DIY portable, useful LiFePO4

[markopolo]

Update: No batteries yet, an order for half of them was refunded as they are presumed to have been lost. I really need some battery cells to see if they will fit in the case with holders & how best to orient the welded on tabs. I chose these batteries mainly because they had tabs. The cells were cheap in price and likely quality at maybe USD $1.25 per Ah. There will likely be impedance variances and I had hoped to group similar cells together to minimize problems from that. I have a specific meter for this project that apparently measures impedance but I haven't been able to figure out how to get that to display. The best laid plans ..........


The meter is model PZEM-015 - if anyone here has used one and figured out if it can be used to quickly test batteries for internal resistance please let me know. Impedance is Ext Resistance on the display ..... That's all I planned to use this particular meter for.





10 tiny chargers are ready to go to work with input and output leads soldered on. 6 are CN3058E chip controlled and 4 are TP5000 chip controlled. I didn't need that many but the cost was low. My preference is the CN3058E chip based chargers but I really wanted to see the TP5000 chip chargers in action.



I also have an EDB-M05 to do some testing:






I'm looking forward to using that.

[markopolo]

I tried the PZEM-015 meter again just now and Ext Resistance aka Impedance displayed no problem. I must have done something wrong when I first tested it.

I tested two very different fully charged lead acid batteries with the same load and got very different Ext Resistance aka Impedance results so maybe it works!

Any suggestions as to what to use for a load when testing the 3V+ battery cells? I have 12V incandescent bulbs and various resistors on hand.

The plan is to fully charge the batteries using the CN3058E chip based chargers then do a quick Impedance test.


Edit: I also have some LEDs that can run at 3.2V. My guess is that a fully charged LiFePO4 cell will be around 3.4V. I think I'll do testing with the LEDs & resistors I have to see what the current is. I could make 10 or more LED/resistor combos if needed to create a load.

[Winston]

What is your target test current?

[markopolo]

1A or so.

I tested a 12V halogen bulb and it might do. At 3.4V from a power supply, current was fairly steady at around 1.4A. It did decrease slightly from 1.448A steadily down to 1.436A over a period of 2 minutes (logged to spreadsheet). I don't know enough to know why it decreased or how much that would matter.

On a 6Ah cell, 1.4A is a pretty good load.

[Winston]

That equates to ~3.5 watts . . . so using resistors wouldn't be out of the question. For our 10 amp discharge tests (at 13 volts), we just unwound 100+' of 20 gauge wire . . . 130' of 24 gauge should give you about an 'amp' at 3.4 volts.

The reason for your current going down is probably 'temperature' . . . in our case, we use copper's temperature coefficient to 'micro-tune' the current . . . if the current is too high, we roll-up some of the wire . . . which causes the temperature to increase, resistance correspondingly increases, current drops . . . and, visa versa.

[markopolo]

Thanks for the idea and the resistance/current lesson

I will also do some discharge capacity testing but thought it would be only on a few individual cells. I don't really want to do 40 (or more) individual capacity tests. Current cell order quantity allows for some rejects. I figured most of that type of testing would be on the assembled pack.

One of the devices mention earlier will automate and graph that. I'll be able to see the effects of age and usage on the pack's capacity. IIRC it is a controlled up to 5A discharge rate (60Ah or so pack).


Edit: I guess a question to be answered is: Will a full charge followed by a quick cell resistance test followed by recharge then rest period and a final voltage check be enough to filter out any not good enough cells? Some of that might be answered once the process begins.

[markopolo]

Covered terminals make for a nice finished look.
terminal covers.JPG

I built a portable DC - DC charge controller today.

Communication with it is via PC or App or the interface on the box. It needs a DC power source to work. Input voltage can be 11V to 16V. Maximum output is 20A. Inside the box, the 11v to 16V is stepped up to 24V then fed to the controller. You choose the output voltage and current. I could have 13.6V in and 14.6V out for example.

After much deliberation, I decided to use Anderson type connectors. I wanted cleaner look but the practicality of those connectors is hard to beat.

It was connected a PD converter/charger and a small 12V battery for the initial test.

Portable DC to DC Charge Controller 1.JPG


Portable DC to DC Charge Controller 2.JPG


Portable DC to DC Charge Controller 3.JPG


Portable DC to DC Charge Controller 4.JPG


Portable DC to DC Charge Controller 5.JPG

The same parts could be built into a van. I chose the parts because I wanted precise voltage and current control.

I might add a fan and a shut off relay if needed.

[markopolo]

A couple of screenshots of the app:


Bluetooth App 1.jpg


Bluetooth App 2.jpg


You can start & stop charging, set voltage and current and graph to Excel via the app. It's useful and fun

[markopolo]

Oh no! Looks like Will Prowse says to avoid the BMS I bought - https://diysolarforum.com/threads/fi...otection.2884/ - (item # 2) - hopefully he does a video on it.

Also hope his problems were caused by a bad board, older version board or not the using the best app.......

Mine came from a different seller. Fingers crossed.

[booster]

A bit off of what you are currently looking at, but have you decided at this point what shoot for, if at all, to address the very murky areas of "memory" or need of periodic balancing?


Isn't Will Prowse also the one that said to always operate the lithium in a quite narrow midrange of SOC without going more full or low? This would be directly the opposite direction of what other articles talk about how handle lithiums to prevent capacity loss due to memory and to do a necessary (top) balance.


I kind of fear with all the recent influx of "experts" that the whole thing is getting less sorted out rather than having the range of best practice recommendations narrow as we have expecting and hoped for. The difference between a reccomendation to always stay in the midrange of SOC and one that is never stay there all the time is pretty stark.

[markopolo]

re: memory - My current thinking is that the battery needs a full charge periodically. Take it to the upper limits. That and maybe periodic deep discharge ? ? ?

re: balancing - I currently plan on triggering it periodically. I be able to choose at what voltage it happens and will likely set charge current at around one amp for that specific event. I don't think I'll have it enabled during routine charging.

It's a learn as I go project.

[booster]

Originally Posted by markopolo

It's a learn as I go project.

And the rest of lucky dogs get to learn without all the work as we watch

[markopolo]

If I make mistakes I won't get too upset. Hopefully I have the right tools to really see what's going on with the battery.

Charging: good voltage and current control, logging to Excel, visible graph. PC & App access.
Discharge testing: controlled voltage and current, logged and graphed. PC interface.
BMS: PC program or App access, able to change settings.

I'll be testing LiFePO4 paralleled with lead acid etc.

[markopolo]

I could sure use some soldering advice. I posted a photo of the BMS here: http://www.classbforum.com/forums/f2...tml#post103473

I really had a difficult time trying to solder some small 18 AWG wires onto the large copper pads. I used an 80W and 120W iron. I did eventual get the two test wires to stick using the 120W iron and solid core lead free plumbing solder. I didn't have success with flux core solder. I had cleaned the copper with alcohol & used flux. I also sanded the copper a bit. I think part of the challenge is heating the large copper pad. Any suggestions or advice will be appreciated. I had planned on soldering 10 AWG wires to the large copper pads because it's unlikely that there is enough space for bolts. It's a really tight fit in the case. I have yet tried to pull those connections off as they were needed to test the BMS. I suspect they might release easily.


I chose this BMS because those large pads actually look capable of carrying 150A. Some BMS just don't look like they can carry the rated current.

[markopolo]

Will Prowse's post about the BMS caused me enough concern to make me want to test the BMS and the app(s). I made a small 12V battery using 8 series connected 1.5V AA alkaline batteries and connected the balance wires to the correct voltage points.

Findings:
- The most recent versions of the apps won't connect to my phone. It might be a phone problem. That includes the Play Store version 3.1.1014 and the newer 3.1.1015.

- The (older?) enterprise version of the app Will posted does connect and it does let me change the low temperature settings. I changed it from -5C to 1C. The app is not entirely in English though.

- An in-between version of the app also connects easily. It did not give access to change temperature settings but the settings saved by the enterprise version where already stored on the BMS. I think it was all in English.

I haven't tested it to see if the temperature setting actually works. I don't thinks it's a big concern with a portable battery but I might test it some day. I'll try other app versions at some point and also try an older phone with the newest versions. I have not tried the PC program yet.

Enterprise 2.0.1006:
enterprise.jpg

Presumably newer 2.1.1022:
newer version.jpg

[skunberg]

Originally Posted by markopolo

I could sure use some soldering advice. I posted a photo of the BMS here: http://www.classbforum.com/forums/f2...tml#post103473

I really had a difficult time trying to solder some small 18 AWG wires onto the large copper pads. I used an 80W and 120W iron. I did eventual get the two test wires to stick using the 120W iron and solid core lead free plumbing solder. I didn't have success with flux core solder. I had cleaned the copper with alcohol & used flux. I also sanded the copper a bit. I think part of the challenge is heating the large copper pad. Any suggestions or advice will be appreciated. I had planned on soldering 10 AWG wires to the large copper pads because it's unlikely that there is enough space for bolts. It's a really tight fit in the case. I have yet tried to pull those connections off as they were needed to test the BMS. I suspect they might release easily.


I chose this BMS because those large pads actually look capable of carrying 150A. Some BMS just don't look like they can carry the rated current.

Soldering such a large difference of material is difficult. More heat on the big pad is needed. Tin both sides with solder first. And get solder with some silver in it. And of course use flux. Sometimes using a midsize material to bridge the size difference helps. Good luck.

[markopolo]

Thanks for the advice. I had tinned the wire ends and was trying put a bit of tin on the copper pad. It just wouldn't stick & I don't give up easily. The solder that eventually stuck was 97% Tin 3% Copper. No doubt you're right about the heat. The 97Sn/3Cu solder does have a higher melting point than the other solder I tried. It's also 1/8" solder so the larger quantity = more thermal mass and thermal transfer in its liquid state.

Do you think the 97Sn/3Cu is adequate or is some silver content preferred/advised?

[markopolo]

App screen captures: ( 8 x 1.5V AA alkaline in series just for a quick test )

more screen captures 3.png

more screen captures 4.png

more screen captures 5.png

more screen captures 6.png

more screen captures 7.png

more screen captures 1.png

more screen captures 2.png

[booster]

On the soldering.


The lead free solder is horrible stuff to get to melt right, especially with big/small like you have. Get some of the normal 60/40 solder and it will be much easier and take a lot less heat. 120 watts is a big iron and probably should work for what you have. If it doesn't have the coated tip, just plain copper, having the no lead solder will be even worse because it will not tin the bare copper properly.


The big iron will undoubtedly be non temp controlled, so it will get hot enough to burn the flux if you don't watch it closely. At best it will have a knob that just reduces wattage, and may have an on/off switch as mine does. Plug it in and keep right at it, dragging a piece of solder with a bit of paste flux, across the tip until it starts to mark and tin the tip. As soon as you can, tin the tip, wipe it with a damp cloth and start to solder. If you have everything ready to go the big lugs may keep it cool enough to not burn the flux. If it does start to char, stop and shut the iron off and let it cool a bit and wipe it with the damp cloth. If it burnt bad, you will have to let it cool and sand or file the tip, and start again.


For the actual soldering that kind of stuff, I have had the best luck by fluxing the big pads and putting a good sized puddle on them with the big iron one after another. Don't worry about letting them cool, as it probably is good in this case. When you have all the puddles on and well attacked (be sure to check for good edges), tin your wires heavily, put bit of flux on top of the puddle on the big tab, heat, clean, tin, the big iron to the right temp and solder on the wires right down the line to keep the iron cool enough. I like to just lay the fluxed wire on the fluxed tab and then put the big iron on top of the wire and push down a bit. At this point you just need to get the puddle to melt enough to let the wire go down to the tab, so the whole puddle may not melt. If you put a bit of solder on the iron itself, it will hang on the underside as liquid and really speed up the heat transfer when you do this.



If you feel like having all the temp thing taken care of without any worry on smaller pieces like up to 10 ga, you can get a really nice temp controlled iron that doesn't need the tether to a workstation controller, plus it heat up in 30 seconds. I got one of these a couple of years ago after trying one of the knockoffs which didn't make rated wattage or last more than a month, and it is by far the best soldering iron I have ever used, including all the models of industrial Weller temp controlled ones.


https://www.amazon.com/Hakko-FX601-0...6&sr=8-1-fkmr0

[markopolo]

Thanks for the info. Yes, the 120W is BIG. It is a Weller with no controls, just plug it in. Huge 1/2" chisel type tinned tip. I did tin it and wipe it on the damp sponge. Yes, I was getting charring & had to clean it up. I'll fine tune my methods based on the advice received & try to lay down some big puddles of solder. The plan is for 6 X 10 AWG, pos & neg so 12 solder connections needed.

I could have used clips for the test but I'm glad I tried soldering on those pads.