Insane Hydraulics
Bold and audacious blog about fluid power
Most of you already know that I primarily work with hydraulic stuff that has something to do with mining - call it a perk or a curse, but my current location pretty much mandates it. I'll always enjoy a good "underground troubleshooting challenge", but I will never get used to coughing out stuff that I usually cough out when I spend enough time underground. Yes, even with the dust mask. So this is definitely a love-hate relationship, and even though I already have "divorce plans" underway, it is what it is for now.
But Lady Destiny always keeps things in balance, which means that when you go to the worst locations, you are guaranteed to go to the best ones too - or at least that's what I was thinking when I got a call from a friend welder, asking for help with a hydraulic problem of the luxurious yacht he was working on. I had sold him this tiny 24VDC power pack and a matching wireless remote control the other day (for the hydraulic swim platform that he manufactured and installed on the said yacht) and it worked OK for a couple of test runs, but then suddenly stopped working - the DC motor was turning, there was oil in the tank, and yet - the cylinders would not move.
We have things like WhatsApp these days, so it was easy for the man to show me exactly what was happening, and as soon as I saw the tiny power pack "fail" as the man was pushing the buttons on the remote control - I knew why the cylinders were not moving.
The system was as simple as it could possibly be - a 3L, 24 VDC power pack from Hydronit, equipped with an NG06 4/3 directional valve to open and close the platform cylinders, a Quick RRC R02+ 869 MHz receiver and a 2-channel RRC P02 Pocket Transmitter. All I needed to know to recognize the malfunction I'm about to describe was that a DC power pack + solenoid valve combination was sold to a user, and a random person performed the installation. Here's a pic of this unit just to give an idea of what I am talking about. Just bear in mind that you're looking at an installation that is far from being finished:
But I am not on the boat yet, I am still on the WhatsApp call. And what do I see? I see that both of the LEDs in the DIN connectors of the directional control valve light up when a button is pushed, and, obviously, when you power both of the coils at the same time - nothing good happens. So, now I ask you - can you tell me the most probable cause for this to happen? Let me give you the context one more time - this a DC power pack, it has a solenoid-operated directional valve, and a "random craftsman" did the installation - in this case, the fact that it has a remote control is not important, it might as well have been a couple of push buttons - and the malfunction - both of the coils getting power at the same time - would have been the same.
And the answer is... (drum roll) ...diodes! Yes - diodes - the check-valves of the electrical world, which can be used for "logical powering" of components in DC systems. In the case of this (very common) system, you need to power the motor relay every time you power a solenoid of the directional control valve, and a couple of diodes are all you need to do so elegantly:
When a diode fails, it usually becomes a short rather than a gap, and now you should be able to see why, when the diodes shorted (and both of them did!) - both of the the DCV coils were receiving power whenever a relay in the remote control box was closing.
But why did the diodes fail? They failed due to the incorrect choice of their current rating. Certain components - like the DC motor relays, can pull higher than nominal currents (especially when cold), and if you choose a 1A diode for a 1A component - it will get fried into a short, but most likely not instantly, which will add to the confusion, because the system will function for a while, and then it will not. This pic shows the "original" diodes next to the ones I had in my toolbox that fixed the issue:
Diodes' current rating should be over-sized by 4-5 times (at least) for such an application.
So, in a nutshell - whenever I come about a system that has a valve or a motor relay that needs to be powered along with several other (presumably directional) electric functions - I think diodes - because this is how a lot of folks solve that "logic powering" problem, and then I recall how many times I've seen people use diodes with insufficient current rating and how a fused diode can cause unwanted actuation.
This is the moment when you ask me: "Dude, wait... If you're so good and knew what was happening to the system via a WhatsApp call, why did you end up on the boat then? Couldn't they just replace the diodes on their own? And what's with the wireless measuring gear hooked up to the power pack that we can see in the picture? You're not telling us everything, are you?"
You're totally right! Of course, when I saw the two LEDs light up at the same time, the first thing that I did was ask the man to remove one of the DIN connectors and see if the system would start to work - which it didn't, and then I asked him to take an Allen key and place it next to the coil to see he could feel the attraction of the magnetic field - which he totally could, so I had to go there anyway to see what was going on. So yeah... Go to the Algarve? Work on a Luxurious yacht? I guess I'll bite the bullet and make the sacrifice!
What was the problem then? Aside from the helplessly fried diodes, the power pack had an extruded o-ring in the pump's fanged connection (possibly due to me being not too careful during the assembly), and the leak was enough to make the system non-responsive (given the tiniest displacement of the GR0.5 gear pump):
I guess the biggest takeaway of today's rant would be the following advice:
Get yourself a strip of 10A rectifier diodes and always carry it in your electrical supplies toolbox. It will allow you to fix fried diodes on the spot, and with a little bit of "creative thinking", you'll be able to fix relay-based logic issues as well (at least temporarily)!