help please with toroidal transformers selection

[m_c]

For a read of the how/why behind choosing a toroid based on steppers, have a look at my post in my Triac retrofit thread - http://www.mycncuk.com/threads/10344...5703#post85703

Although having just skimmed over the post, I've just realised I never mentioned about sizing the capacitor. It's a 100V 22'000uF from a reputable source.

[Tom J]

For a read of the how/why behind choosing a toroid based on steppers, have a look at my post in my Triac retrofit thread - http://www.mycncuk.com/threads/10344...5703#post85703

Although having just skimmed over the post, I've just realised I never mentioned about sizing the capacitor. It's a 100V 22'000uF from a reputable source.

That kind of answer I was looking for.
33VAC - 52VDC, big boost over calculation, any idea why was like that?

My both 420VA & 720VA has 30VAC and gave 41.5VDC (calibrated Fluke 87V and 1587)
Secondary coil was ~32VAC


picture shows Amp meter after calibration, voltage was set too

[Clive S]

My both 420VA & 720VA has 30VAC and gave 41.5VDC (calibrated Fluke 87V and 1587)
Primary coil was ~32VAC

Tom you are reading too much into all this. It has been done to death many many times on the forum.

Have a look at the quote and notice you are saying primary coil is 32 AC. The secondary would be the the 32 volt coil.
It is facts like these that can mess people up.

Also you are stating a 1.57 A load is that on the primary or secondary as they would be different.

All this can be very confusing for people seeing the thread title thinking this is the right way to pick a Tx.

[m_c]

You need to allow for mains voltage tolerance (230V -6/+10% or 216 to 253VAC), transformer load regulation (the toroid spec I just looked at was 5%), and a lower volt drop over the bridge rectifier when zero load.

So taking a 33VAC toroid, applying 10% more power (mains voltage here is at the higher end of tolerance) gives 36VAC (we'll round for simplicity) at rated load. Add 5% load regulation, which means we bump our basic unloaded voltage to 37.8AC.

Multiply by root 2 (or 1.41), gives us 53.3VDC. Take away a little bit volt drop for the bridge rectifier, and we have in the region of 52VDC.

[Tom J]

Tom you are reading too much into all this. It has been done to death many many times on the forum.

Have a look at the quote and notice you are saying primary coil 32 AC the secondary would be the the 32 volt coil.
It is facts like these that can mess people up.

Also you are stating a 1.57 A load is that on the primary or secondary as they would be different.

All this can be very confusing for people seeing the thread title thinking this is the right way to pick a Tx.

yes , sorry corrected to "secondary coil was ~32VAC"

1.57A has nothing to do with transformer, just a picture. VOLT/AMP meter red/blue LCD shows the same voltage as calibrated Fluke - that was my point.
I had only picture with Amp displaying on Fluke which also was calibrating. I know I confused enough but some guys say that my meter might be off.

[JAZZCNC]

This F@C£ING STUPID and Dangerous.! . . . LEE STOP It PLEASE. . . . Far too many errors and misunderstandings.

Tom I'm not having a go at you personaly here and see your just trying to elp and give back but this is potentialy dangerous to others and shouldn't be put over has " How To Guide".
I'm helping and dealing with people young and old all the time who never post or ask questions, which they should but don't for what ever reason. Some do have the good sense to ask privately and this is my concern.

I'm for ever helping people, esp the young who haven't got the patence to read past first few posts and when the First post comes over in manner where looks like OP knows what doing they take it has Gospel.
They then proceed to go out and buy everything mentioned without any regards to if correct or not and follow to the letter whats wrote.
This isn't so much problem if it's frame related or Even some components like ballscrews rails etc because worst case they end up with under performing or over expensive machine.
But when comes to Mains electrics like this then it's Bloody dangerous in the wrong hands so unless the OP is Expert which clearly isn't the case here then shouldn't be allowed to proceed any further.

Anyone who's been on here long enough should know how much I hate Moderation and Censorship, Bloody hell I've come close to being banned in protest to it so it should show you how strongly I feel about this because this NEEDS STOPPING or at least Moderating closely.!

[Lee Roberts]

Hi guys,

After receiving a couple of reports on the original thread (it needing attention), I decided to split the discussion, allowing it to continue regarding the selection process, with a new discussion for the PCB side of things, as both topics deserve the proper observations.

You can find the links to each discussion below.

Tom J
Thank you for your efforts and suggestion, however due to errors and inconsistencies in your original approach to this, I feel it is in the best interest if we strip this thread of any kind of guide/tutorial type wording or suggestion it may have, as it's just not ready for that yet.

Please don't be discouraged in your efforts, the original idea was a good one and would be an asset to the forum, however due to the severity, that kind of article/document needs to be correct in its absolute entirety before it can boast as being the definitive. Please try again once you have everything worked out.

Thank you to everyone involved, feel free to continue both discussions:

Link 1: Help please with toroidal transformers selection

Link 2: Please don-t push 14A through that PCB !!!

.

[Neale]

I don't want to get hung up on this transformer voltage business (except that I was surprised by the toroidal transformer I bought recently that measured about 5% above nominal voltage when off-load - the "regulation" factor that's mentioned above which I hadn't expected) but I am interested in the practical choice of smoothing capacitors. I am assuming here that the linear PSU is feeding only the stepper drivers and nothing else, which I think is generally the case.

Stepper drivers can cope with fairly wide voltage ranges. From memory, the EM806 which I am using is rated at 24-80V absolute min/max, for example, although the Leadshine recommendation is to stay at least 10% away from either extreme. We are not building audio amplifiers here, so we're not interested in hum levels on the output. The capacitors are being charged at 100Hz (assuming the usual bridge rectifier) but the steppers are pulsed at a few KHz, so any given pulse will see only the variation in voltage during that pulse - small compared with the variation across a half-mains cycle? On top of all that, one of the stepper driver's main jobs is to control and limit current through the stepper coils, so one thing it can do very well is cope with a range of input voltages while trying to maintain the target current through the stepper coils. So do I really care if the DC output voltage sags by a few volts, across a half mains cycle? In practice, then, just what size capacitor will do an adequate job without going OTT? What is the effect of a too-small capacitor? Don't know the answer myself, but once my machine is back running I'll stick an oscilloscope on the PSU output and see what's happening, just in the interests of science.