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Discussion Starter · #1 ·
Hello, experts:

I've got an older Duffy Electric Boat with a 48V system using 8 X 6V GC2 FLA batteries rated at 220Ah in series. These batteries are getting close to end of life and are beginning to weaken, so I'm wanting to convert to LifePO4 (LFP) batteries to enjoy longer life, less maintenance, and reduced weight. The boating range provided by the current FLA battery pack is sufficient for my needs on an inland lake, and I live in South Carolina, so winter cold will not be a problem with the LFP batteries. The motor is a 48V 5hp DC motor, and the controller is a Zapi 350A 48V controller

At this point, I'm considering using 4 X 12V 105Ah LFP batteries in series from Lion Energy Lion Safari UT 1300 - Lion Energy These batteries have a 1344 Wh rating, which is similar to the 1320 Wh rating of the FLA batteries. Does this approach seem reasonable?

I have 2 additional questions or issues:

- Using 4 X 12V in series is essentially a "drop in" replacement for my boat, in terms of wiring, space and layout of batteries, etc. This works well for me from an installation standpoint, but I've also been told by another battery supplier that a single 48V battery is preferable, since the BMS's of 4 individual batteries in series will not necessarily charge and discharge the batteries equally. Is this a valid concern?

- I currently use a Delta Q charger with a Trojan T105 FLA charging profile, but I believe it has an AGM charging profile. Would this be an acceptable charger for the LFP batteries, especially considering the higher charging voltage of the AGM profile? I've recently acquired a Delta Q charger that is supposedly a lithium ion charger for EZGo golf carts, but I haven't yet been able to confirm the actual charging profile programmed into this charger. I'm not convinced that it's anything other than an AGM profile. Your thoughts on either charging approach?

Thanks very much for your advice and insight into my little project!
 

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These are made to be put in series of 4 a bit less than the 1320 Wh fla but more usable Wh . FLA even deepcycle doesn't like to be discharged much more than 60-80 % 792Wh-1056 Wh. 1280Wh @80%= 1024Wh
later floyd
PS buy a 48V LiFePO4 charger that allows you to set the voltage. set the voltage low for longevity higher if you need the extra range when needed.
 

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Discussion Starter · #3 ·
These are made to be put in series of 4 a bit less than the 1320 Wh fla but more usable Wh . FLA even deepcycle doesn't like to be discharged much more than 60-80 % 792Wh-1056 Wh. 1280Wh @80%= 1024Wh
later floyd
PS buy a 48V LiFePO4 charger that allows you to set the voltage. set the voltage low for longevity higher if you need the extra range when needed.
Thanks, Floyd ---- this is an interesting option. I assume that these do not carry a warranty of any kind?

In terms of your comment about the charger, when you say set the voltage low, exactly what voltage would you recommend?

Thanks for the response!
 

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At this point, I'm considering using 4 X 12V 105Ah LFP batteries in series from Lion Energy Lion Safari UT 1300 - Lion Energy These batteries have a 1344 Wh rating, which is similar to the 1320 Wh rating of the FLA batteries. Does this approach seem reasonable?
You would be cutting the total energy capacity in half, unless you mean that you would run two banks of 4 X 12V 105Ah LFP batteries in series each. Are you assuming that you can discharge the lithium-ion battery to twice the depth of discharge as the lead-acid? That may be an optimistic assumption.

- Using 4 X 12V in series is essentially a "drop in" replacement for my boat, in terms of wiring, space and layout of batteries, etc.
The 12V 105Ah LFP units are roughly similar in size to the GC2 lead-acid batteries, but if you are considering using four of them they would drop in, but would use half the space in a layout with half of the units. If you are considering two strings of four 12 V LFP units each, then the space is the same but the wiring interconnections are a bit different (which isn't a problem).

This works well for me from an installation standpoint, but I've also been told by another battery supplier that a single 48V battery is preferable, since the BMS's of 4 individual batteries in series will not necessarily charge and discharge the batteries equally. Is this a valid concern?
I think that BMS coordination is a valid concern. There are two solutions: a ~48 V battery (or more than one of them in parallel), or modules that connect to a central BMS. The central BMS approach is how EVs work, but I think that there are also some lithium-ion systems offered for solar and marine applications that work the same way.

While some LFP battery suppliers seem fixated on drop-in replacement for 12V lead-acid batteries (even though most applications would actually replace 6V GC2 batteries), others offer more sensible choices, including large ~24 V and ~48 V formats.

The size of the GC2 and other common batteries is determined by what a maintenance person can reasonably lift, solo. With the density of lithium-ion cells at about half of lead-acid, it would make sense to use larger (in dimensions and energy capacity) units of about the same weight, so this boat's battery could be in four units rather than eight. If they're all ~48 V, they would need to be 25 Ah to 50 Ah each (depending on your tolerance for depth of discharge) and connected in parallel (generally a bad idea, but maybe the way to go if forced to use independent BMSs). If you can lift 77 pounds and can arrange two large batteries in the space, you could even do it with just one or two units at 100 Ah each, such as the Dakota 48 V 96 Ah.

If you're shopping online and notice that some brands seem to be identical to other brands, don't be surprised - many North American brands are just generic units from China with house branding labels, and even those assembled here are typically built from the same cells and BMS units as other brands.
 

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You would be cutting the total energy capacity in half, unless you mean that you would run two banks of 4 X 12V 105Ah LFP batteries in series each. Are you assuming that you can discharge the lithium-ion battery to twice the depth of discharge as the lead-acid? That may be an optimistic assumption.
1320x4=5280Wh for the 48V FLA vs 1344x4=5376Wh for the 48V LFP

80% values FLA 4224Wh LFP 4300.8Wh
later floyd
 

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Thanks, Floyd ---- this is an interesting option. I assume that these do not carry a warranty of any kind?
I doubt tthey would offer a warranty. On the other hand you could buy 2 sets of 4 12V 100Ah batteries for less than the cost of 4 of the batteries you linked.
In terms of your comment about the charger, when you say set the voltage low, exactly what voltage would you recommend? 54.4V - 56V you don't gain much capacity from 2.4V-4V less than 10 % and you gain cycle life. as long as the Cells in the batteries are balanced there in no need to charge to 58.4V 14.6V per 12v battery.

Thanks for the response!
 

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Discussion Starter · #7 ·
You would be cutting the total energy capacity in half, unless you mean that you would run two banks of 4 X 12V 105Ah LFP batteries in series each. Are you assuming that you can discharge the lithium-ion battery to twice the depth of discharge as the lead-acid? That may be an optimistic assumption.

The 12V 105Ah LFP units are roughly similar in size to the GC2 lead-acid batteries, but if you are considering using four of them they would drop in, but would use half the space in a layout with half of the units. If you are considering two strings of four 12 V LFP units each, then the space is the same but the wiring interconnections are a bit different (which isn't a problem).

I think that BMS coordination is a valid concern. There are two solutions: a ~48 V battery (or more than one of them in parallel), or modules that connect to a central BMS. The central BMS approach is how EVs work, but I think that there are also some lithium-ion systems offered for solar and marine applications that work the same way.

While some LFP battery suppliers seem fixated on drop-in replacement for 12V lead-acid batteries (even though most applications would actually replace 6V GC2 batteries), others offer more sensible choices, including large ~24 V and ~48 V formats.

The size of the GC2 and other common batteries is determined by what a maintenance person can reasonably lift, solo. With the density of lithium-ion cells at about half of lead-acid, it would make sense to use larger (in dimensions and energy capacity) units of about the same weight, so this boat's battery could be in four units rather than eight. If they're all ~48 V, they would need to be 25 Ah to 50 Ah each (depending on your tolerance for depth of discharge) and connected in parallel (generally a bad idea, but maybe the way to go if forced to use independent BMSs). If you can lift 77 pounds and can arrange two large batteries in the space, you could even do it with just one or two units at 100 Ah each, such as the Dakota 48 V 96 Ah.

If you're shopping online and notice that some brands seem to be identical to other brands, don't be surprised - many North American brands are just generic units from China with house branding labels, and even those assembled here are typically built from the same cells and BMS units as other brands.
Yes, Brian, I am assuming that I can discharge the LFP battery to twice the depth of the FLA battery. You're right, that might be optimistic.

My current battery layout is two banks of four GC2's each, with one bank on the right and one on the left sides of the boat. Each bank of four batteries is below a seat. I was originally considering installing two 12V 100Ah LFP units below each seat on both sides, since the wiring is all there to connect these in series that way. I could easily double that to a total of 4 batteries on each side, but I'm not sure I need that much extra range.

I'm certainly considering the 48V battery option, but these tend to be fairly expensive. I at least have space below each seat for batteries the size of the Dakota 48V 96Ah. If I needed to add a second battery of this size, rather than connect them in parallel, I've also considered having the capability to independently switch between the two batteries. I believe this would solve any BMS issues, since each battery would charge and discharge independently.

Brian, thanks very much for your insightful response. This gives me plenty of food for thought.
 

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Discussion Starter · #9 ·
I doubt tthey would offer a warranty. On the other hand you could buy 2 sets of 4 12V 100Ah batteries for less than the cost of 4 of the batteries you linked.
Yes, I didn't see anything about a warranty. Yes, they are cheap, but I don't want to go through this project just to find out that the batteries fail in a short time and I have to end up replacing them all with something better. Thanks again for your response!
 

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My current battery layout is two banks of four GC2's each, with one bank on the right and one on the left sides of the boat. Each bank of four batteries is below a seat. I was originally considering installing two 12V 100Ah LFP units below each seat on both sides, since the wiring is all there to connect these in series that way.
...

I at least have space below each seat for batteries the size of the Dakota 48V 96Ah. If I needed to add a second battery of this size, rather than connect them in parallel, I've also considered having the capability to independently switch between the two batteries...
Although you're calling them "banks", they're all connected in series so it is functionally one bank split between two locations. The parallel 48 V lithium-ion batteries would functionally be two banks, with each bank consisting of a single battery.

If there are parallel banks or strings, I agree that it makes sense to be able to select one, or the other, or both, for reliability if nothing else. A car stranded at the roadside by battery failure is annoying; a boat adrift without power seems more serious to me.
 

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Discussion Starter · #12 ·
Although you're calling them "banks", they're all connected in series so it is functionally one bank split between two locations. The parallel 48 V lithium-ion batteries would functionally be two banks, with each bank consisting of a single battery.

If there are parallel banks or strings, I agree that it makes sense to be able to select one, or the other, or both, for reliability if nothing else. A car stranded at the roadside by battery failure is annoying; a boat adrift without power seems more serious to me.
Fortunately, I live on a 300 acre inland lake, so if I have a failure and end up adrift, I can call a neighbor for a rescue tow. I've done it before, but not because of a battery failure.......
 

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Discussion Starter · #16 ·
Okay, so after a lot of research and comments, I'm now considering a single 48V 150Ah NMC battery pack, 13S @ 4.2V, with a max of 54.6V to replace the FLA batteries in my Duffy Electric Boat.

My motor controller is a 48V Zapi SEM-1, which works well with my 5hp motor and current FLA batteries in the Duffy boat. Should I be concerned at all about the NMC battery providing 54.6V? Is this a risk for the controller, or are they generally able to handle this level of over-voltage?

Thanks in advance for your helpful comments!
 

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Okay, so after a lot of research and comments, I'm now considering a single 48V 150Ah NMC battery pack, 13S @ 4.2V, with a max of 54.6V to replace the FLA batteries in my Duffy Electric Boat.

My motor controller is a 48V Zapi SEM-1, which works well with my 5hp motor and current FLA batteries in the Duffy boat. Should I be concerned at all about the NMC battery providing 54.6V? Is this a risk for the controller, or are they generally able to handle this level of over-voltage?
The "48 volt" values for the original configuration is nominal, but the 54.6 V value of the NMC pack is maximum. Lead-acid cells are assumed to operate at 2.0 V per cell (that's the nominal value), but vary well above and below that as they are charged and discharged; similarly, a lithium-ion cell with NMC cathodes has a nominal voltage around 3.7 V/cell but varies in use up to over 4 volts.

So a "48 V" lead-acid battery has 24 cells in series (four cells in each of 6 boxes in the case of the original configuration) and will be at up to about 50 V fully charged and will be charged at up to several volts higher than that. The manufacturer of this pack has chosen 13S so that the nominal voltage will be about 48 V, and the maximum voltage will be within the range of a lead-acid "48 V" charger.

The controller is normally designed for at least the fully-charged voltage of a lead-acid battery of the stated nominal voltage, and to avoid problems should really be able to handle the maximum charging voltage of that battery (even though it might never be turned on at the same time as the charger).

Zapi still has a product web page for the SEM-1 (as a "legacy product", since they no longer make DC motor controllers). It has only vague specs, and links to an installation and user manual which still only refers to nominal voltages. You can draw your own conclusions from that - it looks to me as if they are not concerned enough about the input voltages that might be seen in a nominally 48 V system to warn about exposing the controller to charging voltage.
 

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Discussion Starter · #18 ·
The "48 volt" values for the original configuration is nominal, but the 54.6 V value of the NMC pack is maximum. Lead-acid cells are assumed to operate at 2.0 V per cell (that's the nominal value), but vary well above and below that as they are charged and discharged; similarly, a lithium-ion cell with NMC cathodes has a nominal voltage around 3.7 V/cell but varies in use up to over 4 volts.

So a "48 V" lead-acid battery has 24 cells in series (four cells in each of 6 boxes in the case of the original configuration) and will be at up to about 50 V fully charged and will be charged at up to several volts higher than that. The manufacturer of this pack has chosen 13S so that the nominal voltage will be about 48 V, and the maximum voltage will be within the range of a lead-acid "48 V" charger.

The controller is normally designed for at least the fully-charged voltage of a lead-acid battery of the stated nominal voltage, and to avoid problems should really be able to handle the maximum charging voltage of that battery (even though it might never be turned on at the same time as the charger).

Zapi still has a product web page for the SEM-1 (as a "legacy product", since they no longer make DC motor controllers). It has only vague specs, and links to an installation and user manual which still only refers to nominal voltages. You can draw your own conclusions from that - it looks to me as if they are not concerned enough about the input voltages that might be seen in a nominally 48 V system to warn about exposing the controller to charging voltage.
Thanks, Brian! Your conclusion is similar to my own-----I've looked through the Zapi manual for the SEM-1, and they actually mention to not run the motor when connected to a charger, which is probably a CYA statement. The reality is that I've run my boat's motor while tied to the dock and connected to the charger with no ill effects. So, I'm probably going to press ahead with the NMC battery within the next few weeks.

Thanks again for the insightful response!
 
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