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Macbook pro charger triggers BMS disconnect

Tasemu

Tasemu

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Joined
Dec 23, 2020
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41
Hi all!

I've got my new lifepo4 battery bank installed and connected to the inverter. Everything seems to be running fine until I try to charge my macbook pro, at which point it seems the BMS cuts all power from the battery and everything shuts off.

Could anyone advise why this may be happening?

BMS = Daly 100a smart BMS
Laptop = Macbook Pro 15 with 87w fast charger

Thanks in advance!

UPDATE:

I notice when running the laptop charger or tv from the inverter, the current out on the BMS sits at about 8-9 amps, then (and this is strange to me) the pack voltage slowly starts dropping down to 12.4 (which i have set as the pack low voltage disconnect). The BMS then cuts all power until i reset the BMS, at which point the pack voltage is back to 13.2v.
 
Last edited:
What battery and what SoC is the battery?
Is your MBP the only load that does this?
Do you have a way to see how much your power brick is actually pulling, including surge?
 
MisterSandals said:
What battery and what SoC is the battery?
Is your MBP the only load that does this?
Do you have a way to see how much your power brick is actually pulling, including surge?
Click to expand...

1: Self build 280ah Lifepo4 Cells - SOC was charged to 100% a few hours ago and very little usage since
2: I've just noticed that it happens when the tv is on too
3: Yeah the BMS has an app. I notice the current out sits at about 8-9 amps, then (and this is strange to me) the pack voltage slowly starts dropping down to 12.4 (which i have set as the pack low voltage disconnect). The BMS then cuts all power until i reset the BMS, at which point the pack voltage is back to 13.2v.
 
12v pack also, should have stated that earlier.
 
Last edited:
Can you test the battery voltage directly when this happens? Its sounding like its either your
battery getting sagged down more than one would expect or the BMS is doing something
unusual. If you can narrow this down, it will help find the problem.
 
Will do that now, i've just tried a heat gun on the lowest setting directly from the inverter socket and the power cuts out immediately. About half a second. Unsure if the batteries could sag that fast.
 
The battery appears to be sitting at 13.1v even with -15A current being drawn... This was definitely causing the power cuts earlier today that caused this post.. I'm very confused now. Running the battery charger and the TV at the moment...
 
Ok i've got it to happen again now. I do see the voltage at the battery terminals pulled down to 12.9 briefly, then 12.6 for a split second before the BMS shuts down. Otherwise it sits happily at 13.1v regardless of the current i'm seeing drawn.

Also its worth noting I haven't had this issue with anything else on my boat, only through the inverter does this happen.
 
Tasemu said:
voltage at the battery terminals pulled down to 12.9 briefly, then 12.6 for a split second before the BMS shuts down.
Click to expand...
I suspect there is a voltage sag in one of the cells that the BMS detects that shuts it down.

If you can watch the voltage of the individual cells (from its terminals, one at a time of course), it'd likely confirm or disprove this theory.
 
Hi Tasemu,

Seems to me your BMS is doing what you set it to do - cutting off power at the low voltage you set - 12.4V

Seems to me also, regardless of what your battery shows as voltage with no load - 13.2V - the battery is not charged "much" so as soon as you put a load on it via the items plugged into your inverter, it doesn't have enough charge, so it drops to 12.4V.

How did you determine the SoC of the battery?

Good luck
 
MisterSandals said:
I suspect there is a voltage sag in one of the cells that the BMS detects that shuts it down.

If you can watch the voltage of the individual cells (from its terminals, one at a time of course), it'd likely confirm or disprove this theory.
Click to expand...
I'll do this test now for each cell.
KauaiMolokai said:
Hi Tasemu,

Seems to me your BMS is doing what you set it to do - cutting off power at the low voltage you set - 12.4V

Seems to me also, regardless of what your battery shows as voltage with no load - 13.2V - the battery is not charged "much" so as soon as you put a load on it via the items plugged into your inverter, it doesn't have enough charge, so it drops to 12.4V.

How did you determine the SoC of the battery?

Good luck
Click to expand...
Top balanced the cells using a bench power supply and then charged to 14.6 using a sterling procharge ultra until the current hit 0.
 
Side Note: I'm not sure if this is a point worth making, but my 12v fridge just turned on, drawing about 7 amps and the battery is not breaking a sweat. 13.1v and chugging along. Maybe its a faulty inverter...?
 
I would try using individual loads on the battery - nothing but the inverter, then nothing but whatever else you said was drawing 15A, then the inverter only with the MacBook charger plugged in...
 
MisterSandals said:
Yes if set at 12.4v. But that is an unusually high LVD for a BMS. Normally they are in the 10v to 11.x range by default.
Click to expand...
I set it specifically in the app because... i saw it somewhere in a thread on here? Could you recommend a LVD?
 
KauaiMolokai said:
Yeah, but in his initial post he said he set it to 12.4V
Click to expand...
Ha! Okay, i missed the update, thanks for getting me up to speed.

Your BMS is your last ditch safety switch for your battery. The primary cell level protection numbers are 2.5v and 3.65v. I personally would like something a bit higher for the low end, perhaps 11v.

What is the individual cell cut off for your BMS? Is this configurable?
I would like to be safely above the damage level, perhaps with 2.75v per cell to be safe. If you need to squeeze out more power, 2.5v is supposed to be safe (but will stress the cells a little more of course).
 
MisterSandals said:
Ha! Okay, i missed the update, thanks for getting me up to speed.

Your BMS is your last ditch safety switch for your battery. The primary cell level protection numbers are 2.5v and 3.65v. I personally would like something a bit higher for the low end, perhaps 11v.

What is the individual cell cut off for your BMS? Is this configurable?
I would like to be safely above the damage level, perhaps with 2.75v per cell to be safe. If you need to squeeze out more power, 2.5v is supposed to be safe (but will stress the cells a little more of course).
Click to expand...

Cell volt disconnect = 3.1v
Sum total volt disconnect = 12.4v

With the new daly BMS smart bluetooth thingy, it seems most parameters are configurable.
 
Tasemu said:
Cell volt disconnect = 3.1v
Sum total volt disconnect = 12.4v
Click to expand...
Those are unnecessarily conservative numbers. But, you have YOUR comfort level to live with. The cells are supposed to be safe down to 2.5v. Find a number that does not shut your system down unnecessarily and lets you sleep at night.
 
MisterSandals said:
Those are unnecessarily conservative numbers. But, you have YOUR comfort level to live with. The cells are supposed to be safe down to 2.5v. Find a number that does not shut your system down unnecessarily and lets you sleep at night.
Click to expand...
I've just set my cut-off to 11v, perhaps its just the inverter and the stuff using it pulling a surge of power briefly, which triggered my high LVD. Currently running the TV, Laptop and Inverter and it has yet to disconnect. Lets see how she goes, thanks for all the help. Will report back with results either way. :)
 
Update: yet to have a LVD, but when running 80A through a heat gun it did cut off, maybe because its a daly and isn't actually able to handle the claimed 100A?
 
Tasemu said:
I've just set my cut-off to 11v
Click to expand...
Just out of curiosity, does it also have a cell level disconnect?

I ask because...
It would not be wildly unusual for an 11v battery have cells with voltages: 3v, 2.9v, 2.8v, 2.3v
In such a scenario, the 4th cell would be well into the danger/damage zone (below 2.5v).
 
MisterSandals said:
Just out of curiosity, does it also have a cell level disconnect?

I ask because...
It would not be wildly unusual for an 11v battery have cells with voltages: 3v, 2.9v, 2.8v, 2.3v
In such a scenario, the 4th cell would be well into the danger/damage zone (below 2.5v).
Click to expand...
It allows you to only set a cell disconnect, then it derives the total voltage disconnect from it, which is not settable itself. :)
 
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