Series Power Supply Safety Circuit

[ronv]

I'm just going to think out loud a little bit. How about a switch like this:
https://no.mouser.com/ProductDetail...MAyF9RBguZAyGKGYIat%2bCQnNZ8Ptq/2NdKqHxz1yw==
Thru one set of momentary contacts we run the AC line to the supplies, so when you push the switch they turn on, when you release it they would turn off, except we will wire a relay across the contacts.
https://www.mouser.com/ds/2/418/NG_DS_ORWH_series_relay_data_sheet_E_0411-124938.pdf
The relay turns on if the voltage is above 18 volts (your comparator idea) and keeps them on. If the voltage is not above 18 volts they will turn back off when you release the switch. To turn it off you press the switch in the opposite direction and it turns the relay off. I think we could power the comparators from the big supplies. Maybe we could light a red light if you press the button and both supplies don't come on and a green one if they do so there would be an indication of power on and of a fault.

 

[jocanon]

Nice, I'm liking it...I think the indicator lights are a fantastic idea. I could put it all in an enclosure mounted on top of the power supplies, or as another option in-line with the power cord hanging behind the supplies...

 

[ronv]

OK. Let me see what I can come up with. Right now I'm kind of the opposite of you. I'm a hobbyist by day, and a CPA by night. Meaning I have to get my tax stuff together.

 

[jocanon]

OK. Let me see what I can come up with. Right now I'm kind of the opposite of you. I'm a hobbyist by day, and a CPA by night. Meaning I have to get my tax stuff together.

I hear ya...right now I am a CPA by day and by night! Still at work now.

 

[ronv]

How's the new job?

 

[jocanon]

It's great. I really like where I am at now.

 

[KeepItSimpleStupid]

Let's ask a question:

What should happen when there is a brief power failure?
1) Come back on
2) Stay off

On (2) kinda thinking about an ON/OFF type switch with an ON and momentary ON. The ON turns on both supplies and ignores protection. Once they are up and running, the next momentary pulse enables protection until a power fail or voltage fail.

Implementation - not even thinking about it right now.

 

[jocanon]

Hm, interesting question. Kind of leaning toward comes back on. I can't really think of any reason to not have it come back on. But if that ended up creating problems, I don't think it would be a big deal if it stayed of and it had to be power cycled to come back on either...so I guess either way seems fine to me.

 

[ChrisP58]

If these supplies are originally computer supplies, do they have a low power "on" pin that needs to be grounded to enable them? If so, you could probably do something with that pin and a couple of opto-couplers to shut down both supplies unless both are OK.

You may still have a startup issue but, if the supplies have a low power "always on" output, you could probably work out a rising edge detector from that to get it all started.


As for your earlier question about one relay or two, you would need two 12V parts because, once energized, a relay will stay engaged even after the voltage drops to below 20% of it's rated voltage. So a 24V relay will stay on even when it is only feed 12V.

 

[4pyros]

As for your earlier question about one relay or two, you would need two 12V parts because, once energized, a relay will stay engaged even after the voltage drops to below 20% of it's rated voltage. So a 24V relay will stay on even when it is only feed 12V.

The relays are cheep. And yes you will need a start/stop switch.

 

[Misterbenn]

On the off chance, just check your power supply doesn't have a control line, a type of logic level input which might allow PSU on/off control.

-- Edit --
ChrisP58 got there first!

 

[jocanon]

It does have a way to turn it off as Misterbenn and ChrisP58 suggested. But I want to see how expensive it would be to make an AC power cord that will do this because a lot of guys I know already have these power supplies that they bought either from me or someone else on the secondary market and they do not really feel like/comfortable doing ANY mods themselves, even if it is very simple. I was thinking if I could just give them a power cord that will take care of it. But by the time we are done, I need to see what the total cost to build comes to and that will also factor into it (if it cost too much, may not be worth it).

edit:
Also, I was hoping to find a universal solution that will work with any 24v power supply made up of 2 x 12v supplies in series.

 

[KeepItSimpleStupid]

There may be another option and that is to use an electrically operated circuit breaker. Remember, I'm thinking out load here.

With these types of breakers, a contact closure is provided to the breaker and that contact MUST be powered from the switched side. Once the contact is closed, the breaker unlatches (sometimes by heat) and the power is removed from the equipment.

SO, it gives you a nice power switch. Alarm contacts on the breaker can be had too.

==

That out of the way, the other issue is the 50 A that we could be dealing with. Somehow, one needs to make those wires safe and with that means a connection up close. Fused up close would work.

A 555 timer can be used as a comparator and that could be a place to start.

By assuming that you will always have a functioning supply, we are assuming that only one will fail at a time.

So, think of a device that hooks to the output of the supply, with the inputs fused as soon as possible and provides a contact closure to a externally mounted breaker.

Many supplies have a NOT SHUTDOWN pin and it's possible that could be exploited.

When having protection and two power switches, you may not be able to get the devices on unless you turn BOTH on together.

It takes some time for a aux trip breaker to function.

Again, thinking out loud.

So, yea, it's not too hard to provide a signal that the power supplies are good, BUT you have to provide a start-up mechanism (delay) before it functions. Usually you also provide a delay before it reacts too, so you don't get nusense trips.

Mounting part of the device inside of the supply solves some problems - namely high current lines exposed. It might require two internal devices; one for each supply.

Some things my crystal ball can't see. i.e. do the supplies have a power switch? What's the mechanism of turn-on? Is turning on two together OK?

One note, is that operating power supplies in series, you should have protection, A big high current diode reversed biased at the output might be all you need for a more reliable system. The big guys recommend these when the supply is operated in certain ways, but they are not usually included.

If it were me, that's what I would do first.

 

[jocanon]

There is an on and off switch just a simple switch in-line with the AC power cord. more or less same concept as plugging them into a multi-outlet and then using the multi-outlet as your on/off switch. Correct my if I am wrong, but I don't think we have 50 amps on the relay circuit...that is at 110VAC 15 amps max. The only thing we need to do on the DC side is tap into it to get the voltage reading, but the current draw will be next to nothing. The power supplies are rated up to 50 amps on the DC out put, but out little relay is not drawing any DC current, right?

It is fine if they come on together, in fact that is how we do it. I have one switch, again, in the AC power cord, to turn them both on. Basically I switch the hot wire on the AC power cord.

I don't want to do any internal mods for this because I want someone that doesn't know anything about it to be able to just pick it up and use this as their power cord with built in on/off switch and shut down protection.

What's the reason for the big high current diode at the out put? I know a ton of guys that put these together in series and I know of nobody that uses that...not saying your wrong, I just don't know why it's needed.

 

[jocanon]

...double post

 

[KeepItSimpleStupid]

These are the diodes I'm talking about: https://power-topics.blogspot.com/2009/07/operating-power-supplies-in-series.html

I'd say, add the diodes and forget about the failure, because the failure may by the result of the lack of a diode. One supply tries to drive the other one in reverse and bad things happen. Battery charing requires a different sort of protection. The diodes only conduct in a fault situation.

My concern, is to how to safely connect two small wires that have the capability of carrying 50 amps. If those itty bitty wires short, you have a possible problem. An inline fuseholder like use din the auto industry would be fine. You might have 6" of unprotected wire hanging about. Something like: https://www.delcity.net/store/ATC-&...t_1.r_IF1003?gclid=CNqZ1Or70b0CFSqXOgod2FIAPA or similar.

PS: The breakers I talked about are called shunt trip breakers.

 

[jocanon]

Thanks, I'll have to look into that. Just to clear something up though, I am not having multiple problems with failures. Overall things have been pretty rock solid. Out of over 200 sold 9 have failed and it's almost always due to the fan going out which I think is just bad ball bearings in the fan.

 

[KeepItSimpleStupid]

Fan failure is a typical failure mode. Way back when, changing fans was part of the PM procedure for minicomputers. The bearings collect dust and then the fan stops. I've taken lots of them apart, at leasts the ones that I could, and salvaged them.

Turning booth supplies on at the same time is better for the supplies or put another way, the less likely the need for or a diode.

 

[crutschow]

Large Schottky diodes should limit the reverse voltage to about a half volt across the OFF supply terminals. I wouldn't think that would be a problem for any supply.

 

[jocanon]

I know that the power supplies are always turned on at the same time, or used separately (i.e. not connected in series) because what happens when you don't turn on one but connect them in series anyway and attach a load (i.e. only 12v but current running through the dead/turned off supply) is the problem that lead me here in the first place, you get smoke coming out of the turned off one. So if they are not turning them on at the same time I would definitely be hearing about it.