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It works!
Posted: Fri Jan 19, 2018 12:04 am
by DICKEYBIRD
Woo-Hoo, it works like a champ! I was hoping for a little more loss across the rectifier so that the output voltage would be less than 50 but hey, at least it didn't pop the little breaker on the power strip when I pushed the button! So Marty was right, as usual. No inrush current limiting device needed.
The DM542A stepper driver spec sheet says use a 20-50V input & that it has built in over-voltage & over-current protection but I dunno how conservative the voltage rating is. The drivers are mounted on an aluminum plate with a large fan moving a lot of air across them. Maybe that would help? Anybody have any 1st hand experience pushing the upper voltage limit a bit with these Longs Motor DM-542A drivers?
The 50.9V is with no load so maybe I should make a guess at how much current these things draw & make up a dummy load to check the voltage while it's actually loaded.
Re: It works!
Posted: Fri Jan 19, 2018 12:14 am
by martyscncgarage
DICKEYBIRD wrote: ↑Fri Jan 19, 2018 12:04 am
Woo-Hoo, it works like a champ! I was hoping for a little more loss across the rectifier so that the output voltage would be less than 50 but hey, at least it didn't pop the little breaker on the power strip when I pushed the button! So Marty was right, as usual. No inrush current limiting device needed.
The DM542A stepper driver spec sheet says use a 20-50V input & that it has built in over-voltage & over-current protection but I dunno how conservative the voltage rating is. The drivers are mounted on an aluminum plate with a large fan moving a lot of air across them. Maybe that would help? Anybody have any 1st hand experience pushing the upper voltage limit a bit with these Longs Motor DM-542A drivers?
The 50.9V is with no load so maybe I should make a guess at how much current these things draw & make up a dummy load to check the voltage while it's actually loaded.
Don't quote me on this, but most times there is a +/- 10% safety factor. You are definitely pushing it. Did you reread the driver manual to see if there was a safety margin?
The drivers have heatsinks. If you could put a cooling fan to move air across those heat sinks, that would help the drives live....I don't know how much room you have but I would make room. I noted you have it mounted on an aluminum plate. Might add some thermal compound between the drive and the plate. Whatever you can do to keep them cool would help when they are working hard.
What kind of current are you going to draw from them? Close to their peak?
Marty
Re: It works!
Posted: Fri Jan 19, 2018 12:54 pm
by DICKEYBIRD
martyscncgarage wrote: ↑Fri Jan 19, 2018 12:14 am
Don't quote me on this, but most times there is a +/- 10% safety factor. You are definitely pushing it. Did you reread the driver manual to see if there was a safety margin?
The drivers have heatsinks. If you could put a cooling fan to move air across those heat sinks, that would help the drives live....I don't know how much room you have but I would make room. I noted you have it mounted on an aluminum plate. Might add some thermal compound between the drive and the plate. Whatever you can do to keep them cool would help when they are working hard.
What kind of current are you going to draw from them? Close to their peak?
Marty
Thanks Marty, I didn't see any safety margin mentioned so I'm going to chicken out on trying to run it as-is. I have high airflow over, under, around & through the heat sinks already designed-in but I'm thinking when they say 50V, they mean it. The finished machine won't need blinding speed at my experience level anyway. Other electronics gurus have advised me that I can add an "overwind" on the primary side to reduce the output voltage. I'm going to try that this weekend with the goal of getting the DC output down to 45V to allow a safety margin of 10% to compensate for line voltage fluctuations & hopefully promote longer driver life. If it gets to the point where I'm cussing its slow speed, I'll get you to teach me all about servos & make the switch.
Re: Inrush current limiter?
Posted: Fri Jan 19, 2018 4:06 pm
by Dave_C
Milton,
If you are using steppers they pull a decent amount of current when standing still. Some of the more sophisticated stepper drives let you program this "holding current" while others do not.
More to the point, you will see a drop in voltage as the current draw goes up. I have a chart on my 75VDC torrid and it drops considerably when it is loaded to full load. At least 10%!
Does your stepper drives have any over voltage lights or anything of the sort to let you know it has an issue or does it just let the smoke out when it ain't happy?
Dave C.
Re: Inrush current limiter?
Posted: Fri Jan 19, 2018 4:37 pm
by DICKEYBIRD
For the price I paid for these, I'm not thinking they have an overvoltage warning but you bring up a good point. I'll read the docs more thoroughly & see if it mentions anything. I didn't see anything on a quick read when I first got them.
Re: Inrush current limiter?
Posted: Fri Jan 19, 2018 7:13 pm
by RayL
What you have to watch our for is back-EMF from the motors back-driving during deceleration, raising the support voltage enough to damage the drives. Operation with the nominal supply voltage at, or above, the rated voltage for the drive is asking for trouble... PMDX.com has some nice power conditioning boards that will absorb the back-EMF and protect the supplies.
Regards,
Ray L.
Re: It works!
Posted: Sat Jan 20, 2018 6:43 am
by jazzcnc
DICKEYBIRD wrote: ↑Fri Jan 19, 2018 12:54 pm
Thanks Marty, I didn't see any safety margin mentioned so I'm going to chicken out on trying to run it as-is. I have high airflow over, under, around & through the heat sinks already designed-in but I'm thinking when they say 50V, they mean it. The finished machine won't need blinding speed at my experience level anyway. Other electronics gurus have advised me that I can add an "overwind" on the primary side to reduce the output voltage. I'm going to try that this weekend with the goal of getting the DC output down to 45V to allow a safety margin of 10% to compensate for line voltage fluctuations & hopefully promote longer driver life. If it gets to the point where I'm cussing its slow speed, I'll get you to teach me all about servos & make the switch.
I can tell you with 100% certainty that if you run at 50V you will Kill the drives. Over the years I've used many these drives and even at 45V you can run the risk of damage in an unregulated system due to power line fluctuations and back EMF.
If all the stars align wrong then they are very touchy when it comes to Voltage and even thou they say have overvoltage protection it doesn't work very well and will damage them.
In my experience, 42V is safer voltage and never had any fail at this level but I have at 45V.
Re: Inrush current limiter?
Posted: Sat Jan 20, 2018 6:54 am
by DICKEYBIRD
Thank you for the advice. That's exactly the kind of info I need!
Re: Inrush current limiter?
Posted: Sat Jan 20, 2018 1:25 pm
by ScotY
Hi Milton,
I asked the Chinese person (hard to understand) I bought my drivers (exact same one as you) and she said regulated 48v input was too high. She recommended I continue to use the 36v switching PS.
Re: Inrush current limiter?
Posted: Sat Jan 20, 2018 1:25 pm
by ScotY
Duplicate post