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# DC/DC converter: 0-60V to 60V

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#### jumpjack

##### Member level 1
I want to add ultracapacitors to the battery pack of my scooter.
Scooter has 1500W/60V motor and 60V battery.
I'd just need, for now, 2 seconds of high energy.

How can I build, or where can I buy, a DC/DC converter capable of using whole voltage range of a 60V ultracap (0-60V) to give a constant 60V voltage?

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The boost converter calculator suggests (theoretically) that a 22 uH coil, at 20 kHz, could provide 1500 W at 60V.

That is if your ultracapacitor can provide 91 A, in a range of 20-60 V, during the two seconds you are asking.

It will be a challenge to build such a converter.

So?
Suggestion?
How can I determine which coils and capacitors to buy?
How would frequency and voltage range reduction affect circuit complexity?

If your motor draws 1500 W at 60 V, then it draws 26 A and has a net impedance of 2.3 ohms.

I find that if I start out my simulation with a 2.5 Farad capacitor, its output drops to 42 V at 18 A after two seconds. Power is about half what you started with.
Therefore if you want 60 V continuous output then your boost converter must draw 80 A bursts at a 50 percent duty cycle.

In reality you would use a bank of several capacitors (or supercapacitors), to divide up the amp flow.

A low frequency is associated with a large Henry value coil (and correspondingly larger size and expense).

If you use continuous conduction mode, it permits you to use a coil with a lower inductive saturation current rating.

If your motor draws 1500 W at 60 V, then it draws 26 A and has a net impedance of 2.3 ohms.

I find that if I start out my simulation with a 2.5 Farad capacitor, its output drops to 42 V at 18 A after two seconds. Power is about half what you started with.
Therefore if you want 60 V continuous output then your boost converter must draw 80 A bursts at a 50 percent duty cycle.

how did you calculate this?

f you use continuous conduction mode, it permits you to use a coil with a lower inductive saturation current rating.
what does this mean?

Therefore if you want 60 V continuous output then your boost converter must draw 80 A bursts at a 50 percent duty cycle.

how did you calculate this?

I let the simulator calculate for me.
Otherwise I could have used the RC time constant formula.

I used my brain for a rough calculation to get the 80 A figure. I guessed that the converter will operate at 50 percent duty cycle. Therefore to maintain 1500 W when the incoming volt level has dropped to half, you'll need 4 times the amperes during the switch-On period.

My figures are rough since there will be losses, but it gives you an idea how difficult it will be to achieve your goal.

I wrote:
If you use continuous conduction mode, it permits you to use a coil with a lower inductive saturation current rating.

You wrote:

what does this mean?

This is a mode of switching a coil at a fast enough rate that it never fully discharges.

CCM is in contrast to discontinuous mode. In DCM the coil discharges and is idle for part of the cycle. (You probably will not use discontinuous mode for this project.)

CCM versus DCM is an operating parameter for a switched-coil converter.

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