GoneDiving
Senior Member
The following is how an idiot, namely myself, builds a 840ah 48v Lifepo4 battery. Follow at your peril. Or you could just learn from my mistakes and do it properly.
So your going to take the plunge and convert to lithium power. You've done the calcs, would like a few niceties, and realise that's it's time to go big or go home.
Jump on AliExpress, wait for one of their frequent sales and promo deals and order your cells. Of course, the price drops again two days after your order. Think that lithium is shipped as Dangerous Goods so order months earlier than you need them to allow for delays. But there aren't any and the cells arrive in a month to sit on your garage floor for ages until your ready. Open a box or two to admire your purchase. Even invite the neighbours around to confirm your brilliance and the scope of the project. Everyone thinks that blue tissue boxes are sexy, don't they? Don't worry about opening everything to check that you have enough of everything: busbars, bolts, washers etc. That can wait for a couple of months until your ready to build everything. Jimmy Wong will be so attentive then, if any parts are missing or you need more busbars...not! Of course you didn't think ahead and order a few extra busbars for cable connections, but you did save $3 by selecting those stupid little bolts that barely thread into the terminals. M6 * 25mm studs would have been so much better but it's ok if you strip a couple of the terminal threads, isn't it?
A big project like this is a good excuse to buy some more toys, I mean essential tools. A power supply will come in handy if you are going to be charging cells in parallel. The inverter(s) will likely only operate at full pack voltage. Lots of cables, lugs and terminals. You can never have enough. Don't check the actual diameter of the studs on the inverter, breakers, distribution busbars etc first. Just order lots of everything and then do multiple trips to the store when things are the wrong size. No need to buy quality components. Save 1% of the project cost by buying the cheapest crap you can find on eBay or AliExpress
Ok its B-Day: Build Day. Don't sit down and hash out a plan of what your doing and what's needed. You've watched a few YouTube videos so you've got this. Go for it. No need to write down target voltages: you'll be able to work out 16*3.65 in your head for the 800 times you will want to know it. Safety is for lib-tards so don't tape off tools or remove any electrically conductive jewelry. You will be super careful and the only guy ever who has assembled a big, powerful pack with no Oops moments.
It's a big system that's going to be full more than it's empty so let's top balance. All the cells were likely shipped about half full. Grab your busbars and bolts and wire all the cells up in parallel. What? They only ship enough busbars for series connections and parallel connection needs twice as many? Back down to the hardware shop to get Reward Points for aluminium flat bar to make some more. It's ok, you know everyone's kids names and school grades by now anyway. Link everything up in parallel, set your power supply to your target voltage for balancing and wait. And wait. And wait. You've got 48 cells being topped up ~100ah and your charging at 20a. Lucky you bought a big power supply. This should only take about 10 days!! Screw this. Pull everything apart. Again. Remember those easy to disassemble studs you didn't order? Wire the pack up in series and start charging at full voltage and power. Illuminate the sky with welders flash when you realize that the sequence is to power up the power supply BEFORE connecting to the battery and that connecting while it's turned off give a dead short. You can even jury rig your inverter to perform utility charging duties too. Now you are charging at 48v * 100a = 4800w not 3.6v * 20a = not many watts. Check your cell voltages. They are all really close. 3.31 or 3.32v. Repeat every 5 minutes just to check for any rogue cells. 2 hours later the cells are...3.31 or 3.32v. 4 hours later one cell has jumped to 3.33v. Progress!! Hours later we pass 3.40v and things are moving unbelievably slowly. Then in the blink of an eye all hell breaks loose. Most cells are 3.42 or 3.43v. A few others are 3.6v. A couple are 3.7v. Panic stations! Shut down the chargers! Thoughts of '000s of dollars of cells going up in smoke. Quickly wire in some bridging wires to connect the highest voltage cells with the lowest. Where did I put those damn crimpers? They balance out quickly so crisis avoided. No house burnt to the ground insurance claims. Disassemble the pack. Again. And reassemble in parallel, though not all at the same time this time. 16 near full cells charge and equalise pretty quickly. The power supply is slowly working its way down to 0.00a so go grab some dinner. After dinner it is showing 0.something amps. Close enough. Chicken's done! Move all the busbars (yes, those studs that you didn't order again!) to the next set of cells and check voltages. WTF? How does charging to 3.60v give cell readings of 3.70? Maybe you should have checked the power supply's calibration and watched the first set more closely? They soon drop to 3.59 to 3.60v at rest so all is ok. Drop the indicated charge voltage down a little and do the next two strings to get all cells balanced at 3.60 +/- 0.01v
Let the cells rest for an hour to check for any issues. There are none so tear everything down. Again. Reassemble in series strings and use the inverter to draw the pack down to the operating voltage of 3.3 to 3.4v. Stand back and admire your brilliance because no one else cares.
Rebox everything and ship it to the boat. All 12 boxes of cells, 2 inverters and countless bits of hardware. Swear that next time assembly and commissioning will be done once and once only on the boat not in the workshop/garage.
Learnings:
Failing to plan is panning to fail. It's an oldie but true.
Big battery packs are immensely powerful. Take safety seriously.
You will not pick exactly when cells reach a certain SOC. Allow leeway.
Charge in parallel, using your biggest bulk chargers, to 95% full, then in parallel to balance at your chosen voltage, before any cells reach over voltage.
Don't leave cells sitting for an extended period at high voltages. It just promotes degradation.
So your going to take the plunge and convert to lithium power. You've done the calcs, would like a few niceties, and realise that's it's time to go big or go home.
Jump on AliExpress, wait for one of their frequent sales and promo deals and order your cells. Of course, the price drops again two days after your order. Think that lithium is shipped as Dangerous Goods so order months earlier than you need them to allow for delays. But there aren't any and the cells arrive in a month to sit on your garage floor for ages until your ready. Open a box or two to admire your purchase. Even invite the neighbours around to confirm your brilliance and the scope of the project. Everyone thinks that blue tissue boxes are sexy, don't they? Don't worry about opening everything to check that you have enough of everything: busbars, bolts, washers etc. That can wait for a couple of months until your ready to build everything. Jimmy Wong will be so attentive then, if any parts are missing or you need more busbars...not! Of course you didn't think ahead and order a few extra busbars for cable connections, but you did save $3 by selecting those stupid little bolts that barely thread into the terminals. M6 * 25mm studs would have been so much better but it's ok if you strip a couple of the terminal threads, isn't it?
A big project like this is a good excuse to buy some more toys, I mean essential tools. A power supply will come in handy if you are going to be charging cells in parallel. The inverter(s) will likely only operate at full pack voltage. Lots of cables, lugs and terminals. You can never have enough. Don't check the actual diameter of the studs on the inverter, breakers, distribution busbars etc first. Just order lots of everything and then do multiple trips to the store when things are the wrong size. No need to buy quality components. Save 1% of the project cost by buying the cheapest crap you can find on eBay or AliExpress
Ok its B-Day: Build Day. Don't sit down and hash out a plan of what your doing and what's needed. You've watched a few YouTube videos so you've got this. Go for it. No need to write down target voltages: you'll be able to work out 16*3.65 in your head for the 800 times you will want to know it. Safety is for lib-tards so don't tape off tools or remove any electrically conductive jewelry. You will be super careful and the only guy ever who has assembled a big, powerful pack with no Oops moments.
It's a big system that's going to be full more than it's empty so let's top balance. All the cells were likely shipped about half full. Grab your busbars and bolts and wire all the cells up in parallel. What? They only ship enough busbars for series connections and parallel connection needs twice as many? Back down to the hardware shop to get Reward Points for aluminium flat bar to make some more. It's ok, you know everyone's kids names and school grades by now anyway. Link everything up in parallel, set your power supply to your target voltage for balancing and wait. And wait. And wait. You've got 48 cells being topped up ~100ah and your charging at 20a. Lucky you bought a big power supply. This should only take about 10 days!! Screw this. Pull everything apart. Again. Remember those easy to disassemble studs you didn't order? Wire the pack up in series and start charging at full voltage and power. Illuminate the sky with welders flash when you realize that the sequence is to power up the power supply BEFORE connecting to the battery and that connecting while it's turned off give a dead short. You can even jury rig your inverter to perform utility charging duties too. Now you are charging at 48v * 100a = 4800w not 3.6v * 20a = not many watts. Check your cell voltages. They are all really close. 3.31 or 3.32v. Repeat every 5 minutes just to check for any rogue cells. 2 hours later the cells are...3.31 or 3.32v. 4 hours later one cell has jumped to 3.33v. Progress!! Hours later we pass 3.40v and things are moving unbelievably slowly. Then in the blink of an eye all hell breaks loose. Most cells are 3.42 or 3.43v. A few others are 3.6v. A couple are 3.7v. Panic stations! Shut down the chargers! Thoughts of '000s of dollars of cells going up in smoke. Quickly wire in some bridging wires to connect the highest voltage cells with the lowest. Where did I put those damn crimpers? They balance out quickly so crisis avoided. No house burnt to the ground insurance claims. Disassemble the pack. Again. And reassemble in parallel, though not all at the same time this time. 16 near full cells charge and equalise pretty quickly. The power supply is slowly working its way down to 0.00a so go grab some dinner. After dinner it is showing 0.something amps. Close enough. Chicken's done! Move all the busbars (yes, those studs that you didn't order again!) to the next set of cells and check voltages. WTF? How does charging to 3.60v give cell readings of 3.70? Maybe you should have checked the power supply's calibration and watched the first set more closely? They soon drop to 3.59 to 3.60v at rest so all is ok. Drop the indicated charge voltage down a little and do the next two strings to get all cells balanced at 3.60 +/- 0.01v
Let the cells rest for an hour to check for any issues. There are none so tear everything down. Again. Reassemble in series strings and use the inverter to draw the pack down to the operating voltage of 3.3 to 3.4v. Stand back and admire your brilliance because no one else cares.
Rebox everything and ship it to the boat. All 12 boxes of cells, 2 inverters and countless bits of hardware. Swear that next time assembly and commissioning will be done once and once only on the boat not in the workshop/garage.
Learnings:
Failing to plan is panning to fail. It's an oldie but true.
Big battery packs are immensely powerful. Take safety seriously.
You will not pick exactly when cells reach a certain SOC. Allow leeway.
Charge in parallel, using your biggest bulk chargers, to 95% full, then in parallel to balance at your chosen voltage, before any cells reach over voltage.
Don't leave cells sitting for an extended period at high voltages. It just promotes degradation.
