticking. I just ordered a replacement.
More technical--- When my new one arrived, I took apart my old one to look at the motor, which still works. (I am a motor control engineer.) The motor is not a DC motor with brushes, which is good as brushes wear out. It is a brushless AC PM (permanent magnet) motor that a finger test shows will spin in either direction (at roughly 200 RPM). The 2.5V from the solar cell is converted to AC by a tiny circuit board mounted above the coil. The board's active component(s) is covered by glop, but it is probably a single IC clocked by an external crystal, which seems like overkill.
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