Energy storage - alternatives to batteries

[Daniel_B]

I'm designing a remote controlled electric car. The easiest solution would be of course batteries, but I would like to do it in another way.
The energy storage should...
-not be expensive
-have a long life (usable multiple times)
-be environment friendly (sustainable, recyclable), if possible

My main concern with batteries is that they have to be replaced and even secondary batteries degrade over time. It would also be more interesting to use something else.
The consumption of the car should be between 1 and 10 watts and the energy storage should last atleast a few minutes. However, if it can do more, that's better.

The solutions I'm aware of:
Supercaps: They could provide enough energy on paper, but they require a complicated circuit to keep the supply voltage constant. Also, they are quite expensive and only provide just enough energy.

Solar panels: Unreliable.

Heat engines: I don't know any that would be cheap enough or could be built at home. Although i do have a generator.

Hamster engine: I don't have a hamster.

Mechanical energy storages: Again, i don't think i could build them at home.

If you think I should just use batteries, which type of secondary battery would you recommend? (It should be made of the most environment friendly material)

Thanks in advance!

 

[Alec_t]

Twisted rubber bands?
Clockwork?

 

[Daniel_B]

But can they store at least 1-2 kJ? Taking energy losses also into consideration, they don't seem to be a viable solution.

 

[Harald Kapp]

LiIon, LIPo LiFe are commonly used. NiMh is an inexpensive and easy to handle alternative.
Environmentally friendly? As long as you take care of correct recycling these are as good as any other alternative.

 

[Audioguru]

My local hobby store has many radio controlled model cars, trucks, boats, airplanes, jets, helicopters and drones. Most are powered with Li-PO batteries. The hobby store sells many batteries and chargers for them.
My Li-PO batteries last for about 600 times or 3 to 4 years. I store them at 88% voltage each winter.

 

[Bluejets]

Put the garage at 5,000 ft.

 

[dave9]

Have you ever seen the cartoon, the Flintstones?

Seems like a bad design to build a remote control car that needs electricity anyway and not use the same battery pack for propulsion when it needs to be so tiny/slow that it can run 10 minutes on 10W or less.

Why are you reinventing the wheel anyway, is this a homework question?

 

[Daniel_B]

Thanks for the answers.
I think I'll use the LiIon battery for my first prototype, because it's still relatively cheap and it's simple. Although I'm thinking about building a steam engine to power my next car. The only problem is that with its size it will, at most, have an overall efficiency of 5% or less, but if use another type of electric motor and i can manage to run the engine at a slightly higher pressure, it could potentially reach 10%.

I think you misunderstood dave9. The car is going to run with an electric motor. The question was how to deliver the electricity. There are, for example, hybrid electric vehicles in reality (Although they are a lot more efficient because of their size and superior manufacturing process).

 

[Audioguru]

Ate you aware that a Lithium battery can explode and/or catch on fire if it is charged or discharged wrongly? If it is discharged to a voltage too low it is ruined and might catch on fire if a normal charge is attempted.

 

[Daniel_B]

Yes, but I'm going to use way less current (also taking the starting current of the motor into consideration) than it is specified on the product, so I don't think it's going to be a problem.

 

[dave9]

You seem overly vague and all over the place with illogical concepts. Where do I even start?

- You are trying to make a toy that nobody will use for long because it is underpowered and excessively expensive, so there is the manufacturing impact and the landfill impact. It is not appropriate to think of this like "environmentally friendly". Batteries are far more recyclable than an entire integrated product (like a toy car) is.

- Whatever you build, without a year worth of man-hours development, the rest of the design probably wouldn't last as long as the first set of rechargeable batteries, but those can be replaced and the originals, recycled. Degrade over time is not a rational argument, you select the battery capacity so it is still sufficient once it has degraded some, accepting the eventual replacement of the battery.

- What fun is a sub-10W car that only runs a few minutes? You are wanting to design something that nobody wants to buy or play with. Other alternatives are powerful enough to use a long time, on rougher terrain, with hundreds of watts motors, and necessarily longer distance remote control.

- Solar panels are not unreliable. They're just too bulky to be practical and limit the use environment without having a battery they recharge anyway so simply not needed unless a special application where grid power is not available... like a helicopter on mars.

- "Heat engine". "Steam engine". Too vague. Where are you getting the heat from, shoveling coal into a little compartment while you follow the toy around with a tiny shovel? Burning liquid fuel you could have just used to power a 2 cycle engine?

- Current R/C toy cars on the market are an EVOLUTION over decades, choosing the most appropriate design with all things considered. You have not invented any new technology that changes that, no magical new power source so the best you can do is learn about why they are designed the way they are and spend years trying to replicate that with an equal result so you have an equally desirable toy, or cobble together already-engineered R/C toy parts, except at small scale and to fund the development, the cost per unit will be absurd so I don't see the point.

You are trying to reinvent the wheel and hoping to choose any shape except round.

Also, it has nothing to do with using way less current. A proper battery protection circuit cuts off power when the voltage drops too low, whether it is high or low current. Low current continuing to drain a Li-Ion cell will still damage it.

How about a younger target user, say 3 years old who pushes the car around by hand? Make it out of wood, someday it rots and becomes compost. Plant a tree to replace the one cut down. It is sustainable.

The most environmentally friendly approach is do something that performs its job well and doesn't wear out for decades. Somewhere out there are the wooden push toy cars I played with as a child, still just as usable decades later... though might need a paint job by now.

 

[Audioguru]

Of course an explosion or fire will be a problem because lithium is a very active element. A charger must be properly designed and a low voltage cutoff circuit must be used. An over-current circuit must work when it is needed.

 

[Daniel_B]

Thanks for the tips on the Li-Ion battery, I will do more research on the matter. If the protection circuit will prove too difficult for me, then I will simply use another type of battery.

dave9:
I will try to explain things:
1. It's not like i want to make a commercial product. Later on I do want to make something more advanced, but trying to build something extremely complicated on the first try wouldn't end well. Experience is important in all fields of life. First i start with something small and cheap and then I increase the complexity just a tiny bit. I have my own set of tools, which I have to learn to use efficiently, and I have to learn new techniques. Furthermore, I enjoy tinkering, so this is also for my own enjoyment.

2. I didn't want to put so much emphasis on "Environment friendliness". Like i said, experience is important for me, so doing something correctly right from the beginning is not bad. Since energy density is not a problem in this case, I had to look on the other properties of batteries. Particularly on the environment impact of different battery types I didn't find anything, so I wanted to hear more about that here in the forum, because, for example, I didn't hear nice things about lithium. Its mining is problematic and last time I checked its recycling was not commercial, so there was almost no recycling at all.

3. The first car I design is relatively small and is built for indoors, so a small motor is fine. According to the requirements, I will use another motor.

4. By solar panels being "unreliable" I meant that they will cease to generate power under some conditions. The car will be used indoors.

5. A 2 cycle engine is also a heat engine. Although I did find some relatively cheap engines, I had several problems with them. I do have a policy to only buy things, if they meet a certain level of quality. Something that's half the price but lasts a lot less and does a lot less is not the cheapest solution for me. I had these problems with cheap designs:
-According to reviews, they don't last long, require a lot of maintenance and are very sensitive.
-They use special fuels which is very problematic.
-The cheapest ones still require other components to function and there's little documentation. They are meant as a replacement, so I could just buy the models that use them, but then I could just buy something good.
I would like to eventually use ICEs, but since the proper ones cost more, I want to first have a lot more experience and better tools before I waste a lot of money and time.

6. The steam engine is just an idea. It is something that i could potentially build with my current tools and fueling it with liquid fuel makes them really flexible, but if I get there, my calculation might show that they won't produce anything but entropy or I might not be able to properly manufacture its components.

7. This is kind of off topic, but while it is true that It is very hard to design something that will outperform a product on the market in cost effectiveness, it is still possible to make it better or better suited for a specific job. One of the biggest advantage but also the biggest disadvantage of the things on the market is that they are profit oriented. Although it's not appliable to all cases, like it is higly unlikely that i could produce with whatever tool and time a better processor than AMD or Intel, but i could build a furniture of my own taste. However, in all cases it is simply not worth the time unless somebody like me enjoys the building part itself. My first prototype car definitely won't outperform any RC-car, but I will have fun with designing it, I'll learn from it and it will still be unique in some way.

 

[hevans1944]

I'm designing a remote controlled electric car. The easiest solution would be of course batteries, but I would like to do it in another way.

Everyone involved with electric vehicles, whether that be Tesla's full-sized tractor-trailer behemoths of the highway, or 1/24-scale, remote-controlled models of popular ICE (Internal Combustion Engine) vehicles... all would like to do it another way... without batteries.

Batteries are not an ideal electrical energy source for much of anything... except maybe my heart pacer/defibrillator implant or the "black box" flight recorder on the next airplane that falls out of the sky. And cell phones of course. Civilization uses a lot of batteries every day, with little or no consideration of their chemistry, or the long-term effect on our environment, after their eventual disposal.

The "dirty little secret" about electricity is there is no inexpensive, or even very practical, means of storing electrical energy after it is created. Whether it be a massive power plant burning natural gas, coal, or oil, or using nuclear energy to boil water to make steam, or just a backyard solar array or wind-powered generator, the electricity must be used "on the spot" because there simply is no practical and simple way to store useful quantities of electricity. Well, if you have a lot of land and a lot of water, you can use electricity to pump water up-hill to fill a large water reservoir. Then you let that stored "water energy" flow down-hill through turbine alternators and... voila! You have electricity again! Wash, rinse, and repeat as often as necessary to obtain a steady supply, but be prepared to spend some big bux on maintenance of your plant..

Why do we continue to use so many batteries? Perhaps greed plays some part, but follow the money as usual. Cost and convenience are the main factors. Does anyone here remember the Leclanché cell, also known as the zinc-carbon battery? These came in the same popular sizes that are still in common use today:
From left to right: C, AA, AAA, N and PP-3 (9 volt)
Missing from this picture are D and larger battery packs and cells.

Almost all of the zinc-carbon cells have today been replaced by alkaline cells. Why? Shelf life was the most important factor. A zinc-carbon cell self-discharges from 1.5 volts down to practically zero volts after two or three years of non-use on the shelf. So, you pick up your four D-cell flashlight, that you loaded up with "fresh cells" just a year ago, only to just now find out that you have an expensive club instead of a bright light in your hand. Arrgh! Finding that expensive box of D-cells ain't gonna help, 'cause they have all self-discharged too, either in your flashlight or on your battery vendor's shelf!

Flash back a little less far, to the 1960s, and a new competitor to the zinc-carbon cell appears on the scene. Alkaline cells were considerably more expensive then, but most of them had much better shelf life. And about five times more energy density, too, so alkaline cells last a lot longer under continuous use, as well as non-use on the retailer's shelf. What's not to like, except the price? Eventually the price came down as competition entered the picture, and zinc-carbon batteries virtually disappeared.

And then along came lithium chemistry. Same long-term shelf life (ten years or more), but higher energy density. This battery chemistry is what makes electric airplanes and electric automobiles possible and even practical. But even lithium-ion chemistry still isn't an efficient way to store electrical energy. No such portable and practical means exists today.

We make do with what we have until something better comes along. The world still awaits to bestow great wealth upon the manufacturer of an efficient, portable, and inexpensive electrical energy storage device. That could be this year or sometime much further into the future, but I personally believe the day will come when a coin-sized cell will be developed that can store and deliver a megawatt-hour of electricity. Don't carry that puppy in your pocket though! It will have a really nasty bite.

In the meantime, I'm not waiting for technology to catch up with my ambitions, and neither should you. Build your remote controlled electric car with a nice, commercially-available, lithium-ion cell technology. It would be better to purchase a battery system, including battery management circuitry and a mating battery charger, rather than trying to mix and match components to get the best price.

To ensure availability of off-the-shelf parts for your prototype, consider designing it to a common modeler's scale, such as 1:24. Your actual scale will no doubt be determined by the size of your battery pack of course. Some LiPo packs are quite small, so investigate FIRST what battery you will design your prototype around. Delivering 100 watts of rechargeable electrical power for thirty minutes or so is not easy or inexpensive, but if you can afford it, it can be done.

I just purchased at a "big box" home improvement store, an EGO electric lawn mower, electric string trimmer, and electric leaf blower in a package-deal that included two rechargeable batteries, one 5 Ahr and the other 2.5 Ahr, as well as two "smart" chargers for the batteries. I "plan" to purchase on-line a 7.5 Ahr or 10 Ahr battery to complement these two and still have a battery to "play" with. Only problem is the US $350 price tag for the 7.5 Ahr and US $450 for the 10 Ahr. I can think of a lot of things that I need to spend that much money (or more) on right now, but maybe I can "borrow" one of the smaller batteries I now own, as long as it isn't being used to run a leaf blower or the weed whacker...

Please keep us posted on the progress you are making on this project. Pictures would be much appreciated, too. The remote control aspect sounds like fun, although there is plenty of that stuff already commercially available off-the-shelf. No need to re-invent remote control... after all, Tesla "perfected" that technology for his model boats in the 19th century. I can't seem to find any copies of his laboratory notes on that subject, although his "experiments" were reported in newspapers of the day. Oh, well... if we can fly drones from remote locations on the other side of the world, some improvements must have been made since Tesla took his model boats to the water. Maybe you could look into remote control via satellite communications, perhaps using an existing infrastructure like DishTV? Or the Iridium sat-phone network?

I first used an electric lawn mower years ago, in the early 1950s, to mow a small lot that was part of residential property our Air Force family rented in Lake Charles, Louisiana. Dad was stationed there as a bombardier/navigator assigned to a B-47 bomber wing. The Cold War had just begun. Dad had fitted to this four-bladed reel push mower a large universal motor he got from his father, a retired electrician who "salvaged" it from a deep coal mine in Maitland, West Virginia. Worked real fine unless you tried cutting wet grass, in which case you were subject to getting an electric shock. Except for the inconvenience of trailing a 50-foot extension cord, and worrying about cutting said cord by accidentally running over it with the lawn mower, this was a really great means of taking care of a small lawn. After I grew up, married, and bought a house in the early 1970s in Dayton, Ohio, I decided a small commercial electric lawn mower would be just about right-sized for my postage-stamp size yard. Eventually the electric mower broke down, but I replaced it with a less-expensive, gasoline-powered, self-propelled, push-mower version.

That gasoline fueled replacement mower came with us to Venice, Florida in 2016 after I retired. Problem we had here was the size of the lawn to be mowed. We now had a 100' x 100' corner lot with 1875 sq.ft. of house on it. The difference in area has to be mowed on a weekly basis. And the summer heat is virtually unendurable. Up at the "crack of dawn," and by 10:00 AM it is already too hot to work outside... at least for a seventy-something year old man recovering from open-heart bypass surgery with an underlying heart condition that only pumps ten percent (ejection fraction) of its new-born capacity.

I'm not absolutely sure that fifty-something years of daily drinking a 6-pack of Coca-Cola, eating dozens of Hostess Twinkies and fried pies, and smoking two packs of cigarettes per day, while consuming at least a fifth-sized bottle of Old Granddad bourbon every week had anything to do with my declining health, but I am pretty sure now, with 20-20 hindsight, that none of that was exactly healthy. Perhaps fortunately, I am not allowed to do any of that anymore, probably under penalty of death.

So, wife bought me a used John Deere riding tractor-mower. I managed to damage something under the mower deck twice during the next two years, and it is still waiting for me to have it repaired again at almost $500 for pickup, repair, and return. If I still had my pickup truck, I could get by with just $200 or so for repairs, but I no longer have the strength to remove the mower deck to attempt a repair myself... at least not yet. Maybe if I buy a cheap auto hydraulic lift jack at Harbor Freight, I can see and work under the tractor, but I'm getting a little old for that sh!t. The green plastic hood also literally disintegrated under the hot Florida sun after just one year of use. It was stored outdoors under a tarp, which should have protected the plastic from damaging UV rays but it didn't. Plastic hood became very brittle and pieces started breaking off. But why store things outdoors instead of in our attached two-car garage? Gasoline vapors. The vapors released in the garage somehow found their way into our HVAC system and made it impossible to live, sleep, or breathe inside the house. No more VOC (volatile organic compound) storage in the garage, probably under penalty of divorce if not death... maybe both.

Eventually, the gasoline mower from Dayton also died. I am sure that a small-engine repair shop can get it going again, but we found a used Toro self-propelled front-wheel drive push-mower for sale for $50. After driving some five miles or so to a gated community (they are really popular here in southwestern Florida), we met with an ancient, armed-services, veteran. After I identified myself also as a veteran, he said he was just about to lower the price of the mower from fifty bux to zero for anyone willing to cart it away. I guess it had been advertised on a local on-line bulletin board for more than a week without any takers, and he just wanted to get rid of it. So, for the expense of a little gasoline for the round-trip, we got ourselves a free lawn mower!

I know this has been one of my typically long-winded "wall of words" posts, but I hope you received some inspiration from this and other posts on this thread. Your project is quite ambitious, and I wish you the best of luck in completing it. Feel free to post specific questions if you get stuck or just want to share some notes. There is a deep pool of talent here, perhaps too deep for the newbie to swim in just yet, but keep coming back, keep asking questions, and more will eventually be revealed. Or drive on by to your next gig. We won't mind your not wasting our time.