LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[john61ct]

Originally Posted by evm1024

1000 amp shunt

Just an example specifically because they're unwieldy, also lower accuracy at low currents, hence my reco to use the minimum needed.


> 5C ?

No, by "0.4-5C" I meant 0.4C to 0.5C so only 150A max for a 300Ah bank.

It is not healthy for longevity to do a full re-charge faster than 90min to 2 hours, unless the cells are already quite warm, even hot for over 1C.



And of course good chargers don't cost much less, or even more than the banks they charge, isn't that generally the case? Unless you don't mind waiting for 8-10 hours, and that's usually only a luxury afforded by those with mains available overnight. . .

> With the (lack) of accuracy I've measured it is quite possible to over or under charge at least one cell in your pack

No way I'd use even a super-expensive SoC meter to determine charge termination, unless absolutely necessary (Cpt Pat's unusual use case, maybe).

With cheap gear like this, just for monitoring, usually while discharging, and yes known to just be a ballpark guesstimate. And staying well below even half max rated current.

_____
I prefer to stick with proven OTS components, but yes I've followed others tinkering with DIY and the TI BQ769x0 is well respected.

For working at propulsion voltages, I think serial'ing lower-count modules would help to keep costs under control, once you get past 12S everything starts getting crazy pricey. 6-8 in series plenty more competition, consumer-grade stuff you can afford to carry spares.

[john61ct]

Originally Posted by SweareDeep

REC-BMS sell a Bistable Latching Relay Driver which, I think, does what you want. It's listed under Accessories on their website.

Also check out the Philippi box

http://www.cruisersforum.com/forums/...ml#post2997399

[evm1024]

Originally Posted by newhaul

mike thank you for the information it was just what I was looking for.
I fully intended to get the 350 amp shunt just in case I ever need to draw more than .5C out of my bank . Or I ever upsize the bank beyond the current 240ah as to the shunt I have access to a 3d printer so I can design a plastic base to securely mount the unit to the bulkhead .

Now the real question
before or after the bms? I'm thinking before ( on the battery side )

How about this for a base?

https://www.aliexpress.com/item/3282...8-f29e51fe8aeb

[newhaul]

Originally Posted by evm1024

How about this for a base?

https://www.aliexpress.com/item/3282...8-f29e51fe8aeb

That is the base you get if you order on Amazon for an extra 8 bucks.
Becides i got my boys a 3d printer for christmas i deserve it

[evm1024]

Originally Posted by newhaul

That is the base you get if you order on Amazon for an extra 8 bucks.
Becides i got my boys a 3d printer for christmas i deserve it

You are the man and on top of it.

[evm1024]

Originally Posted by john61ct

Just an example specifically because they're unwieldy, also lower accuracy at low currents, hence my reco to use the minimum needed.


> 5C ?

No, by "0.4-5C" I meant 0.4C to 0.5C so only 150A max for a 300Ah bank.

Typos do slip in and make a big difference. Even getting 0.5C cn be quite hard...

No problem with a 1000 A shunt in off-grid / grid-tie applications. Fixed location of course.

It is not healthy for longevity to do a full re-charge faster than 90min to 2 hours, unless the cells are already quite warm, even hot for over 1C.

And that is why I questioned your specing ( or so it appeared 5C charge.

SNIP

Now I'm more confused:

Maybe my next DIY portable powerpak I'll give them a try and post feedback.

I prefer to stick with proven OTS components, but yes I've followed others tinkering with DIY and the TI BQ769x0 is well respected.

I guess you mean that you have not used the bq769x0 in any of the portable power packs you have done before your next one.

[john61ct]

Only saying

1. for the various functionalities usually implied by that (IMO overloaded) term "a BMS", I prefer to buy proven products OTS, and

2. if I ever **did** get interested in DIYing a monolithic BMS - that line of ICs seems a good one, despite their limited series-count / pack voltage

[evm1024]

Originally Posted by john61ct

Only saying

1. for the various functionalities usually implied by that (IMO overloaded) term "a BMS", I prefer to buy proven products OTS, and

2. if I ever **did** get interested in DIYing a monolithic BMS - that line of ICs seems a good one, despite their limited series-count / pack voltage

Oh, well - too bad. I am thinking about putting together a "smallish" "portable" pack out of small cells, much like the battle born batteries. It would go power the windless and have an integrated BMS and buck/boost charger. Plus enough smarts to make it all work together.

I was hoping that you had put together a portable powerpack so that I could learn from your experience. I do recall that you were looking for a source of cylindrical cells from one of your prior posts.

I go back and forth between prismatic and cylindrical cells. Easy to grow the pack with cylindrical cells in small increments.

Did you ever decide on a vendor and form factor for your cells? Right now I only have 8 in the 18650 form factor. Samsung if I recall correctly.

[john61ct]

Well as soon as you get away from LFP (and maybe LTO) then the fire risk from thermal runaway skyrockets,

and the need for multiple layers of fancy anti-KISS failure-prone protective electronics becomes more critical.

Same with using such tiny mAh capacity cells, so much work, every added connection increases risk of failure.

DIY a spot-welder before you even get started?

meh

20Ah cells would be the lowest I'd recommend
and LFP only, except as a hobby science project that stays well away from any living space, especially in a mobile context. Certainly not for life on a boat.

[evm1024]

Originally Posted by john61ct

Well as soon as you get away from LFP (and maybe LTO) then the fire risk from thermal runaway skyrockets,

and the need for multiple layers of fancy anti-KISS failure-prone protective electronics becomes more critical.

There you go again - Let's not head off on a tangent. We are only speaking of LiFePO4 cells. (in a Star wars voice - Stay on target, stay on target)

Same with using such tiny mAh capacity cells, so much work, every added connection increases risk of failure.

DIY a spot-welder before you even get started?

meh

38120 cells are running 10 AH or more. Hardly tiny! plus they are available with screw terminals - no spot welder needed. (stay on target!)

20Ah cells would be the lowest I'd recommend

Is that what you are using? Good on you. I'm OK with 10 AH cells - That appears to me to be a good balance of the various factors that I'm interested in. Oh, by the way - what do you base your recommendation on? I might have overlooked something so if you would list your criteria I'll take a look and see what I have overlooked.

and LFP only, except as a hobby science project that stays well away from any living space, especially in a mobile context. Certainly not for life on a boat.

Stay on target! LifePO4 please - no red herrings.

I was hoping to come to understand your recommendations. So far (IMO) null content.

[newhaul]

Originally Posted by john61ct

DIY a spot-welder before you even get started?

meh

.

why not it took me all of about 15 minutes to scrounge up the parts and assemble them for a 12v spot welder. Easy peasy.

Runs off of a riding lawnmower battery.

That's how I built my 100ah Lfp bank out of 25ah prismatic cells

[gscriba]

Originally Posted by SweareDeep

REC-BMS sell a Bistable Latching Relay Driver which, I think, does what you want. It's listed under Accessories on their website.

Thanks for that, SweareDeep. I have two already. Below is one along with 4 of the most adorable little electrical thingys. I don't have a flying #@*% idea what they are, what they do or how to connect them.



I'm sure this is stupid simple for some, but without specific instructions, when it comes to this, I'm lost.
I'm quite frustrated by this part of my set up; I've always been able to figure things out, but I am having trouble at this point. I'm humbled.
And when I do finally get the bistable latching relay drivers wired in, I still need to be able to program the REC. Again, not my skill set to say the least.

Anybody able/willing to provide a step-by-step to attach the REC bistable latching relay driver to the ML RBS 7700 AND program the REC to open and close the RBS 7700 LVC and HVC? Tall order, I realize.
Thanks.

[john61ct]

Originally Posted by evm1024

Let's not head off on a tangent. We are only speaking of LiFePO4 cells

You're the one brought up Samsung 18650s, are you trying to say they come in LFP?

Have yet to hear anyone I'd trust give good long-term feedback on Headways, much less any no-name stuff. And have you priced how much 100Ah (smallest I'd make) would cost?

In cylindricals so far A123 (now part of Lithium Werks slong with Valence & Super B) is the only maker I'd bother with, and then only if I needed something pocket sized.

For prismatics, only Winston/Thundersky, CALB, GBS and Sinopoly.

[john61ct]

Originally Posted by newhaul

18650 cells most definately come in lfp.

I never said they didn't. "They" refers to **Samsung** 18650s, which dozens of instances none are LFP.

I also stated I have no interest in the cylindricals in general, which out of dozens of form factors also happens to include the tiny 18650s.

[newhaul]

Originally Posted by john61ct

I never said they didn't.

If we "really need" to be snide about it,

maybe you need to try improving your reading skills.

Now personally, I'd really prefer it if we could refrain from the personal sniping newhaul, don't you think that wojld be nice?

I attempted to correct my post but my phone wouldn't let me for some reason

Samsung 18650 Lfp cells

https://voltaplex.com/lithium-ion-ba...8&s_chemabv=22