# What powers auto-flush toilets? **URL:** \ **Category:** Factual Questions\ **Created:** [January 13, 2007, 5:51am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807 "2007-01-13T05:51:12Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![LivingInThePast](https://avatars.discourse-cdn.com/v4/letter/l/e19b73/32.png) [@LivingInThePast](https://boards.straightdope.com/u/LivingInThePast)\ **Post date:** [January 13, 2007, 5:51am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/1 "2007-01-13T05:51:12Z")
I’ve been puzzling over this for a while… On the auto-flush toilets (the ones with the sensor that causes them to flush when you depart), I’ve never seen any sign of a power source. Do they have batteries? Little photocells? Tiny generators that charge a capacitor when the water flows thru? 😕 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 13, 2007, 5:55am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/2 "2007-01-13T05:55:12Z")
[Automatic flush toilets](http://en.wikipedia.org/wiki/Flush_toilet#Automatic_flush): > [@](#): > > “Automatic flush” refers to a triggering mechanism, rather than a water propulsion mechanism, although is usually implemented together with direct flush systems. Autoflush systems, as the name suggests, flush automatically once the user has left. Typically, an override button is provided if the user wishes to trigger flushing earlier. In retrofit installations a flushometer can be replaced with a self-contained battery-operated machine vision system that actuates a solenoid when a user departs. ---
**Author:** ![LivingInThePast](https://avatars.discourse-cdn.com/v4/letter/l/e19b73/32.png) [@LivingInThePast](https://boards.straightdope.com/u/LivingInThePast)\ **Post date:** [January 13, 2007, 3:39pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/3 "2007-01-13T15:39:43Z")
Thanks, **Q.E.D.** , now I know about retrofitting with battery-powered units. What about new units. I’ve never seen anything that looked like a connection to a power supply? Still 😕 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 13, 2007, 3:49pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/4 "2007-01-13T15:49:51Z")
I assume new units are also battery powered. Using mains power could be problematic, although it’s not out of the question. I’ve never seen one that looked like it was line powered, either. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [January 13, 2007, 3:52pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/5 "2007-01-13T15:52:33Z")
methane? ---
**Author:** ![ScoobyTX](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@ScoobyTX](https://boards.straightdope.com/u/ScoobyTX)\ **Post date:** [January 13, 2007, 5:19pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/6 "2007-01-13T17:19:28Z")
A lot of them are are battery-powered, while others are wired in. The hard-wired ones are usually 24v, with only low voltage going to boxes in the walls behind the flush valves. There will be a transformer for stepping down from 120V to 24V somewhere near, hidden behind an access door or ceiling tile. ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [January 13, 2007, 8:04pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/7 "2007-01-13T20:04:45Z")
While standing in front of them, I have theorized that it would be possible to design a unit that needed neither mains power nor a battery that would have to be replaced periodically. You could use the water flow to charge either a capacitor or a rechargeable battery. Just put a little turbine in the flow, connected to a mini generator that would recharge the power source. The system could be designed such that if usage was low, it would automatically flush to recharge the battery/capacitor before it ran down. (Yes, this would waste water, but in many areas this is not a major issue, and would be preferable to having to replace batteries.) I posted my theory in a similar thread here on the SDMB, and another poster provided a link to a system that worked exactly that way. I was pretty proud of myself for figuring it out. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [January 13, 2007, 8:37pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/8 "2007-01-13T20:37:57Z")
[This one](http://www.airdelights.com/installation/AutoFlush_instructions.pdf) uses 4 C batteries. (PDF) [This one](http://www.wasauna.com/urinal-31002.html) is wired into household AC. > [@](#): > > What every man desires; what every man deserves; what so few men ever achieve: A urinal in their own home with a Wasauna Wall-Hung Auto Flush Home Urinal. [These](http://www.plumbingsupply.com/autoflushvalves.html) can be AC or DC powered. You didn’t ask for it, but [here’s some commentary on self-flushing toilets](http://www.slate.com/id/2137256/) with regards to ergonomics: > [@](#): > > The auto-flush toilet violates two basic rules of technology adoption: Never replace a technology with an inferior technology; and never confiscate power from your users. Still, hands-free technology is flushing the competition. According to Pete DeMarco, the director of compliance engineering at American Standard (the largest toilet manufacturer in the world), auto-flushers constitute 30 to 40 percent of commercial sales today, and that number continues to rise. Haven’t found any self-powered ones yet, though. That would seem like a giant step forward. What happens with the battery-powered ones when the batteries run down and no one changes them? Are they then un-flushable? ---
**Author:** ![sturmhauke](https://avatars.discourse-cdn.com/v4/letter/s/e47c2d/32.png) [@sturmhauke](https://boards.straightdope.com/u/sturmhauke)\ **Post date:** [January 14, 2007, 12:44am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/9 "2007-01-14T00:44:46Z")
I really hate it when the autoflusher decides to flush when I’m still doing my business. Perhaps they are powered by rage. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [January 14, 2007, 1:20am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/10 "2007-01-14T01:20:57Z")
I hate that too. It seems to happen more often in airports and low-end department stores. What boggles my mind is that the ones at work operate when the power is out. The battery part understand. I just don’t know how they know I’ve moved when it’s pitch dark in the room. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [January 14, 2007, 1:21am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/11 "2007-01-14T01:21:59Z")
[QUOTE=Yllaria] What boggles my mind is that the ones at work operate when the power is out. The battery part understand. I just don’t know how they know I’ve moved when it’s pitch dark in the room. [/QUOTE] Infrared. To the sensor, you glow in the dark. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [January 14, 2007, 3:41am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/12 "2007-01-14T03:41:53Z")
Slight hijack-I was using the urinal in a facility with auto-flushers, and a little kid asked his Dad how the urinal knew when to flush. Techno-Dad replied that behind the little red window was a tiny man who pushed a button to activate the flush cycle. :eek: Toilets-R-Us: Now Hiring. Persons wanted to watch others urinate and defecate. No previous experience needed. Will train. Competitive salary and benefit package. Toilets-R-Us is an equal opportunity employer. 😛 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 14, 2007, 3:50am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/13 "2007-01-14T03:50:43Z")
[QUOTE=danceswithcats] Toilets-R-Us: Now Hiring. Persons wanted to watch others urinate and defecate. No previous experience needed. Will train. Competitive salary and benefit package. Toilets-R-Us is an equal opportunity employer. 😛 [/QUOTE] Man, what a shitty job. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [January 14, 2007, 2:26pm UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/14 "2007-01-14T14:26:55Z")
[QUOTE=danceswithcats] Toilets-R-Us: Now Hiring. Persons wanted to watch others urinate and defecate. No previous experience needed. Will train. Competitive salary and benefit package. Toilets-R-Us is an equal opportunity employer. 😛 [/QUOTE] I believe they are in the same union with the little men who watch your food spoil and turn on the light inside your refrigerator. ---
**Author:** ![According\_to\_Pliny](https://avatars.discourse-cdn.com/v4/letter/a/8e7dd6/32.png) [@According\_to\_Pliny](https://boards.straightdope.com/u/According_to_Pliny)\ **Post date:** [January 15, 2007, 12:41am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/15 "2007-01-15T00:41:52Z")
Seems like they should be able to run one with a combination of abmient power and water power. The water pressure can do the work to move the parts around and reset things after the flush, and the electric eye simply power a release catch. With all the public johns in the world, somebody will make a mint off this idea, so you electronics wizards should go rush home to your work benches. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [January 15, 2007, 12:57am UTC](https://boards.straightdope.com/t/what-powers-auto-flush-toilets/387807/16 "2007-01-15T00:57:38Z")
[QUOTE=According to Pliny] Seems like they should be able to run one with a combination of abmient power and water power. The water pressure can do the work to move the parts around and reset things after the flush, and the electric eye simply power a release catch. [/quote] Good idea. That should make the battery life not much different from shelf life. 5 years? 10 years?