DIY 18650 24v 103Ah lithium-ion Battery 2600wAh Under $400.00

Bart

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Jun 30, 2020
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20
I have not posted in three months been working and getting everything ready for this battery build also working on my RV's interior and as you all no it takes up to three months to get parts from China. "BMS only cost me $55 each when I order them directly from Daly's site on Ali-Express.

I just finished the first of three battery I'm building, the actual cost of this battery is $382.00. A total of around 2600wh each "see the picture of the capacity test below" This will be running my electrical needs in my RV renovations. The 18650 batteries are from battery hookup averaging 2850mAh each, "LG Pegatron Modem Packs LGABB41865" in a 38p 7s configuration, BMS from Daly, "7s Bms 29.4v Lithium Battery Bms Charging Voltage 29.4v 100A with fan" the wire comes from Windy Nation, 125amp DC breaker and volt meter came from AliExpress, I 3-D printed a few of the parts, the rest of the parts come from Amazon.

Each of the seven cells in the battery are connected with fused nickel strip from battery hookup and have two 10 gauge wire from Windy Nation on the positive and negative sides and are joined at the top of the battery with an 8 gauge pure copper lug also from Windy Nation. Also added a separate connector for balancing, this way I am able to parallel balance the cells when needed.

Each of the batteries are connected in series and I have six gauge wire running to the breaker and the terminals. I also bought some chair rubber stoppers from Menards to cover all the terminals they work perfect.

I just ordered another 120 modem packs from battery hookup so I will be able to build one more battery and as soon as more of these modem packs come available I will build the third battery I have already purchased all of the supplies needed for the rest of the battery build, I'm just wanting to use the exact same cells in each battery for this project. As I'm still about three months away from finishing RV renovation no rush.

Finally when I did my capacity test I charge the battery to 29v and discharge to 21v with a total of 2637.11Wh sorry about the rest of the data on the screen when I was pulling it up to take a picture I hit the clear button and it zeroed out the Ah and it took 24 hours to do the test and I didn't want to do it again, I believe it was around 103Ah at the time which would make the nominal voltage of the battery around 25.6v.

The battery has a maximum voltage 29.4v and a maximum discharge voltage of 19.25v but I plan to only charge the battery to 29v and discharge the battery to 21v.

P.S. Just a side note these battery modem packs from battery hookup are great it ended up costing $.75 per cell "cells never cycled" and the specs on the battery state they're only 2600 mAh but I average 2900 to 2800 on every single cell. But I'm finding I have to check the site every day as these modem packs sell out within minutes of being posted I missed the last two postings as they sold out that quick and I was able to get 120 this time so hopefully they will have more come available soon.
 

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italianuser

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Feb 25, 2020
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246
Looks simply great, man! Congrats (y)I'd love to see how you connected the fused nickel strip, this month I'll start my first battery, too. Nickel strip VS copper bar is my dilemma right now... lol
 

Bart

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Jun 30, 2020
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Looks simply great, man! Congrats (y)I'd love to see how you connected the fused nickel strip, this month I'll start my first battery, too. Nickel strip VS copper bar is my dilemma right now... lol
I had previously made a few power supplies over the last 12 months, and my biggest issue in just using nickel strip to make one big battery pack was once you do that you can no longer parallel balance the batteries if needed, doing it this way allows you to parallel the batteries once and while to make sure they're well balanced always, I have a good BMS with balancing but it's always good to be able to parallel balance the batteries just in case from what I understand as I'm only very new to this and only been building power supplies and batteries for 12 months. I will add some more pictures of the individual cells give me a little bit I'll have to break down the battery but happy to do so.

Thanks for your great comment.🤟
 
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Bart

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Jun 30, 2020
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20
Looks simply great, man! Congrats (y)I'd love to see how you connected the fused nickel strip, this month I'll start my first battery, too. Nickel strip VS copper bar is my dilemma right now... lol
On each cell I have two 10 Gauge wires attached to the nickel strip on both the positive and negative side by soldering going up to an eight gauge 1/4" lug, the lugs are cold welded with 40 ton crimper, then I use brass nuts bolts and washers to connect each cell, the additional wire is for the balancing leads for the BMS. I spot weld the nickel strip to the batteries with an "Sunkco 709A" four spot welds per battery.

I have the positive and negative wires at the top and bottom to allow for good flow of current through the cell, and I alternate the length of the positive and negative leads on each different cell so you get good flow of current through the whole battery. From what I've read this helps but as I stated earlier I'm very new to this.

Bart
 

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ajw22

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Nov 16, 2018
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597
Very nice! Have you monitored the cell temperatures under load?
Looks like the cells don't get any air flow due to the Kapton tape, and the box seems to have a gasket around the lid preventing outside air from entering? The small exhaust grille on top won't do jack unless there is at least one inlet, ideally near the bottom of the box to create a chimney effect.
 

Bart

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Jun 30, 2020
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Very nice! Have you monitored the cell temperatures under load?
Looks like the cells don't get any air flow due to the Kapton tape, and the box seems to have a gasket around the lid preventing outside air from entering? The small exhaust grille on top won't do jack unless there is at least one inlet, ideally near the bottom of the box to create a chimney effect.
With a load of 50amp's continuous the battery was only heating up to 89° I have not pushed it to 100amp's as once I set this up in my RV with two other batteries the most I will ever pull is around 30amp's so active cooling is not needed, I will keep monitoring it though just to make sure and once I set it up I will have temperature monitoring on the batteries. But yes I do have a vent on the backside at the bottom the same as the one on the top.
 

cak

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Mar 14, 2021
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Nice battery. I am doing a somewhat similar one in the metal ammo cans, I should actually remember to get some pics to share now that I am a few versions in. The only red flag I saw in your design is the breaker is oversized for the wire gauges and connection to the nickel strips. It sounds like you are not planning on using the full 125 amps but it would probably be best to use a smaller breaker anyways to prevent too much overheating of the wires and or the cells. I also use two parallel 10awg wires but only do 90 amp max draw(and breaker) I also connect the wire to each row of cells/nickel since according to BH they are rated for 10amp per row. the way you have it you would likely get a lot of heat buildup where you connect the wire to the nickel at higher amp loads.

Nice info about the 2600mAh cells because to me they didn't seam worth the extra $0.25 for only a few hundred mAh. How do you test(mAH load, tester, etc)?
 

Bart

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Jun 30, 2020
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I use a C4 battery tester to check the capacity of all the batteries at .5 amp. I first fully charge them and then do a normal test here are two of the batteries I have left over from my last lot of batteries I processed, these batteries have been sitting for almost 3 months with almost no discharge, I inspect, label and re-sleeve all batteries. The reason I didn't use these two batteries is because 2820 what is too low the 3010 was too high I like to keep all batteries in a battery pack within 50 mAh.

I also check all batteries for resistance and these are good like below 30-50 mohm, I also check weekly for four weeks for self-discharging and I have not come across a single battery that's self-discharges from these modem packs, but one of the main things with these packs is they've never been cycled. Maybe I've just had good luck so far, from time to time I do come across a damaged battery that is why I re-sleeve all the batteries I have now come across nine batteries with the same issue and it can usually be identified by a small amount of rust on the bottom of the battery and when you remove the sleeve you see a small split along the edge.
 

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