# Experience with DC injection braking?



## Forge Boyz (Nov 7, 2014)

I'm not a pro at this stuff, but from what I've picked up, you might be better with a clutch/brake setup that leaves the motor run.

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## Peewee0413 (Oct 18, 2012)

How long is the the conveyor and whats the load on it? 

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## gpop (May 14, 2018)

What makes the conveyor stop ?

Sometimes its easier to adjust the stop and calculate the over run then trying to make a sudden stop.


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## cmdr_suds (Jul 29, 2016)

Peewee0413 said:


> How long is the the conveyor and whats the load on it?
> 
> Sent from my VS995 using Tapatalk


 8 ft long belt. ~10 lb load


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## Peewee0413 (Oct 18, 2012)

How long does coast to stop take? 

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## Peewee0413 (Oct 18, 2012)

Try Ramp to stop and drop the times. See if your bus voltage goes up too high. Doubtful, but anything is possible.

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## Jay Freeman (Aug 2, 2017)

edit


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## Jay Freeman (Aug 2, 2017)

cmdr_suds said:


> They warn of motor heating when using it. Is it really a problem on such a small motor? I do stop it quite often, once every 5-10 sec. Will I need to add anything to the drive if I use? Any thoughts?


I don't usually use DC injection myself.  If your VFD has the capability, I'd just experiment with different DC voltage levels and try to get the lowest amount of DC voltage to get the desired amount of braking. If the motor overheats at that setting then of course you'll need to try something else... like an external brake.

You shouldn't need to add anything else. The VFD generates the DC that creates the braking effect.

It is odd that your ramp isn't working though. The drive should be able to bring the motor to zero hertz before the "Stop" button lights up.


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## oliquir (Jan 13, 2011)

i used it a lot on small motors at low voltage without problems, i only use it for few seconds while stopping and maybe hold 1 sec after motor is completely stopped (those were used in a delta vfd, not sure about ab programming).

test with the lowest voltage you can inject and raise it if not enough


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## JRaef (Mar 23, 2009)

The heat increase in the motor using DCIB is essentially equal to the heating effect of starting it across-the-line. So look at your motor's Starts-per-Hour rating and cut it in half when using DCIB. On a 1.5HP motor, the S-p-H rating is likely around 25, so figure you will drop to 12 to be safe. So that's one start / brake every 5 minutes (with at least 38 seconds between them). Here is a chart on NEMA motor standards; 

https://www.landbelectric.com/download-document/78-maximum-nema-inertia-starts.html

Note that there is a "lesser of two" set of columns, one based on the load inertia, because the higher the load inertia, the higher the heating effects. Since this has a VFD, which essentially creates LESS heat in the motor on starting, you can just use Column A.


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## cmdr_suds (Jul 29, 2016)

Jref, does my thoughts about ramping it down so quick that the motor ends up coasting to a stop holds water?


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## JRaef (Mar 23, 2009)

If you have the VFD set to Coast to stop (P045 = 1 or 5), the Decel ramp time will have no effect on making it stop FASTER. 

If you have the VFD set to Ramp to Stop (P045 = 0, the default setting or 4), then setting the Decel time (P042) _*shorter* *than the natural stop time*_ will turn the motor into a generator and trip the drive on Over Voltage, unless you add a Braking Resistor to it. If you do add a braking resistor to it, then you are using what's called "Dynamic Braking" (DB) where the VFD turns the kinetic energy of the load into braking energy to make it stop quicker. But DB suffers from the law of diminishing returns in that the slower the load gets, the less braking energy remains, so it sometimes cannot "finish" the job of stopping, especially if there is low friction and high inertia (which is not likely the case with a conveyor) or if the natural stopping time is already really short and you want it even faster, because it can take a few seconds for the voltage to build up and get dumped into the resistor. That's where you must use the DCIB function (P045 = 2 or 6).

If you are on Ramp to Stop and you set the Decel time to MORE than the natural stop time, the VFD will actually INCREASE the time it takes to stop.


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## cmdr_suds (Jul 29, 2016)

Thanks! That kind of confirms what I thought. I have P045 set to 0 and a decel time of .1 sec. surprisingly no problem with DC bus overvoltage fault even without a braking ressistor. I will be trying the DCIB the next chance I get.


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## Jay Freeman (Aug 2, 2017)

One question that comes to mind... Is this a new install? If not, why is this braking issue suddenly a problem?

I see this type of thing over and over where someone will get me to look at a problem and then I find out that the machine never worked right to begin with.


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## telsa (May 22, 2015)

That many starts and stops practically screams: "Forced cooling!"

Motors don't get decent air flow across their windings until they're revving along. 

OP's proposal smells 'toasty.'


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## Peewee0413 (Oct 18, 2012)

telsa said:


> That many starts and stops practically screams: "Forced cooling!"
> 
> Motors don't get decent air flow across their windings until they're revving along.
> 
> OP's proposal smells 'toasty.'


Ya its quite an agressive application.

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## tates1882 (Sep 3, 2010)

Change the motor over the a braking type and set the VFD up to release the brake when the run command is given. I use high speed roller doors [email protected] that open close upto 240 times per hours.


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## JRaef (Mar 23, 2009)

tates1882 said:


> Change the motor over the a braking type and set the VFD up to release the brake when the run command is given. I use high speed roller doors [email protected] that open close upto 240 times per hours.



Or that... :thumbsup:


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