Lithium Bank Voltage Drop.....

[UFO]

So I come into the saloon and notice the batteries reading 12.05V, which set me into a bit of a panic, until I noticed the other half happilly running both induction rings at full power and our large toaster as well! To be fair we have been off the boat for a year and it must of slipped her mind about the use of such appliances.

Anyway, before killing the toaster I had a quick look at the amps going out - 595, which is a pretty hefty amount that I have never done before, maybe why i have never seen the bank reading so low.

So the question is with an EVE 1120Ah bank, is such a voltage drop to be expected (without the induction/toaster load they were sitting at around 80% charged and 13.25V) or is that not a good sign?

On a different note the bank were all within 30mV of each other.

[s/v Jedi]

Originally Posted by UFO

So I come into the saloon and notice the batteries reading 12.05V, which set me into a bit of a panic, until I noticed the other half happilly running both induction rings at full power and our large toaster as well! To be fair we have been off the boat for a year and it must of slipped her mind about the use of such appliances.

Anyway, before killing the toaster I had a quick look at the amps going out - 595, which is a pretty hefty amount that I have never done before, maybe why i have never seen the bank reading so low.

So the question is with an EVE 1120Ah bank, is such a voltage drop to be expected (without the induction/toaster load they were sitting at around 80% charged and 13.25V) or is that not a good sign?

On a different note the bank were all within 30mV of each other.

It’s why people like me recommend to go to 24V or even 48V. It would have reduced current from 600A to only 300A for 24V or a meager 150A for 48V. This would have reduced your voltage drop to just half or a quarter of what you got

[Pete7]

That's north of 7kW. I might be more worried about the wiring and connections with that sort of power going through them and getting a tad warm. Still you're here to tell the story.

On a much smaller scale, we have seen a voltage drop to 12.8v from a single 120A LFP drawing perhaps 100A. Also seen 11v from a pair of 85Ah LA when I forgot to parallel the LFP into the circuit. Inverter whinged a bit, but the kettle continued to boil.

Pete

[Fuss]

But what job onboard needs 2 elements on full and the toaster at the same time, this could only be a mistake. Normally toaster and 1 element is 5kw but this is only for a minute or two. Normally elements are never on full so 500w x 2 + toaster 2500w = 3500w for 90 sec then back to 1000w for sustained element cooking. Sounds a lot worse at 12v of course so I would make some more strict rules if I did not have 24v systems.

[Scottyyachty]

Wow, 595 A what size wire and fuses are you using? I'm surprised, nothing melted. If you really want to pull these kind of amps going to a 24 V or 48 V system would make the most sense.

[CaptainRivet]

Originally Posted by UFO

So I come into the saloon and notice the batteries reading 12.05V, which set me into a bit of a panic, until I noticed the other half happilly running both induction rings at full power and our large toaster as well! To be fair we have been off the boat for a year and it must of slipped her mind about the use of such appliances.

Anyway, before killing the toaster I had a quick look at the amps going out - 595, which is a pretty hefty amount that I have never done before, maybe why i have never seen the bank reading so low.

So the question is with an EVE 1120Ah bank, is such a voltage drop to be expected (without the induction/toaster load they were sitting at around 80% charged and 13.25V) or is that not a good sign?

On a different note the bank were all within 30mV of each other.

No thats is by far too much...the bank can handle that but obviously your busbars and also most likely cabling not. 30mV deviation at 600A is good means your bank is in balance and cells are very equal.

What size and material are your busbars and main battery cable as well as cable to inverter(s).
Did you measure busbar temp with an ir gun when pulling the 595A? As the load is mainly inverter and induction cooktop the real load its actually 1.4x595A=830A on/off multiple times in a millisecond.

I am at 12,8V with 600A, so 3.2V per cell also with around 30mV deviation
My install is rated and speced for 600A and i run 6x70sqm positive and negativ...4x for the 2 inverters within 1m from bank and one main load and one main charge cable. I have 10mmx80mm alu busbars. I have 1088AH in 4P4S 272AH Lishen cells, quite identical to the EVE with the difference the EVE are packed internally in z Layers while Lishen wraps them around anode an catode which the safest way to build prismatic cells but you loose 8AH in the same case size packing it that way internally.

[CaptainRivet]

Originally Posted by Pete7

That's north of 7kW. I might be more worried about the wiring and connections with that sort of power going through them and getting a tad warm. Still you're here to tell the story.

On a much smaller scale, we have seen a voltage drop to 12.8v from a single 120A LFP drawing perhaps 100A. Also seen 11v from a pair of 85Ah LA when I forgot to parallel the LFP into the circuit. Inverter whinged a bit, but the kettle continued to boil.

Pete

If your equipment can pull this kind of loads you have to make sure your install is capable of it or limit it by adjustments in the system and breaker that trip when exceeding your stress tested system load.
I done the ultimate stress test on mine...fired all up i had including maxing the 2 inverters out and run that from 100% SOC till lithium shut off...nearly 100min of 614A...shunts where really hot but rest 10 degrees above ambient.
I normally pull around 200-260A when cooking normal dinner, if cooktop and oven runs together its 350-380A for maybe 10-15min max...the oven was running 30-45min to make a roast and big load oven vegetable at 130A and i am making pasta or rice with sauce the last 10-15min with the cooktop in parallel...you could do that serial but why if i can....
Till 250A the victron can handle all, above that the 2nd staged inverter shuts on and supplies 2300W base load while victron supplies the rest plus surges and peaks.
I can rise the 2nd inverter to full 16A and 3500W base load but thats not necessary and thats how i limit the system to around 500A. Cooktop and oven on full blast is 4600W, both inverter together can do 6.5kw constant.

True it would make sense to go 24V with the inverters and run dual voltage banks. I decided against at the time i done the install first but it grow...still thinking of going dual voltage with inverters (and actually have 2 Studer 24V lying at my parents) but system runs absolutely fine (besides that DVCC sh... problem that i will also have with 24V) that i am hesitant to invest time and money to change. I guess i keep on running at 12V till one of the inverter dies...

[Pete7]

Originally Posted by CaptainRivet

If your equipment can pull this kind of loads you have to make sure your install is capable of it or limit it by adjustments in the system and breaker that trip when exceeding your stress tested system load.

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

[s/v Jedi]

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

I believe the ampacity of a 35mm2 cable is more than double that so no worries there. The question is how long is the cable and how much voltage drop is acceptable.

[SailingHarmonie]

Originally Posted by s/v Jedi

It’s why people like me recommend to go to 24V or even 48V. It would have reduced current from 600A to only 300A for 24V or a meager 150A for 48V. This would have reduced your voltage drop to just half or a quarter of what you got

Is this actually true, assuming the total kW-hr capacity of the battery bank was the same? The voltage is being measured at the battery (I assume!), so the voltage drop in the wiring is irrelevant to the case.

In the OP's case he has a 1120AM 12V bank. If he replaced that with a 24V bank, he'd likely end up with a 560 A-hr bank.

In the 24V case his Amp draw would, of course, be 50% of the base case, but in terms of load on the batteries in terms of a percentage of C it would be exactly identical, and I'd expect the voltage sag to be twice as large in absolute terms (since it is a 24V system). So instead of dropping from 13.5V to 12.05V, it would drop from 27V to 24.1V. If not, why not?

[s/v Jedi]

Originally Posted by SailingHarmonie

Is this actually true, assuming the total kW-hr capacity of the battery bank was the same? The voltage is being measured at the battery (I assume!), so the voltage drop in the wiring is irrelevant to the case.

In the OP's case he has a 1120AM 12V bank. If he replaced that with a 24V bank, he'd likely end up with a 560 A-hr bank.

In the 24V case his Amp draw would, of course, be 50% of the base case, but in terms of load on the batteries in terms of a percentage of C it would be exactly identical, and I'd expect the voltage sag to be twice as large in absolute terms (since it is a 24V system). So instead of dropping from 13.5V to 12.05V, it would drop from 27V to 24.1V. If not, why not?

Wow… voltage drop is the current multiplied by the resistance of the wire. If you have half the current in the same wire then you have half the voltage drop… expressed in absolute Volts, not a percentage of battery voltage.

It gets worse. A 3% voltage drop requirement for a 12V battery means you may drop 0.36V. For a 24V battery it means you may drop 0.72V. So you only drop half because the current is half, while you are allowed to drop double, so you end up doing 4 times as good, although for new installations people use smaller wiring of course.

[Pete7]

Originally Posted by s/v Jedi

I believe the ampacity of a 35mm2 cable is more than double that so no worries there. The question is how long is the cable and how much voltage drop is acceptable.

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

[s/v Jedi]

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

Yes, short circuits always win. I go through lengths to minimize… the lengths

[SailingHarmonie]

Originally Posted by s/v Jedi

Wow… voltage drop is the current multiplied by the resistance of the wire. If you have half the current in the same wire then you have half the voltage drop… expressed in absolute Volts, not a percentage of battery voltage.

It gets worse. A 3% voltage drop requirement for a 12V battery means you may drop 0.36V. For a 24V battery it means you may drop 0.72V. So you only drop half because the current is half, while you are allowed to drop double, so you end up doing 4 times as good, although for new installations people use smaller wiring of course.

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.

[SV Confianza]

We decided to stick with 12v instead of doing a hybrid 12v/24v setup. I kind of regret it, but the goal was to keep the complexity down.

We kept a limit on our power demand by just not upgrading our inverter. So if someone accidently runs a blowdrier or a heat gun while the A/C and hot water heater are on, the inverter will let us know =).

I know I’ll have to change this when we go to induction…