Need Help! E-Stop Power Dump Confusion

I'm adding an electro mechanical estop circuit to my existing K2 cnc router with Gecko 320DC drives. I'm basing it on the diagram on the Gecko website that I've attached below. Not having much experience with electronics there are some points I'm confuseded about.

I wrote Gecko support and asked if the filter cap "C" in their diagram was the filter caps in my power supply or a seperate component. The answer I received was that it was independant of the power supply Caps. Wouldn't that place the new cap in parallel with the PS caps and change their value? Would this change the PS Caps operation or would the effect it be negligable?

I had also asked if there was a formula that would indicate what value the new power dump cap should be if running a 24vdc system, but didn't get an answer. Any suggestions would be appreciated as I can't implement this system without knowing the correct value.

As a side note, I had read somewhere that when changing 24vac to dc with a rectifier, the voltage was increased by a factor of 1.4. Therefore 24vac becomes 34vdc. I later measured them both with a volt meter and no increase occurred. 24vac became 24vdc. I guess it pays to actually measure!

Thanks

Quote:

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Originally Posted by bmcd

As a side note, I had read somewhere that when changing 24vac to dc with a rectifier, the voltage was increased by a factor of 1.4. Therefore 24vac becomes 34vdc. I later measured them both with a volt meter and no increase occurred. 24vac became 24vdc. I guess it pays to actually measure!

Thanks

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It does when a capacitor is added, when rectifying DC you measure the RMS of the 100% ripple present, if a significant capacitance is added, then the capacitor charges to the peak DC which is x 1.414 of the RMS.
Al.

I'm pretty sure the Cap show is the main filter capacitor. But if your running just 24 volts as a PS then you may want to lower the resistance of the dump resistor to maybe 10-20 ohms.
If you measured 24 volts AC coming in and just 24 volts DC at the capacitor, then the cap isn't big enough or working at all. It should be about 22000 uF.

Al and Larken, thanks for the input. When I measured the dc voltage it was at the output of the rectifier. No filter caps were hooked up. I'll measure again with the caps in the circuit and see if I get 34vdc.

Larken, when I first saw the circuit diagram, I thought it was the main filter caps also. To be sure, I asked Gecko support and was told it was a separate component. It doesn't make sense to me, but I have little background in electronics so thought I'd put it out on the forum. The main filter caps in my system are two 35v 10000 uF, so must be in series or something. Gecko recommends the load dump resistor be V/10, so 24vdc would get a 2.4 ohm, while 34vdc would get 3.4 ohm.

My basic understanding of an estop is when the power is cut by the relay, the load dump resistor connects to ground and drains the PS Filter Caps and any current coming back from the motors as they wind down. I don't understand how adding another capacitor would improve that, but I'm open to being educated!. Any other thoughts would be welcome.
Bob

Al, I measured the voltage at the filter caps and it's 34vdc as you stated. Thanks for the tip (lesson)!

So according to Gecko's recommendation the dump resistor should be 3.4 ohm. Regarding the capacitor in the circuit this is the response I got from gecko when I asked if that was the filter caps the dump resistor was connected to:

"The capacitors in that circuit would be independent of your filter capacitors on your power supply. "

Unfortunately, no formula or suggestion as to the value of that capacitor. At this point, I'm completely at a loss as to what to do other than connecting the dump resistor to the PS filter caps and hope nothing bad will come of it.

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Originally Posted by Larken

I'm pretty sure the Cap show is the main filter capacitor. But if your running just 24 volts as a PS then you may want to lower the resistance of the dump resistor to maybe 10-20 ohms.
If you measured 24 volts AC coming in and just 24 volts DC at the capacitor, then the cap isn't big enough or working at all. It should be about 22000 uF.

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Just a shot in the dark here
The transformer when de-energized produce a voltage spike, I suspect that resistor is put in parallel with the output to either protect your motors.or stoping them faster by discharging the capacitor.

This remind me of the reversed bias diode put across a relay to eleminate the high voltage produce by the rapid drop of current when you disconnect the relay.

Well, with a lack of any specific info on the Gecko estop capacitor, I've decided to just try what makes sense to me. I'd appreciate everyone taking a look at my wiring posted below and let me know if there is anything I'm missing that could cause a problem. Thanks in advance for any feedback.
Bob

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Originally Posted by bmcd

Well, with a lack of any specific info on the Gecko estop capacitor, I've decided to just try what makes sense to me. I'd appreciate everyone taking a look at my wiring posted below and let me know if there is anything I'm missing that could cause a problem. Thanks in advance for any feedback.
Bob

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some explanations for you bmcd...http://www.parkermotion.com/dmxready...er-dissipation

Thanks Claude for the link. I read through it and I must admit it devises a formula for the value of the power dump resistor, though it's a bit complicated. Electronics is not my strong point, but this project has forced me to start looking at it a bit more. I will study the article and see if I can get the specifications needed and do some of the calculations.

From what I think I infer from this link is the basic design of what I've posted seems to be correct (I hope). Possibly the only thing to consider is the value of the dump resistor, which I just used Gecko's formula for my posted circuit.

Bob

The full current, although low, because its the primary of the step down transformer is flowing thru the estop ...I think this circuit is much better, depending on your setup many estop buttons can be installed in serie with just the relay coil current going thru them (less expensive components)

http://www.geckodrive.com/electromechanical-estop

the following is from gecko 320 application notes and gives more info on the resistance value...
http://www.geckodrive.com/returned-energy-dump

Claude, your last gecko link has a resistor value in the circuit that contradicts the previous link's value. They are 2 different circuits, but they're trying to accomplish the same thing... dump residual energy. It's a little bit confusing. So, what I think I'm going to do is to use the 20w 3.3 ohm wire wound resistor as in the electro-mechanical estop circuits formula, as I already have that component. I will power up and hit the estop button a couple of times with the Gecko's out of the circuit. That way I can look for excessive sparking and double check all energy has been dumped. If that goes well, I'll hook up the Gecko's and continue testing. I'll post the results.

What I find interesting about the previous link (returned-energy-dump) is that that circuit also has a capacitor with (value indicated) just before the drives. Don't know what function it has and if it should be incorporated in my circuit. That is a question I haven't been able to get an answer for.

I think both circuits do the same thing, the second is solid state.

the first link has a the formula for the resistor...The size of this resistor "R" should be picked so it carries about 10A at the power supply voltage. For example, use a 6.8 ohm resistor for a 68VDC power supply voltage (R = V / 10). It is very important to use a wire wound resistor as they are designed to sustain the momentary power overload that will result without damage. A 20W rated resistor will handle power supplies up to 1.5kW.

so at 34 volts you should be ok with 3.3 ohms.

not sure if the capacitor value can be interchange in both circuits...

[QUOTE=bmcd;1605660]Claude, your last gecko link has a resistor value in the circuit that contradicts the previous link's value.

well not really since they state that the R3 also serve as a current limit for the transistor protection ,also this circuit is for max voltage for the drive (80volts)+ whatever voltage spike the regenerative effect produce...

[QUOTE=bmcd;1605660]Claude, your last gecko link has a resistor value in the circuit that contradicts the previous link's value. They are 2 different circuits, but they're trying to accomplish the same thing... dump residual energy. It's a little bit confusing. So, what I think I'm going to do is to use the 20w 3.3 ohm wire wound resistor as in the electro-mechanical estop circuits formula, as I already have that component. I will power up and hit the estop button a couple of times with the Gecko's out of the circuit. That way I can look for excessive sparking and double check all energy has been dumped. If that goes well, I'll hook up the Gecko's and continue testing. I'll post the results.

I fail to see how this can be done... is it not the servo motor, driven by the gecko driver, that is causing the regenerative effect?
And I dont think you will see spark but rather a voltage higher than your supply voltage , this will cause the current to change direction and trigger the dump transistor thru R3, as stated the process should only last half a second so you
probably need an oscilloscope to see that.

Oh sorry, not talking about the same circuit... with the e stop circuit you should be able to measure the drop of voltage at the capacitor...