Old traffic lights used about 200 W bulbs, maybe 3 ea. 1 W LED's / 5 steps ??

 

Can you tell us something about the 300 W load dump, rated V, resistance. The 50 A meter most likely
has an internal current shunt of 1 m ohm, .001 ohm. @ 50 A, V = 50 mV, not a lot of V to directly work with.
A current shunt of .01 ohms would be about right. @ 13 A, V = .13 V, W = 1.69 W. In the range of 300 W dump ?

 

Here is one version that should work. N ch FET , 2 A or better, 30 V or better, Rds .1 ohm or less.

 

The 10k , 10 turn pots can be other values, say 1k to 20 k, 3 turn to 10 turn. the top of pot should be about .16 V.
A semi log setting can be tried. Bottom to top, adj. tap 1, .053 V, 2 .07, 3, .114, 4, .13, 5, .143, 6, .15 = 15 A.
Where to find .01 3 W resistor? Maki it, 2 strips of copper 9 ( 1 X 4 cm ) spaced 46.7 mm apart. Solder 4 lengths
of stainless steel, 1 mm dia., about 19 ga. I use acid flux. I measured a length of SS wire until it measured 1 ohm, 46 in. Drill a hole in each end for connections. 50 A meter can be added in series with .01 R & 300W dump R.

 

Hi Marley, Just wondered if you've managed to have a look into this? it'd be fantastic if you could still do me a circuit diagram

Thanks

Sorry, been away. Write-up with circuit diagram attached. Contact me if you want any more help.

 

Sorry, been away. Write-up with circuit diagram attached. Contact me if you want any more help.

Hi Marley,

Thanks again so much for the diagram, I know its been a while but I've finally found time to put this together and now I'm ready to start building! Just one thing, I cant seem to work out where the Trimmers go on the diagram?

Thanks

 

They are the 10k resistors with the small block beside connected to the comparator +ve inputs. The small block is the slider connection on the trimmer. Usually the centre pin.

So the +ve input of each comparator will get a voltage that can be adjusted between approx +2.5V and +5V depending on the trimmer setting. The 1M resistor between the comparator output and the +ve input is a small amount of positive feedback that should make the output "snap" between on and off.

If you use the current sensor shown, its output varies between 2.5V and 5V depending on the current in the wire (goes up with increasing current). If you find that its output varies between 2.5V and 0V (goes lower with increasing current), then you have the current flowing the wrong way in the wire through the centre. Reverse the wire.

Keep us posted with progress!

 

Hi Everyone,

Just a quick update. I've built the board from the diagram Marley sent over. I've tested it however unfortunately I can't seem to get the relay to turn the lights on. Is there anything I could do to test this? I've checked voltages and they seem correct and I've also adjusted the trimmers however I'm not having any luck.

Any suggestions would be fantastic

Thanks

Mike

 

Mike, I assume you have the circuit diagram I posted here some time back. Some things you can do to test:

Connect a digital voltmeter (DVM on the DC volts range), and check that you have a supply voltage of about 12 to 14V. Check that the output of the regulator/dropper is 5V. The negative probe of the voltmeter should be connected to the 0V supply for all tests.

One at a time, try shorting pin 7 or pin 1 (the comparator outputs) to pin 4 (0V) on the IC with a link of wire. Each time, this should light one of the lights. This tests that your lights and the solid-state-relay is working.

Next, connect the digital voltmeter positive on the 100k resistor (the output of the current sensor), negative to 0V supply. You should see a voltage that is about 2.5V with no current and that increases when current flows. If the voltage decreases with increasing current then reverse the wire that goes through the hole (reverse the current flow).

Pins 3 and 5 on each comparator should have a voltage between 2.5V and 5V. (Negative of the meter on 0V). This voltage should be adjustable with the variable resistor for each channel.

Sorry I have not been back here earlier. Report back with the results of your tests.

 

Just a quick update. I've built the board from the diagram ....

A photo or two of your build might help the diagnosis. Sometimes a simple mistake is the hardest to see yourself.