Capacitor calculation for toroidal transformer and rectifier bridge

[Azalin]

Thanks.

50000uf on ebay is very expensive but 47000uf is cheap. I can buy 3x 47000uf 50v. What do you think?

[Al_The_Man]

The down side is the larger the cap bank value, the higher Kva required for the transformer when used at maximum load.
Al.

[Bdrangdo]

Thanks.

50000uf on ebay is very expensive but 47000uf is cheap. I can buy 3x 47000uf 50v. What do you think?

Sorry I should have said 47000uf, it is a standard size. You should be fine with those. Most servo's are fairly tolerant to a small ripple and you will never get a perfectly smooth supply no matter what you do. I would strongly recommend you fit discharge resistors to avoid any accidents. they can hold their charge for many hours when OC.

[Azalin]

Got it. Thanks.

Just ordered two 47000uf 50v.

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[A_Camera]

Got it. Thanks.

Just ordered two 47000uf 50v.

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Take the safety warning very seriously. If one of those explode in your face you might lose an eye or two. Especially true with the cheap ebay capacitors.

[Azalin]

Sure.

Is a discharge resistor same as bleeder resistor? (please see the attached image)

Then I have new questions

- Do I need to use a discharge resistor on each capacitor?
- What value of a resistor I need to use for 47000uf 50v?

[davidloomes]

If you want to know how much the voltage across the capacitor will sag between charging pulses from the rectifier, it's pretty simple to calculate. Just type the following into Google and it'll tell you

3kW / 24V / 47000e-6F /(2 * 50Hz)

Adjust any of the nos as you want, but I think you'll conclude you've been very poorly advised and it simply isn't going to work.

[Azalin]

I'm always open to good advises.

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[Azalin]

If you want to know how much the voltage across the capacitor will sag between charging pulses from the rectifier, it's pretty simple to calculate. Just type the following into Google and it'll tell you

3kW / 24V / 47000e-6F /(2 * 50Hz)

Adjust any of the nos as you want, but I think you'll conclude you've been very poorly advised and it simply isn't going to work.

Why did you say that, really?

[Bdrangdo]

If you want to know how much the voltage across the capacitor will sag between charging pulses from the rectifier, it's pretty simple to calculate. Just type the following into Google and it'll tell you

3kW / 24V / 47000e-6F /(2 * 50Hz)

Adjust any of the nos as you want, but I think you'll conclude you've been very poorly advised and it simply isn't going to work.

That doesn't make any sense, I admit I am not an electronic engineer but surely the "voltage sag" as you refer to will depend entirely on the load, which is something of a variable in this case. I agree that higher capacitance equates to a smoother output but the application does not require a perfectly smooth or stabilized supply. A quick look at many servo amplifier specs show an huge tolerance to voltage variations and from personal experience I can vouch for this.

[oscilloman]

The speed controller is a CC Edge 130a brushless speed controller. Normally this thing is designed to work with LiPo batteries so voltage droop is not a problem.

Simply, can we say the more uf and v on the capacitor is the better?

You might want to look up the duty cycle on that ESC, because of rc components are usually never ment to be run at full load over time. U probably want some good airflow going over that thing as well.
Are you putting this on a lathe?

[Azalin]

You might want to look up the duty cycle on that ESC, because of rc components are usually never ment to be run at full load over time. U probably want some good airflow going over that thing as well.
Are you putting this on a lathe?

I'm putting it on my mill.

A good air flow is the next thing I'll do after I get all the thing running. I'll build a box with 2 large fan on sides. I'll also use a big aluminum heat sink on the bridge.

I didn't say I'll run the motor at full power but this is a electric heli ESC. Electric helis usually run at full speed plus governed. When the heli bogs down the ESC pushes it even more to recover the head speed.

[Azalin]

Maybe this video will give you an idea what this ESC is capable of. Actually the ESC used on the heli is the 100a version.

[grg12]

That doesn't make any sense, I admit I am not an electronic engineer but surely the "voltage sag" as you refer to will depend entirely on the load, which is something of a variable in this case. I agree that higher capacitance equates to a smoother output but the application does not require a perfectly smooth or stabilized.

He used transformer power rating to roughly estimate maximum amperage - worst case scenario. Number you get from this equation is higher (larger "sag") than i Praxis since equation assumes capacitors will be charged in pulses - when input voltage reaches maximum. Nevertheless - its a simple equation that can give you useful estimation.
Helicopter esc may work with large range of input voltages but no idea how it would react to pulses...
Reading posts from OP i get the feeling that this transformer may be repurposed welding trafo - hopefully not a cheap one that will overheat after 5 minutes.

[Azalin]

The trafo was a special order. The company uses all copper material on their products so I hope it'll work cool

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