We are now all familiar with the primary advantages (life expectancy, weight, usable capacity etc.) of lithium iron phosphate (LiFePo4) batteries. What is absent, however, is a broad appreciation of the many other features of LiFePo4 batteries, that fall outside the normal promotional material. These features are important and affect how the 12 V electrical system of a sailboat needs to be reconfigured to accommodate LiFePo4 technology.
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What are the recommended temperature ranges for the batteries. I don’t plan on using my boat in sub freezing temperatures, but it would be nice to know how much capacity you loose.
That’s obviously a question to direct at the manufacturer of the battery you are considering buying (they may even supply some temperature curves) but my understanding is that the temperature range of LiFePO4 typically only becomes a material consideration if you were considering doing something extreme, such as the high arctic in winter.
You haven’t addressed how to charge your Li battereis reliably from the alternator. How about you leave your existing alternator charged starting lead acid battery bank alone and have an inverter installed on the lead acid bank which feeds a dedicated LiFePo4 charger for your LiFePo4 battery bank?
This is addressed, in some depth, in the next article in the series. I think the equipment you are probably referring to is a DC to DC Converter.
This is a REALLY good article. I have started a similar battery replacement process on our twin diesel power catamaran. We are replacing a large 520 Ah AGM battery bank with 3 same-size Lithium batteries totaling 480 Ah. We will continue with our current AGM start batteries. This article has helped a lot to alert us to some of the common misunderstandings around installing Lithium batteries. Fortunately, in my case, we are having a highly experienced marine technician plan and do the installation.
A DC to DC charger such as those available from Victron is connected to the lead acid start battery which is receiving its charge from the alternator. The alternator only “sees” the start battery. The LifePo4 batteries then receive a regulated charge from the start battery and are never directly connected to the alternator.
Correct. That is the subject of the next article in the series
Correct. That is the subject of the next article in the series.
DC to DC charge is definitely a solution to that problem, however in this case the rate of charging of lithium battery is limited by DC to DC charger capacity. That means you will lose 1 of major advantages of lithium battery, which is ability except charge quickly. Unfortunately the better solution is much more expansive – instillation of an external regulator. in this case you will charge lithium battery ( house bank ) directly from the alternate either through the external regulator. following that you connect house bank ( lithium batteries) to the starter battery (lead acid) through the DC to DC charger.
DC to DC Converters are discussed in the next (second) article in the series and the sizing of a DC to DC Converter capacity is discussed in the third and final article. As explained in this article, external regulators only solve one of multiple issues that arise with a direct alternator to LiFePO4 connection.
Good introductory article. It would be helpful to point to other resources. There are several Facebook groups that focus on LiFePo4 “drop-in” batteries for boats. There’s also Rod Collin’s site Marinehowto.com. Nigel Calder has some great information on Boathowto.com. Plenty of others.
I was concerned with uninterrupted power for critical loads when designing my new lithium system. My design utilizes a battery combiner that can pull power from either my lithium house bank or my AGM starter battery. It selects the bank with the higher voltage, which is almost always the lithium bank. In the event of a BMS dump, critical loads will be supplied by the starter battery. An alarm notifies me of the failure. A battery protect device on the start bank will shut down the loads before the voltage gets too low and prevents me from starting my engine. I will also say that while charging the AGM battery direct from the alternator is the safest way, you are then very limited in the ability to quickly charge the lithium bank (a Victron XS DC-DC can provide up to 50a which is still not much). For a lithium bank of any reasonable size should really be charged directly from the alternator and should be externally regulated. While there are newer and better regulators out now (Zeus and Wakespeed), a Balmar 614 or 618 will do just fine if programmed properly. Finally, lithium bulk/aborption charge voltage can be safely reduced to 13.8-14.0v without negative impacts to battery life. You won’t get quite as much capacity compared to say 14.4-14.6 but you will avoid issues with cell over-voltage in the event one cell is out of balance.
There is a lot in your comment, but taking them one by one.
1. What is the combiner you are referring to? Is it an old fashined electro-mechanical ACR (in which case I would not recommend it, for reasons explained in the next article) or some form of Uninterruptable Power Supply (in which case I am not familiar with it);
2. If your alternator is big enough, there is no reason why you cannot have two DC to DC converters in parallel, to increase capacity. That is the set up I have on my boat (two x 40 A, with the second engaged manualy above 1,300 RPM);
3. As discussed in this article, external regulators only solve one of a series of issues with charging LiFePO4;
4. Correct, undercharging your LiFePO4 battery is not a safety issue but i don’t know why you would want to do so, as you then get less usable capacity than you paid for plus, long term, you are likely shortening battery life and invalidating any warranties.
Victron Diode Battery Combiner. It does not “combine” batteries like an ACR. It draws power from one or the other depending on voltage. It is specifically meant for critical loads.
I considered adding a second XS to my system but they are really expensive and then I only get 100a of charging. I opted to use my Balmar MC-614 external regulator to charge my lithium directly so that I could use all 120a from my Balmar alternator. The DC-DC then can supply up to 50a to my start battery for critical loads in case of a BMS shutdown, which is plenty. The key here is to research the regulator settings thoroughly. As a baseline, I used the settings that Stan Honey used in his lithium setup here. His settings and his thoughts on lithium are easily found on the internet.
External regulators solve more than one problem as far as I’m concerned. They can also monitor the alternator temperature. The programmable nature makes them adaptable to any lithium manufacture’s charging spec (they vary considerably).
You should ask Ben Stein from Panbo what his results suggest for charging at a lower voltage or see his article on Panbo. This is what he said recently:
Several newer batteries, most notably the Epoch 460s, utilize full charge protection. As a result, we are seeing more and more recommendations towards charging below 14 volts. Rod Collins has long advocated for this less aggressive charging. But, what happens to capacity and charge times? I did a series of tests to determine just that. The short answer is capacity barely changes at all while charge time does increase some. The closer you stay to 14 votls, the less the impact on charge time.
I found your article to be very informative and well written. I am looking forward to future articles in what sounds like will be a series on this topic. When will the next article be published?
I think the magazine intends to space them one week apart, so not long to wait.
You clearly have done your homework.
Firstly, let me say that this series of articles is aimed at the large community of small boaters who neither have access to a licensed professional electrical designer /installer nor the personal skills or inclination to undertake the sort of research you have. So, yes, there will always be room for one off installations, like yours, but this series of article is aimed at the large community of small boaters that seek a simple, effective and affordable approach that they can manage themselves ie while not exactly a simple ‘drop in’, the closest we can currently get to it.
As to the specific points you raise:
1. The critisism that DC to DC converters limit charging capacity is often made but is largely flawed thinking. Manufacturers could, in theory, sell you any size of converter (or combination thereof) – the limitation is generally with the alternator.
2 A manufacturer may quote 120 Amps nameplate rating for their alternator but that is a performance maximum under perfect (primarily temperature and RPM) conditions. When hot and/or at idle, the output will be significantly less.
3. In the third article in the series I quote a figure of 75 – 80% being a recommended maximum nameplate converter rating vs. alternator nameplate rating but I gather some alternator manufacturers argue that even this figure is too aggressive (ie they would prefer converters to be sized smaller, relative to their alternator). This ultimately plays out in alternator life expectancy and, potentially, warranty claims, such that they generally encourage a conservatively rated converter.
4 Yes, an external regulator can give many benefits but it is not always a silver bullet and the temperature issue will remain, unless it includes internal temperature feedback (ie if it is simply reading chassis temperature it will likely not respond quickly enough) plus some means of responding with current limiting (which some, but not most, external alternator regulators can provide).
5. There can be some benefits to charging LiFePO4 at a lower voltage, such as reducing the risk of a voltage spike on disconnection (arising from a high voltage BMS shutdown OR poor voltage regulation) but this can also lead to a gradual degradation in terms of cell balance, if the BMS is a passive balancer (many BMS can drift in accuracy at low current) and so benefit from being reset to 100%.
6.. Real world operational deployment of LiFePO4 is still relatively recent, such that a broad consensus on the best approach to achieving maximum longevity has not yet been fully achieved. One school of thought (with some evidence) suggests that cycling between 50 and 75% will achieve a longer life than (say) between 40 and 100% but the reality is that the average boater will not notice any material difference and the boater will likely have more important operational considerations.
On the subject of whether LifePo is apropriate for more modest vessels, I always consider LeadCarbon options from North Star(EnerSys) or Trojan. They are significantly less expensive than LifePo, while at the top of the AGM scale. They offer higher life cycles than standard AGM and greater resistance to problems from low SOC. They are a nice bridge between the other technologies. And they don’t just turn off like LifePo. I hate it when that happens. Few installtions have a good solution, but the Victron diode switch may be an elegant solution.
On the subject of whether LifePo is apropriate for more modest vessels, I always consider LeadCarbon options from North Star(EnerSys) or Trojan. They are significantly less expensive than LifePo, while at the top of the AGM scale. They offer higher life cycles than standard AGM and greater resistance to problems from low SOC. They are a nice bridge between the other technologies. And they don’t just turn off like LifePo. I hate it when that happens. Few installtions have a good solution, but the Victron diode switch may be an elegant solution. Although they do induce a 1/3 to 1/2 voltage loss on the critical load circuits.