Proper ways to fuse your machine electronics

[freak_brain]

Can anyone tell me the proper way to fuse my electronics? I am using gecko G201's with 4.2V--4.7A steppers, 4 Wire. Do I fuse between the capacitor and the gecko on the "-" side as shown here


http://www.cnczone.com/forums/attach...achmentid=7925


or do I fuse between the geckos and the motors on each phase? or maybe both???

Also, I would assume if one is fusing the motor phases then you would use slow blow fuses slightly higher then the motors rated amps? For example, my motors (again 4.7A) I would use 5A slow blow on each phase, Would that be correct?


Thanks for any advice you could offer
-Allen

[gar]

050713-1515 EST USA

freak_brain:

Rather than answer your questions I want you think them through with the help of the following questions.

What is the peak inrush current to a stepping motor coil?

What determines the peak stepping motor coil current?

What is the shape of the motor coil current?

What is the thermal time constant of a motor coil?

What shunt current paths exist, or could exist?

At 150% of rating how long does it take a slow blow fuse to open?

What is gained by directly fusing a motor coil?

How or what is the relationship between the Gecko common and the control common?

What was the source of information that the creator of the referenced circuit used? Go to this source and determine if it is a reliable source for defining the location the indicated fuse?

Why would you want to fuse the motor leads directly if a fuse preceeds the Gecko drive?

See Littlefuse or Buss for fuse current vs time curves.

What is the thermal time constant of a typical semiconductor device compared to a motor coil?

Why do you use a slow blow fuse on a standard induction motor?
or At the input to your power supply?

Any time you are using a fuse or circuit breaker ask the question --- what are you trying to protect?

Making you ask and answer questions yourself is a technique that one of my old professors used. Most of our tests were open book and these were far harder to do than closed book. This prof would not answer any questions during a test, you were on your own. Even in non-test conditions he would try to make you analyze the problem yourself. He was the author of our textbook on electron tubes and created questions like what electric and magnetic fields were required to make an electron entering a hole on one side of a box spiral and exit a hole on the other side. The holes were not necessarily aligned.

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[rboeser]

This may help some if you need a visual, compliments of Phils' website:

http://pminmo.com/simpleps.htm

[gar]

050713-1750 EST USA

There is a serious error in the circuit diagram of the previous post. Can you see it?

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[rboeser]

The bridge has only the ac connection. The DC connection is missing/ connected directly to the AC line. Good thing it is fused...

[pminmo]

Good catch, man did I over look that one!

Phil

[pminmo]

..........what mistake ?................

[GARG69]

the one thing they hammered into my head was a fuse is used to protect upstream components only.
hope this helps
gary

[gar]

050713-2010 EST USA

GARG69:

What do you mean by upstream?

If you mean the source, then I disagree. For example the circuit breakers in your house, shop, B1 airplane, or whatever are there to protect the wiring on the load side, or if at the equipment to protect the equipment.

A 20 amp breaker on a nominal #12 wire circuit (meaning reasonable length and not confined in a hot area) is selected to generally prevent overheating of the wiring and a possible fire. In my home with 200 amp service and a pole transformer of 100 kva and if there were no circuit protection, then shorting the end of the #12 circuit would not have much effect on the transformer or service entrance wiring, but would start a fire from overheating the #12 circuit.

By the way if you have aluminum wiring in you home get rid of it. This stuff is very dangerous and should never have been allowed by UL. Even if you are told you can coat connections to prevent high resistance joints do not trust this as a solution. You and your home are too valuable.

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[freak_brain]

I guess I will need to ponder your questions for a bit, lol...


Thanks all
-Allen

[CJL5585]

Gar:
There is a serious error in the circuit diagram of the previous post. Can you see it?
----------------
1. 120 VAC line is not protected via a circuit breaker or fuse.
2. The drive power switch is in the power supply common side. (WRONG)
3. The fuse is on the power supply common side. (WRONG)
4. The lamps are rated @24 VDC -- Actual voltage to lamps is 33.9 VDC
5. The large capacitor should have a bleed off resistor across the + and - terminals to discharge the capacitor when the power is cut off. Otherwise, the circuit will be energized with the power off. Not really a shock hazard, but could cause you to blow up the Gecko drive if connecting or disconnecting motor, etc.

Note: Never put switches OR fuses in the negative lead. This is contrary to code.

The fuse for the Gecko drive goes in the + Voltage lead between the capacitor and terminal 2 on the Gecko. The fuse should be a 5 Amp fuse rated at 250 Volts (fastblow electronic fuse).

EDITED LATER after next post: On the other schematic, (Pminmo) the negative side of the supply is tied to chassis ground. Additionally, the transformer primary center tap is connected to chassis ground.

Jerry

[gar]

050714-2012 EST USA

CJL5585:

Jerry you did your homework on the first circuit presented by freak_brain. You have a very sharp eye.

Jerry my serious comment was directed at the pminmo post but no problem that you applied the comment to the first post by Allen. It brings up good talking points.

My question to Allen on what Gecko considered to be common for the chopper part of the circuit and whether this shared a common with the logic was directed at your point about switching the negative side. This really depends upon how the Gecko circuit is designed. If it is a don't care, then I would prefer to switch the positive side. This may also bring up the question of which, the negative or positive, side of the motor power should be tied to machine chassis and earth ground.

On the primary side as well as adding a fuse or circuit breaker I would insert an appropriately sized negative temperature coefficient resistor to limit inrush current and allow a lower rating on the protective device. Under steady state conditions it consumes some power, but it is a very useful tool.

Incandescent lamps of 24 v rating won't last long here. Also incandescent lamps on dc have a much shorter life than the same lamp on ac with the same rms current. The 757 pilot lamp was originally rated at 50,000 hours, but later reduced to 5000 hours because of dc applications.

If these are LED lamps then more needs to known. We use a high intensity Stanley LED for pilot light purposes using 20k ohms and 12v input. This same combination could run at 40v and not exceed the rating of either the LED or 1/4 watt resistor, at 40v the dissipation is 1600/20,000 = 0.08 watt. Even a higher voltage if you wanted to. At 40v the LED current is 0.002 amps ( 2 milliamps ).

It sure needs a bleeder.

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