Off The Grid

When we are using water, it is ok to depend on the thread itself being a sealing surface. But when it comes to gas lines or refrigerant lines, we use what's called a flare fitting. There's a tool that forces the end of the tubing to flare out and that's the sealing surface. note with these fittings the thread inside the nut is not tapered, its is a straight thread. Also note that for gas that is breathable like oxygen, the flare fittings use a normal right hand thread. But for gasses we should not breath like LP gas, argon (welding), CO2 (welding) the threads are left hand threads. The turn backwards to a normal nut and bolt. So if you find a thread that looks odd or screws together backwards let that be a warning that it could be a flammable gas or a poisonous gas line.

We also find threads used on pipes. With pipes we want them to fit tighter and tighter as we screw them together. The idea is that if you tighten them enough they won't leak. So these threads are tapered... kinda cone shaped. So when you see NPT (national pipe thread) you know it will be a tapered thread.

Sometimes we find different thread shapes. A buttress thread is commonly used on plastics like IBC tote lids. Sometimes we find screw mechanisms that push and pull things and for those we use a knuckle profile packed with small ball bearings so there is no backlash.

https://tameson.com/pages/tap-drill-chart

Screw Threads. There are many profiles of screw threads but the most common is 60degree. What's magical about 60degree thread angle is that the cos of 60 degrees is 0.5. So the depth of a thread is 0.5 on one side , or 1.0 of the diameter. This means that you can calculate the inner diameter of a hole you intend to thread by taking the 1/(number of threads per inch) and subtracting that from the nominal diameter of the bolt. Here's an example... 1/4-20 thread... major diameter is 1/4inch (0.25"), the threads take up 1/20" (0.05). So 0.25-0.05=0.20. So the pilot hole (minor diameter) should be 0.20inches. Metric is even easier... M6x1 means the major diameter is 6mm and the thread pitch is 1mm, so 6mm-1mm= 5mm. The pilot drill should be 5mm. There are variables that machinists apply to change the fitment. Depending on the application you may want a small gap between the bolt threads and nut threads for dirt or grime, or you may want a tight fit. But this is good enough.

Old timers always have the best stories I cant deny.

LFP batteries.... These are the most common battery used in solar systems these days. Unlike other lithium chemistry they do not catch fire. Well, they can but they can't sustain the burn. Other lithium batteries like 18650s and NMC bring their own oxidizers and burn fiercely. LFP does not do this. Now, when we talk about a battery, we are talking about a collection of cells. 48v LFP batteries are made of 16 LFP "cells". Cells are always 3.2v and range from 100ah to 628ah (amp hours). So 16 in series makes votlages add, and thats 16 x 3.2 = 51.2v. The amp hours can be multiplied by the voltage to get watthours or kWh. So a collection of 16 314ah cells makes 51.2v x 314 = 16,076wh or 16kwh. Now we are the point that I'm writing about today.... some chinese companies are offering batteries that exceed 16kwh. If they do it with "MB56" 628ah cells, that's wonderful. But most of them are doubling the number of cells. Since they have to have groups of 16 cells, what they do is put additional groups of 16 cells in parallel. The problem with this is if one cell was to short out, the other one(s) in parallel with it would dump power into that bad cell. They should fuse them in this configuration but they don't. If things went really sideways you could have a fire from the heat of the shorted battery discharging.... but not from the chemicals in the LFP cell! So if you are going to get a battery larger than 16kwh make sure it is the MB56 628ah cells and not two 314ah cells in parallel. Models that I cannot recommend because of the parallel issue are Docan Dolphin series with 32 and 48kwh.

This can't be good. https://fedscoop.com/palantir-deal-with-agriculture-department-usda-farmers/