How to connect a BMS to 48 Nissan Leaf Modules in a 24V configuration
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Ampster
Renewable Energy Hobbyist
This is what the G-1 modules look like in parrallel The copper strips you will need to make or have made. The length will depend on final design. It is more mechanical issues than electical. One BMS will save money.
Well if we end up using the charge controller to feed the rest of my system using the leaf batteries, we can
If I end up using this charge controller to feed the titan with the leaf batteries I will need to end up buying a second charge controller for my 5 300w panels to feed the leaf batteries. This should work right? Or do you see complications connecting two charge controllers to the same battery. (one through solar input and one through the battery output)
GXMnow
Solar Wizard
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How much are you will to spend towards a test to see if it will work so you can still use the Titan in this setup? If the budget is tight, this is not a good idea. Sell the Leaf battery modules and buy LFP cells that you can tie into the Titan in an 8S setup.
I did a bit of thinking towards how this might all work.
Yes. You will need one charge controller that will take the solar panels and properly charge the Leaf batteries at your desired current and voltage limits. It will seek maximum power and always just try to top out the battery bank.
Then you need to feed that energy down to the Titan 21 to 29.6 volt battery bank. A proper DC to DC battery charger would be ideal, but I did not have any luck last night trying to find one designed for that purpose for these voltages at a decent current. Using a solar charge cntroller is not ideal, but knowing how some of the cheaper MPPT ones work, there is a good chance it will fall back to the set battery charge current on the output side. But there is also a problem on that. Let's say the batter in the Titan is low for whatever reason. If you use a charge controller that is set to truly charge up a 24 volt LFP pack, it will want to pull it up to 29.6 volts at the set current. You want to be able to use full power of th Titan inverter, so you set that current at 100 amps, but the inverter is not pulling much at the moment. This setup will push almost the full 100 amps into the relatively small battery in the Titan. That will likely destroy the batteries. For safety, I think the voltage will need to be set a little lower, and you should ensure the Titan's internal battery starts ABOVE the voltage set in the charge controller before connecting the system and turning it on. This way, the charge controller should be in a limited current mode as it thinks the battery is already at this now lowered absorb voltage. Let's say 26 volts should be safe. That would be 3.25 per cell, maybe go a little more, but this will have to be worked out on how well the system performs. The highest I would go is 27.2 which is 3.4 per cell. Any higher would hold the cells up to where they are being stressed. If the Titan is fully charged up, the cells go to 3.65 volts, but start to settle a bit. When you connect it, the Controller from the 48 volt pack sees a full battery and limits the current low. You start to pull current and the Titan battery voltage starts to drop. Ideally, the charge controller will see this and start to supply current. It will ramp up the current either to the set limit, or until the voltage hits the absorb setting where it should reduce current again. In a perfect world, the charge controller will just put out the right current to feed the load while holding the Titan battery at the fixed voltage.
Here is the other problem using a solar charge controller like this....
If it is actually a good charge controller, it will have time limits for the absorb mode, and it might force a wait time or a low voltage point where it will go back into charge mode. You don't want either of those features for this to work. Those are good if it is just charging a battery, but in your use case, they will cause more cycling of the Titan battery, and even worse, if it allows the battery voltage to fall too far, it could end up hitting it with the 100 amps again. So without bench testing to see how it will respond, this is a science experiment.
As for the Leaf battery setup, if you still want to use them...
You have a few options for configuring the battery bank. If you want to end up with a roughly 48 volt 14S the best you can do it use 42 modules and have 6 spares. To make them line up nice like Ampster's picture, it would be dropping out either 6 of the A type or 6 of the B type. You end up with 7 stacks like in that picture, with each stack of 7 alternating A type and B type. I don't know which is which, but let's say "A" has the + on top and the - on the bottom. The the "B" would have the - on top and the + on the bottom. The first 6 modules go just like that, but then the bottom buss bar gets jumped to the next group of 6 that look just lie that, but have the opposite polarity. Then the next groups top buss bar goes to the next group of 6.
If you start with 6 "A modules, then you have 6 "B", then 6 more "A", 6 more "B" , 6 more "A", 6 more "B", and finally the last 6 "A" and you are left not using the last 6 "B"'s. AAAAAABBBBBBAAAAAABBBBBBAAAAAABBBBBBAAAAAA
The first module buss bar hitting just 6 is the full pack negative, and the last module Buss bar hitting 6 is the full pack positive. Each BMS lead will but a buss bar. Full negative is either lead 0 or 1- depending on hos the BMS is labeled. Then the fist middle bar from there is cell 1+ then the large buss bar from module bank 1 to module bank 2 is actually Cell 2+. The next middle bar is Cell 3+. Next large bar from module 2 to module 3 is the Cell 4+. And you just repeat the pattern just like the original video you linked with 7 modules, only each module is actually a stack of 6 modules bussed in parallel to act as a single much larger module.
Having all 42 modules in one straight string is easy, but it does get to about 7 feet long. Think about where you want to put it and how it is going to fit. You can also break is at the junction between the 3rd and 4th or the 4th and 5th and fold it back bu using a cable instead of a straight buss bar for that junction, but it must be at split between the groups of 6. So you have a line of 4 groups and a line of 3 groups.
AAAAAABBBBBBAAAAAABBBBBB
AAAAAABBBBBBAAAAAA
Something like that.
If you do it with 2 BMS units, it would be 2 strings using groups of 3 modules.
AAABBBAAABBBAAABBBAAA
BBBAAABBBAAABBBAAABBB
Doing it like this, you could also end up with 3 spare "A" modules and 3 spare "B" modules. Just make sure to watch the + and - and keep the strings all in the right order.
I did a bit of thinking towards how this might all work.
Yes. You will need one charge controller that will take the solar panels and properly charge the Leaf batteries at your desired current and voltage limits. It will seek maximum power and always just try to top out the battery bank.
Then you need to feed that energy down to the Titan 21 to 29.6 volt battery bank. A proper DC to DC battery charger would be ideal, but I did not have any luck last night trying to find one designed for that purpose for these voltages at a decent current. Using a solar charge cntroller is not ideal, but knowing how some of the cheaper MPPT ones work, there is a good chance it will fall back to the set battery charge current on the output side. But there is also a problem on that. Let's say the batter in the Titan is low for whatever reason. If you use a charge controller that is set to truly charge up a 24 volt LFP pack, it will want to pull it up to 29.6 volts at the set current. You want to be able to use full power of th Titan inverter, so you set that current at 100 amps, but the inverter is not pulling much at the moment. This setup will push almost the full 100 amps into the relatively small battery in the Titan. That will likely destroy the batteries. For safety, I think the voltage will need to be set a little lower, and you should ensure the Titan's internal battery starts ABOVE the voltage set in the charge controller before connecting the system and turning it on. This way, the charge controller should be in a limited current mode as it thinks the battery is already at this now lowered absorb voltage. Let's say 26 volts should be safe. That would be 3.25 per cell, maybe go a little more, but this will have to be worked out on how well the system performs. The highest I would go is 27.2 which is 3.4 per cell. Any higher would hold the cells up to where they are being stressed. If the Titan is fully charged up, the cells go to 3.65 volts, but start to settle a bit. When you connect it, the Controller from the 48 volt pack sees a full battery and limits the current low. You start to pull current and the Titan battery voltage starts to drop. Ideally, the charge controller will see this and start to supply current. It will ramp up the current either to the set limit, or until the voltage hits the absorb setting where it should reduce current again. In a perfect world, the charge controller will just put out the right current to feed the load while holding the Titan battery at the fixed voltage.
Here is the other problem using a solar charge controller like this....
If it is actually a good charge controller, it will have time limits for the absorb mode, and it might force a wait time or a low voltage point where it will go back into charge mode. You don't want either of those features for this to work. Those are good if it is just charging a battery, but in your use case, they will cause more cycling of the Titan battery, and even worse, if it allows the battery voltage to fall too far, it could end up hitting it with the 100 amps again. So without bench testing to see how it will respond, this is a science experiment.
As for the Leaf battery setup, if you still want to use them...
You have a few options for configuring the battery bank. If you want to end up with a roughly 48 volt 14S the best you can do it use 42 modules and have 6 spares. To make them line up nice like Ampster's picture, it would be dropping out either 6 of the A type or 6 of the B type. You end up with 7 stacks like in that picture, with each stack of 7 alternating A type and B type. I don't know which is which, but let's say "A" has the + on top and the - on the bottom. The the "B" would have the - on top and the + on the bottom. The first 6 modules go just like that, but then the bottom buss bar gets jumped to the next group of 6 that look just lie that, but have the opposite polarity. Then the next groups top buss bar goes to the next group of 6.
If you start with 6 "A modules, then you have 6 "B", then 6 more "A", 6 more "B" , 6 more "A", 6 more "B", and finally the last 6 "A" and you are left not using the last 6 "B"'s. AAAAAABBBBBBAAAAAABBBBBBAAAAAABBBBBBAAAAAA
The first module buss bar hitting just 6 is the full pack negative, and the last module Buss bar hitting 6 is the full pack positive. Each BMS lead will but a buss bar. Full negative is either lead 0 or 1- depending on hos the BMS is labeled. Then the fist middle bar from there is cell 1+ then the large buss bar from module bank 1 to module bank 2 is actually Cell 2+. The next middle bar is Cell 3+. Next large bar from module 2 to module 3 is the Cell 4+. And you just repeat the pattern just like the original video you linked with 7 modules, only each module is actually a stack of 6 modules bussed in parallel to act as a single much larger module.
Having all 42 modules in one straight string is easy, but it does get to about 7 feet long. Think about where you want to put it and how it is going to fit. You can also break is at the junction between the 3rd and 4th or the 4th and 5th and fold it back bu using a cable instead of a straight buss bar for that junction, but it must be at split between the groups of 6. So you have a line of 4 groups and a line of 3 groups.
AAAAAABBBBBBAAAAAABBBBBB
AAAAAABBBBBBAAAAAA
Something like that.
If you do it with 2 BMS units, it would be 2 strings using groups of 3 modules.
AAABBBAAABBBAAABBBAAA
BBBAAABBBAAABBBAAABBB
Doing it like this, you could also end up with 3 spare "A" modules and 3 spare "B" modules. Just make sure to watch the + and - and keep the strings all in the right order.
Ampster
Renewable Energy Hobbyist
I agree there are some risks and I do not know charge controllers like @GXMnow does. and no one has chimed in with any better ideas.
If we want to do some outside the box thinking in terms of trying to look long term here are a couple of ideas or variations on the ideas @GXMnow suggested:
If we want to do some outside the box thinking in terms of trying to look long term here are a couple of ideas or variations on the ideas @GXMnow suggested:
- Sell the Leaf modules and buy some LFP batteries that could be wired in parallel with your existing pack in the Titan. You would still need a charge controller and a BMS but there is greater certainty that solution would work and you would be dealing with new LFP batteries and might be able to be sized for your needs. We could work through the numbers but LFP batteries are less than $125 per kWh. I see Leaf modules on Craigslist for $50, so you might be able, with some effort, reduce your risk, have less parts and less space taken up with batteries because the LFP are more compact.
- Sell the Titan and buy a 48 volt inverter that would work with the Leaf modules. The Titan is backordered and there may be a market for a slightly used model. You could easily find an Inverter, and maybe one with a charge controller and shore power. You would only commit if you had a buyer for the used Titan. This does not reduce the risk that is inherent in the used Leaf modules as I have discovered over the past 4 years using Leaf modules.
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where can you buy LFP for less than $125 per Kwh? What are the main risks to the leaf battery's that you have encountered?
Ampster
Renewable Energy Hobbyist
I have purchased forty four 280 Ahr cells from China through Alibaba from 3 different vendors over the past five months. My last purchase of 8 cells was for $850 which is 7 kWh. Lots of threads here.
The Leaf batteries are used and you never know if that car was in a hot environment like Phoenix where the Leaf batteries
suffered serious range loss. If you have modules from different vintage vehicles they could have significant differences in capacity. The weakest module will limit the capacity of the pack. There is some advantage putting many modules in parallel like I did with my Frankenpack but long term you will see big variations in voltage as you approach the knees of the charge discharge curve.
Would you mind dropping a link to the cells you bought?
Ampster
Renewable Energy Hobbyist
The first one was a complete pack that I had to disassemble myself. It came out of some garage in East LA. I bought four from a guy in Vegas but I think he is out of cells or out of business. The last group were the best and this is a guy in Healdsburg CA just 30 miles north of me. Here is his CL ad:
Nissan Leaf Batteries & EV Systems, Sparrow - auto parts - by owner...
Nissan Leaf Batteries for your Sparrow or other EV System Project. Yes we have Leaf Batteries$ 4...
sfbay.craigslist.org
If he is getting $100 for 500 Watt hour modules that is $200 per kWh and that is why I decided to not spend more money to expand my pack when I can get new ones for less. I am going to list mine for $50 on CL and the better ones with tested capacity maybe here for a little more.
where did you order those bus bars from?
Ampster
Renewable Energy Hobbyist
It was six years ago so I do not remember the exact source. I have used online metals, McMaster Carr and maybe an ocassional Ebay vendor.
Haven't heard from you in a while. I assume you settled on a strategy for your build?
Yes, I ended up selling the Titan and just bought a charge controller and 5000w PSW inverter to use on the Nissan leaf battery's. Now I am unsure which bms to use, I was looking at Daly smart BMS 14s 150a but it says the 18650 Li-ion battery pack will stop charging when its voltage reaches 4.25V and stop discharging when its voltage reaches 2.7V. Is this okay since each leaf module is essentially 2 batteries connected in series and 2.7 would be a good cutoff voltage of half the module? or is the cutoff voltage way too low since the nissan leaf module sits around 8 volts?
Ampster
Renewable Energy Hobbyist
You have to think of a Leaf module as two batteries in series. That is why in the earlier picture I posted the thin middle buss bar is only used for the BMS wire. It represents internally where the positive of cell #1 connects to the negative of cell #2. It doesn't actually carry much current and could be even thinner or just wire if you wanted to save time. You do need to connect the middle buss bar to the same number of terminals as the larger current carrying bars. That way you get cell group level monitoring rather than module level monitoring on your BMS. I don't know of any BMSs that can do module level monitoring because the voltages are so high so that comment is moot.
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GXMnow
Solar Wizard
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The BMS high and low voltage cut off is just there as a safety if a cell gets too far out of balance. You should have the Charge controller stop at your desired full voltage, and the inverter should shut down before the battery goes too low. These limits should be well inside the extreme limits of the BMS protection. For a 14S (7 leaf modules) you should keep the pack between 3.1 x 14 = 43.4 volts and 4.1 x 14 = 57.4 volts and the cells should last a good long time.
Since I am running in AC coupled, I have my inverter shut off a bit early at 49 volts now. This way, if I am in a power failure, I can always lower the voltage and get the inverter back online when the sun is up to get the system charging again. If I let my battery run too low at night, it won't be able to start up and create the "local grid" for the micro inverters to sync up and provide power. This is not as much of a concern for a DC coupled system. But in any case, you should never depend on the BMS to be your charge controller. It is a protection device for when something is going wrong. If you have a weak cell it could top out during charge long before the others get charged past 80%, and on discharge, that weak cell could go completely dead while the rest of the cells are still at 40% charge. If you use the numbers I posted above, it looks like this.
One cell hits 4.25 volt BMS shut off, the other 13 cells are still at just 4.058 volts and the charger is still charging. Oops.
One cell runs down to 2.7 volt BMS shut down, but the rest are still at 3.14 volts with the inverter still running. Oops
As long as the cells stay balanced, the BMS just balances the cells while the charge controller and inverter manage the full pack voltage.
Since I am running in AC coupled, I have my inverter shut off a bit early at 49 volts now. This way, if I am in a power failure, I can always lower the voltage and get the inverter back online when the sun is up to get the system charging again. If I let my battery run too low at night, it won't be able to start up and create the "local grid" for the micro inverters to sync up and provide power. This is not as much of a concern for a DC coupled system. But in any case, you should never depend on the BMS to be your charge controller. It is a protection device for when something is going wrong. If you have a weak cell it could top out during charge long before the others get charged past 80%, and on discharge, that weak cell could go completely dead while the rest of the cells are still at 40% charge. If you use the numbers I posted above, it looks like this.
One cell hits 4.25 volt BMS shut off, the other 13 cells are still at just 4.058 volts and the charger is still charging. Oops.
One cell runs down to 2.7 volt BMS shut down, but the rest are still at 3.14 volts with the inverter still running. Oops
As long as the cells stay balanced, the BMS just balances the cells while the charge controller and inverter manage the full pack voltage.
great! so for the 42 modules I will be running in 7s6p (14s6p) the daly BMS in the link below should work well? or would you recommend a different brand? I have heard mixed reviews from daly saying you can only get 50-70% of the advertised amperage.
https://www.amazon.com/DALY-Battery...0+amp+bms&qid=1607717830&s=electronics&sr=1-2
Ampster
Renewable Energy Hobbyist
I don't think any of the FET based BMSs should be run at more than 50 percent of rated current. I am using them on 12 volt packs but for anything approaching 100 Amps I prefer contactors. Others prefer SSRs. I forgot what your use case was. RV or Van?
It is a Bus, what is the difference between Fet, contactors and ssr's?
Ampster
Renewable Energy Hobbyist
FET is a electronic switching device sometimes called a MosFET. A contactor is a more expensive type of Mechanical relay and a SSR is a solid state relay. If your loads are less than 100 Amps I think you can get by with a BMS that controls everything with FETS. Most people recommend sizing a BMS for 50% use so buy one with 200 Amp capacity. Earlier you said you had a 5000 W inverter and my calculations are based on that at full throttle pulling 105 Amps.
Do you put the Bus bars on in any particular order?
GXMnow
Solar Wizard
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The only thing you need to be very careful about is when you connect cells in parallel. You have to be sure that they are very close to the same resting voltage before a parallel connection, otherwise, the higher voltage cell will discharge into the lower voltage cell. And the current can become very high and possibly damage the lower voltage cell from excessive charge current. There are also "A" and "B" modules that have the + and - terminals on opposite ends. double check with a meter before putting on a buss bar to ensure you have the correct polarity cells before putting on the buss bar. How many modules are you going to use? How many in S and how many in P? Are they all "A" or all "B" style? You can flip over a module to use a "B" in place of and "A" but the spacing may be a bit different. Once you have them physically arranged how you want them, you can plan out the series and parallel connections, and verify them all with a meter. Then you can start connecting the buss bars. You can parallel all the negative terminals (or positives) but not both yet. Then check the cell voltages, and check between the posts of the cells being connected. If cell voltages are different in a P connection, you need to charge the lower and/or discharge the higher to bring them close before making the connection. One easy trick is to use a few incandescent tail light bulbs as a high power low ohm resistor. If it lights up bright, the cells are in the wrong polarity, don't connect them, figure out where you went wrong. If the cells are only 0.5 volt different, the bulbs might not light at all, but they will pull current and push power from the higher cell to the lower one. Check it with a meter, and once the difference is below 0.03 volts or so, you should be able to solidly connect them together with the buss bar. Good cells can be as low as 0.003 ohms of internal resistance. That would mean a current of 10 amps at just a 0.03 volt difference between cells. That is acceptable, and the cell charge levels should then balance out pretty quick. But if the cell voltage was different by 0.3 volts, then it would be 100 amps. Not good.
Once all of the buss bars are connected, use the meter again to verify the voltages and make sure that each cell group adds about the same voltage to the pack total. If one group is reverse polarity, it will show up again in this test. Black meter lead on pack (-) connection, first cell measures around 3.8 volts, each cell up the chain should go up about that much. cell 2 = 7.6 volts, cell 3 = 11.4 volts, cell 4 = 15.2 volts and on up the chain. The Leaf modules are already in a 2S internally, so the center post of the first module is cell 1, and the positive post on the first module is cell 2. Seven modules in series makes up a 14S 48 volt battery bank. At 100% charge, it will measure up to 58.8 volts, and fully discharged will come down to about 42 volts. Once you are sure all of the buss bars are properly connected, then you can add the balance leads and connect them to the BMS and/or balancer module. Each balance has it's own instructions, but most want the high current (-) lead connected first, then connect the cells from the cell 1 (-) and then the (+), then cell 2 (+), then cell 3 (+) etc. until all cells are connected in the right order. The balance cable usually plugs into the BMS. Most connect all the cell leads with it unplugged from the BMS, and then plug the connector in after the cells are verified in the correct order once again. Follow your BMS's instructions.
Once all of the buss bars are connected, use the meter again to verify the voltages and make sure that each cell group adds about the same voltage to the pack total. If one group is reverse polarity, it will show up again in this test. Black meter lead on pack (-) connection, first cell measures around 3.8 volts, each cell up the chain should go up about that much. cell 2 = 7.6 volts, cell 3 = 11.4 volts, cell 4 = 15.2 volts and on up the chain. The Leaf modules are already in a 2S internally, so the center post of the first module is cell 1, and the positive post on the first module is cell 2. Seven modules in series makes up a 14S 48 volt battery bank. At 100% charge, it will measure up to 58.8 volts, and fully discharged will come down to about 42 volts. Once you are sure all of the buss bars are properly connected, then you can add the balance leads and connect them to the BMS and/or balancer module. Each balance has it's own instructions, but most want the high current (-) lead connected first, then connect the cells from the cell 1 (-) and then the (+), then cell 2 (+), then cell 3 (+) etc. until all cells are connected in the right order. The balance cable usually plugs into the BMS. Most connect all the cell leads with it unplugged from the BMS, and then plug the connector in after the cells are verified in the correct order once again. Follow your BMS's instructions.
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