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.
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)? ]
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.
Helium328PU:
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.
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.
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:
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.
Monitor the secondary current (which is charging the capacitor) until it drops to zero. Then start the cycle again.
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.
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.
sabbir:
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.
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.