Carl Nystrom

+ Follow
since Sep 03, 2020
Merit badge: bb list bbv list
Homesteading on 80 acres of forest in the northern Willamette valley. We have year-round streams, steep slopes, and acidic clay and silt-loam soils. We have dry mediterranean summers and winter lows in the 20s most years. We get about 50 inches of rain.
For More
Clackamas County, OR (zone 7)
Apples and Likes
Total received
In last 30 days
Total given
Total received
Received in last 30 days
Total given
Given in last 30 days
Forums and Threads
Scavenger Hunt
expand Pollinator Scavenger Hunt
expand First Scavenger Hunt

Recent posts by Carl Nystrom

Hmm. Moon power? Sounds like interesting science fiction, but a dang hard engineering problem. How exactly is the power getting from the spinning space probes back to the surface? Magnetic field strength drops off as a square (or is it cube?) of the distance, right? This is why the air gap in a generator or motor is measured in fractions of an inch. Low earth orbit is like 250 miles, and even that might be too close, as the there is atmosphere there that will slow a satellite and eventually crash it.

Also, the probes will need fuel to make the course corrections needed for each gravity assist, right? Even an ion drive would need reaction mass refills.

Also, if you need to build a superconducting ring on the surface of the moon, how much is it going to cost to launch all of that? The Apollo program cost nearly 200 billion in todays dollars, and all they sent was a few little buggies.

And the last thing that comes to mind for me is what sort of protection is all of this equipment going to need from solar storms? No magnetosphere in the moon, right? Giant superconductors might do interesting things during a big CME. Which reminds me, that the surface of the moon gets up to 250F during the 2 weeklong day, so you are going to need to cryogenically cool the loop anyway.

All of this makes me wonder if maybe it would be easier to build solar panels in the desert in Nevada, and just deliver the power with a superconducting electrical grid?
2 years ago

I just don't see how spinning a weight can be so much more expensive than batteries

The problem is how fast the weight needs to spin in order to store any meaningful power. Chemical energy is just very dense compared to basically all forms of mechanical energy storage. Giant flywheels are a neat idea, but they have to be engineered very well or else they become a serious safety concern. Can you imagine what would happen if 40 kwh of spinning steel in your garage was to suddenly dump that energy? Kaboom.

As for costs, LiFePO4 batteries at present you can buy cells and a BMS for around 225$/kwh. My understanding is that the auto companies are getting prices closer to 100$/kwh for batteries. They should easily last for a decade or two, contain no toxic metals, weigh like 15lbs/kwh, and while they are not really recycled at present I suspect that in a few years time they will basically all be reclaimed and either reused/refurbished or recycled.

I just do not see batteries falling out of favor for small-scale power storage, and the technology keeps getting better. Energy density might be approaching its limit, but I think there is still a lot of room for things like cycle life to improve.

2 years ago
So, Michael seemed to miss that you mentioned that both systems are 12 volts. Back in the old days, 12v was basically the only option, but now most everything is available as 12 or 24, and even 48 is not hard to find. I have a little DC chest freezer that will actually run on 12 or 24. Charge controllers can be programmed to any voltage, so the only real picky piece of hardware is the inverters.

The big problem with 12v systems is how many amps it pulls. You mention having 2 charge controllers, but each one would need to deliver over 100 amps to handle a 2.5kw array. A 3000 watt inverter at 12v would draw 250 amps, which would need cabling the size of your thumb.

Also, with that many batteries in parallel it would be tempting to wire them up in a "ladder" configuration, with 10 sets of 2 in a line, and all the positives and negatives chained together. This saves wiring complexity, but can lead to imbalance, where the cells on the end do more of the work due to the difference in resistance. It could be that they were wired correctly, but it would be quite a complex arrangement. Do you have a picture of the battery bank?

Since lead acid batteries will likely only give you 3 or 4 years of service when cycled daily, I would really suggest thinking about changing to a higher voltage down the road. Since you have so many batteries, you could even split off a portion to make a new separate system. When going completely off grid, redundancy is nice to have. Maxing out the amount of panels that you have is also a good idea, and by upping the voltage you could effectively double the panel wattage without getting any more charge controllers (which are often a big portion of an off grid systems budget).

Anyway, none of that really answered your actual question, which I think I understood to be: "How do I avoid over-discharging my bank?"

So, first off, you did not mention a battery monitor - which is critical. If you do not have one, invest in a monitor that records amp hours in and out. You can also set them up to remind you to equalize your batteries, which you should ideally do every month or so. The newer stuff just has a little clamp that goes over the main power lead, otherwise you will need to wire in a big shunt.

Next, making a point of knowing the cut-off limits of your inverter is helpful, although in my opinion they set the limits so low that a lead acid battery is going to be degraded anyway if you rely on that as your safety measure. Lead acid batteries are pretty terrible. The only thing they really have going for them is that you can buy them at any store on a moments notice. They are no longer cheaper than lithiums when you look at lifecycle cost, so there is really no reason to buy a new bank of lead batteries unless you want something quick and easy and that will handle abusive charging. Anyway, also not really on topic, but to quote Bob Dylan, "Times they are a changing." If you really want to protect your batteries from an inverter, the easiest thing to do is get an inverter with power save mode. The cheapest thing to do is turn the inverter off at night. The most fun thing to do is track down a free starter solenoid (contactor, relay, etc) that can handle a few hundred amps, and wire it up to a simple voltage-based relay controller. Some of the battery monitors may have this function as well. Then you just program it to cut the contact to the inverter once your battery voltage drops to whatever you feel like it ought to be.

Anyway, I sure do love talking about batteries. I just finished installing a 1.5kw array for my cellar today. I built a 7kwh lithium iron phosphate bank using bare cells that ran me 1650$ with the BMS. I fit them all into a milk crate, and can still lift it (although the day is coming where I will need to split it into 2 milk crates to get it back out of there). To get an equivalent amount of storage, you would need over 600 lbs of lead batteries.  I can post some pictures of the setup if anyone is curious.
2 years ago
They will be fine. Grapes are really tough. It seems a little late to me, but in our climate the grapes are growing by may, and that makes them a little more fragile to handle and ship. Ideally youd want to dig them up before the buds break, but i suppose depending on where the nursery is, that might still be the case. Anyway, stick them in the ground when you get them, keep them watered, and they should be off and growing in no time.
2 years ago
HEPA simply means High Efficiency Particle Absorbing. To meet a true HEPA classification, the filter needs to remove 99.97% of particles that 0.3 microns across. They are actually even more efficient at particles larger and smaller according to wikipedia - the 0.3 micron size being chosen as the reference simply because it is the hardest to capture.

Basically, the material is made of very fine fibers in a random arrangement, and the tiny particles bump into the fibers and get trapped by static cling. It does not sound like vacuuming them out will help much, and washing actually makes them worse:

If the air purifier is doing a critical job, then you will be best served with a scheduled replacement of your filter. Could there be a way to mitigate the problem that the air purifier is solving? Selling your house and moving to a state with better air quality might not be cost effective compared to those filters, though :)

You might also look into electrostatic precipitators, which are filter-less, but I think they have their own drawbacks.

Finally, a DIY true HEPA is likely going to be a very tough project, but you might be able to cobble something together that is good enough. I would start with researching world war 1 era gas masks, which probably used the closest thing you will find to sustainable materials for a high efficiency filter. Let us know if you find anything interesting. Wildfire season will be here before long...
2 years ago
Grapes are typically trained as a single trunk to the fruiting wire. From there, you either use cane pruning (where you leave a long shoot of the previous seasons growth) or cordon (also called spur pruning, where you build lateral limbs with short stubs of last seasons growth)

All grapes fruit on new wood that grows from the buds on last seasons canes. This means that you need to remove most of last seasons growth or the whole plant quickly turns into a dense and overgrown mess. It is important to establish "form" so that the vine can be trained to the trellis in basically the same way year after year.

Cane pruning and spur pruning have various tradeoffs, depending on the variety and its characteristics. Cane pruning is better for grapes with smaller clusters and less vigor, and spur pruning is generally used on larger-clustered more vigorous varieties.

The european grapes tend to have a more upright growth habit, so they are often pruned with low trunks, and the new growth is tied in place as it grows upwards during the spring. This is often called vertical shoot position or VSP. Some american varieties (like concords, I want to say, although I have never grown them) tend to take on a more trailing form, and are sometimes trained along a high wire and allowed to drape down like a curtain. For a small number of vines, any of these systems will work. Upright types can be grown on a high-wire trellis; they simply flop over once they get to a certain size. High winds can be a problem with this method, but where practical, it does save a lot of labor in the early season.

The nice thing with grapes is that they are tough. It takes a lot to kill them. You can cut an established vine to the ground, and completely retrain it and have it start producing again within a couple of years. They are also very easy to propagate from cuttings. You should strive to keep big pruning cuts to a minimum. If you lop off a limb that is over an inch thick, it will take it a long time to heal, and the vine can get fungal infections that will eventually kill it.
2 years ago

everyone keeps talking about elevation drop to create force to push water up, but won’t shear force of water flowing create the same force?

Water only flows when there is elevation drop. The available power is a function of drop times flow. A very gentle slope can produce enough power to move water up a hill if there is sufficient flow volume.

You will likely need at least 2 or 3 feet of elevation from the inlet to the outlet of the "drive pipe" for a ram pump to function. On a gently sloped site, you would probably need to build a dam. If the site is very flat, that will likely flood a fairly large area. The drive pipe needs to be a certain length - I forget the ratio now - but I think it was based on the drive pipe diameter.

There is lots of good info on building ram pumps out there, but first you need to evaluate your site. Google earth shows elevation in the bottom corner, and is a good way to figure out the local topography. You can even use the polygon tool to figure out how much land you will flood if you dam up your creek.
2 years ago
Yeah, I think this is a topic that might be of interest to others as well. I am thinking of using a wooden frame as a stop-gap to an eventual concrete tank, and I figure the plywood ring will make nice formwork to apply cement to.

Also, if I lay down a compacted gravel bed, filling a tank with 27,000lbs of water a couple of times should help the ground do any settling it is going to do before I move to a less flexible concrete liner. I have access to a bunch of old 12 foot pieces of sheet metal, so I think I will put some sort of shed roof up over mine to hopefully give the liner a fighting chance at lasting more than a year. Also, I am going to build it in the woods, so It will keep leaves out.
2 years ago
Ram pumps do not need very much drop to operate, although there is a sweet-spot in terms of drive pipe drop to pump output rise. I want to say 1:7 is the ideal, but it has been a while. That would imply that you would like to see 10 feet of drop to pump water 70 feet. You could likely make do with much less, you would just need to make the pump bigger, and recognize that you were maybe not going to pump as much water as a percentage (although you have so much flow that it likely is not going to be a problem to move quite a lot of water).

I built a pump that had about 10-15 feet of drop in 2" pipe, and it delivered several thousand gallons of water a day. I was not pumping more than maybe 20 or 25 feet, but I observed it reach 40PSI once when I kinked the output tubing. Whether it could still deliver meaningful flow at that pressure is unknown to me, but 70 feet of head only needs 30PSI to overcome. There is lots of good info out there on building ram pumps.

Your first step is to figure out how much drop you can manage to get. Then depending on how much water you want to move, you can size things accordingly. Its a fun project; I kind of miss the sound of it running - they are far from silent in operation.
2 years ago