Your dock neighbor just switched out her old 12-volt lead-acid batteries for lithium-ion batteries. Should you? The lithium solution will be more expensive, but there are benefits, and we will offer some additional lithium background as we dig into this highly charged subject.
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RE: Lithiums…. I have had one for my house battery on my own boat for a good number of years. I am very happy with it’s performance.
As a marine electrician, I have installed a number of Lithium systems for my customers. I agree… It is definitely important to take a systems approach. Items I focus on are:
1) Alternator needs an external regulator that monitors the alternator temperature and throttles it back if it gets too hot. A single 100 Ahr Lithium can and does absorb 40-50 amps of charging when charging first starts.
2) Alternator output wire must be large enough…….. I find most boats are badly undersized.
3) Is there a voltage sensitive switch being used to share charge with other banks (e.g. Blue Seas ACR)? These will not work because Lithium resting voltage is too high. This will have to be replaced with a Lithium compatible product (eg Victron Cyrix Li Ct).
4) Most Lithiums are not designed to be start batteries. The BMS will shut down the battery with the high amps required for engine cranking.
5) The DC/DC transformers that I have seen tend to have very low amp outputs. Using these to charge Lithiums, in my mind, defeats the Lithium advantage of fast charging. I try to avoid them.
Dakota and others are beginning to offer batteries they claim are suitable for starting. I’ve got a cat w/ Yanmar 57hp engines, the starting batteries sure are a lot of weight in the rear of the boat. Would love to upgrade them to lithium – Practical Sailor – would be a great follow-up article on the things to watch out for when converting to Lithium starting batteries.
New subscriber here but already impressed with my subscription.
One thing I would like to point out in this very good article is the statement “Many better battery makers build a BMS right into their batteries, but they can also be added to the system externally.” is misleading.
It implies that a built-in (serial) BMS is, in some way, a better design than an external (parallel) BMS control circuitry. Notwithstanding that “better” and “best” are subjective and are largely dependent on the design of the system, there are several external BMS/battery designs such as Lithionics, Victron, MG, and others, including some DIY battery external BMS’s (REC) which offer safety capabilities well beyond the drop-in style LFP battery.
In addition to the basic BMS battery protective functions (cell and pack), they have communications (CAN) with an external alternator regulator which allow the BMS to manage the charge source safely, including a pre-signal to gracefully shutdown the high alternator current prior to an impending BMS disconnect (load dump). There are CAN communicating serial BMS’s but I have yet to see one be able to control the Wakespeed or Zeus through the CAN bus. This is a part of the E-13 recommendations (notes) which, disappointingly, did not get integrated into the standard as a minimum. (Standards are a consensus process and often get political with legacy product manufacturers lobbying hard for their installed base and less capable designs.)
I really liked the article’s theme of a systems approach. Too often consumers look only at a spec or price ($/Wh) as the overriding criteria and not the whole electrical system. It frequently ends with a diminished capability and frustration.
It truly is awesome to have air conditioning on the hook without a genset.
We have had a LFP house bank for a year. We have AGMs for start and bow thruster. Basically all charging charges house bank (alternators, inverter/charger, solar). Alternators have Balmar MC614 external regulators. The house bank charges start and thrusters batteries thru 3 30amp DV to DC chargers. Seems to work great. Very happy with upgrade!
I have 3 – 100Ah LFP batteries, and one 100 Ah AGM as a start battery, in a 37 foot sailboat. My 120 amp alternator is governed by a Balmar 614 regulator, and the connection between alternator and start motor is removed. Thus my system is: Alternator to positive buss of the LFP batteries; a lead from here to a DC to DC converter which leads to the AGM start battery; a ‘smart shunt connected to the negative buss of the LFP batteries; then to ground.
At this point (one year in) I have used the Balmar 614 ‘s belt load management to de -power my alternator to about 85 amps. All this is working well and all of the advantages of LFP batteries are evident, including much faster charging form my two 60 watt solar panels.
There is however an assumption in all of this which I’d love your comment on: The LFP batteries have a built in BMS. I’m assuming that should the BMS want to stop all current input, that the DC to DC converter would still feed current to the start battery, and thus not shut the system down?
Great column, and yes for me lithium is the future for boats, and the cost is pretty similar to top grad AGMs.
I recently went on a journey to replace the flooded lead acid house bank batteries on my Tartan 37 with lithium ion batteries. I am keeping the AGM Start battery. After many hours reading the horror stories and bad advice on how to combine these different chemistries, It turned out to be relatively simple. Most of the information on this subject comes out of the RV domaine. It assumes that the primary charging method is the alternator. A sailboat relies more heavily on solar and wind. Consider the direction of power flow. For an RV it is from the alternator to the AGM start battery to the lithium ion house bank. On a sailboat the direction is different. From the alternator, solar, wind and shore power to the house bank and then to the AGM start battery. In each case there is a dc-dc charger between the AGM battery and the lithium ion batteries. My conversion involved replacing the alternator voltage regulator, the magnum inverter charger, and reprogramming the solar controllers to the lithium ion battery charging parameters. I then added a DC-DC charger programmed to the AGM charging parameters. This essentially created a trickle charge from the lithium ion batteries to the AGM to keep it topped off and ready to start my engine.
Like many other articles I have read this one talked about Lithium being similar or even cheaper over the battery lifespan than lead acid. This may be true if compared to AGM or any other ‘sealed’ lead acid and possibly true compared to flooded 12v batteries. If comparing Lithium to quality 6v flooded lead acid it is probably not true. In a typical cruising boat with a house bank of 350Ah/hrs or above, 6v lead acid cells have a very similar cycle capacity to Lithium at a much lower cost and can be expected to have a lifespan of 10-15 years when properly managed. Most people do not realize how much difference there is between a true ‘deep cycle’ lead acid 6v battery and the lightweight 12v flooded or sealed one marketed for RV’s and small boats which at best can be expected to last 3-5yrs.
I’d be interested in information on how best to store Lithium batteries when the boat is hauled out for 3 to 9 months. I’ve read that 60% charged is better than 100%, but how do you maintain that level? Thanks