# 240kW DC to 3 Phase Inverter Drive



## aeroscott (Jan 5, 2008)

sounds like a great find ,can you post pictures . how big are the caps?


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## major (Apr 4, 2008)

Hi Morf,



Morf said:


> And someone please tell me about grounding a drive that carries this much potential. The hazzard warnings in the manual are clearly eye catching, and to be respected. But going from a grounding rod to a mobile situation seems to me to warrent additional care. How does Tesla have a safe ground?


On EVs these systems are isolated, not grounded.



> One last bit of advice from the owners manual for anyone who finds themselves in the company of big caps, the warning is that if the equipment has been sitting for a considerable length of time, that a cautious SLOW process of bringing the caps up to power is required, not just recommended. I hope someone will talk about this, as it is supposed to be a prevention from messy explosions.


This sounds to me like precharge. Which is done with the DC controllers as well. It involves connecting power to the inverter bus thru a resistor before closing the main contactor. This allows the internal DC bus caps to charge at a reasonable current over a few seconds and avoids the high inrush current which would occur if the main contactor was simply closed into capacitors in a discharged state.

Regards,

major


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## Morf (May 29, 2009)

Major,
The user`s manual states `the drive has a capacitive leakage current`. I also read somewhere what that number is. I will find it and report it to see if that number presents some insurmountable problem in converting from stationary apps to mobile. Thanks much. 

For Aeroscott, I will put up photos when my camera is returned. The Eaton LCX9000 is still being made, so that googling Eaton Drives will show you the unit. The drive is new, `old` stock, and I haven`t been inside it, will go when I have finished reading several hundred pages of user and apps manuals. 

The seller of this drive had two units. They were purchased initially by a wind turbine manufacturer/installer for a project that was cancelled. I made the purchase from Ebay. Morf

Thanks for the replies,


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## DJBecker (Nov 3, 2010)

major said:


> This sounds to me like precharge. Which is done with the DC controllers as well. It involves connecting power to the inverter bus thru a resistor before closing the main contactor. This allows the internal DC bus caps to charge at a reasonable current over a few seconds and avoids the high inrush current which would occur if the main contactor was simply closed into capacitors in a discharged state.


It's not precharge. The capacitors need to be conditioned before use.

The internal insulation is an oxide layer, usually aluminum oxide. When the capacitor has been sitting unused for a long time, the electrolyte eats into the oxide layer. If you apply full voltage immediately, the thin spots break down and BOOM.

To condition the capacitor you need to very gradually increase the voltage to allow the oxide layer to re-form in the thin spots. The voltage ramp should be over several hours or even several days.

The exact method to do this depends on the equipment. The traditional method was using a variac, but that won't work with modern power supplies.


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## Morf (May 29, 2009)

Hello DJBecker,
Thank you much. I have calls in now to help define what constitutes ``time between use`` special treatment for the caps. Most likely that time element is not a generalized rule, but also product specific. 

My call in should also shed light on the purchase of a new inverter (my case) which has acquired some shelf sitting time, and what similar ``gentle adaptation`` proceedures are to be considered. Perhaps that is just rephrasing the first question. 

Anyway you have been very helpful. Do you know if all large caps have a small current leakage? My motor rating is for 90 amps, 170 max. My inverter is rated 240kW,the motor 49kW, so perhaps there would be some proper way to replace the caps with smaller ones, if the leak would be `eliminated`. I would think that change could conceivable allow a trouble free isolation as mentioned by Major. Regards Morf


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## DawidvC (Feb 14, 2010)

Your Drive has about the correct rating for the motor you have. Co not attempt to change the caps. The leakage is common and is the reason all industrial equipment must be grounded. A vehicle is already isolated from ground due to the tyres, so the same isolation rules cannot be applied. The best compromise regarding the drive / motor installation would be to insure that the motor is properly grounded to the drive, as per the instruction manual. That should take care of cable leakage and motor circulating currents, which should be your only concern.

Regarding regenerative braking - it may not be mentioned as an option on your drive, but a PM motor operate as a generator when it is being driven, which will be the case when you want to slow down. You will have to experiment with your drive settings to find the optimum way of using regen.

Regards
Dawid


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## Morf (May 29, 2009)

Hello DawidvC,
Your post dealing with caps resulted in Eaton apps folks sending me this, which is relevant to all brands, the document states. 

www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=204704 

The next step appears to be learning the period of time my caps have been unused/idle. 

I also appreciate your input on the isolation factors, and grounding. The apps fellow is now checking with Vacon to determine what a regenerative brake addition looks like. (Vacons of Helsinki make the LCX9000).

Great help. Thanks, Morf


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