Super Capacitors for "Burst Mode"?

sleepy_tired said:

The first beat hits and immediately afterwards the amplifier sees a massive voltage drop as it's competing with the capacitor for current.

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No. It does not "compete with the capacitor for current." The capacitor is discharging during that time, not charging.

It's easy to see this in action. Hook up a scope and play a source with a wide dynamic range. Then add a capacitor. The voltage ripple will go down overall. It's how all bulk capacitance works, and it's why people add bulk caps to motor inverters.

Sure, the capacitor 'smooths things out', but it smooths things out to a lower level that causes the amp to overheat

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Again, no. Try it and see.

sleepy_tired said:

It actually makes sense for car stereos. Just think of it like this, a car audio system's load can rapidly fluctuate from 10-100%, based on when a bass drum is hitting, or not. Reproducing low frequencies takes a lot of electricity, and the low frequency hits are intermittent in most music.

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So you have a car with the the amp is hooked up to a 12v system that can't generate enough current to keep the amplifier happy. This includes both the alternator (primary) and battery (secondary) hooked up to a amp in your trunk with wiring that is much too thin. Between the sub amp and the rest of the system you have a gigantic capacitor. So you start up the car and turn on the receiver and the amp is happy and sees 12-13 volts from a happy system... until you turn the volume up.

The first beat hits and immediately afterwards the amplifier sees a massive voltage drop as it's competing with the capacitor for current. Every beat followed by voltage drop. If the music is loud and the wiring and/or alternator is particularly inadequate then the amplifier that is designed for a 12 volt system is going to see as sort of pulsating voltage that, I am guessing, could range between 6 and 10 volts.

So all you accomplished was to trade a short duration voltage drop for a much longer duration voltage drop.

Sure, the capacitor 'smooths things out', but it smooths things out to a lower level that causes the amp to overheat, or protection circuits to kick in (or whatever other terrible things happen) due to having the amplifier hooked up to a a power supply that is, on average, running at a lower voltage system then it was designed to operate at.

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caps in car systems is stupid usually, if you need such massive caps to keep a amp fed you need to improve the battery setup, not plaster on a band-aid wich is what those caps are.

amps -just like our controllers- already have plenty of caps inside. adding caps does nothing in making you faster.


still looking for someone to give me a reason why they would need supercap discharge rates on a ebike/scooter and what they hope to achieve with adding them.

CryB4Die said:

What about using supercaps with a hydrogen fuel cell?
The fuel cell is rated at a low power but with capacitors the car can accelerate like a normal car

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Sure, ..for a few seconds. (Notice the 50kW regen was a “max” figure )
But what happens when you are cruising at 60mph. (8kW) and you then have to climb a long slow hill?, ..or there is a 30 mph headwind ?
But first i want to see that car start on / drive up a car park ramp !

What about supercapacitors for just a 5 sec burst. I was just brainstorming about building a really fast E motor scooter. A big QS motor that can handle 30kw peak in the rear and one in the front. 2 big controllers, a simple 4kwh 100v 18650 pack for cruising around town at max 8kw of power.

But for a 5 sec drag race use a supercapacitor bank.

Like my own ebike has this 3 way power switch. And program the first at let's say 40amp. Per controler. And program the second switch to 300a.

Make a push boost button on the steer. With a supercapacitor level meter indicator like in a racing game " asphalt" when the level meter is fully charged by slow charging from the pack. Just a few amps. ( or make a charge button, press for a while to charge the capacitor bank ) You press the boost button and there is a parallel connection between the battery pack and the capacitor pack. And also a direct acces to the 300 Amp per controller by selecting the 3 way power switch to 300amp, all in the same button.

So 60kw to the wheels for 5 seconds to make it really fast and than release and ride with max 8kw which is enough for cruising. You don't need a Hugh big expensive bulky pack that can handle 60kw.

Just a fantasy guys I want to share. Wrong idea?
I did not yet calculate how much capacitors weight or volume is needed for 60kw for 5 seconds. Maybe here something goes wrong.

Bazaki said:

Just a fantasy guys I want to share. Wrong idea?

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yes, wrong idea. capacitors dont work that way.

Bazaki said:

What about supercapacitors for just a 5 sec burst. I was just brainstorming about building a really fast E motor scooter. A big QS motor that can handle 30kw peak in the rear and one in the front. 2 big controllers, a simple 4kwh 100v 18650 pack for cruising around town at max 8kw of power.

So 60kw to the wheels for 5 seconds to make it really fast and than release and ride with max 8kw which is enough for cruising. You don't need a Hugh big expensive bulky pack that can handle 60kw.

Just a fantasy guys I want to share. Wrong idea?

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For 60kW for 5 sec, from a 4kWh lipo pack, it would only be a 15 C “burst” output.
There are plenty of 18650 cells that can do that , without all the impractical complications of “ Supercapacitors”.
..... PS.. you would have more issues finding motors and controllers that could hhandle that level of boost power !

No. It does not "compete with the capacitor for current." The capacitor is discharging during that time, not charging.

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Capacitors don't magically disconnect themselves from their current source when they are being drained. The forces that cause them to build up charge are going to be in effect even when they are being used.

The only time they are not going to suck current down from the battery is when they are fully charged and not being used for anything.

This means that if your battery can't keep up with the current demands of your battery adding large caps is only going to make it worse. Unless you have some sort of special controller that isolates caps from the battery somehow.

Bazaki said:

So 60kw to the wheels for 5 seconds to make it really fast

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Let's do the math!

60kW for 5 seconds is, of course, 300,000 joules. (300 kilowatt-seconds.) E=.5CV^2, so assuming 100 volts, you'd need 60 farads if you could get 100% of the charge out of the caps. You can't, of course, since your motor won't run when your capacitor has dropped to 10 volts. So assuming you can run from 100 to 50 volts, you will need 120 farads. (Since 3/4 of the energy comes at the higher voltages due to that V^2 term.)

Let's see how big that would be.

A Maxwell 125 volt, 63 farad cap bank weighs about 135 lbs and you'd need 2 of them, for a weight of about 270 pounds. Each is about the size of a large truck starter battery.

https://www.maxwell.com/images/documents/125V_Module_datasheet.pdf

Are you sure you wouldn't rather build a battery to handle the current?

Bidirectional buck-boost converter

sharkmobil said:

Bidirectional buck-boost converter

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??...60kW..??

Thanks guys, you are right.
I never calculated it with the size and weight of the caps. And indeed, the promised farads are from 100v to 1v orso
And not in a range between 100v to 90v for example.

So there goes one of my fantasy balloons