Why did the Hitachi 18V drill light stay on?

[coopec43]

Just curious that's all.
I was packing all my tools away this afternoon and noticed the guide light on the drill was "ON". To save the battery charge I detached the 18V battery from the drill but the light remained on for about ½ an hour.

Where was the light getting power from?

[Simi 60]

Magic

[Wotname]

The wireless back up standby power reserve.
The later wifi/bluetooth ones stay on 24/7 (unless you are out of wifi coverage).

[coopec43]

Originally Posted by Wotname

The wireless back up standby power reserve.
The later wifi/bluetooth ones stay on 24/7 (unless you are out of wifi coverage).

Errrr? "The wireless back up standby power reserve" What are you saying?

It's an 18V Drill (not a radio)

[coopec43]

Originally Posted by Simi 60

Magic

Maybe Elon Musk would be interested?

[Nicholson58]

We never leave batteries attached. Store in a clean absolutely dry place. The lithium batteries have a BMS built in, circuit boards etc

[OneKoolCat]

The circuit in the drill has a capacitor in it. Depending on the power demands of the LED and the size of the cap it can stay on for a while. If there is something you can do to short or drive up the load it would go out quicker.

Some of the capacitors can hold a fair amount of charge.

Cheers,
Peter

[roverhi]

Good idea always set the direction switch to neutral. Bouncing around in a bag something can contact the trigger and turn on the drill/etc. and you know how I learned that.

The light staying on is a feature, PROBABLY. Really nice if the light turns on before you start a drill/screwdriver and remains on for a short time after use. Nothing more frustrating than trying to start a screw in a dark location when trying to find that sweet spot on the drill trigger that turns on the light without starting the drill. We want more capacitors and we want them now. Of course if the light stays on because there is short in the drill, that's not good as removing the battery is the only way to live with it.

[jmschmidt]

We call it PFM.

[CassidyNZ]

Given the very light draw of a small LED it is conceivable (as others have said) that a capacitor could keep it running for an extended period with zero battery drain. Makita lights turn off after about 5 seconds (in my experience).

A more pertinent question for me (and probably off-topic) is why can’t they design these tools so the the light actually reaches the spot where the tool (driver, drill) contacts the work piece? My Makita 18v drill/driver places a pool of light around the point of contact but the actual point of contact is in shadow. In a dark space this makes it harder to see the point of contact than if there was no light at all. Quite irritating.

[coopec43]

Originally Posted by OneKoolCat

The circuit in the drill has a capacitor in it. Depending on the power demands of the LED and the size of the cap it can stay on for a while. If there is something you can do to short or drive up the load it would go out quicker.

Some of the capacitors can hold a fair amount of charge.

Cheers,
Peter

Thank you Peter, that explains it perfectly.

[coopec43]

Originally Posted by jmschmidt

We call it PFM.

PFM?

Wonderful thing this google (What would we do without it)

"Piezoresponse force microscopy (PFM) is a technique used to characterize the electromechanical coupling of piezo- and ferroelectric materials. This effect results from the linear interaction between electrical and mechanical states in piezoelectric materials."

That makes sense

[coopec43]

Originally Posted by roverhi

Good idea always set the direction switch to neutral. Bouncing around in a bag something can contact the trigger and turn on the drill/etc. and you know how I learned that.

The light staying on is a feature, PROBABLY. Really nice if the light turns on before you start a drill/screwdriver and remains on for a short time after use. Nothing more frustrating than trying to start a screw in a dark loca drill, that's not go as it.

Good idea setting the direction switch to neutral, but maybe better to remove the battery?

I should have been forewarned about the danger of leaving "things" plugged in. Many years ago on the week-end I had been using the angle grinder in my workshop and when I finished I switched the grinder off at the power-point (yeah, I know ). The following Wednesday my Son woke me up and asked if I would expect the swimming pool pump to start up? On investigation I found the grinder had started up and sparks were flying as it ground away at an aerosol can.

I replaced the power-point switch but mentioned the incident to a household electrician who did not seem unduly surprised at what had happened.