Ok, this is a bit out there, even for this forum but in one of my classes at school we make electric "go-karts" and race them state wide. this biggest things with these cars is efficiency. My group is trying to think of a way to do regenerative braking, and i have researched it a bit, and not much has come of it. I looked on wikipedia, looked othere places, and didnt get any where that could explain to me how to implement regenerative braking. I understand the basic concept. in an electric car you have a motor that moves you forward when you apply the "regenerative brake" some how, the engine works backwards, and a) causes the car to slow, and b) function as a generator to charge the batteries. Now that i understand the "basics" of the basics, i am trying to understand a) how to make the engine switch into this regenerative state b) how it slows the vehicle If any one here can enlighten me, or point me in the proper direction(or have any other good idea's for efficiency in a small, 3 wheel, 1 electric motor and 2 battery car(made primarily from aluminum tubing) let me know
okay, I assume that since the DC motor will always be connected to the driveshaft of your vehicle the motor will always be turning. In theory you could create a circuit that when you left off the gas (or just button/pedal to activate motor) it kicks in and uses a simple charging circuit to give the battery back some of what it is giving out, YOu would of course need a voltage regulator or some other such way for your circuit to accept a wide input range, the motor will give different output voltages as it spins faster or slower, get your voltmeter out for that one. A simple diode should be used at the battery side to keep power going back into your circuit. The more load you hook into the motor the more force it will take to turn. if you just connect the two leads together it should get harder to turn, now this should not take place of a real brake. but you can use them in conjunction. if any of that makes any sense, also just give it time for one of the electronics experts to give you a possibly better description.
that is one of my primary concerns, not sure if it would work the same way, or if its possible like that.. While what you said in the first part makes complete sense, the only thing is that during these endurance races you never let off the accelerator, and brake as little as possible. the race is over 1 hr long and if you run out of battery juice you cannot win. the biggest energy lose we can think of is with the minimal braking we do( necessary through some turns)and then after the turn we need to speed back up to speed . basically what i am trying to say is while that may work with some more consideration, we rarely take our finger off the accelerator(use a thumb accelerator) and when we do it is to brake(which is why we are trying to figure out regernative braking) the part i dont understand is the last part what i want is something that makes the engine slow its turning(as you said), but i do not understand how i would place this load on the engine, when i think of load i think of weight, and electricity(which we cannot waste!!) what do you mean when you refer to load? Let me know what you think, i apppreciate the prompt responce, and i hope for follow up and more help!! Thanks
Basically, when your motor is acting as a generator, ie: something is making it spin while you are not supplying it voltage. Load in this case is electrical load, such that, the more things you have the motor supply electrical power to, effecively the harder the motors shaft will be to turn. I guess that could help in braking. One thing you may want to consider is solar power, you can use it to supply the batteries with a little more power. Also you may want to consider having a backup power system. Such that say after 30 minutes your main batteries start to get depleted, you should switch to a second set of batteries. During that time you would give your primaries time to rest and regain a little strength, and charge them via a means such as solar.
I belive that if you can get a hold of a motor controller specific for this application, those already have a regenerative breaking circuit. If you are doing it yourself, it will get a bit more involved. You will need to have a circuit to sence when you "generator the motor" so all the power goes to your charger. I would look into a DC-DC switch mode converter for this job since it can take a wide range of inputs (which the motor will output as it's RPM vary with breaking) and efficently output a regulated voltage. Linear regs waste a LOT of power. Then, you can control the brake force by placing a higher load on the charging circuit. The more current a generator has to source, the harder it is to turn, it is conservation of energy. The trick is how to increase the load and still put as much of that current as possible into the battery. I have no idea how you'd do this though.
QED make smallish controllers in the UK for electric golf carts and do several types, with an emphasis on battery efficiency. Have a look round their site for ideas, they have lots of basic circuits (though not of the ones they sell ).
I don't think you'd have enough mass to make it worth anything. The whole point is that you recover the kinetic energy (1/2mv^2) of the car to the battery. But for a go cart, this mass should be very little. Also, how much will you be breaking? I say max speed, the whole time :-D. I think its more important that you lookinto getting light, efficent parts on it (especially batteries), and a good aerodynamic design.
The kinetic energy of the car has almost nothing to do with regenerative braking. Well, the velocity is important, but the mass is not directly related. If somehow the polarity of the motorshaft was reversed, the rotating wheels of the car would be charging the battery slightly, and the car will slow down and brake a bit due to the electrons encountering resistance as they're forced through the circuit.
You would need a second motor circuit attached to the brake switch and use that as a way to contorl the amount of energy used to charge the battery, 0% brake circuit to charger open 100% brake only as much resistance as copper wire has using a variable current regulating circuit would be the most efficient. Try solar power. The main thing will be to get high power deep cycle battery (Lithium Polymer) a good high torque medium RPM DC brushless motor. (AC motor with Speed control) If the race is only 1 hour then you will need the average current yoru motor will draw in Amp hours. + 10 or so to make sure you have extra peak power. I would say that the regen. brake is a little hard but not hard you will need to use only brake or only gas. So maybe a kill switch when the brake is on so you don't have to let go of the gas...relay anyone? and just have taht 2nd circiut off the motor.
I kinda explained it in my previous post, but I'll ellaborate a little more as to more thoroughly answer your two questions. a) I suppose you would need to implement a sensor into the gas pedal so that once you release pressure, a relay or other switch is flipped so that the motor's electrical contacts are reversed. Once the gas pedal is depressed again, it should then reengage the motor to its proper operational configuration. b) I'm not really sure how regenerative braking works, to be honest. In my opinion, it can be used to brake ever so slightly while in coasting mode. I suppose that if you hit the brakes, it will kick in as well to assist in the braking and to charge up a little bit, but I can't see it charging the battery too much. Without knowing too much about this, this is my logical theory as to how it works. When charging a capacitor or battery, it gets hot, right? Why? There is charge within the battery, and forcing more charge to flow through it creates kind of an impeding force. I'm having a really hard time trying to come up with an appropriate analogy. Maybe what I gave you will be enough for you to understand some more references.
