Pages: [1]   Go Down
Author Topic: DC to DC boost converter  (Read 912 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 2
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi, I have been recently working on a hybrid car model project. Now I have a small motor/generator which generates 2V - 18V depending on the speed/rpm.  My plan is to use a DC to DC Step up Boost Converter to boost the variable input (i.e.  2.9V to 18V) to provide a 24V stable output for charging a super capacitor.? Is it actually possible in a sense that can any converter provide a constant output over a large input range?

I have been looking at chips which provides large output for a variable input range. Though I am not sure wheather the output voltages will change with input??

Please I need help on this urgently. Replies are appreciated.
Logged

0
Offline Offline
Shannon Member
****
Karma: 214
Posts: 12406
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You surely want a variable voltage output supply to charge up a capacitor (in
this case a very flexible boost-buck converter).  Or is the supercap array already up
to full voltage?

[ or are you already using a buck converter from 24V to the cap(s)? ]
Logged

[ I won't respond to messages, use the forum please ]

Czech Republic
Offline Offline
Newbie
*
Karma: 0
Posts: 30
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I think taht there is no step-up in this voltage class. Problem should be input voltage - 2,9V is really small to step-up to more than 5V. Yes,many these converters that has so low input steps only to 5V max. The cheapest way is to use step-up to 5V and second boost to 24V. That could be possible, but not with one boost converter.
Logged

0
Offline Offline
Shannon Member
****
Karma: 214
Posts: 12406
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I think taht there is no step-up in this voltage class. Problem should be input voltage - 2,9V is really small to step-up to more than 5V. Yes,many these converters that has so low input steps only to 5V max. The cheapest way is to use step-up to 5V and second boost to 24V. That could be possible, but not with one boost converter.

The input is a wide range, so you would need a boost-buck converter to get to 5V anyhow.
Logged

[ I won't respond to messages, use the forum please ]

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 631
Posts: 34488
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

The difficulty here is not the voltage boost but the current required to acheave that.
It is likely that at 2v9 there will not be very much current avaliable and in practice the voltage will drop to zero when you try and draw current from it.
Logged

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 149
Posts: 5626
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Is it actually possible in a sense that can any converter provide a constant output over a large input range?

Yes.

http://www.ebay.com/sch/i.html?_nkw=dc+boost+adjustable
Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

United Kingdom
Offline Offline
Tesla Member
***
Karma: 227
Posts: 6637
Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

It sounds to me like a job for a custom-built flyback converter, using a transformer rather than a simple inductor. The transformer secondary would charge the supercap via a Schottky diode. The operating method would be:

1. Connect the primary to the incoming supply until a time limit or the desired primary current is reached (whichever happens first). Then disconnect the primary. The flyback voltage induced in the secondary then charges the supercap via the diode.

2. Monitor the secondary current (which is charging the capacitor) until it drops to zero. Then start the cycle again.

3. Also monitor the supercap voltage, and stop charging when it reaches the maximum.

There are probably switching power supply control ICs that you can get to do all or most of this.
Logged

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Oregon, USA
Offline Offline
Edison Member
*
Karma: 68
Posts: 2323
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

This adjustable boost converter from Pololu can generate 4-25V from as low as 1.5 V http://www.pololu.com/catalog/product/799
Logged

"It seems to run on some form of electricity"

United Kingdom
Offline Offline
Tesla Member
***
Karma: 227
Posts: 6637
Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

That looks nice! However, it requires the input voltage to be less than the output voltage (like most boost converters). That's why I suggested using a transformer-coupled flyback converter, because it allows the output voltage to be higher or lower than the input voltage.

It would be possible to power that Pololu boost converter via a buck converter, with the buck converter limiting the input voltage to the boost converter. However, that would require an extra diode voltage drop, which would absorb a significant amount of power at low input voltages.
Logged

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 149
Posts: 5626
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

And remember that too multiply the voltage by (eg) 4, you also need four times the amps.

Also, no converter is 100% efficient. You might only get 80%, maybe even less if you try extreme boosts.
Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Oregon, USA
Offline Offline
Edison Member
*
Karma: 68
Posts: 2323
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

This is what the OP wants to do:

My plan is to use a DC to DC Step up Boost Converter to boost the variable input (i.e.  2.9V to 18V) to provide a 24V stable output for charging a super capacitor.?

The Pololu boost converter I linked will do exactly that, with the proviso that the input voltage to the converter cannot exceed 16V. I would add a 16V Zener diode in parallel with the variable input to prevent overvoltage.  Only experimentation will tell if the OP's motor/generator provides enough current to run the boost converter. The docs state that the quiescent current of the regulator varies from 2-30 mA, depending on the input and output voltages.
« Last Edit: October 14, 2013, 12:34:03 pm by jremington » Logged

"It seems to run on some form of electricity"

Lacey, Washington, USA
Offline Offline
Edison Member
*
Karma: 162
Posts: 2428
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

As pointed out, you can't just feed a supercapacitor with a stiff 24V. Rather, you want a constant current, or at least a current-limited charge, with a voltage limit of 24V.

As pointed out, however, multiplying the voltage to the output results in multiplied -current- to the input. So 500mA charge current at 24V would be 4A at 3V input. However, the switching upconverter chip will have peak currents much larger than that, 2 to 3x larger.
Logged

Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

Pages: [1]   Go Up
Jump to: