Putting together a battery/solar powered 3-phase system for CNC machine  - Page 1
Forum section: electronics / general

author: Civilenjuneer
author_rank: Newbie
timestamp: July 30, 2022, 05:28:33 am
content: I have a CNC mill and lathe that are currently in an industrial building with 208V 3-phase power. They are both on 30A breakers but they never draw anywhere near that in operation.I need to move them to my home, but I don't have 3-phase power there. I also want to put them in a garage that only has a 120V 20A circuit going to it, not enough to operate a phase converter. The garage is far from the power panel so running new/more lines to the garage isn't an option.I only run the CNC machines for an hour or two at a time, a couple of times per week. What I want to do is put some solar panels on the roof and also use the existing 120V 20A circuit to feed a battery bank, then have a 3-phase inverter that will draw from the batteries to power the CNC machine. I figure 168 hours (24x7) of solar and 120V/20A input power will be more than enough to power 4-5 hours total CNC machine operation.I just want to buy stuff off-the-shelf but I am not sure what to get. I figure I need a 3-phase inverter that will take battery input power. Then I need a battery bank. Then I need a solar/AC input charger/controller that will use incoming solar and 120VAC power to charge the batteries, then I need to size all the components to provide sufficient power.Can anyone help or make some product recommendations?

author: PaulAm
author_rank: Frequent Contributor
timestamp: July 30, 2022, 04:18:04 pm
content: Might be better off finding a small 3ph diesel generator, maybe 25KW or so. Or, reconsider running a 240V line out and a phase converter, it will be the cheapest option. Although conduit is preferred, in most areas of the US you can direct bury UF cable and it only has to be around 12 inches deep. #8 UF is around $3/ft at Lowes.The motor starting surges will be a problem, lack of 240 will be a problem. Problems can be solved, but it will cost $$$ and I don't think you will find a single magic box to do it for you.Look at phasetechnologies.com for their 3ph inverters to get an idea. If I won the lotto I'd put one in my shop. My smaller CNC is run off a phase converter, I have a 45KW diesel to run the big CNC lathe (that one has a 100A breaker on the machine)

author: Siwastaja
author_rank: Super Contributor
timestamp: July 30, 2022, 04:55:34 pm
content: Best option, by far, would be to install VFDs to run the 3-phase motor(s).After all, using general purpose 3-phase inverter to generate 60Hz to drive induction motors is fundamentally the stupidest thing you can do, when a VFDisan inverter, but one actually designed to drive motors.Most of the rated current of induction motor is inrush current during the startup condition when the motor is driven at the fixed mains frequency and efficiency is close to zero. A VFD drives the motor with suitable frequency and voltage, resulting in current you can control to whatever value you have available. Motor is then highly efficient over the whole operating range (removing the massive inrush current), and by limiting current from the VFD settings, you just limit torque.120V 20A might still be too little, but that depends on how much power the machines are actually consuming doing useful work after being upgraded with VFD. It could come close. If your load pattern is peaky and the peaks are short, 20A fusing and cabling will easily tolerate up to say 30A for many seconds.If you want to use batteries, then VFD is still the right tool for the job: some have exposed connection to the internal DC bus, so you can power them from a DC source, which could be a large battery bank say maybe at 200-300V or so. This bank could be charged from the 120V 20A source, or solar of course. But this would require quite some understanding to build safely, and it won't be cheap.3-phase genset is indeed likely the most economical and also simplest option, given your low number of running hours. It's good to have as backup when the shit hits the fan, anyway.

author: themadhippy
author_rank: Super Contributor
timestamp: July 30, 2022, 04:58:25 pm
content: QuoteDont you have steel wire armour in the states?

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 30, 2022, 09:38:34 pm
content: Quote from: Civilenjuneer on July 30, 2022, 05:28:33 amConvert that circuit to a 240V circuit to get double the power. Pretty easy to do, just change the breaker to a 240V breaker, remark the neutral wire, and change the outlets to 240V outlets.Have you considered a custom extension cord along with adding an outdoor 240V outlet? Might be the cheapest solution if 20A of 240V isn't enough.

author: Faringdon
author_rank: Super Contributor
timestamp: July 30, 2022, 10:27:12 pm
content: Any good?...

author: Civilenjuneer
author_rank: Newbie
timestamp: August 01, 2022, 02:25:08 am
content: The last video posted just above looks very interesting!Running a new cable is not an option. It's not a matter of digging a trench, the whole area is paved and jackhammering up the asphalt is not happening.As for 240V, the problem is there are outlets, lights, door openers and such in the garage. There is just one circuit going there so switching it to 240V isn't as easy as it sounds.Putting VFD's on the motors... I don't even know where to begin with that suggestion so I won'tI do like the 240V/PhasePerfect idea, and the custom extension cord one ain't too bad either... although the logistics of that are prohibitive.

author: Berni
author_rank: Super Contributor
timestamp: August 01, 2022, 05:48:11 am
content: You can use a transformer to get 120V from 240V again in the shop. Since you don't need isolation you can actually just buy a 120V 1:1 isolation transfer and connect the windings in series. This effectively makes a 240V variac that has a fixed 50% tap, so it gives 120V. Doing this also uses both windings effectively in parallel so you get double the power rating of the transformer, so for a full 1.5kW circuit you only need a minimum 750VA transformer. Also do give it an appropriate separate circuit breaker to make sure you can't overload it.Then now that you have both 240V and 120V i would use the 240V to run a 3 phase VFD since that is the easiest way of getting 3 phase power and it gives you speed control as a bonus.The other way to do it is indeed using a so called rotary converter. You can get a large 3 phase motor and run it from single phase, as it spins it creates the missing 2 phases as a generator. This requires the motor to be overrated a fair bit since it is getting all its power on a single phase and starting it is a bit tricky. You need to either spin it by hand to start it or use start capacitors to first get a phase shift going. During startup such a large motor will try to draw huge amounts of current and will definitely trip your breaker without some form of soft start circuit. I would only go this route if you just happened to already have a giant 3 phase motor laying around.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 01, 2022, 09:27:01 am
content: Yes, changing wiring in the main distribution box to supply the garage with 240V, then add a transformer to power the existing lights and 120V outlets, then retrofitting the CNC machines with VFDs running out of the 240V 20A supply seems to be the best one can do, I think.Some costs and work is involved, but there is no super cheap / easy way out of this.

author: themadhippy
author_rank: Super Contributor
timestamp: August 01, 2022, 02:11:21 pm
content: Quotesounds like a job for a molehttps://en.wikipedia.org/wiki/Moling

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 01, 2022, 02:30:47 pm
content: You're not going to use a VFD to supply power to a CNC, the spindle already is run by a VFD. The controls may not be happy and it will probably fault when the machine starts up.120V at 20A is probably not enough to run a CNC, changing it to 240V may be enough, although you may need 30A to run a full size machine.You can get around the jackhammer problem by having a directional boring outfit bore a hole for the cable/conduit. You can also use a diamond saw and cut a foot wide path out, bury the cable and cap it back. You see that done all of the time.Unless you have small machines, you will have an issue if you're limited to 20A.You could use transformers at each end and run 480V down that line so you don't exceed the ampacity of the feeder, that would get you 40A at 240V which would be adequate for a small shop. That's around a 10KVA transformer, so not exactly small. That assumes the feeder is rated at 600V and is in decent condition. Then run everything else in the garage off a 120V tap.Note: this is why it is always a good idea to run cable in conduit, you can always upgrade by pulling a different cable through (subject to size constraints). I never bury anything smaller than 1 inch.BTW, I run a 7.5HP rotary converter off a 30A 240V line. With careful tuning, that will run anything up to 5hp without tripping the breaker and my Bridgeport CNC is reasonably happy with it. With a 20A 240V line you might get away with a 5hp rotary, just watch the starting surge.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 01, 2022, 03:03:11 pm
content: Quote from: PaulAm on August 01, 2022, 02:30:47 pmDid I miss something or do you have secret information about the machines OP have?Obviously if it already has a VFD, it's worth checking if it could be made run with a single phase supply without replacing anything. Single-phase wiring to the VFD could be as simple as just having limited power available, and we don't know how much power OP actually needs. The great thing with VFD is, you still get all the torque at lower RPMs and no issues with motor ramp-up inrush current, justpower(rpm * torque) is limited.Also nobody suggested powering the whole machine with a VFD. It's a motor driver. Rest of the machine is very likely built out of 1-phase circuits.

author: PaulAm
author_rank: Frequent Contributor
timestamp: August 01, 2022, 03:21:56 pm
content: QuoteSince these are 3ph machines, I assumed that these are industrial machines. Industrial CNCs, both lathes and mills, have used VFDs to control spindle speed since well into the last century. This may be different for hobby machines, but they are unlikely to be 3phin the US.The OP wants to run his machines, not rewire them. This can be nontrivial. The schematics for my lathe take up 8 "E" sized sheets. Much simpler to just supply the power they ask for.

author: free_electron
author_rank: Super Contributor
timestamp: August 01, 2022, 03:39:31 pm
content: Quote from: Civilenjuneer on August 01, 2022, 02:25:08 amhow about an overhead cable ? or an above ground EMT solution ?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 01, 2022, 05:19:57 pm
content: Quote from: PaulAm on August 01, 2022, 03:21:56 pmThat's why I am asking do you have information of the OP's system or not?I have seen countless OLD CNC machines, starting from 1970's, in hobbyist's garages (both personally, and on videos and pictures). Many use AC induction motors driven from mains frequency for spindle.But indeed, if it already has VFD, it's only better. Worst case, you need to replace it with another VFD, no worse than adding a VFD to a machine that does not have it. Best case, the existing VFD directly supports running from 1-phase system.QuoteOh, so now you also have secret information what OPwants.But I don't care. I give best possible suggestions I can think about regardless of somebody thinking somebody else might not want to implement them. They are free to decide what to do, given as much different options as possible.Or are you the OP double posting with another account? Or just generic dickhead troublemaker?

author: Berni
author_rank: Super Contributor
timestamp: August 02, 2022, 05:53:05 am
content: Yep it is perfectly possible for a very old CNC machine to have a regular old induction motor for the spindle and gearing to change speeds. Power electronics ware a lot harder to make in the old days.If it is a more modern machine with a VFD already in it then i would just look up some documentation on it. It is possible that it supports running from single phase already. Sometimes you can just feed 2 phases from live and neutral and leave the 3rd phase disconnected, or if it has a neutral connect live to all 3 phases together. But this has to be done with consultation to the manual since there is a whole zoo of various voltages it might expect for individual or between phases. For example i have a huge 3kW and 5kW rack mount lab PSU that is designed for American 3 phase input of 208V. Plugging that into our 400V 3 phase would blow it up, but turns out the manual actually shows how to connect it to 220V single phase, so it runs fine. The input stage of the PSU is just simply 3 phase rectifiers with no PFC anyway.Replacing the VFD is not always easy because the new VFD might not know how to communicate with the CNC control electronics to set the speeds.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: August 02, 2022, 01:22:00 pm
content: Something like a Victron Multiplus might suit you. You can link three of them together to make a 3phase output if nescessary.It can charge batteries from the grid but prioritise solar MPPT input. Also it has a feature called 'PowerAssist' where it will synchronise with your incoming AC power and be able to supply the sum of the max AC supply plus the max inverter output. e.g. Your AC supply is limited to 2.4kVA, and if you had a 3kVA inverter it would be able to supply a 5.4kVA load. I think for this to work with a 3ph output, you'd need a 3ph AC input though but it might be worth looking into.