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Information on wiring a 5vdc fan and a 6vdc pump in a circuit

Sam.robo

Aug 13, 2017
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specifically I would like to know what power supply i would need.
Fan 5vdc 0.4A
pump 6vdc 0.25-3A

Is it better to wire in series or parallel?

also is there anything else i should do to make the circuit safer as I intend to leave it switched on and unattended?

I do not have access to any decent electrical shops so I would need to be able to find everything on the internet that delivers to italy.

The components i have listed can be changed as i haven't bought them yet, Its just what i could find on amazon.it as i was trying to get it to 12vdc to use a 12vdc adaptor.

any additional information is much appreciated

Thanks
 

Alec_t

Jul 7, 2015
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Welcome to EP!
i was trying to get it to 12vdc to use a 12vdc adaptor.
Why? Can't you run both the fan and pump from a mains-to-6VDC power supply (wall-wart)?
The fan probably wouldn't complain if the supply were 6V, but to be safe you could run it with a silicon diode (a 1N 4003, say) in series.
Putting fan and pump in series wouldn't work. The connection would need to be parallel.
 

Minder

Apr 24, 2015
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If wishing to use the same 6v supply, just use a couple of diodes in series from the 6v supply for the fan.
Are you looking for ac mains powered? if so a 6v wall-wart/adaptor should work.
M.
 

Sam.robo

Aug 13, 2017
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Welcome to EP!

Why? Can't you run both the fan and pump from a mains-to-6VDC power supply (wall-wart)?
The fan probably wouldn't complain if the supply were 6V, but to be safe you could run it with a silicon diode (a 1N 4003, say) in series.
Putting fan and pump in series wouldn't work. The connection would need to be parallel.

Thanks for your reply, can you explain the purpose of running it with a silicon diode please. It was my understanding that a diode simply ensures that the current runs in one direction and would offer minimal resistance. Could I not run it with a resistor to the fan to reduce the voltage?
 

Sam.robo

Aug 13, 2017
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If wishing to use the same 6v supply, just use a couple of diodes in series from the 6v supply for the fan.
Are you looking for ac mains powered? if so a 6v wall-wart/adaptor should work.
M.

Thanks for your reply, I would ideally run it from ac mains, would the 6v adaptor need to supply accurately the sum of the amps of the fan and pump 0.3A+0.4A or would a 1A current be ok?
 

duke37

Jan 9, 2011
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A diode does indeed pass current in one direction only but does not have minimal resistance. The voltage drop will be somewhat above 0.7V up to perhaps 1.2V at high currents. This action is different to a resistor which has a voltage drop proportional to current.

A voltage drop of 1V at 6V is significant but at 500V is insignificant.
 

Sam.robo

Aug 13, 2017
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A diode does indeed pass current in one direction only but does not have minimal resistance. The voltage drop will be somewhat above 0.7V up to perhaps 1.2V at high currents. This action is different to a resistor which has a voltage drop proportional to current.

A voltage drop of 1V at 6V is significant but at 500V is insignificant.

Thanks, In this given example would you say I would need to include a diode into this circuit or would running the 5v fan at 6v burn it out quickly?
 

duke37

Jan 9, 2011
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I cannot say whether the 5V fan will burn out on 6V, it all depends on the fan.
The speed of the fan will be roughly proportional to voltage but the torque and hence the current will be proportional to speed squared.
At 6V the speed will go up by 20%
At 6V the current will be up by 44%
At 6V the power consumed will be up by 73%
Use one or two diodes as suggested (they are cheap) or spend some time playing with various resistors to get 5V.
 

Sam.robo

Aug 13, 2017
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I cannot say whether the 5V fan will burn out on 6V, it all depends on the fan.
The speed of the fan will be roughly proportional to voltage but the torque and hence the current will be proportional to speed squared.
At 6V the speed will go up by 20%
At 6V the current will be up by 44%
At 6V the power consumed will be up by 73%
Use one or two diodes as suggested (they are cheap) or spend some time playing with various resistors to get 5V.

Thank you very much for your help, much appreciated.

With my power supply, do I need to find a 6vdc adapter that is the exact ampage or will the components draw what current they need? E.G in my example the total ampage is 0.7A will a 2A adapter supply 2A constantly or will the components draw the correct 0.7A?
 

Alec_t

Jul 7, 2015
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do I need to find a 6vdc adapter that is the exact ampage or will the components draw what current they need?
They draw what current they need, so as long as the adapter is rated for at least their total current it's fine. A 2A adapter is good, because it allows a good safety margin. It is never good practice to run things at their absolute maximum rating.
 

tedstruk

Jan 7, 2012
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pumps draw a sh*t load of current when they start. always use capacitor start pumps or you will fry all your fuses. A fan doesn't draw much current but can spin up and cause a no load situation that is just about backwards to the pump draw current problem... what you need is a circuit to control the draw amps of the pump, and hook it up to the pump circuit. Then you need a dedicated resistance circuit that drives the fan with minimal volts, without reaching the fans ohmage... usually like .05 ohms or something like that... reaching the fans ohmage will shut the fan off. then hook this circuit up to the fan... what you want is a ground circuit that allows only the nessesary ohmage..ie. resistance, to drive the fan and stop current generation. you chose the two hardest devices to wire in a circuit....usually they are connected direct through a switch. use all the right stuff... 6v for 6v devices, 50ohms for 50ohm devices, and so on...
 

Alec_t

Jul 7, 2015
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Oops. Re post #10, scrub the reference to 2A being fine. I overlooked the pump start-up current that Tedstruk mentions above.
 

Sam.robo

Aug 13, 2017
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pumps draw a sh*t load of current when they start. always use capacitor start pumps or you will fry all your fuses. A fan doesn't draw much current but can spin up and cause a no load situation that is just about backwards to the pump draw current problem... what you need is a circuit to control the draw amps of the pump, and hook it up to the pump circuit. Then you need a dedicated resistance circuit that drives the fan with minimal volts, without reaching the fans ohmage... usually like .05 ohms or something like that... reaching the fans ohmage will shut the fan off. then hook this circuit up to the fan... what you want is a ground circuit that allows only the nessesary ohmage..ie. resistance, to drive the fan and stop current generation. you chose the two hardest devices to wire in a circuit....usually they are connected direct through a switch. use all the right stuff... 6v for 6v devices, 50ohms for 50ohm devices, and so on...

thanks, even on such a small pump I would need a capacitor?

can I add a capacitor to my circuit or is it complicated (if you haven't guessed already I'm a novice)
 

Bluejets

Oct 5, 2014
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Forget the capacitor ....no help what-so-ever.
Just follow other comments.
 

Bluejets

Oct 5, 2014
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Show details of the dc motor and it's application and we will see. Otherwise you may be able to tell me how long is a piece of string.
 

Minder

Apr 24, 2015
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Starting current is usually VERY brief, the only reliable/simple way is to calculate the initial resistance is by locking the motor rotor, applying a very small DC voltage and measuring the current and calculate from there.
If possible, measure at a couple of spots on the armature and take the lowest reading.
Do NOT try and measure with a ohm meter, it is not reliable enough.
In most applications the period is so short that it is often not worth worrying about.
M.
 

BobK

Jan 5, 2010
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Unless, of course the motor might be mechanically stalled, then you get the start up current continuously,.

Bob
 

BobK

Jan 5, 2010
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applying a very small DC voltage and measuring the current
Isn't that what an Ohmmeter does? Not arguing with you, but I would like to know why and Ohmmeter would be unreliable.

Bob
 
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