12V portable pack, LiFePO4

okent

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Oct 8, 2017
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Thanks to all who have posted on this forum. It's been my go to source to try and put together this project.
Planning for a 12V system that gives me approximately 100Ah.
Tenergy 32650 cells, 80, arranged in 4s20p configuration. 3.3V with 5.5Ah per cell.

I have an iCharger 206B with RC Power P350 power source.
Ebay spot welder
Ebay battery holders
Ebay Nickel strips


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Put it all together today rather quickly for an outing where I needed a portable power source.


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I'm charging the individual packs tonight. 2.7A with 3.6V max


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Thermal closeup, no hotspots.


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Next step is to get some fuses in there, I'm thinking on each series pack, and then wire it up to balance charge with the 206B.
Having some trouble finding exactly what wiring harness I need.
Also am in the process of finding a battery monitor that will measure output and have a low voltage cutoff so I don't accidentally over-discharge the pack.
And then a case to house everything so I can pick it all up and walk out the door if needed.

Eventually would like this hooked up to my 200W solar panels but I'm looking for a good solar charge controller.
 
Welcome!!!

Not too familiar with this model battery but cell level fusing has been best practice. Are these cell brand new?

As for charge controller the PCM60X from MMP Solar is a popular choice. Seems like you will need something portable though. This one is not for portability. Any how I'm sure you will get much feed back on your project. Updates and pics are always welcomed.
 
Welcome!

LiFePo4 is several times more safer so I wouldnt personally even bother with fuses per cell on those.

I would put them together and add like XT90 plug for powering the pack and then a balance lead (JST) and you are good to go. balance charge it with you RC charger when needed. Perhaps even Add a bms on the JST plug. But since its portable you want it simple and still reliable.
 
Yes, new cells.
Next is to calculate wire size for the packs and leads and then add plugs.

Special thanks to daromer, DarkRaven and Korishan for all the input and keeping me safe!
 
Good job!
Once you have proper connections on the packs you can charge them with a lot more than 2.7A :)
I wouldn't fuse these cells either, but fusing the packs, or rather the completed battery, is a good idea. You can fuse the individual, serial connected packs as well, but since the current is the same for all four it is enough to fuse the completed battery, i.e. the main + and - terminals.

Also, good to see you are using LiFePo4 cells! I remember telling you to get a 7S charger and use a 7S configuration and a DC-DC converter because 4S configurations for 12V with any other cells than LiFe are tricky :) Somehow I haven't realized you were planning with LiFe :)
 
Yes, I went with the LiFe so I could get to a reasonable 12V system.
I added some weight but sure feel like I gained a safety margin for a first build.
I'm thinking on a 200A breaker since the cells are rated at a max discharge of 9.9A. This setup theoretically put out 200A though I can't see ever needing that kind of power.
 
Just putting a 200A breaker into the circuit because this is the maximum continuous discharge of the battery isn't always the best option. The breaker isn't there to protect the battery, it protects the wires and it protects you from fires started by hot wires or connections. If you want to use a 200A breaker and therefore allow a current of 200A then you should be using massive copper wires. Something like 35mm at least, 50mm to be safe.

You should figure out what your maximum continuous current and maximum peak current will be. Based on that you can size the breaker and the wires.
 
The breaker should be your weakest point. So as DarkRaven said you need to dimension everything else based on that. Or else they do no good.
 
Yes, in my solar shed I have a 2000W inverter which could draw up to 200A. It's highly unlikely that will ever happen but it's a theoretical upper limit of what the pack should do and could be drawn. I was planning on some heavy wire, like for a car battery, just in case.
 
200A is a lot, that's why there are many 2000W inverters that take 24V or 48V. But alright, if you want to size it like that, then go ahead. It is certainly possible.
 
If you are going to run 12V setup and you're going to make it that large, you really need to pay attention to layout so you can keep the cables as short as possible. 12V will have lots of voltage drop unless you use 0 or 00 gauge wiring. I wouldn't use anything smaller than 2 gauge, and that's pushing it. Choosing that size wire is for current handling and to keep voltage drop to an absolute minimum.
If you have 2 12V inverters, you could make a 24V pack setup and wire the inputs of the inverters in series. That would at least lower your power loss. But, both inverters would have to be running at the same time. Neither one should run without the other or you could blow something up.
But ultimately, I'd go with 24V minimum if possible. To replace the 12V inverter with a 24V might seems costly, in the end, it'd be cheaper as the wiring is less, the voltage drop is less which means less wasted energy, and better efficiency of the unit.

But that's my 2 cents worth.
 
Understood. 24V makes more sense.
I can't really think of an application where I will need 200A though I want to make sure the wire is sized to the battery capacity.
 
You wire to the battery amperage, not capacity. Unless you mean amperage capacity. Capacity usually is in reference to mAh of stored energy ;)
 
Sorry, yes, amperage not capacity.

The 80 individual 32650's can put out 2C or 9.9Ah theoretical max. I figure this draw as a surge not continuous. With the 4s20p configuration that makes 200Ah which is where I got that number.
Planning on 6 gauge wire for the connections between cells and 0 gauge for the main leads. I got those numbers from an online calculator where I plugged in a 1% loss, .25 meter length, 12V, 200A for the series connections.

If my thinking is off please let me know. I appreciate all the input.

Edit: dumb question: With the JST-XH pigtail being 22G will this run into issues with balancing? Best I can figure it's only rated for right at 1amp. I'm charging at 2.7A.
 
The current on the main wires is as big as the current between the 40p modules so the wires should be the same thickness. And on the individual cells you have current/40.
However, that way you are using a lot of material that might be unecessary. As I said, this is not how you do it. Figure out the load and then you know exactly what sort of wire you need.
Look at the biggest device you want to power (or the joint highest power by several devices) and size everything accordingly.

Balance wires can be rather small, balacing currents on most charger rarely exceed 1A. Most BMS with balancing will balance with less than 400mA, big chargers like the Junsi iChargers balance with max. 1.2A per port and cell.
 
Finally got around to assembling the pack.
I went with 12G wire soldered to the nickel strips.

This is probably a stupid question but I am using an iCharger 206B and the factory voltage setting for a 4s pack is 13.2 volts.
Can't figure out how to change that to 14.6( 3.65 x4)
If it's not necessary that's OK but just thinking of trying to hit 3.65V per pack to get approximately 90% SOC.


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okent said:
Finally got around to assembling the pack.
I went with 12G wire soldered to the nickel strips.

This is probably a stupid question but I am using an iCharger 206B and the factory voltage setting for a 4s pack is 13.2 volts.
Can't figure out how to change that to 14.6( 3.65 x4)
If it's not necessary that's OK but just thinking of trying to hit 3.65V per pack to get approximately 90% SOC.


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Is that on the LiFe setting on your charger, ifthere is one?
 
You can scroll though to different charing modes on the iCharger. Select LiFe setting for that chemistry, and if you need to fine tune or set a custom termination voltage, you can do that in settings for that specific chemistry profile .
 
13.2V is the nomimal voltage for a 4s LiFePO battery. The default end of charge voltage is 3.6V per cell, 14.4V for 4s. At least that's the factory setting on my 4010, I guess it's similar on the 206. You can change the voltage in the settings.
 
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