Flyback diodes on boats

[markxengineerin]

I have been using a diy "chain counter" and "head flush stroke counter" (to see when tank is getting full), both based on counting pulses of this sensor with an Arduino


They work well, but increment falsely when I let off the windlass power button, and when the main house fresh water pump turns off. I fixed most of the problem by ignoring all pulses that are too close together, but there's still a single false one on each event. Not enough to make a difference, but I'd still like to get rid of it.

A flyback diode is commonly use to eliminate sudden voltage spike when current drop across an inductive load.

I have seen these in automotive circuits (big fans), but don't think in any boat application yet. Wouldn't windlasses need them, considering the power involved? What's a good size or part number for these things, and is there any disadvantage to going too big in power rating?

Installing them might not only be good for these prox probes, but also for life of electronics in general, if there really are voltage spikes happening. How fast would an oscilloscope need to be to catch these potential spikes? I might try measuring if what I have is fast enough.

[Wotname]

There isn't a lot of power in inductive spikes, there is lot of voltage but not much current so choose the diode on it's V rating rather than it's A rating. If it is too small and goes OC, get a bigger one.

Inductive spikes are long time events so most 'scopes will find display them.

[markxengineerin]

Thanks, how does this one look? The windlass is rated to 200 amps, so I know the current isn't the key spec, but I figure more is better, and this goes to 600 amps surge, 1000V, highest I could easily find. Still inexpensive

https://www.amazon.com/Madd-10A07-Di.../dp/B08KSF469V

[Lake-Effect]

Your sensor circuit to the Arduino input may simply be too sensitive. Try lowering resistance values on the interface circuit to attenuate interference, induced spikes etc. The sensor has a transistor buffer built-in and can apparently sink up to 300 mA, so there's lots of drive capability there.

Also make sure the Arduino is well-protected from glitches on its power rail, or entering via other inputs.

[Wotname]

Originally Posted by markxengineerin

Thanks, how does this one look? The windlass is rated to 200 amps, so I know the current isn't the key spec, but I figure more is better, and this goes to 600 amps surge, 1000V, highest I could easily find. Still inexpensive

https://www.amazon.com/Madd-10A07-Di.../dp/B08KSF469V

The diode goes across the motor, not in series with it. In normal operation, the diode is blocking and becomes conducting when the voltage (thus current) is removed from the motor. The back EMF is always of the opposite polarity to the operating polarity.

So the operating current of the motor is irrelevant.

[markxengineerin]

This advice found on another site (not directed at my application) made it sound like current could be important. Maybe not the operating current of the motor, but the current from the back EMF? I imagine this could be somewhat proportional to the size/current of the motor, and windlass motor is pretty big. I ended up getting a variety pack that was more cost effective, with the most promising candidate in it being 10A10. Will see how it does. Since these are so cheap, do most DC motors used on boats already have them, internally? If not, why not?

@lake effect, the power to the Arduino is coming from one of MPJA's cheap dc/dc step down converters, I have several varieties but I think this one:
https://www.mpja.com/Micro-Adjustabl...info/35371+PS/ takes the boat's 11 to 15volts and makes a steady 5V that I feed right to the 5V pin.

The circuit to read the prox sensors uses the internal pullup resistor available on the Arduino. I think they are between 20k and 50k ohms.

the larger the resistance for the pull-up, the slower the pin is to respond to voltage changes. This is because the system that feeds the input pin is essentially a capacitor coupled with the pull-up resistor, thus forming a RC filter, and RC filters take some time to charge and discharge.

If I understand you correctly, you're suggesting to use an external pull up resistor instead, of a larger value. Any suggestion for what value?

[team karst]

Originally Posted by Lake-Effect

Your sensor circuit to the Arduino input may simply be too sensitive. Try lowering resistance values on the interface circuit to attenuate interference, induced spikes etc. The sensor has a transistor buffer built-in and can apparently sink up to 300 mA, so there's lots of drive capability there.

Also make sure the Arduino is well-protected from glitches on its power rail, or entering via other inputs.

Yes; both these actions are headed in the correct direction. High Z lines “out in the world” are trouble. They become like a sensitive antenna, picking up noise. Plus, working with low power circuitry will be easier, done once, rather than attacking all the high power culprits.

[markxengineerin]

More detail on each action would be helpful- the reading I did suggested a higher resistance for the pull up resistor to improve filtering, not lower, so I must not understand what you mean by the interface circuit. And is a cheap DC/DC converter considered good protection from power rail spikes? There are no other inputs to the Arduino besides the Prox Probe, although outputs, between the two applications (each has it's own Uno) include LED lights, a buzzer, and a LCD display.

[team karst]

Originally Posted by markxengineerin

More detail on each action would be helpful- the reading I did suggested a higher resistance for the pull up resistor to improve filtering, not lower, so I must not understand what you mean….And is a cheap DC/DC converter considered good protection from power rail spikes? .

High pull up R is bad. I would be thinking on the order of 1kOhm. That will settle down the input. As far as power in, what is the mA power draw of the up system? Or just try the 1k and see where that gets us. Also, what is the max pull down mA allowed?

[markxengineerin]

I will try the 1kOhm and also try to measure the current on this circuit. Now that I think about it, I can't remember how I powered the proximity sensors- but probably they got 12V power directly from the battery, since they need >6 volts (would not work from the 5V dc/dc supply that powers Arduino). Basically would look like this:

Except using internal pull-up resistor instead of the 10K external shown here. So the suggestion is to do this instead, with 1K replacing 10K.

what is the max pull down mA allowed?

The proximity probe says 300mA sink, is that what you're asking?

[team karst]

yes, that 1k ohm is well within the limit. 12mA vs 300. Running raw 12V is a risk, since 12V in the boat runs about everywhere, and is considered "dirty". If the 1k helps but not enough, I'd might consider a 12v to 8V regulator. like a 7808 or similar...

One of the first rules in EMC control is to know 3 items. Culprit, victim, and transmission path. The transmission path is still sketchy here...

[dfelsent]

Or a filter cap on the input along with a 1k series resistor. 0.1 microfarads goes a long way. So from the signal 1k in series then 0.1 uf to ground then on to the input. Or even 1uf. Use 50v ceramic capacitors. Keep the cap leads short to filter high frequencies effectively.
I like the idea of the diodes too. Water pump 1N4004 or thereabouts. Windlass might have enough stored energy to blow one of those out so I’d go for a bigger diode. Much of the stored energy in the inductive load ends up in the diode. So a fatter ( higher current rating ) diode might survive better. And on the windlass don’t forget to snub the solenoids/relays. My gut says they are more likely to be the culprit than the motor. And depending on the motor (2 wire vs 3 or 4 wire) you may need to use a transient suppressor rather than diode because of the reversing polarity. A small cap can help there too. Don’t use a big one as the surge on energizing the motif can be tough on the relay. It use a 1uf in series with a 1 or 10 ohm resistor to limit the surge.

Lots of ways to address this. Many will work. Good luck!

[markxengineerin]

So many ideas, thanks! I'll start with the easiest, which for me is to supply 8V instead of 12V using a 7808, and swapping to 1k resistor. Will report back in a few days.

[hjohnson]

For your holding tank, I’d wager that a throw in pressure sensor is probably a more reliable measurement. They’re made from stainless steel, and draw between 4ma and 20ma depending on how deep the water is. They also cost $40, so cheap and reliable. Panbo had an article on this in reference to the victron gx tank 140, but there’s no reason you couldn’t use the sensor with an arduino. I’m monitoring my Bilge sump, holding tank, and hard potable water tank this way.

[markxengineerin]

It might be possible to add a sensor to the holding tank, but I have no space on top (v berth mattress sitting directly on top). I do have a SCAD TM2 tank monitor that does it wirelessly from one of the side walls, but it can be flaky at times when it's humid out or when the wall it's mounted to gets wet (condensation, from cleaning, whatever). So far, the repeatability of this stroke counter thing is +/- 5 pumps on 460, pretty good! I've been using it for 3 or 4 months now.