Questions about shunt usage with a separate port BMS

[Andrewr05]

How would one go about wiring up a smart shunt to a battery system that has separate inputs and outputs?

I'm using battery packs with separate port BMS (opposed to common port) output leads and input leads.


As of right now I have my shunt connected to the output of my system and it will tell me when my voltages change and what the amperage draw is on the battery (And then therefore calculate my battery capacity correctly) but after I draw down the battery system and then recharge it, the SOC percentage never goes back up because it's not wired in a way that senses the current coming in.

I'm not sure what to do in this specific instance.


Also what do y'all recommend for a cheap alternative to a Victron smart shunt now that the Fusion TBD shunt seems to be unavailable on amazon anymore?

 

[Ampster]

I'm using battery packs with specific separate output leads and input leads.

Those presumably are the BMS leads. If you have access to the insides of the battery you will see there is only one lead each to the positive and negative cell terminals. You may have to add an extra wire to install the shunt to one of those terminals.

 

[Andrewr05]

Those presumably are the BMS leads. If you have access to the insides of the battery you will see there is only one lead each to the positive and negative cell terminals. You may have to add an extra wire to install the shunt to one of those terminals.

Yeah, they connect to the BMS.
These packs had their original limiting factory BMS removed and then had new a new separate port BMS installed.

I don't think wiring anything directly to the battery packs is a good idea.

 

[Ampster]

I don't think wiring anything directly to the battery packs is a good idea.

I am sure you have a good reason and I would not want to change your opinion. I do think other readers with a similar system might find it useful for a different reason. Of course it depends on how accurate the internal current measurement of the BMS is. My BMS is very good and has a very accurate Coulomb counter. I rely on it for SOC and voltage measurements more than the data from my SolArk.

 

[Andrewr05]

@sunshine_eggo
Do you still stand by this?

Separate Port BMS & Shunt

Hi all, New to the group. I've in the process of deciding where to put my shunt. I have a separate port BMS with the extra negative charge cable. All setups i've seen show the BMS attached to the P- cable, after the BMS. However, I can't seem to find the correct position for a separate port...

diysolarforum.com

I'm just legitimately wondering how that would work.
If the charging port has a lower amperage limit than the output port couldn't the return current try to go into the charging port and trip the BMS?

or I guess in that case it would be split between the two so the current would be halved going back in anyways.
or maybe I'm dumb, do they have diodes or whatever to only allow the current to flow in one direction?

I considered straight up asking if you can just wire both negatives together, but reconsidered because I didn't want to sound dumb.

 

[Ampster]

I'm just legitimately wondering how that would work.

In my case, my Orion BMS is a single port BMS but when communicating with my inverter it can tell the inverter to use separate charging and discharging values. Even in open communications different values can operate a contact closure or trigger an alarm. None of that helps answer your question, but conceptually is a feature that may be implemented in other BMSs.

 

[Andrewr05]

Unfortunately my system is super budget and nothing communicates to anything else, besides the shunt reading volts and watts and temperature.

 

[Andrewr05]

I don't want to blow my house up by imploding 10 NMC li-ion packs in my living room.

I wish I had a few more people chime in on this.

 

[Andrewr05]

Bump

 

[hwy17]

I have a separate charge and discharge design for my system, so I'm familiar with some of the logic but not practiced at it.

You can shunt it like this for one:

Battery-Shunt-BMS

If you wanted to shunt multiple in parallel, I think you can't.