On generators and physics
On tuesday here we had a massive wind storm come through. 25-35mph winds with gusts up to 75mph or more, along with heavy rains and near freezing temps. It’s a pretty crazy thing to experience in the forest. 250-300ft douglas fir trees swaying 30 or 40 degrees in the winds, branches coming off and flying by. A large gust came through and broke 3 of our large trees off and pulled another one out by it’s roots. Very sad to see these big trees go.
But to bring things back to a tech focus, also on tuesday due to the storm, we lost power for about 16 hours. We had gotten a generator to handle just this situation and had run it happily for a spring outage earlier in the year. We were running on 20lb propane tanks (since they are so easy to get). In the spring we were getting about 5-6 hours of use out of a tank.
So, I fired up the generator and we got about 3 hours out of a partial tank, where I switched to our last full tank and headed into town to stock up. I exchanged the empty tank and got 3 more. That last full one was out when I got home, so I swapped another full one in and… it stopped after an hour. At first we were wondering if we had some heavy load on the generator we didn’t realize, but on checking that wasn’t the case. We looked for leaks in propane, but wait… the tank is all covered in frost and all frozen up. Here we realized the real problem.
Propane in tanks is in a liquid state, under pressure. When you open the valve, propane comes out and changes into a gas to power your whatever. This state change requires energy. Usually this is just pulled from the tank shell and everything is fine. However, when it’s cold, the tank gets colder and colder and can’t supply that energy anymore and with no gas flowing anymore, the regulator cuts off the generator.
So, at first we tried putting the tank in the garage instead of outside, wrapping it in blankets, etc. But that didn’t really help too much. So, then we got a tub and filled it with water and put the tank in there. That helped quite a lot, we managed to get about 4 hours out of a tank then. At the end the tank had a 1 inch or so ‘wrapper’ of ice, but it did get the tank lasting longer.
So, whats the solution here? Well, I think getting just one larger tank (say a 100lb one) would help a lot as it will have a ton more surface area. Not as easy you move around, but oh well. Also, they make apparently powered heating blankets for the smaller tanks. I’ll probibly pick up one of those in the short term. So, lesson learned: temperature has a lot to do with how well your propane generator will work.