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ICC
Member
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# Posted: 24 Oct 2024 01:45am - Edited by: ICC
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So it needs to be very reliable. I had an EarthX in the Bearhawk, but that was big enough to crank the engine and they don't have small batteries. One thing I was looking at was how reliable was the BMS, as if the BMS craps out it may shutdown the battery. Maybe Steve has an idea?
A friend decided to assemble his own LFP from grade A LFP cells and opted for no builtin BMS. His idea was to omit the possible problem of a bad BMS. But he is OCD about many things. He also loves doing odd things and thinks nothing of manually keeping the cells evenly balanced as necessary.
The weight saving is nice in a small aircraft.
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Steve_S
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# Posted: 24 Oct 2024 11:52am
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Not using a BMS is borderline insane, sorry but there it is. As for weight, what's a couple of ounces. Seems a Reversed OCD by allowing for risks and possible bad things happening... WEIRD !
If a BMS fails for any reason, it won't harm anything but the battery won't be useable till the BMS is replaced. They are pretty reliable in general. There are BMS' with Relays and rarely a Relay could fail but that's really rare.
@Fanman
I don't know of any companies personally making small <10AH batteries. I know they are out there but it is not something I ever looked at honestly. One thing I will say plainly AVOID RENOGY or as a Great Many of us call then RUN-Ohhh-Geez ! The tremendous amounts of complaints & issues is amazing yet they keep on selling... Even on DIYSolar, most of us see the word Renogy in a question, we move on by without even touching it.
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Steve_S
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# Posted: 24 Oct 2024 12:11pm
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Quoting: gcrank1 Think Im glad to know the HVD will trip <14.6. Iirc charging too high is harder/maybe dangerous? on an LFP than going deep discharge (and the LVD should stop that).
Actually, the only time to bring LFP cells up to 3.600-3.650V per cell is to Top Charge & activate all the electrolytes after manufacturing or if the batteries have been stored (no power movement) for a long period (1 yr +, some suggest after 6 months)
Once fully activated & in production/operation there is no need to go above 3.500V per cell and most folks choose to just Bulk/Absorb to 3.450-3.475 which allows the cells to settle post charge to just around 3.400Vpc. right at the top of the Working Voltage Range.
About my numbers:
A 12V Battery Pack has 4 Cells (4x3.2V LFP) while 24V obviously has 8 Cells and 48V 16 Cells.
LFP has 2 Voltage Ranges. Allowable & Working.
Allowable (2.500-3.650) is the range that causes no harm to cells but is NOT the operational deliverable AmpHours.
Working (3.000-3.400) is the range that delivers the actual rated AmpHours.
Nominal Voltage is 3.200 Volts for LFP (50% SOC)
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SOK & Others use excellent cases and most use cells with Screwed on busbars between the cells making them more serviceable if the need arises. I have also switched my previous packs and built my new packs using a Similar Heavy Duty Casing. Now some of these commercially assembled battery packs in steel cases now come with laser welded busbars between the cells, so not easy to swap if something goes wrong (extremely rare).
Picture below is a WIP photo of what I been up to this summer (in part anyways)
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paulz
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# Posted: 24 Oct 2024 01:16pm
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Quoting: paulz I return to the cabin later today after 4 days of power off sunny solar charging. Hoping for some good bank usage. Yes Steve, this is the decade+ old Valence pack. I don’t have a specific load/health tester.
Back to the cabin yesterday after power off solar charging for 3 days, not much really, a few hours of 20 amps or so per day. Voltage 13.4 when powered up, quickly dropped to 13.2 with small cabin load, 6 amps or so. This morning still 13.2. See photo. Still seems to be hanging in there.
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ICC
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# Posted: 24 Oct 2024 01:55pm - Edited by: ICC
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I said he was weird, strange.... His plane is a single seater and in the back of my mind I was sort of happy about that.
@fanman.... Have you looked at batteryhookup?
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Steve_S
Member
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# Posted: 24 Oct 2024 01:55pm
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Those numbers are pretty good, the cells are all nice & close and look like they are doing fine at that point.
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paulz
Member
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# Posted: 24 Oct 2024 05:04pm
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Thanks Steve. You mention earlier about charging to over 14v to test condition. Don’t recall ever seeing my batts that high, even though the Valence spec says 14.6 charge voltage. I could test and run the genny charger for a few hours and see how high they get, would there be any point in that or might I be creating a problem I don’t have?
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Steve_S
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# Posted: 24 Oct 2024 05:25pm
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It should not cause any problems but what you will see after the cells 3.400V will be pretty diagnostic as far as seeing any cells run up or if they stay even up to max before High Volt Disconnect. Those Valence Batteries are really quite tough and very well made (no cheap B grade or Bulk cells in them).
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Fanman
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# Posted: 25 Oct 2024 12:56am
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Quoting: Steve_S If a BMS fails for any reason, it won't harm anything but the battery won't be useable till the BMS is replaced. They are pretty reliable in general.
The issue in an aircraft, of course, is that if BMS craps out, you have no power, and if the battery is powering a flight critical system...  Some prefer to have no BMS, preferring to let the battery sacrifice itself to keep critical systems running.
My application is less critical, but I may use two batteries with a switch to select between them.
Quoting: ICC I said he was weird, strange.... His plane is a single seater and in the back of my mind I was sort of happy about that.
Well, I'm kinda weird too, and my plane is also a single seater...
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ICC
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# Posted: 25 Oct 2024 01:58am - Edited by: ICC
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Quoting: Fanman My application is less critical, but I may use two batteries with a switch to select between them
Quoting: Fanman Well, I'm kinda weird too, and my plane is also a single seater
I will be looking over a 9 year old American Super Legend near Santa Cruz (CA) on Sunday. Not officially for sale but my friend Lee knows the owner and says he has been talking of selling it because of eyesight issues. We'll see.
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paulz
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# Posted: 25 Oct 2024 12:26pm - Edited by: paulz
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Quoting: Steve_S It should not cause any problems but what you will see after the cells 3.400V will be pretty diagnostic as far as seeing any cells run up or if they stay even up to max before
Right as always Steve. Yesterday I ran the genny charger for 3+ hours straight, finally saw 14.00 volts at the bank. But, some variance at the cells, here’s a quick rundown. Bat 3 lagged behind the others for some reason.
3457,3458,3453,3442 bat3
3501,3510,3502,3536 bat4
3482,3505,3617,3511 bat2
3481,3505,3514,3515 bat1
More info in the photos
On the bright side the bank hung at 13.3 before bed and at 13.2 now, higher than it has been after just solar charging. Looking at the cells now, all bats show only a hundredth or two between cells, all bats 13.21 or 13.22.
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Steve_S
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# Posted: 25 Oct 2024 02:42pm
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B3 the Lagger will pull down the others as they will attempt to backcharge within the bank. Although internally it's fairly snug for numbers.
Valence has Passive Balancing. Means it burns off Hi Volt cells to match up to the lowest or to be within 0.010mv of each other. This is where an Active Balancer real;ly does the good work. Cannot change that, it is what it is.
13.3V/3.325Vpc is not bad ! Assuming this is Post Charge, Settled for at least 1 hour without load/charge.
3.200=50%, 3.300=75%, 3.400=100%
3.325 = 81% roughly.
BATS 1,2 & 4 look much better, they'll outlive batt-3. Try keeping BAT-3 three off and try again by fully charging up with the genset & Powersupply + solar if ya got it and see how they then settle & sit. Might be an eyebrow raiser ! (pssst take note of start & end times for charging up.)
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Lithium Batteries in Vehicles (any kind) that operate essential equipment (so not batts in an RV for RV powring stuff) should NOT use a BMS system without Relays/Contactors that come from Tier-1 Quality producer, MOST ESPECIALLY anything to do with non-ground/water transport ! If the battery fails while on a road or in a lake, you won't crash 15,000 feet ! It's just inconvenient, but not with Aircraft !
PSSST ! Altitude DOES affect various battery chemistries. BE AWARE & LEARN IT or suffer potential consequences.
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paulz
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# Posted: 25 Oct 2024 03:43pm - Edited by: paulz
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Ok can do. Just have to figure out which is which, no serial numbers on the outside.
I just checked again though, all cell numbers almost identical. Maybe bat 3 has pulled the others down. Bat numbers are in upper right in photos.
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Steve_S
Member
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# Posted: 25 Oct 2024 11:09pm
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The weakest battery will always pull down others at higher voltage, regardless of chemistries. That's the gotcha with Parallel banks.
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Fanman
Member
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# Posted: 25 Oct 2024 11:36pm
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Quoting: Steve_S Lithium Batteries in Vehicles (any kind) that operate essential equipment (so not batts in an RV for RV powring stuff) should NOT use a BMS system without Relays/Contactors that come from Tier-1 Quality producer, MOST ESPECIALLY anything to do with non-ground/water transport ! If the battery fails while on a road or in a lake, you won't crash 15,000 feet ! It's just inconvenient, but not with Aircraft !
Right, so who are those Tier-1 producers? That's why I asked the question.
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Steve_S
Member
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# Posted: 26 Oct 2024 01:27pm
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Here are a couple of them. Be Warned $$$$
https://www.rec-bms.com/
https://www.batrium.com/
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gcrank1
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# Posted: 26 Oct 2024 01:30pm - Edited by: gcrank1
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My LFP that I charged in the prev posts was still at 13.4 yesterday when we went to the cabin and I put it back in service. It had settled to that quite quickly after charging.
It was 43*f so we fired up the 30k btu lp heater And the ceiling fan on low to mix the air. It ran for about 4hr steady and upon turning off the bat read 13.3v, was still at that 1/2 hr later. All I did was burn off the 'top charge'?
Yeah, I know, voltage is a poor way to try and track the bat SOC.....but all Ive got. The cheap meter on this one does read the volts and shows 'battery bars', a quick visual anyway. Iirc this is about how my other 100ah LFP runs (that Ive thought is the better of the 2 by a bit).
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Steve_S
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# Posted: 26 Oct 2024 04:26pm
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You know how many times I have heard that you can't use Voltage to determine SOC with Lithium Packs ? You know that is 100% BUNK ! The lame excuses., reasons & juistifications are incredible too and MANY don't even grasp chemistry differences & methods.
Even with really accurate Coulomb Counting is won't be that accurate. OK some think it has to be Milliamp Accurate, they can go smoke some Wonder Weed and try to reconnect to reality.
Shunts, Coulomb Counters (even the more precise) all suffer some losses & deviations and do not register internal (to battery pack) losses (which even a BMS running can affect). They also most often cannot read low amps/volts passing through so it "gets lost" If there is less than 1A (mid to good grade device) it does not get seen or accounted for.
That being said, a Respectable Smart Shunt that can be programmed (by user) for 0% and 100% SOC Voltage and then properly calibrated it can get 95-98% Accuracy for SOC. We do not use DOD ! That is a Leadism. My own SmartShunt is 97% Accurate and honestly that is good enough! It also fully resets upon reaching 100% so there is no ongoing dragdown.
The real GOTCHA that throws people for a loop is that Lithium Based batteries are Millivolt & Milliohm sensitive. Effectively you need 3 Decimal Place accuracy to properly do the math. Most shunts are 2 Decimal place accurate and MANY are single decimal place and that really sux for lithium batteries.
IE take LFP: 3.300 to 3.400 is 25% Working Capacity just between that 100 Millivolts. The whole working range is 400 Millivolts !!!
For a Good to High quality shunt that has at least 2 decimal place accuracy can be had for around $100 USD (Not Victron obviously, Massive Markup !!!) a 3 decimal accurate one your getting into the 200-250 USD zone (non Victron).
PS those little LED Status bar display doodads are quite "sloppy" I was given a few to try & test and holy cow, after 4th one I told the supplier that I couldn't even mention them.
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gcrank1
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# Posted: 26 Oct 2024 04:42pm
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Guess I'll just recharge to 13.8v and let it run down to LVD and note what that is.....then live happily in the middle 
That'll work for me
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paulz
Member
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# Posted: 26 Oct 2024 09:44pm
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My bat3 issue is fixed! I went to remove it today as Steve suggested, this terminal was loose. Not much, two flats maybe, but you could move the cables. Tightened it up, charged to 14+ volts, same as the others.
Amazing how a wiggly terminal can cost voltage. And it didn’t show in the low 13v range, only when higher charge.
IMG_3790.jpeg
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Steve_S
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# Posted: 27 Oct 2024 04:19pm
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Hmmm and the LESSON LEARNED ?
I learned to NOT Assume that proper checking of everything had been done and eliminated the obvious potential issues. BAD STEVE ! succumbing to ASSumptions.
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paulz
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# Posted: 27 Oct 2024 05:25pm
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Yeah one side of me feels pretty dumb, the other side glad that bat is still equal to the others. I think what happened is I recently moved the Meanwells chargers to outside so I don’t have to listen to their fans, and when doing so I had to remove its cable from bat4 next to it and must have jostled the bat3 connector cable enough to loosen the bolt. That’s my excuse.
Speaking of the chargers, as you may notice by the photos they were charging at about 60 amps total using my old gas genny. My bigger LP genny gives them about the 80 the Meanwells are rated at 40 each. Takes 2-3 hours to get up from 13.0 to 14. But I do have a decent leftover next morning, compared to the more meager sole solar max of 13.5-6.
I have one more spare Meanwell at the house, theoretically I could run all three off the big genny and pump in 120 amps, about 30 per bat. Still safe I assume.
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Steve_S
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# Posted: 27 Oct 2024 05:51pm
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Still safe, YES but you are loosing a lot for each charger unit. Everyone has losses regardless.
You will also notice the Bank will charge faster & more efficiently now and it will retain the voltage far better. Take the lessons learned, double check everything across the whole system, then relax and call it "Job Done".
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paulz
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# Posted: 1 Nov 2024 12:00pm - Edited by: paulz
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Quoting: Steve_S You will also notice the Bank will charge faster & more efficiently now and it will retain the voltage far better.
Looks like you’re right about that too Steve. Got back yesterday after 3 days gone, 13.8 volts on the meter, up about .3. This morning after fridge/modem all night 13.3, again up .3. Don’t fully understand how that loose bolt accounts for all that, we’ll see if it continues through the weekend, but it sure is nice to look over and see those numbers!
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gcrank1
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# Posted: 1 Nov 2024 12:53pm
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Anything that affects that full contact area between conductors will cause loss of 'the flow', same thing as when you have a poor connection at a car bat terminal that only clicks the solenoid but the bat has enough beans to spin the starter. A lot of folks buy a new bat when all they had to do was clean the clamps and posts and fully charge the bat (because it wont have been getting charged well either).
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paulz
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# Posted: 1 Nov 2024 01:19pm - Edited by: paulz
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That makes sense. I’m just not used to more than one battery powering anything.
Originally I had two batteries in my bank cabled together, positive off one, neg the other. I cabled two more later, pos off bat4, neg off bat1. The loose connection on bat3 still seemed to pas the juice on, others equal voltage. Those two cables apparently still had ok connection, even though on loose bolt.
Yeah, I should make bars.
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gcrank1
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# Posted: 1 Nov 2024 02:52pm
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When I had 4, then 3, then 2 when they died off, in parallel I used equal length cables from each to a common 'bulkhead bolt' to connect to the inverter and scc.
It was one point of a stack of ring terminals, not really considered ideal, but easy to pull and clean and retorque Very tight together.
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paulz
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# Posted: 1 Nov 2024 03:02pm - Edited by: paulz
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That’s the better way to do it (sans bars). I was just adding bat3 and 4 peacemill. The cables connecting them are thick (car size) and under a foot each.
Seems I’m good for now but when these (dated 2012) bats give out…
These just popped up in NorCal. Interesting but slightly used, no return and a way south for me. I think Izzy was just down that way.
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gcrank1
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# Posted: 1 Nov 2024 07:47pm - Edited by: gcrank1
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Im patiently waiting to see how long your current bats really last....ie, if it aint broke......
I think you are our long term tester
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paulz
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# Posted: 1 Nov 2024 11:04pm - Edited by: paulz
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I’ve only had them for about half their life. Back when I got them around 2018 the hospitals were changing them out due to age, they probably didn’t get used much in their life saving equipment or whatever. Don’t know the whole story but they sure are getting used now! As Steve has mentioned they were top of the line grade A stuff back then.
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