Useful Circuits #1 Battery Backup cRIO Systems

[swatts]

How-do Lovelies.

I thought it might be useful to do a complimentary set of articles on useful circuits and hardware we have employed in some of our projects. This one was used as a battery back-up for a monitoring system monitoring Azipods on ships.

What is an Azipod I don't hear you cry. Check out https://en.wikipedia.org/wiki/Azipod to learn all about them. Below is the first one!

https://en.wikipedia.org/wiki/Azipod

The system had a fair few requirements regarding materials, explosion and water ingress. One of the requirements was coping with a dodgy and interrupted power supply. Why not use a UPS I hear you ask...we couldn't and it was neater to package our own is the answer.

From a design perspective this would be a bit of kit that could be deployed on various ships, monitor various things and have very different power requirements so putting the batteries in a separate box worked nicely.

Having a nice wide range of inputs on the PSU makes life easy and this can both charge the batteries and power the equipment.

One useful piece of kit was the monitoring relay (Carlo Gavazzi DUA52). The blurb from the manual describes it like this..

"DUA52 is a voltage monitoring relay that measure its own power supply. The measuring ranges are 8-28 VDC and 38-58 VDC. It has separate potentiometers for setpoint and hysteresis. Typical applications are monitoring of backup batteries, batteries on diesel generator sets and the like."

In short it measure the power supply and switches on at a certain voltage and off at another voltage, there's some potentiometers on the body that allow you to adjust these values. You set the value and the hysteresis. In our case we set the relay to turn off at 18Vdc and back on at 22Vdc.

I'm told this scheme is good for the lifecycle of the battery. (2 off Yuasa NP 12-12 in series, lead acid was a requirement).

Also the cRIO doesn't like having power removed in an unplanned manner, if you find you're having reliability problems it's almost always to do with this. So it's a good idea to shut down the cRIO before the monitoring relay goes off. A monitor line was added to allow this. Even if you don't do this it is good practice IMO to drop the power out at a low voltage and only apply it again when the voltage is higher.

If this type of article is of interest, the next one will be about custom keyboards for cRIOs.

Lots of Love

[Thoric]

Cool. Thanks for sharing, this could prove useful in future systems. Although I've never yet suffered a brown-out issue on my own cRIOs, I have heard of problems associated with power disturbances.

In one of my installations, the cRIO isn't ever shutdown, the power is simply pulled. This is because there wasn't a simple way to setup a clean power down, that I could see, so the application is simply killed dead with a power off. So far (hundreds of power off instances) I've had no issues from this, but my system is local and easily repaired if something goes wrong. For your application above I can see the need for reassurances that it won't ever go wrong! Great work (to use your own terminology) matey.

[swatts]

There is a known issue with linux systems (and cRIOs) when the power is jittered on and off rapidly if I remember. On the whole they are very robust tho'.

[Swinders]

Interesting to see details on the 'other' parts of the system. From what I can work out the battery is being charged while the main power is applied but takes over on loss of power. The clever monitoring relay then disconnects the power from your equipment when the voltage drops too low and reconnects when it has recovered sufficiently. Nice.

@Thoric - I was looking at a way to cleanly shutdown a cRIO and came across a document that may be useful if it's running NI Linux Real-Time: Shutdown NI Linux Real-Time Devices via Software

There seems to be a missing image but it's making use of a call to a standard library 'glibc'. Seemed to work well at the time.

[swatts]

You got it Swinders!

The job was a mad rush (4 weeks to design, build, CE mark, deliver and fit!), so there may be improvements that can be made. It worked pretty well in practice.

[PiDi]

To add a bit more options for battery backup / power jitter elimination when using cRIO, there are some out-of-the-box solutions, like:

• UPS modules for DIN rail mounting, like this: https://www.phoenixcontact.com/online/portal/pl?uri=pxc-oc-itemdetail:pid=2906994&library=plpl&tab=1
• power buffer modules (to eliminate short drops in power): https://shop.murrelektronik.pl/index.php?lang=14&cl=search&searchparam=mb+cap

I'm not selling anything here, just sharing some findings, there are a lot more companies that do such things. And as non-electrician I'm sometimes suprised and amazed by the components you can find 🙂

[swatts]

We use a lot of phoenix contact stuff in our wiring, I like their stuff a lot. 

I agree, there's loads of interesting kit out there. 

[Intaris]

This post led me down a rabbit hole of reading about the relative efficiencies of front-mounted and rear-mounted propeller systems. "Lost" a day. My father was a fisherman and the fuel cost was always the main thing to be aware of (well, aside from catching fish of course). The differences in efficiency I've been reading about would have made a huge difference to the cost-efficiency of the entire industry (And CO2 output, just in case Greta passes by).

I love learning about things I currently don't know. So cheers for that! Now there's only infinite minus one things I don't know. 😂

[swatts]

Even the word azipod is cool to me!, I love all the maritime stuff, because is it is so different to what we normally do.

Maritime Baby!