Help with building a low cost LiFePO4 trolling motor battery

smithmal

1 mW
Joined
Sep 24, 2018
Messages
13
I've read several battery pack build threads on this forum, but usually the person already has battery cell in mind when building their pack. In this case, I'd be very interested in hearing from everyone if they were going to build build a sub $500 50-75Ah 12V LiFePO4 battery (with continuous 60A draw) from scratch, how would they do it?

My only bottleneck is with the case since I already have a Hardigg case (13" x 15" x 13") that I'd like to use to put the battery into and then to construct into a PowerBox.

Questions I have are:

1. What battery, voltage, capacity and manufacturer makes the most sense to use for this application? I was thinking 18650 or 38120 since from what I understand they both provide good cycling and are thought to be high on safety performance, but what would you choose?
2. What orientation would you put them in to get a 12V and 50-75Ah battery pack (remembering my dimensional issues)
3. What BMS would you suggest (I'd personally like one with BT so I can monitor and adjust via a smart phone)
4. What charger would you suggest?
5. Is there an off the shelf product available (maybe from China) that would be as reliable, high quality and cost would be similar (say maybe $100 more) vs. building a DIY battery?

Thanks,

smithmal
 
Okay... sorry for the edit but decided to go with HEADWAY 38120 HP 3.2V 8AH LIFEPO4 LITHIUM BATTERIES 25C cells since I got a good price on them (reclaimed cells) for $10 a cell: https://www.ebay.com/itm/4-HEADWAY-...TTERIES-25C-200A-12V-SUPER-CELLS/183397230915

Specs on the Headway 38120 cells can be found here: http://www.litrade.de/pub/HeadWay LiFePO4 38120__ Specifications1.pdf

So now, the question is:

I'd like to build a 48Ah 12.8V battery pack (4s6p):

1. What busbars do you suggest I purchase?
2. What would be the best orientation of the busbars on the top and bottom of the pack (keeping the pack smaller than 12" x 12")
3. What BMS-BT module should I get?
4. What gauge wiring should I use?
5. What charger should I get?

Thanks,

smithmal
 
Below is a pic of how I would arrange the batteries for this pack in a 4s6p orientation. Please let me know if this is incorrect:

https://drive.google.com/open?id=1nVejypWLYV13upVyiJavYu5GQA9cAe0c

The most current my trolling motor could pull (Minn Kota Endura Max 55) if I had it on full throttle is 50A. In terms of a BT BMS I was thinking of this: https://bmsbattery.com/bmspcm/882-smart-bms-3s5s-80a-with-blue-tooth-android-app.html

I realize that an 80A BMS might be a little overkill, but I wanted to have the versatility of hooking just about anything to this battery (i.e. future proof) and since the cells have a 200A capacity, the sky is pretty much the limit. Has anyone had any experience with this BMS and/or products from this site? Are the BT modules that they are selling functional across Android/iOS? How well do they work with older and newer BT versions? I've read about other BT modules that manufacturers attach to their BMS that have significant user connection issues.

Also, I'm assuming that I would need to use 2 hole and 6 hole busbars and that I should shoot for copper at the material. Are there any sources you would suggest I use? How thick should the busbars be?

Thanks,

smtihmal
 
So...why ask for advice picking a battery, then not even wait a couple hours for responses, before just buying something anyway?


FWIW, "reclaimed" batteries (regardless of what a seller might say) could be in any kind of condition, so I'd recommend doing what we advised the other person whose thread you were asking questions in to do, and test the cells thoroughly to characterize them before building a pack with them and using it. Then you will at least have some idea of why there are problems when they start happening.
 
amberwolf,

The reason that I choose the 38120 batteries without getting advice from the forum was a deal on salvaged cells sprang up right after I started the thread which I thought was too good to pass up so I jumped on it. I thought about changing the thread title to "Help building a 12V 48aH LiFePO4 Battery" but I don't believe you can do that once the thread is started.

I will most definitely be testing and verifying the capacity of all my cells (especially since there is a 60 day warranty with them). Could you (or anyone) provide me with thoughts on which charger would be best for:
1. Charging the battery pack (I believe my battery would have 614 watt hours so I'm thinking a 100 watt battery should provide me with full charge in 6 hours. Is that correct?)
2. Balancing each battery

Also, in terms of bottom balancing them. Is that done with each battery, or once the battery is put into a series and then each series is bottom balanced?

Thanks,

smithmal
 
Does anyone have any thoughts about the following charger:

https://www.amazon.com/Ultra-Power-...s+&+Games&sr=1-2-fkmrnull&ref=sr_1_fkmrnull_2

Video Review on it here: https://www.youtube.com/watch?v=BdWN6UWI2RQ

Charger Specs:
Input Voltage: AC 100-240V, DC 11-18V
Charge Power: max 100W
Discharge Power: max 10W
Charge Current: 0.1-10A
Discharge Current: 0.1-5A
LiPo/Li-ion/LiFe/LiHV cells: 1-6
NiCd/NiMH cells: 1-15
Pb cells: 1-10

I like that you can discharge using up to 5A to allow for faster bottom balancing. Would this be serviceable for testing, balancing and charging the pack I intend to build?

Thanks,

smithmal
 
those headways will never supply that current without killing them.
 
flippy said:
those headways will never supply that current without killing them.

Flippy,

Sorry, confused. Do you mean the Headway's won't provide the 50A (needed for the trolling motor) or take 5A of discharge (for draining and bottom balancing/cycling the batteries?

Thanks,

smithmal
 
6p I wouldtry it if good cells. Put a bunch in parallel and charge the group to 3.6v as a group then disassemble in that rest check out what are the weak ones in each group after 2 days of rest. If they hold 3.5v or so good. Then do your other test.
 
smithmal said:
Sorry, confused. Do you mean the Headway's won't provide the 50A (needed for the trolling motor) or take 5A of discharge (for draining and bottom balancing/cycling the batteries?

headway grossly overstate their ratings. i got brand new ones "back in the day" and they were seriously lacking. at high discharges (5A or more) they heat up and wear out real fast. internal resistance rises within 100 cycles or so and they heat up more, hold less charge and sag more under load.

i find them a waste of money. a couple of thundersky/winston blocks will preform and last way longer, are basically waterproof and you can buy them in 12v blocks matched in the factory so you dont need balancing boards or a bms.
 
flippy said:
smithmal said:
Sorry, confused. Do you mean the Headway's won't provide the 50A (needed for the trolling motor) or take 5A of discharge (for draining and bottom balancing/cycling the batteries?

headway grossly overstate their ratings. i got brand new ones "back in the day" and they were seriously lacking. at high discharges (5A or more) they heat up and wear out real fast. internal resistance rises within 100 cycles or so and they heat up more, hold less charge and sag more under load.

i find them a waste of money. a couple of thundersky/winston blocks will preform and last way longer, are basically waterproof and you can buy them in 12v blocks matched in the factory so you dont need balancing boards or a bms.

Interesting, the tests that Jehu performed in this video back up the claims in terms capacity and current:
https://www.youtube.com/watch?v=MdhyOFeOqyE

Also this video review backed up the capacities that were stated from the same source that I obtained them from. I believe the tester observed even higher capacities than what the seller stated: https://www.youtube.com/watch?v=XbuZbFq25gE&t=1464s (see 21:37 in the vid)

By the way, these are 25C rated batteries which are much higher than other 38120s that are available on line (the 10AH ones).

smithmal
 
Those cells they tested are brand new. After 100 cycles you will see very different values.

This is why i have a machine that can do lifetime cycles and plot the performance after a few months of daily use.
 
flippy said:
Those cells they tested are brand new. After 100 cycles you will see very different values.

This is why i have a machine that can do lifetime cycles and plot the performance after a few months of daily use.

flippy,

You are incorrect. The cells tested in those videos I linked above are not brand new. They come from the same eBay seller I bought mine from (alarmhookup). The seller indicates testing capacities of these cells @ 90%-102%. Richard Lloyd's video saw all of his used cells testing at above 95% capacity:
https://www.youtube.com/watch?v=XbuZbFq25gE&t=1464s

Thanks,

smithmal
 
smithmal said:
flippy said:
Those cells they tested are brand new. After 100 cycles you will see very different values.

This is why i have a machine that can do lifetime cycles and plot the performance after a few months of daily use.

flippy,

You are incorrect. The cells tested in those videos I linked above are not brand new. They come from the same eBay seller I bought mine from (alarmhookup). The seller indicates testing capacities of these cells @ 90%-102%. Richard Lloyd's video saw all of his used cells testing at above 95% capacity:
https://www.youtube.com/watch?v=XbuZbFq25gE&t=1464s

Thanks,

smithmal
they are unused samples. and capacity ratings done at 0.2C are meaningless.
hitting the rated capacity is not a indication for quality.
if i were to acutally pull 200A from it cand charge them at 80A they would die/explode within a hour.
i know this because they already got above 50C at 40A draw and because i dont want to burn my workshop down i concluded it is not safe to pull more power.

they are fine for battery replacements in cars and low power applications like ebikes but i would never ever use them near their "offical" ratings.
 
flippy said:
smithmal said:
flippy said:
Those cells they tested are brand new. After 100 cycles you will see very different values.

This is why i have a machine that can do lifetime cycles and plot the performance after a few months of daily use.

flippy,

You are incorrect. The cells tested in those videos I linked above are not brand new. They come from the same eBay seller I bought mine from (alarmhookup). The seller indicates testing capacities of these cells @ 90%-102%. Richard Lloyd's video saw all of his used cells testing at above 95% capacity:
https://www.youtube.com/watch?v=XbuZbFq25gE&t=1464s

Thanks,

smithmal
they are unused samples. and capacity ratings done at 0.2C are meaningless.
hitting the rated capacity is not a indication for quality.
if i were to acutally pull 200A from it cand charge them at 80A they would die/explode within a hour.
i know this because they already got above 50C at 40A draw and because i dont want to burn my workshop down i concluded it is not safe to pull more power.

they are fine for battery replacements in cars and low power applications like ebikes but i would never ever use them near their "offical" ratings.

flippy,

Thanks for the reply. Not sure of the origin, but yes I would never attempt to use them near their official ratings. Plan on charging/discharging below 0.5C for my pack (48Ah pack making 0.5C = 24A). Most likely will charge @ 10-15A (146 - 219 watts) which would take 3 hours to completely charge my pack if empty (8.0A).

smithmal
 
999zip999 said:
Carry on. Please don't over tighten the screws !!!

Yes, absolutely and great advice. Have read alot about people warning not to over-tighten the cathode/anode screws and breaking the stud loose from the main battery (i.e. ruining the battery).
 
BTW, don't forget a bit of thread locking goo. Always a drag when you have to take apart a pack while on the water to find the loose screw.

My 15ah Headways (40152S) lasted a long time. Over 5 years and more then 14,000 miles My controller is 30a and my cells have never gotten anyway near self destruction, BUT....they no longer take a 12 amp charge without getting hot. I now only charge them at 5 amps. They never seemed to deliver the 2c output that were advertised, but they never got hot going WOT up a hill. Now they really sag on the hills. However, they still deliver 500 watts and I don't have any long hills around here anyway.

So, as stated, test each cell carefully and know that used ones will delver less then advertised performance of new ones.

If you can, overbuild the pack.

:D
 
Pulling teeth so you're going to build a 4S 10p pack ? 400.00 dollar pack can be charged at 20amps ? 2-3 houts. Charging to 14v or 3.5v per. Tops. Run time 5hr. If no wind from nature ? Just asking ???? Boat time ? Beer time.
 
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