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Old 17-05-2021, 08:42   #1
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LiPo 4 charging speed

I have 450 ah of Lifeline AGM which when discharged 50% only accept 50/60 amps from my 100 amp charger.
It takes a couple of hours to recharge to an acceptable capacity.
I am thinking of going down the Lithium route so how much faster would they charge back up compared to the agms.
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Old 17-05-2021, 08:47   #2
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Re: LiPo 4 charging speed

Lithium batteries can accept a charge current which can smoke your alternator due to their low internal resistance.


You should look at the specifications of the lithium batteries you are considering.
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Old 17-05-2021, 08:53   #3
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Re: LiPo 4 charging speed

I assume you mean LiFePO4 or LFP as Lithium Polymer (LiPo) is usually not used on boats for safety reasons.

LFP batteries can usually be charged from 0.5 to 2.0 C, which roughly equates to 130 min to 45 min (taking into account a bit of absorption time).

Of course this depends on the particular battery. You can check its datasheet and see what charge rate they recommend. Furthermore, your charger should be able to deliver sufficient current, otherwise you remain limited by your charger.

Assuming your charger can deliver 100 A continuously (not all chargers can) and you have a 200 Ah pack that has been discharged 80 % (20 % left), the charging will take about 100 min (200 Ah * 80 % / 100 A = 96 min).
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Old 17-05-2021, 14:32   #4
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Re: LiPo 4 charging speed

I have 200ah Winston cells and this far they have accepted anything I have thrown at them. I think they are rated at max 3C which would mean they could accept 600A charge current and go from empty to full in 20 min. The max I have tried is a little bit over 100A which they gladly accepted for 15 min. Then my new extra charger that I tested for the first time got toasted.
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Old 18-05-2021, 09:12   #5
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Re: LiPo 4 charging speed

A good rule of thumb for long battery life is 0,7C charging rate, that is 70A for a 100Ah battery. And yes, you will need a limiter for what the battery is able to absorb from your alternator. A good solution according to my experience is the Victron Energy DC-DC charger.
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Old 18-05-2021, 09:58   #6
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Re: LiPo 4 charging speed

I think you are missing the point of LFP batteries. Forget lead acid, LFPs don't have to be or want to be fully charged.
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Old 18-05-2021, 10:23   #7
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Re: LiPo 4 charging speed

I am definitely going LiFePO4 when I get ready to do the systems.
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Old 18-05-2021, 10:57   #8
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Re: LiPo 4 charging speed

We just completed an upgrade from a 1200ah Mastervolt AGM house battery bank to 1200ah Mastervolt Lithium.

While still at the service dock I shut off shore power and allowed the new house battery bank to discharge to 50% SOC over 3 days, then turned on shore power and it took 3 hours to charge to 100%. I was ecstatic.

We have 200 amps of charging capacity and charging amperage was 196 for the first hour to 70%, then 168 for the second hour to 90%, and in the final hour dropped from 145 to float.

After cruising for 3 years living on the hook full time with AGMs that performed as you describe, this was astounding and worth the investment for me.

It took 7-8 hours to charge my AGMs to 100% and routinely it took 2-3 hours in float to go from 97% to 100%. Charging amperage in bulk mode always started at 190 then quickly dropped to 145 and rarely stayed there for more then 30 minutes before dropping to 90 and below. Awful and frustrating.

In normal use I would run the generator for 2-3 hours to get the AGMs to 95% or so then shut off, but they need to be topped off to 100% at least once a week or their performance will degrade. We lost 2 of the original 6 batteries because I was reluctant to do so.

We are excited about our new lithium batteries which will serve our cruising lifestyle far more effectively than our previous AGMs

Our house battery bank of six 6v Mastervolt AGMs provided 1200ah at 12v, which is 600 usable ah (50%). Current cost of this battery bank is @$4,300.00

Our new lithium battery bank of three Mastervolt 12v 400ah batteries also provide 1200ah, of which 960 is usable (80%). Current cost of this battery bank is $18,000.00. We could have used just two of these batteries instead of three, but I wanted the higher capacity to go longer between charges.

We originally wanted lithium when refitting Grace for cruising 3 years ago but the cost was prohibitive. Since then the cost has come down, the tech is better, and our frustrating experiences cruising with AGMs has motivated us to upgrade. The actual cost over time for lithium is lower for cruisers like us who live on the hook.

Factors include:

- Usable ah- can go longer between charges.

- DoD cycles- Mastervolt AGMs are rated for minimum 2000 charging cycles, lithiums for minimum 3000 charging cycles, 33% longer life.

- Charging time- As described above, it took 3 hours to charge the new lithiums from 50% to 100%, which would be 6-8 hours for the AGMs.

- Charging SOC- Lithiums are fine, even prefer, not being charged to 100% so I can use the peak charge curve for 1-2 hours and stop wherever that is as often as I like. AGMs MUST be charged to 100% at least once a week or so to keep them functional. Not doing so for the first year of cruising lost me 2 of the six batteries I started with.

- Solar/Wind generation- AGMs HATE the variable charge levels of solar and wind generation and require charging to 100% once a week or their ability to accept a charge greatly degrades/diminishes. Lithiums are able to maximize the energy generated from our solar and wind generation.


This past winter I had to change generator oil once per month or so (every 100 hours), a ridiculous amount of generator use. With the lithiums I should be able to get by with wind and solar most of the time and use the generator once or twice a week during the winter for a couple of hours- 12 hours per month vs. 100 hours per month is a BIG difference that figures into the cost and quality of life on the hook.

As a side benefit, lithiums are significantly lighter, so Grace's weight distribution problem from replacing a 110 gallon fuel tank with a 90 gallon fuel tank is fixed, no more 2 degree list when the tanks are full!

In case you worry about safety and fires with lithium batteries, that is an issue with going cheap and not having the proper setup, which can be expensive. Most of what I needed was already in place from Grace's electrical refit of an integrated Mastervolt system, and the battery monitoring and management systems have double and triple redundancies. Lithium is a waste for dock queens, but we are on our boat 100% of the time and pay close attention to all of Grace's systems, so if there's a problem we will know it almost immediately.

Fun fact- we like to use an AC popcorn air popper every evening while watching TV and with the AGMs we would run the generator for 5 minutes to do so (if not charging). With our new lithiums we can do so from battery power without the generator. That one little change is a great metaphor for the difference these batteries will make for us.

We are happy and excited about our new lithium batteries!
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Old 18-05-2021, 12:08   #9
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Re: LiPo 4 charging speed

As folk have mentioned LFP will accept very high charging rates. If you donít need to charge quickly and you want to get good life from your batteries then stay in the 0.3C range. For a 300ah bank charge at roughly 100 amps not more.
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Old 18-05-2021, 12:29   #10
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Re: LiPo 4 charging speed

https://www.cruisersforum.com/forums...ml#post3409627
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Old 18-05-2021, 17:08   #11
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Re: LiPo 4 charging speed

something is wrong with your bank or wiring. probably in bad shape. I bet brand new lifelines would take ~200 amps at 50% but would drop off pretty quickly as it charged.


lithuims will take the full 100a from the charger untill they are full.

so at 50% of a 450ah bank it would take 2.25 hours. vrs around 5h+ for the agm
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Old 26-05-2021, 21:53   #12
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Re: LiPo 4 charging speed

The best we have seen when all 3 charging systems were running in parallel was 300 amps, 100 amps from the solar, 150 amps from the Victron inverter/charger and 50 amps from the DC to DC ....all into a 200Ah Winston 8 cell 12v battery. The wiring is the real limiting factor, at 50 amps through 6 B&S cable (13.5mm sq) the cable gets quite warm after an hr. 300 amps through 0 gauge cable ( 53.3mm sq) the cables get quite hot and floppy.
Even thought the battery can handle the high current, make sure your wiring is up to the task, there is no limiter like there was with lead acid batteries so it is easy to overload the cabling.

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Old 26-05-2021, 22:03   #13
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Re: LiPo 4 charging speed

Lithium battery charge rates often are limited by the BMS. My Battleborn batteries spec a 0.5c maximum charge rate. Since I have a 1600AH bank, this isn’t a problem. They also come with a 10 year warranty - something you won’t find with any AGM.

Here is the best primer I’ve seen:
https://marinehowto.com/lifepo4-batteries-on-boats/
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