Lithium battery C-rate question

[john61ct]

Of course would be great, but

I would advise restricting it to practical HowTo stuff, motors, gearing etc,

and not let it get the usual "whether EP is worthwhile or not" derail treatment.

[jonase]

@Jatar: Have you talked to Super B yet?

The Super-B SB12V160E-ZC battery is listed as a "hybrid drive" battery. My comment regarding 0.5C as the optimal discharge current is related to Winston/Thundersky prismatic cells. The recommended optimal discharge from some of the better manufacturers of prismatic LFP cells (check with the manufacturer for the specifics of the individual cells) are the following according to EV-Power:
Winston/Thundersky: 0.5C
CALB: 0.3C
Sinopoly: 0.3C

I think that Super-B is using cylindrical cells. I am not as familiar with prismatic cells but they might have a different optimal discharge. Super-B is listing their battery with 3C as Max. continuous discharge current e.g. max 480A for their 160Ah battery.

So maybe you would need less Ah to reach an optimal discharge rate from a battery with cylindrical cells compared to prismatic cells. But that is beyond my knowledge.

If the data from Super-B is correct you could connect 8 batteries similar to a 2P4S battery ((2 parallel connection x 160Ah@12V) x 4 serial connections) = 320Ah@48V

That would give you a 320Ah@48V battery pack with a max continuous discharge of 960A@48V. Would only last you around 30 minutes at full throttle if you need 600A@48V. But it is the smallest pack you could get that can handle 600A continuous discharge.

[Jatar]

Originally Posted by jonase

@Jatar: Have you talked to Super B yet?

The Super-B SB12V160E-ZC battery is listed as a "hybrid drive" battery. My comment regarding 0.5C as the optimal discharge current is related to Winston/Thundersky prismatic cells. The recommended optimal discharge from some of the better manufacturers of prismatic LFP cells (check with the manufacturer for the specifics of the individual cells) are the following according to EV-Power:
Winston/Thundersky: 0.5C
CALB: 0.3C
Sinopoly: 0.3C

I think that Super-B is using cylindrical cells. I am not as familiar with prismatic cells but they might have a different optimal discharge. Super-B is listing their battery with 3C as Max. continuous discharge current e.g. max 480A for their 160Ah battery.

So maybe you would need less Ah to reach an optimal discharge rate from a battery with cylindrical cells compared to prismatic cells. But that is beyond my knowledge.

If the data from Super-B is correct you could connect 8 batteries similar to a 2P4S battery ((2 parallel connection x 160Ah@12V) x 4 serial connections) = 320Ah@48V

That would give you a 320Ah@48V battery pack with a max continuous discharge of 960A@48V. Would only last you around 30 minutes at full throttle if you need 600A@48V. But it is the smallest pack you could get that can handle 600A continuous discharge.

My main problem with Super-B batteries is the price. They are something like $3,300 per battery. I am seeking a bank size of somewhere around 800Ah@48v. That requires 20 Super-B batteries. 20x $3,300 = $66,000 USD. Yikes. I'm not on a tight budget, but that's still really high. So, for now, I'm looking at other options, so no, I haven't contacted Super-B.

[jonase]

Originally Posted by Jatar

My main problem with Super-B batteries is the price. They are something like $3,300 per battery. I am seeking a bank size of somewhere around 800Ah@48v. That requires 20 Super-B batteries. 20x $3,300 = $66,000 USD. Yikes. I'm not on a tight budget, but that's still really high. So, for now, I'm looking at other options, so no, I haven't contacted Super-B.

If you build your own battery using LFP prismatic cells it will be cheaper. But will require a lot more work and you need to add a BMS. For me this was the only option due to size constraints in my 39 foot yacht. Where I am located (Europe) the Winston cells are popular due to their production quality and are easy to get. Have not heard anyone that have had any issues with these cells. I ended up with a LFP battery of 320Ah@12V in a 2P4S configuration in less space than what was used for 440Ah AGM Deep Cycle with a third of the weight.

Not sure where you are located. Seems like most people in the US prefer CALB since they are easier to get hold of in the US.

The largest Winston cells are 1000Ah@3.2V. If you build a 4P4S battery pack using those cells you would end up with a 1000Ah@48V battery. The optimal discharge would be 500A@48V and maximum discharge of 10000A@48V. I assume that is close to what you would usually use assuming that you are not planning to run full throttle all the time.
https://www.ev-power.eu/Winston-40Ah...l-product.html

The cost would be around 20,000 USD for the 16 cells excluding BMS, connectors, relays etc. Would recommend the Orion BMS rather than the BMS123 since BMS123 is not really optimal for a marine environment.

If you would go this route instead of Super-B I recommend that you join the facebook group regarding lithium batteries on boats and spend a lot of time doing research. Or get a professional that is experienced and a track record of building large LFP batteries.

https://www.facebook.com/groups/427372107686109

[css145hs]

Originally Posted by Jatar

My main problem with Super-B batteries is the price. They are something like $3,300 per battery. I am seeking a bank size of somewhere around 800Ah@48v. That requires 20 Super-B batteries. 20x $3,300 = $66,000 USD. Yikes. I'm not on a tight budget, but that's still really high. So, for now, I'm looking at other options, so no, I haven't contacted Super-B.

You’ve probably already been in contact with oceanvolt but if you go with a custom battery you’ll lose some of their charge control automation that prevents over charging the batteries. I don’t recall the exact specifics but it was enough that I wasn’t keen on manually controlling the regeneration.

[OceanPlanet]

"If you build a 4P4S battery pack using those cells you would end up with a 1000Ah@48V battery."

For 48V you mean 16S, not 4P4S.

For 48V stuff things get very tricky...should have pre-charge before connecting contactors, etc. Switches can weld closed, etc. Not recommended for the average DIY builder.

[Jatar]

Originally Posted by css145hs

You’ve probably already been in contact with oceanvolt but if you go with a custom battery you’ll lose some of their charge control automation that prevents over charging the batteries. I don’t recall the exact specifics but it was enough that I wasn’t keen on manually controlling the regeneration.

I will discuss any batteries I might be looking at with Oceanvolt, prior to making a choice. However, I already know I won't be building a DIY bank.

[jonase]

Originally Posted by OceanPlanet

"If you build a 4P4S battery pack using those cells you would end up with a 1000Ah@48V battery."

For 48V you mean 16S, not 4P4S.

For 48V stuff things get very tricky...should have pre-charge before connecting contactors, etc. Switches can weld closed, etc. Not recommended for the average DIY builder.

haha ;-)

Yes, I absolutely mean 16S. Was a bit late when I wrote my post.

[jonase]

Originally Posted by OceanPlanet

For 48V stuff things get very tricky...should have pre-charge before connecting contactors, etc. Switches can weld closed, etc. Not recommended for the average DIY builder.

The initial charge and top balance at 3.65V on the cells with a laboratory power supply and 16 cells in parallel would be quite a big task. 16000Ah@3.2V would take quite a while...

[smac999]

Charging at 1c. 480a at 48v. Good luck. You’d need a 30kw gen. And a lot of chargers.

[Jatar]

Originally Posted by smac999

Charging at 1c. 480a at 48v. Good luck. You’d need a 30kw gen. And a lot of chargers.

I plan on two, a 20kw and a 10kw, this gives me options (see below). However, I doubt I will choose to charge at 1C the vast majority of the time, it's too hard on the batteries. Most of the time I will charge at 8 to 10kw, most often while motoring, using the 20kw gen to send 6kw to each motor and the rest heads into the batteries. After a 75% discharge of the bank, this will take 3 - 4 hours to recharge them.

Of course, that is only during a long passage, and when there isn't sufficient wind. The rest of the time, I'll just charge off of solar and regen, or, while at anchor, just the solar (which will take two to three days, but who is in a hurry?)

If I'm at anchor and there is no sun, I'll use the 10kw gen. If I'm in an emergency, and really want to charge as fast as possible, I'll run both generators, for a total of 30kw. If either generator goes down, I can still use the other one until I get it fixed.

[john61ct]

Originally Posted by jonase

The initial charge and top balance at 3.65V on the cells with a laboratory power supply and 16 cells in parallel would be quite a big task. 16000Ah@3.2V would take quite a while...

No need to do the bulk charge at the low voltage.

Get the whole bank up to say 56V before breaking out the individual cells for top balancing.

Only need the manual PSU approach for the last few Ah. . .

With balance leads available, could split the bank in two, keep 8S units together and use a good quality hobby-type charger on each half.

[nebster]

I have a 36kWh bank for house loads. 53VDC effective pack voltage. 15kW of load, in theory. 11kW of charging, in theory. 20kW genset, in theory. In real life everything derates somewhat because of heat.

1) You will need a lot of copper to do all that charging you're describing, if you are using standard AC generator heads and converting down.

2) Do you have to use 48V motors? You could simplify some parts of the system substantially if you could run at higher voltage. (I don't know very much about DC propulsion.)

3) You mention diverting some of your generated power to the motors when moving. How will you make that DC power?

3b) Is the approach you are envisioning capable of providing that power even if the main lithium bank suffers a shutdown because of a fault? If not, I encourage you to look at a dual-bus design at minimum and preferably a multi-string (parallel pack) design for redundancy. Both require even more hardware and control, but completely losing propulsion sounds unacceptable.

4) You are a little sloppy with A, Ah, W, Wh, and other units. Don't take it personally, but you need to get un-sloppy and be crystal clear in your thinking and writing if you're going to be involved in engineering a system at this level. If you're going to pay someone else to do it, no big deal.

5) BMS, heat, contactors, sensors, interconnect, and overcurrent protection all get much more "involved" at these power, current, voltage, and C-rates. Sounds like fun, though.

[Jatar]

Originally Posted by nebster

1) You will need a lot of copper to do all that charging you're describing, if you are using standard AC generator heads and converting down.

A: I'm using DC generators.

2) Do you have to use 48V motors? You could simplify some parts of the system substantially if you could run at higher voltage. (I don't know very much about DC propulsion.)

A: I'm using Oceanvolt SD15 servoprop sail drives. No other viable options have been presented (of found), at the same weight, power, and regeneration capabilities.

3) You mention diverting some of your generated power to the motors when moving. How will you make that DC power?

A: Using a 20 kw DC generator, if battery power is not available.

3b) Is the approach you are envisioning capable of providing that power even if the main lithium bank suffers a shutdown because of a fault? If not, I encourage you to look at a dual-bus design at minimum and preferably a multi-string (parallel pack) design for redundancy. Both require even more hardware and control, but completely losing propulsion sounds unacceptable.

4) You are a little sloppy with A, Ah, W, Wh, and other units. Don't take it personally, but you need to get un-sloppy and be crystal clear in your thinking and writing if you're going to be involved in engineering a system at this level. If you're going to pay someone else to do it, no big deal.

A: (to 3b and 4): I am having the entire system professionally built, I am not a DIY builder. And yes, I have lots to learn. Part of that learning was asking about C-rates in these forums.

5) BMS, heat, contactors, sensors, interconnect, and overcurrent protection all get much more "involved" at these power, current, voltage, and C-rates. Sounds like fun, though.

A: I agree, sounds like fun.

[newhaul]

Cure is 48v dc genset .
A friend did that to his 38ft mono . Only a small Fla bank and a 5k military surplus 48v dc generator.
Like this would work

[url]https://polarpower.com/products/dc-generators/8080y-40205-diesel-dc-generator/[/url

You may need 2 on the cat.