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How to connect a BMS to 48 Nissan Leaf Modules in a 24V configuration

That DC to DC converter does have a good range of input voltages. It does say not to be used to charge batteries and it is not specific about the exact voltage it outputs.
  • - Do you know the specifics about what the charging voltages the Titan needs or what range of voltage it can receive?
  • - You have still not answered my question about the capacity of the Titan battery in kWhs and your daily consumption in kWhs?

Those numbers are critical for any further discussion or decision about a DC to DC converter. That decision may determine whether you put six or seven modules in series.
I am waiting on a response from Point Zero on the range of voltage it can receive, but didn't I say I have one Titan battery with 2 kWhs? Since that battery is connected to the Titan and if we had that 60a step down converter that outputs 1440 watts wouldnt that add up to 3440 watts pushing into the inverter?
 
Since that battery is connected to the Titan and if we had that 60a step down converter that outputs 1440 watts wouldnt that add up to 3440 watts pushing into the inverter?
You are confusing a battery that can store 2kWhs and a converter that can output 1.4kWs in an hour.

The inverter is only going to pull enough Watts to service the loads that you put on it and that is the number that I keep asking you about. If you don't know or don't know how to find out just say so and we can walk through it and make an educated guess based on your appliances. If you want some help here, please make an effort to answer the questions so that I can help you find a solution. Perhaps the Titan has a meter that will answer that question. Have you used it yet?

For example if you consume less than 10 kWhs in a day you might be able to buy a less expensive converter that would keep your Titan full of energy, allow you to run some heavy appliances and then slowly recharge your Titan in the background. Does that sound like something that would interest you?
 
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I am waiting on a response from Point Zero on the range of voltage it can receive, but didn't I say I have one Titan battery with 2 kWhs? Since that battery is connected to the Titan and if we had that 60a step down converter that outputs 1440 watts wouldnt that add up to 3440 watts pushing into the inverter?

It does not quite work like that.

With that converter pushing 1440 watts at just 24 volts, the internal Titan 2 KWH battery will start supplying power until it runs down to 24 volts. That is probably a little below half of the capacity. At this point, it will begin pulling power from the step down converter from the 48 volt (51.8 volt nominal) and the battery in the Titan will basically just sit there at this state of charge. So the inverter will be able to pull up to 1440 watts at this point without dragging the internal battery any lower. We don't know for certain how the DC-DC buck converter will act if you try to pull more than it's rated 1440 watts. It might just drop a bit in voltage and limit to the power, or it could shut off. If the voltage just drops, then the internal Titan batter will again start supplying more power, but it is already getting low. If the converter shuts off, then the Titan battery will get hit with the full load and you will not have much time left. It will hit low voltage shut off. But then the converter may power up again, and you end up with it kicking on off on off etc.

Basically, don't pull more power than the converter from the 48 volt pack. Even earlier, when the Titan has a full charge, you are still limited to the capacity of the Titan inverter. I think it is something like 2,000 watts. If you do need that kind of power, you may need two of the buck converters to keep up with the demand.
 
You are confusing a battery that can store 2kWhs and a converter that can output 1.4kWs in an hour.

The inverter is only going to pull enough Watts to service the loads that you put on it and that is the number that I keep asking you about. If you don't know or don't know how to find out just say so and we can walk through it and make an educated guess based on your appliances. If you want some help here, please make an effort to answer the questions so that I can help you find a solution. For example if you consume less than 10 kWhs in a day you might be able to buy a less expensive converter that would keep your Titan full of energy, allow you to run some heavy appliances and then slowly recharge your Titan in the background. Does that sound like something that would interest you?
Yes, that would interest me. The heaviest appliance I am running is my A/C which pulls about 1100-1400 watts an hour, I would like to be able to run the A/C while I have my refrigerator, desktop, and monitor going, all this adds up to about just under 2kwh. The manual just says it can be charged using the car adapter, charge controllers, and A/C wall charger. Not much else is mentioned in the manual.
 
It does not quite work like that.

With that converter pushing 1440 watts at just 24 volts, the internal Titan 2 KWH battery will start supplying power until it runs down to 24 volts. That is probably a little below half of the capacity. At this point, it will begin pulling power from the step down converter from the 48 volt (51.8 volt nominal) and the battery in the Titan will basically just sit there at this state of charge. So the inverter will be able to pull up to 1440 watts at this point without dragging the internal battery any lower. We don't know for certain how the DC-DC buck converter will act if you try to pull more than it's rated 1440 watts. It might just drop a bit in voltage and limit to the power, or it could shut off. If the voltage just drops, then the internal Titan batter will again start supplying more power, but it is already getting low. If the converter shuts off, then the Titan battery will get hit with the full load and you will not have much time left. It will hit low voltage shut off. But then the converter may power up again, and you end up with it kicking on off on off etc.

Basically, don't pull more power than the converter from the 48 volt pack. Even earlier, when the Titan has a full charge, you are still limited to the capacity of the Titan inverter. I think it is something like 2,000 watts. If you do need that kind of power, you may need two of the buck converters to keep up with the demand.
The Titan inverter is 3000watts w/ 6000watt surge, so if I buy two converters I can pull double the power from my leaf batteries?
 
Great that gives us some more options. Off the top of my head the AC is going to be the biggest challenge.
I can run the A/C with the Titan battery alone, I was just thinking the 1 converter would be enough. Would it be more beneficial for me to get an adjustable converter to run @ 28v or whatever the full charge voltage ends up being for the titan battery even if the converter amperage is less so as soon as there is a load on the Titan the leaf battery can start charging it. Am I correct in my thinking?
 
Okay I need to check my assumptions.
You have a bus that you want to live in as a tiny home.
You have a Titan solar generator that has an output of 3kW and a surge of 6kW. It has storage capacity of 2kWhrs. The batteries in the Titan can be charged from 120 volts AC, 12 volts DC, or solar. The batteries have a nominal voltage of 24v. It is unknown if they can be accessed directly to charge from an alternate source. Point Zero is clarifying.
You have 1500 Watts of solar panels.
You have 48 Nissan Leaf modules with an unknown capacity but can we assume conservatively they have 12 to 20 kWhs.
You have 2kW of loads that run for 8 hours a day. The big unknown is how long you want to run the AC and the loads during the other 16 hours of the day.
 
I can run the A/C with the Titan battery alone,
But you only have two hours at the most run time of the A/C from the Titan battery. Earlier I thought the A/C was going to be the problem when I thought it was a smaller inverter. The AC is still an issue but the biggest bottleneck is getting the energy from the Nissan Leaf pack into the Titan so it can be used. The 12 volt adaptor is going to be too slow at probably less than 200 Watts an hour.
How were you going to connect the converter to the battery of the Titan?. Is there an outside connect for something like solar? I am just throwing out ideas in case @GXMnow has any thoughts.
On my earlier list of assumptions I realized I did not list whether you had a charge controller that you were going to use with the solar panels?
 
Okay I need to check my assumptions.
You have a bus that you want to live in as a tiny home.
You have a Titan solar generator that has an output of 3kW and a surge of 6kW. It has storage capacity of 2kWhrs. The batteries in the Titan can be charged from 120 volts AC, 12 volts DC, or solar. The batteries have a nominal voltage of 24v. It is unknown if they can be accessed directly to charge from an alternate source. Point Zero is clarifying.
You have 1500 Watts of solar panels.
You have 48 Nissan Leaf modules with an unknown capacity but can we assume conservatively they have 12 to 20 kWhs.
You have 2kW of loads that run for 8 hours a day. The big unknown is how long you want to run the AC and the loads during the other 16 hours of the day.
12-20v dc for the car charging port, you can access the battery directly. The battery has two Anderson connectors at the top and bottom (4 total) that are meant to charge while disconnected from the titan module or use while stacked under the titan and charged through the two ac charging ports, dual mppt chargers, or the car charging port. Not sure about the nominal voltage on the Titan battery, the 48 Nissan leaf modules are probably at least 14kwh, I'll find out tomorrow when I capacity test one. That is the big unknown, its going to depend on location and the weather. However I am not buying any more batteries, so I will have to make due with the 16kwh I have now.
 
This whole time I have been assuming the Titan battery was 24 volts. Do we know for sure?. Above you say it is 12-20 volts. That range is workable with Nissan modules and a possibly modest DCto DC converter.
 
This whole time I have been assuming the Titan battery was 24 volts. Do we know for sure?. Above you say it is 12-20 volts. That range is workable with Nissan modules and a possibly modest DCto DC converter.
Its for sure a 24v battery just not sure what the nominal voltage is, however the input voltage for the car charging port is 11-20v DC Max charging 160watts. When I read that I saw that the two AC charging ports on the Titan module have a max of 50A per port @ 29.2V, not sure if this information helps.
 
Yes that helps. It can be used to confirm the assumption that we made earlier that the pack is 8S which I derived by dividing 29.2 by 8 and got 3.65 volts which is the high cell voltage of a LFP cell. That is consistent with the statement of @GXMnow that 24 volts for 8 cells would only be 3 volts per cell. Now I understand why you were thinking of a 60 Amp converter. In reality from the load of 2000 Watts it would 83 Amps that you would need to just keep the Titan battery even. Anything less and the Titan battery would slowly drain.
I am not familiar with DC to DC converters enough to know if there is one that could be configured to supply a Voltage of 27.2 volts (3.4 per cell)
I think that is the issue and I think we have framed it more than we had in the beginning. I also don't know how to get the issue more visability to get other usage. I think you have reached the extent of my knowledge. I will let @GXMnow speak for himself.
Perhaps a new thread looking for a 48 to 60 volt input DC to DC converter that can charge an 8S LFP pack at 80 Amps.
I
 
29.2 volts is the proper absorption voltage of 8S LFP (LiFePo4) at 3.65 volts per cell
 
Now this might actually do the job. Some MPPT controllers may go stupid when fed from a battery, so there is a chance of failure.


It is actually kind of cheap at about $280 It claims it can properly charge LiFePo4 at up to 100 amps from an input from 36 to 96 volts. So your 58 volt max from the Leaf cells should work just fine. It is meant to track the MPP of a solar panel, but if it is getting it's input from the Leaf batteries, the maximum power point will be much greater than 2600 watts. Hopefully it will have the intelligence to just back off current to limit the power going into the 24 volt batteries. Since it does claim to be MPPT, it must use a buck converter to drop the voltage down and regulate the current to the batteries. But the one bad possibility is if the MPPT keeps trying to find max power, it could overload it's input and fail. So if you do try domething like this, star with a smaller fuse like 20 amps on the input and program it for it's lowest charge current and see what it does. This is an amazing price point for a 2600 watt, 100 amp charge controller. So the quality is probably not the best. But a dumber MPPT might actually help in this application. I am trying to download an instruction book for it, but no luck so far.
 
Now this might actually do the job. Some MPPT controllers may go stupid when fed from a battery, so there is a chance of failure.


It is actually kind of cheap at about $280 It claims it can properly charge LiFePo4 at up to 100 amps from an input from 36 to 96 volts. So your 58 volt max from the Leaf cells should work just fine. It is meant to track the MPP of a solar panel, but if it is getting it's input from the Leaf batteries, the maximum power point will be much greater than 2600 watts. Hopefully it will have the intelligence to just back off current to limit the power going into the 24 volt batteries. Since it does claim to be MPPT, it must use a buck converter to drop the voltage down and regulate the current to the batteries. But the one bad possibility is if the MPPT keeps trying to find max power, it could overload it's input and fail. So if you do try domething like this, star with a smaller fuse like 20 amps on the input and program it for it's lowest charge current and see what it does. This is an amazing price point for a 2600 watt, 100 amp charge controller. So the quality is probably not the best. But a dumber MPPT might actually help in this application. I am trying to download an instruction book for it, but no luck so far.
This is giving me some serious hope for my system! I'll definitely be on the lookout for that instruction book.
 
This is giving me some serious hope for my system! I'll definitely be on the lookout for that instruction book.
In the meantime you can do some thinking about how to parallel those Nissan Leaf modules. Do you know if they are G-1 or G-2?
Do they look like sardine cans with a lip or just a module without a lip?
 
In the meantime you can do some thinking about how to parallel those Nissan Leaf modules. Do you know if they are G-1 or G-2?
Do they look like sardine cans with a lip or just a module without a lip?
G1 modules with a lip, 24 type A and 24 type B. I have seen people put the entire modules in parallel having three long bus bars, one on all the positive terminals, one on all the negative terminals and one on all the center terminals. I just haven't seen anyone install a BMS on those systems. Just the systems that use 7 or 8 modules in series.
 
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