LiFePo4 100 aHr build

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LiFePo4 100 aHr build

Postby TimC » Mon Aug 23, 2021 5:17 pm

I thought I would briefly document my build of a 100 aHr LiFePo4 battery bank. This is an upgrade from my AGM. Less than half the weight of my 144 aHr AGM bank and about half the space. Some may argue that this wasn't a true build and I accept that. It is a kit that includes four cylindrical 3.2v cells (100 aHr) to be wired together with the included BMS (battery management system). My source is batteryhookup.com and this kit is the currently available "12v 100ah Lifepo4 Kit w/ BMS & Low Temp" kit which totaled about $285 shipped. I can not compare this kit to other materials available. It is my first build and I am just reporting what I have experienced with it.

You can build a bigger and maybe better quality LiFePo4 for a little more money. I just wanted a kit with matched components and didn't care to do the research to figure that all out on my own. I welcome any and all critiques of my methods and the product.

This is the (+) terminal of one cell. The (-) negative terminal is the same with a black shrink tubing. I will refer to the cells (-) and (+) terminals as the battery posts. They are not technically posts but for the purposes of this build I will refer to them as posts. On these cylindrical cells the battery "posts" are lugs with multiple wires running into a single positive and a single negative wire lug. I cut away a small amount of the cell pack's shrink wrap to allow the wires to flex easier.
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This is a mock up of my layout of the battery. This is a "4S" (four in series) configuration to add up the 3.2v cells to 12.8v nominal voltage. This is only a mock up at this point to build a container and double check the connections. The copper links are homemade from 1/2" hard copper flattened and drilled. Soft copper would have been easier but this is what I had on hand. I have learned that compressing cylindrical cells is not necessary like prismatic cells. I did no compressing and just built a plywood box to contain them.
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The cells come without a full charge and should be top balanced. I won't go into what that is or why as Lauren has described the process very well here...
http://www.tnttt.com/viewtopic.php?f=30&t=74022

I did deviate from Lauren's method by wiring the bank as a 4S including the BMS wiring and charged the bank this way for five hours. This theoretically shortened the top balancing time. Using my Noco 7.2a 12v charger fed three times the watts into the battery per hour compared to when I was top balancing at a lower voltage (more about that later).

To top balance the cells I had to wire up as a 4P configuration (four in parallel). In this configuration the bank starts out at 3.2v, 100 aHr. I purchased a bench power supply to top balance the bank. It is a $50 unit and is the same PS that Will Prose used in his video about top balancing a LiFePo4 battery. I also used a multimeter many times during this process to verify the PS was reading accurately.
https://www.youtube.com/watch?v=x5ABvbbics8&t=237s

The leads from the power supply that are shown are the leads that came with the PS with banana plugs and alligator clips. I made a set of my own using 12awg with ring terminals on each end and hard wired them to the bank. This resulted in less resistance and a more solid connection.
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This was the first time I had ever used a bench power supply and I learned a lot by watching YouTube tutorials about their use. The unit I purchased did the job. It has some drawbacks, like only reading to a tenth of a volt, however, for the number of times I'll use a bench power supply it was fine.

Top Balancing
The process I used to top balance is as follows... Leave the leads disconnected (and sparated). Turn both amp and volt dials all the way down on the power supply. Plug in the PS and turn it on. Turn the amp dial all the way up (10a on my PS). Turn the voltage dial to 3.4v. Turn off the PS. Connect the leads to the (-) and (+) posts of the 4P battery. Turn the PS on. This is important to remember... The readout on the PS will show 10a and whatever the current voltage of the battery is, not what you set the dial at. You don't want to adjust the PS while it is on. When the voltage approaches 3.4v the amp reading will drop to near zero. Because I pre-charged the pack (4S) with my Noco 7.2a charger this process took about 50+ hours.

Now repeat the above process, everything disconnected, setting the amperage all the way up and the voltage at 3.6v. Attach the leads and turn on the PS. When the amp reading drops to near zero turn off the PS and let the battery rest for an hour or more. Take a voltage reading. It will have dropped a fraction of a volt or more. Leaving the PS set at 3.6v connect it back up and turn on again. When the amps drop to near zero turn off the PS and let it rest. Take a voltage reading. I repeated this process about four times with the last two charges the PS was set at 3.7v. I was trying to get that last hundredth of a volt to reach a resting voltage of 3.65v. Resting voltage reading ideally should be taken after many hours of rest. An hour or two at the end was close enough for me.

After Top Balancing build the 4S
In this photo I have the cells laid out in their case. The blue straps on the bottom of the box are just scrap straps to help me pull the battery box out of the back of my cabinet.
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And in this photo I have the bank BMS taped down to the bank and the bank's negative wire hooked to the B- post of the BMS, the first cell's positive wire connected to the second cell's negative wire, and the second cell's positive to the third cell's negative. That pattern is continued until all that is left is the last cell's positive is connected to a fuse and then to the battery post. The C- post on the BMS has a 10awg wire running to the (-) post.
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I believe it is best practice to not plug in the BMS balance wire harness plug until the battery is completely wired. Hooking up the BMS' five wire harness is simply connecting the first (black) wire to the B- post, and in order the next wire to the first cell's (+) post, next wire to the second cell's (+) post and so on until all the wires are on the cells. Again the first wire goes on the BMS which is the negative lead to the BMS. Then each of the rest of that harness goes in order to each cell's positive post.

These next photos are a bit messy, but, nobody sees this but me (and the tnttt world). The white tape is non-conductive and really just keeps the excess wire from flopping around.
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I'm about 27% of the way through my capacity test. 446 wh is about 27% of the expected 1200 wh this bank should have. It is going slowly as I don't have an inverter and only low draw 12v appliances. I'll update this thread when I 'm done with the results of the capacity test. Probably tomorrow.
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What I learned or would do differntly...

-Any experienced battery builder will notice my battery box posts are a little unorthodox. I went to four local hardware stores and could not find brass 5/16" bolts. To get the job done I flattened more 1/2" copper and wrapped the top of the plywood box with a U shaped "lug" and drilled a 5/16" hole through the box and the lug. Then I used a zinc bolt to tie the battery leads and the load leads to the box. The lugs are tight against the copper on each side. I did a resistance check of the copper versus just a piece of 10awg and there was no difference. Next time I go the the "big city" I'll pick up some brass bolts and eliminate the copper lug wrap thingy.

-After top balancing and then building the 4S bank I hooked up the battery to my teardrop and could not get more than 2.4v to the battery posts. Luckily we have flboy and saltydawg who both have experience with this type of BMS and I was advised to hook up a charger to the battery to wake up the BMS. Apparently the BMS must have a charge of more than the battery voltage to turn on. It had the 14.2v from the battery. It wanted a 14.3v charge in the other direction. This was done with the bench power supply hooked up driving 10 amps at 14.3 volts for less than a minute. When I shut off the power supply everything was humming.

- Without Lauren's encouragement I probably would have replaced my batteries with 100 aHr AGMs. I had actually had two of them in a cart online at $175 each. Thanks Lauren for not giving up on me. This was fun and a little stressful when I couldn't get 14.2 volts out of the BMS. But it is worth the trouble.

- I hope to figure out how to program my Epever Tracer 3210 and MT50 meter to limit charging to 80 or 90 percent. I have no idea how that is done but I'm playing around with the charge controller to figure that out. I'm guessing it has something to do with telling the charge controller to stop charging at a certain voltage. I guess that will be more apparent after figuring out what a full charge voltage and a drained voltage are.
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby TimC » Tue Aug 24, 2021 8:08 am

After about 24 hours the BMS shut off current to my loads. I was a bit confused earlier this morning when I saw 11.96v and 1454 wh on the ammeter and all the loads still burning, including the fridge.

I was wondering;
#1 - if the BMS was going to shut off current soon. I expected 100 aHr capacity but not 121 aHr and still going.
#2 - Should I end the test without knowing if the BMS will shut down.

In the end I let the test go another 1/2 hour and the BMS shut everything down. The capacity is 1483 wh which is 123.6 aHr at 12v. Using a 13v average it is still 114 aHr. Not bad for a 100 aHr battery kit.

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I hope some experienced builders can chime in and verify my conclusions.

Update (Aug 25, 2021):

I've installed the battery "permanently" after charging up to 13.9v. My Noco 7200 would have been slower so I connected the bench power supply (10a) and charged using that. After it reached 13.9v I shut it off for a few hours and the battery voltage dropped to 13.3v. I turned the charger back on and in about an hour it was back up to 13.9v.

I was also concerned about using my Epever Tracer 3210AN charge controller and the MT50 remote meter in my previous post. Since then I have resolved that with help of flboy and Will Prose's video on how to program the MT50/Epever for optimum performance.
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby featherliteCT1 » Wed Aug 25, 2021 7:25 pm

Thanks for the informative posts. :thumbsup: I look forward to hearing if you are able to figure out how to program your Epever devices to limit charging to 80 or 90 percent.
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Re: LiFePo4 100 aHr build

Postby TimC » Wed Sep 01, 2021 9:34 am

As I don't have a clear understanding of the parameters of the Epever MPPT I decided to leave the settings that Will P suggests in his video for this charge controller and a Battleborn battery. I'll just keep an eye on the ammeter to see at what point it stops charging. Just to remind you, I want to only charge this LiFePo4 bank to 80 to 90%. So I'm hoping it will max out at 13.8v ish.

I'm out boondocking for its trial run. I'm on a site I call Rocky Top and where I park I don't get full sun at any time of the day. That's called parking in partial shade!

This is approx 48 hours of use...
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The highest production I've seen for my 200 watts of solar is around 25 watts. Of course I haven't been looking real often. The MPPT is showing four out of five bars so I'm assuming it is using every bit of sun to charge the battery at this point. I left home about 48 hours ago and after resetting my ammeter maybe I've gotten a half hour of good direct sun on my way here. Still, I've used 485 wh and produced 398 wh. Converting that to aHr my charging is approximately 13 aHr behind my consumption. Not bad for partial sun. All the while the battery is maintaining around 13.3v. If I understand this part correctly it will not likely drop to under 13v until it is 80% depleted so I'm not sure monitoring voltage tells me much. I think monitoring the ammeter is more valuable info since I know the theoretical capacity of the battery.

I'm open to any and all suggestions or comments if I am making bad assumptions. Overall I am very happy with the change to LiFePo4. I could have spent alot more but feel if this battery holds up I made a good decision.

Tim
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby TimC » Wed Sep 01, 2021 9:50 am

Top photo: I pulled out from under the trees for better access to the sun. It's still not directly overhead at this point in the morning... 133 watts

Bottom photo: And by the time I got home, about 45 minutes, it appears the MPPT is sensing near full charge and is just trickling watts into the battery under full sun.

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Last edited by TimC on Thu Sep 02, 2021 6:20 am, edited 2 times in total.
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby saltydawg » Wed Sep 01, 2021 6:54 pm

Its official I dont like those gauges at all. Too much to look at, I like the ali monitor. I want to see amps I push a button and I see if the amps are going in or out. I want to see % of charge I push a button, I can also see how many amps I have used and how many I have left.
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Re: LiFePo4 100 aHr build

Postby Graniterich » Wed Sep 01, 2021 10:18 pm

saltydawg wrote:Its official I dont like those gauges at all. Too much to look at, I like the ali monitor. I want to see amps I push a button and I see if the amps are going in or out. I want to see % of charge I push a button, I can also see how many amps I have used and how many I have left.
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Re: LiFePo4 100 aHr build

Postby TimC » Thu Sep 02, 2021 6:19 am

I should have put a warning in the caption about having to do the math! :)

It might help if I labeled the meters Load (top ammeter) and Production (bottom)
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby saltydawg » Thu Sep 02, 2021 7:25 am

Math is not an issue, esp with the power of google. :NC

The problem I see with them is over a few days or weeks, sure you know how much you used, and you know how much you have produced. Its never a quick look to see how much is left.

I can understand having one on production, if you want to track the solar gain. In my mind I could care less how much solar I get or dont get, I want to know how much power I have left and there fore do I need to find another way to charge.
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Re: LiFePo4 100 aHr build

Postby TimC » Thu Sep 02, 2021 3:37 pm

Salty, maybe my theory doesn't hold water but with my cheapo ammeters this is how I determine where I am as far as capacity. And full disclosure, I typically use less than 25 aHr per day and some of that is replaced during the daylight hours so right now I am not too worried about draining the bank. On a cloudy day I might replace 1/3 to 1/2 of my consumption.

I know from my capacity test that my bank is over 100 aHr. So I am going to conservatively assume I have 80 aHr to use. Before a camping trip I reset both of the ammeters when I know the batterie's charging voltage is 13.6 - 13.8v. I assume that when I am getting full sun and the Epever MPPT is only putting 20 or 30 watts into my batteries that it is fully charged. At least to my desired 80-90%.

Each morning I take the wh readings of the production meter and the load meter and figure out the difference. That tells me that production still has some catching up to do to match my demand. By the noon on a sunny day the values are closer to equal as my demand is low during the day and production is higher. The next morning I notice the production is behind the demand again (wh). By noon, if a sunny day, I'm back to almost even production and demand wh. My conclusion is I am at 80 to 90% capacity.

If my demand stays much higher than my production for several days I can do the math to figure out how far from full charge I'm at by converting to aHr. For example, If I am still 130 wh behind after a couple cloudy days I know that my bank is down about ten aHr. 260 wh behind and I'm down about 20 aHr. Beyond that if clouds persist I kick into conserve mode. Turn off my fans during the day. Only charge my electronics during the day. Turn the fridge up to 38 degrees and cover it with a blanky.

I don't need to do math other than subtracting cumulative production from cumulative demand (demand usually being higher each morning). I'm getting used to using wh as a measurement but if I want aHr then I just divide that wh difference by 13 (see, I learned. I don't divide by 12 anymore!). ;)

I have basic understanding of 12v and 120v, watts, volts, amps. If the method I'm describing is faulty please let me know. I've learned a lot from you guys over the last few months and have come up with a way to interpret what the ammeters are telling me. I'm not ready to advance to the ammeter type you are referring to as I just installed these and I've learned to work with them.
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby saltydawg » Thu Sep 02, 2021 4:38 pm

Its not faulty in any way, its just extra steps. I can see in a off grid house needing to monitor actual production when you need it to live where a 10% difference in production can be a signal of loosing something.

But in our little world I dont think its needed. But I say that with a completely over built over complicated camper, including electric.

BTW the name is Scott, see below
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Re: LiFePo4 100 aHr build

Postby TimC » Mon Sep 27, 2021 12:28 pm

I have about a month and three camping trips experience with my new batteries and so far I'm very happy with them. My demand is fairly low so I am not stressing the system much. That's OK. I know I have a sizable reserve.

One area I am confused about is what to do when freezing temps arrive (we are already there on some nights). Asking around I was told not to worry about removing the battery/BMS in the winter. Just unplug the battery. I am assuming they mean unplug any charging system.

I understand the BMS is equipped with low temperature cutoff for charging. I've been told to not worry about the battery being kept in a frozen state as well. Just don't attempt to charge it when below 32 degrees. That's not a problem. I do want to test the low temp cutoff when I get a chance to be sure it works. Didn't think of that while building this thing in 90 degree weather.

What do all you LiFePo4 proponents do in the winter when your teardrop is in storage? Unplug charge systems? Remove the bank to a warm environment? Keep it on a charge system and rely on the BMS to do its job?

I see some use a beehive heater system but I don't contemplate using the camper once winter arrives. Though that does seem to be a nice, low cost method to protect the battery in the winter.
Tim
Niagara, WI
My First Benroy Teardrop Build Thread - A 5x8 Woodie - http://www.tnttt.com/viewtopic.php?f=50&t=63575
My Second Teardrop (partial) Build Thread - Started August '16 - http://www.tnttt.com/viewtopic.php?f=50&t=66939
#3 My son's Benroy Foamie team build - Started July '20 - http://www.tnttt.com/viewtopic.php?f=50&t=72877

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Re: LiFePo4 100 aHr build

Postby saltydawg » Mon Sep 27, 2021 5:31 pm

I just shut down everything and let it rest last year. I did go check on it a few times.

I have the heaters on a switch and thermostat, which controls a relay to interrupt the charging circuits if the battery is below 35 degrees. So If I want I just flip the heaters on and the charging and once the batteries get warm they are allowed to charge. Its a I wont be camping in extreme cold, but I have used it down into the low 40's so Its nice to just turn on the heater switch and not have to worry, if they get cold they get warmed.
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