Running DC motors from solar.

I am looking into the possibility of running DC motors ,more or less direct from solar panels,or a Li battery..(or lead battery ).....I have an old diesel electric crane to wreck,and it has a variable voltage system,max 200V,or thereabouts.The motors are only small,5hp max,but are series wound ....Firstly can I run these with say just switching and overload relays from solar,secondly,can I fit solid state speed control to a series motor.....The crane also has some higher HP motors,up to 40 hp series..for the future.

john.k said:

I am looking into the possibility of running DC motors ,more or less direct from solar panels,or a Li battery..(or lead battery ).....I have an old diesel electric crane to wreck,and it has a variable voltage system,max 200V,or thereabouts.The motors are only small,5hp max,but are series wound ....Firstly can I run these with say just switching and overload relays from solar,secondly,can I fit solid state speed control to a series motor.....The crane also has some higher HP motors,up to 40 hp series..for the future.

Click to expand...

Solar recharge of cordless tool power packs should be eminently feasible. The control technology comes already packaged with the "smart" battery + "smart" consumer-tool controls package.

Old "bare naked" integral HP motors tend to be well-enough suited to their original purpose, but also of of rather low efficiency, absent some clever dirty-beach-sand.

Do the math. Nameplate FLA @ Voltage = KVA for same-nameplate rated HP. Now compare to theoretical "motor HP" for same KVA.

Unless you have the terrain for it, or funds for a water-tower such that pumped-storage is feasible, you'll need a good sized battery plant as well as a rather large acreage of solar collectors before you get past 5 HP heading for 40 HP for anything but short, intermittnt-duty use (as-with vehicle winches, etc.).

A Diesel genset, run only when NEEDED may have a lower life-cycle cost. Methane digester and NAT gas engine is another possible. See also bio-diesel, Ethanol, and "wood gas".

Public / co-op Utility grid, if available, lower-cost, yet.

That's why they exist, after all.

OK,advertised/claimed 6kw solar systems seem to be commonplace here,....is 200v doable?....I know you can directly charge lead/acids,and a system is under $100 local....The battery/s is for current smoothing and starting surges....The whole idea is to be offgrid,as the current term goes....I have also looked at gas producer from wood running a 3 phase alternator.....but the solar seems more attractive....Basically,with a bit of work,i could set up a i/c generator right now to produce 3 ph 415v.....which is what we have here.....I might mention that the electricity grid here is a tool of state government designed(and operated) to advantage the large operator ,and strip bulk money from the majority of residential users..............and add that the 40 hp motor is the traction motor,and has sufficient heat shedding ability to work continuously for hours on end driving a self propelled 12 ton weight on the roadway...And has towed loaded semi trailers round the yard....And sufficient guts to break a rear axle 3" in dia.of HT steel.

john.k said:

OK,advertised/claimed 6kw solar systems seem to be commonplace here,....is 200v doable?....I know you can directly charge lead/acids,and a system is under $100 local....The battery/s is for current smoothing and starting surges....The whole idea is to be offgrid,as the current term goes....I have also looked at gas producer from wood running a 3 phase alternator.....but the solar seems more attractive....Basically,with a bit of work,i could set up a i/c generator right now to produce 3 ph 415v.....which is what we have here.....I might mention that the electricity grid here is a tool of state government designed(and operated) to advantage the large operator ,and strip bulk money from the majority of residential users..............and add that the 40 hp motor is the traction motor,and has sufficient heat shedding ability to work continuously for hours on end driving a self propelled 12 ton weight on the roadway...And has towed loaded semi trailers round the yard....And sufficient guts to break a rear axle 3" in dia.of HT steel.

Click to expand...

Solar arrays can be seriesed-up, but I would not. Better to stay at sub 24 VDC, parallel them, charge a battery bank, use DC-to-DC converters (or DC-to-AC inverters).

We were "off-grid" 1760-odd same County of VA => WBGVA until Dad essentially blackmailed the Powerco. Seems they had built a rather large and costly generating station atop a not-deep-down-enough prehistoric peat bog and it was settling. He was one of two USACE experts who knew how to stop that, but had to take leave (with the Corp's blessing) to be involved in it.

His price? "Wire Middle Run, Lewis County, WVA. I start when you finish."

They put 8 holes, poles, and lineman teams onto about three miles, five families, and finished in three days from a cold-start.

Active entrance panels were initially but 30A service, then 60A, but it was all we needed in all-gas homes with gas lights, gas stoves, gas HW, gas heat, gas fridge/freezers, later even gas Air-con. Most everyone had at least one well. We had five, 3 on Dad's place, two on mine.
Gas company does it all, pays 1/8'th the production to the mineral-rights owner, also provides "free" gas to the surface-owner.

You want "off grid", gas wells in the midst of hardwood forest where soils are rich, game and useful plants abound, water and sewage are gravity-operated is the ticket. We also had a "bank" coal-mine, tapping a seam of the "Waynesburg" coal for blacksmithing operations and supplemental heat. With the WV tax allowance on over-65? ISTR they paid out about $26 a month for the phone bill and the modest electricity needs for the TV and lighting, bought equities and such with the rest of the pension check!



Here? On-grid. Unless it takes a dump. Then MEP-803A.

I DOOO have taxes, "means test" denies me the VA exemption, so utilities are not the major worry!

What are you hoping to use the motors for?

Series wound motors don't have a back EMF (they do, but not at all like permanent magnet motors) so they don't have a voltage dependent maximum RPM. This means they will continue to spin faster until they are at their maximum power, which if unloaded may be when the windings fly out. I don't know at what horsepower rating this becomes the common mode of failure, but whenever I hear about it it's usually crane motors.

So don't test these at full voltage unloaded. Be mindful of RPM.


You can fit a speed controller, but IR compensated speed controllers will be set up for permanent magnet motors and won't maintain a stable speed open loop. IR compensation should still be doable with series wound motors, but I've never seen it done, but I also haven't looked.


I don't have experience with high voltage battery systems but I do know they are a force to be reckoned with if you mess up. You can't turn off a battery for service.

thermite said:

Solar arrays can be seriesed-up, but I would not. Better to stay at sub 24 VDC, parallel them, charge a battery bank, use DC-to-DC converters (or DC-to-AC inverters).

Click to expand...

Opposite advice to standard practice.

High voltage panel systems and mppt chargers are the efficient way... Batteries maybe 24 or 48V. higher would be better but inverters are not common.

I was hoping to avoid any inverter devices,but if max. battery voltage is 24V,then thats likely not usable with the crane motors.I was going to use the motors in a lathe,and a mill.I also have some big aircraft generators that are 24v,likely usable as motors......The other question of speed controll.........the 40hp motor has a centrifugal switch stuck onto one end,and it rings a bell in the cab when the motor is overspeeding..............which is easy to do as the thing gets a go on downhill...the back brakes are oilsoaked,and it stops only on the fronts...The first motor spun the armature windings being towed by a truck without putting the transfer case in neutral....I found a new one...its a BTH...beautifully made.

john.k said:

I was hoping to avoid any inverter devices,but if max. battery voltage is 24V,then thats likely not usable with the crane motors.

Click to expand...

You probably should forget about the old motors. Unless you want to run a Diesel. Or find a used Rooshin Kilo class sub and drag it home for its battery plant and switchgear. Or cut a deal with Tesla.

For most "civilians", 48 VDC is as high as you want to go. Safety reasons. Electric FL, Golf carts, etc usually stop around 36 VDC. There's your motor source. Electric FL goods MEANT to be run off 24 and 36 V batteries.

Even telcos and data centers use more and more 24 VDC gear and less and less our classical neg-48 each passing year.

The inverters are part of essentially any solar rig with battery plant, however modest, or any "puter-gear "UPS", to power "ordinary" AC loads, so have gone dirt-cheap in volume. If "off grid" is your goal, you don't need the extra goods in "grid tie" systems - nor their costs.

Even HF has the small ones, about 5 KVA, on the shelf. They cost less than my oldest, a 100 Watt 12V unit that ran a small B&W TV in the 1979 Grand Wagoneer. My UPS in HKG was a 48 V unit. The high volumes of UPS are another reason inverters are so cheap.

Bigger ones fill rows of rack cabinets. Efficiency is high enough the smaller wire alone offsets the cost of high-amperage, short-range DC's massive conductors. "Arrays" are already provided for. Look for a "sync" terminal so 3 one-by can be used for 3-Phase, or "many" can share any high-amperage load.

From ABB to Zeversolar: The Top 19 Companies in the Solar PV Inverter Market - Technavio

DC-to-DC converters use AC "in between" for Voltage shifting, then simply rectify the AC back to DC. I used one in a circuit ages ago to provide power for a serial link off 5 VDC VCC rail. It was the size of a Bournes trimpot, eg about 1/4 the volume of a common coffee-service sugar cube.

Economical ones - either tribe - are largely Chinese made. Of course.

But we are talking "solar", and they're trying to cover the Gobi desert and run tens of millions of electric scooter/mod-peds, taxis, and motor buses before they - and their KIDS - choke to death on fossil-fuel smog, so whom else is as motivated?

Your Aircraft generators almost certainly have shunt field windings and can be used as motors. I have a 24V 200A generator coupled to a gasoline engine and start it by hooking it to a battery. When the engine fires, it overspeeds the generator so it shoves current back into the battery.

Aircraft generators usually don't turn that fast so you can do a lot of speed control by varying the field voltage with a Variac and bridge rectifier if AC is available or with a resistor if it isn't.

Shunt field coils are easy to make and you can replace the series coils with them. A simple form for a lathe is all that is required for winding. You have slots on the forms for ties to hold the coil together off the form and then wrap them with fiberglass tape. The only special equipment needed is a vacuum pump and chamber to vacuum impregnate them and an oven to bake the varnish. If you don't have them, send the coils to me and I will do it as a mitzvah. I have made countless ones, mostly for locomotive fuel transfer pumps.

Bill

Thanks for your kind offer....but Im a fair way from Missoura.......anyhoo,I will be just going conventional with an inverter.....all storebought stuff........I was hoping the panels could run in series,I think any 24v motors are going to be too bulky...........the aircraft generators are 400 a ,and very heavy,I have previously used one as a welder generator......years ago before I got a Lincoln 400as.

You absolutely CAN run panels in series.

EVERY serious solar installation does. Residential need to keep voltage below 150V, but other setups go higher. Most keep the voltage below 600V with standard panels, the panels will carry a rating for max voltage, and UL goes only up to 600V. (No idea what your equivalent to UL does, I am familiar only with CE and, for Aus, "c-tick", which is EMI related, not safety)

Residential solar often runs series up to around 120V, the usual MPPT controllers run at about that max input voltage. Folks I know run that way, although they are mostly charging 12V batteries. 24V, or 48V would be better and can be done the same way, via an MPPT controller.

Maybe you could describe your preferred setup a bit more clearly? That will probably get better answers and less "noise".

john.k said:

Thanks for your kind offer....but Im a fair way from Missoura.......anyhoo,I will be just going conventional with an inverter.....all storebought stuff........I was hoping the panels could run in series,I think any 24v motors are going to be too bulky...........the aircraft generators are 400 a ,and very heavy,I have previously used one as a welder generator......years ago before I got a Lincoln 400as.

Click to expand...

As said, 48 VDC is a pragmatic upper bound. Shock hazards in a residence, not major utility Solar "farm", can be kept within due bounds, the economy of battery plant built with 12V or 24 V modules and LESS, cost of controls, inverters, who has to wire higher-voltage stuff, etc.

KISS.

The most basic of 24 VDC banks is but two marine/RV deep-discharge automotive-size-format batteries from Costco or such, under a hundred bucks each, and good for better than five years. Arrange those as balanced 12V supply outputs, one can also use either/both of 24V or 12V mass-market goods from the auto/marine/RV arena as well, 24 VDC to 120 VAC inverters for "legacy" appliances..

"China Battery" makes good stuff. I've relied on it in telco & IT Data Centers all over Asia.

Mass-market inverters even from Harbour freight "work OK" (better yet, go find better ones, online).

"Suck it and see" before sinking big bucks into it.

Modular expansion is about as easy with Solar as it can be, compared to ANY other energy source.

And yes, a gen set for peak loads "now and then" WILL be economically viable vs so much cubic money sunk into solar you can't get a decent return out of it. Not even if you go the extra cost of grid-tie for sell-back.

That deck of cards is being stacked against smallholders already. Major utilities are simply building out SERIOUS solar farms of their own with far better economy of scale.

My own provider:

Harnessing Solar Energy | Solar Generation | Dominion Energy

Industry highlight of two years ago, already:

Top 10 utilities for solar power - Electric Light & Power

Oz? dunno WHERE you are but "stations" had to DIY for a very long time. Far too long the distances, way too few paying users, mebbe 80% of the whole country to RUN much of a "universal" grid economically.

OTOH, you are more likely to have more SPACE, most of Australia outside those major towns and cities, so solar groundmounts can go right large.

Your timing is good, too!

Australia's solar power boom could almost double capacity in a year, analysts say | Australia news | The Guardian

Clean Energy Council - Large-scale solar PV

Hi John.k, just to give you some Oz context, our very modest solar array has an open circuit DC voltage of 348V & a short circuit current of 5 A. This is bog-standard as installed during a local Council promotion by one company that virtually did every installation in the Barossa Valley. I suspect such domestic installations are heavily mandated by the OZ/NZ Wiring Rules & would limit your scope if you desire to remain legal. If I were you I'd leave the traction motors alone, their characteristics are suitable for what they were made for .. traction. I suggest you talk to people here (in Oz) who have done what you intend, that way you'll be safe & happy & not investing in a locally unsupported branch of the technology. BTW our array was simply a 'test the water' effort, never likely to pay back its cost, doesn't do much more than recoup the GST on our power bill. Size was limited by the area of correctly oriented un-tree-shaded roof space.

Uneconomic on supply tariffs maybe......but not uneconomic on a $15-$20,000 cost to get 3 phase installed to a shed on a property.........with a wood pole costing $1500 installed,and needing half a dozen poles.There is no problem with shade,my only concern was hail.

Hi John,had a few hailstorms since installation (6 or 8 years)including one featuring golfball size .. no problems. Our array is flatter than it ought to be for optimum collection .. installer REFUSED to comply with optimum angle, said he HAD to match roof pitch!

john.k said:

Uneconomic on supply tariffs maybe......but not uneconomic on a $15-$20,000 cost to get 3 phase installed to a shed on a property.........with a wood pole costing $1500 installed,and needing half a dozen poles.There is no problem with shade,my only concern was hail.

Click to expand...

OK, say $1500 AD => $1,100 USD, about $7,000 USD the lot, presumes that included the frame and arrays atop each pole, etc. What, then, of battery bank, controls, etc? None of this s**t just leaps out of a box, self-installs, self-wires, generates switchgear etc, either.

Figure you are into Aud $15 - $20 k anyway, as all the maintenance, rolling replacement plan budget / escrow, and such is thence on you, not on powerco.

One can still save off their recurring tariffs if the service life of your gear is decent, but ..
With what you'll have sunk into it, you should plan to utilize the BEST match of motors as can be afforded.

There no money left on the table for screwing about with salvaged motors that cost NADA but want the whole plant done less advantageously to make them usable at all. And they are still of dead-lousy efficiency, design-wise, DC hoisting and traction, because conversion efficiency - current flow to twisting stuff on its asskiss - is not what they were designed FOR. Smooth, fine-granulariy control, rather. Which is not the same thing as a "free lunch".

Nope,$1500 is for a wood pole dropped into a 3 metre deep hole,and rammed to spec.....wiring and connection costs are extra,and all borne by the consumer.......and that assumes the supplier.....did I mention the supplier is owned by a greedy state government....that assumes they wont want a transformer installed on the supply pole ,because the 415 circuit is overloaded already,and they are sweating on someone to pay for a 1100v to 415v.boost to the system.

john.k said:

Nope,$1500 is for a wood pole dropped into a 3 metre deep hole,and rammed to spec.....wiring and connection costs are extra,and all borne by the consumer.......and that assumes the supplier.....did I mention the supplier is owned by a greedy state government....that assumes they wont want a transformer installed on the supply pole ,because the 415 circuit is overloaded already,and they are sweating on someone to pay for a 1100v to 415v.boost to the system.

Click to expand...

End of the day, its all down to time and motor fuel ain't it?

As-in live someplace you like, commute to some other place the machine-tool power-budget likes.

JST said:

You absolutely CAN run panels in series.

EVERY serious solar installation does. Residential need to keep voltage below 150V, but other setups go higher. Most keep the voltage below 600V with standard panels, the panels will carry a rating for max voltage, and UL goes only up to 600V. (No idea what your equivalent to UL does, I am familiar only with CE and, for Aus, "c-tick", which is EMI related, not safety)

Click to expand...

For information my residential system runs 350V DC into the inverter, which goes to 240V AC. This is on a small 3.8kW array. I'm not sure it helps the OP. Any real solar usage for motors that size is going to require a large array and large battery bank, how large depends on duty cycle, but could be insanely large.

JCByrd24 said:

For information my residential system runs 350V DC into the inverter, which goes to 240V AC. This is on a small 3.8kW array. I'm not sure it helps the OP. Any real solar usage for motors that size is going to require a large array and large battery bank, how large depends on duty cycle, but could be insanely large.

Click to expand...

240 VAC is neither more nor less "lethal' than any other source of it. All around most of us, managed to "codes", and we Just Deal With That.

350 VDC is one seriously nasty stick-and-fry rectumfrying bitch.

Commercial farm the size of a County, professionally operated and maintained? Not a problem, even at higher-voltages by far. Some of our longest unrepeatered submarine telegraph cables were once keyed at 8,000 Volts DC to carry 4 WPM traffic, simplex phantom.

Residential? WTF. Extra conductor mass for heavier-current, lower voltages are short ones.
Batteries are inherently 2 V per cell or LESS, most any technology out there, Edison onward, and inverters can boost the voltage as easily as not.

But why would any money-grubber give the least of a damn about safety when they have to "make their numbers"?



Telegraph & Telephone companies, 1800's onward didn't migrate off 130 VDC - and HIGHER - to neg-48 VDC by accident.

We made that move BECAUSE of accidents. Fatal ones. And more than a few.

Whole cities and nations were once wired with overhead lines, and they began as BARE WIRE!
Not to mention that insulation FAILS now and then, too. Or lines get downed or damaged.

Piss-away 150 years of hard-learned lessons, every continent and island on the globe?

Have at it.

Surely won't be the first time.

Irony? First, most successful, and one of the most enduring of telephone switch designs, EVER, anywhere, and everywhere? "SXS" Step-by-step. Strowger.

Almon B. Strowger's "Day Job" profession?

He was a mortician!

"The more things change...."