[trubleshtr]

Need some advice on what size bridge rectifier to use on my power supply.
also does anyone re-call the formula for approximating the output after rectified? there was a magic # to multiply by but I can't re-call it.
I tried to attach a quick drawing of my design, hope it turns out, please feel free to comment on the design.

[trubleshtr]

Oh ya the drawing is in auto cad 2000

[Al_The_Man]

If you post it in DXF more people can read it. My Acad 14 does not. The number after rectified and smoothed (capacitor added) is to multiply the ACV x 1.414 minus around 1.3v for each rectifiers drop.
Al

[sendkeys]

unless that is a mistype running 50 volt caps like that will end up burning up or going pop :P your voltage will be 80 or so. if you mean "ac 60 out" not dc 60 out. think that was just a typeO :P

[trubleshtr]

Thanks, that 1.414 I always forget.
Sendkeys you are right that is a type-o, 60vac out of the toroidal then rectified (60 * 1.414 = 85 vdc) yup, that will deffinetly blow those 50vdc caps. I guess I can unwind a few rolls on the xtransformer?
Any Idea how much to remove? I need to run my servos at 50 vdc. I was told the 60vdc is unload voltage and once loaded will drop into the 50 vac range? does that sound right? (then 50 vac * 1.414 = 70 vdc) still too high for the 50 vdc caps?
probably.....

[trubleshtr]

Here is the simple drawing again, thanks for the tip Al.

[trubleshtr]

Ops, just realized It did not up-load, I get invalid extension when trying to upload as a .DXF file?

[Al_The_Man]

It is best to find out the turns/volt before you take turns off, put a temporary winding on off any kind of insulated wire, a piece of stranded 24g can be used if you do not have magnet wire, wind about 10 turns and power up the txfr and measure the voltage on the temp winding to find out the turns/volt. On a toroid, you will probally find it is around 2 or 3 turns/volt.
Al

[Al_The_Man]

Ops, just realized It did not up-load, I get invalid extension when trying to upload as a .DXF file?

Upload shows DXF as a valid extension, was it the size?
Al

[trubleshtr]

I get "invalid file type"?

[sendkeys]

Thanks, that 1.414 I always forget.
Sendkeys you are right that is a type-o, 60vac out of the toroidal then rectified (60 * 1.414 = 85 vdc) yup, that will deffinetly blow those 50vdc caps. I guess I can unwind a few rolls on the xtransformer?
Any Idea how much to remove? I need to run my servos at 50 vdc. I was told the 60vdc is unload voltage and once loaded will drop into the 50 vac range? does that sound right? (then 50 vac * 1.414 = 70 vdc) still too high for the 50 vdc caps?
probably.....

should be around 69 or so (after the -1.3 for brige)
for what im told most you can push a cap 10% ,so that is alot more. you can run them side by side with a resistor jumping over to make a 100 volt cap. but then it will only be 5,000 uf that sounds to small to me.

http://www.digikey.com/scripts/DkSea...352407&Site=US is a 15,000 uf for 14 bucks. sounds alot cheaper then maybe making a cap go pop and killing your controllers.

[trubleshtr]

Ok, I have figured out what I did wrong. Here are the very rough drawings of my intended plan. the first one with caps. in para;;e;; wont work for my purposes, the second one includes 2 bridge rectifiers which I need help figuring out sizing on, and putting the cap's in series to get 100vdc capability?
please correct me and my drawings if I am wrong.
thanks
and if I don't reply for a few days merry xmas to all.....

[trubleshtr]

[ you can run them side by side with a resistor jumping over to make a 100 volt cap. but then it will only be 5,000 uf that sounds to small to me.

The cap's are 100000 uf each,(total of 200000 uf) in series would that not mean they would be 100000 uf?
My plan is run the servos at 50vdc 12 amps max each (3 motors) meaning 36 amps max,I also know from the manufacteurer of the motors they need 2000uf/amp to operate nicely.
2000 * 36 = 72000uf used, Am I doing the math wrong?

Also I noticed the "de-mag" current is 20 amps,hmmmm
3@ 20 = 60amps * 2000uf =120000uf needed???? does this DE-MAG. current play a big roll or should I base the math on the 36 amps??

[Al_The_Man]

Firstly your second schematic shows the caps in parallel as far as I can tell. The value in series, if both are the same capacity, will be equal to half the value of one of them.
i.e. two 100,000 in series = 50,000 uf
Why do you need two bridges?
Al

[fyffe555]

trubleshtr,

I'd suggest looking at www.plitron.com a toroidal transformer manufacturer and they have some tech info and circuits on their site.

maybe I'm misunderstanding what you've drawn but it looks to me that your capacitors are in parallel on both circuits. Parallel capacitance is Ctotal=C1+C2+Cn. Capacitors in parallel need to be rated for the full rectified voltage.

Toroidal transformers do not drop the voltage under load as much as square types and you shouldn't rely on that to lower your voltage. Mine don't drop more than a volt or two under load.

I don't understand why you need two rectifiers as shown in circuit 2 in the mix either? I wouldn't recommend trying it since they will not evenly balance the load if that's what you're trying to do.

To calculate your Vdc from rectified Vac you can uses Vdc=Vacx1.414.

Plitron, a manufacturer of toroidal transformers use Vac=0.8x(Vdc+2) for a torid transformer/recifier/capacitor Full Vave Bridge circuit. Or to put it another way Vdc=(Vac/0.8)-2

Your Transformer is 60Vac? that's ~73-85vdc after a rectifier and cap, depending on what calc you use. In the few PS's I've built my figures have always matched the Plitron calc.

To Size a regctifier you just need to size it greater than the Vac and Amperage rating of the transformer. What is the VA rating of the transformer? If your transformer is 60Vac and 600VA then that's 60Vac @ 10amps. If you look at someone like Mouser the rectifiers are pretty cheap for huge capacities and it's often a matter of selecting by mounting or connections than capacity alone.

For Sizing Capacitors you need to have at least the recified Vdc rating, personally I'd go for 100v caps. For Cap size the most commonly used calculation is C=(80,000*I)/Vdc. For the illustration 60vac 10amp transformer C=(80,000*10)/73 or ~11,000uf.

Hope that helps.

Andrew

[trubleshtr]

I should stop drinking....Your right, they are not in series,but that was my intent...
I was told that using 2, 35amp bridges in parallel would "minimize heat caused derating" I was also told to put the cap's in series so they could handle more than the 50vdc rating?
So putting 2, 50vdc 100,000uf caps in series would only give me 50,000 uf??
If that is the case I need to get a hold of the person who sould me this set-up

[sendkeys]

yep if you hook 2 in series of the same size. it will only make 50% of the one uf rating. Kind of suckers i know also you got to remember you have to hook a resistor over the top to let them bleed over the votage or one side will be higher than the other.

[fyffe555]

Hey, don't stop drinking, just send me one....

As Al the man says two 100,000uf ( is that really 100,000uf?) in series would total 50,000uf.

To calculate capacitance of Caps in series it's Ctotal=1/(1/C1+1/C2+1/Cn). For two caps in series its also Ctotal=(C1xC2)/(C1+C2). Note that what I've read recommends that the cap voltage rating needs to be at least Vdc for both parallel and series wiring, some over rating is preferable.

If the rectifier is rated for the voltage and current then there shouldn't be any heating or derating. The higher rated rectifiers are Al. cased and bolt mounted to deal with heat. Paralleling two supposedly identical rectifiers would give the possibility that one is a slightly different tolerance and characteristics than the other and one would carry the majority of the load. If each rectifier is not rated for the full capacity then there is the risk of driving a rectifier over its rated capacity, heat, derating and letting the magic smoke out.

I don't think its worth worrying about paralleling rectifiers. If you look at the cost's a rectifier of this capacity is pretty cheap, around three or four bucks but two would still be unnecessary expence. Instead I'd be concerned that you've got 50v caps and at least 73vdc from the rectifier. You also only need about 11,000uf at 73Vdc for smoothing caps.. ....

[trubleshtr]

ok,
I spoke to the guy I bought the set-up from, I am being told that putting, two, 50vdc caps in series, will handle 100 vdc, because they are in series, but only handle (as most have noted) only half the capacitance of 1 of the capacitors. this is the sober version of my terible cad drawing. :cheers:
how does this look?? feel free to comment/correct me please, I value your input.

[trubleshtr]

ok I just noticed my +/- are backwards on the caps.....