Maker Pro
Maker Pro

what transistor

fastpcuser

Apr 8, 2012
31
Joined
Apr 8, 2012
Messages
31
I have a water pump with DC motor but I don't have a data sheet and couldn't find one. So I measured amps with multimeter and when it is running it uses around .6A continuously and when I try to stall it it uses 3.6 Amps, so my questions is should I use transistor which is rated above 3.6A or one with 1A should do it. Also I'm using the transistor as switch for relay.

Thanks
 

wingnut

Aug 9, 2012
259
Joined
Aug 9, 2012
Messages
259
I have used TIP 122's and TIP 127's in the past to drive relays and motors as they are high power Darlington pairs and come with their own protective diode. If you use a relay, then that would mean no spike across the transistor. Just protect the base of the TIP with a 500 ohm resistor.
 

fastpcuser

Apr 8, 2012
31
Joined
Apr 8, 2012
Messages
31
Anything with smaller footprint (running out of space) ? I tried to use 2N2222 but it is rated only for .6A max and I think it started causing some problems. What I'm trying to do is auto top off water controller. Everything was working fine for about a week then I started having issues with relay not turning or for some reason the whole thing would turn off but it may be little different problems somewhere...
 

wingnut

Aug 9, 2012
259
Joined
Aug 9, 2012
Messages
259
The 2n222 as you say is a low power transistor, not really designed to drive much. Maybe after a week, the 2n222 overheated.
 

fastpcuser

Apr 8, 2012
31
Joined
Apr 8, 2012
Messages
31
its for aquarium so it is about 4 liters a day, but it fills it when the level drops so maybe 250ml in few hours and it ony stays on for couple sec ( maybe 10-15)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
The other thing you'll need is a diode across the motor. If you don't have one the high voltages generated by the motor can damage the transistor quite quickly.
 

fastpcuser

Apr 8, 2012
31
Joined
Apr 8, 2012
Messages
31
Transistor is driving relay and I have diode between the transistor and the other end of the relay coil
 

davenn

Moderator
Sep 5, 2009
14,040
Joined
Sep 5, 2009
Messages
14,040
Transistor is driving relay and I have diode between the transistor and the other end of the relay coil

no, thats not correct, and not what steve said ;)
you need the diode across the relay, like this.....

attachment.php


Ignore the voltages etc just note the wiring of the diode, relay coil and transistor :)

cheers
Dave
 

Attachments

  • Relay-Motor Sw.GIF
    Relay-Motor Sw.GIF
    2.4 KB · Views: 6,922

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,613
Joined
Nov 17, 2011
Messages
12,613
Can you post a schematic of your circuit? To me it looks like we are talking at cross-purposes. Does the transistor drive the relay, then the relay drives the motor? Or does the transistor drive relay and motor? Or do you have two transistors, one for the relay, one for the motor?
 

wingnut

Aug 9, 2012
259
Joined
Aug 9, 2012
Messages
259
its for aquarium so it is about 4 liters a day, but it fills it when the level drops so maybe 250ml in few hours and it ony stays on for couple sec ( maybe 10-15)

The vessel you pump the water out of would also have to be replenished on a regular basis - not so?

I have a similar need to yours and two mechanical rather than electronic solutions have come to my mind.

1) To install a square bucket (like a toilet cistern) with a float valve like they used in old toilets. You can take a pipe from this to your aquarium and never have to worry again.

2) The second idea I am toying with is to build a water dispenser similar to those used in bird cages but bigger (like an upside down bottle filled with water in a bowl). If the mouth of the bottle dries, more water runs out. The water reservoir could be far from your tank with the opening of the pipe at the level you want it in your aquarium.

At any rate I am interested to know how you keep the vessel you pump water from, filled with water :)
 

fastpcuser

Apr 8, 2012
31
Joined
Apr 8, 2012
Messages
31
wingnut:

I made and stand which looks like piece of furniture and put 12G tank inside. it last for 7-10 days they I refill it manually when I do my water chage. Also my Ato has 20 sec timeout on it so if it runs too long its either Float bad float switch or empty reservoir. after 20 sec I get error Led blinking and I know somethings is wrong. the pump won't turn on untill I hit reset button on the ATO.controller
 

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,613
Joined
Nov 17, 2011
Messages
12,613
Yes, The transistor drives relay and relay drives the motor, I have it wired exactly like the diagram above shows
In that case the transistor rating depends only on the relay, not on the motor.
The relay, in turn, must be rated so it can turn on and off the motor.

The diode in dave's schematic is correct. When turning off the relay, it will dissipate the energy that is stored in the relay coil.
You should add a second diode (likewise catode to plus, anode to -) across the motor terminals. Otherwise the energy stored in the motor's coil will lead to arcing when the relay contacts open.
Alternatively you can use a snubber circuit.
 
Top