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"Smart" separate port BMS?

princhester

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Feb 7, 2021
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Hello all,

The thread title says it all really. Can you buy a seperate port and "smart" BMS?

I accept that neither feature (let alone both) is really necessary. But I thought I might get one nonetheless, and then discovered that either my search capabilities have gone to heck, or they don't exist.

Firstly, is this correct? Secondly, is there some reason why? It just seems like an obvious combination of features and yet...?
 
Hello all,

The thread title says it all really. Can you buy a seperate port and "smart" BMS?

I accept that neither feature (let alone both) is really necessary. But I thought I might get one nonetheless, and then discovered that either my search capabilities have gone to heck, or they don't exist.

Firstly, is this correct? Secondly, is there some reason why? It just seems like an obvious combination of features and yet...?

I am searching for a separate port, BT capable, smart BMS also, and having apparently same trouble finding one.
Please let me know of you find something, and I will do likewise.
 
I am curious why you prefer a separate port BMS?....
There is much confusion on the terminology, Many people still think/talk in terms of the separate / common port binary. I suspect OP just wants separate control of charge and discahrge, and isn't overly concerned with the physical topology. But I should not assume. Op what are your priorities?
 
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I am curious why you prefer a separate port BMS?....
As I said I'm not overly concerned about it but basically I was poking around looking at BMS's of various types and became increasingly curious when I realised that I was seeing nothing that was both smart and separate port. The more I failed to find such a thing, the more curious I became about this (seemingly glaring) gap in the market.

As to separate port, I suppose my reasoning is that I can't see any good reason not to have separate ports. The only reason I have seen is that the separate port BMS's seem only to be able to handle relatively low charge current but this isn't a difficulty for me with my planned set up - and if it ever became a problem, using the charge port to control a heavy duty relay is a simple fix.

Contrastingly, I understand a possible problem with a common port BMS is that if it chops the common port while a solar panel is producing substantial power, it may damage an MPPT. Will's suggestion to avoid this is to connect the MPPT directly across the batteries but it seems a pity to have a BMS that has the capability of controlling the charging process, but then connect up the system such that this capability is thrown away.

Dzl, I take it that there is more to it than a simple separate/common port binary, and that there is some middle ground. I'd be very interested to learn more. Could you point me in the right direction? Btw while I'm new to this particular field I have certain amount of background in electronics so feel free to be technical.

Thanks for your help guys.
 
Dzl, I take it that there is more to it than a simple separate/common port binary, and that there is some middle ground. I'd be very interested to learn more. Could you point me in the right direction? Btw while I'm new to this particular field I have certain amount of background in electronics so feel free to be technical.
Yes, for FET based BMS', there is 'separate port', 'common port' and a hybrid middle option.
The middle option is what @FilterGuy labeled as 'hybrid.' This type is wired like a common port BMS but has similar functionality to a separate port BMS.

In other words, there is just one physical connection for chargers and loads (like a common port BMS), but charge and discharge can be controlled individually (like a separate port BMS). The BMS Overkill Solar sells would be one of the more common examples of this.

This resource is a good short overview of the different types/functions

Then there are the different external relay based solutions, or solutions like the SBMS0 that directly control chargers and load control devices.


----

Part of the confusion on this is because there doesn't seem to be any industry standard term of this middle type of BMS (what we call Hybrid, or Hybrid port) and it is sometimes just grouped in with common port (since it is physically similar). Unless a better term comes along I prefer to use Filterguy's language and call it Hybrid or Hybrid port, but even better in my eyes is to talk in the language of function ("independent control of charge and discharge") rather than topology (common/separate port) since that is what is more important to most people.
 
Dzl, I take it that there is more to it than a simple separate/common port binary, and that there is some middle ground. I'd be very interested to learn more. Could you point me in the right direction? Btw while I'm new to this particular field I have certain amount of background in electronics so feel free to be technical.

Thanks for your help guys.
You may want to review this:

Contrastingly, I understand a possible problem with a common port BMS is that if it chops the common port while a solar panel is producing substantial power, it may damage an MPPT. Will's suggestion to avoid this is to connect the MPPT directly across the batteries but it seems a pity to have a BMS that has the capability of controlling the charging process, but then connect up the system such that this capability is thrown away.
I have heard some folks say that disconnecting the battery while the solar is connected can damage the charger..... but there is some debate as to whether that is true. My personal feeling is that any MPPT that has that restriction is not a good one to use.

Either way, disconnecting the battery could happen with almost any BMS. Single port or dual port.
 
Thanks guys, very interesting.

I basically knew all the stuff in that guide with the exception of the hybrid thing, which my reading had totally missed. So thanks for that. All is clearer now.

Yes FilterGuy I couldn't agree more about the personal feeling that an MPPT with the relevant potential flaw is not a good MPPT - but my thinking was that if a separate port BMS might avoid the issue altogether, then I may as well get one.

As it happens, I bought this BMS: https://www.aliexpress.com/item/4000776528805.html

... which looks like its the OEM for the Overkill unit, or then again maybe not, who knows? Anyway, I'll reverse engineer it when I get it and see.

Either way, you guys have been a lot of help so thanks, really appreciate it.
 
Thanks guys, very interesting.

I basically knew all the stuff in that guide with the exception of the hybrid thing, which my reading had totally missed. So thanks for that. All is clearer now.

Yes FilterGuy I couldn't agree more about the personal feeling that an MPPT with the relevant potential flaw is not a good MPPT - but my thinking was that if a separate port BMS might avoid the issue altogether, then I may as well get one.

As it happens, I bought this BMS: https://www.aliexpress.com/item/4000776528805.html

... which looks like its the OEM for the Overkill unit, or then again maybe not, who knows? Anyway, I'll reverse engineer it when I get it and see.
Yea, I'm 95% sure that is the same family (possibly model) as what Overkill sells. However, I don't think the company you bought from is the manufacturer either. I believe Shenzhen E-Fire is a reseller (of various BMSes and other electronics). The furthest upstream I've been able to follow this BMS is JBD / Jaibaida / LLT power which appears to be the manufacturer but I can't say with 100% certainty. Either way, you chose a popular BMS at a good price.
 
Yea, I'm 95% sure that is the same family (possibly model) as what Overkill sells. However, I don't think the company you bought from is the manufacturer either. I believe Shenzhen E-Fire is a reseller (of various BMSes and other electronics). The furthest upstream I've been able to follow this BMS is JBD / Jaibaida / LLT power which appears to be the manufacturer but I can't say with 100% certainty. Either way, you chose a popular BMS at a good price.
There is no end to the rabbit holes of Chinese manufacturing and re-sellers!
 
There are many BMS that have the capability to stop charging/discharging without disconnecting the battery.
This is the method i prefer.
 
Thanks guys, very interesting.

I basically knew all the stuff in that guide with the exception of the hybrid thing, which my reading had totally missed. So thanks for that. All is clearer now.

Yes FilterGuy I couldn't agree more about the personal feeling that an MPPT with the relevant potential flaw is not a good MPPT - but my thinking was that if a separate port BMS might avoid the issue altogether, then I may as well get one.

As it happens, I bought this BMS: https://www.aliexpress.com/item/4000776528805.html

... which looks like its the OEM for the Overkill unit, or then again maybe not, who knows? Anyway, I'll reverse engineer it when I get it and see.

Either way, you guys have been a lot of help so thanks, really appreciate it.
BTW: That BMS is what I call a 'Hybrid' BMS. I have used several of them.
 
Hi everyone can anyone explain to me why a daily BMS did not kill the connection when a cell hit 3.75v the settings are set to 3.65v

Should i be concerned ?
 
Should i be concerned ?
The answer was Yes as soon as you said Daly BMS.:oops:

Sorry..... I could not resist the smart-arse comment.

In fact, if the BMS is not stopping at the programed voltage, something is wrong that needs to be addressed. 3.75V is not good but as long as it did not sit at that voltage for a day or more, the cell should be fine.
 
Thanks I thought as much no only spiked for 2 seconds I was monitoring. Utter rubbish then I am using SSR one on the positive to the inverter and one now on the negative from the Victron MPPT 100/50 I realised I was risking my batteries charge protection solely on the MPPT. I wanted the BMS to cut the charge if cells went over 3.65v but not kill the load so I need a 3 cable BMS with separate charge. I’m only using it to switch the feed off from the SSR so it can be a small unit the SSRs are 500a I pull 100a when cooking, 24v system 3kw Victron inverter/ charger. Can anyone suggest a good quality separate port 8s BMS that’s not daily?

I’m going to test this again with the solar off and connect one of the BMS wires to my Dc charger and bring it up slowly to 3.7v and see if it will kill the connection obviously that cell will be disconnected.
 
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