I'm still doing duediligence on what lithium to put in a sailboat. Initially had thought LiFePO4s.. but now more likely LTO.
The larger form factor (66160) should mean less mechanical connections and work. My intention of this thread is to solicit responses and update my body of knowledge by linking elsewhere in this forum as I find relevant references.
The boat.
Existing
1. 300W solar
2. 4.5kWh diesel generator
3. 100A alternator on main enging
4. Currently 450AH (3x 150)lead acid (LA) house battery. I run this to just 30% (135AH) between charging to extend cycle life. Approx 100A start battery. Do not plan to replace start battery..
5. 12V System
6. Have 3 separate marine type ACs (Master berth 5kBTU, main cabin 16kBTU and rear cabins 12kBTU). I will be installing a soft start for the 5kBTU if required.
7. 2KW Charger Inverter. Will be switching this over to full Victron set up prior to new battery (3kVa Multiplus (2.4kW), Solar Charge Controller etc).
8. Boat is located in hot climate near equator.
Objective/s
1. Replace existing LA.
2. Significantly upgrade to approx 9.2kWhbattery to allow silent running of 5kBTU AC overnight.
There marine ACs are not so efficient.. Based on the measurements I've run all have a COP of about 1.3. Since all 3 are about the same I've concluded this is due to the high sea water temps 30-32 deg C.
I'm assuming running the 5kBTU AC overnight for 12 hrswith a 50% duty cycle (this confirmed by meter readings in marina).
So 5kBTU * 12 *.5 / 3.4 (BTU to kW cooling)/ 1.3 (COP)= 6.78 kWh ie 73% of target 9.2kWh battery.
So there are several things to be deducted.
Q1. Just what is the nature of these LTO cells available from China. Are they second hand , or discarded new.. and discarded why? because they cant be charged fast enough in bus / truck situations.
Q2. What is best configuration for pack/s. This needs to account for any bms / balancing required.. also the ability to manage the back .. a single 10kW pack is not viable (too heavy).
Q2.2 Is there are neat module size (series or parallel) that can be then expanded.
Q3. Just what is the safety of these cells vs others... presumably better than LTO>>LiFePO4>>liOn.
So far.
1. New electrics on order , still to arrive and be installed.
2. Have received 5 x 40AH 66160 LTOs from China. have configured them into 1S (12V).
3. Yet to receive a sample BMS and separate balancer only.
The 5 cells arrived with either 2.23 (x2) or 2.22 (x3) volts on them, open voltage. I thought that indicated similar SOC. Once I put them in series I connected them to a small 8A 12V smart lead acid charger.
All looked fine...charging away merrily for about 3 hours. The voltage steadily increasing from 11.1 to about 12.5. I looked away for about 5 mins and it shot up to 13.5. One of the cells hit 3.1. Not good (max from supplier is 2.9). I paralleled all the cells for about an hour and got back to 2.54V cells. Reconnecting in series and connecting the charger again.. and once again the two cells that had the highest initial reading once again started increasing in voltage faster.. I disconnected the charger once the hightest hit 2.8.. the second was at 2.7.. the other 3 all at 2.54.
Approximately 12 hours later the 2.8V unit is not 2.65. I have not tried to figure out if they are at their rated 40AH capacity but it suggest the high voltage reading (ie 2 cells) e are of lesser capacity than the others.
This now creates another question
Q4. Does this variability add significantly to the amount / type of BMS that needs to be used.
Q4.1. If this variability is manageable from a BMS point of view , do the life cycle projections (15000+) for these cells still hold, or is that for ideal.
Q4.2 BMS lifespan . Most only are 30000 hours , or 5 years when quoted. How do square that with cells that can last 30-40 years. eg planned BMS replacement every x years? External notification when BMS fault detected? BMS will now be important if cells are so variable.
So let me add some hypotheses to disprove.
1. LTO Cell variability can be managed, probably just with a beefy balancer.
2. BMS lifespan can be managed.. by putting in short term solution now, looking for longer term one.
3. Modular design (for weight management) for 12V system can be reached accounting for BMS needs, eddy currents.
The larger form factor (66160) should mean less mechanical connections and work. My intention of this thread is to solicit responses and update my body of knowledge by linking elsewhere in this forum as I find relevant references.
The boat.
Existing
1. 300W solar
2. 4.5kWh diesel generator
3. 100A alternator on main enging
4. Currently 450AH (3x 150)lead acid (LA) house battery. I run this to just 30% (135AH) between charging to extend cycle life. Approx 100A start battery. Do not plan to replace start battery..
5. 12V System
6. Have 3 separate marine type ACs (Master berth 5kBTU, main cabin 16kBTU and rear cabins 12kBTU). I will be installing a soft start for the 5kBTU if required.
7. 2KW Charger Inverter. Will be switching this over to full Victron set up prior to new battery (3kVa Multiplus (2.4kW), Solar Charge Controller etc).
8. Boat is located in hot climate near equator.
Objective/s
1. Replace existing LA.
2. Significantly upgrade to approx 9.2kWhbattery to allow silent running of 5kBTU AC overnight.
There marine ACs are not so efficient.. Based on the measurements I've run all have a COP of about 1.3. Since all 3 are about the same I've concluded this is due to the high sea water temps 30-32 deg C.
I'm assuming running the 5kBTU AC overnight for 12 hrswith a 50% duty cycle (this confirmed by meter readings in marina).
So 5kBTU * 12 *.5 / 3.4 (BTU to kW cooling)/ 1.3 (COP)= 6.78 kWh ie 73% of target 9.2kWh battery.
So there are several things to be deducted.
Q1. Just what is the nature of these LTO cells available from China. Are they second hand , or discarded new.. and discarded why? because they cant be charged fast enough in bus / truck situations.
Q2. What is best configuration for pack/s. This needs to account for any bms / balancing required.. also the ability to manage the back .. a single 10kW pack is not viable (too heavy).
Q2.2 Is there are neat module size (series or parallel) that can be then expanded.
Q3. Just what is the safety of these cells vs others... presumably better than LTO>>LiFePO4>>liOn.
So far.
1. New electrics on order , still to arrive and be installed.
2. Have received 5 x 40AH 66160 LTOs from China. have configured them into 1S (12V).
3. Yet to receive a sample BMS and separate balancer only.
The 5 cells arrived with either 2.23 (x2) or 2.22 (x3) volts on them, open voltage. I thought that indicated similar SOC. Once I put them in series I connected them to a small 8A 12V smart lead acid charger.
All looked fine...charging away merrily for about 3 hours. The voltage steadily increasing from 11.1 to about 12.5. I looked away for about 5 mins and it shot up to 13.5. One of the cells hit 3.1. Not good (max from supplier is 2.9). I paralleled all the cells for about an hour and got back to 2.54V cells. Reconnecting in series and connecting the charger again.. and once again the two cells that had the highest initial reading once again started increasing in voltage faster.. I disconnected the charger once the hightest hit 2.8.. the second was at 2.7.. the other 3 all at 2.54.
Approximately 12 hours later the 2.8V unit is not 2.65. I have not tried to figure out if they are at their rated 40AH capacity but it suggest the high voltage reading (ie 2 cells) e are of lesser capacity than the others.
This now creates another question
Q4. Does this variability add significantly to the amount / type of BMS that needs to be used.
Q4.1. If this variability is manageable from a BMS point of view , do the life cycle projections (15000+) for these cells still hold, or is that for ideal.
Q4.2 BMS lifespan . Most only are 30000 hours , or 5 years when quoted. How do square that with cells that can last 30-40 years. eg planned BMS replacement every x years? External notification when BMS fault detected? BMS will now be important if cells are so variable.
So let me add some hypotheses to disprove.
1. LTO Cell variability can be managed, probably just with a beefy balancer.
2. BMS lifespan can be managed.. by putting in short term solution now, looking for longer term one.
3. Modular design (for weight management) for 12V system can be reached accounting for BMS needs, eddy currents.