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Old 07-23-2014, 11:41 AM   #11 (permalink)
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Quote:
Originally Posted by hamsterpower View Post
I think the confusion here is thinking polarity changes while regen.
The polarity (ie. direction of flow) does not reverse during regen. It continues to flow around the circuit in the same direction. Only the motor is now pushing - to the battery instead of pulling from the battery + .

Hope this clears things up.
I was indeed thinking that the direction of current flow reversed during regen. The motor and controller basically acting like a charger.

I had a quick look at this site Understanding Regeneration | Roboteq and it says that current flow reverses during regeneration.

Even though the amount of current during regen isn't as high as the currents when the motor/controller are acting as a load. I was still worried that the potential across the contactor terminals would be the reverse of what was marked on it.

But from reading the other comments is sounds like with the contacts closed the reversed current flow won't cause any issue.
It is only if the contacts try to open whilst high regen currents are flowing that the reversed flow may cause issue.
In normal operations, when high currents are flowing the main contactor should never need to open so being in regen mode or not makes no difference.

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Old 07-23-2014, 04:21 PM   #12 (permalink)
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Take your time deciding on a contactor. I just lost around 16 hours of work (over the last 2 days) on the PCB, because it got corrupted by DesignSpark! They are working on it, to see if it can be recovered. Most of the time was spent on the layout for the driver section. Well, I finally decided on a good driver section layout. They can't erase it from my mind! The schematic part is done now. So, it's just laying it out and routing it again, and hoping it doesn't happen again. I reinstalled designSpark. Hopefully that will help.

One nice thing is, if there is a short circuit condition on any of the igbt half-bridges, the offending hardware overcurrent will turn off all high and low side IGBTs in a couple microseconds. A separate desaturation detection circuit that's on each igbt (6 in total) will also turn off all igbts. Also, the software will stop making sine waves in less than a microsecond if any of those faults happen. If there's a failure of igbts so you get a dead short to ground, there should be a fuse that blows quickly. I can't think of a situation where regen will be a problem with the contactor. Especially, since the controller would have control of the contactor, and would know if regen was happening anyway, because of the current feedback.
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Last edited by MPaulHolmes; 07-23-2014 at 04:46 PM..
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Old 07-23-2014, 07:44 PM   #13 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
Take your time deciding on a contactor. I just lost around 16 hours of work (over the last 2 days) on the PCB, because it got corrupted by DesignSpark! They are working on it, to see if it can be recovered. Most of the time was spent on the layout for the driver section. Well, I finally decided on a good driver section layout. They can't erase it from my mind! The schematic part is done now. So, it's just laying it out and routing it again, and hoping it doesn't happen again. I reinstalled designSpark. Hopefully that will help.
...
Ouch, having to do all that rework is horrible.
Best to think of it as a chance to improve upon what you lost.
Not sure how to put a positive spin on the lost 16 hours tho.
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Old 07-24-2014, 12:45 AM   #14 (permalink)
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I've finally got a new layout that is BETTER than before! Hurray! It was worth losing the other one. Well, they are similar to each other, but this one is a tiny bit better. The driver section symmetry is so glorious I can hardly stand it. haha. I want to tell it to stop being beautiful, but it just won't listen!

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