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Author Topic: Power Supply Unit  (Read 44446 times)

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Offline kolias

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Re: Power Supply Unit
« Reply #140 on: January 31, 2011, 12:12:51 AM »
I totally agree Al, as a hobbyist we just want things to run and forget about the details. Nothing wrong with that.

But electronics has always fascinated me and I always want to learn more, just for the fun of it. In this case I value the time people spend to teach others their knowledge.

We all try to help each other, isn’t it wonderful?
Nicolas

Offline alenz

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Re: Power Supply Unit
« Reply #141 on: January 31, 2011, 12:23:43 AM »
Agreed, my sentiments exactly :).

Offline Hood

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Re: Power Supply Unit
« Reply #142 on: January 31, 2011, 03:55:49 AM »
The problem then arises that when things are going wrong Mach is blamed and the lack of capacitance is overlooked ;D

Hood

Offline kolias

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Re: Power Supply Unit
« Reply #143 on: February 08, 2011, 10:26:31 PM »
Soon I will be starting putting together this power supply unit and I have 2 questions

First from the attached picture how do I know which is the +/- terminal on each capacitor? I noticed one of the terminals is lighter color than the other so perhaps the darker terminal is the + ?

Second and from my recent post "Power supply overheating" I learned that this unit may generate about 250 watts of power and subsequent heat. Therefore should I make allowances on the metal enclosure I will get to have a fan for cooling ?
Nicolas
Re: Power Supply Unit
« Reply #144 on: February 08, 2011, 11:34:32 PM »
Here is a list of the basic capacitor parameter you should consider when selecting a capacitor. This is only a starting point as there are other parameters to consider when selecting a capacitor for a power supply.

Series type
Manufacturer
Tolerance
Lifetime @ Temp.
Operating Temperature
Features
Ripple Current
ESR (Equivalent Series Resistance)
Impedance
Mounting Type
Package
Case Size
 ???
It would be better to consider the power as only the small part of the total system design. If your system contains just one motor, power supply and controller it’s must simpler to design than a system with 4 motors and 4 controllers which all maybe interacting because of a common power supply design.

Good luck.
 ::)
Re: Power Supply Unit
« Reply #145 on: February 08, 2011, 11:42:15 PM »
The information you were given in that other thread is absolutely incorrect.  If it were, you'd have to put twice as much power into the input of the supply as you get from the output, which is NOT the case.  The supply will NOT be dissipating 250W.  The only significant power dissipation in the supply itself will be in the bridge rectifier, which may be dissipating a few watts, and that only when the supply is providing high current to the motors, which it should never be doing for very long.  It should be heat-sinked (i.e. - mounted to a metal plate, smeared with silicone grease at the interface). 

Those are some gnarly looking capacitors.  How old and.or abused are they?  Old electrolytic caps do not perform well, and can go "boom".  On the blue plastic sleeve you should see a minus sign, or a string of them, running the length of the capacitor, near one of the terminals.  That is the minus terminal.  Do NOT power it up unless you are certain it's connected correctly, or it WILL go BOOM as soon as you apply power!

Regards,
Ray L.
Regards,
Ray L.

Offline kolias

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Re: Power Supply Unit
« Reply #146 on: February 09, 2011, 12:35:49 AM »
Thanks Ray for your input

Since the information on the other thread is incorrect, why that 36VDC power supply unit has its cooling fan going on for so often? is it normal?

Regarding  the rectifier, I attach a picture of it which shows a thin aluminum plate at its base. Is this sufficient to dicipate heat or I should mount it in another piece of aluminum? And we just bolt it down through the hole it has in the center?

Calling those capacitors “some gnarly looking capacitors” Hood is not going to like that because he was good enough to send them to me all the way from Scotland since I could not find anything similar. There is a string of dotted lines running the length of the capacitor but I thought that was part of the label because under those dotted lines are the specs of the capacitor. I know nothing about capacitors so I will let Hood inform that they will NOT go BOOM when I apply power.

Thanks again
Nicolas

Offline kolias

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Re: Power Supply Unit
« Reply #147 on: February 09, 2011, 12:36:37 AM »
Sorry forgot the cap picture
Nicolas
Re: Power Supply Unit
« Reply #148 on: February 09, 2011, 12:41:07 AM »
Perhaps your other supply simply has a defective temperature sensor?  Is the air coming out of the supply warm?

Go to Radio Shack, or any electronics store, and buy a small tube of silicone heat sink grease.  Put a thin coating on the underside of the rectifier, and bolt it yo your metal enclosure.

If Hood sent you those caps, I"m sure they're fine.  The dashed line running up the side is the minus indicator, so the near terminal is the minus.

Regards,
Ray L.
Regards,
Ray L.

Offline Hood

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Re: Power Supply Unit
« Reply #149 on: February 09, 2011, 03:25:31 AM »
Yes the caps should be fine they look a bit grungy as they were in the junk drawer in my outside store but they should be fine and unless they have degraded during transit your pics are making them look a lot nastier than they actually do ;)

As Ray has said the  line down the side denotes the negative terminal.
Hood