# COMMUNITY : FORUMS : TECH

## How can I slow down my electric leaf blower?

I have a 18 volt battery powered leaf blower. It has two speeds. How difficult would it be to slow it down a bit so the battery lasts longer? Right now even on the slowest speed it blows way more air than what I need.

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Jack A Lopez5 months ago

The usual way battery powered power tools implement speed control is by way of PWM (pulse width modulation), with a typical being a cordless drill.

Essentially there is a circuit that can produce this PWM signal with a duty cycle (i.e. fraction of the time it is on) varies in proportion to the distance the trigger is pulled. For example, if the trigger is pulled 25% of the way in, it gives PWM on 25% of the time. If the trigger is pulled 67% it gives PWM on 67% of the time. Et cetera.

Then that PWM signal drives a big fat transistor, often a MOSFET, for to switch voltage to the motor in time with the PWM signal, so the time averaged voltage seen at the motor is 25%, or 67%, or whatever percent, of the full battery voltage.

So that kind of makes it clear why people replying to this thread are suggesting you are suggesting you pull the guts out of a cordless drill, and use that.

However, what I think those people are failing to consider, is the question of, "How does your leaf blower implement its existing speed control?"

I know you said it was only two speeds, but is it making that happen by way of PWM plus big fat transistor? That is not an outrageous assumption. A lot of battery powered power tools use that method, but maybe for your thing, the designer decided not to make it proportional, but rather just two levels, selectable by a switch.

I mean, it would be kind of a lucky break if most of the PWM stuff was already there, in your leaf blower, and all you had to add was a potentiometer.

Or that might be wishful thinking, for it to be that easy.

In any case, the peoples who are telling you to use PWM, or the same kind of motor control found in a cordless drill, I think those peeps are on the right track.

5 months ago

Really cheap tools with just two power settings actully use a DC motor.
A bridge rectifier gives the full power and a single diode in front of give about half the power.
A switch bridges the single diode to go between full and low power.

5 months ago

That, rectifier that is switched from half-wave to full-wave, would be really easy for a mains powered tool, since mains power is AC, but I do not see how that works in a battery powered tool. Like, where does the AC come from?

It seems to me, for a battery powered thing, a PWM circuit would be at least as cheap as making AC from DC, and then rectifying it.

5 months ago

You're right of course, this is only for mains power.
But as said I think the easiest way is by using an exit pipe, or add a piece with bigger diameter.

Downunder35m5 months ago

Voltage regulator from an old cordless drill?

5 months ago

+1.

JavaScriptMikeC5 months ago

If it were me, I would use a Radio Control ESC to control the speed of the motor to any level I would like. It allows for 100s of levels blower power. Just pull the trigger how much you want it.

dawn456qs5 months ago

Cover some of the holes, it will suck less air through. You're welcome.

5 months ago

Bad idea as the motor not only needs to work harder but also has a much higher chance to overheat.
If anything then an exit tube with a much greater diameter will reduce the airflow properly without any changes or ill effects to the motor.