BBSHD 52V Battery Low Voltage Protection Setting Confusion

[mlustig]

Hi. Need some advice on setting Low Volt Protection level on BBSHD.

Battery is 52V w the following specs:

• 52V, 14AH, 30A continuous discharge
• Protection: Over Charge/Discharge, Short Circuit, Cell Balancing
• Operating Voltage 36.4V-58.8V

What would be the BBSHD programming setting for LVP for this battery? Stock programming said 41V, several charts say 46V, Bafang says 40V, etc.

Thanks!

 

[m@Robertson]

I set mine to 41v, which on paper is a terrible idea (see 52v chart below). you have to remember your battery will sag below what its actual resting voltage level is, so a 41v setting isn't really going to be 41v. 41v under power - which is where the motor will trip - is probably an actual 43v level if you stop and just sit and watch the voltage level without powering the bike.

Li-Ion Ebike Battery Charge Charts

Whats an 80% charge on a 48v battery? These charts give answers to questions like this on common ebike battery voltages: 36v, 48v, 52v, 60v and 72v.

talesontwowheels.com

If you want to be a little safer, set it to 43v. Myself I NEVER let my pack get down that low so its not much of a risk for me. My floor is around 46v under load, and if I really drain it I see it sag to maybe 44 or 43.

 

[harryS]

I don't think it matters how low you set it. The battery BMS will often react first That's usually set at 3V per cell, which is 14 x3 or 42 volts, But like Mac sez, there's voltage drop. A BBSHD on throttle might pull 4 volts sag on a good 30A battery, so the battery will shut down when it gets to 46V.
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[mlustig]

I don't think it matters how low you set it. The battery BMS will often react first That's usually set at 3V per cell, which is 14 x3 or 42 volts, But like Mac sez, there's voltage drop. A BBSHD on throttle might pull 4 volts sag on a good 30A battery, so the battery will shut down when it gets to 46V.
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Thanks. This is why Im confused. The battery operating voltage says 36.4v-58.8v. Why is the chart showing zero % at 43v and you are recommending 42v and m@r at 43v? If this matters the batteries are 2900mah.

 

[harryS]

You have to go the tech aspect, Lithium cells are rated to work safely between 2,5V-4,2V, Risk of fire when you exceed this, For extra safety and longer life, hardly anyone runs then below 3V/cell. All controllers, including the BBSHD, can only see the total battery voltage coming into the wires. You should set it above 3V/cell, which will be at least 42 volts.
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In a perfect world, there is no voltage sag but it exists. The current running thru your battery connectors, the wires, and inside the myriad connections in the battery will drop some voltage, In addition, depending on the quality of the internal lithium cells, the cells will drop some voltage too as current goes up. Running your BBSHD at a nominal 200W, I estimate this sag shuld be under 2 volts, but it means that if your battery cells are at a nominal 44 volts, by the time the controller sees it, it will be 42V and it shuts off.
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As for the chart saying 0%, that is BS. If you maintain a short circuit on your battery at 43 volts, it can overheat and burn your house down. Zero percent is based on the external electronics shutting down the battery. There is like 30% of the actual battery energy still hanging around, ready to kill you if you let it out.

 

[m@Robertson]

0% on the chart is a function of the theoretically usable charge left, not all of the actual gas still left in the tank, so to speak. If you look at those charts I linked, at the text on the right, it says

Cell is assumed to be a typical 18650 with full charge at 4.2v and full discharge at 3.0v

And that is the typically quoted expectation for Li-NMC type cells (its also true for 21700's of the same chemistry. I should edit that chart for clarity as it was written before those cells came into common use).

So "full discharge" is not meant to be zero charge left in the cell. That value is 3.0v. There is a second chart on that page that lets you do the math yourself. If you then look at the columns of numbers just to the right of the colored percentage chart, you see the cell voltage that corresponds to each entry in the charge chart. So now refer to the 'charge calculation method' box on that page which tells you how every number is arrived at. The 42.0 volts value on a 52v (14s) battery is 14 x 3.000 = 42.0. Zero left.

As also noted on that page, mathematically correct does not equal real-world. Don't take it down that low if you want your battery to live. Deep depth of discharge on this battery chemistry is not something you want to make a habit of.

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

 

[mlustig]

Ok. Thanks. Would 44V setting be a good trade-off between battery-life and capacity? I typically charge to 90% and only once let it get to low voltage cutoff.

 

[Gionnirocket]

As you state the actual battery operating voltage says 36.4v-58.8v... So I'd base my settings on that and use 42v knowing that this will give me the most battery with still a safety margin. I also understand that I take responsibility if I'm near that low voltage shutdown and ride gingerly to avoid large sags and get myself home.

 

[AHicks]

Just for reference, I ride an Ultra powered bike (set up for 30a max draw) with a 48v battery. This bike will shut right down with a wide open burst of throttle with a voltage in the low 46v range - due to the voltage sag in this system. This is NOT handy (or particularly confidence inspiring) when crossing a busy road for instance. For this reason, NOT because I couldn't ride it "safely" at a lower voltage, I charge when I see the volt meter at anything under 47.0v.