Lithium Bank Voltage Drop.....

[CaptainRivet]

Originally Posted by Pete7

Me or UFO? 100A isn't a problem with 35mm cable, never gets warm and there is sufficient in reserve to pull more. Space for more electrical galley items is a natural limiter for us.

Pete

Obviously UFO

[CaptainRivet]

Originally Posted by Pete7

Oh its tiny, first corner of the Trojan just showing on the right is now the first LFP. However, LFP master switch to Blue Seas circuit breaker and on to inverter is 50mm x perhaps 40cm because the chandler had some short cut offs left over and I am a regular.

Voltage drop of less than 3% for solar panel wiring, less worried about the inverter circuit etc so over spec'd the cable to be safe, because you only want to do it once.

Little boat, low power requirements, low budget achieved and simple to fault find by follow the wire

Pete

All done right
...combining FLA in a small boat like you acceptable but not to copy this setup for bigger boats.

[s/v Jedi]

Originally Posted by SailingHarmonie

JEDI,

You are missing the point, and are way to quick to assume my posting was stupid. Read my post again, and this time answer the ACTUAL question...

If he is reading the voltage on his battery monitor that is surely connected BEFORE the wiring!!!! The resistance of the wiring is irrelevant to what is being measured.

Or maybe I am wrong and the battery monitor voltage actually measures the wiring voltage drop, but how is that possible? To my mind the wiring voltage drop is, as far as the battery monitor is concerned just part of the total load and can not be deconvoluted from it.

What is being measured here, and being discussed is NOT the voltage drop in wiring, but the voltage sag AT THE BATTERY TERMINALS. Two totally different things.

You may assume I am stupid but I did read the subject and it clearly states voltage drop and not voltage sag at the batteries.

My post clarifies the 4x boost in performance when doubling battery voltage. It will be 8x for 48V.

As the OP doesn’t supply more info everything written is simply conjecture. I expect voltage drop on battery/cell terminals, crimps, jumpers etc. way before lithium cells sagging.

There’s more: I’m not sure but think this may be a diy battery with parallel cells? In that case you can’t assume the current is equally divided over the parallel cells. With these capacities I suspect there are four 280Ah cells in parallel. One can only expect trouble with that and (undetectable) unbalance between cells is the least worry.

[CaptainRivet]

Originally Posted by s/v Jedi

You may assume I am stupid but I did read the subject and it clearly states voltage drop and not voltage sag at the batteries.

My post clarifies the 4x boost in performance when doubling battery voltage. It will be 8x for 48V.

As the OP doesn’t supply more info everything written is simply conjecture. I expect voltage drop on battery/cell terminals, crimps, jumpers etc. way before lithium cells sagging.

There’s more: I’m not sure but think this may be a diy battery with parallel cells? In that case you can’t assume the current is equally divided over the parallel cells. With these capacities I suspect there are four 280Ah cells in parallel. One can only expect trouble with that and (undetectable) unbalance between cells is the least worry.

The sag at the terminal clearly indicates a very high resistance at the busbar to cell terminal connection and the busvbars size is too small.
Thats exactly the issue i had in my intial install and exactly the same sagging he has when putting a high load...the eaton busbars i received in 5x20 where wrongly stored and transported by the supplier result in longitudinal twist and not straight means the connection of 4 cells in parallel was bad, 2nd the size not appropriate for the current, even Eaton certified it was.
That causes the cells to sag as the first cell carries the most load and resistance is high, the other follow.
To troubleshoot that simply put the 600A back on and use a IR temp gun where your heat candles are and how hot the busbars above ambient are.
Solution where 10mmx80mm alu busbars, lapped 100% even and immediately covered in No-Al-ox.
To avoid parallel cells drifting the 4p battery must be 100% symmetrical build and offloading must be symmetrical too. means min doubled identical long battery cables and 1 goes between cell 1 and 2 and the other 3 and 4, same on negative terminal.

[Fuss]

I think this all shows why you should not put cells in parallel, you lose control of the individual cell. Make individual 280ah batteries and connect these in parallel. You spend more on BMS‘s but get redundancy.

[more]

try again with thermal camera.
i also think busbar problem.
also for b/c class eva cell (nobody can buy A grade except couple mw monthly long term buyer.) this amerage you pull is not big problem. maybe voltage drop to 13,1

[CaptainRivet]

Originally Posted by Fuss

I think this all shows why you should not put cells in parallel, you lose control of the individual cell. Make individual 280ah batteries and connect these in parallel. You spend more on BMS‘s but get redundancy.

True for him the way to go, get 3 jk BMS 200A with 2A active balance, build 4 batteries and parallel them. Even he doesn't have problems now as 30mV difference now with 595A shows its perfectly in balance. But he will.

For me not possible as the ElectrodacusBMS is spider in the web and can therefor only control one bank.
I would need to change the whole system design.
But i know how to build and deal with 4P systems...just got tricked out by premium Eaton busbars that where not straight and didn’t fit spec published and thought i can do a shortcut by going straight from terminal to shunt but didn't take into account that shunt emits heat and will transfer that into busbars. Well fixed all and runs like a charm.
A better proof as 100min with 600A and no defect or heatup anywhere you cannot have that your system is robust...try it with yours Fuss.

[more]

Originally Posted by CaptainRivet

True for him the way to go, get 3 jk BMS 200A with 2A active balance, build 4 batteries and parallel them. Even he doesn't have problems now as 30mV difference now with 595A shows its perfectly in balance. But he will.

.

JK BMS explicitly exclude their BMS working in parallel strings.
or USE with ultra fast fuse for eletronic Like BS fuse, CBBF,MRBF

[CaptainRivet]

Originally Posted by more

JK BMS explicitly exclude their BMS working in parallel strings.
or USE with ultra fast fuse for eletronic Like BS fuse, CBBF,MRBF

Where is that standing, never heard of that.
Still works like a charm...andi from offgrid garage is testing them since 3 years. And maddie has them even as BMS for her propulsion bank, 8 of them parallel.
Jk is still the best 12V mosfet BMS of all the china stuff...if you live in Australia the mueller JK BMS which is 250A with calibrated mosfets but it costs quadruple compared to standard JK BMS.
And JK BMS 24 smart inverter BMS is explicitly for parallel BMS even with master and slave configuration possible...regarding price/value the best 24/48V mosfet BMS.

[Captain Bill]

Perhaps UFO could chime in and tell us if he saw the voltage on a battery monitor and settle the argument. I suspect since he was in the salon he was looking at a monitor. Every monitor I have ever seen measured voltage at the battery side of the wiring, so though he said drop I think he was looking at sag. Lifepo4 batteries do sag under load, just not as much as LA. I remember seeing a youtube video by one of the Lifepo4 gurus(don't remember which one) where the guy compared a Lifepo4 100ah battery against two paralleled AGM 100AH and ran a heat gun through an inverter. The Lithium sagged to about 12v and the AGMs sagged to the low 10s. I have 300 AH of 12v Lifepo4 and drop to about 12.8 when running a heat gun and I know my voltage is measured at the batteries so voltage drop is involved. Dropping to the low 12s with nearly 600a load seems perfectly plausible to me.

[s/v Jedi]

Originally Posted by more

JK BMS explicitly exclude their BMS working in parallel strings.
or USE with ultra fast fuse for eletronic Like BS fuse, CBBF,MRBF

Having multiple batteries is different from connecting parallel strings.

[CaptainRivet]

Originally Posted by more

try again with thermal camera.
i also think busbar problem.
also for b/c class eva cell (nobody can buy A grade except couple mw monthly long term buyer.) this amerage you pull is not big problem. maybe voltage drop to 13,1

I buy my cells via a buddy that is CEO of an NPO producing powerwalls and commercial EVs...he gets 2 container from Lishen and EVE each 2 weeks...grade A+. And when i want cells then he goes the extra mile and choses from a whole delivery the cells that are metricously matched in capacity and internal resistance. With this you can build 4P4S banks.
But your right i won't do that with grade B cells.
Due to EV crises you get grade A cells that they cannot sell. Nkon.nl sells grade A if they explicitly tell you its grade A. They also sell grade B but mark that clearly. Good a cheap seller for europe for the normal customers....

[more]

Originally Posted by CaptainRivet

Where is that standing, never heard of that.
Still works like a charm...andi from offgrid garage is testing them since 3 years. And maddie has them even as BMS for her propulsion bank, 8 of them parallel.
Jk is still the best 12V mosfet BMS of all the china stuff...if you live in Australia the mueller JK BMS which is 250A with calibrated mosfets but it costs quadruple compared to standard JK BMS.
And JK BMS 24 smart inverter BMS is explicitly for parallel BMS even with master and slave configuration possible...regarding price/value the best 24/48V mosfet BMS.

JKong factory direct support contact. No logic but his answer is exact this no parallel any voltage. later from usa group push and explain more with designer and he say ok but fast acting fuse between group.

[CaptainRivet]

Originally Posted by Captain Bill

Perhaps UFO could chime in and tell us if he saw the voltage on a battery monitor and settle the argument. I suspect since he was in the salon he was looking at a monitor. Every monitor I have ever seen measured voltage at the battery side of the wiring, so though he said drop I think he was looking at sag. Lifepo4 batteries do sag under load, just not as much as LA. I remember seeing a youtube video by one of the Lifepo4 gurus(don't remember which one) where the guy compared a Lifepo4 100ah battery against two paralleled AGM 100AH and ran a heat gun through an inverter. The Lithium sagged to about 12v and the AGMs sagged to the low 10s. I have 300 AH of 12v Lifepo4 and drop to about 12.8 when running a heat gun and I know my voltage is measured at the batteries so voltage drop is involved. Dropping to the low 12s with nearly 600a load seems perfectly plausible to me.

Correct Lifepo4 do sag but not that much...additionally the alu or copper busbars you typically get with cells are good for around 150A.
Thats why you also see a voltage sag to low 12V as a heat gun is typically >200A..put correct busbars and its much less. You mean andy from offgrid garage or the guy from DIY solar...both used standard busbars and 200-250A.

600A for 4 parallel 280AH cells is 150A per 280Ah cell, so 0.55C...kindergarden for a cell that can do 2C...

And yes it was either BMS measured at busbar/cell stud or battery monitor shunt on negative terminal. I have a difference of 0.05 till 0.1V at 600A between the 2 as i have both.

But his sag is by far to big...if your system can do that you need to spec it for that or limit the output of it to your spec.
Have a basically identical system and described the ranges of sag thats ok if properly speced.

[CaptainRivet]

Originally Posted by more

JKong factory direct support contact. No logic but his answer is exact this no parallel any voltage. later from usa group push and explain more with designer and he say ok but fast acting fuse between group.

Which model?

The 24V and 48V smart inverter BMS is explicitly allowed to parallel and even has a master BMS and slave BMS functionality to act as such.

What you have to do but thats for every mosfet BMS that if paralleling (if not explicitly stated different) the current rating is half of each BMS due to uncalibrated mosfets.
Means 200A and a 2nd in parallel is 300A for both, 3 in parallel is 400A and 4 is 500A...more then 4 not more current capabilities but to extend capacity you can parallel as many as you want.
The reason many drop ins limit paralleling to 4 batteries.