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Credit: Cassie Langstraat

In podcast 295 Paul, Rick, Jason, Steve Heckeroth, and Stuart Davis continue talking about the projects they experimented with at the solar workshop. They began by discussing their time spent with fresnel lens. They did indeed manage to get some stuff set on fire but for the most part it was pretty cloudy, making it ineffective. Paul describes how his main points regarding the fresnel lenses involved safety. He talks about how there are few practical uses for them besides setting shit on fire. He goes on to explain that they can work fine when you use them for small indoor things like reading but when you get the sun involved, they get freakishly dangerous.

The guys briefly jump back into discussing Tim's truck and mull over the type of inverter he used. The inverter Tim wanted needed to have 3000 watt capabilities for running big power tools. So he ended up getting one with a hybrid sine wave. However, the guys talk about how the modified sine wave makes motorized things, anything with induction in fact, sad. If monitored, this can work but Paul says it's better not to depend on human discipline.

Moving right along, Paul brings up his preference of tractors over horses. The guys consider how horses take up a lot of space and rarely get used enough to justify their presence on a homestead. They talk a little bit about other animals and the pains that goats often cause.

The next topic that gets covered is the voltswagon. They discuss its original design failures and talk about how the new trailer Tim is making is much better. The new one has a much stronger frame to hold the heavy batteries but is still small enough for electric vehicles to pull. They then consider the problem of the actual solar panels being sufficient to run the saw mill,which was the voltswagon's original purpose. It seems close to impossible to switch the voltages but one of the guys does mention possible optimization.

The crew then dives into deliberating the whole idea of biodiesel and biogas. They sort of come to the conclusion that these processes are fine if they are using waste products, but when it turns into a whole new excuse for tons of land to be used in a unproductive monocrop way, it becomes a bad idea.

The last topic they get to in this portion of the podcast is different types of batteries. Steve spends some time advocating for lithium batteries for various reasons. For his tractors, lead acid work fine because they need the heavy weight but the lighter lithium batteries work way better for electric cars. They also last 3 times as long.

This leads them into a consideration of nickel iron batteries. They have a way longer lifespan than lead acid or lithium batteries, but they are not as readily available or even known about. In addition the nickel iron isn't as toxic as lead. However, these nickel iron batteries cost way more and discharge themselves quite a lot more than the alternatives. So, the guys conclude this topic by noting that there is definitely room for optimization with the nickel iron batteries but they could potentially end up being awesome.

Relevant Links

Wheaton Laboratories Electric Tractor
Solar Electric Sawmill
Solar Generator
Mobile Battery Bank in Your Vehicle

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Posts: 232
Location: S.E. Michigan - Zone 6a
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I am very interested in how to pick the right inverter. I asked Steve Harris via TSP about pure vs modified sine wave and his answer was it was only a problem with synchronous AC motors which would be a special condition for a homeowner to have. But that doesn't sound like what was disused on this podcast. Now I'm more confused.

I understand that most electronics convert the power to low voltage DC right away so I get why modified sine-wave wouldn't be a problem. If only I could find a 36V DC chainsaw most of this would go away as that is when I really want to power with my 36V electric tractor.

PS you can hear Steve Harris' answer to my question at this episode of TSP about 30 minutes in.
Posts: 18
Location: Santa Cruz Mountains, CA
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Hi Jerry, It is an advantage to use a pure sine wave inverter from the standpoint that it will run any kind of load. Pure sine wave inverters are more efficient as well. You’ll get more out of your battery bank and solar modules as a result.

Some inductive loads will not work well with a modified sine or square wave inverter because of the higher frequency harmonics of a modified sine or square wave. These high frequency waves cause heating in the core material of most inductors/transformers that are designed for use at 60 Hz. For example a step down transformer in a piece of equipment would likely get hot and eventually fail if ran on a square wave. Many AC motors accept the AC power directly without any filtering or conditioning and therefore being inductive devices may be damaged and fail prematurely. I had a blender fail prematurely due to overheating as a result of running from a modified sine wave inverter. I’m not sure I would take a chance on a frig with a compressor motor. At times we have no way of knowing what the electronics of a particular device is or what kind of load or motor is inside the device.

In general switching power supplies have no problem with a modified sine wave or square wave. Most all our electronic devices such as computers, TV, and the like are based off of switching power supply technology these days so if that is what you will be running from the inverter you should be fine. However, if you will be running a microwave oven or any AC motor device it may not work because you have no way of knowing how the signal is conditioned before leading to the motor or inductive load of that particular piece of equipment. By not using a sine wave inverter there is a chance something will be damaged. While running devices pay attention to how hot they get. For example, on power tools the motor is exposed enough to feel if it is getting hot. If it is getting hot, don’t use it on the modified sine wave inverter. The reason the inductive load fails is because the insulating material in the coil of the inductor gets so hot it melts. Then shorts result. Some motors and transformers can run hot no problem, but this heat is another source of inefficient use of your battery bank and solar modules.

Hope that helps.
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After catching up with the podcast,
1-have you thought of using a used truck frame as the base of the trailer?
2-Surplus military trailer

a used small truck frame or used military truck trailer would be road worthy for other uses.
Posts: 30
Location: Altadena, CA, USA
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I have experienced that some Stereo and TV equipment does not like MSW so much and produce a fairly loud acoustical humming. They still work but it is annoying - with pure sine this is not the case.
On the other hand are pure sine much more expensive and have a higher idle consumption than MSW. I would suggest you could buy a MSW from a store that will take it back in case you run into these problems.
Diego Footer on Permaculture Based Homesteads - from the Eat Your Dirt Summit
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