Thread: DC alternative to phase converter?

Originally Posted by dkmc

Well, wait. Who said a 75KVA set? He needs a 150KVA, Detroit 2 stroke powered for best torque response.

The second link I posted was a 500kVA Detroit. It sagged just as bad as any 4 stroke. Bunk.

Originally Posted by jz79

a generator with a MASSIVE flywheel would make much more sense...

A big old 2 cylinder 80 horse Fairbanks Morse comes to mind - if you don't mind pouring a new foundation for it!

At that point it would be cheaper to just buy a proper 400 amp service.

As far as the hazards of DC: DC is less of a shock hazard than AC. The human body is a capacitor - it will pass AC more readily than it will DC because of capacitor reactance. On the other hand, DC is much more of a *fire* hazard. Quenching DC arcs is an order of magnitude more difficult than quenching AC. And when you're dealing with storage batteries, there is no "off" switch or fuse other than that which you install. If something falls across the terminals of a big bank of batteries you are *going* to have a bad time no matter how many fuses you install.

My two cents: If you have to ask how to Mac-Gyver a 40 horsepower motor drive, then you have no business Mac-Gyvering a 40 horsepower motor drive. Pay a licensed, bonded and insured professional to solve your power shortage the right way.

Hay sparky I see you have never been nailed by dc, it bites way harder than ac and you stick to it, wrecks your mussels and burns like hell, I will take ac any day over DC, I have been bit by both, DC is far more deadly,... shock, burn, and arch it never quits..The op was just asking the question, there is no way this will ever be Jerry rigged, come on 350 volts from car batteries...Phil

Originally Posted by Garwood

Instead of feeding a CNC spindle drive 3 phase AC would it be possible to feed the drive 340V DC power from a battery bank?

The Louis-Allis drive in my old K&T rectified the AC to DC then chopped that up to run the spindle motor. The DC was 385 volts.

But that was all internal to the drive and had a lot of circuitry controlling and monitoring that voltage. I don't think you could just tap 385 v from an external source in there and have it stay happy.

Newer drives are most likely even more complex.

Detroit generator sounds like the better solution to me ....

@Phil - have to agree. Worst shock I ever got was from a stupid 12v dc doorbell line. I thought the fricking thing was going to kill me. Arms didn't work for an hour after.

Ya that inductive kick back is a bitch try 2500 volts dc (BC 610 and a rf amp meter, and a brain fade)...Phil

Got nailed, luckily all in one hand, when I somehow got the base of my thumb stuck into the bottom of one of the old-fashioned capacitors that have several sections in a vertical can with tabs out the bottom. I don't recall just how, since it was probably 45 years ago, but it was on an example of HP's first product, an audio oscillator (tube, of course), powered by 400VDC or so.

Blew a pattern of little pits in my hand to match the tabs. Stung a bit, too........ and it was an hour or so before all the muscles were back to working normally.

I've been zapped by AC as well, and never had that reaction. DC is nasty stuff.

Originally Posted by EmanuelGoldstein

@Phil - have to agree. Worst shock I ever got was from a stupid 12v dc doorbell line. I thought the fricking thing was going to kill me. Arms didn't work for an hour after.

LOL! Ignorant straight-line (mostly..) "open wire" has inductance, too, yah get a few MILES of it into play.

Nominal Neg 48 VDC at the serving Central Office? Meahhh.

But ever' now and then, output of an Old Skewl motorized dynamo ring-generator was dropped onto a pair @ 90 Hz-interrupted-20?

Life in the holes-and-poles biz could get kinda .... "enlightening"!

And then yah gave THANKS a ring-tone was NOT "continuous"... and that a McCulloch-Loop BA / FA circuit was one of the world's slowest telegraph signal senders!

Originally Posted by Phil in Montana

Hay sparky I see you have never been nailed by dc, it bites way harder than ac and you stick to it, wrecks your mussels and burns like hell, I will take ac any day over DC, I have been bit by both, DC is far more deadly,... shock, burn, and arch it never quits..

I've been hit by 350 volts DC. Attention-getter but not painful. I can't even feel 80 volts DC.

120 volts AC on the other hand hurts like hell. Even 24VAC is a bit of a zing.

But that's all just anecdotal bullsh*t which doesn't mean a damn.

There's more to it than just voltage and frequency. It depends on how moist your skin is, how conductive your body is on that particular day, what sort of path the current takes, how deep the conductor gets stuck into your skin, etc. Your skin is your biggest source of resistance - breach it in the wrong places and the 9V battery in a multimeter can kill you. AC has a much stronger tendency to fibrillate the heart. Both AC and DC have "let-go" currents at which point it becomes impossible to let go of an energized conductor. All things being equal (bearing in mind that they never are in reality), AC of a given potential presents a greater shock hazard than DC.

http://www.wright.edu/~guy.vandegrif...%20Dalziel.pdf

Of particular note is the chart at the top left of page 51, some of the conclusions, discussions and "Opinions of international authorities".

First thing, does the drive have DC link terminals? Many larger drives do to allow you to use a common DC bus or DC input, and connecting a brake resistor requires one of the two terminals anyway.

If you only have one terminal, you may be able to use that terminal and connect the other polarity to all three input phases. Some drives with configuration allow you to use the brake terminal as the second bus connection because of the FET body diode IIRC.

Bear in mind that you also need to check whether the drive will power up from a DC supply or do the electronics require AC input (some drives may have 24VDC inputs to bypass this, and you may need to add your own inrush current limiting.

Any contactors, breakers, and switches inserted in the DC circuit need to be rated for a suitable DC voltage. This is probably going to mean using two poles of an MCCB in series. If you use a 170V centre-tap or floating topology, you likely need four-pole equipment.

You'd obviously take the DC to only the main spindle drive (maybe other drives) and run all other equipment off standard 3~ or single phase via other routes.

Be sure to check how the safety system is designed and that you're not bypassing anything.

Originally Posted by thermite

LOL! Ignorant straight-line (mostly..) "open wire" has inductance, too, yah get a few MILES of it into play.

Your house must be pretty big. It was only ten or fifteen feet from the button to the buzzer for me.

Originally Posted by EmanuelGoldstein

Your house must be pretty big. It was only ten or fifteen feet from the button to the buzzer for me.

US home is average enough. Doorbell run about the same.

Telecoms biz we ran just a leeetle bit further!

Not to HJ a thread, but the body is not a cap, it is a resistor made up of water, salt, and fat...The lucky one that gets electrical shock will have 5 ma across the heart and go into arrest and died quick, But the poor sob that gets a DC shock will have his insides boiled and they explode... do to the steam from the heat boiling the water out. With DC it may not shut down the heart if the path is not tru the heart but the death is very slow and painful. Now lets say it a little shock, ac hurts but unless its a rf burn ac doesnt go very deap and spreads out over the skin, DC goes deep into the mussels and rips them ... doing what mussels do contract with a vengeance, (thats why you stick to the energized part) Must of the time there is not a large amp capacity in the DC supply to really get you, But in vfds the DC buss has large caps and it will kill you in a very bad way, or at best you will lose the finger, arm or what ever take the blunt of the shock, you will have a hand, arm ect that will never work . This type of damage does not happen with ac most of the time. Thats is why DC is more harmful than Ac if you don't have a heart shut down...Phil

Wish this thread had more discussion about possible solutions to the problem instead of all the different ways you can die from high voltage...

Originally Posted by mmurray70

Wish this thread had more discussion about possible solutions to the problem instead of all the different ways you can die from high voltage...

You just hook up DC power to the big drives and AC power to the little stuff.

Hope the VFD doesn't throw any codes. If it does, hopefully you have a manual and hopefully those errors can be programmed out.

And then you try not to die. You probably still will, but try not to.

Hay if you are going to dive into the water you better know what is in there to eat you and how deep the water is,...Phil

Originally Posted by mmurray70

is this for lathes too? Any idea it this will work on a Doosan Lynx 300? No number listed. Just says Fanuc I control, or Fanuc I plus control.

I don't really know but if it is like a 16i/18i and has a serial spindle interface you want to look at parameters 4000-4351ish. These will not be in the control parameter manual but rather the spindle motor parameter manual. I have a note of 4082 being accel/decel and 4166 being limitation of regen power. This is on an alpha spindle motor I have, never researched a Doosan.

I would post something in the CNC sections and maybe one of the Doosan guys can help. Locknut still works for them and DouglasJRizzo used to work for them. Both are very helpful

Originally Posted by mmurray70

Wish this thread had more discussion about possible solutions to the problem instead of all the different ways you can die from high voltage...

I agree. Both can kill you and there are so many variables that you need to specify the exact conditions before an anecdote has value.

Re the original problem, it is limited by the service, regardless of how you dance around it, so I am in the "get the right service" camp.

Bill

We just did a project where we could deliver 100kW @ 480V 3 phase for bursts that lasted several minutes when needed when we only had a 1kW power feed nominal with 300kW peak for a fraction of a second . . . all you need are a few of these - SkelMod 170V Ultracapacitor Module and a bit of hardware / software to keep charging currents under control.

We ended up with 9 Farads rated at ~800VDC for our system - worked great!

Originally Posted by motion guru

We ended up with 9 Farads rated at ~800VDC for our system - worked great!

They don't make capacitors that large - you probably had 9,000,000 microfarad capacitors!

Originally Posted by jim rozen

They don't make capacitors that large - you probably had 9,000,000 microfarad capacitors!

Supercap arrays like that do exist and will do the job... at a cost of $7,000 apiece! Assuming you can find a way to charge them and keep them balanced and don't burn out the spindle drive trying to reverse engineer it.

$14,000 for capacitors or $14,000 for an electrician?

Or maybe just wait to spring on a machine that is more your size when one pops up. You have to include the cost of getting the thing running when evaluating a machine that is available for "pocket money". Pocket money plus a new 600-800 amp transformer, paralleled service entrance conductors and a switchboard capable of actually running the damn thing.

If you're lucky and your building is served by a utility-owned transformer you can probably get them to eat the cost of a new one - leaving you to cover only new service conductors, a panel swap (or grouped service disconnects/sub-feed) and a new branch circuit. And for that investment you'll be able to put two or maybe three of these sized machines in your shop and let 'em rip at full speed... instead of dumping all that money and labor into hacking just one to make it limp along all half-assed like.

Originally Posted by 9100

I agree. Both can kill you and there are so many variables that you need to specify the exact conditions before an anecdote has value.

Re the original problem, it is limited by the service, regardless of how you dance around it, so I am in the "get the right service" camp.

Bill

Agree on the right service....

The OP was, however, talking about a bunch of batteries to build up the DC bus voltage.

That's all very well, but somehow, a high current connection has to be made between each of the batteries. After a few are connected, you will be working, hot, with a fairly high voltage....not good to be bolting the connections. You cannot shut off a battery, and you will probably be adding water, measuring gravity, etc, i.e. potentially making contact with high voltage parts.

So connections would be probably by some Andersen SB 120 or similar connectors. Those in particular are UL to 600V, but only IP10, not impossible to contact, or difficult to short if foreign material is in the area, so probably a better protected connector is in order.

The last connection is going to be the full DC voltage, with a lot of current capability behind it. The comments about dangers are, I think, very appropriate.