Strange power supply output

[Aleks]

Hi all,

I have a Weir SMM 50/15 A24 switch mode power supply that has 230VAC input and -15, +15, 5 and +24V output. The strange thing about it is that on the -15, +15 and +24V output terminals the voltage is pulsing ruffly about 1 time a sec. Is this its normal operation or is something wrong ?

In any case, what should I do to make it give a stable output ?

Thanks in advance,
Aleks

 

[MikeMl]

Likely you are running it either unloaded, or overloaded. What currents are you drawing off the supply while it is misbehaving?

 

[Aleks]

I really can't tell an exact number because I don't have a reliable ampere meter but, I know that a 12V car light bulb is flickering (1 time a sec) and my Kenwood TM-401A (which is rated to have around 0.5 - 0.6 A in stand by mode) is going wild.

PS: Forgot to mention that the 5V output is stable ...

 

[MikeMl]

I have had trouble with multiple-output switchers being unstable unless all outputs are loaded. Without a schematic and trying to rebuild it, I dont know what to suggest, except hooking a power-wasting dummy load on the unused outputs.

I see people here advocating the use of multiple-output PC switching supplies as general purpose lab supplies, and always see this as an accident waiting to happen...

73, de WA7ARK

 

[Aleks]

Uh... I'll try to dummy-load the rest of the outputs and see if that does any good.

Thanks for the advice,
73, de Z32AL

 

[Vizier87]

I know that a 12V car light bulb is flickering (1 time a sec)

From my understanding, a supply which has protection shuts itself off if it receives a certain impedance, like bulbs, they certainly have very low values. By the look of it, perhaps the supply flickers because of the heating which fluctuates the resistance between the terminals. My wall-wart behaves the same sometimes.

Are you using only the light bulb to indicate the stability? Have you powered up any other electronic circuits?

Cheers.

 

[Aleks]

From my understanding, a supply which has protection shuts itself off if it receives a certain impedance, like bulbs, they certainly have very low values. By the look of it, perhaps the supply flickers because of the heating which fluctuates the resistance between the terminals. My wall-wart behaves the same sometimes.

Are you using only the light bulb to indicate the stability? Have you powered up any other electronic circuits?

Cheers.

As I said above, my Kenwood TM-401A transceiver does that same thing, powers on and off in 1 second. Also I have connected a 24V rated FAN to it and it was not operating at full power and I could hear and feel a "bump" every 1 second when the 24V were high.

 

[Vizier87]

I'd put a monolithic capacitor between the outputs then. See if that helps. Use rated values.

 

[Aleks]

I'd put a monolithic capacitor between the outputs then. See if that helps. Use rated values.

Ok ... will try that if I find a monolithic cap.

Anyhow, I just tested it again using a screwdriver with a light bulb inside (rated from 6 to 12 V), hooked it up on the 15V outputs and its stable. On the 24V output its stable for a few seconds and then it starts to blink.

Now, when it is connected to the 15V outputs, and if I connect my transceiver in parallel its starts to blink and my transceiver starts to go on/off again. The interesting thing is that when I disconnect the transceiver the light bulb stays blinking but when I disconnect it and connect it again, it stops.

Is this due to bad impedance ? I though that impedances are only present when there is AC current and voltage, this is supposed to be a stable PSU.

 

[Aleks]

I connected a 2200uF/25V cap, parallel to the 15V output and the flickering somewhat reduced its intensity but it is still visible on the light bulb and my transceiver dims. If I connect more caps in parallel, will it do any good at all ?

 

[JimB]

I really can't tell an exact number because I don't have a reliable ampere meter but, I know that a 12V car light bulb is flickering (1 time a sec) and my Kenwood TM-401A (which is rated to have around 0.5 - 0.6 A in stand by mode) is going wild.

Are you connecting the TM401 to a 15v output? Very bad idea!
What is the maximun supply voltage for that radio?

12v lamp, dont forget that an incandescant lamp has a low resistance when cold, much lower than the normal operating resistance, and so could trip the overcurrent protection in the PSU.

PS: Forgot to mention that the 5V output is stable ...

It could be that the PSU is built from several separate modules, I have seen PSUs like that before.

JimB GM3ZMA

 

[Aleks]

Are you connecting the TM401 to a 15v output? Very bad idea!
What is the maximun supply voltage for that radio?

13.8 +- 15% VDC, 15 volts are in those 15% of power tolerance.

12v lamp, dont forget that an incandescant lamp has a low resistance when cold, much lower than the normal operating resistance, and so could trip the overcurrent protection in the PSU.


It could be that the PSU is built from several separate modules, I have seen PSUs like that before.

JimB GM3ZMA

Anything (but the lightbulb in the screwdriver) flickers.