Pipsqueak

Somehow this post got posted twice so I'll edit the second one with some more useful information. I remember reading somewhere in this thread where somebody was asking how long you run the freeze cycle with pre-frozen food. I have my chest freezer set to -12F, and I usually let the freeze dryer cool for an hour before I put the frozen food in. After I load the food in I wait another half hour to start the drying process. I've had a lot of cycles that the total time between pulling one batch out and starting the drying cycle on the next is around 2 hours. I'm running mine in a cold garage, so it cools down pretty quickly. If you have yours in a warm room it would probably take a little longer. Obviously things like ice cream and marshmallows you would want to let the freeze cycle run longer. When I'm ready to start the drying cycle, I open the door, remove the insulator, and check the temperature of the food on the trays with an infrared thermometer. As long as it's below -10F I start the dry cycle. A side note for TonyC, have you ever thought about attaching a mirror to each side of the tray rack to reflect the radiant heat back in to the trays? I've looked at some mirror finish stainless on ebay, and it looks like you could do it for about $40. Not sure if it's worth a try or not. I would think it would let you get more water out in a cycle because the radiant heat wouldn't be warming the ice on the chamber walls. Just a thought....

I know this was like forever ago, but I thought I would respond anyway. I haven't been on much in a while, I only run my freeze dryer in the winter. So I think you'll find it's a lot harder to remove water vapor from a vacuum than just using desiccant, as the vacuum will just pull the water out of the desiccant. The only way I know to filter the water vapor out would be a cold trap. They usually use liquid nitrogen or dry ice to keep the temperature low enough that all the water condenses out. Obviously you would need a supply of the liquid nitrogen or dry ice that would probably not be cost effective for most of us. http://www.bestvaluevacs.com/coldtrap.html The other option to get that cold would be to use a cryocooler and build a cold trap around it. It could be done, but would be pretty expensive. I've been watching some electronics on ebay that have cryocoolers in them, but the cheapest I've seen is around $600. Still not a cheap option, but you wouldn't need dry ice or liquid nitrogen to feed it. http://www.ebay.com/sch/i.html?_odkw=superfilter&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H1.Xsuperconductor+superfilter.TRS1&_nkw=superconductor+superfilter&_sacat=0

Your electricity usage will be dependent on your ambient temperature where the machine is running, and how big of a batch you are running through the machine. If you pre-freeze the food, that will save you time and electricity. If you've read through this forum, you probably have an idea of how the cycle works, so I'll give you some rough numbers on electricity usage. My unit runs approximately: 365 Watts on the refrigeration unit 300 Watts on the vacuum pump 825 Watts on the heaters The first 9 hours of the cycle is cooling only, so 365 W x 9Hr = 3.3KWH. If I pre-freeze the food to -10F in my chest freezer I pre-chill the unit for an hour, put the food in, let it freeze for another hour, and then kick it into dry cycle. That will save you about 7 hours. Once the unit kicks into dry cycle, the heaters kick on and off to keep the ice evaporating. I would say my average electricity usage for a dry cycle is around 1100 watts, but that varies a lot depending on ambient temperature. The colder your ambient temperature, the more efficient the refrigeration unit runs, and the faster food will dry. It seems like my average usage per cycle is around 20KWH, but that is an average that can vary widely. A batch of herbs that only has 8 ounces of water in it can be done very quickly, for probably 7KWH, but when it's really cold in my garage in the winter, I can load 10 pounds of apples in it and run a really long cycle which probably takes more like 30KWH. (When the ambient temperature is around 40F, I can easily take out a gallon of water in a cycle, I've dried trays of apples sliced an inch thick.) You'll just have to play around with it and see how it works for you. I was using a Kill-a-watt meter to check the electricity usage of all my cycles, but I had a momentary power failure on one of the cycles, and when the power came back on it blew the internal fuse in the meter. I replaced the fuse, but haven't hooked the meter back up. So this probably doesn't really answer your question, but hopefully gives you a general idea how it will work out.

I wouldn't expect yours to be as bad as mine, I abuse it a little. I haven't been keeping track of how often the oil needs changed. I've been drying fruit that is really thick - apples almost an inch. I pre-freeze everything in my chest freezer, and chill the freeze dryer for about an hour before I put the food in, and then let it cool for about 2 hours after I put the food in. A lot of cycles I get almost a gallon of water out. The really heavy loads I've been running 16 hours on the final dry cycle. I use a hair dryer to defrost, so a lot of the loads the vacuum pump is only off about 4 hours between cycles, and then running for over 24 hours. I should probably change the oil every 5 cycles or so. It looks like if you let the used oil set for a month the nasty stuff all settles to the bottom, and the oil on top looks pretty clear. You could probably dump it back in. I plan to filter mine and use it again. I'll probably start changing it more often.

My vacuum pump came with a booklet that gave instructions on removing the cover and cleaning inside the pump. I haven't done it yet, but it didn't look that hard. I'll probably try it next time I change the oil. The instructions said it was designed to be field serviced so I don't think you need to worry about ruining the seals or anything. I'm trying to find a way to recycle the oil so I can just change it more often. If you could get the moisture out of the oil and filter any dirt out of it, you could probably dump it right back in. Getting the moisture out is the hard part. If you could recycle the oil, the cost wouldn't be an issue so you could probably just change the oil every few cycles and the pump wouldn't get as dirty. I've been running mine constantly for almost two months and I've only changed the oil twice. It's probably pretty nasty inside by now.

Just a few thoughts to throw out there on the oil issue. All the options for a vacuum pump that's impervious to water vapor seem to be too expensive to be practical. So I have an idea, not sure if it's even practical, but I'll throw it out there anyway. Somebody will probably explain why it wouldn't work. The issue with the oil is entirely caused by the water vapor. If you could keep the water vapor out of the oil, it would probably last a really long time. One way to keep the water vapor out of the pump is to have a cold trap that the water condenses in before it gets to the pump. The problem with using this method is that you have to keep it really cold to condense the water. You would need to use liquid nitrogen or dry ice to keep it cold. Both options are expensive, especially compared to just buying more oil. So what would happen if you used a second vacuum pump, attached to the exhaust of the first vacuum pump, and used a gas ballast on the second pump to leak air into the line between the two? If you could keep the vacuum level on the exhaust from the first pump at 5 torr or less, the water should never condense in the pump because the pump would be to warm at that pressure for condensation. The second pump would have enough air blowing through it to blow the water vapor through. You can get a rotary vane vacuum pump fairly cheap that would probably work for the second pump. Not sure if this is practical or not, or if you can even run the vacuum pump with a vacuum on the exhaust port. Could we possibly put a valve on the vacuum line and shut off the vacuum pump after the air is removed? Once the air is removed, all that's left is water vapor so as long as no more air gets in, you dont need to pump it out right?

I agree with that. Maybe a deluxe model in the future... It's easy to stand back and say I would have done this or that different, but if I could make a better unit, I would be doing it, not talking about how somebody else should make theirs different. I may still try to re-control mine though. I ordered a Raspberry Pi to play around with, but I have no experience programming in python, so I have a lot of learning before I could even think about running the freeze dryer on it. Most of my programming experience is from Arduino, which is basically C, as well as Kuka Robot Language, which is similar to Pascal. Theoretically, for about $150 and countless hours of programming, I can add everything on my wish list. The $150 I can swing, not sure about the countless hours...

My understanding of the process is pretty limited, so anything I say should be regarded as suspect, but here is what I think is happening. In a vacuum the heat transfer from the heaters to the food is primarily radiant, rather than convection, because you can't have convection in a vacuum. It is probably hard to get an accurate temperature reading from a sensor because the chamber walls are much colder, and the shelves are much warmer, and the radiant heat from the shelves will be affecting the sensor temperature. The heaters come on at 500 mtorr, and start to heat the food past the vaporization point, which produces water vapor which then condenses on the chamber walls. The heaters can produce more heat than the refrigeration unit can carry away, so the pressure starts to rise as the surface of the chamber walls warms up. Once the pressure rises to 620 mtorr, the heaters shut off and the refrigeration unit cools the chamber enough to condense the water vapor down to 500 mtorr, and then the cycle repeats. I have my freeze dryer in the garage, and the ambient temperature is greatly affected by the outdoor temperature. When the ambient temperature in the garage drops to around 35F the freeze dryer kicks into the final dry cycle after only about 2 hours, but I always have to increase the dry time a lot. I think this is because the cold air makes the refrigeration unit more efficient, so it can condense the water vapor much more quickly, therefore the heaters can run longer without raising the pressure. When the ambient temperature is around 65F the freeze dryer doesn't kick into the final dry cycle for about 8 hours, but I don't have to run the final cycle as long. The heaters appear to have a thermostat that keeps the temperature from going too high on the final dry cycle, because my power draw drops down later in the cycle. I need to watch it run more though before I can be certain of this. My background is in electrical engineering, and I have a little experience in refrigeration, so when I see a machine like this, I immediately start thinking of what I would do different to make it better. Here are my suggestions for anybody from HarvestRight who may be listening. 1 A time out for the vacuum pump if vacuum doesn't drop to 500 mtorr within 15 minutes. 2 A way to set the final dry cycle time before it actually kicks into the final cycle. 3 A way to adjust the heat power based on what you are drying. Things like ice cream could use a more gentle heat cycle. This could be done by adding a solid state relay and pulsing the heaters. Those are the basics. Now here is my dream list. 1 A touch screen. This is 2015 after all... 2 A strip chart on the touch screen showing the pressures and times and any another information you could want. 3 Internet. I want to be able to control this thing from my phone at work. 4 Open source hardware and software. Don't take this the wrong way, this is already an incredible machine. The engineer in me just sees things I would like to change.

My unit turns the heaters on at 500 mt, and off at 620 mt. In theory, you can get the temperature based on the pressure. With mtorr being roughly equivelent to microns, you can get your temperatures from this chart: Boiling Temperature Vacuum Pressure (oF) (in. Hg) Microns 212 0 762000 192 10.24 500000 152 22.05 200000 125 25.98 100000 101 27.95 50000 84 28.74 30000 72 29.13 20000 63 29.33 15000 52 29.53 10000 39 29.69 6000 29 29.76 4000 15 29.84 2000 1 29.88 1000 -12 29.90 500 -21 29.91 300 -28 29.91 200 -33 29.92 150 -40 29.92 100 -50 29.92 50 - 29.921 0 However, I'm sure the pressure reading isn't completely accurate because the pump is only good to 25 microns, and if you were to drop below 50 microns you would begin to draw water vapor off the ice on the chamber walls. ...And the forum totally slaughtered my chart. I tried to clean it up. hopefully it's better this time.

A Watts Up meter is like a kill-a-watt meter with a data logger. You could monitor the whole cycle and export the information to a graph to see what the whole cycle looks like. You would be able to see when the heaters kicked on and off etc. Unfortunately they're about $200 so it's hard to justify it just to see what a cycle looks like on the freeze dryer. Maybe we should start a thread for the tinkerers among us trying to reverse engineer this machine.

Thanks! Those power factor readings seem similar to what I'm getting, but my power draw is a lot higher - about 1650 when refrigeration/heat/vacuum are all running. My amperage reading is around 18. The refrigeration cycle seems similar to yours, but my heater amperage and my vacuum amperage seem a lot higher. I think the heaters say 165 watt on them, and there are 5 of them, so that would be 825 watt just from the heaters, but it seems like when the unit is in the final countdown, the wattage goes down. Maybe the heaters have some sort of thermostat on them? I would think that if it really was running 825 watts in a vacuum chamber the shelves would get a lot hotter than they do. Maybe I can talk my wife into letting me get a Watts Up meter to find out what's really going on...

Hi everyone, some great information here, thanks for everybody's work. I have a couple of comments and a couple of questions. I've had my freeze dryer for about a week and my third batch is running right now. My first batch I ran some strawberries through, quartered they were about 3/4 inch thick. I ran the dry cycle for 8 hours but they weren't quite completely dry. It didn't really matter though because we had them all eaten by the next day. So my question is, do you have any sort of guideline on how to know when the thicker items are finished? Can you tell by the mtorr readout? Or do you just get a feel for it after using it for a while? I saw in one of the earlier posts somebody mentioned they have a kill - a - watt meter running on their freeze dryer, but I can't Remember who it was. Have you ever checked the power factor when your unit is running? Mine runs about .4 when the heaters are off which seemed pretty low, but I didn't know what to expect. Anyway, a couple ideas to throw out there and give back to the community a little. An easy way to check the door seal when you close the door is to shine a flashlight into the edge of the acrylic door. The ring where the seal makes contact will light up and you can see if you have contact all the way around. One thing I noticed when I had the door seal off was that the surface on the stainless steel cylinder edge was a little rough. I polished it by hand with some microfinishing film to get it smooth all the way around and it seems like it holds the vacuum a little better. The heaters kick in about 6 minutes after the pump comes on. Has anybody done any reverse engineering on the electronics for this machine? It looks like it's running on an atmega88pa processor. There are 6 pins on the board right next to the processor that may be for a serial connection though I haven't traced them out. If that is the case you could possibly update the firmware on the board. I'm not sure how much support you would get from harvestright on that though. Alternately, somebody could retrofit a unit to an arduino controller and write their own program for it. It would be a fun weekend project.