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Old 07-06-2021, 11:09   #1
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max. amount of Lithium batt. in parallel

Hi there . I'm in the process of building my new lithium battery bank and red somewhere that you are not suppose to connect more than 4 batteries in parallel
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Old 08-06-2021, 18:48   #2
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Re: max. amount of Lithium batt. in parallel

To build a system that will not give you hassles later on, the maximum number of batteries is one, just built to the capacity you require. Every additional battery will be at either a higher restance or lower resistance to the other batteries in parallel. Lithium batteries have very low internal resistance, unlike lead acid batteries, so they will not load share until the voltage in the battery with the lowest resistance drops below the voltage of the other batteries in parallel, then the next lowest restance battery with a high enough voltage takes over .... it still doesn't share the load with the first battery that was doing all the work. Charging is the reverse, the battery with the lowest resistance is the first charged and to force charge into the other batteries in parallel, the first battery to reach 100% must be over voltage charged so the other batteries in parallel will get charged. One out of 4 batteries doing the majority of the work and getting over voltage charged as well, how long before that battery starts to fail? One battery dying in a parallel set up will kill the other batteries well before you realise there is a problem...... That is exactly what happens with lead acid batteries in parallel ......

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Old 08-06-2021, 19:44   #3
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Re: max. amount of Lithium batt. in parallel

Here is a very detailed article on lithium batteries on boats:
Lithium batteries typically have a Battery Management System (BMS) which do disconnect the batteries.

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

Lithium batteries typically have a Battery Management System (BMS) which do largely allow the batteries in parallel to act as if they were all alone, and a good BMS helps keep the individual cells within the battery to stay matched as for discharge and charge capacity. This is why, unlike lead-acid batteries, you can generally upgrade a lithium bank with a new battery on an older bank. Can't do this with lead-acid because adding a new battery to an old bank quickly "ages" the new battery.



An excerpt regarding charging lithium batteries with an alternator:

The alternator for the Volvo MD2030 with 300 Amps lfp 14.6 max lasted a few hours. I believe BMS was switching on to off I to keep the lfp voltage to safe measure? Boat service replace alternator and it happens the second time? I now read your story on lfp and it explain to me why.”
Unfortunately the reader above learned the hard way. Ask yourself what happens when your alternator is in bulk charge, supplying all the current it can, and the internal BMS decides to “open circuit” or disconnect the battery from the boat? I’ll help out a bit here.
A) The alternator diodes, unless avalanche style, (rare in many existing marine alternators) but all Balmar alternators now use them, can be blown and the alternator can be rendered non-operable. Two years ago I did exactly this. Using the alternator test bench here at CMI the alternator was running at full bore charging an LFP battery. The “system” I set up had a .3A dummy load on, light bulb, to simulate a depth sounder. With the alternator running at full bore I disconnected the battery, just as an internal sealed BMS would do to protect the LFP cells. Poof went the alternator diodes and the light bulb! Worse yet the voltage transient I recorded on the “load bus” (think your navigation electronics) using a Fluke 289 was 87.2V. Ouch. Even if your alternator uses avalanche diodes, like Balmar’s do, the voltage at which they begin to protect the alternator is far too high for the vessels load bus equipment so you still need a way to protect against a load dump.



And view this:


https://youtu.be/jgoIocPgOug
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Old 08-06-2021, 19:47   #4
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Re: max. amount of Lithium batt. in parallel

Quote:
Originally Posted by T1 Terry View Post
To build a system that will not give you hassles later on, the maximum number of batteries is one, just built to the capacity you require. Every additional battery will be at either a higher restance or lower resistance to the other batteries in parallel. ...
Which is why you need a good battery management system (BMS) with lithium banks.
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Old 09-06-2021, 07:10   #5
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Re: max. amount of Lithium batt. in parallel

Most of the batteries I'm looking at have BMS already built in. What I learned so far , to deal with the alternator going on the wiled spin is , you must add a battery to battery charger that I assumed will divert the load to the lead acid starting battery. Going back to my question. So ,is it OK to have 6 Lithium batteries if they have a BMS ?
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Old 09-06-2021, 07:19   #6
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Re: max. amount of Lithium batt. in parallel

There are several ways to protect your alternator , one is to use a lead acid battery permanently connected to act as a “ sink “ for the alternator. This protects the alternator if the bms opens all the connections to the battery

The other involves signals from the bms to the alternator regulator etc. More complex
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Old 09-06-2021, 15:31   #7
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Re: max. amount of Lithium batt. in parallel

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Originally Posted by T1 Terry View Post
To build a system that will not give you hassles later on, the maximum number of batteries is one, just built to the capacity you require. T1 Terry
You may think about getting "individual cells" that you first connect in parallel to create "battery cells" of the desired capacity, and then connect those "battery cells" in series to get the desired voltage (4 in series for 12v).
Big advantage you can chose the BMS that suits your needs and will not only protect the battery against critical situations, but also manage the onboard energy for maximum battery life.
I know it seems more complicated that a so called "drop-in" battery, but that way you know what is inside and you are in control
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Old 09-06-2021, 16:00   #8
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Re: max. amount of Lithium batt. in parallel

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Originally Posted by goboatingnow View Post
There are several ways to protect your alternator , one is to use a lead acid battery permanently connected to act as a “ sink “ for the alternator. This protects the alternator if the bms opens all the connections to the battery

The other involves signals from the bms to the alternator regulator etc. More complex
Yes, my installation is like that... but after the bad experience of a friend I am thinking about an alternative
My friend's experience last week: after 3 days of grey stormy weather he could could not start his engine in the morning! It was a user error as he did set his BMS early warning too low (11.6v or 2.9vpc), so he discharged both his lithium house and his starter battery...
On my installation I will review the BMS low voltage pre-warning that is currently at 2.95vpc (11.8v) and/or replace the manual battery coupler with a solenoid commanded by either engine contact.
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Old 09-06-2021, 16:22   #9
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Re: max. amount of Lithium batt. in parallel

The definitive source

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

Each cell gets a BMS or you buy the new generation drop in replacements which have the BMS built in.

No Float! Float will kill your Lithium

Since Li cells are a bit over 2 volts each, you put cells in series to get the required volts. Cells are placed in parallel to increase amps. Just the same as regular batteries.
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Old 09-06-2021, 19:13   #10
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Re: max. amount of Lithium batt. in parallel

I'm getting a 'drop in' boxes with BMS built in. Electrical and electronics are not my forte , so i would like to make it as simple as possible. So, getting to my first questions. If I will get 6 batteries, 12 V, 100 AH each and connect them in parallel,would BMS take care of even charging distribution ?
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Old 09-06-2021, 23:47   #11
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Re: max. amount of Lithium batt. in parallel

Time to put logic into play. If the battery has a BMS that can measure the cell voltage in each cell and disconnect the battery from charging or discharging while the balancer unit evens out the cell voltages .... where does it fit and how can they build a battery with the same capacity, and a quality BMS included, cheaper than the cost of buying the same capacity quality cells on their own?

Now you need to ask yourself, what quality would the BMS be if it does fit inside the battery case and how does it cool with no ventilation in the sealed battery?

Expecting a BMS designed for say a 10Ah bicycle battery to be able to handle the 100Ah or 200Ah capacity of the drop in battery is ludicrous. Now consider the charge and discharge rates you are expecting from this miracle battery compared to the load and charge rate of the bicycle battery ..... are you planning on recharging at 5 amps or less and discharging at a max of 50 amps for a few mins ...... I doubt it, so how can you expect the token BMS that is inside the drop in battery to do the same job as the built for purpose unit that costs about the same if not more than the drop in battery ......

Look at the price of Victron drop in lithium batteries and all the devices needed to go with them to make them work for the expected cycle life and not fail with zero warranty because not all the Victron equipment required was fitted .....
Do you really think the quality of the drop in battery with built in BMS would be equal quality of the Victron battery yet a fraction of the price????

Yes, you can have drop in lithium batteries that will actually work as you expect and require, but the price is way more than building one battery and one quality BMS system ....

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Old 10-06-2021, 00:13   #12
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Re: max. amount of Lithium batt. in parallel

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Originally Posted by henryk View Post
I'm getting a 'drop in' boxes with BMS built in. Electrical and electronics are not my forte , so i would like to make it as simple as possible. So, getting to my first questions. If I will get 6 batteries, 12 V, 100 AH each and connect them in parallel,would BMS take care of even charging distribution ?
If you want to make it as simple as possible, contact Julia Yu and buy four Winston 700Ah cells which you connect in series and add a 400A class T fuse. Now let someone on the forum recommend the best BMS and main switch/solenoid for that.

Your concern is settings for chargers, inverter/chargers, DC-DC converters and solar controllers. Those setting will all need to be done either way. Make a list of brands and models of what you have and ask here if they are compatible orwhat you need to buy.

With the Winston cells, you do have to initially balance them which is easy but requires a special charger ($100 if you’re patient, $300 does it 6x as fast) and you have to deal with the BMS settings. You win back a lot of time by not having to deal with wiring 6 batteries which easily wins back a day of your time. Just order busbars with the Winston cells and install is done in minutes.

The info from Rod Collins is highly recommended and your admission of not being very knowledgeable on electric boat installations is a much better start than most who claim to know it all but don’t and mess up. I’m also sure you can find someone to help you, even here on the forum as we have members all over the world.
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Old 10-06-2021, 00:22   #13
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Re: max. amount of Lithium batt. in parallel

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Originally Posted by T1 Terry View Post
Yes, you can have drop in lithium batteries that will actually work as you expect and require, but the price is way more than building one battery and one quality BMS system ....
T1 Terry
That is very location dependent. The costs of import duties and transport costs for an individual could easily strip away the benefits of importing and building your own system over a drop in. Buy it in your own country with and there are likely consumer rights if it doesn't work. What sort of warranty do you offer on your batteries?

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Old 10-06-2021, 00:29   #14
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Re: max. amount of Lithium batt. in parallel

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Originally Posted by henryk View Post
I'm getting a 'drop in' boxes with BMS built in. Electrical and electronics are not my forte , so i would like to make it as simple as possible. So, getting to my first questions. If I will get 6 batteries, 12 V, 100 AH each and connect them in parallel,would BMS take care of even charging distribution ?
yes. also all this post up is mubo jambo for you. don't worry. normally be better if you build 1 baterry 600A
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Old 10-06-2021, 00:53   #15
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Re: max. amount of Lithium batt. in parallel

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Originally Posted by s/v Jedi View Post
If you want to make it as simple as possible, contact Julia Yu and buy four Winston 700Ah cells which you connect in series and add a 400A class T fuse.
good advice, also for fuse this American https://www.bluesea.com/products/519...k_-_30_to_300A
is also good option

MRBF fuse on both sides +- after wiring to battery switch, after this to battery panel with fuse.
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