Can lithium batteries be damaged by providing too much current?

[Privilege]

I'm in the process of replacing my 600ah AGM house bank and am considering lithium's. I note that many of the lithium batteries on the market have a maximum charge current of 50 amps. I have a Mastervolt 100 amp charger as well as a large solar panel array which, on a good day, can comfortably output in excess of 50 amps (Both my charging systems can be set for lithium's). Do these batteries 'pull' the current that they need for charging in the same way as lead-acid batteries or will they be damaged by the having too much current available?

I'm a lithium beginner so any advice is appreciated.

[Maine Sail]

Originally Posted by Privilege

I'm in the process of replacing my 600ah AGM house bank and am considering lithium's. I note that many of the lithium batteries on the market have a maximum charge current of 50 amps. I have a Mastervolt 100 amp charger as well as a large solar panel array which, on a good day, can comfortably output in excess of 50 amps (Both my charging systems can be set for lithium's). Do these batteries 'pull' the current that they need for charging in the same way as lead-acid batteries or will they be damaged by the having too much current available?

I'm a lithium beginner so any advice is appreciated.

Focus on marine specific LFP batteries such as the OPE-Li3 (Lithionics/Ocean Planet), Mastervolt or Victron and you won't see these low charge current ratings.

These low charge amperage ratings are because the vast majority of Chinese LFP drop-ins use internal BMS switches that utilize FET's as opposed to contactors (heavy duty switches). FET BMS's can be made to handle more but they add to the cost. If an LFP battery can't accept a 1C discharge or 1C charge find one that can. Not all LFP batteries are created equal...


There's a lot on LFP & boats here:

https://marinehowto.com/lifepo4-batteries-on-boats/






.

[john61ct]

The answer to your title question is yes.

The unit for current relative to size is C-rate.

Let's say you bought or built a 400Ah LFP bank.

Most cell makers list maximum charge rate as something like 5C, or 2000A in this case.

That is because most cell manufacturer specs are absolute maximum ratings, the limits to which the devices can be stressed without instantly causing permanent and irreparable damage. These limits are not recommended for normal operations.


Operating at these absolute maximum ratings for extended periods will produce reduced reliability/lifetime.

So **if** you are willing to include "reduced cycle lifetime" in your definition of "damage",

most would say to keep your maximum charge rate below 0.3C. Some will go to 0.5C or higher if they really need to reduce charge time.

That means 120A and 150A respectively, the former getting the bank, even if 80% DoD depleted, to "working Full" in about three hours, the latter a bit over two.

Of course few boats are set up to produce / handle that much current, so such a high CAR (Charge Acceptance Rate) is often a moot issue.

However, a critical point to understand, any energy source you apply to charging your LFP bank **must** feature robust current limiting. Not just over-current protection, where charging effectively stops while in that mode, but continuously holding current under a maximum rate while striving to reach the Absorb / CV voltage setpoint.

Ideally both parameters are custom-user adjustable.

As opposed to lead, where the bank's greater resistance / lower CAR is in effect self-limiting wrt current, and therefore a very high "available" C-rate is not a concern as long as CV stage voltage and Absorb Hold Time can be adjusted to get to Full without overcharging.

In practice, as Maine Sail noted above, the BMS will often specify a maximum charge rate much lower than what the cells will tolerate.

Especially for LFP "drop-ins" and "portable powerpaks" (sometimes fraudulently labeled "solar generators") you really want to check that spec, it may be **much** slower than desired, sometimes requiring six hours or more to refill.

Hope this helps.

[Privilege]

Thanks for your input (and Patience), I appreciate it. John, that does help a lot. What I hadn't considered, and if I understand correctly, is that if I have 3 x 100ah batteries, each battery doesn't receive 100 amps but rather 33 amps each, effectively giving a 0.3C charge and I should therefore be OK, even if it maintains that maximum current?

[noelex 77]

Originally Posted by john61ct

Of course few boats are set up to produce / handle that much current

Boats capable of producing a 2,000A charging current !

I don’t think many owners would suggest this is common .

[john61ct]

Yes exactly what I said

[john61ct]

Originally Posted by Privilege

Thanks for your input (and Patience), I appreciate it. John, that does help a lot. What I hadn't considered, and if I understand correctly, is that if I have 3 x 100ah batteries, each battery doesn't receive 100 amps but rather 33 amps each, effectively giving a 0.3C charge and I should therefore be OK, even if it maintains that maximum current?

If you mean a nominal 12V bank, so 4S is assumed.

And you parallel connect to create a 300Ah bank, so a 3P4S layout, then yes,

a 100A charge current (1380W) is at .33C and should be fine. It is possible if otherwise treated perfectly (not using those canned LFP settings on your chargers), that keeping to .2C would extend lifespan by 10% or 15%, no one knows the precise relationship.

But if that means 12 years daily cycling rather than 11, would that be important enough to make **you** buy the necessary gear?

Now if you meant to put those 4S packs **in series** to 12S in order to get to nominal 36V, that remains at 100Ah and your 42V charger putting out 100A (4140W) is at 1C.

Which would **greatly** reduce the bank longevity, maybe knocking several years off daily-cycling lifespan.

Note that in propulsion usage like ebikes, EV in general, consumers demand fast charging for convenience.

Which is why the cell makers only quote a few thousand cycles, and charging at higher voltages has a relatively minor impact on those shorter lifetimes.

[FabioC]

Most if not all LiPo battery have some sort of protection circuit to limit the charging current (the probability of explosion increases exponentially with the charging current), some more effective than others.

The lifetime of the battery depends on the charging current (measured in C). Generally speaking, most batteries are built to be charged at 0.5C (normal charge) to 1C (quick charge). The number of charging cycles in the lifetime in the specs is always given assuming "normal" charge. Sometimes, there is even a spec for "slow charge" (e.g., 0.3C), but more often than not, slow charging has undesirable side effects. With quick charge, the number of charging cycles decreases significantly with respect to "normal" charge (to about half or even one third), but not all batteries specify by how much.

Some batteries are built to withstand higher charging currents, but most simply "cutoff" somewhere around 1.2C, to avoid damages. Not all batteries have very effective cutoff circuits, though, because these circuits are expensive.

So, batteries are typically optimized (and spec'd) for a certain charging current that is a fraction of C (e.g., 0.5C), and the assumption is that most of the times, the user will charge at that current. It is also assumed that occasionally the user will "quick" charge at a current around 1C, without much reduction in the lifetime of the battery, as long as the quick charge does not become the habit. It is never a good idea to charge with currents much higher than what is spec'd. Even batteries with expensive protection circuits are designed to withstand the occasional over-current, not the norm.

[Cpt Pat]

I second everything john61ct wrote in post #3. I'll add this: beware of any charging source that has the label "lithium" on it. Often, the name is just slapped on a lead-acid charger/charge controller without any regard for the real needs of lithium batteries.


And in post #2: there have been some very troubling reviews of Mastervolt batteries. Here's one: https://www.pbase.com/mainecruising/...ifepo4_autopsy

[john61ct]

Originally Posted by FabioC

Most if not all LiPo battery

No one is talking about LiPo.

They have no place on a boat.

LFP shares very few characteristics with the dozens of other LI chemistries. Perhaps LTO, but that's even more different from the rest.

Both is extremely safe, not at all susceptible to thermal runaway.

[john61ct]

Note that pbase article is very old, from MS' obsolete site, and he did not apparently see fit to migrate it over to the new one.

Lots of factors change quickly in this sector in that amount of time.

And Maine Sail has specifically mentioned Mastervolt, along with OPE-Li3 (Lithionics/Ocean Planet) and Victron as recommended makers of packaged systems

within the last 48 hours.