Solar charge controllers

[elkowalski]

hello guys, i am building a solar go kart with 2 solar panels of 125 watts rated 18 volts 7 amps and i will be connecting it to a charge controller of 24 volts to the electric motor rated at 24v 300 watt max. so i was wondering if when i connect the 2 solar panels in series the voltage will raise to 36v but when it passes through the controller would it lose the power? because we get 24 volts after the controller and i dont know if the current increases more likely as a buck converter. please give opinions and if someone can answer my question regarding the controller it would be great. thanks in advance guys

[Mike90250]

This is where a MPPT controller will boost your amps, and give the full 250W to the batteries. A PWM controller will only deliver about 2/3 of that power.

[elkowalski]

so it acts as a buck converter right? thanks mike for the quick response. also i am building a solar go kart without the use of batteries. 2 solar panels in series and then connected to the mppt solar charge controller and from there to the scooter electric motor of 300 watts. it needs 24 volts and the rated current is 16 amps for 2700 revolutions. would it work? any advice that you could give me will be greatly appreciated. thanks in advance

[Sunking]

so it acts as a buck converter right?

That is exactly what a MPPT controller is.

thanks mike for the quick response. also i am building a solar go kart without the use of batteries. 2 solar panels in series and then connected to the mppt solar charge controller and from there to the scooter electric motor of 300 watts. it needs 24 volts and the rated current is 16 amps for 2700 revolutions. would it work? any advice that you could give me will be greatly appreciated. thanks in advance

Not going to work because solar panels are not voltage sources, they are current supplies. When the controller senses there is no battery, or voltage it will just shut down and you no go.

[elkowalski]

@ sunken
so therefore, since i need a voltage source and i dont want to add too much weight on it. should i just add a battery of 24v with like 15 amphours so that i can keep it constantly charging it and last for an hour or so? or if you have any other suggestion of what to use to build the solar go kart it will be nice to hear. btw it is for a school project. thank you

[Sunking]

You will have to have a battery. Motors, especially DC motors are strange beast. Torque is proportional to current, and on a DC motor the highest torque is at 0 RPM and decays as RPM goes up. What this means is the motor needs many multiples of it rated current. If you starve or cannot supply that heavy current, no torque and NO-GO. Solar panels cannot supply that large current, only a battery can do that. That little 300 watt motor that is rated for 10 amps will require 100 to 300 amps to get it moving from a standing start.

You will also discover at least one more major hurdle on this project, but I will let you discover it on your own. When you figure it out you will understand why there are no solar powered vehicles on the roads.

Good Luck

SK

[elkowalski]

that is why in order to get the go kart moving you will have to push it first for the start and then i wouldnt need to have the 100amphours. because as far as i know in order to turn something on it requires at most 10 times more power and then it goes back to 10 amphours or so and stays the same. thanks for the comments it would be nice if you can give me more tips because the project is for middle school students and i have to help them out with a go kart so i wouldnt like the idea of getting not to work at the end haha. thanks sunken again. another question that i would like to ask you is that if i apply less voltage to the 24v electric motor would it stop going or it slows down? if i want to increase the speed of the go kart, do i have to increase the current and keep the voltage the same (24v) but without exceeding the rated current?

[Sunking]

that is why in order to get the go kart moving you will have to push it first for the start and then i wouldnt need to have the 100amphours. because as far as i know in order to turn something on it requires at most 10 times more power and then it goes back to 10 amphours or so and stays the same.

Hold the bus. Amps and Amp Hours are not the same thing like watts is not watt hours.

Amps is just a measurement of current at a specific moment in time. Amp hours is a unit of energy over a period of time mathematically = Amps x Hours. A 5 AH battery can deliver 100 amps. From that you can determine how long a 5 AH battery can deliver 100 amps by factoring out the time unit HOURS. 5 AH / 100 A = .05 hours or 3 minutes.

So you do not need a 100 AH battery to supply 100 amps briefly.

Now with that said if you use a 24 volt 15 AH battery, what you are going to find out is when you drive the cart, it will come to a stop in about 1 to 1-1/2 hours.

[elkowalski]

oh yes sorry for the misunderstanding. can you suggest me what charge controller mppt for 24 volt system should i use? and also what kind of battery? in order to increase the speed of the car i need to provide more current, so what can i use to increase the current that goes to the motor? how does it work?

[Mike90250]

Better step back and answer these questions first, before you sink any $$ into this.

Kart & Motor. How much amps, for how many hours, does it need ? Or Watts & watt hours. 600w for 1 hour = 600Wh consumed

Battery - assume 2, 90A deep cycle 12v, to give you 24VDC
Charge controller MPPT amps to match your solar panel watts @24V
360W of PV / 24V = 15amps One hour charge = 15Ah or 360Wh.
Mrningstar SunSaver 15 Amp MPPT

PV = needed to recharge batteries, size depends on how long you want to wait between 15 minute trips.

(whoops better back off, or Sunking will be upset with my spilling his secret)

[elkowalski]

thanks mike. i need the kart to last atleast 30 minutes, the motor is a 300 watt electric scooter motor. i am not sure how much weight it can handle or if i should use 2 300 watt motors together.
for the batteries i am thinking about using 2 batteries 12 volt with 10 to 15 amphour rating.
mike i was wondering if i can get an mppt charge controller cheaper from another website or something.
i am planning to use the following solar panel(2):

Power at STC ( Pm): 125 Watt

Maximum Power Voltage ( Vpm ): 18.1 Volts

Maximum Power current ( Ipm ): 7.14 Amp

Open circuit voltage ( Voc ): 22.4 Volts

Short circuit current ( Isc ): 7.72 Amp

since i need 24 volts to go to the battery i will put these 2 in series.
what do you mean with how long i want to wait between 15 minute trips? does the go kart needs to be at rest while charging?

(whoops better back off, or Sunking will be upset with my spilling his secret)

haha thanks for the help guys i appreciate the time that you are taking to support this project.

how can i calculate how much weight can a 24v electric motor can support?
the specs for the 24 volt electric scooter motor is as follows:


Model: MY1016

Voltage: 24VDC

Rat Speed: 2750RPM

Rated Current: 16.4A

Output: 300W

and as far as i know in order to start the kart going i might have to push it a little bit.

[Mike90250]

....
mike i was wondering if i can get an mppt charge controller cheaper from another website or something.

You can get cheaper. If it will really work, is a whole different question. There are a LOT of bogus controllers out there. There is another thread on this site, about some folks finding and buying some cheap "MPPT" controllers, but the manual is badly written and conflicting data in it.

i am planning to use the following solar panel(2):
Power at STC ( Pm): 125 Watt
Maximum Power Voltage ( Vpm ): 18.1 Volts
Maximum Power current ( Ipm ): 7.14 Amp
Open circuit voltage ( Voc ): 22.4 Volts
Short circuit current ( Isc ): 7.72 Amp
since i need 24 volts to go to the battery i will put these 2 in series.

OK.

what do you mean with how long i want to wait between 15 minute trips? does the go kart needs to be at rest while charging?

Calculate the battery size. Calculate the Solar size. = run time & recharge time between runs.

how can i calculate how much weight can a 24v electric motor can support?

When it burns up, you exceeded what it can support

Motors are not designed to carry much weight on the shaft. the Axles carry the weight.

Rat Speed: 2750RPM Thats way faster than you will spin kart wheels, so you need some sort of reduction / transmission system.

[elkowalski]

well since i did some calculations i am thinking about using 2 45watt solar panels in series because the run time will be like 5 minutes and then 5 minutes of completely stop so with the solar panels charging it while running and in completely stop that will charge more likely half of what has been discharged while running am i correct? or kind in the same track?
the current of the panel is 2.5 amps
the battery that i am going to use is rated at 15amphour
motor 300 watt 24 volts

since this is a middle school project and we dont have enough funds to buy such an expensive controller i was wondering if i could use a pwm charge controller. i accept any suggestions of what controller to use that are less than 100 dollars.
i would like to get approved by you guys mike and sunken about the part list that i have just to make sure i dont waste the money in stuff that i dont need and make sure i have the right material to work with. thanks

edited.

Parts list:
1. scooter electric motor 350 watt 24 volts
2. 350 watt speed controller
3. 2 solar panels 45 watt
4. 2- 12 volt 15amphour batteries
5. 2- mc4 connectors
6. 1 mppt charge controller
i guess this is what i need for the go kart excluding the frame. any suggestions that you might have about the list, please let me know.

[Sunking]

well since i did some calculations i am thinking about using 2 45watt solar panels in series because the run time will be like 5 minutes and then 5 minutes of completely stop so with the solar panels charging it while running and in completely stop that will charge more likely half of what has been discharged while running am i correct? or kind in the same track?
the current of the panel is 2.5 amps
the battery that i am going to use is rated at 15amphour
motor 300 watt 24 voltss

Well this is where you are running into my little secret. It is known as the Law of Physics and no matter what you try, you cannot violate the Law of Physics.

First thing when a motor is rated 300 watts is a bit misleading. Put a load on the motor, a heavy person in the driver seat and try to drive up an incline and that 300 watt motor will burn well over a 1000 watts, and will eventually overheat and burn up.

So here is some math fun for you:

Watt Hours = Watts x Hours
Watts = Volts x Amps
Battery Capacity in Watt Hours = Voltage x Amp Hours x C: C= = a number less than depending on the discharge rate.

So you have a 300 watt motor and want to run 30 minutes, so you will consume 300 watts x .5 H = 150 Watt Hours.

To replace 150 watt hours in the battery, you have to generate 300 watt hours to overcome all the losses.

You never want to discharge your battery more than 50% or you will destroy it assuming you will use a lead acid type battery. So total battery capacity to run 30 minutes needs to have a capacity of 300 wh. So for a 24 volt battery the AH capacity before Peukert Law is applied 300 wh / 24 volts = 12.5 Amp Hours. Apply a 30 minute discharge correction factor will be around .5. So 12.5 AH / .5 = 25 Ah battery required to give you 30 minute run time.

So how fast do you want to replace the 150 watt hours you used. Lets say 1 hours at 12:00 noon. The panel wattage required to do that = 300 wh / 1 hour = 300 watts.

Now you have a problem on your hands. The panels are going to be much larger than the cart and weigh in around 90 pounds, plus a 40 pound battery. Now you have a lot of extra weight and wind load to over come. That means you need a larger motor, battery, and solar panel wattage. Add then and you hit the wall again. It is a viscous Law of Physics.

[elkowalski]

Now you have a problem on your hands. The panels are going to be much larger than the cart and weigh in around 90 pounds, plus a 40 pound battery. Now you have a lot of extra weight and wind load to over come. That means you need a larger motor, battery, and solar panel wattage. Add then and you hit the wall again. It is a viscous Law of Physics.

yes in fact i was thinking of maybe doing a solar golf kart of something like that. but since i dont have enough funds we posponed it.
so sunken, how can i calculate the max weight that i can put into the go kart to be able to move it with a 300 watt electric motor? or should i use a 500 watt? it doesnt have to go fast is just a middle school project we are going to build 2 go karts and then race them i might say maybe hopefully get 5 mph if we are able to.

First thing when a motor is rated 300 watts is a bit misleading. Put a load on the motor, a heavy person in the driver seat and try to drive up an incline and that 300 watt motor will burn well over a 1000 watts, and will eventually overheat and burn up.

so in order to prevent more current to flow, we need to add some sort of limiter which i dont know the name of it. right?