Author Topic: New 12 volt power supply.  (Read 375 times)

hutch--

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New 12 volt power supply.
« on: October 29, 2019, 02:41:06 AM »
Inbetween most other things, I needed a bigger 12 volt power supply for some of the other stuff I have been making. The biggest transformer I could get at split 9 volt was 80 VA which is a bit small but the spec was 8.8 amps at 9 volt AC which will do for the moment. 10 thousand micro farad capacitor, 35 amp bridge rectifier and a mains extraction fan to keep it cool and it seems to work OK, outputs 13.4 volt with no load which seems to be normal.









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felipe

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Re: New 12 volt power supply.
« Reply #1 on: October 29, 2019, 09:02:43 AM »
Nice box  :azn:
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HSE

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Re: New 12 volt power supply.
« Reply #2 on: October 29, 2019, 10:20:17 AM »
Very Nice!

I think you need another window, opposite to the fan, to provide air flux.

hutch--

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Re: New 12 volt power supply.
« Reply #3 on: October 29, 2019, 11:46:49 AM »
I cheated, I put the intake holes in the bottom to get the maximum turbulence.
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HSE

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Re: New 12 volt power supply.
« Reply #4 on: October 29, 2019, 01:33:29 PM »
 :thumbsup:

daydreamer

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Re: New 12 volt power supply.
« Reply #5 on: November 01, 2019, 03:54:05 AM »
nice :thumbsup:
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K_F

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Re: New 12 volt power supply.
« Reply #6 on: November 03, 2019, 01:27:33 AM »
Make sure the fan airflow direction is blowing into the box, as hot air sucked out by the fan causes faster wear and tear on the fan 'bearings'.
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hutch--

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Re: New 12 volt power supply.
« Reply #7 on: November 03, 2019, 02:03:24 AM »
Too late, I designed it as an exhaust fan so it pulled air from below the case through a number of big holes to maximise the turbulence. Its the transformer and big capacitor I need to ventilate well, the rectifier (35 amp) is on a piece of aluminium angle to act as a heat sink. The 80 VA torroid works OK and outputs 8.8 amps but I think I have found a source for a 160 VA torroidal transformer which will give me over 16 amps output.

I just got a number of tiny Chinese 12 volt power supplies which deliver the voltage but the claimed 5 amps does not handle DC motor startup spikes and cuts in and out with a larger DC motor. They should be OK for the smaller ones.
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K_F

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Re: New 12 volt power supply.
« Reply #8 on: November 05, 2019, 08:45:27 AM »
Too late, ...
Turn the fan around and add a grid ;)
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Re: New 12 volt power supply.
« Reply #9 on: November 05, 2019, 08:50:49 AM »
All 'uncontrolled' motors require approx 3x - 5x normal running current (power) at startup.
You can get motor controllers that have torque compensation to reduce startup current - They startup slower.
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hutch--

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Re: New 12 volt power supply.
« Reply #10 on: November 05, 2019, 09:10:39 AM »
I am still waiting on some bi-directional pulse width modulators to arrive from China which will solve most of the startup current problem but from what I have seen with switch mode power supplies, you should only run them at about half of their rated amperage. For anything that matters a transformer based power supply is cleaner, quieter and more reliable.

I just lifted the lid on my old transformer power supply that I built over 20 years ago and its still perfect, the 8000 uf capacitor may be a bit long in the tooth but there are no signs of it leaking and I still have 3 of the same size as I used to use them for audio power supplies long ago.
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hutch--

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Re: New 12 volt power supply.
« Reply #11 on: November 06, 2019, 04:50:34 PM »
 :biggrin:

I just found an Australian vendor for a split 9 volt 160 VA torroidal transformer, I left enough room in the new power supply above for a bigger transformer and this one should output about 17.5 amps at 12 volts.
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K_F

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Re: New 12 volt power supply.
« Reply #12 on: November 07, 2019, 07:07:18 AM »
...but from what I have seen with switch mode power supplies, you should only run them at about half of their rated amperage.
All depends on the design and price. Cheaper ones use lower grade components and then yes, you'd want to run them at half power.
They also make them so compact that they just want to 'explode' from heat.

Switching suppliers are more efficient at around 90% power rating with efficiencies running at 95%, compared to standard toroidal/bridge PSUs which max out at approx 60% efficiency.

Standard toroidal/Bridge PSU's are much noisier (electrically), and gets a lot worse as the power goes up. These supplies can cause malfunctions in other equipment connected close to the same power line.

;)

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Re: New 12 volt power supply.
« Reply #13 on: November 07, 2019, 10:35:44 AM »
The stuff from China is a funny mix, I just received 5 x 12 - 24 volt 10 amp speed controllers at $5.00 each and on test, they are far quieter than the $35.00 one I bought locally. Has a decent heat sink clamped on 2 flat pack items that I can't identify and a knob that has an off position and variation up to full power. The 5 amp switch mode power supplies appear to deliver 5 amps but cut out with startup transient spikes where a transformer/recitifier/capacitor will routinely handle massive transient spikes.

I used to build audio power supplies and for big power amps I was using 300 - 500VA torroids with split 50+0+50 volt and similar and you used big rectifiers and usually 2 x 10000 mf capacitors and they performed really well, massive reserve and very quiet. I used to test power supplies on an oscilloscope and these were very good. At one stage I built a number of replacement amplifiers for musicians and the first thing you did was test the original amplifier with a square wave on an oscilloscope and you would have died laughing at how bad they were, usually a single sided supply with one 3055 to3 can transistor and some rediculous amount of cabling complete with earth loops.

Removed them with a pair of side cutters and replaced them with a 100 watt RMS amp that was dead flat up to the 113 watt output then they would clip the tops off wave profiles. Many musicians were tuned to these old crapheaps and used to turn the volume up until they heard the clipping.
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K_F

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Re: New 12 volt power supply.
« Reply #14 on: November 09, 2019, 07:09:29 PM »
. The 5 amp switch mode power supplies appear to deliver 5 amps but cut out with startup transient spikes where a transformer/recitifier/capacitor will routinely handle massive transient spikes.
Ja, that's a design and chip selection issue.
Part of my maintenance/repair profile are smps's that deliver 50% overload capability, at 200W to 30KW.
« Last Edit: November 09, 2019, 09:10:04 PM by K_F »
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