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Need help buying cylidrical LTO cells
#11
(10-27-2019, 05:20 AM)flint Wrote: I am building a small power pack which can be recharged via solar and can power equipment in a remote wilderness location for a decade or more without maintenance.

My goal is to use enough cells that the power pack has extra capacity, and then if some cells fail they can be disabled and the equipment can run off of the remaining cells.  That is why high power output is important.  Less runtime is fine, but not having enough output watt capacity is not.  I need to be able to draw 5-10 C from the batteries.

The extra safety of LTO, not needing to worry about fires if the cells get damaged, is a big bonus too.  I like that LTO is pretty worry free, even in rugged wilderness environments.

With those requirements, why won't LiFePO4 work? Not trying to dissuade you away from LTO, just curious as to your reasoning. LiFePO4 cells also have an extremely hard time catching fire or causing issues and can discharge at high C ratings as well. And they come in very different form factors, more than LTO and probably even more than Lithium Ions.
flint likes this post
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#12
(10-27-2019, 10:01 AM)Oz18650 Wrote: Will the pack be used in multiple locations? Ie how moveable does it need to be?
If it is being used for 10 years or more in one remote location, would a larger number of cells being used at lower currents work for you? Ie a more typical powerwall like most people here are building?
You mentioned low temperatures.  Would a solar based heater work for temperature control for the cells - vacuum tube water heaters work in very low temperatures as long as there is sunlight on the tubes.
Just some ideas to consider.

Hi Oz18650,

A solar-based heater would be pretty cool!  Direct solar heating would be even cooler than electric heating.

For this particular battery pack though I need to keep things as simple and reliable as possible.  A solar-based heater might be a good way to extend range short-term or extend life long-term.  But if it failed I would still need the battery pack to work fine (i.e. "gracefully degrade").

I have an idea for a second residential installation though, if this first one works out well, and your solar-based heater idea could be awesome for that one.  Plus fun to play with. Smile

Flint

For the current battery pack, I'm also going to have to find an inverter and charge controllers which can last a very, very long time without maintenance.  That's coming up on my list after I sort out the cells.
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#13
Dig a hole 1.5 to 2m deep and put your battery pack there, any chemistry will work fine and temperature stabilized.
Theft not an issue.
With the relatively small sized pack, use a post hole borer, 6in - 8in in diameter. Get some underground waste pipe, put an end cap on the end in the ground (waterproof seal) and then use the pipe as a liner. Follow through with insulation cap at the top (6in thick polystyrene).

Cost of hole is less than the premium of LTO ?

The odd requirement to have a massively undersized battery pack (peak loading 10C) and seemingly quite small Wh is curious as to what over a 10 year time frame is being powered (electric gate ?)
100kwh-hunter likes this post
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#14
Something must be taking in consideration:
Polystyrene is moist sensitive, it will attract and store moist, very hard to get rid of.
Insulation value drops to near zero when its 40-50% saturated.
Pir sheets are less sensitive but in the long run(3 years) the value can drop to half it original R number
I would go for xps or such, moist does not have a chance to get in, and thus will keep its insulation value.

With pir sheets i would do 3 or 4 inch, xpm 1,5-2 inch.
Besides the ground is at a stable temperature, make a u bend at the upper end no need for a insulation cap.
Heat will stay below, how strange it my sound, people that have a fireplace with chimney will understand Angel
In deep ponds also, surface will freeze over and below it can be 10C.
Electric gate to keep people out or keep the cows inside, big difference between those two Big Grin  Exclamation

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