Hi folks. My project revolves around a design for budget e-bikes to sell to the locals here in the Philippines. So far, I think I've solved that and can make complete e-bikes for about $200 (sell for around $250ish). Understanding that the most current pulled from the battery's capacity is starting from a dead stop, I have an idea where I could use a small bank of 9x lithium-ion 4v/1100F supercapacitors to handle this. I think this could add to the battery life. The goal is to get as close to 20 miles on a 36v/4ah li-ion battery system. The supercapacitor bank of 9 caps are calculated to hold 1.22 amp/hour (in theory). These new lithium-ion supercapacitors (1100F) are actually smaller than 18650 cells, charge in a matter of seconds, and hold 1200mah each!

Anyways, I need some help. Correct me from here on out...

I'm imagining, at a dead stop, a button on the handle bars, when pushed, will switch on the NO cap bank and switch off the NC battery. When reaching optimal/efficient motor RPMs, release the button and the cap bank is disconnected, the battery is re-connected and the charger connects but only when there is detectable motor RPMs and zero accelerator (brakes will have nothing to do with this). A motor controller will be double lugged at the inputs with the battery leads and cap bank leads; and, the cap charger will be fed from the motor leads replaced with large current carrying conductors (#12awg) to enable the cap bank to be quickly and easily recharged with a 20amp charger module when slowing down/coasting. I assume I'll need a diode here and there to keep the current from flowing in the wrong places?

Of course, this all exceeds my original plan to stay in a budget; but actually, the extra stuff will only cost maybe another $100, I think.

Sadly, all I can think of is using little switching/etc modules available online to do all this fancy switching. Maybe it's too much action and not realistic? Is this a good time to learn how to use an Arduino? Are the Battery and capacitor likely to blow up?

Cheers...

 

“Understanding that the most current pulled from the battery's capacity is starting from a dead stop, I have an idea where I could use a small bank of 9x lithium-ion 4v/1100F supercapacitors to handle this.”

Unless you use regenerative braking the energy to initially rev up the motor will have to come from the battery (as it will ultimately in any case). Why not make one, test it, and go from there?

 

^^ Agreed. How would you charge the supercaps, other than by using energy from the battery?

 

The proposed concept could reduce the startup current draw on the battery, and that may allow longer drive times, but the energy consumed would be, at best, the same. A scheme that was available on the very first small-engine motor-BIKES was to have pedals available as well as the engine. Back then, human power for startup was accepted and worked well, saving clutch wear.
Regenerative braking is a proven concept that does extend driving range on cars. It would be worth considering.

 

The most straight-forward plan would be to simply limit the
maximum Acceleration-Rate using the existing Motor-Controller-Electronics.

Does your Chip have built-in Adjustable-Current-Limiting ?, that's all You need for extended-range.

"There's no Free-Lunch", and no way to cheat the system.

Regenerative-Braking may be worth a little "something", but it won't set any records.
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I worked with someone that thought putting capacitors across a battery will help. Under load the battery voltage dropped 0.01V which pulled almost no current from the capacitors.

 

...The main problem with batteries is their slow charging rate. Conventional regenerative Braking only re-charges the batteries at their slow nominal rate, not their discharge rate the rest is wasted. Capacitors charge WAY faster- I can scavenge way more back EMF if I direct it into a cap bank instead of the battery; no?

Since an empty supercapacitor bank is basically a dead short, I'm thinking of connecting the motor leads to a separate motor controller backwards and actuated by a lever or thumb lever to act as a break by easing onto it and gradually/gently allowing Back EMF current into the capacitor and as a brake too? Treating the motor as the power source and the capacitor bank as a load.

 

The most straight-forward plan would be to simply limit the
maximum Acceleration-Rate using the existing Motor-Controller-Electronics.

Does your Chip have built-in Adjustable-Current-Limiting ?, that's all You need for extended-range.

"There's no Free-Lunch", and no way to cheat the system.

Regenerative-Braking may be worth a little "something", but it won't set any records.
.
.
.

Regenerative braking, as far as I know, simply charges the battery for the "brief moments" a vehicle is slowing down or coming to a stop and doesn't help much, I'm sure. However, capacitors charge in "brief moments". Why not charge the capacitors instead? After coming to a stop the capacitors could continue discharging into the battery too. Also, these LIC supercapacitors are new. My idea is quite straightforward and already in the works elsewhere in the automotive industry- so I've recently just now learned.

Maybe you should've browsed around a little before making the comment "There's no free lunch and no way to cheat the system".
Cheers...

 

For at least one battery powered car a useful scheme with capacitors charged during regenerative braking did provide a worthwhile benefit. The capacitors accepted the charge and then used it to assist in staring up motion again. The logic is that every stop is followed by a start. It totally avoids the battery not accepting charge rapidly, but the cost is quite a bit more capacitors required. Another consideration is driving style. For some folks the power recovered will be quite a bit, while for others it will be very little. I get behind those fools, they run-up on the car ahead and then jam on their brakes. They do it repeatedly and it slows traffic. Others of us just back off and can hold a constant distance and seldom even need to brake at all.

 

^^ Agreed. How would you charge the supercaps, other than by using energy from the battery?

I forgot to mention that- haha. It's a single phase controller where the positive input/output terminals are bonded, so I'm thinking I could reverse the negative connections with a switch, and use the controller as a charger by applying it with the accelerator?

 

A very interesting idea. 9x 4v/1100F gives you a 36V, 122F battery holding 4,392 Coulombs. Energy stored is 79,000 W-s. That is 4% of the battery capacity. For us Americans that is 1 horsepower for 106 seconds if all the energy was extracted. Without an added DC-DC converter I can see discharging the cap bank from 36V down to perhaps 30V. The energy taken from the battery is 24k W-s or 1 horse power for 33 seconds. Without going further into e-bike kinetic energy and all that your cap bank sure seems like it can work.

You ask Sadly, all I can think of is using little switching/etc modules available online to do all this fancy switching. Maybe it's too much action and not realistic? Is this a good time to learn how to use an Arduino? Are the Battery and capacitor likely to blow up?

This is job for a power electronics engineer. As to the capacitor blowing up, I'd be concerned about the capacitor explosively vaporizing the wiring or the DC-DC when something fails. I've had some electronic devices explode from cap banks holding 1000 W-s and that is a lot less than yours. A fuse is a good idea. I used a super cap bank for a home project with good results.

Supercapacitors are used in some EVs. See What is a supercapacitor? The next step for EVs and hybrids explained
https://www.carmagazine.co.uk/car-news/tech/what-is-supercapacitor-battery-ev-and-hybrid/

And e-bikes. Dutch E-Bike Brand Ostrichoo Uses Supercapacitors To Power Its Bikes
https://insideevs.com/news/702321/ostrichoo-supercapacitor-ebikes/

Pi-pop, Ebike without Battery: Are Ultracapacitors a Viable Alternative?
https://www.ebike24.com/blog/pi-pop-ebike-without-battery

Good luck on your e-bike project!


Q = CV
Q = i x t
W = 1/2 x V^2 x C (energy stored)
1 HP = 746 W-s

 

Regenerative braking, as far as I know, simply charges the battery for the "brief moments" a vehicle is slowing down or coming to a stop and doesn't help much, I'm sure. However, capacitors charge in "brief moments". Why not charge the capacitors instead? After coming to a stop the capacitors could continue discharging into the battery too. Also, these LIC supercapacitors are new. My idea is quite straightforward and already in the works elsewhere in the automotive industry- so I've recently just now learned.

Maybe you should've browsed around a little before making the comment "There's no free lunch and no way to cheat the system".
Cheers...

The energy to charge the caps will load the motor and the bike will slow down. No matter what, you are going to be doing regenerative braking but with your scheme it is involuntary, and no doubt the rider will increase the throttle in response disconnecting the caps. In other words, if you don't use the caps for braking you won't find them charged to start the bike.

Thinking further, you will have to monitor the state of charge of the caps to decide if they can be used or not, or if they have been depleted before the bike is up to cruising speed. The complexity suggests you are better of implementing traditional regenerative braking since—there's no free lunch and no way to cheat the system.

 

Using the capacitors for braking makes sense, and to avoid throttle while braking a simple interlock can assure that never happens. Certainly variable braking will be needed, not ON/OFF braking, and so the controls will be a bit more complex.

 

The Philippines has four electric vehicle standards that apply to electric mopeds. These may help with the design.

"Department of Trade and Industry’s Bureau of Philippine Standards (DTI-BPS) adopts the following International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC) standards on electric vehicles as Philippine National Standards (PNS):"

https://bps.dti.gov.ph/press-releas...-international-standards-on-electric-vehicles