Teej's Honda Element Tiny RV

[tjoiner1986]

It reached 3.56 this morning, occasionally blipping to 3.57, so I put cell #1 back in parallel with the rest of the pack and began charging to 3.60. Once it balances at 3.60, I'll set it to 3.65 or maybe just call it "close enough" at 3.60. I haven't decided yet.

 

[luckielab]

If you haven't already stumbled across it, I found some of the info in this top balancing resource useful. It has some comments on 3.60 v 3.65, etc.

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

 

[meetyg]

Very strange that the cells voltages are far apart.
I would check your bus bars and connections. Make sure all contacts are clean and tighten the nuts accordingly (cells should have a torque spec, don't over do it, or else you risk damaging the terminals/cells).

 

[tjoiner1986]

Getting a little frustrated here.

I've got it set to 3.60 here at work. Multimeter is showing 3.57 between the positive of cell 4 (where I have the positive lead from the power supply) and the negative of cell 1 (where I have the negative lead from the power supply).

Cell 1: 3.56
Cell 2: 3.40
Cell 3: 3.35
Cell 4: 3.34

Current readout from the power supply just seems to bounce around 5.2 and 5.3 amps. ?‍

Seeing as these are new cells that have not seen service, everything should be squeaky clean. Everything is nice and tight -- not torqued to spec but definitely not overtightened. Any chance these beefy copper bus bars are too much? Either way, I'm going to shut it all down, take it all apart, and reassemble. I might even charge each cell individually, then parallel everything and charge as a whole.

EDIT: High pitched squeal, not loud but audible, coming from the power supply when set to 3.56 and attached to cell #4. Removed everything. Decided to balance cells 3 and 4, since their measured voltages are about equal, to match cell 2. Power supply set to 3.40. Current readout is 4.800 and falling. Will leave it like this until current reads zero (or my dental appointment at 2 PM, whichever comes first). Then will balance cells 2, 3, and 4 to match cell 1 @ 3.56. Then balance everything to 3.60. Will decide what to do from there when I get there.

 

[tjoiner1986]

OK, let's try this again.

Voltage readings of each cell, everything disconnected and bus bars removed, using a multimeter are currently:

• Cell #1 = 3.39 V
• Cell #2 = 3.37 V
• Cell #3 = 3.38 V
• Cell #4 = 3.36 V

Going to put them all in parallel, set the charger to 3.60 volts with the current @ full (10.25ish amps according to the power supply's readout). The studs are tight and I've got split lock washers on the power supply studs to keep the cables from coming loose. The nuts are tight on the bus bars. Everything is secure. I see no reason other than a defective power supply and/or battery pack why this should not top balance correctly.

With the entire pack reconnected in parallel and supply powered on:

• Voltage readout on the power supply is 3.52 volts (supply was set to 3.60 while disconnected).
• Amperage readout on the power supply was initially bouncing between 9.652 and 9.653, gradually climbed to 3.662, and began falling once the power supply fan turned on. Began slowing climbing again when the fan cut off.
• Voltage readout from the multimeter between cell 1 (-) and cell 4 (+) is 3.39.

In other news:

• Returned the MPP Solar 1012 because it didn't have low temp. disconnect.
• Sold the Renogy DCC30 and Bluetooth adapter due to reliability and Bluetooth connection concerns.
• Found a great deal on a Victron SmartSolar 100/30 ($175 new) and BMV-712 ($140 open box, unused) along with this article explaining how to use the BMV's relay to trigger a low temp. disconnect from the DC-DC charger I plan on getting in the future.
• Ordered this JBD 150A BMS. I currently have a 120A Daly smart BMS but the general consensus seems to be that JBD is far more reliable. For the same price I paid for the Daly, I'm getting Bluetooth connectivity, more balance current (I understand there's some debate here), 30 more amps, a built-in temperature sensor + two external temp. sensor ports, and heater output if I ever venture down that road.

 

[MisterSandals]

Voltage readout on the power supply is 3.52 volts.

Just to confirm you are setting the voltage while NOT connected to the battery/cells, right?

 

[tjoiner1986]

Just to confirm you are setting the voltage while NOT connected to the battery/cells, right?

Correct. Everything is being set with, at the very least, either the positive or negative cable removed from the cells. Should I need/want to adjust anything, I power off the supply, disconnect, turn the supply back on while disconnected, adjust voltage, power off, reconnect, power on.

 

[tjoiner1986]

I finally have good news to report!

Yesterday, with all of the cells ranging between 3.36 and 3.39, I decided to change plans and top balance incrementally. I set it to 3.40 and ran that for most of the day. The current was, if anything, increasing and the voltage reading on the power supply showed 3.41 even though I had set for 3.40. I felt that was odd as my understanding is that the current will decrease once the supply reaches the target voltage.

With that, I decided to increase the voltage to 3.50, so I disconnected everything, turned it to 3.50, reconnected, and left it running through the night. When I got back to work this morning, I was delighted to see 3.50 volts / 0.044 amps / 0.154 watts. At this point, I believe I'm top balanced to 3.50.

From here, should I let it continue all the way to 0.00 amps or is it close enough and time to charge to 3.60 or 3.65?

Top photo was taken when I left work @ 5 PM. Bottom photo was taken when I got here this morning at 8:00.

 

[luckielab]

From here, should I let it continue all the way to 0.00 amps or is it close enough and time to charge to 3.60 or 3.65?

I'm new at this (did my first top balance on my cells two weeks ago), but I can't think of a reason why it'd be important to let the 3.50 run amps drop any more.

 

[tjoiner1986]

Just now, I decided 0.037 amps to go was close enough, disconnected, increased voltage to 3.60, and resumed balancing/charging/whatever.

The current started at 3.something and has been falling rapidly.

Update: Already down to 0.860 amps and falling.

 

[MisterSandals]

Once you get over 3.50V, there is very little capacity so the voltage changes quickly with little time/power.
You will be fighting the self discharge a little so do not fret about getting current to exactly 0.00.A.

 

[tjoiner1986]

Once you get over 3.50V, there is very little capacity so the voltage changes quickly with little time/power.
You will be fighting the self discharge a little so do not fret about getting current to exactly 0.00.A.

Thank you for the help! So relieved!

Bumped it up to 3.60 and let it go until it was at about .18 amps. Disconnected, increased to 3.65, and resumed just now. It's already fallen fast to 0.835 amps. I'm glad to finally see this working as it should. Not sure what the difference was but I won't question it. I'm just happy to know I'm on my way to having electricity again.

After this, I'll have to wait for my new BMS to arrive. Not sure when that will be so I can either put in the Daly I already have or wait until the JBD gets here (AliExpress, so March?) and use my crippled Renogy 100Ah AGM (won't charge more than 50% or so it seems) for the time being. Then again, I currently don't have a charge controller anyway -- the SmartSolar 100/30 hasn't shipped yet -- so there really isn't much I can do except wait and enjoy knowing I've got a top balanced pack.

Side Note: The BMV-712 arrives tomorrow and the temperature sensor for it arrives today.

UPDATE: The charge controller is scheduled for delivery on Tuesday.

 

[MisterSandals]

When finished with top balance, disconnect and take note of each cell voltage. Then in an hour then 24h. Good data is key to diagnosing issues or making decisions how to build your pack.
The quick self dischargers may be the weakest (lowest capacity).
And, all the wired chit happens on cell 1 & 4 positions (this is why I recommend labelling your cells with letters, A, B,… since cell position is a number already).
So putting weakest cells in positions 2 and 3 is a good initial strategy.

You’ll see. Take good notes to make informed choices.

 

[tjoiner1986]

When finished with top balance, disconnect and take note of each cell voltage. Then in an hour then 24h. Good data is key to diagnosing issues or making decisions how to build your pack.
The quick self dischargers may be the weakest (lowest capacity).
And, all the wired chit happens on cell 1 & 4 positions (this is why I recommend labelling your cells with letters, A, B,… since cell position is a number already).
So putting weakest cells in positions 2 and 3 is a good initial strategy.

You’ll see. Take good notes to make informed choices.

Thanks for the tip. Labelling that way does make sense, as does measuring the voltage. I appreciate all the help!

As of this post, I'm right at 0.100 amps @ 0.357 watts. As long as this is here with me at work, I can't do a whole lot except let it charge -- after all, they don't pay me to work on personal projects -- so I'll just let it do its thing until I leave at 5:00 and take the pack with me so I can measure after work.

 

[Bubba1]

You are done. Cells are top balanced. I would remove it from the power supply.

 

[tjoiner1986]

You are done. Cells are top balanced. I would remove it from the power supply.

Woot! OK, so I've got a combined pack voltage of 3.68 in parallel. Just a hair overcharged I suppose but I'm assuming that will decrease as the cells stabilize.

Individual cell voltages with everything disconnected and bus bars removed:

• Cell #1 = 3.68 V
• Cell #2 = 3.68 V
• Cell #3 = 3.68 V
• Cell #4 = 3.68 V

I'll measure again at 4:30 (an hour from now).

I think what I'm going to do is leave the cells positioned in parallel but wire them in series. That way, if I ever need to top balance again, I don't have to take the pack apart. I think I've got just enough copper left for 3 extra long bus bars. If not, I've got plenty of 4 AWG and crimps.

UPDATE: The charge controller is scheduled for delivery on Tuesday.

 

[Bubba1]

You will probably not have to top balance again. I never had to. I would arrange them in series. That's what everyone does. Shorter bus bars and easier.

 

[tjoiner1986]

Voltage after 90 minutes:

• Cell #1 = 3.68 V
• Cell #2 = 3.67 V
• Cell #3 = 3.66 V
• Cell #4 = 3.66 V

 

[tjoiner1986]

Voltage as of 8:30 PM after sitting in the car for 3 hours* in 30°F weather:

• Cell #1 = 3.67 V
• Cell #2 = 3.65 V
• Cell #3 = 3.65 V
• Cell #4 = 3.65 V

* Visiting mom. ?‍

 

[tjoiner1986]

Last night, so the pack wasn't stealth camping with me in temps that dipped into the low 20s, I brought the pack to my storage unit (somewhat climate controlled).

This morning, as of 7:45, the voltages are:

• Cell #1 = 3.66/7 V
• Cell #2 = 3.64 V
• Cell #3 = 3.63/4 V
• Cell #4 = 3.62/3 V