All i had was 1N4001. I'd like to engineer it to use 15 amps, unless there's a reason not to.
Looking at another example on the site a bridge rectifier is used. Maybe this would be a better alternative to individual diodes?
Other example:
http://www.circuitous.ca/OptoBOD.html
rectifier: something like this
Skeeterweazel:
Would a comparitor work as a "test" to check for voltage difference in the 2 blocks? The output could go to the gate on the mosfet?
Thx.
Better to measure the current for each block I'd have thought. In other words use proper shunt resistors rather than hoping the wiring loss does the job.
Skeeterweazel:
Lots of good stuff here. Thx.
I don't need the east/west sensing. Could i delete these parts?
IC2
IC3
R9,10,12,7,11
D5,6,7,4
The upper rail is +5v and the blue rail is 0v?
Could it be powered by 12v? And would that require some changes to the resistors?
Thx.
Marty
The non-direction sensing version is here:
http://www.circuitous.ca/DccBOD339393.html
In the first example here, why couldn't you use the optoisolator to turn on the LED directly, and not use the comparator?
Thx.
http://www.circuitous.ca/OptoBOD.html
To get a well defined threshold and clean on off behaviour? I don't think it is needed.
Skeeterweazel:
In the first example here, why couldn't you use the optoisolator to turn on the LED directly, and not use the comparator?
Thx.
http://www.circuitous.ca/OptoBOD.html
Actually, that circuit is not good enough, even with the comparator. The current pulses as they appear in the opto output are too small, the comparator provides amplification and clipping. A practical detector needs a "hold" timing circuit because the track current pulses are variable and intermittent. Also, you need an output that can drive external circuits reliably. Here's a link to the detector that I have, it uses discrete transistors as drivers and has capacitors for the "hold" function:
Thx for that link.
I kinda understand it. But have these questions:
What are the Sj1-SJ4?
Are the outputs on X4-1 to X4-4 positive or ground? I need a sinking output.
Thx.
Marty
Skeeterweazel:
Thx for that link.
I kinda understand it. But have these questions:
What are the Sj1-SJ4?
Are the outputs on X4-1 to X4-4 positive or ground? I need a sinking output.
Thx.
Marty
SJ1-SJ4 are PCB shorts (normally closed jumper), to enable a low voltage option that I don't fully understand. But the normal build would include the jumpers (traces connect directly, do not cut), and omit resistors R9-R12. It has something to do with negative feedback in the transistor circuit.
The output is a sinking type.
Question re: mosfets: i bought a couple of these to try. I played w/ one today; used it to power the train @ 1amp and 20 volts.
One i have is p40nf10. I bought it just based on it's amp capacity.
It is getting really hot. Poking around for answers this evening it appears maybe it is not turning on all the way. I have the gate connected to 5v. Datasheet says VGS +- 20v, and VGS threashold of 4v. I'm not exactly sure what these mean. I saw a Youtube video where mosfet was turn on/off just by touching it, because gate is looking for a "charge" as much as voltage.
If someone wouldn't mind educating me a little on mosfets , and maybe suggesting a better part i'd would appreciate it.
Thx.
Marty
Edit: Trying it again tonight with a lighter amp load, it has almost a 4v drop across the source and drain. Guessing that is not right.
Skeeterweazel:
Datasheet says VGS +- 20v, and VGS threshold of 4v. I'm not exactly sure what these mean.
It means the FET is not actually turning on at 5 V, just passing enough current to heat it up.
You will need to apply about 10 V to the gate to turn it on satisfactorily, not 5 V. See the bottom line of table 4 where it says that RDS(on), the Static drain-source on resistance at VGS = 10 V, ID = 25 A is 0.025Ω typical, 0.028Ω maximum.
If you want it to turn on at 5 V, you need a "logic level" FET which specifies RDS(on) at 4.5 V. 