LED status indicator

[VinceB]

Hey guys,

I have finished the prototype of my shunt regulator, using the homepower design. The 555 timer generates a pseudo-PWM because it is used in the monostable mode. What I would like to do, is indicate the duty cycle of the said PWM using a couple of LEDs (let's say 5). Zero LED means not dumping. 1 LED = low dumping, 2 LEDs = higher.. and so on. All LEDs being light would mean around 100% duty cycle = heavy dumping.

The thing is I am not sure which way to implement it. I figured an integrator with an op-amp could do the job of providing different voltages in function of the duty cycle. Then, a few parallel branches, with different zener diodes could allow to light specific LEDs at different voltage level.... I am thinking maybe there is a simpler way of doing it, so if anyone could provide some help, it would be great!

thank you

Vincent

[SamoaPower]

Take a look at the LM3914.

[(unknown)]

hmm, could rectify, feed a filter cap and feed the variable voltage to a bar graph display.

[Flux]

Yes the LM3914 bar graph driver should be your first choice. Download the data sheet, it has all the basic ideas for what you want. I did a crude ammeter with one some time ago for someone who wanted a wind turbine for show more than use.

Flux

[VinceB]

Cool cool! I'll have a look at it!

Sounds better than my initial idea!

thanks

Vincent

[Opera House]

I think you ought to use a diode and measure the temperature of the load resistor.  For that circuit you will need an integration time of over a minute if you try to measure the voltage on the resistor.  That homepower circuit is the greatest evil since elevator music.

[rossw]

Just thinking "outside the square" for a moment.

You have an output that goes high, stays high for a fixed period, then goes low for a variable period yes? The shorter the "low" period, the higher the dump rate.

Conceptually, then, a fairly simple counter could be used.

Reset on the falling edge, gate the count pulses while the output is low.

If you used something like a 4017, you could drive one-of-(n) LEDs.

If you don't put a led on the last output, when the "low" interval is too long, there will be no LEDs lit. Its then just a matter of picking a suitable clock speed to scale your LEDs to the dump rate.

Just my 2c worth.

[wooferhound]

LED Voltmeter

http://www.fieldlines.com/story/2005/2/3/63131/25107

[commanda]

If you're going to use an LM3914, why not lose the homepower circuit altogether. Use the led outputs to switch small pnp transistors which sequentially switch fets. If you scale the voltage range to cover the full battery voltage range, you can use the top one or two outputs to switch in dummy loads.

The small pnp transistors go in series with the leds. From the positive rail to emitter of transistor, base of transistor to anode of led, kathode of led to LM3914 as usual.

Collector of transistor to gate of fet.

If you have a look at circuit 1 in my dump load controller should give an idea of what the circuit looks like.

http://www.fieldlines.com/story/2006/6/22/04750/5496

Amanda

[Dave B]

I designed and built this output meter / variable load controller a few years back and it works fine. Rectifying a tap off the alternator for the LM3914 input with a pot for adjustable full range output. The power resistors you see are just what was handy to work with the pot I had handy to knock down the DC for the input, no heat there. DC wall wort powers the leds and solid state relays are swithced directly off the selected leds lit for load control by way of toggle switches. Resistive elements for the load are plugged into the switched receptacles. 15 leds using 2-LM3914's  5 green 5 yellow 5 red. Simple is good,  Dave B. Don't know why the photo shows large, it's a small file.

[VinceB]

Wow!

That's really interesting. I never thought of it this way.

The LM3914 actually provides the voltage reference, comparators and outputs all in one chip!! I am working on the circuit right now... Trying to figure out how I will set it up.

[VinceB]

Hello Dave B,

I would like to have more details about the general design of that controller.

From what I see, you seem to have two dump loads, did I get that right?

What is your voltage scale, min and max value? Which values turn the loads on?

thanks!

Vince B

[Dave B]

Hi Vince,

  I cascaded (2) Lm3914's to allow for a 15 led scale. I have a pot on the DC input to allow any range of full scale min to max. Yes, the photo shows 2 solid state relays and they are triggered by the output of any led selected when lit. This is done with simple toggle switches run parallel off the led out put to the relay input. I run this in bar mode so each previous led remains lit. I will be modifying this for 3 phase for my new 18' that I am currently testing, this was originally run on my single phase switching 2 different hot water elements at different rpm. It works very well and is simple. I will wire this for overspeed protection as well as battery back up for powering the leds in case of a power outage on the grid. Maybe get rid of the dc power supply altogether and make it self contained. I used the dc power supply because with 15 leds lit at times there was minimal voltage to enrgize the relays. Simple is good and I may even elect to just use it as a voltage / rpm indicator on my 18' with no load control. Less chance of failure the better, overspeed is a scarey thing.  Dave B.