Lithium battery from electric cars for boat use

Hi everyone, let me start this thread with description how we adapted electric car lithium module for boat use.
This is how it looks finished:


Internal structure (at moment of photo made is not connected everything):

It consist one battery module from Chevrolet Bolt electric car, BMS and contactor, driven by BMS.
Tech specs:

• The total battery weight is approximately 39 kg.
• Available energy for operation is 5.5 kWh of the total 6.5 kWh (limited by BMS settings)
• The voltage of a fully charged battery is 41.5V, and fully discharged at which the BMS disconnects the load - 31V.
• Battery dimensions - 540x480x125 mm
• Cell Chemistry - LiNiMnCoO2

I tested this battery this year with 65 Amps charge and discharge (2.3 kW at 36V) and monitored it heat under load. Maximum cell temperature under load was +3 celsus comparing to ambient temperature.
This battery is used as electric drive battery at my small sailboat.

Some more details for battery here.

 

NICE!

 

At 40V that looks like a dangerous setup. The voltage is enough to kill a person.

 

42 volt electrical systems were seriously considered by the automotive industry about twenty years ago. The rationale I heard for 42 volts was that it was sufficiently below the voltage which could harm humans.

 

That's what the phone company did so many years ago with land lines.

 

Electric powered outboards for boats - Torqeedo https://www.torqeedo.com/en/products/batteries
Torqeedo sell boat batteries of 24V, 48V and 355V. 355V batteries have same chemistry as cells at battery I made. I used another 48V batteries (not torqeedo) at boat for two years and 36V battery, described at this thread for one year. A bad weather was sometimes. No problems yet. May be it is dangerous but not for me, at last for three years.

P.S. considering this
Electrical Safety: The Fatal Current https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html
the fatal current is 0.1 Amps.
Is I am correct if according to Ohm's law:
I = V/R
current via human body will be I = 41 V / 1000 Ohms = 0.041 A
where 1000 Ohms - resistance of wet skin.
So, 0.041 A is lower than death current 0.1 A.

Dry skin have resistanse 500.000 Ohms, then
I = 41 V / 500 000 Ohms = ‭0.000082‬ A or 0.082 mA

I considered only skin resistanse. We also have an internal resistanse which is not depends on wet/dry conditions:
"internal resistance (less the skin resistance) is only 100 ohms, while from hand to foot is closer to 500 ohm"

Consider lowest internal resistanse (100 Ohms) and wet skin resistanse 1000 Ohms:
I = 41 V / 1100 Ohms = 0.037 A

 

It is enough to produce painful shock:
Electrical Safety: The Fatal Current https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html

However, the voltage generated by the field collapse when a motor is turned off can have a peak voltage much higher than the source

 

How many full charge discharge cycles do you bank on getting?

 

Don't know exactly.
First battery (48V 75Ah) from E-car was created at 2016 and after ~300 cycles it still have 75Ah.

 

How did you measure 75Ah?

 

Discharge range 54.6V -> 35.75V, discharge current was 40A

 

You can use Peukert's equation to normalize the test. What kind of equipment did you use to maintain constant current?

 

It was nichrome wire spiral with big cooling fan. Wires connected to load and to battery was 6 mm². Current measured by wattmeter with external shunt

 

In that case what you got is constant load, not current. You would have to measure the current values and integrate to be able to calculate capacity.

 

Why I need to calculate capacity if I have wattmeter attached? Current may change sligthly, not 40A exactly during discharge. Voltage will drop during discharge. Watt-hours counted correctly. Overall this battery show itself very good during last years.