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Old Apr 09, 2011, 12:53 PM
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Idea
Water activated switch?

Hi folks I was thinking is it possible to make some type of switch that turns on my 12V bilge pump when it (The switch) gets wet? I could just put in a servo actuated switch but I would like the pump to just come on automatically. This way I reduce the chance of it running dry or sinking.

Thanks for the time and advice.
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Old Apr 09, 2011, 01:05 PM
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From our combat web page. We use these to activate our bilge pumps on our combat warships.
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Old Apr 09, 2011, 01:10 PM
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Thanks. That's just the kinda thing I was looking for. I hope our local Radio Shack has the stuff.

I will be running in fresh water, How long before the plates need cleaning?

The thing in the bottom center of the pick is the pump right?

Thanks again.
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Old Apr 09, 2011, 03:03 PM
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Check at the Radio Shack. Years ago they sold a water alarm, battery powered, that was the same idea all built. Used on my sump pump for years. Also Google high water alarm under shopping. Many, many.
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Old Apr 09, 2011, 06:37 PM
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they sell things called float switches specifically for bilge pumps at boating stores.
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Old Apr 10, 2011, 01:24 AM
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Ram Bilge Pump Boat Saver

Try a web search on that. The first one I found was: http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXDZ48
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Old Apr 10, 2011, 10:02 AM
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Two strips of metal with wires soldered to them between the power source and the pump will work. One strip is placed vertically a little higher ( the strip to the pump) than the other verticle strip and both about an inch apart. When the water gets to both strips it makes contact and starts the pump. Shuts off when the water gets below the higher strip. Used that on a bunch of real boats over the years. Pete
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Old Apr 10, 2011, 10:30 AM
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Thanks, That was my first idea. It cant be that simple, Can it? I'll have to solder up some wires and start playing around. This sounds like a great way to get a few 12V wake ups. Thanks again.

Funny thing is, The boat that I thought was leaking from the stuffing tube was really leaking from a hole in the hull. I had to tear everything out to find it tho......So Now I don't really even need the switch but I still like the idea.

Thanks again.
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Old Apr 10, 2011, 02:30 PM
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We battle usually once a month, so, in prepping the boat for combat these systems are all checked. So, clean once a month.
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Old Apr 10, 2011, 05:08 PM
Thermite + ice = Big boom.
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Look at either the Century or Flying Fish RC boats, they are juvenile but they have a water safety system, I do not know exactly how it is wired but It only runs the motors in water. Another way is to make two contacts, one with a hinge and metal strip protruding, and a float, so when the water ascends the float comes with, and touches the second contact.
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Old Apr 10, 2011, 09:35 PM
Chuck
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I have built and used the circuit described by Tachikaze. It is simple to build, inexpensive, and reliable. It's easily tested before each use by immersing both electrodes in a cup of water (just don't let them come in direct contact.)
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Old Apr 11, 2011, 05:22 AM
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Harbor Models has them in stock.
http://www.harbormodels.com/site08/pumps.htm

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Old Apr 11, 2011, 07:12 AM
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Not being an electronics guy, I wondered why Tachikaze's schematic included a transistor.

From my reading, it appears that the TIP 120 transistor allows one to switch on a 12 volt motor using only a 1.4 volt activator (the current running through the bilge water). Since pure water is a insulator, it does not conduct electricity well unless there are some ions (salt) dissolved in it. You can't know how salty your bilge water will be if you run in fresh water. Thus, the voltage across probes dunked in freshwater will likely be much lower than the 12 volt battery input. The pump would likely run slow, if at all.

As the "alternate water sensor" on Tachikaze's diagram indicates, you have to have the probes very close to ensure getting enough voltage flow to run the 12 volt pump.....unless you use the TIP 120 as the sensor/switch.

Combat guys like Tachikaze probably know more about the practical end of bilge pumping than most modelers :-)

http://www.radioshack.com/product/in...ductId=2062617

http://wiki.bildr.org/index.php/TIP1...ton_Transistor
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Old Apr 11, 2011, 12:35 PM
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The TIP 120 is the activating switch for the circuit. Most of us are running on 12V as the motors we use for the most part are running on 12V. The motor is a little Mabuchi motor set into an acrylic base with the copper tabs attached to the sides. Depending on how you have it set in your boat, anything above 1/8" of water will activate it. I will try and get a photo of one of our units posted tomorrow.
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Old Apr 11, 2011, 01:21 PM
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Water Level Sensor

The circuit in Post #2 does use a transistor. A TIP120. Looking up the specifications for it the only ones of real importance here are; how much current the transistor can carry, how much voltage it can safely tolerate when it is off, what its current gain is, and the maximum input current it can handle.

Maximum current rating is 5 Amps. So if your pump motor is rated at 5 amps or less you're OK there. Not sure what your pump draws when it is pumping water? Put it in cookie sheet on the kitchen counter. Pour in about a 1/2" of tap water into the cookie sheet. Run the pump from the same battery you will use in the model, and measure the current the motor draws while pumping water into the sink.

Maximum voltage rating is 100 volts. Obviously 100 is more than 12, but here that only gives you a safety margin of 88 volts. Again, this is OK.

The current gain of this transistor is 1000. Lets us assume for a minute that your pump draws 5 amps when running. So 5 amps of pump current divided by a input current gain of 1000 is .005 amps. This means that you only need .005 amps of input current minimum, to get the transistor to turn on enough to carry 5 amps. More is OK to a point as long as the input current does not go over the maximum input current.

Maximum input current is .12 amps. Looking at the circuit, when the plates are in water, current goes from the positive plate through the water to the input plate. If that current is .005 amps or more you're OK there. But I notice the design calls for a 2K Ohm (2000 ohms) current limiting resistor. In this circuit configuration the input of the transistor needs to be 1.4 volts higher than battery minus. Or it needs to measure 1.4 volts, which it will once the input current goes up to .005 amps. what does the resistor do? It limits the input current from going too high. 12V minus 1.4 volts equals 10.6 volts. If the sensor plates were shorted together you would have 10.6 volts divided by 2000 ohms equals .0053 amps. A tiny bit more than needed. But still less
than the maximum allowable input current . So again, that is OK.

Pure water is an insulator you say? I believe that you are right sir. But when was the last time you went out to the pond you run your boat in and drank some of the pond water? Pond water contains ions, dissolved metals like iron, zinc, copper, minerals, and a host of other chemical and biological ingredients from fish foul and other sources. All of those things tend to make it a virtual liquid short. If you were a poor unfortunate who had to run in a very clean pond you would just make the sensor plates bigger to trigger the pump. One could also reduce the value of the resistor to 1K Ohm if bigger sensor plates did not work.

If anyone who as actually built this circuit could please tell us how big the sensor plates were that they used, how far apart and so on, even better a picture or two of them would be nice.
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Old Apr 11, 2011, 02:05 PM
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Sensor plates are tiny...

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Old Apr 11, 2011, 02:34 PM
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Umi beat me to the picture.
They appear simple and they are. These are very effective as we rely on them in combat. With one of these pumps running, one can keep a small DD afloat in battle with one hole. Start to get more than one hole and you better run for port.
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Old Apr 12, 2011, 06:44 AM
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Yes, real water has ions in it. But it's not a "virtual short," for low voltages, anyway. Examples from the modeling field:
1)It is common to run-in a brushed motor (to seat the brushes) by hooking it to a D-cell battery & dunking the motor in a glass of water.
2) My RC sailboats, in particular the Pamir, make no provisions for keeping the battery and it's terminals dry. The rx and servo doubler's will fail if they get waterlogged, but the battery (voltage = lipo 3-cell) has no problem with pond water.
3) Some RC subs place the battery (7 cell NiCd) and it's connectors outside the watertight cylinder (WTC) due to space or cg considerations. The battery attaches to the motor, which is within the WTC, via studs that protrude from the WTC. Again, the water does not short out the battery.

Thus, the need for something (TIP120) that will switch on the pump, even though the water may not pass much current or voltage.

btw, even Firemen are not too chuffed by squirting on 110volt household wiring. They don't stand in water and stick their finger in a socket, of course. But spraying live 110v wires from a distance poses no life-threatening problem. There may be a tingle, which new firemen are exposed to in training so that they won't be surprized and drop the nozzle.
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Old Apr 12, 2011, 06:57 AM
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Umi, or Tachikazi, how long do your pump motors resist rust, ie how often must they be replaced? I'm building a portable RC & motor unit to attach to dead hulls (Lego boats, plastic models, etc.); it'd be easier to construct if I could move the motor outside the WTC.

Nice photo of a battered warrior :-)
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Old Apr 12, 2011, 02:49 PM
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That picture I posted is of the INS Alfredo Oriani, she has at least 10 years of combat experience, and I think she still has her original bilge pump, if not then on her second.
At the end of the season, the pumps are pulled out, flushed with rubbing alcohol and allowed to run a little bit and then oiled and run for a little bit and then placed back in the boat, awaiting next season.
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Old Apr 12, 2011, 06:01 PM
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Thanks, Tachikaze, that was what I needed to know :-)
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Old Apr 13, 2011, 12:14 PM
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They are not shown in the circuit, but show in the photo Cap across the motor leads. If you leave them off your radio will not like you. The first model I built with a working fire monitor I didn't add them. When the monitor was turned on the throttle would osculate between full forward and reverse and the rudder would go hard over, the only channel not effected was of course the one holding the monitor on. I had to wait untill the battery ran down before a rescue could be made.
Regards,
Gerald.
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Old Dec 03, 2011, 11:12 AM
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Correction

I bought the parts for the float switch at Radio Shack today.

In the schematic at Post No. 2, the part number for the 2.2k Ohm (1/4W) resistor should be 271-1325 instead of 271-1235.

The RS guy said the first one doesn't show up on his computer.

Ed
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Old Dec 03, 2011, 03:05 PM
Thermite + ice = Big boom.
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i built one using a TIP 29, a 1k resistor, and a 9v battery, works perfectly in my soldering iron- sponge water, although i'm sure that is mostly metal and lots of ions.
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Old Dec 13, 2011, 03:07 PM
Thermite + ice = Big boom.
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this is mine
P1120003 (1 min 14 sec)
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Old Dec 13, 2011, 05:04 PM
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Hi All,
Obviously the circuit is well used and accepted but from an electronic viewpoint the circuit can operate in linear mode if the bilge water is quite clean.
If the TIP120 is hard on or hard off then the power dissapated is relatively low but if it is half on (due to limited conduction) then it will drop half the supply at half the pump load current. This is likely to be a few Watts. Also the saturation voltage of a Darlington configured transistor pair is rather poor - perhaps a bit over 1V so even when fully turned on you will dissapate about a Watt per Amp of current drawn.

The ideal topology would be a voltage comparator function, with slight hysteresis, controlling a small power fet. This would be either on or off with no "maybe" state and have minimal power dissapation when running.

Cheers,
David
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Old Dec 13, 2011, 05:19 PM
Chuck
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Quote:
Originally Posted by KiwiDavid View Post
.

The ideal topology would be a voltage comparator function, with slight hysteresis, controlling a small power fet. This would be either on or off with no "maybe" state and have minimal power dissapation when running.
Say what???? All I know is that it works very well for my bilge pump..............
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Old Dec 13, 2011, 08:42 PM
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Quote:
Originally Posted by KiwiDavid View Post
The ideal topology would be a voltage comparator function, with slight hysteresis, controlling a small power fet. This would be either on or off with no "maybe" state and have minimal power dissapation when running.
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Old Dec 13, 2011, 10:33 PM
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Hi,
Yes that circuit has all the right attributes including AC drive to avoid plating or corroding your sense contacts. The 4093 device has the hysteresis built in (Schmitt function) so the drive transistor and relay will switch cleanly and abruptly rather than go through a protracted period of buzzing before making its mind up.
Only comment would be that it's not kind to run CMOS gates directly in to a transistor base without a series resistor. This is effectively a short on the CMOS gate's P channel FET but will survive due to its moderate channel resistance. Somewhat tacky.
A small N ch FET would be a better option and could drive the pump motor directly saving the high cost of a relay and the need for the base resistor.

Cheers,
David
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Old Dec 13, 2011, 10:51 PM
George Jure
Hamilton, Ontario
Joined Aug 2005
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Water activated switch?

Hi KiwiDavid

How about posting a modified circuit to that you taked about to the one posted above with a parts list etc. ?

Thanks in advance.
George
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Old Dec 14, 2011, 03:57 AM
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Hi George,
I'll see what I can do but I'm also very aware that some folk don't have any electrical resources and where they may build the simple circuit without a a pcb as soon as you add a few parts it becomes impossible for many to build.

Cheers,
David
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Old Dec 14, 2011, 05:15 AM
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A circuit for something like this should be simple enough to use PC board or Perf board available from Radio Shack with most of the other parts needed along with some 30 gauge wire wrap wire.

If you want to go as far as etching a board, here you go... DIY - How to etch a PCB
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Old Dec 15, 2011, 02:33 AM
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Hi All,
Something like this should offer better switching and lower losses.
Changing the power FET should allow currents up to 10-15A if required.
It doesn't use AC drive for the sense terminals so if this is an issue then use the previous circuit (with logic gates) and change the transistor/relay for a power fet. Otherwise just keep the terminals clean.

Fit 0.047ufd ceramic caps across the motor terminals to the motor body and then ground the body to the -ve side of your supply. The diode across the motor catches the inductive spike when the motor turns off but most fets will absorb this as they go in to avalanche mode.
So far this is only simulated but I will try to build it up in the next day or so.

Cheers,
David
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