question about a DC voltage doubler

[Snaz]

i found a schematic of a DC voltage doubler and my big question is, what will this due to battery life?

**broken link removed**

reason this could be a big deal is because we use fans in our helmets to help keep us cool, and most use a 9V batt. well if we can still use a 9V batt. yet get the fan to turn faster, it would be great.

 

[audioguru]

The very simple circuit uses a lot of power to work. Even if the fans were not connected the current used by the circuit would kill a little 9V battery quickly.
The boosted voltage would double the fan's current so the little battery would die very quickly.

 

[Snaz]

is there anyway to increase DC volt yet not use any more batt life?

 

[audioguru]

is there anyway to increase DC volt yet not use any more batt life?

Impossible. The motors use more power when their voltage is higher.

When the voltage is doubled (two batteries in series) then the current is also doubled. Then if the batteries are strong they would last half as long as with one battery. But your little 9V batteries are not strong so two in series might last much less than half as long.

If you had a miracle circuit that doubled the voltage of one battery but the circuit uses no power, then the poor little battery will need to produce 4 times as much current as a single battery.

 

[Henry T]

**broken link removed**
SP6661 Datasheet pdf - High Frequency 200mA Charge Pump Inverter or Doubler - Sipex Corporation
SP6661, can double or invert your input voltage, with only a couple of components, I don't know how much current you need, but this one should be able to give 200mA...

 

[audioguru]

Look at the datasheet for a 9V alkaline battery.
An Energizer battery is almost dead in half an hour when its current is 400mA (the fan has 100mA at 9V or 200mA at 18V).

 

[Henry T]

The battery, especially a 9V block will be empty in a heartbeat indeed, maybe you should look at something else, an old cellphone battery or something...
But that sp6661, I used it for a project last year, and it has quite some efficiency, also look into some other buck boost pumps...

 

[dknguyen]

is there anyway to increase DC volt yet not use any more batt life?

Only one way...and that's for your load to use half as much current with a twice as much voltage (but you still have the same power output). This means that you would have to swap out your motor with one of the same power output but designed to run at double the voltage (which means it will draw less current). But it still has the same power output so you wouldn't be any cooler.

But if your load uses the same amount of current before the voltage is doubled and after the voltage is doubled, it means its using twice as much power when the voltage is doubled so that means more energy. Energy doesn't come from nowhere so you get shorter battery life or you need bigger batteries. Otherwise we would have perpetual motion machines.

Best way would probably just to use four 9V batteries...two in parallel and two in series. Double the speed with the same run-time. I doubt the weight of 3 more 9V makes that much of a difference, but it depends on the weight of the helmet and other things. Or just use different battery technology that is lighter and more energy dense.