Nice site thanks for the information. I am learning and this is another page added to my library of knowledge. I am obviously a stubborn individual. I guess the diode is necessary when running many solar panels in SERIES due to the possible reverse biasing when one is shaded. Thus said i ask the question and is as follows; the solar car would run and possibly benefit without it depending on the weather of the day? If it is to be a bright sunny day then take it out. [noparse][[/noparse]Yes - No] Also i think that running some of the cells in parallel would divert the problem.
I suppose careful, but no incredibly complex calculations could solve the questions at hand; however more information about the solar panel and battery/s would be needed.
This continues to be a exciting topic...
Post Edited (grasshopper) : 10/29/2007 5:17:22 PM GMT
Grasshopper,
I previously mentioned that the team might provide a means to bypass the blocking diode if it is very sunny on race day. But, if the sun suddenly goes behind a cloud, all may be lost because the solar cell might make you slower.
Parallel or series, the dark cells would still drain. If it is series, you would have a voltage drop; if it is parallel, you would have a current drop. But, I don't think there are enough panels to be concerned indivually - put them in a series set up and exploit the highest possible voltage - then one blocking diode has the least impact.
Calculatons may not help you so much as trying to grasp a 'general idea' of it all.
I am also very interested in the SF52 diode of the Maxi-minimizer because it allows 'freewheeling' - very important. Without it, the motor would act as a brake when there was no power to it. The 'SF' is for super fast. Can some one locate 'ultra super fast' diodes or am I dreaming? Ideally, an 'utra fast Schottky diode' would be perfect, but do they exist? Maybe not.
Also, though expensive, ball bearings in all wheel axles would reduce the drag. I have seen wheels in hobby shops that have built in ball bearings and I've seen very tiny ball bearings that can be inserted in an existing motors. {you have to drill out the bronze bearing and insert the new ones with a bit of super glue. - micromechanics}
As i said before, there may be a lot of loss on the mechanical side -- others may never address it as you have to disassemble the motor and rebuild it.
Rotational balance is important. One can also remove the rotor from the electric motor and see if it always turns to one side up. That would indicate it is 'out of balance' or heavy on the opposite side. So you have to drill holes in the low side until the rotor no longer prefers rotation to one side up - you eliminate drag. So eliminates wasted energy.
And, if that is too much, you might even be able to buy balanced motors with ball bearing inserts at a hobby shop that services competitive events. The rotor may also be rewound to give more zoom.
I did all this with competition slot cars in the 1960s.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
You could add reflectors on the sides to increase the amount of sunlight on the solar panel. The picture below shows an end view of the car. The blue lines represent reflective panels that run the full length of the car. With a little bit of trigonometry I determined that the sun must be at least 60 degrees above the horizon to prevent shadows from the reflectors. According to your profile you are located in NSW, Australia, which is 30 to 35 degrees south latitude. At noon the sun will be about 70 degrees above the horizon. By the time of the solstice in December the noon sun angle will be about 80 degrees.
If the race is run when the sun is lower than 60 degrees you would have to add servos to move the reflectors up and down as the car goes around the track. The reflector on the sunny side of the car would have to be lowered so it wouldn't cast a shadow. The reflector on the other side of the car would be raised to the appropriate angle to reflect the sun onto the solar panel. The angle could be programmed just before the start time of the race, or you could use a real-time clock and a look-up table to determine the angle of the sun. A couple of photo sensors could be used to determine which side was facing the sun.
The reflectors could be made out of cardboard or thin plywood covered with aluminum foil or sheet metal. This would require more work to build, but you could get 25% to 100% more power depending on the angle of the sun.
Both reflectors and fressnel lenses are good ideas to concentrate solar power. Mylar backed foil [noparse][[/noparse]used in packaging and mylar ballons] is probably the best light weight reflector. Try a building supply for either mylar backed foil or paper backed foil. These are used for added home insulation and don't have printing on them.
I'd rather depend of the lens than the reflectors if their is any question of them shading the actual panel. The season down under is late Spring and offers good solar prospects and higher sun angle. Maybe cut those reflections down by 50% to avoid potential shade.
Long ago, auto supply houses sold a square vinyl fressnel lens that you placed in the back window of your SUV or Van for easier wide angle views to the rear. That could either be used whole or cut to shape. Maybe, they still do.
It crossed my mind that· all 2AH batteries may not be the same. Primary batteries [noparse][[/noparse]one-time use] have a much more sustained output than secondary [noparse][[/noparse]the rechargible ones]. The problem is that the rechargible ones come with Amp Hour ratings as part of their advertising, while you have to dig to get the same informaton on primary batteries. It may be that all primaries are generally much higher, like 5AH.· You might find AAA primary batteries are 2AH, which AA secondaries are usually that capacity.· Here is an oportunity to reduce your overall weight.
While, one might say that 2AH is all the same, no matter what battery is used. It really should be, but you could test their specs and lables against the same load [noparse][[/noparse]an LED] by timing it. The lables may not reflect reality. Some suppliers my even cheat and merely upgrade lables while selling a lower rating.
In the U.S., Radio Shack used to sell the best batteries for a good price. It was a way of attracting customers into the store. In Taiwan, the electronic supply houses do the same thing. And of course, it is important to use NEW batteries from a source that sells a lot of new batteries as they get old by just sitting on the shelf.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Also from the Renewable Energy UK (REUK) website: Note that the diode will reduce the voltage sent to the batteries by the solar panels by as much as 0.7 Volts so you may choose to omit the blocking diode from the circuit accepting small amounts of losses from the batteries in return for faster battery charging. For small 12V set-ups like this the diode is not really necessary and will almost certainly have an overall negative effect.
The Fresnel lens might be the best solution. Alltronics has one for $79 that is 36" by 20.5". The focal length is about 25". If the solar panel is 60cm by 30cm then the lens should be mounted about 10" above the panel. This would concentrate about 0.48 square meters of sunlight onto the 0.18 square meter panel. That's a factor of 2.7! That might be too much sunlight for the panel or motors!
The Fresnel lens could be mounted closer to the panel to reduce the power gain or a smaller panel could be used. Extreme care must be used if a Fresnel lens is used. There are web sites that describe experiments where Fresnel lenses of a square meter in area were used to focus the sun to a small spot. This produces an extremely hot and bright spot.
Concerning the 2 WHr battery, it seems like this is fairly insignificant compared to a 30W solar panel powered for 1 hour. It's less than 7 percent. The circuitry that supports the use of the 2WHr battery would have to ensure that you don't lose 7% of the 30W panel's power just to break even.
"Zero voltage diodes can be made using a power MOSFET"
That is the most interesting item that has been posted here in some time. Beau also mentioned it a month or so ago, but I don't fully understand the concept. Some one else told me that you need at least a 3volt difference for it to work and that did make it any clearer to me.
I'll take a good look at the html.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Use caution with some of the Zero voltage MODFET designs.... many don't take into account the internal reverse biased diode that is part of the process design. One way to avoid the internal diode is to use two MOSFETS back to back and arrange them so that they BOTH turn on when you want them to conduct. I'll try to dig up a valid schematic.
Here the LT4351 creates an almost "ideal diode" by monitoring·the Input vs the Output and turns on the Back-to-Back MOSFETS when the Input is greater than the Output. It's capable of regulating this down to 15mV.· So effectively you have a diode with only a .015· Voltage drop.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 11/2/2007 6:18:34 PM GMT
Hi Beau,
Am I wrong, or is there a way to make a MOSfet into a blocking diode that has a lower voltage drop than a Schottky diode?
This product - a PolySwitch - claims a mere 0.1v drop as a blocking diode!· Can that be true?· Someone has appeared to developed a polymer state changing·semiconductor.· What's happened to good old solid state crystals? I hope these devices have a fast recovery.
Thank you all.
Will pass this information onto the group.
We pulled the diode out of last years car and it improved greatly. Will look into the lenses (not literally ) and the reflectors.
Reflectors might be a bad idea due to the collisions that can happen throughout the race and the added weight.
Thank you
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Check out my robot using the propeller RECONAUTOR
Our car came third.
We tried the caps however the charge didn't last long enough (they lasted 1-2 seconds).
The lenses and reflectors would have added to much weight.
We had no diode on the solar panel.
We used 4 lithium batteries equaling just over 15 volts as backup/power boost.
The maximiser worked a treat.
Thank you all for your advice.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Check out my robot using the propeller RECONAUTOR
kramer said...
This product - a PolySwitch - claims a mere 0.1v drop as a blocking diode!· Can that be true?· Someone has appeared to developed a polymer state changing·semiconductor.· What's happened to good old solid state crystals? I hope these devices have a fast recovery.
The PolySwitch works like a variable resistor. It allows current in both directions with low voltage drop it only blocks current when it gets hot as it's resistance goes up. When it cools it again allows current to flow with a very low resdistance.· I use a 100mA PolySwitch in a solar battery charging setup (with a TVS diode)·to protect against reverse battery connection. i also have to use a shottky diode to prevent reverse current when there is lower voltage on the panel than the battery. So no, the polyswitch is not a diode it's a variable resistor and the current heats up the part to increase its resistance.
These are great to use for all battery designs to protect from reverse voltage and to protect the circuits from shorts as well. Similar to the way a bench supply can be set to cut out at a specific current level.· If you know your circuit should only take 100 mA for example, a PTC in series with the positive supply can stop components from burning up if they get shorted for example or protect an SX chip if it latches up for example.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
I suppose it ought to be noted for safety's sake that PolySwitches and other similar variable resistance products are quite slow to "blow" (interrupt the current) as compared to an equivalently sized tin-lead link type fuse or even some circuit breakers. Thus, make sure your circuit and wiring can handle a temporary overload or short if you use them in lieu of a tin-lead link type fuse.
I did some testing with a 125mA buss fuse and a 100mA PTC fuse.
You are correct they are slower, how slow really depends on the range of current you are working with.
For example, using 5V with a 10 ohm resistor we will get 500mA without a fuse
With the 100mA PTC fuse it limited the current to about 300 ma within 1us·but took 14 seconds to limit below 100mA
Lower impedence circuits or short circuit condition the reaction time is much faster.
Using a 1 ohm resistor we would get smoke at 5A
Using the 100 ma PTC fuse it was able to react and hold the current below 100 mA faster than 1us my scope is not fast enough to measure any less timeframe.
The standard 125ma buss fuse allowed 400ma for less than 1us and dropped to 20ma and blowing·after·14us
Testing a single white LED with no resistor using just the PTC it allowed 200mA through the LED, very bright but·no sings of damage after a few seconds.·Using no PTC I got smoke after a few seconds.
Working with devices like 555 timers and op amps that have latched up turned to smoke on me·while under test typically due to static electric charges because of the long wires and breadboard environment do not happen when I am using the PTC fuses·as a maximum·current limit device. If they do latch·up it protects them pretty well.
While·I was testing with the 1 ohm resistor i connected the 1 ohm directly across·an unprotected 5V·accidently! Burned the tip of my finger and it let out smoke. Ouch! So I recommend using them in the design phase to prevent smoke and burned fingers because sometimes there are so many wires I get confused.
I·use one in a automobile design with a zener diode to limit voltage. The voltage can be from 6 to 8 volts and sometimes over 14V if someone tries to charge the 6v system with 12V charger since it limits the current through the zener at whatever voltage is applied. They do drop more than the rated current when hot though so it is not like a 100ma PTC will just give you 100mA at any voltage above·a threshold voltage·but they do work great for voltage limiter designs using zeners.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Comments
Nice site thanks for the information. I am learning and this is another page added to my library of knowledge. I am obviously a stubborn individual. I guess the diode is necessary when running many solar panels in SERIES due to the possible reverse biasing when one is shaded. Thus said i ask the question and is as follows; the solar car would run and possibly benefit without it depending on the weather of the day? If it is to be a bright sunny day then take it out. [noparse][[/noparse]Yes - No] Also i think that running some of the cells in parallel would divert the problem.
I suppose careful, but no incredibly complex calculations could solve the questions at hand; however more information about the solar panel and battery/s would be needed.
This continues to be a exciting topic...
Post Edited (grasshopper) : 10/29/2007 5:17:22 PM GMT
I previously mentioned that the team might provide a means to bypass the blocking diode if it is very sunny on race day. But, if the sun suddenly goes behind a cloud, all may be lost because the solar cell might make you slower.
Parallel or series, the dark cells would still drain. If it is series, you would have a voltage drop; if it is parallel, you would have a current drop. But, I don't think there are enough panels to be concerned indivually - put them in a series set up and exploit the highest possible voltage - then one blocking diode has the least impact.
Calculatons may not help you so much as trying to grasp a 'general idea' of it all.
I am also very interested in the SF52 diode of the Maxi-minimizer because it allows 'freewheeling' - very important. Without it, the motor would act as a brake when there was no power to it. The 'SF' is for super fast. Can some one locate 'ultra super fast' diodes or am I dreaming? Ideally, an 'utra fast Schottky diode' would be perfect, but do they exist? Maybe not.
Also, though expensive, ball bearings in all wheel axles would reduce the drag. I have seen wheels in hobby shops that have built in ball bearings and I've seen very tiny ball bearings that can be inserted in an existing motors. {you have to drill out the bronze bearing and insert the new ones with a bit of super glue. - micromechanics}
As i said before, there may be a lot of loss on the mechanical side -- others may never address it as you have to disassemble the motor and rebuild it.
Rotational balance is important. One can also remove the rotor from the electric motor and see if it always turns to one side up. That would indicate it is 'out of balance' or heavy on the opposite side. So you have to drill holes in the low side until the rotor no longer prefers rotation to one side up - you eliminate drag. So eliminates wasted energy.
And, if that is too much, you might even be able to buy balanced motors with ball bearing inserts at a hobby shop that services competitive events. The rotor may also be rewound to give more zoom.
I did all this with competition slot cars in the 1960s.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
If the race is run when the sun is lower than 60 degrees you would have to add servos to move the reflectors up and down as the car goes around the track. The reflector on the sunny side of the car would have to be lowered so it wouldn't cast a shadow. The reflector on the other side of the car would be raised to the appropriate angle to reflect the sun onto the solar panel. The angle could be programmed just before the start time of the race, or you could use a real-time clock and a look-up table to determine the angle of the sun. A couple of photo sensors could be used to determine which side was facing the sun.
The reflectors could be made out of cardboard or thin plywood covered with aluminum foil or sheet metal. This would require more work to build, but you could get 25% to 100% more power depending on the angle of the sun.
Dave
I'd rather depend of the lens than the reflectors if their is any question of them shading the actual panel. The season down under is late Spring and offers good solar prospects and higher sun angle. Maybe cut those reflections down by 50% to avoid potential shade.
Long ago, auto supply houses sold a square vinyl fressnel lens that you placed in the back window of your SUV or Van for easier wide angle views to the rear. That could either be used whole or cut to shape. Maybe, they still do.
It crossed my mind that· all 2AH batteries may not be the same. Primary batteries [noparse][[/noparse]one-time use] have a much more sustained output than secondary [noparse][[/noparse]the rechargible ones]. The problem is that the rechargible ones come with Amp Hour ratings as part of their advertising, while you have to dig to get the same informaton on primary batteries. It may be that all primaries are generally much higher, like 5AH.· You might find AAA primary batteries are 2AH, which AA secondaries are usually that capacity.· Here is an oportunity to reduce your overall weight.
While, one might say that 2AH is all the same, no matter what battery is used. It really should be, but you could test their specs and lables against the same load [noparse][[/noparse]an LED] by timing it. The lables may not reflect reality. Some suppliers my even cheat and merely upgrade lables while selling a lower rating.
In the U.S., Radio Shack used to sell the best batteries for a good price. It was a way of attracting customers into the store. In Taiwan, the electronic supply houses do the same thing. And of course, it is important to use NEW batteries from a source that sells a lot of new batteries as they get old by just sitting on the shelf.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
Post Edited (Kramer) : 10/31/2007 2:02:02 PM GMT
http://www.reuk.co.uk/Voltage-Doubler-for-Solar-Battery-Charger.htm
Also from the Renewable Energy UK (REUK) website: Note that the diode will reduce the voltage sent to the batteries by the solar panels by as much as 0.7 Volts so you may choose to omit the blocking diode from the circuit accepting small amounts of losses from the batteries in return for faster battery charging. For small 12V set-ups like this the diode is not really necessary and will almost certainly have an overall negative effect.
The Fresnel lens could be mounted closer to the panel to reduce the power gain or a smaller panel could be used. Extreme care must be used if a Fresnel lens is used. There are web sites that describe experiments where Fresnel lenses of a square meter in area were used to focus the sun to a small spot. This produces an extremely hot and bright spot.
Concerning the 2 WHr battery, it seems like this is fairly insignificant compared to a 30W solar panel powered for 1 hour. It's less than 7 percent. The circuitry that supports the use of the 2WHr battery would have to ensure that you don't lose 7% of the 30W panel's power just to break even.
Zero voltage diodes can be made using a power MOSFET and some circuitry to drive it. One example is shown at www.solarbotics.net/library/circuits/misc_switching.html
Dave
That is the most interesting item that has been posted here in some time. Beau also mentioned it a month or so ago, but I don't fully understand the concept. Some one else told me that you need at least a 3volt difference for it to work and that did make it any clearer to me.
I'll take a good look at the html.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
Edit
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1142,C1079,P2173,D2942
Here the LT4351 creates an almost "ideal diode" by monitoring·the Input vs the Output and turns on the Back-to-Back MOSFETS when the Input is greater than the Output. It's capable of regulating this down to 15mV.· So effectively you have a diode with only a .015· Voltage drop.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 11/2/2007 6:18:34 PM GMT
Am I wrong, or is there a way to make a MOSfet into a blocking diode that has a lower voltage drop than a Schottky diode?
This product - a PolySwitch - claims a mere 0.1v drop as a blocking diode!· Can that be true?· Someone has appeared to developed a polymer state changing·semiconductor.· What's happened to good old solid state crystals? I hope these devices have a fast recovery.
http://circuitprotection.com/litbrochures/ReverseBatt.pdf
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:
Do you want a quickly operational black box solution or the knowledge included therein?······
Post Edited (Kramer) : 11/3/2007 2:45:42 PM GMT
Will pass this information onto the group.
We pulled the diode out of last years car and it improved greatly. Will look into the lenses (not literally
Reflectors might be a bad idea due to the collisions that can happen throughout the race and the added weight.
Thank you
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Check out my robot using the propeller RECONAUTOR
We tried the caps however the charge didn't last long enough (they lasted 1-2 seconds).
The lenses and reflectors would have added to much weight.
We had no diode on the solar panel.
We used 4 lithium batteries equaling just over 15 volts as backup/power boost.
The maximiser worked a treat.
Thank you all for your advice.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Check out my robot using the propeller RECONAUTOR
These are great to use for all battery designs to protect from reverse voltage and to protect the circuits from shorts as well. Similar to the way a bench supply can be set to cut out at a specific current level.· If you know your circuit should only take 100 mA for example, a PTC in series with the positive supply can stop components from burning up if they get shorted for example or protect an SX chip if it latches up for example.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
I suppose it ought to be noted for safety's sake that PolySwitches and other similar variable resistance products are quite slow to "blow" (interrupt the current) as compared to an equivalently sized tin-lead link type fuse or even some circuit breakers. Thus, make sure your circuit and wiring can handle a temporary overload or short if you use them in lieu of a tin-lead link type fuse.
Regards,
Bruce Bates
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You are correct they are slower, how slow really depends on the range of current you are working with.
For example, using 5V with a 10 ohm resistor we will get 500mA without a fuse
With the 100mA PTC fuse it limited the current to about 300 ma within 1us·but took 14 seconds to limit below 100mA
Lower impedence circuits or short circuit condition the reaction time is much faster.
Using a 1 ohm resistor we would get smoke at 5A
Using the 100 ma PTC fuse it was able to react and hold the current below 100 mA faster than 1us my scope is not fast enough to measure any less timeframe.
The standard 125ma buss fuse allowed 400ma for less than 1us and dropped to 20ma and blowing·after·14us
Testing a single white LED with no resistor using just the PTC it allowed 200mA through the LED, very bright but·no sings of damage after a few seconds.·Using no PTC I got smoke after a few seconds.
Working with devices like 555 timers and op amps that have latched up turned to smoke on me·while under test typically due to static electric charges because of the long wires and breadboard environment do not happen when I am using the PTC fuses·as a maximum·current limit device. If they do latch·up it protects them pretty well.
While·I was testing with the 1 ohm resistor i connected the 1 ohm directly across·an unprotected 5V·accidently! Burned the tip of my finger and it let out smoke. Ouch! So I recommend using them in the design phase to prevent smoke and burned fingers because sometimes there are so many wires I get confused.
I·use one in a automobile design with a zener diode to limit voltage. The voltage can be from 6 to 8 volts and sometimes over 14V if someone tries to charge the 6v system with 12V charger since it limits the current through the zener at whatever voltage is applied. They do drop more than the rated current when hot though so it is not like a 100ma PTC will just give you 100mA at any voltage above·a threshold voltage·but they do work great for voltage limiter designs using zeners.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!