# Using my VFD as a charger?



## dbeluscak (Mar 2, 2013)

Someone else had brought this up on another thread and I think it'd be perfect for me. Because charging 1000v of batteries will be no easy task. I thought it'd check with the experts. My drive its configurable for almost any motor, in this case, any "load". I do have 690VAC readily available at work and soon in my own garage. So in theory I can charge using the DC bus. Or for more control I can rectify the 690 to just under 1000VDC. I will be designing my own BMS to save cost. I can datalog and monitor charging through ethernet (through I will probably try and use a Profibus setup because I already have software and hardware) I'll be using an active BMS to try and save cost on charging. And I'd program the VFD with a "charge" setting where the current is limited by the batteries temp and max currents. Then the BMS is tied to the enable circuit in the VFD to stop charging once the batteries have reached full voltage.

Um, sounds too simple in my head. Am I totally wrong or off base here.

Thanks again! 

And...I realized I'm not doing this to save much money. At 0.09/kwh it will cost me about 9 dollars per charge!
[email protected]=100kwh

Its about the love!


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## cts_casemod (Aug 23, 2012)

Sure you can. 

But not sure what you are designing that takes 1000V DC, my good advice is to take some time to think about what you are doing and go no higher than 600VDC. Look at the tube/trains. For some reason they use 750V. It would be cheaper for them to go higher, untill someone gets killed.

DC Current is i real hazard, not like AC in our homes. Once an arc starts it will not stop and that means fire.

Now back to the VFD you can create a circuit that gives the unit a feedback to keep your voltage and current controlled within a defined value, since the VFD will output a certain ammount of V/Hz.

You'll have to rectify and filter this AC current comming out of the VFD so you can use it as your charger. The VFD acts as a PWM controller. You'll have no isolation from the mains.

I am sure you'll find easier ways to do this, buy yes, it can be done. If you can remove some of the IGBTs so you'll have only the low side working. This way you avoid rectifiying the AC.


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## dbeluscak (Mar 2, 2013)

The real reason I'm designing the system at 1000v is I already have the drive. The pack and charging expenses are ridiculous! It does seem crazy, I'll be the first to admit that. I work with 690AC and 1000DC on a regular basis. Unfortunately, I am all to aware of their dangers. A couple months back I had a 3200A contactor blow up on me. I have also seen a VFD basically melt during testing. Our largest machines use 6 drives with 12 250hp motors that produce 13,000,000 ft/lbs of torque to bore through anything that gets in their way.

The reason behind my madness is higher voltage means lower amps. In turn if I barely push it. I should be able to get decent efficiency out of my 8000lb truck. I'd also like to make it run some quarter mile blasts. That is, if I can get all that power to the ground.

Im working out the design of my tube chassis to house all the batteries with safety as my main concern. The cab will need to be completely isolated from the lethal voltage. 

I will run some tests at 600v, the drive will power on around 550-575VDC. This will limit motor voltage to under 400vac. The 690 motors are pretty easy for me to come buy as we rebuild and send them back into service quite frequently. I'm trying to do this conversion with some spare parts. The real expense will be the batteries and BMS system. 

Thanks for you're input. I'll keep everyone updated with progress. I'm expecting this project to take 5 years, hopefully by that time we'll see some cheaper lithiums.


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## PStechPaul (May 1, 2012)

This is an intriguing project, using 1000VDC and 690VAC. One way to make the battery packs safer is to build them in 20 modules of 48VDC each, with relays inside that must be energized in order to get pack voltage out. You would need to synchronize the relays so they all opened simultaneously and shared the total 1000VDC when breaking the circuit, but this could be done with a 60V TVS diode on each contact.

Can you show some pictures of the high power motors and switchgear and the application where they are installed and used? I assume it for some sort of mining purpose, and I know they have some huge motors. There is a rock quarry only a couple miles from my house and I can hear some of the heavy activity late at night:
http://articles.baltimoresun.com/2007-10-15/news/0710150071_1_rock-quarry-lafarge-quarry-blasts

There are also some huge machines at the landfill/recycling center across the street from the quarry.


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## dbeluscak (Mar 2, 2013)

Hi Paul, 
I like the use of the word intriguing! That's what got me started. I have access to most of my components that were discarded as "junk" I recently scrapped about 8 of these drives and kept the best two. One with a "saturation"fault and the other had a bad capacitor. I'm young and definitely learning as I go. 

I do intend on splitting up the packs in case of malfunction. I wouldn't want to tie 300 batteries together and watch my truck incinerate itself! Not only for safety but cost as well. But that's the idea behind designing my own tube chassis. Everything will have its own place. 

I can gladly provide with you with some pics I've taken but I don't have any of our largest machine. It was built before I started. It is being used to divert water for the Niagra turbines. It holds the world record for tunnel boring machines at 47' in diameter. 

I'll try and email you some pics I've taken. In the meantime, you can check out our website or Youtube channel.

TheRobbinscompany.com

Btw, the avatar photo I'm using is one of our motors. 690v @ 350A and 250HP. Unfortunately it weighs a ton (literally), I'll be looking for an aluminum frame. And I don't think I'll need half the HP. 

Another idea I've been kicking around is making the truck 4wd with 2 motors back to back.But this adds weight, money, etc,etc.


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## cts_casemod (Aug 23, 2012)

dbeluscak said:


> The real reason I'm designing the system at 1000v is I already have the drive. The pack and charging expenses are ridiculous! It does seem crazy, I'll be the first to admit that. I work with 690AC and 1000DC on a regular basis. Unfortunately, I am all to aware of their dangers. A couple months back I had a 3200A contactor blow up on me. I have also seen a VFD basically melt during testing. Our largest machines use 6 drives with 12 250hp motors that produce 13,000,000 ft/lbs of torque to bore through anything that gets in their way.
> 
> The reason behind my madness is higher voltage means lower amps. In turn if I barely push it. I should be able to get decent efficiency out of my 8000lb truck. I'd also like to make it run some quarter mile blasts. That is, if I can get all that power to the ground.
> 
> ...


 
I dont want to put you down, just warning that 690VAC is not half as dangerous as 1000VDC because on AC the arc will self extinguish. I have a grinder with a dual pole switch and if i am using DC from my packs nothing happens when I turn the switch off at 300V. The arc keeps the current flowing untill you take the plug off. Make sure that the batteries are protected in case of an acident. I find it a terrible idea to fill the under bonet area with batteries for this reason on some conversions I've seen. The real danger is the arc. Think of a welder at over 1000Amps going throught metal. I did some tests on a contactor while carrying my conversion and the contactor contacts were eaten by the arc as if we were talking about a fuse much before the actual electrical contact was done. 

Other than that yes, you want a good BMS and also good cells that can keep a balance. You might find that using a standard AC motor rated at 208V is an option, since even at 650V you can take twice the continuous power and up to 6x peak. I moded some of my VFD to operate at half voltage, sure you can do that as well. In any case you should have more than enought current capability on those units, just make sure you play safe and all your components (cable, fuses, contactors) are rated for the voltage you want to use and that the batteries are protected in case of an acident.


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