Solar Car Competition Batteries

pizza17

1 mW
Joined
Oct 29, 2022
Messages
10
Hi, my team is in a solar car competition and we need help/suggestions with batteries.
We need to go 40mph for as long as possible.

What would you suggest for batteries? We can use lithium and the rules say we can have a maximum of 720wh (using the nominal voltage eg 12.8v not 12v)

We were considering this drive kit from Thunderstruck
Motenergy ME1718 Motor
350 amps peak at 36 or 48v
175 amps peak at 72 or 96v
https://www.thunderstruck-ev.com/curtis-brushless-16kw.html

Our solar car will be about 550lbs (with driver) when completed. (the competition requires over 400 without a driver)

We would really appreciate your help!
 
For an average vehicle speed of 40 mph that motor / controller combo looks a bit too large, no need for that much power.
Solar car competitions typically end up being aero efficiency competitions more then electrical efficiency competitions.
Your battery is limited to 12.8V ?
What does your vehicle look like ?
Give us more info by posting a link to the rules.

Oh ... Make my order a 17" Hawaiian with extra pineapple, to go. :lol: :lol: :lol:
 
Aerodynamics and weight looks like a real concern for your team. So, look for the lightest batteries that can run the motor your are going to use. In other words, what batteries have the highest energy density for the weight and size. RC lipo has a lot of watt hours for the size and weight, but there might be other chemistry's that are lighter with more energy density then RC lipo. Energy density + lithium battery is a good place to start in your google search.

:D :bolt:
 
What would you suggest for batteries? We can use lithium and the rules say we can have a maximum of 720wh (using the nominal voltage eg 12.8v not 12v)….
720Wh is 720 Wh !, no matter what voltage you use to measure by.
OR,.. are they implying you must use a maximum of a 56 Ah, 12v , battery ?….which sounds dumb and would severly restrict your choice of drive motor etc. so i hope that is not the case.
As e beach said , look for some lithium cells with high ENERGY DENSITY and build the lightest 720Wh pack at what ever voltage you decide to run.
 
Thanks for everyone's help and suggestions! I am excited to share your ideas with my team. Here is a screenshot of the rules regarding batteries.

 
Is this the competition ?

https://esvc.in/
 
pizza17 said:
Hi, my team is in a solar car competition and we need help/suggestions with batteries.
We need to go 40mph for as long as possible.

What would you suggest for batteries? We can use lithium and the rules say we can have a maximum of 720wh (using the nominal voltage eg 12.8v not 12v)

We were considering this drive kit from Thunderstruck
Motenergy ME1718 Motor
350 amps peak at 36 or 48v
175 amps peak at 72 or 96v
https://www.thunderstruck-ev.com/curtis-brushless-16kw.html

Our solar car will be about 550lbs (with driver) when completed. (the competition requires over 400 with a driver)

We would really appreciate your help!

Higher voltages lithium batteries typically means more complicated battery management systems (BMS) that are harder to source parts for and end up being hand built.
Lower voltage battery systems are more available "off the shelf" and can be stacked together.
Drag racing motorcycles are known to bunch up multiple battery packs from radio control models because they are light and have high discharge rates.
Batteries from hand tools and garden tractors might be useful.
When discharged they remove from the vehicle and recharged or replaced with fresh.

15 ~ 16 years ago I did the fabrication work to electrify a Kawasaki Bayou 250 ATV
The customer brought me the parts which they purchased from Thunderstruck Motors.
The motor / controller / battery combo was the 48V AC-9, Curtis controller powered by 15 CALB 72ah batteries.
Customers use was for off-road farm duty where it seemed to be ample capable and maybe too fast.

http://www.calbusainc.com/
 
Sounds like you are limited in capacity and must use off the shelf batteries. Suggestion then would be to use lithium ion rather than lifepo4, and to go for the lowest internal resistance, highest current output you can get. Cycle life is not really a consideration as they only need to last the one race.

There are some larger 56V 10 and 12AH battery packs for EGO mowers and similar. With a little engineering these could be adapted.

See https://egopowerplus.co.uk/products/batteries-chargers/BA6720T
 
pizza17 said:
Hey everyone, thanks again for your help. Do you think something like this work too?
It's not ideal, no.

You have 720wh and you want to go 40mph. You should, with a moderate amount of work, be able to build a 550lb car that can maintain 40mph with less than 700 watts. 90% of the challenge is aerodynamic - but there are plenty of designs out there that will work for this.

That means you need a 1C average, 2C peak discharge rate. Generally you will trade off C rate vs energy density - and thus this battery with its 15C discharge rate will be heavier than it needs to be.

Consider an NCR18650B based pack. Those cells are optimized for a 2C draw, so they will be lighter. Plan for some intermediate voltage (36-48V is reasonable) to keep maximum currents down, but also give you lots of flexibility in terms of number of cells. 60 cells would put you right at the energy limit, and you could do that at 36 volts or 44 volts.
 
NCR18650B 60x45,9=2754g
37V 10s6p 40A 19.5Ah 721,5Wh
44.4V 12s5p 33,5A 16,25Ah 721,5Wh
?723,6Wh: https://voltaplex.com/12s5p-43.2v-16.75ah-li-ion-18650-battery-pack-panasonic-b-cuboid

INR21700-50E 39x69=2691g
48,1V 13s3p 29,4A 14,7Ah 707Wh
 
Am I missing something ?
So far with all the suggestions ...
The voltage and watt hour can match up but the discharge amps are way lower then what the 350A Curtis controller wants.
Which brings me back to my first impulse, the motor / controller combo is too large.
A top level 48V X 15ah battery is probably only capable of 200A max discharge ... maybe ?
Am I missing something ?

Love to see a picture of the vehicle and a little history behind the build.

A little edit ...
Batteries are the container storing the horsepower.
Controllers / motors are the devices that convert the stored horsepower to motion.
So, within the parameters of this competition the battery decision comes first.
Controller / motor decision comes second.

Having been involved in lots of racing I've found the lowest weight vehicle usually has the biggest advantage and most options.
Removing weight is the same as adding horsepower.
 
We need to go 40mph for as long as possible.
Why, ? What exactly is the competition objective ?
Longest time at 40 mph ?
Longest distance covered ?
First across the line after a set distance ?
Etc ?
40 mph will suck a lot of power, Aero design will be critical and lower speeds (30-35mph) would save a ton of power .
 
PaPaSteve said:
Having been involved in lots of racing I've found the lowest weight vehicle usually has the biggest advantage and most options.
Removing weight is the same as adding horsepower.

Yep, be sure to take that into consideration when picking all the electrical components.

If you want to be a real weight weenie, running a higher volt/lower amp system means that you can use smaller lighter cables.
 
Weight, aerodynamics and, don't forget tire resistance. Look around to see if you can find low resistance tires that will work for you.

:D :bolt:
 
Pizza17 ... without more info this forum can only guess at what the ultimate goal is.
Is the car being repurposed from last year ?
If this picture is an example of the competition ... working to remove as much weight as possible will yield the biggest payday.
Your first post mentioned the car being 150 pounds overweight ... that's an enormous disadvantage.
Unite the team in a weight reduction program for the car.
Remove weight from the wheels and tires as the first order of business.
Thin, nylon casing, tubeless tires are known for low rolling resistance.
No steel belts in the casing or any other puncture resistance stuff. (motorcycle tires)
Replace steel with aluminum wherever possible etc.

Screenshot-2019-05-02-at-8.14.01-PM-1-740x540.png


(( see post 10 in this thread ~ https://endless-sphere.com/forums/viewtopic.php?f=41&p=1738118#p1738118 ))
 
Thanks again for helping us figure this out! For more information, the competition is for the high school SunChase competition at FGCU. Here is the latest version of the rules https://drive.google.com/file/d/1CeO3uGCLfs_WwGJdsU14qeGHmW8nziZl/view?usp=sharing

It's included in the document above, but the race format is three 3.76 mile sprints around the campus and then an endurance portion. Teams will see who can go the furthest in 30 minutes. You get 1 point for each lap you have in the 30 minutes Throughout the sprints and endurance portions of the race, teams can not finish cannot exceed an average of 37mph (the road speed limit is 35mph). The judges will verify this by making sure our sprint times (2 laps) do not go below 6 minutes.

For reference, our team built the car last year and were under the minimum weight limit even with SLA batteries. We actually had to add extra weight to our car in order to meet the requirements. So although weight is always a chief concern in this type of competition, we have some flexibility in terms of the weight of our batteries.
 
Thanks for the link.
That provides a much clearer picture of what the competition is.
Watching a couple videos it seems that most teams start with the same basic kart and then bolt together whats needed to make a solar electric conversion.
A interesting statement in the rules on page 7 regarding the batteries ... no custom battery packs
Curious how your car gained so much weight since last year ?
What was the previous motor / controller combo ?
Pictures of your creation ... Please
 
pizza17 said:
Thanks again for helping us figure this out! ....

You are welcome. Besides it is fun to figure out stuff like this. It is why we know about it. We like thinking about these kinds of things.

As for your carts build, well, I have been looking at other carts in the Sunchase competition and almost none of the entries did much for the aerodynamics of their carts. So what they became is one big wind dam with no consideration as to finding ways to slice through the air efficiently. Think about wind hitting a brick wall. The air hits the wall and can't go anywhere easily. However, if you shape a go cart in a proper way it can more easily cut through the wind. Here is an example of two Sunchase go carts. One team tried to figure out how to slice through the wind and the other is just going try to plow through it like a brick wall. Which team was thinking about aerodynamics?

Sunchase ex1.JPG


Now, your team could even do better depending on how you think about it. Check out this cart and think about how the air just might move over and through the cart.

Sunchase ex. 2.JPG

The best thing would probably a fully enclosed go cart, but that might be asking too much for what you can do. Unless your team wants to push yourselves. :wink:

Full Body ex..JPG

Here are some other pictures to see what college students did with their Solar Challenge. Obliviously the rules are different, but it might give you some ideas.

https://www.google.com/search?q=The...yC0kQ_AUoA3oECAIQBQ&biw=1440&bih=674&dpr=1.33

And then finally look at this link and start thinking about how you are going to open the air in front of you, AND, how you are going to close it behind you.

https://www.google.com/search?q=tes...OBNsQ_AUoAXoECAIQAw&biw=1440&bih=674&dpr=1.33

:D :bolt:
 
Thanks for the tips. Here is our website and one of the cars we’ve built in the past. We’re in the process of building new cars this year. https://www.carrollsun.org/

Sorry for the confusion but we’ve always been at the minimum weight and we haven’t added anything to make our car weigh more. Our biggest question is which lithium batteries to choose (and possibly drive system) for our competition because that’s a new option this year. And yes, sadly they cannot be custom batteries so we’re looking for off the shelf.
 
pizza17 said:
Thanks for the tips. Here is our website and one of the cars we’ve built in the past. We’re in the process of building new cars this year. https://www.carrollsun.org/

Sorry for the confusion but we’ve always been at the minimum weight and we haven’t added anything to make our car weigh more. Our biggest question is which lithium batteries to choose (and possibly drive system) for our competition because that’s a new option this year. And yes, sadly they cannot be custom batteries so we’re looking for off the shelf.

OK ... Thanks ... Now we're real ! ... :bigthumb:
Car is a stunner, gets beauty points from this judge.
Went ahead and threw $100 in the pot.

For an off the shelf battery the Tattu you previously pointed to looks OK {16ah X 15C = 240A peak discharge rate}
If last year's motor / controller didn't overheat it's probably fine.

Lower your power needs instead.

Aerodynamics, one of the highest areas of drag is under the car. A clean smooth surface underneath can lower power requirements.
Coroplast is a useful material for such tasks. Light and quiet.
Enclosed wheel or fenders ... top of the wheels are also high drag ... tire at ground level sees no wind speed, tires at axle level sees actual speed, top of tire sees double vehicle speed creating higher drag.
Cover the rollbar tubing with wing strut fairings.
Replace all "sealed" bearings with high performance "shielded" bearings. Contact Boca Bearings for advise and possible sponsorship.
Is there any power data collection device in the system ?
New%20Fairing%20Profile%202,%20640.jpg
 
Back
Top