Well yes it will be capable, we have people running this at 7 volts and it works fine.

Basically, if your panel is 20watts at 10volts,
when you stall your motor,
you will get something like 2volts at 10amps on the output.

You may even get something like 1volt at 20amps, it depends on the internal resistance of your motor.

either way, you will always see 20watts on the output
the beauty of a maximizer

Also the unit is 99AUD which is like 65USD.

You'll have a new customer...

The maximizer is capable of the high-current/low-voltage outputs because of its efficient synchronous dc-dc design.

I was playing with my Castle Creations Sidewinder (Motor Controller) today because the sun was bright and wanted to test some settings out and use my EagleTree data logger to record the effects and panel output power.

I was trying the LiPO cutoff setting on the controller. The controller allows me to set the voltage pretty much to anything. My data logger showed the highest power for the panel of 20w @ 8.25V during an estimated 650w/m^2 of insolation. So I loaded up CastleLink and Adjusted the cut-off to 8.2V and went back outside. Sure enough the Cut-off limited the motor current by use of the PWM circuts when the voltage dropped. This keep the regulated the current to be near the MPP. The car seemed zippy and not bogging down.

So my question I pose to you Tony.

How does converting the output of my panel into a lower voltage higher amperage improve the standing starts and other hard accelleration when wattage is wattage? I understand that my IO (Waste Current) will be less of a precentage when more amps are involved, is this where my efficiency gains are from?

Nevermind how providing more Amps at the same wattage is better than less amps more voltage.

kT vs. kV.

Since the motor is drawing more load then kV dosen't do a lick a good if the motor is stalled or near stalling. When the load starts returning to normal levels and car is up to speed that is when Kv matters not Kt.

I feel somewhat like an idiot for not grasping that concept when all I was thinking the wattage is the same which means the "HorsePower" is the same so the accelleration should be the same too.

The torque produced by your motor os proportional to the Amps going in.
The speed produced by your motor is proportional to its voltage.

During acceleration, its better to have higher currents, for increased torque, and as the car speeds up, we convert the torque into speed. The maximizer does this by increasing the voltage and decreasing the current at all motor loads.

When you tested your panel, you found that your maximum power point was at 8.25, and you had 20 watts. When you set your maximizer for your panel, you will see that it will lock onto 8.25 volts as well.

Initially you were only seeing 20watts at 8.25 volts. so you were getting 8.25volts at 2.42 amps.
With that maximizer you will have 20 watts at ALL voltages, that means at a 4 volt load you will get 5 amps.

You would of seen with your data logger that you get a maximum current output of around only 2.8amps. that is when your panel is suffering.

Remember, when your motor is accelerating, because of the kv law, the voltage across it is low, and because of the kt law, your current in it is high.

When you install your maximizer, because it can output voltages from 2volts and up, you can set your low voltage limit on your sidewinder as low as possible. You probably wont even need to set it.

When I tested my panel today with roughly 650w/m^2 of radiance the panel produced 20watts of power at 8.25V and 2.47A. Yes anytime the load was greater than about 2.5A, the votlage dropped as seen on the chart.

I had to estimate the radiance because I lack a meter. It is October and Mid winter is about 70 days away so the value should be close. I used a chart that listed the max at 720w/m for my location and date and time. With it being partly cloudly to cloudy and no clear skys I had to just guess with a lower figure.


http://farm4.static.flickr.com/3167/2940618390_3457074db8_o.jpg

The panel under full summer sun should be higher and from my test drives with a radar gun a few weeks ago I can say that today the car looked slower but not real slow. Top speed two weeks ago was 33kph and today I would estimate around 25 to 27kph. I also need to add that two weeks ago I did not use a data logger running off the ESC's BEC which consumes another watt or two. It will not totally account for the reduction in speed but combine the effects of a lower sun and clouds

The only way I can truely test the MPPT would be a standing start test for a know distance. 25M or 50M should be fine, just need to use a running track so I do not have to mark out the distance. Same gearing for both test. For the 25m test I would guess there could be up to 20% reduction in elasped time and the 50m only 10% as the car will be at top speed longer.

Did you pace the datalogger between the capacitor bank and the solar panel, or between the capacitor bank and ESC?

Between Panel and Capacitor.

The capacitors are wired to the ESC's Power Plug. I didn't think it would matter much since it is only 10,000uf and not a SuperCap. The data logger came with Deans plugs, so I just plug the panel into the logger, then the esc into the logger.

The load spike are from the fact that I am going from one end of the parking lot, turning around and going back. I kept moving most of the time and added a few standing starts.

Looking at that power curve i can see that your panel is only producing maximum power during the spike periods (when you accelerate/or top speed). This means that your capacitors are charging up to full during the periods you arent accelerating or a full throttle. If you use larger capacitors (maybe a 10volt 2 farad supercap) your curve would look much cleaner, similar to a straight line, because your caps will always be charging, and your panel will always be providing max power, and you would have alot more power.

That way, while your car draws little power from your panel, your panel is still producing maximum power, and stores it in the caps for later use, like for better acceleration and top end speed. make sure you place the mppt between the capacitors and the solarpanel.

The power your panel is producing is the area underneath the orange curve. by using larger capacitors, you power curve will look like the one shown below in the red.



As you can see, you will have more power, as the area underneath the red curve is larger than the area underneath the original orange curve.

I just wasn't geared high enough to be pulling the wattage of the panel near top speeds. I did not gear high for a reason, I didn't like the car stalling and powering off from low voltage and with the wayning winter sun it would be pointless to try. My initial goal was just 30kph. , I made my goal, this winter I will work on every detail to increase speed.


And yes a large capactior would help but as to keep with the Solar R/C Cup rules I keep my bank to 10,000uf.
I do have some CAP-XX .33F capacitors rated 4.5V each. I also have some 1F 5.5V memory caps but those suck at putting out the power. Good for LED lights and that is about it.

Hi brightwhite,

Today i finally finished obtaining all the resources i need to build my own RC solar car.
The car im building wont comply with the solar cup rules as im not going to be running in the solar RC cup, however the aim of my project is to build the fastest possible solar car in a 1/10 scale car size.

It will consist of:

1) 12.5volt 55F supercapacitor bank (this will store roughly 30mAH of current @ 12.5volt). We have a total of 5 2.5volt capacitors in series to achieve the 12.5 volts.
2) 2.4Ghz Rx/Tx
3) Easymax MPPT
4) Quark 22a Car brushless controller
5) RC10L3 Donor Car (as suggested by brightwhites tutorial)
6) Generic 3000Kv brushless inrunner motor
7) 13V(oc) Solar panel @ 1Amp, giving nearly 10 watts at 1Sun. (lightweight as well)
8) Futaba s9650 digital servo for the steering

The Aim of the large capacitor bank is to supply enough power during the accelation period of the car. This will also supply enough power to cruise the car through long spots of shade without the ESC going into undervolt protection.

I will have the ESC set to 4 volts undervolt shutdown, however i dont think this will be an issue due to the large capacitor bank.

Basically, the wiring diagram looks like this.

Ill keep this thread updates as i progress through this project.

More Pics below:

Are you just gonna slap the solar panel straight onto the chassis of that car?

that motor looks like it can handle 100watts or more lol. do you really need that?

Tony, looks like you are making a speed demon with that RC10L3 and that Mega Storage Capacitor.

The first speed secret for the pan cars is that they are simple. The second Speed Secret is in the Differential (Get it right, it will be fast around corners) The thrid Speed Secret on pan cars is Capped Tires, which you already have. Capped tires may weigh slightly more than a set of foam tires, or they may weigh the same as a Sedan Rubber tires but the rolling resistance is way lower. I don't know how much you paid for the doner car, but a new set of BSR capped tires cost about $70 USD so smile if you paid that or less for the doner car.

The motor looks semi-hefty for the car, but it will move the car. My first motor was not the greatest but still performed very well. My second motor was more efficient and gave the wheels 1~3 more watts of power.

To answer speed freaks question, about slapping the panel ontop of the car? Why not? Just get some 1cm or 3/8" dowl rod and screw them inplace of the body post on the RC10L3. Using some small angle an aluminum mounting fixture could be made on top. But the option of making a custon chassis like I did could be more stable with the excess weight ontop. http://www.instructables.com/id/Buildin ... red_RC_car

TONY!!!!

I got the MPPT yesterday, and today I did some test!!!

I live in the US and winter is getting very close. 100 miles north of me they are calling for about 10" of snow tonight so that should be a sign of what light I have to work with.

Today it was sunny and windy but not clear skys from the cold front moving in. The MPPT performed like it was designed to. When the motor was bogged down to near stalling the total wattage from the panel remained the same. When I removed the MPPT and run another test, any time the motor bogged down too much the panel voltage dropped as did the total wattage. I would say in near stalling condidtions the motor will have 50% more wattage with the MPPT in use. Of course the MPPT will have little affect on the topspeed of the car. The MPPT does allow me to gear for greater speeds and not worry about the car stalling of studdering during take off.

All I can say is I can't wait to give the MPPT a test drive when the winter weather is being nice.

Brightwhite, im glad the mppt arrived safely .

Also yea you will notice the because the panel wattage is the same under all loading conditions, you will have higher currents under heavy loads.

A simple test to see how many amps the mppt can supply is simply by just connecting an ammeter to the output of the mppt.

And yes, my aim is to biuld a speed demon, thats why i sourced huge capacitors. the aim is for even when im not driving the car, or when the car is still at standstill, the panel will still be producing maximum power, if you know what i mean... so the capacitors are always in the charging condition.

Since I am not running a large capacitor bank to store power, I puf a 3300uf 6.3V capacitor on the RX. The MPPT directly feeds power into my Brushless ESC and if the voltage dips below 4V the cap will keep the ESC and RX alive untill the load surge is over. I could use a 5V regulator to power the ESC and RX directly from the panel to bypass that situation, but the cap is very simple and less likely to cause problems as most ESC BEC's are fairly reliable and one less componet to mess with.

I made the Plug-cap just by triming the leads even, crimping on sevro-connector pins and installing the plug jacket over the pins. Not much weight savings over the 3" of 22ga wire but it does save me the hasssle of mounting the capacitor by either zip tie or servo tape.

TonyB wrote:Brightwhite, im glad the mppt arrived safely .

A simple test to see how many amps the mppt can supply is simply by just connecting an ammeter to the output of the mppt.

.

Why do that when I still have the data recorder installed? I had to make two Large Deans to Micro Deans adaptors to fit the data recorder to the MPPT but in the future when most of the testing is over my connections will be all micro deans.

The voltage shouldn't dip below 4volts if you have the voltage cutoff set to 4volts for the sidewinder.