[m8kingit]

According to this schematic, I should have @40vdc ,but i'm measuring 76v dc at the drives . Can anyone explain? I've attached a schematic of the torroid i used.


This had 4 taps 4 x27vac, but they were in pairs and shared the center tap. I took one set of taps, wired both hots to the rectifier and used only the positive side and the center tap as my ground. I terminated the other taps.

I know i'm missing a point, hopefully someone will help me out. I saw a similar thread here a few months back, but I couldn't remember what the explanation was.

[123CNC]

the math says you likely have two 27Vac windings in parrallel, giving you 54 Vac secondary or ~76.4 Vdc

you would just use one winding to get 27.2 ac/38.4 Vdc rectified, wire one hot and one center tap

you could use the second set for a second power supply, separate bridge and capacitors

[Crevice Reamer]

If you need to be close to 40V, then use just ONE of the 27V AC taps.

CR.

[Al_The_Man]

Also for maximum VA you should parallel the primary's if using 120vac supply.
It sounds like you connected across the outer ends instead of one end a centre tap?
Al.

[m8kingit]

Yeah I know that's what it sounds like, lol i had someone from here tell me to wire it that way. I'm using gecko 201's, will this hurt anything .

I was under the understanding that the terminal connected to the unattached side of the bridge would be terminated, since i only used the + side along with the center tap.

Bottom line, is 76 volts too much for gecko 201's, will it cause them to run hot?
thanks
mark

[Crevice Reamer]

Gecko 201s can take up to 80V. But what about the motors?

CR.

[Al_The_Man]

Unless you are connected in the full wave centre tap mode, then you use half the bridge, or two rectifiers from the outer ends and the centre tap is your common.
You would still only get ~40vdc though.
Al.

[m8kingit]

Also for maximum VA you should parallel the primary's if using 120vac supply.
It sounds like you connected across the outer ends instead of one end a centre tap?
Al.

I see what i did i connected the red and the orange to the bridge and the outer wire as my ground, not thinking , lol.
Al, I did connect the primary paralell the 2 120's and the grounds.

Will this hurt anyhting the way I have this wired, or should i back the voltage down to where i thought it would be.? i'm using geckos201's

[Al_The_Man]

As mentioned, what motors are you using?
The red & orange to the bridge should give you ~40vdc?
Do not connect anything else.
Al.

[m8kingit]

Gecko 201s can take up to 80V. But what about the motors?

CR.

These are cnc masters motors, probably kelling 1200 oz/in 5 amps. but there is no more information to be had. Maybe I'd better'd back off the voltage. This is a cnc masters machine that i revamped the controller on, becasue of too many problems with the way they had it. These motors are not marked, nor do they have any specs.

[m8kingit]

As mentioned, what motors are you using?
The red & orange to the bridge should give you ~40vdc?
Do not connect anything else.
Al.

Al I have the red and the orange attached to the bridge , then i used the postive side and the blue wire from the center tap, and this 76v dc is what I'm getting.

looking at the schematic i have attached, it looks as if i should have connected the red and blue to the bridge then used the orange as the ground( center tap) instead i used the red and orange at the bridge, which i guess expalins the higher voltage.

[Al_The_Man]

The red and orange should go to the bridge and terminate there. there should be no other connection to the secondary of the transformer.
The DC output of your bridge is the the +40vdc and -common marked on the bridge.
You only use the centre tap as common if using two rectifiers from the Red & Blue, then the orange is your -common.
It sounds like you are confusing the two methods?
Al.

[martinw]

Dear M8kingit'

You first of all need 120 volts on the primary side of the torroid.

From your pdf diagram...

Isolate and insulate

a) P2 -2 (blue)

and also

b) P4-2 (orange)

You have no need for those !00 v AC taps at all

Now..

c) Connect P1-1 to P3-1 and connect that to your positive incoming mains voltage (connect brown to grey)

d) connect black and white wires ( both marked 4 on the schematic) to each other, and connect that to the incoming neutral of your 120 mains AC supply.

What you will have done is put the two important primary windings correctly in parallel.

Now we come to the secondaries on the right side of the schematic .


d) insulate and isolate S2-1 (blue)

e) insulate and isolate S4-1 ( blue)

f) connect S1-3 to S3-3. This will be at about 28 volts AC (red and red)

g) connect S1-2 to S3-2. This will be your O volts AC secondary tapping.(orange and orange)

I think we are nearly there....

Connect (f) 28 volts Ac to one corner of a bridge rectifier (red and red)

Connect (g ) 0volts Ac to the other opposite one.(orange and orange)

The bridge rectifier, with capacitor smoothing should give 1.41 times the Ac voltage as a DC output

1.41 multiplied by 28 equals about 39.5 volts DC . Bingo!

Do not ask me why. I am just a bush mechanic.

Depending on your rectifier arrangements, and altenative DC smoothing, you will get other Dc voltages. I have assumed a capacitative filter, bridge rectifier.

Best wishes,

Martin

[m8kingit]

The red and orange should go to the bridge and terminate there. there should be no other connection to the secondary of the transformer.
The DC output of your bridge is the the +40vdc and -common marked on the bridge.
You only use the centre tap as common if using two rectifiers from the Red & Blue, then the orange is your -common.
It sounds like you are confusing the two methods?
Al.

ok al, so I should leave the red and the orange wires on the bridge, then to just connect the two side of the bridge pos and neg from the bridge to the caps. what is the safest way to discharge thsoe caps now, so i can remove and add a wire?
thanks
mark

[Al_The_Man]

Sounds right.
Place a 100ohm resistor across it or a 100w incandescent lamp will do it.
Al.

[m8kingit]

Sounds right.
Place a 100ohm resistor across it or a 100w incandescent lamp will do it.
Al.

So I'm just crossing the cap terminals with the resistor or bulb . do i necessarily need to do this to all of them, i used 30,000 mfd, but i used 6 x7500?

Al, the gentleman that had me wire it that way, said something about only use the half bridge, because it was smoother or something. I didn't come up with this by myself, but i won't say anything, because maybe i justy misunderstood what i was told. How many volts would i have gotten had i wired the blue red to the rectifier and used one lead and the orage as as the ground? Would it have been the same. 76?
Thanks
Mark

[martinw]

Dear m8kingit,

I would imagine that all your capacitors are in parallel. One discharge device should work.

Best wishes,

Martin

[Al_The_Man]

If you had wired it up using full wave centre tap correctly, you would have still got the same 40v output.
The outer red & blue would have gone to the AC input of the bridge and the bridge + would be the 40v+ and the common would be the centre tap of the transformer. This Common would not be connected to the bridge.
The - on the bridge would be left open.
The full wave bridge is considered slightly more efficient than the full wave centre tap as it makes full use of the secondary winding.
Al.

[martinw]

Dear Al,

Absolutely. My route to the finish line does only use one half of the secondary capacity.

It gets there in a clunking fashion, but hey! it gets there.

Best wishes,

Martin