Lithium battery C-rate question

[newhaul]

Originally Posted by Dockhead

In Europe, a lot of folks use these guys:


https://www.ev-power.eu/Winston-40Ah-200Ah/

A serious company with real support, selling the major brands: Winston, CALB, Sinopoly, and not mystery no-name cells buried in some box. Roughly $400 U.S. per kW/h for the cells.


I think it's dangerous wishful thinking, to believe that just because it looks like a lead battery, that you can just hook it up and use it like one. I think one had better start with a clean sheet of paper, especially that paper which is in one's own mind.

just like mainesail says take everything you know about lead batteries and throw it out .

I should have taken a bit more time I can get calb cells 400 ah for $285 U.S. Plus shipping factory direct.

[Jatar]

Originally Posted by Dockhead

As far as I can tell, those batteries, cost more than $3000 each in the U.S. -- https://www.batterypete.com/big-batt...-sb12v160e-zc/. So you're talking about $36,000 of batteries?


Most people trying to do a system like this, like everyone actually, would buy the raw cells at $1.20 per a/h at 3.2v, or whatever -- so $9000 or so for the cells, plus something for a proper BMS which remains and can be used with replacement cells should that be necessary.



Is there any particular reason why you want the batteries to be pre-packaged into lead-like units of 12v nominal at three times the cost? Lithium is very different from lead and needs a different kind of infrastructure. Trying to imitate lead form-factors and package the infrastructure into the same box with the cells seems like an inefficient approach to me. Especially if you're doing it for electric propulsion so you don't have any existing lead infrastructure you are trying to reuse.

I'm not planning on the SuperBs if I can help it. Those are just one of the batteries Oceanvolt recommends for their SD 15s. I'm currently looking for a better option. As I mentioned, I'm looking at Green Orca 1050s, and other options.

[Jatar]

Also, I should mention, I'm not looking for a DIY setup, I want a complete battery system, something like this:

Green Orca 1050
• 505 x 540 x 325 mm (H x D x W)
• Lloyd’s certified
• 52 Volt, 200Ah
• 10.5kWh at 75 kg.
• 200A/1C nominal charge, @23 ±3°C
• 300A/1½C nominal discharge, @23 ±3°C
• 600A/3C maximum discharge,
<10 sec., > SOC 50%
• Stack up to Megawatts and 1,000 Vdc
• Unique BMS with advanced active cell balancing
• NMEA 2000 based CanBus communication
• Designed for marine application, IP65
• Warranty 5,000 cycles at 80% DOD or 10 years
• No electrical or mechanical maintenance

I'm not on a tight budget, so a quality battery is more important to me than saving money. Certainly, I'd like to save money, but that is a secondary consideration.

[john61ct]

Originally Posted by Dockhead

As far as I can tell, those batteries, cost more than $3000 each in the U.S. -- https://www.batterypete.com/big-batt...-sb12v160e-zc/. So you're talking about $36,000 of batteries?

Yes, that is normal for this size capacity, in an engineered packaged system.

Yes I personally would not buy at that level "A".

But others do, and that's fine.


Then you have those who **really** want to save money, or sell on to others at a markup,

and don't believe there are huge differences in quality,

or don't want optimal longevity.

So just pick vendors based on price through eBay, Ali, Walmart, Amazon marketplaces.

I personally would not buy at that level "E", but again, that's fine, it's their money.

My level, call it "C", requires a fair bit of tech knowledge, but if successful, IMO will achieve at least as great longevity as the much more expensive A level.

Which IMO with drop-ins or "cheap" level E, that level will very likely not be reached, but then it might take say 3-6 years to find out.

[john61ct]

Then, you also get the **huge** differences between propulsion and gentler House usage.

Which in itself will cut longevity by 50% or 80%.

And requirements for high density often dictate LI chemistries other than LFP, thus requiring stronger engineering of BMS functionality and Thermal Management Systems, often liquid-cooled.

Really an entirely different market segment, except for the DIY-EV crowd.

[newhaul]

Originally Posted by john61ct

Yes, that is normal for this size capacity, in an engineered packaged system.

Yes I personally would not buy at that level "A".

But others do, and that's fine.


Then you have those who **really** want to save money, or sell on to others at a markup,

and don't believe there are huge differences in quality,

or don't want optimal longevity.

So just pick vendors based on price through eBay, Ali, Walmart, Amazon marketplaces.

I personally would not buy at that level "E", but again, that's fine, it's their money.

My level, call it "C", requires a fair bit of tech knowledge, but if successful, IMO will achieve at least as great longevity as the much more expensive A level.

Which IMO with drop-ins or "cheap" level E, that level will very likely not be reached, but then it might take say 3-6 years to find out.

perhaps you should actually purchase and use them in an application prior to making any other statements concerning the technology

[newhaul]

Originally Posted by john61ct

Then, you also get the **huge** differences between propulsion and gentler House usage.

Which in itself will cut longevity by 50% or 80%.

And requirements for high density often dictate LI chemistries other than LFP, thus requiring stronger engineering of BMS functionality and Thermal Management Systems, often liquid-cooled.

Really an entirely different market segment, except for the DIY-EV crowd.

and you have acquired this knowledge how?

[jonase]

I have only heard good things about Super-B. Many other good battery manufacturers such as Lithonics, BattleBorn etc don't deliver to Europe.

Stick with LFP/lifepo4 if you don't want to have a fire risk.

The C rating limitation in charge and discharge is often related to how much amps the relays etc in the internal BMS can handle. Super-B has one of the better built BMS's that can actually handle higher Amps than many other internal BMS systems e.g. Victron.

A very general recommendation regarding C rating is to stay away from the max values.. Many LFP cells has the recommendation of 0.5 C as Optimal discharge current and Optimal charging current.

The max values are often 10C as Max discharge current and 3C as Max charging current. But please stay away from those values!

With these values you will get the following values for the Super-B:
Optimal discharge current: 240Ah@48V ((3 x 160 in parallel) x (4 packs in series))
Optimal charge current: 240Ah@48V ((3 x 160 in parallel) x (4 packs in series))

Always do the parallel connection first! You want to use a 3P4S configuration of your battery e.g. parallel connect three batteries first to get packs of 480Ah@12V. Then you do the serial connection to get 480Ah@48V.

By doing this you will keep the packs connected in parallel balanced. It's the serial connections that create the imbalance and the fewer serial connections the better.

A 3P4S (parallel connection first, then serial connection) is a fairly common solution when building larger 12V battery packs with individual LFP cells.

[Jatar]

Originally Posted by jonase

I have only heard good things about Super-B. Many other good battery manufacturers such as Lithonics, BattleBorn etc don't deliver to Europe.

Stick with LFP/lifepo4 if you don't want to have a fire risk.

The C rating limitation in charge and discharge is often related to how much amps the relays etc in the internal BMS can handle. Super-B has one of the better built BMS's that can actually handle higher Amps than many other internal BMS systems e.g. Victron.

A very general recommendation regarding C rating is to stay away from the max values.. Many LFP cells has the recommendation of 0.5 C as Optimal discharge current and Optimal charging current.

The max values are often 10C as Max discharge current and 3C as Max charging current. But please stay away from those values!

With these values you will get the following values for the Super-B:
Optimal discharge current: 240Ah@48V ((3 x 160 in parallel) x (4 packs in series))
Optimal charge current: 240Ah@48V ((3 x 160 in parallel) x (4 packs in series))

Always do the parallel connection first! You want to use a 3P4S configuration of your battery e.g. parallel connect three batteries first to get packs of 480Ah@12V. Then you do the serial connection to get 480Ah@48V.

By doing this you will keep the packs connected in parallel balanced. It's the serial connections that create the imbalance and the fewer serial connections the better.

A 3P4S (parallel connection first, then serial connection) is a fairly common solution when building larger 12V battery packs with individual LFP cells.

This is actually why I started this thread in the first place. Oceanvolt SD 15 motors pull over 300 Ah at full speed, and I will have two. Therefore, I need my batteries to be able to discharge at 600 Ah (minimum). Your listing of 240 Ah discharge would make these SuperBs woefully below my needs.

Hence, I was asking about C-rates when batteries are in series and parallel configurations to see if by adding more batteries (configured properly) I can get the 600 Ah discharge I need. And, this needs to be continuous, not burst (in case of an extended emergency, not regular use).

My current understanding (from other replies) is that if I get a battery with a 1C discharge rate, and I configure them to be 600Ah @48v, I would have what I need. Of course, I'd prefer a 2C discharge rate so that I'm not maxing out the battery discharge rate.

[Montanan]

Originally Posted by Jatar

This is actually why I started this thread in the first place. Oceanvolt SD 15 motors pull over 300 Ah at full speed, and I will have two. Therefore, I need my batteries to be able to discharge at 600 Ah (minimum). Your listing of 240 Ah discharge would make these SuperBs woefully below my needs.

Hence, I was asking about C-rates when batteries are in series and parallel configurations to see if by adding more batteries (configured properly) I can get the 600 Ah discharge I need. And, this needs to be continuous, not burst (in case of an extended emergency, not regular use).

My current understanding (from other replies) is that if I get a battery with a 1C discharge rate, and I configure them to be 600Ah @48v, I would have what I need. Of course, I'd prefer a 2C discharge rate so that I'm not maxing out the battery discharge rate.

Jatar, you have correctly identified the crux of the matter as to the SD15 machines require very high amperage draw and your power demands is for two such machines operating at maximum power. The inherent weak point of the SD15 drives is that they operate at a ridiculously low 48 DC voltage, hence are slow machines operating at high amperage. Moderate and high power traction / propulsion motor applications favor high voltage / high speed machines and much lower amperage. The SD15 architecture of motors is upside down thinking. I strongly recommend you pursue machines that will operate at far higher DC supply voltage, say 10X or higher, 480 volts plus which is what one will find on commercial eMarine and EVs. The SD15 machines are basically operating at legacy golf cart voltage schemes, which makes them fundamentally comparatively inefficient, large, heavy, expensive. The SD15 drive is essentially nothing more than a PM motor stuck [likely vertically mounted as to its output shaft] linked to a simple lower end assembly to make a "saildrive", albeit a saildrive with very little gear reduction ratio.

[john61ct]

Nit pick:

Ah is quantity, storage capacity or energy used per time unit, while current amps is the instantaneous rate.

So emergency use of that motor requires a continuous rate of 600A (not Ah).

Which would be a 2C discharge rate from a 300Ah bank, or a 0.5C rate from a 1200Ah bank.

LFP would be fine at 2C once in a while, just not healthy to make a habit of it.

And of course that would empty the bank in well under 30min.

If BMS is the limiting factor, could be bypassed for discharge, use a fuse cor overcurrent / short protection, still use the BMS for all the other protective functions.

Not advising that though, better if you can afford to, keep paralleling to build Ah as above, gives more range too.

But don't forget your genset then needs to run for a very long time to refill the bank, which then leads to a true hybrid setup, which costs a lot of inefficiency, for what purpose again?

[Jatar]

Originally Posted by john61ct

Nit pick:

Ah is quantity, storage capacity or energy used per time unit, while current amps is the instantaneous rate.

So emergency use of that motor requires a continuous rate of 600A (not Ah).

Which would be a 2C discharge rate from a 300Ah bank, or a 0.5C rate from a 1200Ah bank.

LFP would be fine at 2C once in a while, just not healthy to make a habit of it.

And of course that would empty the bank in well under 30min.

If BMS is the limiting factor, could be bypassed for discharge, use a fuse cor overcurrent / short protection, still use the BMS for all the other protective functions.

Not advising that though, better if you can afford to, keep paralleling to build Ah as above, gives more range too.

But don't forget your genset then needs to run for a very long time to refill the bank, which then leads to a true hybrid setup, which costs a lot of inefficiency, for what purpose again?

Sorry, meant 600A. I'm planning an 800Ah battery bank, hopefully with a 2C discharge rate, and even then, the motors only use 600A, max. I don't plan to discharge at max rate for more than bursts, unless in an emergency situation, therefore, I can motor for much longer with less strain. I won't have to fill off of the geneset often since I will have 5kw of solar and the SD15 seroprops are very efficient at sailing regeneration (1kw per motor, when there is plenty of wind, not so good otherwise).

[Jatar]

Originally Posted by Montanan

Jatar, you have correctly identified the crux of the matter as to the SD15 machines require very high amperage draw and your power demands is for two such machines operating at maximum power. The inherent weak point of the SD15 drives is that they operate at a ridiculously low 48 DC voltage, hence are slow machines operating at high amperage. Moderate and high power traction / propulsion motor applications favor high voltage / high speed machines and much lower amperage. The SD15 architecture of motors is upside down thinking. I strongly recommend you pursue machines that will operate at far higher DC supply voltage, say 10X or higher, 480 volts plus which is what one will find on commercial eMarine and EVs. The SD15 machines are basically operating at legacy golf cart voltage schemes, which makes them fundamentally comparatively inefficient, large, heavy, expensive. The SD15 drive is essentially nothing more than a PM motor stuck [likely vertically mounted as to its output shaft] linked to a simple lower end assembly to make a "saildrive", albeit a saildrive with very little gear reduction ratio.

You keep talking about this, but I don't know of any system I could buy.
Please link an electric sail drive, which weigh under 150 lbs., each, and a battery bank at 480v, which weighs under 800 lbs., which is capable of driving those motors on a 13t catamaran for around 3 hours at about 7 knots. Then I might get interested.

[john61ct]

Even near the equator and without shading,

5kW of panels might yield 400Ah per day into that 48V bank.

And that's a lot of panel area, is the boat a purpose-built custom hull design?

[Jatar]

Originally Posted by john61ct

Even near the equator and without shading,

5kW of panels might yield 400Ah per day into that 48V bank.

And that's a lot of panel area, is the boat a purpose-built custom hull design?

Yes, the boat is being modified to handle the space needed for that much solar. 400A is what I expect, though your estimates aren't exactly what I've gotten from other people using solar. One rule of thumb is on a typical day (not right on the equator) you can expect about 5 hours of solar at the rated amount. (You're not getting that much for five hours, this is a rounding of all the daylight hours). That works out, on our setup, to be about 25kw, or slightly more than half our battery bank. However, I won't quibble with you. Even at 400Ah per day, at anchor, I can recharge my bank in two days, likely less since it will almost never be completely empty. If I'm sailing, with decent wind, cut that to one day since I regenerate at 2kw per hour, every hour, as long as there is that good wind. If not, I still get solar, for 400Ah. This is all I need to make the hybrid worthwhile (to me). However, we're getting off subject again, so I am going to stop. I've offered to start a thread to discuss the plusses and minuses of my hybrid setup, and am still willing to do so if you like.