Grin's CA3 questions

[ichiban]

Guys,

I have some problems setting up CA3 with my new bike. This is the 1st time I test the whole bike :

My system :

+ CA3.14 + PR3 + GMAC 8T motor on rear wheel + Grin's thumb throttle + 26" MTB + 20S3P * Samsung21700-40T (72V nom/ 84V max) + JK JBD6A24S10P BMS (100A) + DIY 12-pulse PAS disk (to fit my bike) & Grin's cadence sensor. I bought most of Grin's parts to ensure compatibility


+ After adjusting PAS sensor close enough to magnetic disc. PAS sensor LED blinks 12 times exactly when I turn the crank 1 rev forward. Should be OK






+ Setting CA3 according to Grin's manual and everything looks fine when rear wheel is up on a bike stand. Throttle (Grin's 3-pin) works, PAS OK, PR3 blinks, CA3 also show throttle ramps up. Fast & responsive


+ e-brake L & R sensor (2-pin each) in parallel plugged into single CA3's 4-pin connector (use only 3-pin). Both levers function properly, confirmed by moving brake lever icon on CA3 display every time I squeezed either or both. Also tested before with DMM for continuity - passed consistently. Shown Right magnet & reed switch as brake sensor (normally open) at arrow point. Did this many times with other bikes, never had any problems.

+ CA3 power limit set at 45A 2800w. I know it's wayyy too much. Just my 1st test.

"Throttle IN" :

0% Throttle :



Half throttle :



Max Throttle :



Mode : "Pass-thru"

 

[Blacklite]

Understand that BMS protection limits should be set to a little over the batt Ah capacity and actual usage.

No... the Ah of the pack is the measure of the amount of charge stored in the pack. It's a completely different measure to maximum current draw.

Your battery is not "864W" it's 864Wh, a measure of energy, found by multiplying the Ah of the pack by the nominal voltage of the pack.

No intention of running above 50-60A for long though , but might exceed the 12Ah rated from time to time.

These are two different units, and you can't compare them.

 

[amberwolf]

Understand that BMS protection limits should be set to a little over the batt Ah capacity and actual usage.

No, they should be set to *less* than the actual capabilities of the cells, so it can protect them against exceeding their specifications. That is the entire purpose of the BMS--to protect the cells, which then protects you from the potential for fire. If you don't let it do it's job, you might as well not install it at all.

but might exceed the 12Ah rated from time to time.

You cannot exceed the capacity of the pack by using more capacity than it has.

Doing this will overdischarge the cells and damage them, which creates the possibility for fire at any time after that point, during the recharge after overdischarge, or during discharge the next time, or even just sitting there doing nothing.

You can't know if there is damage that could lead to a fire until the fire happens, so avoiding this damage is your best option.

 

[amberwolf]

In my case, 20S3P Samsung 21700-40T rated at 864w, 72V, 12Ah.

Some thoughts:



If you haven't looked at this yet, you may want to

Battery test-review 26650 comparator

It has this cell, tested up to 30A; you can check out the curves, sampled below:

Full test here

Test of Samsung INR21700-40T 4000mAh (Cyan)

At 30A the voltage drop is almost half a volt per cell, which will affect how much power you can actually get out of your system. Let's just call it 0.4v / cell sag since you're going to use over 25A max per cell at that 80A burst. At 20s, that means 20 x 0.4v or 8v of sag for your pack under that load. If you were at nominal voltage, 72v, then without sag you'd've gotten 72v x 80A = 5760W, but with the sag you'll only get 64v x 80A = 5120W.

Probably makes no difference to your operation, but just pointing it out if you hadn't already worked this out.


Also, none of the tests gave the full 4Ah capacity either, so you don't actually have a 12Ah pack. If you have it fully charged to 4.2v/cell, and it's perfectly balanced all the time, and you discharge all the way to 2.8v/cell (which is hard on the cells, though that won't matter if you don't need a long lifespan), then you get just over 3.5Ah per cell, maybe as much as 3.7Ah. So 3p x 3.5Ah (because they'll also lose capacity with age, and the harder they're used the faster that will happen), is only 10.5Ah. (if you prefer to be optimistic, the highest test capacity was just over 3.8Ah, at low current draw, giving an 11.4Ah pack)

I'm not sure where you get the 864W number, as it doesn't compute from any of the voltage and current numbers.

I thought you might have meant Wh, which is capacity, but the capacity of the pack in Wh is nominal voltage 72v x capacity 10.5Ah which is only 756Wh (assuming you run till all the cells are at 2.8v (or less if they are not all equal capabilities, unmatched/unbalanced)).

If they were actually 4Ah cells, then with 72v and 12Ah you'd get 864Wh of capacity...but that isn't 854W (which is a measure of power, and on a battery normally means the maximum wattage it could possibly output).

 

[ichiban]

Some thoughts:



If you haven't looked at this yet, you may want to

Battery test-review 26650 comparator

It has this cell, tested up to 30A; you can check out the curves, sampled below:
View attachment 332811
Full test here

Test of Samsung INR21700-40T 4000mAh (Cyan)

At 30A the voltage drop is almost half a volt per cell, which will affect how much power you can actually get out of your system. Let's just call it 0.4v / cell sag since you're going to use over 25A max per cell at that 80A burst. At 20s, that means 20 x 0.4v or 8v of sag for your pack under that load. If you were at nominal voltage, 72v, then without sag you'd've gotten 72v x 80A = 5760W, but with the sag you'll only get 64v x 80A = 5120W.

Probably makes no difference to your operation, but just pointing it out if you hadn't already worked this out.


Also, none of the tests gave the full 4Ah capacity either, so you don't actually have a 12Ah pack. If you have it fully charged to 4.2v/cell, and it's perfectly balanced all the time, and you discharge all the way to 2.8v/cell (which is hard on the cells, though that won't matter if you don't need a long lifespan), then you get just over 3.5Ah per cell, maybe as much as 3.7Ah. So 3p x 3.5Ah (because they'll also lose capacity with age, and the harder they're used the faster that will happen), is only 10.5Ah. (if you prefer to be optimistic, the highest test capacity was just over 3.8Ah, at low current draw, giving an 11.4Ah pack)

I'm not sure where you get the 864W number, as it doesn't compute from any of the voltage and current numbers.

I thought you might have meant Wh, which is capacity, but the capacity of the pack in Wh is nominal voltage 72v x capacity 10.5Ah which is only 756Wh (assuming you run till all the cells are at 2.8v (or less if they are not all equal capabilities, unmatched/unbalanced)).

If they were actually 4Ah cells, then with 72v and 12Ah you'd get 864Wh of capacity...but that isn't 854W (which is a measure of power, and on a battery normally means the maximum wattage it could possibly output).

No... the Ah of the pack is the measure of the amount of charge stored in the pack. It's a completely different measure to maximum current draw.

Your battery is not "864W" it's 864Wh, a measure of energy, found by multiplying the Ah of the pack by the nominal voltage of the pack.

These are two different units, and you can't compare them.

Thanks guys for pointing these out. It's the precautions that ones should not exceed the limits of the pack. I do not intend to do that except in absolute necessities.

 

[Blacklite]

Thanks guys for pointing these out. It's the precautions that ones should not exceed the limits of the pack. I do not intend to do that except in absolute necessities.

Having setting that allow for over discharge means a potential fire. Your absolute necessities will cause danger to you and those around you.

Please set an appropriate LVC so at least the BMS will shut off due to cell sag before you blow yourself up.

 

[amberwolf]

Yes. Doing it even once means the pack is a permanent fire risk, forever, and you cannot know if or when it will happen until it does, at which point it is too late as it is on fire (and potentially setting fire to the building(s) people are living in, depending on where it is located at that moment).