Upgrading 15s Battery to 16s

[boarder2k7]

I'm seeing two versions of the Victron SmartShunt on Amazon for the same price. I believe that the one with the connectors on the face is the newer one?

 

[sunshine_eggo]

One on the left is the IP65 version (dust/waterproof)

One on the right is the standard shunt.

I do not believe you can use the optional temperature sensor with the IP65 version.

 

[sunshine_eggo]

Wow... the prices have come down. the BMV-712 is the full feature version of the smart shunt. Differences:

1. Has a relay that can be open or closed based on SoC, voltage and temperature critieria.
2. External display that also allows programming the shunt.
3. Bluetooth radio is in the display unit and has excellent range. The smartshunt range is notoriously not fantastic.

https://www.amazon.com/Victron-BMV-712-Battery-Monitor-Black/dp/B084M2XYK4

For that price difference, I would prefer the 712, but I would buy from Pike Industries rather than the default seller.

 

[boarder2k7]

Thanks for the clarification and the link.

What would the benefit be of the relay? Just something when all else fails to protect the batteries? Trying to think when I'd use that rather than trusting the BMS or the inverter to shut off.

 

[sunshine_eggo]

Thanks for the clarification and the link.

What would the benefit be of the relay? Just something when all else fails to protect the batteries? Trying to think when I'd use that rather than trusting the BMS or the inverter to shut off.

If you have functions that you want to engage based on any of the three parameters. Let's say you have an inexpensive inverter with no programmable lower cut off.... say it defaults to 42V, BUT it has a control relay. You could signal the inverter to shut off based on both SoC and Voltage criteria with the BMV.

Generally speaking, you want to avoid engaging BMS protection UNLESS something is truly out of whack. You want the equipment operating inside the BMS limits with the BMS there to protect if something goes wrong. If the BMS disconnects the inverter it can be a real pain in the ass to get the inverter back online without another 48V source.

 

[boarder2k7]

That makes sense.

I guess I'll spring for the 712 as a "buy once cry once" as I probably couldn't buy a 500 ADC relay for the price difference anyway.

Plus that way I can use it as a disconnect for my initial capacity test on these packs rather than tripping the BMS.

 

[sunshine_eggo]

That makes sense.

I guess I'll spring for the 712 as a "buy once cry once" as I probably couldn't buy a 500 ADC relay for the price difference anyway.

Plus that way I can use it as a disconnect for my initial capacity test on these packs rather than tripping the BMS.

It's not a 500ADC relay. Those are about as big as the shunt itself.

It's a control relay:

3. Installation

www.victronenergy.com

60V/1A max:

11. Technical data

www.victronenergy.com

 

[boarder2k7]

Ahh my misunderstanding, reading things on mobile makes me miss too much, I'll dig in when I get back home.

 

[boarder2k7]

3.45V is very very close to 100% when the current drops to a very low level.

How low of a level could I expect for a single 100 Ah cell? Currently sitting on a power supply pulling 1.3 A at 3.5V on one cell. PSU is set to 3.5V

 

[boarder2k7]

Also I ordered the 100A JK BMSs last night, unfortunately looks like delivery isn't until March.

Also I goofed in ordering these cells, the EVE cell isn't the same shape at all as the ones in the rack currently. Whoops. Much taller and thinner.

Fortunately it should fit in the gap left next to the 15th cell that's currently full of foam, but it will have to be laying down instead of having the terminals up like the rest of the cells.

Live and learn

 

[sunshine_eggo]

How low of a level could I expect for a single 100 Ah cell? Currently sitting on a power supply pulling 1.3 A at 3.5V on one cell. PSU is set to 3.5V

Is the CELL measuring 3.5V? If you're using alligator clips or other high resistance connections, you may see a voltage drop that slows charging.

 

[sunshine_eggo]

Also I ordered the 100A JK BMSs last night, unfortunately looks like delivery isn't until March.

Also I goofed in ordering these cells, the EVE cell isn't the same shape at all as the ones in the rack currently. Whoops. Much taller and thinner.

Fortunately it should fit in the gap left next to the 15th cell that's currently full of foam, but it will have to be laying down instead of having the terminals up like the rest of the cells.

Live and learn

Make sure that EVE permits the cell in that orientation. Depending on cell construction, portions of the cell may be starved of electrolyte in certain orientations.

 

[boarder2k7]

Good point to check, yes the cell is only at 3.3V measured right at the terminals at the moment. I am indeed using alligator clips. I'll switch in a piece of wire bolted down with the supplied hardware and see what changes.

Knowing that it is of course charging slower with the clips, but that eventually it will equilibrate to nominally 0 voltage drop as current approaches 0, what would be the expected "idle current" for a cell of this size? I was seeing some statements that 0.5% C was where current would stop? So here that would be as much as half an amp.

Cell orientation never occurred to me, I assumed that like a lithium ion or lithium polymer that they were not orientation specific. I charged the one server rack battery standing on its back because it was convenient so those cells were sideways for one charge cycle. I'll look in to that further. A quick search didn't turn up a concrete answer. If they don't permit that orientation I guess I have to buy different cells.

Thank you again for all your answers, they are much appreciated. I'm not new to electronics by any means but large lithium packs are certainly new to me.

 

[sunshine_eggo]

Good point to check, yes the cell is only at 3.3V measured right at the terminals at the moment. I am indeed using alligator clips. I'll switch in a piece of wire bolted down with the supplied hardware and see what changes.

Knowing that it is of course charging slower with the clips, but that eventually it will equilibrate to nominally 0 voltage drop as current approaches 0, what would be the expected "idle current" for a cell of this size? I was seeing some statements that 0.5% C was where current would stop? So here that would be as much as half an amp.

Officially, it's 0.05C @ 3.65V or 5A when the cell measures 3.65V

Cell orientation never occurred to me, I assumed that like a lithium ion or lithium polymer that they were orientation specific. I charged the one server rack battery standing on its back because it was convenient so those cells were sideways for one charge cycle. I'll look in to that. If they don't permit that orientation I guess I have to buy different cells.

Prismatic are different construction than cylindrical or poly.

Limited operation in the incorrect orientation is probably not a concern, and it might be fine to have done as you did. You'd need to know what the 15S battery cell manufacturer indicates as approved orientation.

 

[boarder2k7]

Bumped the PSU up to 3.65V and now running at 2.5 A. Fluke on the battery posts shows 3.32V so I guess I have a ways to go.

Unfortunately my attempt to bolt on some wires was foiled by the bolts sent with the battery. They are a length appropriate for busbars but not a ring terminal so back to the alligator clips.

I'm not really sure who made the 15s packs so no idea who to even ask about orientation. Some limited searching on approved orientations turned up a couple threads where people said they even had trouble getting Eve to comment on orientation, so I probably have 0 chance of figuring this out for my nameless packs.

I'm going to hope that one low rate charge cycle in an unoptimal orientation won't have caused much damage.

 

[sunshine_eggo]

Bumped the PSU up to 3.65V and now running at 2.5 A. Fluke on the battery posts shows 3.32V so I guess I have a ways to go.

Unfortunately my attempt to bolt on some wires was foiled by the bolts sent with the battery. They are a length appropriate for busbars but not a ring terminal so back to the alligator clips.

if you have washers, it's okay to use them as spacers between the bolt head and the ring terminal.

I'm not really sure who made the 15s packs so no idea who to even ask about orientation. Some limited searching on approved orientations turned up a couple threads where people said they even had trouble getting Eve to comment on orientation, so I probably have 0 chance of figuring this out for my nameless packs.

I think it was mentioned in the thread by the other guy looking to buy them.

I'm going to hope that one low rate charge cycle in an unoptimal orientation won't have caused much damage.

Doubt it did any damage.

 

[justgary]

Bumped the PSU up to 3.65V and now running at 2.5 A. Fluke on the battery posts shows 3.32V so I guess I have a ways to go.

This seems like a recipe to overcharge to me. Your cut off current is 5A at 3.65V, but you are only charging at 2.5A. Either get some real wire or don't charge above 3.4V or so. I found it easiest to use 12 gauge solid wire for top charging. It is cheap, easy to cut to length, and thick enough that you should be able to tighten the bolts on it.

 

[SeaGal]

Bumped the PSU up to 3.65V and now running at 2.5 A. Fluke on the battery posts shows 3.32V so I guess I have a ways to go.

This seems like a recipe to overcharge to me. Your cut off current is 5A at 3.65V, but you are only charging at 2.5A. Either get some real wire or don't charge above 3.4V or so.

Whilst thicker wires are always better, I fail to see why you say "This seems like a recipe to overcharge to me". If I'm not having a blonde moment, then if the bench power supply is set to 3.65V, it is not possible to "overcharge" the cell beyond 3.65V

 

[sunshine_eggo]

Whilst thicker wires are always better, I fail to see why you say "This seems like a recipe to overcharge to me". If I'm not having a blonde moment, then if the bench power supply is set to 3.65V, it is not possible to "overcharge" the cell beyond 3.65V

3.65V with tail current of .05C is technically over charged if tail current drops below 0.05C

 

[justgary]

Whilst thicker wires are always better, I fail to see why you say "This seems like a recipe to overcharge to me". If I'm not having a blonde moment, then if the bench power supply is set to 3.65V, it is not possible to "overcharge" the cell beyond 3.65V

3.65V *is* overcharged. Using 3.65V to charge LFP is a way to get the charge to complete faster. If you don't stop the charge at 0.05C you will overcharge the cells. If you are going to use little wires, drop the voltage to something safe and give it time. 3.375V is safe for indefinite charge, and anything above that will require monitoring.

If you have a BMS trying to balance multiple cells, 3.4 or 3.45 volts is usually a good choice, but keep in mind that you don't want that going on for an extended time.