Is that 138 kWh their remaining capacity or nominal rated when new?
Two electric unicycles + 140kWh of dead cells + Solar panels (Bayliner hybrid)
- Thread starter HOTOREL
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HOTOREL
XR Developer
Remaining. The original capacity of each module is 500W and 64Ah. The one I found they are tested with at least 41Ah left
yabert
Solar Enthusiast
With such a low power requirement, why don't power everything in 48V?
That will be way more easy and reliable.
Warpspeed
Solar Wizard
High dc voltage and salt water ?
The whole concept absolutely TERRIFIES me.
Two not insignificant dangers, electrolytic corrosion and electrocution.
The whole concept absolutely TERRIFIES me.
Two not insignificant dangers, electrolytic corrosion and electrocution.
justinm001
Solar Addict
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This is AWESOME please keep us informed!! Once my RV remodel is finished and we're bored of exploring the land I'm planning on getting an electric yacht or building my own.
HOTOREL
XR Developer
The thing is that for 48V 4kW is the maximum motor size powervise that you can install. In my case, I’m using this motor just because I already have it and it will help to do all the tests and collect enough data. The thing is that I don’t know anyone who would retrofit the power yacht of this type with electric power yet. So to build something you have to do some research. Plus using 100.8V (I don’t know why I mentioned 96V before…) allows me to scale up my system easily. There are so many cheap options up to 15kW which would be more than enough but again, we will see everything pretty soon. Because right now I already working on the battery for the tests
HOTOREL
XR Developer
Life is a dangerous thing. If you want to achieve something big - you should go out of your comfort zone.
And use technology to make everything safe
Edit:
P.S. I already have 130V DC from my solar panels and will have more than 200V when I finish my setup
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HOTOREL
XR Developer
Thanks for your kind words. More to come soon. Silent 60 is amazing but to unreal for us now. But we will see that will be in the future. Technoloy is already here so it is time to do something cool with it)
yabert
Solar Enthusiast
Yes, I understand. I'm also looking at a motor solution for a big sail boat and it's hard to stay at 48V if the need is 10-15kW continuous.
I would like to find a big 48V hub motor who turn less than 1000 rpm and output around 100 Nm continuous, but this is non existent.
About voltage, with 12S Leaf cells that give you around 45V nominal, so 90V total. Voltage range 72-100V
About your battery, can I suggest you a simple and reliable solution? Instead of building 24 batteries/24 BMS, please do you a favor and build 2 batteries with 2 BMS.
Based on 41Ah cells and 432 modules, you can connect 36 modules together to create one big 7.5V and 1476Ah modules. Then, connect 6 modules in series to create one 45V 1476Ah battery (12S and 66.4kWh).
Do this 2 time and add a simple 12S relay BMS to each battery.
And by the way, do your search, but Leaf cells have terrible degradation and many problem. So I suggest you to take your time and put your hands on better cells. There is plenty of EV at scrap yard and you will end to find something at good price for large battery (60-100 kWh).
Warpspeed
Solar Wizard
I will tell you a true story.Life is a dangerous thing. If you want to achieve something big - you should go out of your comfort zone.
And use technology to make everything safe
Edit:
P.S. I already have 130V DC from my solar panels and will have more than 200V when I finish my setup
Many years ago when I was still a young fella, I helped launch a small aluminium power boat from a sandy beach into salt water.
I was in the water up to my thighs (with wet hands) when I accidentally contacted 12 volts from the top of the exposed on board battery.
I received a hell of a belt, and I will never forget it.
These days I have a solar system with a 100 volt battery (thirty lithium cells) and regularly come into full contact with that, and never feel even a slight tingle.
I guess us old farts tend to have have very dry skin.
So laugh at me if you like, call me a wimp, a coward, or totally crazy.
But I am a retired power electronics engineer, very used to working around dangerous high voltages as part of my job.
That is not a problem, because I know where the dangerous voltages are. Electrocutions always come completely unexpected.
The idea of working and maintaining a system with 350 volts of dc in a salt water boat just scares the shit out of me.
I have no problems working with 350 volts dc on an EV or solar system in a dry environment.
Salt and damp changes everything.
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Hedges
I See Electromagnetic Fields!
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Consider two 48V battery banks wired in series. Place a bypass diode across each (reverse polarity diode, sized and heatsinked to carry 100% of current.) That should protect their BMS from over-voltage if they disconnect.
That gives you 96VDC.
Alternatively, parallel multiple 48V batteries. Connect three European 230V inverters as 3-phase. Feed output to VFD to power motor.
3x Sunny Island would be 18kW.
I think SolArk (check out Deye for 230V model) being 120/240V split-phase and supporting 120/208Y as well, could probably be wired for 240V to neutral.
Other inverters should work - to feed a VFD.
If you had 360V or so battery, that could feed VFD directly. I don't think you can get away with stacking 48V batteries that high, due to voltage rating of EMI components.
That gives you 96VDC.
Alternatively, parallel multiple 48V batteries. Connect three European 230V inverters as 3-phase. Feed output to VFD to power motor.
3x Sunny Island would be 18kW.
I think SolArk (check out Deye for 230V model) being 120/240V split-phase and supporting 120/208Y as well, could probably be wired for 240V to neutral.
Other inverters should work - to feed a VFD.
If you had 360V or so battery, that could feed VFD directly. I don't think you can get away with stacking 48V batteries that high, due to voltage rating of EMI components.
HOTOREL
XR Developer
You should check their website https://www.qsmotor.com/ I know at least a couple of motors with your requirements. And this is exactly why I am going with my motor from EUC (Electric Unicycle) because they have relatively low RPM (800-900 RPM max) and a lot of torque. The motor I have should provide more than 200Nm of torque. But again, we will see how it is going to all work together pretty soon.
Thank you also for your idea, but using only one BMS for the big battery has a lot of drawbacks. First of all, it is not ideal for BMS because it won't be able to manage each cell individually and this is exactly why you want to use BMS. If you have more than 2 cells connected in parallel in your battery pack it is already not good. In my case (when I have 24 BMS) I already have 4 cells connected in parallel so reducing the number of balancing wires will just make me throw my battery away as soon as a couple of cells are destroyed somewhere in the middle of this chain and I won’t be able to track them down at all. Plus when you have a lot of battery modules with each individual BMS you can lose or maintain some of the modules and still have power, while when you have only two batteries every error will leave you without power at all
And yes, I agree with you. If I will be able to find the better deal I will go with it but for now I don’t see any
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HOTOREL
XR Developer
Nobody wants to tell you crazy. But in your story, it was your mistake and the person who left the exposed terminals. It is the same if I put my fingers into the 120V socket, get an electrocution, and tell everyone how dangerous it is. I respect your experience and would really appreciate it if you would share your insides on how to make things even safer but for now, it all sounds like an off-topic. Everyone knows that electricity is dangerous.
P.S. I think I have to update my first post because for some reason everyone still thinking about 350V DC…
HOTOREL
XR Developer
Can you tell me more about using the diode to protect the BMS? I do not really get an idea of how it is possible. And yeah the trick with three inverters is pretty smart. I will think about it if I will go 230V or more but for now, I’m going to stay at 100.8V)
Warpspeed
Solar Wizard
What really surprised me was that 12 volts could even produce an electric shock at all.
The severity of it has remained vividly in my memory for over sixty years.
As I work with electricity, I have had numerous bites and tingles over the years, but that particular one I will never forget.
yabert
Solar Enthusiast
I know QS motor and their 12kW car hub motor is attractive. But spec and reality can be different. A sprint of few minutes in the rear of a motorcycle at 12kW is different of powering a boat at 12kW for hours.
Still, this 12 kW motor is probably a 4-6 kW motor at 48V.
Yes, but how long. A 1 kW bike hub motor can provide 1000Nm... for 2 sec before melting
Ha! really. Ok, I have to tell all the engineers from Tesla, GM, Ford, VW, LG chem, BYD, CATL and other they are idiot because they connect cells in parallel.
HOTOREL
XR Developer
This is exactly why I want to test it out. There is no data on who would ever try to do it.
I don't know about GM, Ford, and others but I studied how Tesla builds their batteries. I've had an internship there and they use the same ideology. They have groups of cells connected in parallel after those parallel groups connected in series in modules and after big modules connected in series into the whole battery pack. At the low level yes, they had to connect 30-70 cells to one balance wire but it was a physical limitation because they had to connect thousands of cells. They are going away from this with each new iteration but the main idea is the same they don't create two high-voltage batteries and just connect them together.
Warpspeed
Solar Wizard
How are these super powerful EV motors cooled ?
I have absolutely no idea, they do seem to be rather small for the power ratings.
I have absolutely no idea, they do seem to be rather small for the power ratings.
Hedges
I See Electromagnetic Fields!
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Bypass diodes in a PV panel prevent current from being pushed through, which would cause a large reverse polarity and blow them out.
BMS in series are fine until they try to disconnect. Typically, someone might have 4x 12V batteries in series for 48V. If one disconnects, the load pulls battery+ down to battery-. A BMS could have 36V from other batteries connected to its (12V) battery negative terminal. Its last cell would be at +48V. Other side of BMS FET would be at 0V, so FET sees -48V and will fail if not spec'd for that voltage.
My theory is that a reverse-biased diode across each battery & BMS assembly would prevent application of that volage. But it needs to be able to carry the current, if remaining 36V is applied to load. In your case, 2x 48V packs, so current if 48V feeds motor when one BMS disconnects.
Just an in-my-head design, but I think it is valid.
HOTOREL
XR Developer
I was thinking of disconnecting the load at all as soon as one of the batteries goes Into over-discharge protection. Because if there is one of the batteries triggers this protection it means all others will trigger it soon. It means that the battery is drained and I had to turn on the generator way before it happened. And in this case, I don’t need to deal with increased current for the rest of the battery because it will be already disconnected from the load
For now, I just think that I will charge my battery to 100% before heading somewhere, and as soon it reaches 50% I will run the generator to move it back to 80% and so on.
