Electronics 2000

Hi folks i'm wondering if anyone here can help me problem solve this and possibly help me get this circuit more stable? I've been using this circuit for a while . However it seems to stop working after a while, the motor starts beginning to need a prod to get going (in terms of moving the spindle and the when i check continuity via the connectors to the motor it seems to be open). With a new motor there seems to be no continuity, and initially the circuit works fine. Also, the 10ohm resistor runs very hot and occasionally has burned up. Here is the motor spec:

Specifications:
Operating voltage: 1.5 to 3V
No load speed: 9,100 rpm
No load current: 200mA
Speed at max efficiency: 6,990 rpm
Current at max efficiency: 660mA
Torque at max efficiency: 6.0g/cm
Output at max efficiency: 430mW
Stall torque: 26g/cm

Cheers

Darren

I don't understand the diagram.

What is DR?

What is the blue arrow for?

How can the resistor be 1r to 10r?

Maybe replace the 10R resistor with one designed to take a heavier current is if it is 1/4 watt replace it with a 1/2 watt 10R.
Maybe replace the motor with a similar load and see if the circuit works OK, to find out if the problem is the motor or the rest of the circuit.

Tar&stuff.

Hi paul:

The blue arrow was just pointing out i can have the ldr and pot either side depending if i want it light or dark fast.

DR is LDR with the L hidden.

I'm unsure of the 1r to 10r... it was a circuit i got off an internet friend, but he was clueless as to why it is breaking down.

is Load is the amount of current something draws? would this be 200ma as it says in the spec?

I will look at another resistor thanks, i didn't realise ones could take heavier current

cheers

With a PNP transistor I'd put the motor up above it (between +ve and collector)
emitter to 0v
base via to the point between the LDR and setup resistor.
You may need to turn the LDR and setup resistor the other way up to make it work

I am not really an expert on transistors, I need the book in front of me or I blow them up.
It seems to me that the 1r to 10r resistor is too low it should have more resistance, I would not like to put a figure on its value I am not sure what it should be and could be wrong.

The circuit now makes sense.

Tar&stuff.

All of the power to the motor passes through the 1R to 10R resistor so it may need to be pretty beefy too.

The motor spec shows 220 mA without load, and 660mA at max efficiency. 3V is presumably the max supply to the motor, so the remaining 3V is dropped over the resistor and the Vce of the transistor (usually about 0.2V). With 2.8V dropped across the resistor carrying 660 mA, the dissipation is near enough 2 watts which is why small resistors will burn up. I would suggest using one of 5W rating. A reverse-biased diode across the motor will help to cut down sparking which is the usual failure mechanism of small motors as the commutator/brushes wear excessively.

A disadvantage with the circuit as shown is that it will to put virtually the whole supply voltage across the motor when the LDR is in darkness.

Hi David. Thanks for your reply here. That makes a lot of sense and thanks for taking your time to explain.

I realised also with the circuit that if it's in too much light and i want the motor to be switched in by a light source that the motor just doesn't get going at all. I now only use the circuit in slightly darker environments, it now seems to be much happier and survived a four hour installation with no miss haps. Phew. I will swap the resistor to what you reccomend adn install the diode. Thanks again

Darren

oh and thanks paul and pirate paul for your input, I'm quite a newbie at electronics and have just been building simple audio pedals etc.... so to try and now make things that exist outa of kits is a bit of a leap. All help and advice is much appreciated.

I've not been able to be on here for a while due to my laptop being a real nuisance.

Cheers

Darren

Pleased that you have made progress! Can I suggest that you get some good books on circuit design - I have seen reference to some good ones on this site.