Powering motor with boost converter?

neuroclast

Hi. I have a blower motor I am trying to run at 20v from a 12vdc system. At 12v it draws 12A, but I need it to get to a higher RPM. I'm not sure what the surge current is (turning on). Anyway, I was talking to someone else and they didn't think increasing the voltage with a BC would increase the fan speed.

I have planned to try and make a BC w/a 555 and see how it runs. The calculations I got for the BC parts @ 77KHz:

Inductor 1.05 uH / 65A
130uF cap
22V 65A diode

SO yeah those are pretty huge current values. I'm not sure if I can even find a 65A components. Is there another way to do this that I might be missing?

Thanks!

berkeman

Use a diode with a higher voltage rating. 22v is way too close to your target output voltage.

What is your feedback regulation scheme? Have you looked at using the National Semiconductor Simple Switcher series of ICs?

berkeman

And what are you planning on using for the switch transistor?

neuroclast

I looked at those Switcher ICs, but it appears none support anywhere near my needed output current. As for the transistor I hadn't picked one yet, I was waiting to see if anyone had better ideas that I hadn't thought of to get this motor to 20V.

Averagesupernova

The switcher ICs are meant to be used as a basis. The data sheets should show how to configure transistors and such to boost the current capabilities of the power supply. Don't listen to whoever told you that increasing voltage with a BC would not increase fan speed. Although it may not be an easy task to do so, once the voltage is at 20 volts the fan speed should definitely be faster than at 12 volts. 20 volts is 20 volts.

neuroclast

Hrm, if there is a way to boost them past the 5v then I don't see how given the inductors are internal on those ICs. I will freely admit I am about as far from an expert on these things as one can be however. Haven't even started my EE classes yet :]

I have made a 12v->400v BC before for charging caps, but never anything high current. That's really why this is so foreign to me. I can get the 555 circuit setup easy enough, and I understand the building blocks for the BC, but the only way I know to get the component values are online calcs. I may be doing those wrong for all I know.

Basically I just need this 12A@12VDC motor to be supplied 20VDC. As for the inductor max current/saturation current/inductance and that stuff I am completely in the dark. I am wondering if maybe those kind of current requirements are impractical for a BC?

berkeman

No, the inductor is not inside any IC. As supernova says, the DC-DC controller ICs generally have a low-current switching transistor inside them, but can be configured to use an external power transistor for higher current applications. You should be able to do some reading at the National Semiconductor website to learn all about how Boost Converters work, and where the design equations come from.