controlling a circuit using a changing current

[DaveK]

Hi - I'm a newbie

I am fitting a small wind turbine (in a school) that is being used to charge a 12V car battery; the voltage is kept at 12V - the current increases with windspeed (0A - 6A @ 12V).

I want a light-based display that will indicate the increasing current as the windspeed increases. I thought of using the changing current to control a flasher circuit (more current = faster flashes) or an led bar display, but despite hunting though my electronics library and the internet, I can't find any circuits controlled by current! Any suggestions welcome! Thanks Dave

 

[ericgibbs]

Hi - I'm a newbie

I am fitting a small wind turbine (in a school) that is being used to charge a 12V car battery; the voltage is kept at 12V - the current increases with windspeed (0A - 6A @ 12V).

I want a light-based display that will indicate the increasing current as the windspeed increases. I thought of using the changing current to control a flasher circuit (more current = faster flashes) or an led bar display, but despite hunting though my electronics library and the internet, I can't find any circuits controlled by current! Any suggestions welcome! Thanks Dave

hi,
Look at the LM3914 led bar driver ic.
The technique is measure the voltage drop across a low value resistor.
The voltage drop is proportional to the current flowing thru the resistor.

OK.?

 

[DaveK]

Thank you for such a quick response!

I looked at the LM3914 driver when I naively thought that the voltage would change until it peaked at 12V! The turbine charges the battery via a regulator. I assume that I put a low value resistor (10Ω?) in the positive line from the generator and use wire from the battery side of the resistor into pin 5 (sig) and a wire from the negative line to pin 2 (V-) with pin 2 also connected to ground

In battery powered circuits where is the "ground"? - can I use the -ve terminal (since ground makes the return part of the circuit) or can I just connect the grounded wires together (is this "floating ground?)

Sorry if I sound stupid, but I have just semi-retired and finally have time to tinker with some electronics. I know that starting with something simpler would be more sensible, but I have to solve this problem if possible! I greatly appreciate your time and expertise! Dave

 

[ericgibbs]

Thank you for such a quick response!

I looked at the LM3914 driver when I naively thought that the voltage would change until it peaked at 12V! The turbine charges the battery via a regulator. I assume that I put a low value resistor (10Ω?) in the positive line from the generator and use wire from the battery side of the resistor into pin 5 (sig) and a wire from the negative line to pin 2 (V-) with pin 2 also connected to ground

In battery powered circuits where is the "ground"? - can I use the -ve terminal (since ground makes the return part of the circuit) or can I just connect the grounded wires together (is this "floating ground?)

Sorry if I sound stupid, but I have just semi-retired and finally have time to tinker with some electronics. I know that starting with something simpler would be more sensible, but I have to solve this problem if possible! I greatly appreciate your time and expertise! Dave

hi,
I dont what the charging current is for your system, but if was say 1amp, then a 10R resistor would drop 10V, not a good idea.

Usually the series resistor is in the order of 0.01R thru 0.1R, in the 0V , common line.
If it was 0.1R then at 1amp charge current you would only have a loss of 0.1V at 1amp.

The normal method would be to amplify the voltage across the the series resistor to give say 5V.
What is the max charge current you get from the turbine gen.?

EDIT:
eg, say the max charge current was 10A and we used a 0.125R as sense resistor.
This would give 0.125V/amp, using the LM3914 in it basic mode would give an extra 'dot for every 1amp of current, upto 10A

 

[DaveK]

Here is a diagram of the basic circuit I'm working with; The charging current into the 12V battery from the turbine rises from 0A @ a windspeed of 5 knots to 5A @ 40 knots;

Sorry to be so dozy! Dave

 

[crutschow]

A 0.1 ohm, 1W resistor connected in series with the battery negative terminal would give 0.5V at 5 amps current. Use the battery negative terminal for your circuit common. Amplify the resistor voltage with a non-inverting op amp connection set for a gain of 10 to give 5V at a 5A current to the LM3914.

For ease of design use a rail-rail type op amp such as a National LMC6081IN or TI TLV2450CP which allows the use of a single power supply.

 

[DaveK]

Thanks very much! I wish that I had found this site years ago!

 

[ericgibbs]

Thanks very much! I wish that I had found this site years ago!

hi Dave,
Where are you located.?

 

[DaveK]

Leeds (UK)

 

[ericgibbs]

Leeds (UK)

Know it well, I'm Yorkshire born and bred, strong in the arm, thick in the head.

How do you want to proceed on this project.?

 

[crutschow]

I miscalculated. It should be a 0.1Ω 3W resistor. The resistor power at 5A is 2.5W.

 

[DaveK]

Where-a-bouts in God's own country?

I'm learning fast! (or at least I hope I am!) - a bit of background - I've got a doctorate in Chemistry, but am an all-round scientist by inclination and fascinated by electronics, in which area I'm a complete amateur. I've built a couple of simple circuits in the past (555 based flashers) and am trying to get over the initial hurdle (like with a +ve and -ve battery terminal, where the heck is the ground?!).

If I modify the diagram I've posted to show what I think the advice means, would that take up too much space on the forum? Dave

 

[ericgibbs]

Where-a-bouts in God's own country?

I'm learning fast! (or at least I hope I am!) - a bit of background - I've got a doctorate in Chemistry, but am an all-round scientist by inclination and fascinated by electronics, in which area I'm a complete amateur. I've built a couple of simple circuits in the past (555 based flashers) and am trying to get over the initial hurdle (like with a +ve and -ve battery terminal, where the heck is the ground?!).

If I modify the diagram I've posted to show what I think the advice means, would that take up too much space on the forum? Dave

hi Dave,
Post your drawing.
We can come up with a circuit, you can get the bits from Maplins or Farnell.


ex Rotherham, now Pompey

 

[rainman1]

Alba-gubra

 

[DaveK]

I'm 25% Scot! (grandfather, mother's side - Robertson tartan!)

 

[DaveK]

Thanks very much, Eric!

 

[DaveK]

Hi - sorry I've been missing for a while - I've tried to understand crutschow's advice about the ground/common and where to tap off readings. I have a 12V battery and want to use it to power the chips I'm supposed to be using (an op amp and led driver). Can it really be that simple?

Anyway, attached is what I think crutschow was trying to say!

Dave

 

[ericgibbs]

Hi - sorry I've been missing for a while - I've tried to understand crutschow's advice about the ground/common and where to tap off readings. I have a 12V battery and want to use it to power the chips I'm supposed to be using (an op amp and led driver). Can it really be that simple?


Dave

hi Dave.
I will post a circuit during the weekend, dont buy any bits till you see it.
The power for the op amp/LM3914 and leds will come from the 12V battery thats being charged.

Q. Do you power other equipment from the 12V battery while its on charge or is it just a battery charger.? ie: whats the battery used for.?

You dont need rail to rail op amps for this application.

 

[DaveK]

Hi - you are very kind;

The battery is going to have a 1.5V output to power a quartz clock that will have the lights around it! (i'm hoping to use a LM317 and suitable resistors to get a stabilised 1.5V output from the battery.

Eventually the battery will also be used to power a small solid state computer and monitor so that the school can show a presentation on alternative energy and what the kids are doing

One thought occurs to me - if I am monitoring a voltage drop produced at a particular current, what effect will the regulator have as the battery becomes charged? Dave

 

[ericgibbs]

Hi - you are very kind;

The battery is going to have a 1.5V output to power a quartz clock that will have the lights around it! (i'm hoping to use a LM317 and suitable resistors to get a stabilised 1.5V output from the battery.
If the clock requires very little power as most quartz clocks do, then we can make a simple 1.5Vdc take off point from the battery

Eventually the battery will also be used to power a small solid state computer and monitor so that the school can show a presentation on alternative energy and what the kids are doing
That should not be a problem

One thought occurs to me - if I am monitoring a voltage drop produced at a particular current, what effect will the regulator have as the battery becomes charged?

If you mean the wind gen charger, you are not monitoring at a particular current. The LM3914 will light upto 10 Leds, one for every 0.5A of charging current.
Dave

Hi Dave,
I have the test circuit working on the bench OK.
Drawing is done, Ill double check and post later today.

How are you planning to build the project, on vero[stripboard] for example,???

Let me know and I will suggest a layout.