lithium iron phosphate trolling motor batteries ?

[Stein]

Cool, thanks.  I'm also thinking about going from a two battery bank to a single and then just have a small jump starter pack, so I need to figure out which way I want to go.

I do like the versions that have bluetooth so you know exactly where they are at, I haven't done enough research to see if they have any alarm features which would give some security.

I talked to a few people who know more than I (chemistry PhD) and their advice was to not leave them on the charger (floating).  It's probably OK, but the battery BMS is likely not expecting or designed for that, so better to pull it off when charged.

I noticed a bunch of existing chargers have slapped Lithium into their title or description, same charger as 10 years ago, but marketing heard they could use it.  There are a few dedicated chargers, but not many.

[CP]

I'm no expert but it would appear that too low a float voltage would drain the battery down to the float level.  I don't think that will harm the battery but it would limit its performance.

A simple DC power supply of steady 14.4 - 14.6VDC is probably the best method of charging these.

[Stein]

Yeah, that's one issue, most chargers are designed to charge, not discharge.  I don't think any of them are tested for reverse current except maybe a few niche cases.

There is also a slight mismatch in cell voltages between the technologies that leads to the slight difference in full charge voltages and most chargers are designed for lead batteries which are slightly lower.  I know my existing charger is pretty smart, the voltage varies over the charge cycle and in addition to the charge cycle it automatically has float and some type of periodic regeneration or maintenance cycle.  Definitely not a good choice for lithium iron phosphate that wants a steady voltage just high enough for 100% charge.

Ironically, with a BMS the charger should be more simple, just apply a set voltage until the BMS shuts it off and then go away.  That's what happens in a simplified discussion of electric vehicle chargers, they produce power until the car (BMS) stops taking it.  This is different than older technology where the charger protects the battery and decides when it has had enough.  Using an old charger on a battery with a BMS means two systems will simultaneously try to control the charging and that's the unknown.  Probably ok if not ideal (potential lower full charger value) and in my personal opinion more likely to harm the charger than battery.

This all assumes the BMS is reliable and when fails, fails safely. 

I would imagine new chargers will come out soon, they should be pretty easy and inexpensive to build.

[CP]

Found an excellent writeup on these batteries, answered a lot of my questions:


https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

[CP]

To follow-up on this thread, I put together a small LiFePO4 battery box with a couple cheap batteries off Amazon.  This was originally to power a kayak fish finder, but it turned out to be way overkill for that.  In fact, this little battery box almost matches the performance of a group 31, 100ah AGM battery and it’s both cheaper and lighter than the AGM.

About 14lbs and $170 vs 69lbs and about $280 for the AGM.

I’m sure that the build quality of these batteries (Miady) can’t match the Battle Born or Ionic but they are about 1/3 of the cost per watthour.

[HUNTINCOUPLE]

Found an excellent writeup on these batteries, answered a lot of my questions:


https://www.solacity.com/how-to-keep-lifepo4-lithium-ion-batteries-happy/

Thanks for that link! Good stuff!

[GWP]

I am coming up on either building a custom battery pack or buying a number of smaller production batteries and linking them in parallel. Prices are coming down enough I may go the ‘link’ method if they have a BMS as I could just bank all of them on a charger at one time. It would almost be worth sending one to ‘The Guy’ and having him tear it down for inspection. Watch his channel often.
Keep us posted on how those hold up!

[CP]

The little battery pack pulled me all over the lake this morning.  Worked great.  The fishing wasn't exactly great though.

 

[Stein]

That's pretty impressive for that size of battery.

[CP]

Yeah it's impressive but I don't recommend doing this.  That motor is capable of drawing 55amps.  Those batteries are only rated for 40 so I've fused them accordingly.  Too aggressive on the throttle and I'll be changing fuses.     

[GWP]

Now you made me curious! I have a few different clamp on style amp meters (Fluke) and may take one with me on the next outing to see how much my 80lb 24v Terrova pulls. It is pretty oversized for my 16ft boat, so I am curious what it will draw wide open. I have hit the 'rabbit' button a few times on the water and it does around 6mph on a GPS.

[Dhoey07]

Yeah it's impressive but I don't recommend doing this.  That motor is capable of drawing 55amps.  Those batteries are only rated for 40 so I've fused them accordingly.  Too aggressive on the throttle and I'll be changing fuses.   

Which batteries from amazon did you go with?  I have a little minnekota that only has a 30 amp max draw. 

[CP]

Yeah it's impressive but I don't recommend doing this.  That motor is capable of drawing 55amps.  Those batteries are only rated for 40 so I've fused them accordingly.  Too aggressive on the throttle and I'll be changing fuses.   

Which batteries from amazon did you go with?  I have a little minnekota that only has a 30 amp max draw.

I used two of the 20Ah but they appear to be sold out of those.  They do have 36ah - one of those might suit your needs.

https://www.amazon.com/gp/product/B089VXSBC6/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1

[CP]

I finally got the SOK 100ah battery and tested it and, yeah, lead acid deep cycle batteries are obsolete.  50 to 60ah of LiFePO4 will easily replace and outperform any 100ah lead-acid battery.

[Stein]

Wow, that's impressive.  I'm seriously considering going to a single battery in my boat.  I think that plus a small jump starter battery pack as a backup would do the trick and save a bunch of weight and space.  Hopefully they are back in stock soon.