# Need some circuit design advice

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Dear all,

I tried to build up a circuit which controls current though a DC motor. The motor needs to generate strong torque; and the input power will be battery ~12V 2400mAh battery pack. Previously, the motor has been tested. The peak current needed is 5A@30V for ~1s. Then there will be 1 second break before another peak.

My plan is to build up a "capacitor train" which has ~5 "high energy density" capacitors. My circuit will include a boost up circuit to change the 12V to 30V DC and then charge the capacitors. After that, the circuit will control the capacitors discharge the energy to motor in sequence; and it will control the recharge of capacitors.

(The circuit has to be as small as possible)

my questions is where I can find the small and "high energy density" capacitors for this circuit?

Not exactly what you ask for, but I thought I'd mentioned it.

If you use a "Spike and Hold" circuit like this one, in conjunction with your 12V to 30V boost circuit, then perhaps you don't need the "high-energy density" capacitors. Diodes and transistors are more compact. This circuit is for operating fast solenoid valves, so it's good for inductive loads like a motor. I guess it all depends on how your boost circuit holds for the duration of the spike...

Not exactly what you ask for, but I thought I'd mentioned it.

I think I should explain a bit more clear

Requirement: Motor generate strong torque for 1s and then have 1s break

Information of the motor: to meet the required torque 5A@30V can do that

Constriction: Use ~12V 2400mAh battery pack and the control circuit as small as possible

My plan was: boost up 12V to 30V and store the energy in capacitors; a controller will control the discharge the power to motor and recharge the capacitors.

My question was: Where I can find the capacitors which is suitable for my project

I think I should explain a bit more clear

Requirement: Motor generate strong torque for 1s and then have 1s break

Information of the motor: to meet the required torque 5A@30V can do that

Constriction: Use ~12V 2400mAh battery pack and the control circuit as small as possible

My plan was: boost up 12V to 30V and store the energy in capacitors; a controller will control the discharge the power to motor and recharge the capacitors.

My question was: Where I can find the capacitors which is suitable for my project

Indeed, it was clear the first time... I just don't know enough about capacitors to provide infos about them and I thought I would point in an other direction. I'll let some other guys chip in on this.

Dear all,

I tried to build up a circuit which controls current though a DC motor. The motor needs to generate strong torque; and the input power will be battery ~12V 2400mAh battery pack. Previously, the motor has been tested. The peak current needed is 5A@30V for ~1s. Then there will be 1 second break before another peak.

My plan is to build up a "capacitor train" which has ~5 "high energy density" capacitors. My circuit will include a boost up circuit to change the 12V to 30V DC and then charge the capacitors. After that, the circuit will control the capacitors discharge the energy to motor in sequence; and it will control the recharge of capacitors.

(The circuit has to be as small as possible)

my questions is where I can find the small and "high energy density" capacitors for this circuit?

Why would you want to use capacitors? Look at using a MOSFET circuit. A FET will most certainly be able to handle the current requirements but it will leave a footprint about the size of a small, surface-mount IC.

Why would you want to use capacitors? Look at using a MOSFET circuit. A FET will most certainly be able to handle the current requirements but it will leave a footprint about the size of a small, surface-mount IC.

I want to use capacitors because I need to make sure the power supply is stable for that 1s. The battery power pack may not be able to generate enough current to meet the motor requirement, so I use the capacitors to store enough energy for the 1s usage. The idea is similar to a "flash" in a camera.

OK, let's do some maths.

If we take 30V x 5A for 1 second, you need 150 Joules of stored energy.

Stored energy in a capacitor is W=0.5*CV^2, so you need at least 1/3 Farad capacitor. If you want to keep 5A for the whole second, make sure you have some margin...

Check out these puppies.

EDIT: I think those are huge... well it depends=> Dimensions: 9"L x 3"W x 3"H

OK, let's do some maths.

If we take 30V x 5A for 1 second, you need 150 Joules of stored energy.

Stored energy in a capacitor is W=0.5*CV^2, so you need at least 1/3 Farad capacitor. If you want to keep 5A for the whole second, make sure you have some margin...

Check out these puppies.

EDIT: I think those are huge... well it depends=> Dimensions: 9"L x 3"W x 3"H

Thanks!

I am trying to look for another information which is the amount of Watts that a 1.5V rechargeable battery can produce. I just read an information which said that a "D" battery can produce 28A. This is too impressive . I am not sure the information is right. However, I only need 4-5 "D" batteries if the information is right

I think I found what I need

ulta-capacitor

Maxwell technology

* BCAP0350E250T03

* ~\$23 each (sale: rell.com)

* 350F/2.5V

* max peak current 220A

* OD = 33 X L = 62 mm

* BCAP0100 P270

* ~\$18 each (sale: Tecate Group)

* 100F/2.7V

* max current 54A

* 0.025 kg

* OD =25.0 X L=50.0 mm

• 3 weeks later...

I think I found what I need

ulta-capacitor

Maxwell technology

* BCAP0350E250T03

* ~\$23 each (sale: rell.com)

* 350F/2.5V

* max peak current 220A

* OD = 33 X L = 62 mm

* BCAP0100 P270

* ~\$18 each (sale: Tecate Group)

* 100F/2.7V

* max current 54A

* 0.025 kg

* OD =25.0 X L=50.0 mm

But to get your 30 V (actually you should go for some margin) you will need more than a dozen of them in series. Seems very costly to me and it will also reduce the total capacitance accordingly.

Ctot = 1 / (1/C1 + 1/C2 + ..... 1/Cn)

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