[robhay2]

Would you buy a corded autonomous tractor? The fact it can work all day and night at different farms is appealing I think.

https://cleantechnica.com/2018/12/1...ic-tractor-with-a-really-long-extension-cord/


Image credit: above url

 

[Nouveau Redneck]

100 kW, even on a 220 volt AC system, is going to draw over 400 amps, and that cord doesn't look heavy enough to handle that much current without burning up. But maybe the tractor is much bigger than it seems so the cord is a larger diameter than it looks... I dunno. Plus that's gonna be one heck of an electric bill.

 

[robhay2]

I found another article that states the transmission voltage is medium voltage DC. The amp draw would be quite low, like less than 20A.

https://translate.google.com/transl...e-traktor-faehrt-rein-elektrisch-und-autonom/

Something interesting to follow...

 

[Nouveau Redneck]

Thanks for that link. Wow, greater than 6000 volts DC at the power cable, converted down to 700 Volts DC at the internal electrical system. So the cable doesn't have to carry much current, but there's still going to be a huge electric bill. Converting 120 or 240 VAC to 6000 VDC and then converting that down to 700 VDC doesn't sound like a very efficient method of delivering power. I would think that a lot of energy in those conversions is going to be lost to heat, so the power coming off the public grid is probably going to be even more than the 400 to 500 amps required to just get 100kW out of the grid.

 

[dave_r]

Thanks for that link. Wow, greater than 6000 volts DC at the power cable, converted down to 700 Volts DC at the internal electrical system. So the cable doesn't have to carry much current, but there's still going to be a huge electric bill. Converting 120 or 240 VAC to 6000 VDC and then converting that down to 700 VDC doesn't sound like a very efficient method of delivering power. I would think that a lot of energy in those conversions is going to be lost to heat, so the power coming off the public grid is probably going to be even more than the 400 to 500 amps required to just get 100kW out of the grid.

They aren't plugged into your house, they would probably just get direct power pole voltage, or something like that, which would also reduce the cost for getting power to the field (so the tractor basically has the power pole transformer).

 

[Nouveau Redneck]

They aren't plugged into your house, they would probably just get direct power pole voltage, or something like that, which would also reduce the cost for getting power to the field (so the tractor basically has the power pole transformer).

No, a transformer can only convert AC at one voltage to AC at another voltage, either step-up or step-down. This thing runs off of DC, which requires a converter in addition to the transformer. The article specifically said that the greater than 6000 VDC (> 6000 VDC) was at the 1km long cable, so the conversion from grid power (220 VAC) to "> 6000 VDC" would have to be before the power gets to the cord, not at the tractor itself, plus the conversion circuitry would add too much weight and take up to much space to efficiently be installed on the tractor itself, plus if the conversion were done at the tractor then you're back to my original statement about needing at least 400 amps in the cable. So if you're going to have the ability to plug in directly at the utility pole, then each utility pole would need a transformer and AC to DC converter capable of converting 220 VAC to > 6000 VDC. And the electric company is going to want to put a meter on each and every pole where you install one of those converters. They might give a discount for being such a large consumer/customer, but it's still going to be one heck of an electric bill.

 

[elvenhome21]

Actually it really wouldn't be terribly hard to do at the power pole. All it would really be is a variable freq drive. There's a lot of huge mining shovels that are electric powered so the converters are already made for similar application.

 

[Nouveau Redneck]

I never said that it would be hard to do, just that it would result in quite a large electric bill at the end of the month.

 

[dave_r]

Grid power isn't 220V, it's a lot higher, to keep amps down for transmission. It is generally stepped down to 220/110 at a pole within sight of your house (if you are in a city). And for industry, they'll provide other voltages as necessary.

For something like this, they would figure out how to minimize conversion losses. 110/220 wouldn't be involved at any stage.

And this is for someone who already has a significant diesel bill every month.

 

[elvenhome21]

Biggest problem with transmission voltage (12,500-14,000 volts) is the hazard and wire shielding. You would need one heck of an insulated cable to stand up to farm use and dragging.

 

[robhay2]

Grid power isn't 220V, it's a lot higher, to keep amps down for transmission. It is generally stepped down to 220/110 at a pole within sight of your house (if you are in a city). And for industry, they'll provide other voltages as necessary.

For something like this, they would figure out how to minimize conversion losses. 110/220 wouldn't be involved at any stage.

And this is for someone who already has a significant diesel bill every month.

This is correct. The voltage at the pole is the distribution voltage coming from the utility. This varies, but typically is from around 13,000 to 39,000VAC. The tractor would require separate equipment at the pole to convert to it's "cable voltage" of ~6000VDC. This equipment would consist of a rectifier (think: larger scale cell phone charger) with 90+% efficiency in a weather-tight enclosure. Then, onboard the tractor is a small buck converter that drops the voltage to 700VDC used for the wheel motors, likely further reduced for the autonomy equipment. None of this is very large equipment since the amperage is so low.

If the same amount of work is getting done, it is going to be cheaper and more efficient to do it by electricity than diesel, so I really think it will save farmers money. Hope so, we really need them!

 

[JohnW]

Doesn't matter what the voltages are somehow I WOULD end up cutting the cord!

 

[Flaken]

I think something is missing from what is described. Tesla, the man not the stupid car, was experimenting with broadcast power. He did build a tower near Colorado Springs, CO for the experiments. perhaps someone else has taken on those experiments. Just a thought, mind you.

 

[dave_r]

Wireless power for an application like this isn't really viable. This tractor uses a lot of power, over an extended period of time, so efficiency is the name of the game. Wireless power transmission is WAY less efficient than having a power cord.

It's really a thing of last resort, like:
1) if you are really really lazy, for example, if inserting a usb plug into your phone is too taxing for you to do every day
2) for low power devices, where environment/design concerns making having a power port/cable requires the device to be too large or more difficult to use
3) if it is very difficult to run a power cable to the device, for example, a satellite, drone, remote wilderness (and for this, you run the cord as close as possible)

 

[Nouveau Redneck]

Tesla's "broadcast Power" never came to fruition as far as I am aware. It is basically radio waves, which dissipate in strength rapidly with the cube of the distance, that is why all radio receivers require amplifiers to produce any audible sound, the incoming signal at the receiver is far too weak despite many modern FM broadcasters putting out power in the megawatt range. By the time it gets to the receiving antenna it is win the milliwatt range.

 

[MARK (LI)]

I saw somewhere in this that the extension cord is a kilometer long....did not say what gauge...forget about the electric bill, can you imagine how much the cord itself would cost? :tango_face_glasses:

 

[Kbeitz]

It would need a auto rewind cord...

 

[dave_r]

Yes, it does include the cord, and a big, automatic rewind spool, as well as the smarts to not drive over the cable.

 

[Alien5044]

Sort of reminds me of the "FlyMo" lawn mower of the early 1960's. Local hardware store actually had one on their sidewalk display for a time. Interesting concept, but the practical application...well...not so much. Wonder what a rural grid would have to look like to support this if it were widely employed.