square laminated or toroid transformer?

[freak_brain]

Well, I'm curious. What is the difference between the square laminated and a toroid transformers? Seems most people use a toroid, is that recommended?

Thanks
-Allen

[jerber]

Toroids have a lower magnetic radition level. I believe they have also a better power/weight ratio.
And ofcourse they are easier to mount.

[Al_The_Man]

Also usually easier to modify by winding or removing turns.
Al.

[freak_brain]

well now I am wondering this.....I have two square laminated 12v transformers in the same case as my geckos and all my other electronics. Will the magnetic radiation cause me problems? They are approx. 5" away from the closest gecko and about 12" from the last gecko. G201's incase that matters

if it's a problem can they be shielded somehow?

Thanks for your help!
-Allen

[Al_The_Man]

The environment you are talking about, I don't think you will have a problem, it is usually when amplifiers with high impedance inputs are sensitive to stray pick up from this type of source that it is causes a problem.
If you are using more than one transformer they can be mounted so the cores are right angles to each other to counteract the effect somewhat.
Al.

[gar]

050709-1330 EST USA

freak_brain:

Try this experiment. Use a Simpson 260, or a digital voltmeter. Make a 1 turn coil about 4 " in diameter. In other words clip the two test leads to the meter together and space them apart about 4". Nothing critical on the dimension.

Put the meter in AC volts. A Simpson 260 lowest range is 2.5 full scale. A Fluke in autorange will read millivolts. Put the coil in any orientation against the EI lamination core and read the meter. With transformer powered and not powered.

My experiment showed nothing on the Simpson and maybe 0.2 millivolts on a Fluke 87III. On the Fluke the general background noise was about 1.2 mv.

Do you have any many multiturn coils in your circuitry? I doubt it. But you do have the equivalent of many different single turn coils on any of your boards, and these are not even close to the core? The answer is yes, and these are all over the board.

If I am building an audio wire recorder or magnetic tape record with a pickup head with a large number of turns and signals in the microvolt range, then I am interested in a low leakage transformer with magnetic shielding.

I see no need to worry about transformer flux leakage in a small cnc system. Far more important to look at common or ground current problems. These can cause volts of noise which are a problem.

Why do people seem to be concerned about power transformer flux leakage in cnc systems? I have no idea. In fact leakage flux and thus leakage inductance may be useful in limiting peak line and diode current.

(edit 050709-1543 EST USA
I setup scope on 5 mv/cm range, sync off of line, and a 10,000 ohm - 0.1 mfd input filter to get rid of high frequency noise. No probe so we are 1 to 1. The one turn coil showed +/- 2 mv peaks from the core saturation. The RMS value is somewhere below 1 mv. This is with the 1 turn coil adjacent to the transformer. Move a short distance away and nothing at this sensitivity, our most sensitive range.
(end edit)

.

[freak_brain]

I have to say, there are some very smart folks on here, especially when it comes to electronics. Al, Jerber and Gar, thank you very much for your input. As always it was very educational.

Gar

Can you help me understand what you mean by

"Far more important to look at common or ground current problems. These can cause volts of noise which are a problem."

I would appreciate it,

Thanks
-Allen

[gar]

050709-1846 EST USA

freak_brain:

Ground loop problems:

Suppose you have a driver power supply and drivers located at the cnc machine. For safety reasons this power supply common and and the machine frame must be connected to the ac line safety ground (that is not the neutral but rather the green wire) per the National Electrical Code. This is for your safety.

Next you have a signal wire from the drivers to your controlling computer. Your computer must also be tied to the electrical safety ground. Suppose this is a different wall outlet and it has its own saftey ground wire. All these safety ground wires terminate at your main breaker box and at this point to the copper water pipe system, gas line, and an earth ground rod.

Next suppose you generate a direct short from your ac hot wire to the cnc machine chassis. This will produce a peak voltage difference of about 1/2 of 120 times 1.414 or 85 volts. This will destory any directly connected integrated circuits at both ends of the interconnect cable.

See a repeat of this discussion at our web site www.beta-a2.com and select NOISE and GROUNDING page and under WHY is a DIRECT .... connection Rrisky.

There are other causes of ground path noise that may produce data errors but not destroy components.

.