Help with components

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SurferMarkUk
Posts: 2
Joined: Tue Jan 10, 2017 5:37 pm

Help with components

Post by SurferMarkUk » Tue Jan 10, 2017 5:40 pm

Could anyone help tell me what type/size components I need with this circuit diagram?
diagram1.jpg
diagram1.jpg (55.64 KiB) Viewed 3505 times
I’m going to be using a pump as the motor rated at DC: 3.5-9v 1-3W and my power supply will be DC 8.4V 1.5A.
pump.jpg
pump.jpg (24.72 KiB) Viewed 3505 times
What capacitor, diode, transistor and resistor do I need? Pin 9 will be connected to an Arduino nano.
Also, if I wanted to connect two pump/motors to the same circuit what would I need?
The pumps will only be on for around 20 seconds at a time every few hours.
I’m guessing the transistor would need to be a NPN BJT rated at least 8.4V and 6W but haven’t got a clue about the rest as I’m still just learning.
Cheers
Mark

David
Posts: 217
Joined: Sun Oct 04, 2015 6:18 pm

Re: Help with components

Post by David » Wed Jan 11, 2017 1:39 pm

This is not a particularly critical circuit, but there are a few things to consider.
1. Do you know the maximum current which can be drawn from the Arduino? That will constrain the value of the resistor so that the Arduino is not overloaded.
2. Can you measure the max current drawn by the pump? It may be about 1/3 amp.
3. Assuming that the transistor and the diode are rated suitably, you can connect a second pump in parallel with the first.
4. The transistor is a NPN type, and must be able to pass the maximum current likely to be drawn by the pump(s). It may be sensible to use a Darlington type - these are readily available. Do you have any to hand?
5. The capacitor is to cut out possible RF interference, and virtually any type will do, except for electrolytics. 25V rating or more will be OK. Again, readily available.
6. The diode is to suppress the inductive pulse when the current through the motor(s) is switched off. It should be able to carry a current equal to that drawn by the pump(s). The In4004 is rated at 1A.
Hope this helps

SurferMarkUk
Posts: 2
Joined: Tue Jan 10, 2017 5:37 pm

Re: Help with components

Post by SurferMarkUk » Thu Jan 12, 2017 6:51 pm

David wrote:This is not a particularly critical circuit, but there are a few things to consider.
1. Do you know the maximum current which can be drawn from the Arduino? That will constrain the value of the resistor so that the Arduino is not overloaded.
2. Can you measure the max current drawn by the pump? It may be about 1/3 amp.
3. Assuming that the transistor and the diode are rated suitably, you can connect a second pump in parallel with the first.
4. The transistor is a NPN type, and must be able to pass the maximum current likely to be drawn by the pump(s). It may be sensible to use a Darlington type - these are readily available. Do you have any to hand?
5. The capacitor is to cut out possible RF interference, and virtually any type will do, except for electrolytics. 25V rating or more will be OK. Again, readily available.
6. The diode is to suppress the inductive pulse when the current through the motor(s) is switched off. It should be able to carry a current equal to that drawn by the pump(s). The In4004 is rated at 1A.
Hope this helps
Wow, thanks for the detailed help 8-)
1. The max current from an Arduino pin is 40mA but 20mA recommended. I've tried this circuit with a 200 ohm resistor and have plenty of other values.
2. I'm going to use a 5V power supply now as the pump was a bit too powerful with 8.4V. My multimeter is rubbish and wont measure more than 200mA so I've tested the pump out of the water with 5v and it drew 180mA. In water it was drawing more than 200mA so I don't know the max current.
3. Glad it's possible to connect two pumps in parrallel so that's what I'll be doing.
4. The only transistors I had was two 2N2222A-PL NPN 40V 600mA which I tried using with this circuit and 8.4v supply. It worked perfectly at first but now doesn't. I've tested both the transistors with the multimeter and it seems I've knackered them as they're not passing the tests.
5. I've got and used a 1uF multilayer ceramic capacitor, is this ok?
6.Yep, luckily the ln4004 is exactly the type I've got.

So using a 5v supply running two pumps at the same time, what type of Darlington transistor do I need?

Cheers
Mark

David
Posts: 217
Joined: Sun Oct 04, 2015 6:18 pm

Re: Help with components

Post by David » Fri Jan 13, 2017 10:53 am

Hello.
If you are powering the Arduino from 5V as well, with a 1K resistor as load, 5mA will be drawn - well within the 20mA recommended max rating.
Maplin does a BD681 Darlington which will handle 4A. It is available very cheaply. You may need to use a heat sink (although I doubt it). Check by holding the transistor - if it is warmish, a small heat sink of a few square inches of metal will probably be enough, but if it is very hot, something is wrong!
The cap sounds OK - in this non-critical application as long as you don't use electrolytic caps, you should be all right.
Don't forget that the diode must be connected as shown in the diagram, with the cathode to the 5v supply (in other words, so that it is reverse biased when the motors are on).
Why not get a better multimeter? Maplin (and they are not paying me a commission!) do a digital one with a DC10A range for £19.99. Better ones are available at greater cost, as you might expect.
Hope this helps - post results here.

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