charge pump - stepper drivers circuit relay

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charge pump - stepper drivers circuit relay

Postby hawlik » Mon Feb 15, 2021 10:12 am

Hi,

I would like to add relay to stepper drivers power supply circuit similar like this example schema.
The problem is that I can't find any relay on the market which is dedicated to work with 40-50V DC and 7-10A of current.

My stepper drivers would be power with about 40VDC and regarding to the documentation driver max peak current is 7A.
Maybe someone cane share example relay model which is capable to manage this kind of load.
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Re: charge pump - stepper drivers circuit relay

Postby ger21 » Mon Feb 15, 2021 12:22 pm

You should never be killing the DC power to the drives, unless you want to destroy them.
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Re: charge pump - stepper drivers circuit relay

Postby cncdrive » Mon Feb 15, 2021 1:09 pm

Gerry, Question: Why would you destroy the drives with switching it's power off?
It is the same condition as if you switching the control box off so the drives power goes off.

The only thing which could damage the drives is disconnecting the motor while the drive is powered.
It can destroy the Mosfets, because there is a continous PWM and current draw into the motor coil and when that current is cut instantly then the Voltage can rise like a spike which could create a higher Voltage than the rating of the Mosfets.
This could easily and quickly lead to Mosfet failure, they are very sensitive to overvoltages.
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Re: charge pump - stepper drivers circuit relay

Postby ger21 » Mon Feb 15, 2021 1:48 pm

It's something I've always heard over the years, that switching DC power can give a voltage spike. More likely when switching the power on.

Maybe this is wrong, but you don't see anyone doing it.
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Re: charge pump - stepper drivers circuit relay

Postby cncdrive » Mon Feb 15, 2021 3:26 pm

OK, but what is the difference between turning the power on/off when you switching your control box on/off and removing the power with a relay?
In my opinion it is the same thing and turning the power on/off is nessessary to operate the drive.
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Re: charge pump - stepper drivers circuit relay

Postby A_Camera » Tue Feb 16, 2021 7:43 pm

hawlik wrote:Hi,

I would like to add relay to stepper drivers power supply circuit similar like this example schema.
The problem is that I can't find any relay on the market which is dedicated to work with 40-50V DC and 7-10A of current.

My stepper drivers would be power with about 40VDC and regarding to the documentation driver max peak current is 7A.
Maybe someone cane share example relay model which is capable to manage this kind of load.


What do you mean by "work with 40-50V DC and 7-10A of current"? The coil voltage is 24V in that circuit, so what you need is 24VDC coil relays. You don't have to use one single relay for R3 in that drawing, you can use 1, 2, 3 or 4 separate relays, just connect the coils in parallel so that all relays pull at the same time when the coil voltage is applied.

You can use this link to find what you need, in my search there are many 24V coil relays which would fit your purpose.

https://www.mouser.se/Electromechanical/Relays/General-Purpose-Relays/_/N-5g36?P=1z0x3vzZ1z0x3x8Z1yznetm

But... why use relays to disconnect power from the drivers? Why not use the ENA input to disable the driver when you want it?

Image

I understand that as an ultimate safety measure, but in my opinion, in that case, it is not the driver power which should be cut, but the main AC voltage, similar to what R4 is doing with the VFD, it should cut PS3 and PS4 also. After all, the results would be the same, just easier to solve. R3 relay R3/3 terminals need a low current relay contact only, to connect I4- to 24V0 contact. That is, unless I am missing something here.

Edit: Looking at that drawing once again, I don't understand where the motor GND is connected on the motor side. My steppers don't have a GND, only A+/- and B +/- What is the point of leading the GND to the motors?
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Re: charge pump - stepper drivers circuit relay

Postby hawlik » Sun Feb 21, 2021 9:51 am

Hi,
What do you mean by "work with 40-50V DC and 7-10A of current"? The coil voltage is 24V in that circuit, so what you need is 24VDC coil relays.


I was referring to Switching Voltage not the coil.
I check many datasheets of available 24V coil relays and all of them had steep drop of switching capacity when switching DC voltage above 30V. Instead of nominal f.e. 10A of current for 30V DC they are capable to handle 0,5A when voltage goes up to 50V.

example:
https://mouser.com/datasheet/2/307/ly_d ... 291204.pdf

page 8.
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Re: charge pump - stepper drivers circuit relay

Postby A_Camera » Mon Feb 22, 2021 9:17 pm

hawlik wrote:Hi,
What do you mean by "work with 40-50V DC and 7-10A of current"? The coil voltage is 24V in that circuit, so what you need is 24VDC coil relays.


I was referring to Switching Voltage not the coil.
I check many datasheets of available 24V coil relays and all of them had steep drop of switching capacity when switching DC voltage above 30V. Instead of nominal f.e. 10A of current for 30V DC they are capable to handle 0,5A when voltage goes up to 50V.

example:
https://mouser.com/datasheet/2/307/ly_d ... 291204.pdf

page 8.

I suggest you click on the link I gave you. All those are 125VDC with coil voltage of 24V.

...but what I'd do would be to modify the design as I described above.

in that case, it is not the driver power which should be cut, but the main AC voltage, similar to what R4 is doing with the VFD, it should cut PS3 and PS4 also. After all, the results would be the same, just easier to solve. R3 relay R3/3 terminals need a low current relay contact only, to connect I4- to 24V0 contact


It is really a simple modification, and I honestly don't understand why it is done that way in that drawing. But if you insist on following that drawing then there are plenty relays for higher switching voltage than 24VDC.
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