Hello All,
I am constructing a hydroponics controller and want a backup power supply, I want to use a couple of computer PSUs one as main and in case of failure one as backup. I will only be using 5v and 12v, about 6 nanos will be connected to the 5v and run pumps and fans, some mains some 12v via relays. My idea was to connect both PSUs to the mains and run the outputs to relays, the primary PSU would be connected to the NO contacts and the coils, the backup PSU would be connected to the NC contacts. In normal mode when both PSUs start up the primary unit would switch its output to the load, if it failed the contacts would automatically swap over to the other supply. As an addition the main supply could also switch the secondary supply into standby.
Any suggestions on this scenario?
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These usually need a minimum load to function properly.
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Old computer power supplies are often overkill.
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It’s best if you draw us a schematic showing all power supply connections.
What load currents do you need ?
When the relay switches there will be a momentary loss of power to all the Nano causing them to reset or possibly freeze. Also other attached electronics may need to be reset.
Is this acceptable?
Sounds viable if interrupted supply switch is acceptable. Also, it would work like expected in case of total failure, like blown fuse. Not so well in case of unstable voltage or continuous shutdown/restart loop.
On the other hand, why should the psu fail and not something else? More circuit means more possible failure-points.
Hello Jim-p
Reset isn't a problem, freeze woud be. Was thinking of capacitors across the nano supply lines to prevent glitches causing a problem
Hello kmin,
Understand your point of view, the PSU would need to be on 24/7 I have ensured the nanos will be an easy swap with spares and will have a watchdog text my phone in phase 2 to the development
So much simpler to use a power bank that is plugged in. If mains power is lost, the power bank will keep everything running for as long as it has power. The larger the bank, the longer the runtime. You can calculate it using your load watts / bank watts
EDIT the formula is upside down, bank watts / load watts will give you run time.
I second @sonofcy's suggestion. Instead of a common wall wart or loose battery, use a power bank with built in charger. They typically have a folding mains plug and are getting cheaper by the day.
If you need more than one voltage, consider using a newer PD capable version along with a USB Type C Power Delivery Dummy Breakout board to select one of the available PD voltages.
Oh, and to get multiple voltages you'll need one with multiple USB-C connectors.
Yes, put a 12V, 7-9Ah SLA battery in parallel with the PSU. When the PSU is on, it will recharge and it will also help the PSU from tripping off unintentionally since PSUs often can source lots of current but sink almost none. So if you have any inductive loads, when they switch off, the battery will help prevent the built in PSU circuit protection from turning your whole project off.
Mine (Ecoflow, purchased on Amazon) includes and LCD screen to let you know the remaining hours given the load at the time. AC and DC sides as well. It's been pretty good so far (only a few months old though)
sonofcy:
Good idea if you want to cover mains down time. Our mains is quite reliable except for winter (when I won't be running the hydroponics) if the systen goes off for a few minutes or even an hour its not a problem, I want to cover the PSU failing hours overnight, or a few days if I am away from home.
They would need to be gigantic.
Do you know the maximum current everything will consume?
This is one option
Same for 5V
You could use the ATX PWR_OK and PS_ON# signals to to something a litle more complicated.
i have had 4 pc's running (intermittently) in my office since 2012 and in all that time have had 1 psu failure.
Of course they are driving loads they are designed for.
I'd suggest the reliability of the psu far outweighs the reliability of the mains supply.
Why do you think failure is sufficienttly lilely to justify the complication?
johnerrington
I have also had computers running intermittently and have had a couple of failures, this system would run 24/7 for 9 months at a time, as mentioned I don't mind if the mains fails for an hour or so and the system starts up again, I am trying to prevent an overnight outage where my plants dry out, which could cost me 8 weeks worth of growing time.
Due to a power failure or a power supply failure?
Using two ATX won't help in a power faiure.
Why don't you buy a real UPS?
jim-p
Yes almost exactly what I was thinking, only using the 5v for the logic (7 nanos + I/o devices) and using the 12v and mains for load, eg pumps, fans, heaters etc. I was also thinking of using a relay to switch the standby on the backup PSU. Not sure why you have the diode and capacitor. I would place a small cap across each Nano to provide power when the system switches. My background is software so my electronics is very sketchy with many gaps, just what I picked up over the years. Will try to include a diagram.
The diode will conduct and supply current to the output while the relay is switching so that the output voltage won't go to zero and cause a system reset. The capacitor will help in keeping the output at 12V while the relay is switching.
Have a look at this device. It's nice because it can do load sharing as well as switch over without any power loss and it's all solid state. You can also hot swap power sources wthout any power loss.