AC / Li-ion Battery Power Supply: 24 V DC Output for DC Amplifiers

[1100xxben]

I'd be careful using switching power supplies in series (bricks, wall warts, etc.). They're not isolated from the AC mains. Putting their outputs in series is like shorting the mains through the switching components. Only transformer based PS's are truly isolated from the mains.

As a general statement, that is not true. Yes, there are switching supplies that are not isolated, but there are plenty of switching power supplies out there that have isolation (I would guess that most like the one linked above do). The one linked above may very well have isolation, but the manufacturer does not supply enough technical information to be certain. The part that says DC24V-4 on it looks like a transformer to me, and there looks to be a clear separation in the board between the input and output side, with the 4-pin through-hole device being an opto-isolator for feedback.

All that being said, there's not enough info from the manufacturer to guarantee isolation, so it would need to be tested. However, based on how the circuit looks and how cheap the power supplies are, you could easily buy 2 and test them.

[dmormerod]

As a general statement, that is not true. Yes, there are switching supplies that are not isolated, but there are plenty of switching power supplies out there that have isolation (I would guess that most like the one linked above do). The one linked above may very well have isolation, but the manufacturer does not supply enough technical information to be certain. The part that says DC24V-4 on it looks like a transformer to me, and there looks to be a clear separation in the board between the input and output side, with the 4-pin through-hole device being an opto-isolator for feedback.

All that being said, there's not enough info from the manufacturer to guarantee isolation, so it would need to be tested. However, based on how the circuit looks and how cheap the power supplies are, you could easily buy 2 and test them.

Thanks. Yes I have 2 on order, as well as 2 of the battery boards. So I'll try feeding each battery board with their own PSU and then put the battery board output in series and see if I get 24v or a puff of smoke..lol..

[Millstonemike]

As a general statement, that is not true. Yes, there are switching supplies that are not isolated, but there are plenty of switching power supplies out there that have isolation (I would guess that most like the one linked above do). The one linked above may very well have isolation, but the manufacturer does not supply enough technical information to be certain. The part that says DC24V-4 on it looks like a transformer to me, and there looks to be a clear separation in the board between the input and output side, with the 4-pin through-hole device being an opto-isolator for feedback.

All that being said, there's not enough info from the manufacturer to guarantee isolation, so it would need to be tested. However, based on how the circuit looks and how cheap the power supplies are, you could easily buy 2 and test them.

I didn't see the link to the supply. With the transformer, it may very well be isolated. But I stand by my original statement for "bricks" wall arts, etc that do not have transformers inside.

[dmormerod]

Our PM reached out to Sure regarding the design. They mentioned the design may cause short circuit and sent over a revised schematic for reference. We are also bringing this in as a Dayton Audio product. Our version will have external LED's and external charge status indicators.

Maybe I'm being stupid but the -ve connections shown in the schematic on the battery boards, are they the VCC GND or the battery -ve?

[dmormerod]

Maybe I'm being stupid but the -ve connections shown in the schematic on the battery boards, are they the VCC GND or the battery -ve?

Ok I was being stupid. Figured it out.

[dmormerod]

Our PM reached out to Sure regarding the design. They mentioned the design may cause short circuit and sent over a revised schematic for reference. We are also bringing this in as a Dayton Audio product. Our version will have external LED's and external charge status indicators.

I'm obviously doing something wrong because as soon as I apply power to the coil my DPDT relay just constantly switches. Could this be caused by the switch mode 120ac to 24v dc power supply I'm using?

[Millstonemike]

I'm obviously doing something wrong because as soon as I apply power to the coil my DPDT relay just constantly switches. Could this be caused by the switch mode 120ac to 24v dc power supply I'm using?

Doubtful is the PS. What I didn't show in the picture (my bad), is that one coil connection is to the PS V+. The other is to the PS ground (negative). Perhaps you have it hooked up someplace else.

[dmormerod]

Doubtful is the PS. What I didn't show in the picture (my bad), is that one coil connection is to the PS V+. The other is to the PS ground (negative). Perhaps you have it hooked up someplace else.

It’s when I connect one side of the coil to the PS +ve and the other side to the PS -ve that I get the constant switching.

[Millstonemike]

It’s when I connect one side of the coil to the PS +ve and the other side to the PS -ve that I get the constant switching.

Pic of the relay showing the part number ...

[dmormerod]

Pic of the relay showing the part number ...

It's this relay : https://www.parts-express.com/nte-r14-11d10-24-10a-24-vdc-dpdt-general-purpose-relay--075-126

All I can think is I've wired it wrong. Looking at the schematic would the connectors read 1-3-5 along the top and 2-4-6 along the bottom?

I think I've wired it as 5-3-1 and 6-4-2 reading left to right.

[Millstonemike]

It's this relay : https://www.parts-express.com/nte-r14-11d10-24-10a-24-vdc-dpdt-general-purpose-relay--075-126

All I can think is I've wired it wrong. Looking at the schematic would the connectors read 1-3-5 along the top and 2-4-6 along the bottom?

I think I've wired it as 5-3-1 and 6-4-2 reading left to right.

I'm confused by your wiring explanation. Looking at the schematic, your number sequences should be aligned with the left side and right side, not the top and bottom.

In lieu of some esoteric problem with the relay, the oscillation when powered points to a coil wiring problem.

This is the schematic for your relay. The numbering is as if your looking at the relay's contacts (not over the top of the relay) You should have 8 contacts (any different and you were shipped the wrong part).

The two contacts at the bottom, their spades orientated different than the other 6, are the coil's contacts. Those would be connected to the PS + and -.. Verify that and we can move on solving the problem.

[dmormerod]

I'm confused by your wiring explanation. Looking at the schematic, your number sequences should be aligned with the left side and right side, not the top and bottom.

In lieu of some esoteric problem with the relay, the oscillation when powered points to a coil wiring problem.

This is the schematic for your relay. The numbering is as if your looking at the relay's contacts (not over the top of the relay) You should have 8 contacts (any different and you were shipped the wrong part).

The two contacts at the bottom, their spades orientated different than the other 6, are the coil's contacts. Those would be connected to the PS + and -.. Verify that and we can move on solving the problem.

I was referring to the wiring schematic for the solution. What I realized is, if you look at the relay diagram, turn the relay 90 degrees clockwise and that's how I've wired it, when I should have probably turned it anti-clockwise. See my attached as to how I've currently wired it.

[Millstonemike]

Perhaps bad wiring is shorting the out the PS when the relay is activated. That will cause the switching PS to shut down, the relay will then release and the PS will recover. Then the relay will close again causing the short and the PS will shut down ... and the oscillations will continue.

Here's the pin by pin wiring for the relay - pin numbers in blue. If the wiring is correct, and the problem continues, then maybe another diode is needed as shown in blue. I seem to remember that the PS + cannot enter the BMM through Bat + (I thought I verified this during the design phase but can't specifically recall that).

[dmormerod]

Perhaps bad wiring is shorting the out the PS when the relay is activated. That will cause the switching PS to shut down, the relay will then release and the PS will recover. Then the relay will close again causing the short and the PS will shut down ... and the oscillations will continue.

Here's the pin by pin wiring for the relay - pin numbers in blue. If the wiring is correct, and the problem continues, then maybe another diode is needed as shown in blue. I seem to remember that the PS + cannot enter the BMM through Bat + (I thought I verified this during the design phase but can't specifically recall that).

Thanks for all your help. I’ll try reconnecting based on your changes and let you know.

[dmormerod]

Perhaps bad wiring is shorting the out the PS when the relay is activated. That will cause the switching PS to shut down, the relay will then release and the PS will recover. Then the relay will close again causing the short and the PS will shut down ... and the oscillations will continue.

Here's the pin by pin wiring for the relay - pin numbers in blue. If the wiring is correct, and the problem continues, then maybe another diode is needed as shown in blue. I seem to remember that the PS + cannot enter the BMM through Bat + (I thought I verified this during the design phase but can't specifically recall that).

I corrected the connections but still had the issue. I added the additional diode and that seems to have fixed it, so many thanks!