Daniel Schmidt

What brand battery are you using? LiFePo batteries have some sort of battery management system (BMS) inside, and different BMS's operate differently.

thomas rubino wrote:Although not cheap, the heat fans that sit on your wood stove produce a significant breeze, using no electricity at all.

 

They have a Thermo Electric Generator (TEG) inside them powered by the heat of the stove. Technically you could rig something up to power them with heat for cooling purposes, but with that much cost it would be cheaper to add more capacity/production to whatever off-grid energy source is being used.

I don't know how useful this idea would be for a multitude of reasons, there is a really good video about more efficient ceiling fans here:


If you already have a decent plan for powering a ceiling fan then finding a BLDC fan is a good option. It's possible to find out the specs of the motor and get a different motor controller that hooks up directly to DC power, but that's pretty technical and probably not worth it if you are only running on a 12V or 24V battery system.

I have taken a bunch of used PC fans and hooked them up in various ways to provide cooling. If you have appropriately sides hole saws, you can mount them to a piece of wood and make a duct to move cool air in or hot air out. I had my bedroom set up this way for several years. Especially when using old fans, they sometimes make annoying resonant sounds at certain speeds. Rather than buying individual speed controllers, I just found a voltage that they would run at without being too loud (such as 9V) and powered them with that. Since they were free, I could use a few extra to make up for the loss of airflow by undervolting them. They are already long lived, and running them slow prolongs that life further. Keep them clean and they can run non-stop for several years.

I was also using this for drying clothes. The rain is pretty much daily and sporadic around here, so just leaving a line out in the sun can be problematic. I had a free sheet of steel roofing that I covered a small rack inside a plywood box and used one of those USB power banks to run 4 smaller fans at 5V to exhaust the moisture laden air. I only used what I had on hand just to see if it worked. Nowadays you can find USB-C power banks that are capable of giving multiple voltages, such as 5V, 9V, and 12V which could be used to power a number of fans. You would have to figure out the current draw of the fans and the rated output of the power bank. They make various adapters (trigger boards and cables) to get a consistent output since USB-C needs to communicate with something to output the correct voltage.

You could also use any type of battery with an appropriate buck/boost converter to give what you need. The benefit to this is you can have a small number of quiet fans closer to you and perhaps a few more fans elsewhere for intake and exhaust. I had some small wires going around my bedroom for fans and lighting, but it would be easy to use separate batteries. Of course this is from the viewpoint of someone that can make battery packs for dollars instead of hundreds of dollars.

All of the videos I am finding right now are people replacing the evaporator line with a new one. I don't see any replacing the condenser. The upright freezers are either frost free (fans blowing through mini 'radiators' for the evaporator and condenser) or they have an external condenser on the back. I did see one video with a chest freezer that had a condenser on the back, and judging by the accent they were an ocean away. I'm extremely hesitant to give any info regarding refrigeration and have someone take what I say as fact when I have no idea what hardware they might be working with. It's very easy to make a logical leap to thinking something 'should' work and cause a serious problem.

A quick google image search for 'chest freezer diagram' brings up a bunch of pics with diagrams for various layouts. I'm not in the business of selling the machines, so I wouldn't know one from another purely by model name or number to be able to tell someone across the internet how to go about such a project. I learned on old cars that had leaked out years before I got to them and replaced the entire system with new parts. Those cars used the same r134a that many freezers use, so functionally they are very similar. If someone is looking for info in general then vehicle AC repair videos can give a basic overview of how the systems operate, as well as common faults that can occur.

I see a few videos of people making functioning systems, but they do things I wouldn't want someone to copy. The basic idea is sound if you know enough not to repeat the mistakes. You could disconnect the lines from an evacuated system, add more interior insulation, install a new evaporator line around the inside in a similar fashion to the original and ultimately get better performance. The reality of doing this successfully with the right ($$$) tools is a completely different matter.

I think I lost the two that I made, but I had taken a branch and made around 1 1/2" diameter versions of the kind without the spring that were flat on top. If I needed to keep an important note or piece of mail easily visible so I wouldn't lose or forget it, I could stick it in one to hold it up on my desk. They were also great for bags of chips, pretzels, etc. They got misplaced when moving, but if I find them or make more I will have to take some pics.

I also needed some medium sized alligator clamps one night to replace rusted ones on a battery charger and had to get creative. I JB Weld'ed some 12 gauge wire to the ends of a pair of the spring type, bent in a shape that would clamp on to a battery terminal. I attached the battery charger wires to that so I could charge someone's battery after their alternator failed. I had seen in years past where someone did something kind of similar, using foil around each end and held an insulating spacer in the end tied to a string. If anything pulled the spacer out, it would complete the connection to a micro controller to turn on a light. If you have to work with what you've got, then having clothespins around is quite handy.

56V on a 48V nominal lead acid battery would be equivalent to 14V to a 12V nominal battery (or two 6V batteries as the case may be). Cars typically put out more than that, so it wouldn't be harmful in the short term to see if it does settle in to a lower float voltage once the amperage output is reduced. A charger has to be at a higher voltage than the battery in order to charge, and if it was still pushing 5A then the battery was taking a charge. My understanding with lead acid is once you start getting below 1/20th of the battery ampacity, that between the design and internal resistance you aren't doing any harm to the battery. With 5A in to 225A it's like filling a bucket not quite one pint per hour.

Another thing I've noticed after a bunch of battery babysitting is the difference between the voltage output at the charger, and the voltage of the battery. This is especially noticeable at higher amperage because the total resistance of the circuit amplifies voltage drop as current draw increases. Plus in the case of lead acid, they have much higher internal resistance than Li-Ion/LiFePo. In extreme cases you can end up with a partially charged battery and the charger stopped because it read the voltage as full, and possibly heat damage around connections because all the energy that didn't make it to the battery turned in to heat. I see lots of people online using thermal imaging cameras to find the causes to issues like these.

If you have a halfway decent meter handy to check the voltage, you can try measuring the voltage directly at the charger terminals while it is giving close to 5A, measure the voltage as close to the battery as possible, and then disconnect the charger for a few minutes (with no other loads or charging) and read the battery again. You will probably end up with three slightly different voltages. This means the voltage the app sees (assuming this is just the charge controller and not a BMS like found on some Li Ion/LiFePo packs) will always read slightly higher than what the battery actually sees. Hopefully you can find someone with the same type of setup and experience with the same charge controller and app.

jason holdstock wrote: without sealing up the old timbers perhaps too much?

This can be a real problem when changing the original design. I have seen a number of videos on YouTube regarding vapor barriers showing how problems can occur, as well as some real world mishaps leading to condensation, rot, and very short service life before needing repairs. A warm roof is assembled differently than a cold roof, and if there are points of the year where those temperature invert for more than a few days at a time, it can quickly lead to condensation. The main takeaway I got from it is that you really don't want to have a lot of wood of other material damaged by moisture or prone to rotting right up against the vapor barrier if possible.

There are different kinds of vapor barriers with various amounts of breathability, and using the wrong one or installing it incorrectly might be worse than not having one at all. Any insulation used could either draw up water and grow mold, or hold it up against something that will grow mold and/or rot. There is a good YouTube channel with a bunch of well explained info here: Steve Roofer - YouTube

Do you have the printer connected to the computer with a USB cable? My mother has used cheap Cannon printers for about 20 years, and some use wifi which may be what it is looking for. As far as I remember, it always worked if I used a USB A to B cable. If that isn't an option then you would have to look up your model number and figure out how to connect it to a local wifi network.

I use cheap knockoffs of the SkyRC iMAX B6 charger from Amazon. After seeing the way many of the big name brand chargers actually operate, they seem more dangerous than what I'm using. I put alligator clips on the charge cables so I can get in to any part of the battery and just charge that parallel set. I trickle charge it and see how it behaves. If it gets over 3V in a rather short time at low current (highly dependent on cells and capacity) then it's usually going to recover decently. Doing multiples of the same packs like I did made it easy to see the few sets of cells that weren't going to take a charge. Obviously I had to babysit this whole thing in a noncombustible place, so I would find things to work on and glace over every so often.

I try to be very judicious with my expectations. If you have a particularly well worn battery and instead of a battery that is more aged than worn then this won't fix that problem. If they were stored poorly for too long then a charger can't fix that either. Trying to push in or draw out the maximum the cell spec sheet says on a used cell has the potential to fail catastrophically.

I've seen too many videos about what and how things go on with the cells, with various debates. Depending on who made the BMS (which can change even on the same model battery) it can work a bit different and have different protections and cut-off points and tons of other factors. There's a great explanation towards the end of the video here:


I just tried out a newly assembled pack while riding from St Augustine to Jacksonville and back by lunch, and I forgot to put sunscreen on my legs!

I've recovered a few hundred cells for my ebikes with good success. A lot of times the BMS shuts off for various reasons. It depends on what happened. If one of the safety features turn it off like a short circuit, or the whole pack starts to fall just below the voltage threshold, then it can usually be jump started like mentioned. It can be the same when you install a new BMS, if it doesn't work, a quick tap of the correct voltage range to the input will turn it on.  

Another thing that happens if a pack is left for many months or more, the battery management circuit very slowly draws power from only one of the parallel cell(s), because it would be too inefficient/costly/heavier to draw from the whole pack and use a larger buck converter to power itself. So you end up with one of the parallel cell(s) much more drained to the point the BMS shuts off. These are the packs that would be dangerous to just throw at the charger. If one cell is too low, the difference will be added to the other cells which over volts them! That's the dangerous part.

Some tool BMS's don't balance the cells with the BMS. Some only do it on the charger like RC cars. Some only balance near the end of charging called 'top balancing', and often this ends up with it trying to burn off a few mA per cell on the higher ones so the low one can catch up. If a battery sat really long or has a dead cell then it may never correct itself and needs those cells charged separately or replaced.

I noticed some of the USB-PD and other car chargers take 12V and 24V input, often having higher output at the higher voltage. I hooked one up to a couple different batteries advertised as 18V-20V and it was able to charge my Chromebook in use for hours which takes 15V.

I realize I'm reading this now entirely too late, but hopefully it can help someone out.

Pearl Sutton wrote:My freezer, similar size, old, used, with 2.5 inches of foam insulation added on all sides (held on with a camo ratchet strap, I'm so stylish!) in 22 hours used 2.08 KWH off the grid.

The inner metal sides of chest freezers have the evaporator (cooling part) in direct contact. You can usually see where the lines are when the frost starts to form. To get rid of the heat, the condenser (hot part) Is connected to the outer sides of the freezer. It's probably harder to tell exactly where those lines are, but they can be felt if you put your hand on the side when has been running for a while. If you move your hand along the surface while running, you can feel warmer parts, and if you keep your hand in place is usually cools down some of the metal, but the thin condenser line stays very warm. The fan on the pump/motor is usually only for those parts, unless it is a frost-free freezer. In most circumstances, you can add a bit of insulation to the top and perhaps the bottom, but insulating the sides is likely to cause it to work much harder.