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12V "suitcase" battery pack, pouch cells
#1
I'm just starting this thread to park info I find for this project. I am open to suggestion for better options, but...

I have a 14V / 100w solar panel kit from harbor freight Tool / HFT. A couple years ago when I bought this, my plan was to buy a deep-cycle lead-acid 12V battery from Walmart. Never got around to it, and in the meantime I have spent a LOT of time researching 18650 lithium cells. I recently wondered what the best components would be for a power-suitcase that could keep my cell-phones, laptop, 18650-flashlights, and TV running in a temporary power outage (no refrigerator, no A/C). I hope to share the info I find, and in exchange I hope to get free advice about the best components.

My work is nearby and has a large V12 diesel generator, so I want a charge ability for 110V AC input. I have a 14V solar panel which includes a simple and crude 12V charger.

HFT now has Apache brand plastic cases, (Pelican clones), and the 2800 model is $30, and looks to be useful (interior face is 12 X 9 inches, when opened like a laptop, five inches thick).

The optimal full charge for 4S LiFePO4 is 3.65V per cell (14.6V for 4S), but they can take up to 4.2V without damage (do not store long-term at 4.2V, for 4S this would be 16.8V). This means that a common and cheap lead-acid 12V charger will only provide a 70% charge at 13.8V, however...this also means that a common car alternator can provide a 70% charge (with no damage) in an emergency.

There is no useful range below 2.8V per cell, but...LiFePO4 can be taken down to 2.0V without damage, and...this wide range of SOC is at the heart of the perceived safety of the LiFePO4 chemistry. By that I mean...your charger and LVC can go off by 10%, and the battery will still not be damaged, or go into a thermal runaway...

What is a reliable and compact 110V AC pure sinewave inverter that would be appropriate for...a little less than 1000W using a 12V battery?

What is a reliable and compact LiFePO4 charger for 4S / 14.6V...110V AC input?

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edit:  Harbor Freight "Apache" case interior dimensions, in inches

1800__8.2 x 5.7 x 3.0 (additional 0.5 of height is available inside lid)
2800__12.0 x 9.0 x 4.5 (additional 1.0 inside lid)
3800__14.5 x 10.3 x 4.5 (additional 1.5 inside lid)

In Le Metric

1800__208 x 145 x 76 (plus 13mm inside lid)
2800__305 x 228 x 114 (plus 25mm inside lid)
3800__370 x 262 x 115 (plus 40mm inside lid)
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#2
Nice idea. Keep in mind that just because the LiFePO4 can go to 4.2V, I wouldn't recommend it and don't use it for overall capacity. Keep them in 4s configuration and charge them normally. 3.8 * 4 = 15.2V. So, as you mentioned, a standard leadacid charger will charge these up just fine without issues. A standard car charger won't go over 13V charging. That leaves you with 3.25V/cell. In a pinch, it'll give you some charge, but it won't fully charge the cells. Unless you go with 3s instead, but then you are taking a chance of constantly overcharging and would need to put a limiter in place.
A standard car alternator outputs around 14.4V. It can peak around 15V, but usually for short periods. I know there are some that will say theirs is at 16V, but I think this is a rare, or specific applications. The reason being, the lights and the circuitry inside the car is designed for 14V max. Try connecting headlight lamps or other bulbs to 16V that is rated for the 12V and you'll see why.
So base your calculations of charge off vehicle related charging from ~14.4V and you'll be good to go. Plus you won't have to worry about added equipment or safety electronics to keep the cells in spec.

I'd like to see another "case battery bank". I think they are pretty neat and there have been some nice ones here on the forum so far Smile
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#3
They should not go above 3.65V in generall but yes they can take higher for short bursts. But depends on the type of LiFePo4

3.25V can be empty but it can also be 90% full on a LiFepo4
They are between 3.1-3.25V in generall where most capacity is.
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#4
Thanks for the replies. I just bought six 350 farad 2.7V Maxwell super capacitors to make a 15V max bank. I'll fiddle with them when they arrive. I almost bought five Amperics 3.0V caps. Same price and same max voltage to add surge capability to a 12V pack. Frank pointed out that the Maxwells had a lower Impedance/Resistance/ESR or 3.2-mOhms...The Amperics would make an easier-to-fit pack of five caps, but the ESR was twice as high at 7-mOhms (who knows if these numbers are accurate, most sellers are "optimistic" when posting specs)

I am looking for a non-LiPo power pack for the kWeld spot welder. I also want a 12V suitcase to power my phone and laptop in an emergency (the Emergency power supply only needS the LiFePO4 pack, no capacitors needed). However, since the kWeld power supply needs to have a huge surge rating with extra low ESR, capacitors are almost a requirement to match the current of the 130C NanoTech LiPo.

The "car starter" booster pack feature needs both battery and capacitors, but not necessarily the low-ESR battery and super capacitors. Of course capacitors can bleed down over time, so some type of isolatable battery is needed. Capacitors work great in cold weather (which is a plus for a car booster pack). They would be separated inside the suitcase due to the bleed-down characteristic. Connect them through a resistor to eliminate a big spark, and in a half minute, the caps are charged up from the LiFePO4.

If I used caps only (charged with a 12V car battery charger), they would bleed down over time, plus they don't have any appreciable range when running as a "battery". The 4S LiFePO4 battery has decent run time, but can be injured by rapid multiple jolts. A combo hybrid seems to be the best option for this.

I decided to use only four LiFePO4 cells, so the cell balancing chores are greatly simplified, and more reliable. because I chose only four cells, I thought I might use the larger headway 40152 cells (16-Ah), for more run time, but...Frank pointed out the smaller 38120's have a lower ESR at 4-mOhms, compared to 8-mOhms for the larger cells.

I could use the $52 20Ah flat cells from A123, 20C, 400A peak (four = $208 plus tax and shipping). however, I wanted to do something that was easily repeatable, and customers can buy the cells themselves (bypassing me, so I don't have to ship lithium cells). The cylindrical Headways have threaded tips, easy to install.

edit: If you charge 4S LiFePO4 with a car alternator, the 13.8V output ends up being only 3.45V per cell, which is below the optimum 3.65V, but...its far enough above 3.2V nominal that plenty of energy is still stored. To measure the actual difference...I'd have to charge to 3.65 and then cycle for capacity, then charge to 3.45V, cycle for capacity...and then I'd know how much % of range I was giving up. However, if charging with a car alternator in an emergency, there are millions of them around, easy to find anywhere. Solar panel charge controllers can be adjusted to make the full 3.65V charge if desired, but...if there is no sun, you can still get an 80%+ charge from a car, or car alternator driven by a lawn mower.
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#5
It's turning out that this style of battery and capacitor bank will not work well for the spot-welder power supply I am also working on. However...the LiFePO4 batteries have been tried and work well for a solar suitcase, and adding $60 worth of capacitors make it suitable to start a car with a low 12V battery.

Multiple cells in parallel require some type of balancing board, but...the BMS is often the death of a pack as much as the amount of times it would save a pack, so...I'd rather use no BMS. That means that I will be using just four large cells, rather than a multi-cell pack...possibly the 20-Ah flat foil packs (prismatic?) $52 each plus shipping, $208-ish for 20-Ah / 12V

I'm told the super caps will drain down over time, so they should not be stored while connected to the battery (they would drain the LiFePO4 to zero volts). Therefore, to charge the caps (when using the case as a car starter), I'd connect them through a resistor to charge the capacitor bank, then after a couple minutes, close a beefy high-amp switch.

I'll test the super capacitor bank by itself as a car starter, so the LiFePO4 would be safer and more protected by staying isolated...

The charging methods would be 1) car alternator, 2) 120V AC wall socket, 3) 14V HFT generic Chinese 100W solar panel. Once all of that is sorted, I'll add an inverter that is as large as can fit...
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#6
(02-11-2018, 01:49 PM)spinningmagnets Wrote: What is a reliable and compact 110V AC pure sinewave inverter that would be appropriate for...a little less than 1000W using a 12V battery?

This inverter isn't exactly compact, but highly reliable. About a year ago I went in search for a true sign inverter in the ball park of 400-800 watts. I was unable to find one in my price range, but then stumbled across this aims 1200 watt inverter. Dollar for watt it was the best I found and I have been running various small power tools from it a few times a week and works awesome for my needs.

AIMS Power 1200 Watt Pure Sine Inverter with Automatic Transfer Switch https://www.amazon.com/dp/B00TI1D5JK/ref...KAbZZ1C2NP
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#7
Thanks! 

$154, dimensions using inches ...15.3 x 9.4 x 3.8...looks like a great bang-for-buck ratio. If Aims is a well known brand that has a reputation for reliability, their other products are likely designed and built to the same standards? Here's some data from the Amazon ads...

$154__390 x 240 x 97mm__1200W / 10A__PWRIX120012S

$205__297 x 140 x 71mm__1000W / 8A__PWRI100012S

$122__230 x 153 x 77mm__600W / 5A__PWRI60012S (more "cube shaped" instead of long and low)

There were even smaller units, but if this power bank was needed in an emergency, I don't want the device turning out to be inadequate or overheating...These model numbers are their "compact" line. It appears they have models with the same specs, but in larger cases. For instance, the 1000W PWRI100012120S is about 1/4 larger in volume. Maybe its the difference between an RV installation and a house? Here's the dimensions for those who prefer inches.

15.3 x 9.4 x 3.8
11.7 x 5.5 x 2.8
9 x 6 x 3
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#8
I've come to the conclusion that...

Always buy a pure sine-wave inverter (for TV and sensitive electronics), and...

For a laptop, also buy a dedicated DC/DC 12V laptop charger (some laptops are 3S, some are 6S). When my Toshiba dies, I plan to replace it with a used Dell.

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As to sine wave, most of the time, some components can take a buzzy / choppy modified wave inverter (much cheaper, like Bestek 300W $28) and charge certain components. However...sometimes a modified wave can kill a cheap charger. Most microwave ovens seem to not work with modified, and motors of all types seem to run hot and draw excess amps from the battery.

DC/DC?...I had always thought it was in-efficient to boost 12V DC up to 120V AC, and then plug that into a charger that converts that into 6S/3S 18650 DC voltage to charge a laptop (two conversion steps). However, in a power outage emergency? all that matters is getting important components to work (my smart phones and USB flashlights charge from 5V USB). I finally found someone who verified that charging directly from 12V DC onto your laptops voltage is the smart way to go...if battery range is important (no wasted energy conversion losses or heat losses).


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#9
Progress report.

I bought the largest Harbor Freight "Apache" case (model 3800), similar to Pelican brand. Heavy duty, and made from thick plastic. There are currently three sizes (insert sizes here), I bought the largest one, so that I'd have a frame of reference for future builds. 

I will not be making these for sale, but...I have relatives for which I'd like to make some up as gifts. I used to live in earthquake-zone California, and now I live in tornado-prone Kansas. I am not really a prepper (nothing wrong with that) but...having no debt and being prepared for realistic issues is a goal of mine. Power outages are real (See: Puerto Rico hurricane).

Interior volume is 14.5 x 10.3 x 4.5..there is 1.5" of foam in the lid that can be removed for extra interior height.

370 x 262 x 115mm (plus 40mm inside lid) 

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I had just decided that I wasn't going to make these with the added feature of being a power supply for a spot-welder (for connecting 18650-cell nickel-ribbon buses), and I had trimmed my plans down to this case being a car-starter, plus emergency power for cell-phones and laptops. Chargeable from a car, solar, and wall-socket from mains.

I was about to order four 20-Ah LiFePO4 pouches from A123, and I suddenly found some LTO cells for sale, very rare occurrence. I bought six of these just for fun. Five to make the 12V pack, and one for destructive testing. 11-Ah each, so I will likely still buy the LiFePO4 cells soon for a second suitcase pack.

Six 2.7V Maxwell super-capacitors arrived (350F / D-cell), this weekend I will make up copper buses to connect them in series for 15V max bank for car-starting. Since I am not using the super-caps as the spot-welder power supply, the five 3.0V Amperics would have likely been adequate for car-starting, and would also be 18% smaller (five D-cells instead of six). An Amperics SC bank and the smaller LTO cells might end up in a mid-sized 2800 Apache case next month or so...
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#10
I was looking at the Aims 12V pure sine inverter web-catalog, and finally found some info I was looking for. To power a full-sized residential refrigerator, they recommend the 1200W continuous unit as the minimum (and more is better). Quote "These units have a 300% surge capability for 20 seconds" (although, the label on the device lists the peak as twice the continuous: 600W / 1200W).

I just saw a couple youtubes that suggested a full-sized refrigerator draws roughly 3.5A continuous when it's running. 120V x 3.5A = 420W continuous, maybe 900W peak on start-up? The biggest amp-draw culprits were a microwave oven and any type of A/C unit. VERY high peak and continuous amps. A 1000W Microwave is common, at roughly 9A

Based on this, I bought a used 2000W UPS from APC to use as a home back-up (can run the microwave without tripping the lights and TV). And for the suitcase, I now plan to buy the 600W Aims unit listed in the post above. The 600W has twice the power output of the 300W unit, but its only slightly larger. Plus it has two 110V AC outlets, while the 300W has only one.

Super capacitors arrived, and bought the 3800 size Apache case from Harbor Freight.
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