DIY portable, useful LiFePO4

[booster]

Originally Posted by Luv2Go

The Tripplite does have two battery types, wet or gel. The gel setting has the lowest bulk voltage 14.2V and float of 13.6V, that may be enough to keep the BMS from opening. The wet settings are 14.4V and 13.3V respectively.

Understood, but you also have to remember that it sets is charge profile times based (loosely) on batter acceptance and voltage it sees. It is very unlikely that it will correctly interpret the higher acceptance and different voltage vs SOC of a lithium on any lead acid setting. Most lithium batteries recommend full cutoff charging these days off of a fixed rate charger, so it just makes sense to me to use a PD fixed rate power supply type model so an extra battery to activate the charging isn't needed. The Tripplite chargers and not very good IMO, compared to other offerings available, we got rid of ours a long time ago because it did such a poor job of charging lead acid batteries even. If there is solar, it is likely that the same issue with the charge controller will show up if there is not a battery in the circuit.

[Luv2Go]

I agree with you, this may be something the OP can try while waiting for another charger to arrive.

I personally do not like the PD charger, it does not have a "float" voltage and relies on the lithium BMS to cut it off by disconnecting the battery. I prefer some redundancy. For example, in my setup the Victron will charge to 14.0V then switch to 13.4V float which is low enough to minimize further charging (3.35VPC). The BMS will disconnect the battery at 14.4V. So normally the BMS is never asked to disconnect...

[booster]

Originally Posted by Luv2Go

I agree with you, this may be something the OP can try while waiting for another charger to arrive.

I personally do not like the PD charger, it does not have a "float" voltage and relies on the lithium BMS to cut it off by disconnecting the battery. I prefer some redundancy. For example, in my setup the Victron will charge to 14.0V then switch to 13.4V float which is low enough to minimize further charging (3.35VPC). The BMS will disconnect the battery at 14.4V. So normally the BMS is never asked to disconnect...

I think that what I look at is that the recommendations for most of the better lithium systems want full cutoff at less than 100% full batteries and no float. I would just use a fixed voltage PD charger and a Victron monitor to trigger a relay to shut off or on for the charger. Best of everything, including having a good shunt based battery monitor. And you still have the BMS in case of a backup protection.

[markopolo]

Booster identified the issues.

You're getting the shutdown because the cells aren't balanced. One or more cell voltage is too high and it triggers the shutdown. Sounds like you skipped the individual cell prep step so you don't know how precisely the cells match.

Are the highest voltage cells #1 & #4?

What is the over voltage set at?

Have you tried selecting Static Balancing and let it run overnight? (Tripp Lite unplugged)


The important thing is to get the cells balanced. Once they are all at the same voltage then the shut down issue should go away and not reoccur provided the cells are matched.

[markopolo]

A few updates on the project.

I now have a couple of measured voltage reference devices and measuring equipment confirmed accurate to around 0.001V (1mV).

I made a very accurate portable DC voltmeter using the shell of an old non-working multimeter. Cost was around $5.

DIY dc voltmeter.JPG

I won't be using the black cases for at least two packs. There just isn't enough space if I use the cell holders and I really want to use the cell holders to maintain separation between the cells.

I'll reduce the number of cells used to 36 in each pack. 4S9P - 6.4Ah*9 = 57Ah battery. That's due to case size again.

I should have a completed battery some time this week. I'm waiting for the new cases to arrive before soldering anything.

The copper is rated for around 20A. It's used to connect the cells together. There will be 12 x 10AWG power leads spread across the pack. I decided to use two layers of copper. 6 positive leads*40A=240A capable. The largest load in my van is around 80A (at 13VDC). Note: 40A refers to copper buss. 10 gauge wire is typically used for up to 30A. 6*30A = 180A possible at the terminals.

36 cell pack 1.JPG

36 cell pack 2.JPG

[markopolo]

Plenty of space using a stackable MTM Case-Gard ACR4 Utility Box: https://www.mtmcase-gard.com/product...ammo-crate.php

Battery Box.JPG

The 300A rated inverter style terminals will still protrude in but there's space for accessories now and room to work.

Maybe some 12V outlets, a meter, etc. etc. ......

12V outlet.jpg

[markopolo]

The additional space provided by the larger case will now let me crimp lugs onto the power wires and then bolt the lugs to the BMS. Additionally, it lets me crimp lugs onto the power wires and then solder the same type open lugs onto the copper battery busbars. Those busbars will be assembled before attaching them to the battery back.

open crimp terminal example.jpeg

The most difficult soldering of the project is gone and the BMS can easily be reused or replaced if ever necessary.

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[booster]

Originally Posted by markopolo

The additional space provided by the larger case will now let me crimp lugs onto the power wires and then bolt the lugs to the BMS. Additionally, it lets me crimp lugs onto the power wires and then solder the same type open lugs onto the copper battery busbars. Those busbars will be assembled before attaching them to the battery back.

Attachment 8883

The most difficult soldering of the project is gone and the BMS can easily be reused or replaced if ever necessary.

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What crimper are you using on those lugs? Sometimes the ones that require the rolling over of the edges can be pretty finicky to get tight if the lugs and crimper don't play well together. I think that is why we are seeing so many more of the tubular type lugs that only require a crush point of some sort.


The good is if they are solid copper you can really easily add backup soldering to them as they heat super fast and are open to add solder.

[markopolo]

I don't have that type of crimper. I'll do a left fold over, right fold over, then crush type crimp & then solder as you mentioned.

It's a good point to bring up. These are going on single 10 gauge wire and also on a few pairs of 10 gauge wire but nothing larger. I'm still using the tubular crush type 1 AWG lugs out to battery case terminals.

I have a pack of assorted sizes & figure they'd be a bit better than the thinner tinned type, yellow sleeved crimp terminals typically used with 10 gauge wire.

[markopolo]

These are the options I have on hand:
lug options.JPG


I could even solder and rivet or bolt to the copper strip busbar.

[booster]

Originally Posted by markopolo

I don't have that type of crimper. I'll do a left fold over, right fold over, then crush type crimp & then solder as you mentioned.

It's a good point to bring up. These are going on single 10 gauge wire and also on a few pairs of 10 gauge wire but nothing larger. I'm still using the tubular crush type 1 AWG lugs out to battery case terminals.

I have a pack of assorted sizes & figure they'd be a bit better than the thinner tinned type, yellow sleeved crimp terminals typically used with 10 gauge wire.

That is what I wind up doing on them also, as the crimpers are always an issue.


The exception for me is the Delphi waterproof GM style connectors I got in a kit that came with a crimper. The connectors are much smaller, but same style with a second crimp (same tool different hole) for the sealed strain relief. The crimper is interesting in that it isn't a releasing ratchet, but it audibly and you can feel it click as it finishes the crimp. Back in the day when I was building special machines as an assembler, than manual ones we had were just long pliers with special jaw shapes so different people got different amounts of crimp based on hand strength and what time of day it was. If you had hundreds to do in a big control cabinet every day, plus add shrink tubing and numbers as you did them, it got mighty hard on the hands and attention span.

[markopolo]

Just adding that the ladder looking strip busbar is for the serial+parallel bridges. It will be folded over or cut in two & soldered together (doubled up) for use on the two remaining only parallel bridges. Six lugs attach to that.

[markopolo]

The first battery pack is nearing completion.

It weighs 18 lbs. I definitely needed the space that the new case provided. I installed the terminals at the rear of the case so there's easy access to the front.

battery pack 3.JPG
battery pack 2.JPG

I will insert foam blocking to eliminate any movement. It'll be a compression fit side to side, back to front and top and bottom.

The cell ends were all covered with Kapton tape. The bottom additionally got a layer of heat resistant foam. The top got a layer of barley paper on top of the Kapton, then heat resistant double sided tape, then 3/16" rubber salvaged from a Navy battery pack. The BMS sits in a cradle or pocket so it can't move.

I added an extra balancing harness for an active balancer that will be shared between all packs that I end up assembling.

battery pack 1.JPG
battery pack 5.png
battery pack 4.png

Next up will be testing and configuring settings etc. Pack two will be the same as pack one.

[JohnnyFry]

Marco,
Can you supply more details of your millivolt resolution DCVM? How did you calibrate it?

Thanks,
John

[markopolo]

This is the voltmeter https://www.aliexpress.com/item/32838869757.html - it's powered by the 9V battery in the multimeter housing I repurposed.

I have a couple of these voltage references: https://www.aliexpress.com/item/32827554463.html

The voltmeter is likely accurate enough as delivered. There is a trimpot on it to adjust it. I tried to make it match the two voltage references. At 2.5V the voltmeter differs from the voltage references by only -0.00033V & -0.00023V for example.

[markopolo]

For a quick start to testing, I loaded the Normal LiFePO4 profile and started a discharge test yesterday. I have a 30W tester so discharge is set to 2A. (2A*13V=26W)

At 11 hours into the test the cells are perfectly balanced

balanced during discharge.jpg

The discharge test cutoff is set to 11.99V. It will be interesting to see how much capacity the pack has at 12V & above.

I tried to change BMS parameters during the test and the upload hung. The pack still functions but I can't reconnect using my preferred app. It appears to be a password problem. I think I'll have to connect via PC after the test to fix it. In future, I won't change settings while the pack is in use.

I am still able to connect using a different app that doesn't need a password.

Voltage displayed by the app is very accurate. Amps, and consequently amp hours, are showing 0.8% high compared to the tester. It's not a large error but I'll want to figure out which is correct. I'm fairly certain that the BMS can be calibrated.

[markopolo]

Notes:

Bluetooth connection via preferred app resumed on its own at the end of the test, no intervention needed.

Amps & amp hours via app look to be off by as much as 5% compared to discharge tester PC program. I haven't looked into calibrating yet.

As with lead acid batteries, charge current acceptance is affected by voltage. For example, at 13.6V the pack would only accept 10A or so but when forcing 14.4V mode the pack accepted the full 45A from the PD charger.

Cell difference of up to 20mV observed on recharge.

I adjusted the discharge test to cutoff at 12.6V. That's the beginning of the voltage drop-off. Almost 54Ah delivered. I think I can draw 50Ah from the pack occasionally and still expect several thousand cycles.

12 point 6 volt cutoff.jpg

[markopolo]

Incomplete idea for paralleling this LiFePO4 pack with lead acid batteries in van:

Separate diode based isolator with 0.6V voltage drop to charge LiFePO4 pack so that lead acid batteries still get as much current as they can accept from alternator via no drop voltage relay.

When I upgraded the van to use a dual sense relay I left the diode based isolator in place and in parallel as a backup so there is already a wire in the van from that isolator. I'd have to test to see if the voltage drop limits current enough.

Add low voltage drop Schottky diode(s) on output from LiFePO4 pack back to lead acid bank. I'd want 120A current capability on that line. Max load expected to be 90A DC.

I have ten 45V 30A Schottky diodes on hand. I'll have to read up on the risks if paralleling 4 or 5 of them.

Problem: too much voltage drop to LiFePO4 pack when on shore power (if diode based isolator power source is lead acid bank) or no shore power charging if diode based isolator power source is the alternator. I could use the DC charge controller I made on that line from the shore power charger but would have to remember to turn it on and off.

I realize that there are DC to DC chargers available but I don't want to limit alternator output to 20A or 40A with the 400Ah lead acid battery bank for example.

[JohnnyFry]

Going back to my days of installing commercial sound systems, I used a lot of crimp ring lugs, mostly with #20AWG wire. I would crimp, leaving some wire pushed through the crimp area onto the ring followed by flowing solder on the wire/lug. It made a very secure and long lasting connection.

[markopolo]

More notes:
Voltage, temperature, idle current, charge current and discharge current can all be calibrated using the PC program.

Voltage reported from this BMS is accurate enough. It might be 2mV (0.002V) high but I'm not certain enough yet to make any adjustment.

Temperature was low by almost 2C and is easily adjusted. I have to test at various temperatures though. Accuracy at around 32F might be more important than accuracy at room temperature for example.

I made an adjustment at room temperature. The pack was placed in the coolest area of the basement right overnight and the temperature reported is again low by 1C or so. I'll lower temperature in that area and check again later. I'd rather that it reads low than high but don't want it to read too low. I'll have to figure out which thermometer device I have is most accurate.

I will get around to adjusting current as initial testing indicates that the BMS might be off by 5%.

I really like that all of the monitoring can be seen on a phone with no additional equipment needed.