BMS Programming Questions

[rg12]

I'm starting to use this awesome ANT BMS with the bluetooth app and so far so good, but since it's my first time programming a BMS, I have a few questions:
- It's default high cell protect is 4.19V while the high cell protect release voltage is 4.1V, is that common to set it to 4.19V? usually it's 4.25V but I don't wanna ever go that high.

- Balance difference to start balancing is set to 0.01V, isn't that too tight? wouldn't it risk the scenario of going into "race" where it balances down non stop and depletes the whole pack?

- There is a setting called Precharge Current and it's set to 20A, any idea what is it?

- There is a setting for short circuit current, any idea what to type there? why would I allow any amount of current in a short circuit? it also has another setting called short circuit delay set to 600ms.

- In addition to the total pack capacity setting it has a setting called total cycle capacity, any idea what they mean by that?

 

[valueseek]

With the cell high voltage protection, you just need to make sure that either your BMS or charger cuts off charge current before it reaches 4.19.

For example, my 10s 36v hoverboard pack and charger go to 42.2v, so 42.5v protection makes sense. Every basic bms and charger I've had do the same thing, they go a bit too high. If i had the option it would stop earlier, and it does on my custom packs.

The short circuit setting is for you to set how much current for how long before it triggers the protection. So if its 100a, it will need to see 100a or greater for .6 of second before it stops shorting out, then it need to meet the release parameter to close the circuit again. Set the current and time as low as you reasonably can, 600ms is too long IMO but that's exactly why i love programmable BMSs.

 

[rg12]

With the cell high voltage protection, you just need to make sure that either your BMS or charger cuts off charge current before it reaches 4.19.

For example, my 10s 36v hoverboard pack and charger go to 42.2v, so 42.5v protection makes sense. Every basic bms and charger I've had do the same thing, they go a bit too high. If i had the option it would stop earlier, and it does on my custom packs.

The short circuit setting is for you to set how much current for how long before it triggers the protection. So if its 100a, it will need to see 100a or greater for .6 of second before it stops shorting out, then it need to meet the release parameter to close the circuit again. Set the current and time as low as you reasonably can, 600ms is too long IMO but that's exactly why i love programmable BMSs.

What's wrong with having the BMS cut off charge at 4.19? why squeeze it all the way to over 4.2?
Also, if it releases at 4.10 then what will happen?
Will it go to 4.19 and not let me charge again unless it goes to 4.10? I guess it wouldn't lock discharge right?

About the short circuit, I understand what it means but I don't understand the concept.
Why would I even let 1A flow for more than a 1ms under the condition of a short circuit?

 

[john61ct]

- It's default high cell protect is 4.19V while the high cell protect release voltage is 4.1V, is that common to set it to 4.19V? usually it's 4.25V but I don't wanna ever go that high.

The point of a BMS is to protect the bank from your other gear failing.

In this case, the HVC needs to be higher than you want any charger to terminate, it only gets activated if a charge source goes haywire, fails to regulate properly.

> Balance difference to start balancing is set to 0.01V, isn't that too tight? wouldn't it risk the scenario of going into "race" where it balances down non stop and depletes the whole pack?

No, that is fine.

> There is a setting called Precharge Current and it's set to 20A, any idea what is it?

To prevent contactor points from pitting, eventually welding closed.

 

[john61ct]

What's wrong with having the BMS cut off charge at 4.19? why squeeze it all the way to over 4.2?

You should not use a cheap BMS to control normal stop-charge, it's a failsafe mechanism.

> Also, if it releases at 4.10 then what will happen?

That is the point that is closes, allows charge current to pass again after HVC event.


> About the short circuit, I understand what it means but I don't understand the concept.
Why would I even let 1A flow for more than a 1ms under the condition of a short circuit

If you actually allow a full short-circuit, huge amps for many ms, everything fries.

This setting is **defining** the trigger to prevent that.

Too low, and you get false positive OCP cutoffs when peak loading.

Set just above what you ever plan to allow in usage.

 

[valueseek]

I stand corrected. I guess you should not use your BMS to set a lower max charge setting than your charger, even if both are within the safe range. So check what your charger stops at and set it slightly above that. So for my hoverboard example with a 42.2v charger, it would be 4.23v max charge and i guess i would set the pack max charge to 42.3v.

 

[rg12]

- It's default high cell protect is 4.19V while the high cell protect release voltage is 4.1V, is that common to set it to 4.19V? usually it's 4.25V but I don't wanna ever go that high.

The point of a BMS is to protect the bank from your other gear failing.

In this case, the HVC needs to be higher than you want any charger to terminate, it only gets activated if a charge source goes haywire, fails to regulate properly.

> Balance difference to start balancing is set to 0.01V, isn't that too tight? wouldn't it risk the scenario of going into "race" where it balances down non stop and depletes the whole pack?

No, that is fine.

> There is a setting called Precharge Current and it's set to 20A, any idea what is it?

To prevent contactor points from pitting, eventually welding closed.

About the precharge setting, I'm not using a contactor, should I leave it at 20A?

Any idea about that question:
- In addition to the total pack capacity setting it has a setting called total cycle capacity, any idea what they mean by that?

and about the short circuit, what do you think would be the lowest amp I can set to not have any false alarms and what same question for the ms setting

 

[rg12]

Bump?
Kinda urgent for me sorry...

 

[john61ct]

What urgent, you start out, leave some settings like precharge and total cycle capacity at default, as you get more info, nothing stopping you tweaking later.

Some, like the short circuit, I'd start lower / shorter and then raise them if I got too many false positives. Called scientific method, aka trial & error.

Just guessing, total cycle capacity might be a maximum Ah you want it to stop charging at, the pack can't possibly be adding anything useful past that point.

 

[rg12]

What urgent, you start out, leave some settings like precharge and total cycle capacity at default, as you get more info, nothing stopping you tweaking later.

Some, like the short circuit, I'd start lower / shorter and then raise them if I got too many false positives. Called scientific method, aka trial & error.

Just guessing, total cycle capacity might be a maximum Ah you want it to stop charging at, the pack can't possibly be adding anything useful past that point.

It's for a customer, first time using this BMS so I can't ride on his bike for many cycles doing the trial and error system.

So if the pack is 45Ah I should just type there 45Ah?
So annoying they don't have a manual and the suppliers have an english that is as good as my chinese.

 

[john61ct]

As I said, no idea.

We must deal with reality as it presents itself.

Personally I would not sell solutions I hadn't thoroughly mastered and tested.

 

[john61ct]

I would not rely on nominal rated specs for "total cycle capacity", but do a full CC load discharge test.

Measure the Ah put out by the charger between the LVC point of the BMS and desired Full SoC.

Add 5-10% for temp variation, bank aging.

Again, just guessing.