'Software' vs. 'hardware only' BMS

[Nearchos]

1) What is the main difference in the way a battery pack is designed when it employs a software BMS as opposed to a hardware BMS?

2) Is there any difference in the way the rest of an ebike is designed when it employs a software BMS as opposed to a hardware BMS?
Any difference with the wiring to the motor or controller perhaps?


Take it easy on me, i only know what Google has to say about BMSs... I am just trying to figure out what the Chinese battery pack builder is trying to tell me. I thought BMSs for ebikes are all centralised and that's all. I didn't know centralised BMSs can be categorized further...

 

[amberwolf]

What is a "software BMS"? I've never heard of one called this, so if it is a term your pack builder is using, you will need to get a definition from them of what exactly that means.

All BMSes must have hardware to do all the stuff a BMS does, so they are all "hardware".

Regarding the differences between the parts the pack builder is telling you about, you must ask them specifically what those differences are, including any connections, wiring, function, etc., as only they will know what those differences are.

Unless you can give us a specific model and brand and part number and a link to at least the sale page where the specifications for it can be found, we cant' really tell you any specifics about what is different from one part to another.

There are literally hundreds of thousands, at least, of different BMSs, and probably dozens (at least) of more or less basic ways they might work or be wired, depending on the specific application and design.

 

[JackFlorey]

What is a "software BMS"?

A BMS that uses one of the common interface ICs out there (like the LTC6813-1) connected to a processor; the processor makes decisions on balancing and shutdown on OV, UV and OC events. For example, the Nissan Leaf BMS uses this method.

 

[Nearchos]

ly hundreds of thousands, at least, of different BMSs, and pr

Thanks, I've had the same query so I have asked for the manuals. the first one I have received is in chinese only...

I also thought the main ways to categorise BMSs was centralised, distributed (master-slave), etc.

 

[Nearchos]

A BMS that uses one of the common interface ICs out there (like the LTC6813-1) connected to a processor; the processor makes decisions on balancing and shutdown on OV, UV and OC events. For example, the Nissan Leaf BMS uses this method.

Thank you very much for this.

Do you know if a "hardware only" BMSs for battery backs up to 52V 21Ah is more likely to

1) fail to perform the balancing function than a software BMS??
2) overheat if employed in hot weather conditions?

Does the above really have to do with software vs 'hardware only' or is it a matter of quality per product?

 

[fechter]

As far as bike packs go, I assume a "software BMS" is one where you can program the settings. All the ones I use are "hardware" and none of the settings can be changed. To me, the software and programmable features are just something else that can fail and as long as I pick a hardware BMS with settings that I like, it eliminates the possibility of improper programming or communications failures.

The current rating is independent of whether it's programmable or not. These things will give off some heat and need some cooling at higher power levels. I generally pick one that's rated quite a bit higher than my maximum expected current draw. They tend to exaggerate the ratings so you need some extra headroom.

 

[JackFlorey]

Do you know if a "hardware only" BMSs for battery backs up to 52V 21Ah is more likely to

1) fail to perform the balancing function than a software BMS??
2) overheat if employed in hot weather conditions?

Does the above really have to do with software vs 'hardware only' or is it a matter of quality per product?

It used to be that software BMSes were less reliable than 100% hardware BMSes - but with maturing controllers, software and software quality processes they are much closer together in reliability. I wouldn't worry about either one if it comes from a reputable company.

That being said, an incompetent designer has more opportunities to screw up with a software-based BMS.

 

[Nearchos]

Then what is supposed to be the advantage of a BMS with a processor/"software" versus a "hardware only"?
Do they execute more functions in theory?
Or it is just that their functions are programmable while "hardware only" are fixed?

 

[JackFlorey]

Then what is supposed to be the advantage of a BMS with a processor/"software" versus a "hardware only"?
Do they execute more functions in theory?

Their thresholds can be adjusted.
They can communicate with another system (like an inverter.)
They can do more complex protection functions (like temperature dependent current limits.)

 

[Nearchos]

Hm. Perhaps the temperature dependent functions is why my battery pack manufacturer prefers a software BMS for hot climates. I'll ask him.

Thanks a lot!!