Building a solar powered go-kart

See some of the previous threads for a good start.......

http://cr4.globalspec.com/thread/8778/Need-help-on-an-Electric-Go-Cart-Project

http://cr4.globalspec.com/thread/9157/Need-more-help-with-electric-go-cart

http://cr4.globalspec.com/thread/8354/Solar-Powered-Go-Kart

http://cr4.globalspec.com/thread/9148/Want-to-increase-the-speed-of-our-electric-go-cart

Thank you!

But is what I want possible? I live in New York and get a decent amount of sun.

PS: Ill register after this post

Geeehh! it sounds fun absolutly, but probably by an artificially build-up solars(Whipped Shaped Antennas) collectors made by an optical fiber materials like (Polar Bears) hairs strings which help them absorb sun ligth/heat interconnecting with some thermocouples junctions and capacitors somehow within power inverters/rectifiers interfaceing in order to end up with enougth output juice to power that puppy up will be a chance to make it run for a while, I guess. Now, also very probably we will need to add on some kind of modify transmission to gear up the power plant speed as well to help with load/speed demands etc. definetly but still sounds a good project to try perhaps, congratulations and have fun in the meantime, enjoy it!

Solar GoCar,

MC

Are you serious?

Because I have no idea what that means. Further help would be appreciated!

Thanks, its me who started the thread

65 mph? Serious project or mental exercise?

If a serious project then go do your homework in the area of high speed streamlined bicycles, learn about aerodynamics, frontal areas and drag coefficients. Then run your calculations on available battery and solar cell capabilities and the weight of the vehicle. Then come back and ask your questions. Do all this before you go buying any hardware, especially batteries.

If you're just into a mental exercise.......this looks like an exercise in futility. 25 mph for a few miles range with day long recharge cycle. Maybe, but you'll have to be a pretty sharp designer to come up with a vehicle that has any practical utility. Your baseline is an electric golf cart with solar panels for a roof. How much can it be lightened in weight and still survive normal driving conditions, moderate roughness in pavements and other routine wear and tear? 65 mph will require 17-1/2 times the power with the same streamlining and equal friction drag such as from tires. A 3hp one person go cart is good for about 25 mph. 5 hp will get you maybe 35 mph. A serious streamlined body might get the power requirement down by 65-75%. Add the frontal area for a second person if they sit side by side. It goes on and on from there.

Ed Weldon, Los Gatos, CA

The short, simple answer is no.

Gas-powered go-cart - will work

Battery-powered go-cart with electric motor - Will work

Solar-powered go-cart with electric motor - No. Solar panels will barely be able to produce enough power to move the go-cart (if its sunny, and the vehicle weight is low, and your on a hill). The power-to-weight ratio is so bad that unless you use expensive super-light weight panels, and a LOT of them, you will not even have enough power to move the weight of the solar panels and motor (let alone a frame supporting a person).

You may be familiar with solar racers that work on solar and batteries but these are wide-profile super-light weight and expensive vehicles specially designed for racing, not transport.

I would advise a bicycle as a much more practical solution.

See previous threads for more detailed information.

If this is simply a hobby / project thing. Why not start out with a basic used golf car and begin your experiments.

You'll never get 65mph out of this thing and if you somehow did there would almost surley be an accident involved but it will give you a working platform to begin testing theory's.

G'day manco12,

Glad to see you have registered and welcome to CR4, I hope you get as much from it and enjoy it as much a I.

It's going to be extremely difficult to run an electric go-cart using the sun for the same reason it's difficult and very expensive to build a solar car. There are two primary reasons for this:

1. Energy Density of Sunlight: You will often hear it bandied about that at the earth's surface the sun supplies about 1,000 watts per square metre or 1 kWm^-2. Unfortunately this is the absolute maximum at midday when the sun is directly over head. If you move away from the tropics, add clouds, time of day you can only get about 400 Wm^-2.
2. Efficiency of Solar Cells: The efficiency of solar converters is not good. If you had a NASA budget an purchased the absolute best cells available you are talking 40% efficiency. Realistically you are talking at about 20% at best and even those are going to be expensive.

Put them together and you will be lucky to get 100 Wm^-2 of electrical energy from any sort of solar energy to electricity system and that's not going to be enough to run your go‑cart.

The only realistic way to do it would be to have a fixed and large enough solar array that charged batteries on the go‑cart. The only trouble with that is you are then limited to where and when you can use the go‑cart and you are more than likely going to want to use it when the sun is at its highest which is obviously the best time to charge the batteries.

Now, before anybody pipes up with the solar car challenges and the vehicles they use, yes, they are solar vehicles. Except, they are very expensive, too large, have woeful performance and handle like a pissed cockroach with lead boots.

It's only the solar power part that is problematic, the electric go‑cart is definitely a goer. With a little research and some smart design you should be no only able to build an electric go‑cart but one that can outperform similar Internal Combustion Engine driven go‑carts.

The main reason for this is the way the two different forms of propulsion deliver the torque to the wheels. ICE give you maximum torque at about ²/₃^rd of their maximum RPM, while electric motors give you maximum torque at or very close to 0 RPM. The time you want maximum torque is when you are starting from standstill and accelerating to normal speed which is the exact opposite of the ICE but exactly the way the electric motor works. Electric motors also operate over a wider range of speeds and can start from a dead stop so you can also get rid of the clutch, gearbox, and if you use multiple motors the transmission and differential as well.

I saw a demonstration where a home built electric car was pitted against a Ferrari and then NASCAR. It might sound strange but even though the Ferrari had a top speed almost three times and the NASCAR over four times the top speed of the electric car they not only couldn't compete with it but lost by a considerable margin.

The reason?

The increased acceleration from a standing start meant that the ICE driven cars ended up behind the electric vehicle from the start and could then never produce a great enough speed differential to get past the electric car. Whenever they got even close to passing as soon as they approached the next corner the added braking and acceleration of the electric car would leave the ICE driven vehicles back behind it again.

So, yes you should not only be able to build an electric go‑cart but with a little effort one that outperforms similar ICE driven go‑carts. The solar bits not that easy, but once you have the thing going then you could always purchase the power to charge it form a renewable energy source like wind, wave, solar or whatever. That way you get the best of both worlds while dramatically reducing the complexity and construction cost.

PS I would still recommend looking at the other threads and reading up on the different types of electric motors and how they work as the selection of the type of electric motor is critical and very dependant on your specific use. You should also look at things like regenerative braking which recovers the energy when you slow down rather than just turning it into heat in the brake system.

Masu -- Very interesting and well written post. You've been following the subject much closer than me.

Do you happen to have any links or search information to find the details of the electric vs. ICE powered car competition?

I am also curious as to the design "sweet spot" (i.e. onboard battery capacity (nd attendent weight) vs. speed achieved for an electric go cart for various drag race lengths 1/16 mile, 1/8 mile or 1/4 mile or even 1 mile, which is land speed territory. Being lazy by nature I'm reluctant to reinvent that "wheel" if some one else already has.

Ed Weldon Los Gaatos, CA

Hello,

I never was going to make it run on just solar power. My very first thought was that mabey I could build a solar/electric from outlet powered go-kart. Now after a little more research, im thinking of building one that just runs on electricity. And off course solar power for some car underglow NEON lights lol. I have a 12HP go-kart that I bought but I cannot pay for gas - $10+ a week! And gas prices just went down. Anyway what size/kind of batteries and what kind of engine should I even start to look at? Any DC motors???

Thanks for helping

12 HP is a pretty big electric drive. You're talking fractions of an hour of run time on 76 amp hours of deep cycle AGM batteries (4 x 19 amp hours to get 48 volts; West Marine, $115/17 pounds ea.). You can buy a lot of $4.00/gallon gas before you'd match the cost of the conversion. How fast do you want to go? How fast can you go in New York City and still be legal except maybe on one of the drag strips out in the burbs?

The electric boat community has gotten into electric drives that size. The cost makes some sense for a 20-25 foot boat, although I don't think you are likely to see anything like that in the rough waters around NYC.

Ed Weldon Los Gatos, CA

I have a gas-powered kart, I just randomly said that. NOt to convert or anything.

Anyway I can go as fast as I want without getting in trouble for the most part. Also, I do not live in New York City, I just live in New York... in more country-sh land but in between. I can ride on an ATV path right by my house. Anyway, couldnt I just get like 12 batteries and "connect" them together?

Thanks.

Like no not that simple

I mean though, isnt it possible?

I always make things sound easier than they are

Manco12 --

I'm assuming here that you need 12 hp to go the speed you want to go. If that's the objective a 48 volt motor is what you'd end up with. 4 12volt batteries can be connected in series to get 48 volts. I think where it gets a bit complicated is in the details like safety (48 volts can kill you) and motor control. Like I said, the boat folks are the ones most up on that for no other reasons than the cost of the boats they are dealing with and the necessary boating safety issues encouraged by governmental entities. You can get a really nice 48 volt drive system for a big boat and you will lay out something on the north side of $10K. I'm pretty certain that's not what you are interested in; but I'd encourage you or anyone else that wants to experiment in this direction to go to that subculture for some useful wisdom to absorb when someone dangles a cheap surplus DC electric motor in front of you and gets your creative thoughts going.

Of course there is also plenty to be learned from the folks experimenting with homebuilt electric cars, scooters, bicycles etc. Only problem there is that there is a power gap between scooters and full size automobiles and it's right in that gap where you are looking for your go-kart concept.

Ed Weldon, Los Gatos, CA

Actually, my 12hp only goes 40mph.

Anyway, I dont exactly understand what you are saying....

What would be the problem other than safety?

Manco 12--

Most of the modern small HP DC motors are permanent magnet types. Unlike the large older types with separate field and rotor windings the DC types require you to somehow limit the voltage getting to them. The requisite devices have a lot of efficiency issues or are just plain expensive to handle high currents once you get past 5 hp. Things are made a lot easier if you can take voltage taps at 12, 24 and 36volts between the batteries to vary your speeds. I don't want to elaborate further because I'm not as conversant with this technology as others with more current experience.

I'm sure you can see the advantage of four easy to handle and cheap mass produced batteries instead of one big expensive thing that takes two people to lift. I use one little 19 amp hour AGM battery in my 14 foot boat to power a 36 pound thrust MinnKota electric outboard. (like maybe 1/2 hp equivalent) I love it because it is so easy to handle in and out. BTW the AGM batteries require somewhat pricey battery chargers to properly charge.

Ed Weldon Los Gatos, CA

To be practical but costly you will need to charge your batteries from a solar array that is stationary with two or more sets of batteries in cages you can easily and quickly change out.

Try this link http://www.homepower.com/home/ Years ago they even featured a battery powered formula v type race car.

The issue you will have is cost vs weight. Lighter batteries cost more, heaver batteries take more vehicle to control. Speed is not a problem, how long you can power your acceleration to have that speed is the issue. One electric drag bike had what looked like 500 C sized NiCads and was good for one quarter mile run then change batteries.

Good luck, to go the speeds you want the wattage will mean high voltage, high amperage or both. Learn from others experience not your own loss.

Brad

So what should I do?

Manco12 --

It's study time. Your problem is unique. No one with credible design competence is going to lay out all the details in a free forum like this unless he/she can simply point to the plans used by someone else to do the same thing.

Unless you've had some serious fabrication experience and have access to a competent design resource either in a friend or your own head then you'd be out of your league. My advice to you if this is the case would be to look for a more efficient IC engine, work on incremental improvements to the mileage capability of the go cart you presently have and forget about electric drive.

Ed Weldon, Los Gatos, CA

Hello again,

I was looking at a couple 12 V deep cycle AGM batteries. What is a "good" weight of the battery itself going to be? And would $70 be an accurate estimated price?

I just dont want to waste much money.

Thanks, I highly appreciate all of you

You can do it, but there is a learning curve. Home Power is a place to start because they have 20 years of articles on electric vehicles, loads of technical references, venders and contacts.

As for how many batteries needed, that is not a strait forward answer. 65Mph for how long, with what type of battery, on how heavy a go-cart, what type of terrain? Each variable changes the outcome.

You also will have many choices for solar cells, charging systems, motors, speed control. You will find a lot of the work already done but what are the best options for your cart only you will be able to decide.

Brad

Thanks, Im gunna look at Home Power more tomorrow. I just briefly read it earlier.

You dont know how much I thank you. Anyway, Ill try to stop playing 20 or 100 questions

Ill start my own research now,

Thanks, Thanks, Thanks!

The f stop adjustment is normally part of the lens and is another adjustment ring like the focus ring except if you have a motorized focus you're not going to have a focus ring.

Anyway, as Vermin said the whole thing is about balancing the sensitivity of the imaging device (in chemical lingo speed or ASA rating) the time the shutter is open and finally the f stop.

With a proper digital SLR you will have a mirror and prismatic system that allows you to look directly through the lens and see exactly what the lens sees including the depth of field as you fiddle with the f stop setting. Then when you take the image the mirror if flipped up out of the way and exposes the imaging chip

G'day manco12 & others,

Here's how I would go about it:

First off you are not going to need anything like 12 hp or 9.24 kW worth of electric motor to get the same performance. There are several reasons for this:

1. Transmission: With an ICE you need to have several gears, clutch, differential etcetera to match the speed of the engine to the wheels. With electric you don't need this because if you engineer the motor correctly it should be able to operate over the full range of speeds without any gearing.
2. Torque: Torque is the rotational way of saying force. Ok, here's where Newton comes into it and we get all scientific. F = ma is the critical part here and as you can see the acceleration a is directly proportional to the force F you apply. Now this is where the ICE fall down because you really want maximum acceleration from a standing start which unfortunately is when the produce the minimum torque. Electric motors on the other hand produce maximum torque when they are not turning which is exactly what you want. To get past the inefficiencies in the way ICE supply torque you have to over size the engine otherwise it would take till the next week to get up to speed and I'm guessing that's not what you would like. Anyway, since electric motors actually produce maximum torque when they aren't rotating, which is exactly what you want, you don't need to have one that produces the same sort of power the ICE engine is rated to.
3. Multiple Drives: At a bare minimum you will be driving the two rear wheels and while many go‑carts don't have a differential it's better for handling if you do. However, with an electric vehicle you are actually better off installing two separate motors one for each of the driving wheels or 4 if you really want to go super fast. As a result you can reduce the power and size of each motor.
4. Impulse or Over Driving: Electric motors can be and usually are overdriven to get them going from a standing start. This is perfectly ok provided you leave enough time between starts for the motors to cool down to their normal operating temperature. Admittedly with a go‑cart you are going to be starting and stopping fairly frequently but you can still give electric motors a bit more grunt to get them going.
5. Regenerative Braking: With ICE driven vehicles the only way to slow down is to turn the kinetic energy of the vehicle into heat in the brakes which wastes all the energy and often overheats the brakes. With an electric vehicle you can turn the drive motors into generators and recover up to about 50% of the kinetic energy. For example when approaching a corner you use the motors to slow you down then dump that extra energy back into the motors as you accelerate away.

These are the main points you need to consider and develop an understanding of to be able to design and build an electric go‑cart.

This is a guess and you will have to do the calculations properly but when you add everything above up you will more than likely be able to get the same sort of performance out of two 1.4 kW (2 hp) electric motors as a single 9.24 kW (12 hp) ICE.

Anyway, I think it's a top little project and you certainly should be able to build an electric go‑cart. Let the information above sink in for a while and get back to me with any questions or queries you have and I will help you with you project as much as I can.

Masu --

Quoting you "you will more than likely be able to get the same sort of performance out of two 1.4 kW (2 hp) electric motors as a single 9.24 kW (12 hp) ICE."

I think you are correct if the measure of performance is driver satisfaction during actual operation. In this case that operation would be in a variety of modes ranging from pavement to moderately bumpy off road conditions with occasional to frequent requirements for short bursts of additional power for acceleration or hill climbing.

But it's important to note that if the vehicle is challenged by long upgrades or wind/rolling resistance then pure horsepower is a prime requisite. The nice but then the limiting aspect of electric motors is that they can be overpowered way beyond their nominal power ratings for as long a period as available cooling and/or heatsinking will keep the internals or other components of the system from overheating. An analogous situation would be using a nominal 4 HP ICE with added on turbocharging or Nitrous oxide which doesn't suffer from the lag of a turbo.

Ed Weldon, Los Gatos, CA

@ masu,

I know nothing about electric motors ect. I have been wanting to build a gas go-kart so I know a little about them but nothing about what you said. Ill try to research this more now and re-read your post later on.

Thanks though

G'day manco12,

• I know nothing about electric motors ect.

Since when has not knowing the first ting about something ever stopped any self respecting engineer from diving in head first. The only thing that's important is that you have to be willing to have a go, do some research and learn by trial and error.

Before you get swamped with the quagmire of different types of electric motor may I suggest starting with brushless DC or stepper motors which are really variations on the same basic principle. They are a little more complex to understand than simple DC motors but have several advantages in this instance:

• Moving Parts: Stepper and brushless DC motors as the name suggests don't have brushes like other forms of DC motor. That means they don't have a commutator as well and that reduced a whole host of bits that are likely to wear out or get messed up with dirt.
• Radio Frequency Interference (RFI): The sparking and arcing you get with a brushed motor are a serious source of RFI that can make you very unpopular with your neighbours. Since stepper and brushless DC motors don't have a commutator or brushes they don't produce anywhere near as much RFI which then means you don't have to worry about shielding, spark suppression etcetera.
• Simplified Control: The speed of stepper and brushless DC motors is governed by how quickly you cycle through the coils. This has two major repercussions:
• No Feedback: Because the speed of the motor is controlled by how fast you sequentially cycle through the coils you don't need some sort of additional sensing mechanism to know how fast the motor is running or how many times it has rotated or moved. It's either going as fast as you are driving it or it's not going at all. Also if you keep track of how many steps it has gone through you know how far it has moved. With brushed and other motors the speed varies according to the voltage, current and load on the motor so you need to have some sort of feed back mechanism that tells the control system how fast the motor is actually turning.
• On-Off Control: Again this has to do with the way you drive the motor. With brushed motors you need to be able to vary the voltage being applied to and current going through the motor. With brushless and stepper motors you either have a particular coil on or off which greatly simplifies the electronics. It also makes them ideally suited for controlling with microcontrollers and you can actually get off the shelf stepper and brushless motor controllers. All you have to do is connect them up and then programme the controller accordingly.
• Burn Out Proof: This is a simplification but with a brushed motor the current going through the coils is inversely proportional to the speed of the motor. This means that if the rotor can not rotate for some reason the current through the motor can be extremely high and has the potential to damage the motor and even start a fire. Because of the way stepper an brushless motors work they don't have the same problem and are perfectly capable of sitting there all day with the power on and not rotating. Actually they are often used in this way to hold something in position.

Stepper and brushless DC motors have been around for a long time but with the cost of electronics becoming steadily cheaper they are becoming more and more common. As a result they and the associated control electronics are becoming easier and cheaper to obtain.

Ok, there's a fair bit there for you to cogitate over and as I am no doubt sure you are aware there is a great deal more to it. However, it should give you a place to start and get you moving in the right direction. Here's a couple of links to get you going.

• Stepper Motors: Wikipedia
• Brushless DC Motor: Wikipedia
• Brushless DC Motor: How Stuff Works

If you think I can help and wish to contact me directly follow this link to the CR4 personal message system and send me a message with your eMail address and I will contact you directly. Don't publish your eMail address here as it's a public forum and you don't know who or what could be reading it.