Alarm and Control Module for dual power supply

Thread Starter

khrissicks

Joined Jul 20, 2022
7
I'm running two Desktop AC-DC power supplies that I wanted to add an alarm/control module to, so that it can indicate to me when one of the power supplies goes bad (below a certain voltage).

Has anyone seen pre-made circuits that can indicate when the power supply goes bad?

Specs:
15V 1A power supply
 

Thread Starter

khrissicks

Joined Jul 20, 2022
7
Yes,

Each are powered separately. I'm navigating through the forum now to see if there is a similar circuit. There's a few drone battery indicator pcb's. But those won't handle the current rating I'm looking for.

Ideally, I'd have two power supplies in parallel, when the indicator goes off on one, I'd quick swap it as it runs on one power supply, so my system does not go down.... Unless they both go down at the same time...
 

LowQCab

Joined Nov 6, 2012
2,342
Can your Load still operate properly if the Power-Supply-Voltage is lowered by 0.7-Volts ?
If so, all you really need is 2 Diodes rated for the maximum Current that you Load draws.
Why do You expect that one of the Supplies may fail ?
What are the consequences of failure ?
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Thread Starter

khrissicks

Joined Jul 20, 2022
7
Yes, the load can still operate properly if the power-supply-voltage is lowered by 0.7 volts.

I expect one of the supplies to fail since they've been used for 5+ years, and others have failed in the past since they are approaching their life span.

Additionally, the load is going to be on for 6 months straight without powering down, and this may cause a power supply to fail.

I want to make a redundant power supply package that will allow me to swap out the bad power supply if one of the two fails.

A diode will work, I'll just have to set it up to signal 2 volts lower than the power-supply-voltage so it can indicate that power supply failed?

Thank you
 

LowQCab

Joined Nov 6, 2012
2,342
OK, so a Diode for each Power-Supply, ( why not run ~3 ),
and a TL431 monitoring the Output of each Power-Supply,
which will provide "up to" a 100ma Digital-High-Signal if
the particular Power-Supply drops below a pre-set Voltage.
( 50ma or less would increase reliability )
( This Output can be increased to ~5-Amps with the addition of a small FET )

The TL431s "act like" an open Collector-Comparitor and are very precise.
What will You be doing with the "Fail" Signals ?
Will You need a Low, ( instead of a High ), Fail-Signal ?
If You need a High Fail-Signal, what Voltage must it be ?
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Thread Starter

khrissicks

Joined Jul 20, 2022
7
With the Fail signal, I'd use it to signal a buzzer or Red LED to indicate the user that the power supply failed. A buzzer would be ideal, but a light indication can work, I would just make a note to check the light indicator daily.

Ideal Function:
15V,1A AC-DC power supply 1 connects to diode, then to section 1 of a two to one power cable that connects to load
15V, 1A AC-DC power supply 2 connects to diode, then to section 2 of a two to one power cable that connects to load
Fault indicator connected to section 1
Fault indicator 2 connected to section 2

- If I place two fault indicators, one in section 1 and another in section two. Then when the fault indicator is triggered (turning LED off or switching from green to red) by a bad power supply (dropping 2V). Then I can visually see that one of the power supplies went bad, disconnect it without disrupting power since the other power supply is running of the split, and re-connect a new power supply, so then the original good one is still there and the bad one has been replaced with a good one, and now the fault indicator component can turn back to green showing that the power supply is good.

The idea is to safe proof the load to never turn off, and having a fault indicator if one of the power supplies was to go bad. If three power supplies is the better approach, then I'll look into pursuing that route.

Thank you
 

LowQCab

Joined Nov 6, 2012
2,342
Here-Ya-go ...........
The FETs were chosen based on the fact that DigiKey has 10,000 of them in stock.
An "ordinary" LED that doesn't Flash is much cheaper,
but I think the flashing will draw more attention.
The Circuit will turn On the appropriate LED when the Voltage Output of the bad Power-Supply
drops lower than ~2.5-Volts below the Voltage of the "good" Power-Supply.
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Power Supply Failure Indicator FLAT .png
 

Baker Steve

Joined Feb 21, 2016
16
This looks pretty close to perfectly suited. And it's cheap, too.
There are also kits in the usual places for this sort of thing. Some are aimed specifically at 12v battery supplies, which is what I use them for. They sound a buzzer when the voltage drops below a preset limit, to prevent complete draining of the battery, which can seriously shorten its life.

I appreciate you're not using batteries, but you might find them helpful nevertheless. Here's one:

<https://www.amazon.co.uk/gp/product/B08DHZNY91/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1>
 
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