ReedStr
Member
- Joined
- Sep 4, 2014
- Messages
- 19
- Location
- USA
- Vessel Name
- Henry Young
- Vessel Make
- Ocean Alexander MK II
I thought I would post my approach and experience transitioning from AGM to lithium for a house bank on a 50’ Ocean Alexander Mark 2 so others might learn from my experience. Sorry for the long post!
In the 2019 preseason I did a capacity check on my 7-year-old Lifeline AGMs only to discover that they were at 60% of capacity and it was time to replace them. This was my third battery replacement cycle and after much research and consideration, I chose lithium and I am glad I did. They are a better match for cruising, easier to charge, and easier to maintain. Here is the background.
Summary
Here is a summary of what I did. The explanation is later.
This system fully charges the lithium and start bank while underway using the alternators (and letting the lithium’s gradually fall back from 100% once charged to increase cycle life) while providing separate charging regimes for the start bank and lithium bank when on shore power/in storage keeping the start bank fully charged and the lithium bank partially charged which are their respective preferred storage SOCs.
Common Beliefs About Lithium Batteries I Don’t Share
There seem to be a number of common beliefs on the internet about lithium batteries that I don’t share. Here they are.
Lithium batteries can accept super high charge rates. Technically true but my advice is don’t do it. While they can accept super high charge rates, they heat up which reduces cycle life and risks the batteries cutting out when their BMS determines that the batteries have overheated. Better to charge at 1/3 or less of their rated capacity and keep them cool.
You can use the entire capacity of a lithium battery. Again, this is technically true but my advice is don’t do it. Technically, you can easily charge them to 100% and they will maintain their voltage right down to when they cut out at the bottom. The problem with draining to the bottom is that often they are at their bottom in the morning when you’re trying to pull up the anchor. If you are down at 5% SOC then that high load may cause the BMS to take the batteries off line due to low voltage and the resulting EMF that is emitted when the anchor winch motor suddenly stops running and there is no battery to absorb it can ruin your electronics. Charging to 100% is not as problematic and as I discuss below I haven’t figured out a way to avoid it but charging above 80% will shorten the cycle life although batteries like Battleborn are guaranteed to have a cycle life of 3000 charged to 100%.
Lithium batteries can cut out and destroy your electronics. Yes, this is technically true but so can lead acid systems and a reasonably managed lithium system won’t cut out any more than a lead acid system. With respect to it not being a new problem, in every system cables can come off of your alternator which will fry it. It’s not common but it happens. With respect to lithium cutout I’ll cover that later in this article.
Rules of Thumb
Let’s start with capacity, weight, and size. For the same amount of usable capacity, a lithium bank will be about ½ the rated capacity, about ¼ the weight, and less than ½ the physical size of an equivalent AGM bank. You can see this a couple of ways. AGM’s have about 30% to 40% usable capacity while lithium’s have about 60% to 80% usable capacity. And a 4D 210 ah Lifeline weights 110lbs while the equivalent Battleborn lithium is a group 27, has 100ah, and weighs 31 lbs.
With respect to price, for the same usable capacity a lithium bank will cost between 1.5 to 2 times as much. My calculation was that if the lithium bank lasted 10 years rather than 7 and instead of hauling around 110lb 8D batteries I was hauling around 40lb group 27 batteries then I was ahead both in price and ease of use. If they lasted the rated 3000 cycles, then I was never going to have to replace my batteries again. Bonus!
In terms of balancing charging and capacity, the rule of thumb is to have 50% of the battery bank usable capacity in alternator capacity available to charge the battery bank. If I have 50% charge capacity, then I can refill the daily usage in 2 hours or less of motoring which is typically what we do around here. Stated in terms of total capacity, 50% of available capacity translates to 30% total capacity and charging at 30% of total capacity will keep the batteries cool which extends cycle life.
Guidelines
Despite the claims for super high charging capacity and the ability to use 100% of lithium’s capacity, you want to
Using Lithium Batteries for a Bow Thruster or Start Bank
I should note that I don’t used lithium batteries for the bow thruster or the start battery. The bow thruster because that bank is relatively small for the size of the load and lithiums will cut out if overloaded which might happen just when you really need the bow thruster to work. The start bank is for the same reason. In contrast, the large size of the house bank relative to the load (and charge capacity) means there is a minimal chance of the lithium batteries cutting out.
Configuration, Charging, and Storage
With a lithium house bank and a lead acid/AGM start bank I faced a conundrum. My boat is wired such that the start bank is charged from the house bank with a Balmar Duocharge that runs whenever the house bank is above a target voltage such as 13.2v which shows that the house bank is receiving charge. Unfortunately, this causes problems because the resting voltage of a lithium bank is higher than the target voltage but the storage voltage for lithium is lower. This is because a lead acid battery is charged at 14.2v, has a working voltage of around 12.5v, and is stored at 13.6v at 100% SOC while a lithium battery is charged at 14.2v, but has a working voltage of around 13.5v and is stored at 13.2v and 50% to 70% SOC. Lead Acid and Lithium match well for charging, not bad for working, and terrible for storage.
Here is what I did to solve this conundrum:
The next question then would be now that I’ve set up the start bank to have separate storage charging from the house bank how did I configure the storage charging for the lithiums? The recommended storage solution for lithium batteries is to charge them to 100% SOC and then disconnect them. Since this may be impractical an alternative is to set the charger on the inverter to float at 13.2v which will keep them at about 65% SOC.
With respect to the fully charge and disconnect option, my boat had combiner switch that combines the start bank and the house bank but I needed to install a house bank cut out switch. At the end of the season I fully charge the lithium batteries, turn the combiner switch on, and the cut out switch off. The lithium batteries will now be sitting with no load and have such a low self discharge rate that they should still be 50% charged with I reconnect them next spring. In addition, the start batteries and start bank charger will now be handling any of season load that occurs. In the spring reverse the process, first bringing the lithium batteries online and then turning off the combiner.
With respect to the float option (which I did before I installed the house bank cut out switch) I fully charge the lithiums and set the float voltage of the inverter/charger for the house bank to 13.2v. The lithiums will gradually lose SOC due to hotel loads until they reach 65% at which point the charger will handle/refill after any loads to keep the lithiums from being fully drained. The start bank will be maintained by the start bank charger at 100% SOC.
Charging and the Fit with Cruising
The first thing I noticed when I started using lithium’s is that they accepted the full rate of charge until they were almost full. Then in the space of 2 minutes they dropped from accepting 170amps to accepting 5 amps. The CAR dropped faster than a ticking clock when the battery was full.
This is from very different lead acid chemistry batteries. Lithium batteries prefer to be used and stored partially discharged. AGM batteries like to be fully charged and when I keep an AGM partially discharged it shortens their cycle life. Dramatically. Lithium batteries charge at full load until they are full so there is no question when they are done. AGM CAR starts dwindling at 80% charged and it takes 8 hours or so get the last 20% in.
This leads to why lithium’s are such a better fit for my marine house bank. When I’m cruising with AGM batteries they are never fully charged until I reach a dock. The last 20% takes 8 hours. I rarely run my engines that long and it’s not enough load for a generator. Consequently, cruising shortened the cycle life of my AGM batteries. In contrast, the last 20% of lithium’s charge time is no longer than the first 20%. Even better, I don’t want to charge the last 20% of lithium except occasionally for top balancing. With AGM I was always trying, and mostly failing, to fill up my batteries and prevent capacity loss. With Lithium however much charge I get every day is fine.
It's also why lithium’s are easier to set up. Historically, battery charging systems monitored charging output and not charge acceptance so they never really knew when the battery was full. Some, such as Balmar, took a conservative approach and they could not be set up to charge beyond 90 or 95% charged. With lithiums you set the bulk voltage to 14.4 and then they hit it you’re 99% full so you drop to an absorb of 13.6 and float of 13.4.
Lithium Cutout
Speaking of drop in lithium batteries cutting out when I looked at this closely, I decide it was a non-issue. Lithium batteries cut out under specific conditions so if my discharge capacity dwarfs the boat loads (it does) and I keep the batteries below 100degrees f and above freezing then they’re never going to cut out except for a cell short which is in keeping with the other cut out risks like the positive cable falling off my regulator.
Here is what Battleborn said about their built in BMS and when it cuts out and in:
The BMS is not bucking or doing any voltage regulation. It is simply monitoring the voltages, current and temperatures and acting as a high current switch, when things are out of whack. Charging and discharging circuits may be opened independently. For each, we have a bunch of high-current MOSFETs (along with some snubber circuitry) doing the switching. Basically, the charging switches will open if one of the following is detected:
You can see that if the system is well balanced and kept at moderate temperatures then they will not cut out.
Finally, the reason I chose drop in batteries is on the one hand when I looked at systems that used an external BMS the expense of refactoring my positive bus into a charge side and a load side so I could put in the cut out solenoids created a wiring bill that increased the cost of the project by 50 to 100% while on the other hand when I looked closely at a quality drop in battery like Batttleborn that has a reasonable sustained output capacity I couldn’t find a downside. The drop in system was simpler and with little downside.
In the 2019 preseason I did a capacity check on my 7-year-old Lifeline AGMs only to discover that they were at 60% of capacity and it was time to replace them. This was my third battery replacement cycle and after much research and consideration, I chose lithium and I am glad I did. They are a better match for cruising, easier to charge, and easier to maintain. Here is the background.
Summary
Here is a summary of what I did. The explanation is later.
- Installed a Battleborn battery house bank as a drop in replacement to the existing AGM house bank. The Battleborn house bank is ½ the rated capacity of the existing AGM bank which gives the same usable capacity as before.
- Installed an AC charger on the start bank. This allows separate storage charging profiles for the lead acid start batteries and the lithium house batteries.
- Wired the Ballmar Duocharge power to the start circuit so that the start bank is only charged from the house charging system when the alternators are charging it and not when the inverter/charger is charging it from shore power. This separates the underway charging from the shore/storage charging.
- Added a house cut out so the lithium house bank can be stored no load for the winter. I already have a start/house combiner switch that allows the use of the start bank as the house bank when the lithium house bank is offline for the winter. An alternative is to use the 13.2v float storage voltage of the inverter to keep the batteries at 65% for storage and not install a house bank cut out.
- Set inverter/charger as follows:
- Bulk charge to 14.4 volts with 1 hour for absorption (anything above 14.2 triggers top balancing, anything sustained above 14.6v will cause the lithium batteries to disconnect). This provides a top balancing charge when attached to shore power.
- Set the bulk charge to happen on first charge and then every 45 days.
- Float charge at 13.2v which means that after I plug into shore power the lithium’s are fully charged and top balanced and then because of the loads on the boat even when I’m not there the batteries will gradually drop to 65% SOC which is their happy place for storage.
- Set the Balmar regulators as follows:
- Bulk: 14.4v for 6 minutes. This charges them fully but does not balance charge them.
- Absorption: 13.6v for 6 minutes
- Float: 13.4v. this allows the batteries to slowly discharge underway after being fully charged but doesn’t let them drain too much. Keeping lithiums full reduces cycle life.
Common Beliefs About Lithium Batteries I Don’t Share
There seem to be a number of common beliefs on the internet about lithium batteries that I don’t share. Here they are.
Lithium batteries can accept super high charge rates. Technically true but my advice is don’t do it. While they can accept super high charge rates, they heat up which reduces cycle life and risks the batteries cutting out when their BMS determines that the batteries have overheated. Better to charge at 1/3 or less of their rated capacity and keep them cool.
You can use the entire capacity of a lithium battery. Again, this is technically true but my advice is don’t do it. Technically, you can easily charge them to 100% and they will maintain their voltage right down to when they cut out at the bottom. The problem with draining to the bottom is that often they are at their bottom in the morning when you’re trying to pull up the anchor. If you are down at 5% SOC then that high load may cause the BMS to take the batteries off line due to low voltage and the resulting EMF that is emitted when the anchor winch motor suddenly stops running and there is no battery to absorb it can ruin your electronics. Charging to 100% is not as problematic and as I discuss below I haven’t figured out a way to avoid it but charging above 80% will shorten the cycle life although batteries like Battleborn are guaranteed to have a cycle life of 3000 charged to 100%.
Lithium batteries can cut out and destroy your electronics. Yes, this is technically true but so can lead acid systems and a reasonably managed lithium system won’t cut out any more than a lead acid system. With respect to it not being a new problem, in every system cables can come off of your alternator which will fry it. It’s not common but it happens. With respect to lithium cutout I’ll cover that later in this article.
Rules of Thumb
Let’s start with capacity, weight, and size. For the same amount of usable capacity, a lithium bank will be about ½ the rated capacity, about ¼ the weight, and less than ½ the physical size of an equivalent AGM bank. You can see this a couple of ways. AGM’s have about 30% to 40% usable capacity while lithium’s have about 60% to 80% usable capacity. And a 4D 210 ah Lifeline weights 110lbs while the equivalent Battleborn lithium is a group 27, has 100ah, and weighs 31 lbs.
With respect to price, for the same usable capacity a lithium bank will cost between 1.5 to 2 times as much. My calculation was that if the lithium bank lasted 10 years rather than 7 and instead of hauling around 110lb 8D batteries I was hauling around 40lb group 27 batteries then I was ahead both in price and ease of use. If they lasted the rated 3000 cycles, then I was never going to have to replace my batteries again. Bonus!
In terms of balancing charging and capacity, the rule of thumb is to have 50% of the battery bank usable capacity in alternator capacity available to charge the battery bank. If I have 50% charge capacity, then I can refill the daily usage in 2 hours or less of motoring which is typically what we do around here. Stated in terms of total capacity, 50% of available capacity translates to 30% total capacity and charging at 30% of total capacity will keep the batteries cool which extends cycle life.
Guidelines
Despite the claims for super high charging capacity and the ability to use 100% of lithium’s capacity, you want to
- Charge them at 1/3 of their rated capacity or less,
- Keep them below 30 degrees centigrade and above freezing,
- Use them between 20% charged and 80% charged,
- Store them partially discharged in the 50% to 70% range. Do not store them full nor keep them “trickle charged” at full.
- In the case of top balancing batteries such as the Battleborns, occasionally charge them at 14.2v for an hour in order to balance the cells. If you don’t occasionally balance charge them then gradually the SOC of each cell will vary and the BMS will take the battery off line when you think they still have 20% SOC because while the battery as a whole may have 20% SOC the unequal SOC state of the cells means one of them is drained to the point where the battery needs to be taken off line.
Using Lithium Batteries for a Bow Thruster or Start Bank
I should note that I don’t used lithium batteries for the bow thruster or the start battery. The bow thruster because that bank is relatively small for the size of the load and lithiums will cut out if overloaded which might happen just when you really need the bow thruster to work. The start bank is for the same reason. In contrast, the large size of the house bank relative to the load (and charge capacity) means there is a minimal chance of the lithium batteries cutting out.
Configuration, Charging, and Storage
With a lithium house bank and a lead acid/AGM start bank I faced a conundrum. My boat is wired such that the start bank is charged from the house bank with a Balmar Duocharge that runs whenever the house bank is above a target voltage such as 13.2v which shows that the house bank is receiving charge. Unfortunately, this causes problems because the resting voltage of a lithium bank is higher than the target voltage but the storage voltage for lithium is lower. This is because a lead acid battery is charged at 14.2v, has a working voltage of around 12.5v, and is stored at 13.6v at 100% SOC while a lithium battery is charged at 14.2v, but has a working voltage of around 13.5v and is stored at 13.2v and 50% to 70% SOC. Lead Acid and Lithium match well for charging, not bad for working, and terrible for storage.
Here is what I did to solve this conundrum:
- Connected the Balmar Duocharge (the device that charges the start bank from the house bank) to the starter circuit so it only runs when the engines are running and the alternators are charging. This keeps the start bank from being a parasitic load when the engines aren’t running but the lithiums have a high enough resting voltage to trigger the duo charge and keeps any charge from going back into the lithiums when the start bank is stored at a higher voltage than the start bank. This shouldn’t happen but if it did then you’d kill your lithium house bank by storing them at too high a SOC and by tying it to the starter circuit it definitely won’t happened.
- Added an AC charger to the start bank that is on when the boat is plugged into shore power. This keeps the start bank charged when the boat is stored for the winter or I’m at the dock for a long period of time i.e. when the engines aren’t running.
With respect to the fully charge and disconnect option, my boat had combiner switch that combines the start bank and the house bank but I needed to install a house bank cut out switch. At the end of the season I fully charge the lithium batteries, turn the combiner switch on, and the cut out switch off. The lithium batteries will now be sitting with no load and have such a low self discharge rate that they should still be 50% charged with I reconnect them next spring. In addition, the start batteries and start bank charger will now be handling any of season load that occurs. In the spring reverse the process, first bringing the lithium batteries online and then turning off the combiner.
With respect to the float option (which I did before I installed the house bank cut out switch) I fully charge the lithiums and set the float voltage of the inverter/charger for the house bank to 13.2v. The lithiums will gradually lose SOC due to hotel loads until they reach 65% at which point the charger will handle/refill after any loads to keep the lithiums from being fully drained. The start bank will be maintained by the start bank charger at 100% SOC.
Charging and the Fit with Cruising
The first thing I noticed when I started using lithium’s is that they accepted the full rate of charge until they were almost full. Then in the space of 2 minutes they dropped from accepting 170amps to accepting 5 amps. The CAR dropped faster than a ticking clock when the battery was full.
This is from very different lead acid chemistry batteries. Lithium batteries prefer to be used and stored partially discharged. AGM batteries like to be fully charged and when I keep an AGM partially discharged it shortens their cycle life. Dramatically. Lithium batteries charge at full load until they are full so there is no question when they are done. AGM CAR starts dwindling at 80% charged and it takes 8 hours or so get the last 20% in.
This leads to why lithium’s are such a better fit for my marine house bank. When I’m cruising with AGM batteries they are never fully charged until I reach a dock. The last 20% takes 8 hours. I rarely run my engines that long and it’s not enough load for a generator. Consequently, cruising shortened the cycle life of my AGM batteries. In contrast, the last 20% of lithium’s charge time is no longer than the first 20%. Even better, I don’t want to charge the last 20% of lithium except occasionally for top balancing. With AGM I was always trying, and mostly failing, to fill up my batteries and prevent capacity loss. With Lithium however much charge I get every day is fine.
It's also why lithium’s are easier to set up. Historically, battery charging systems monitored charging output and not charge acceptance so they never really knew when the battery was full. Some, such as Balmar, took a conservative approach and they could not be set up to charge beyond 90 or 95% charged. With lithiums you set the bulk voltage to 14.4 and then they hit it you’re 99% full so you drop to an absorb of 13.6 and float of 13.4.
Lithium Cutout
Speaking of drop in lithium batteries cutting out when I looked at this closely, I decide it was a non-issue. Lithium batteries cut out under specific conditions so if my discharge capacity dwarfs the boat loads (it does) and I keep the batteries below 100degrees f and above freezing then they’re never going to cut out except for a cell short which is in keeping with the other cut out risks like the positive cable falling off my regulator.
Here is what Battleborn said about their built in BMS and when it cuts out and in:
The BMS is not bucking or doing any voltage regulation. It is simply monitoring the voltages, current and temperatures and acting as a high current switch, when things are out of whack. Charging and discharging circuits may be opened independently. For each, we have a bunch of high-current MOSFETs (along with some snubber circuitry) doing the switching. Basically, the charging switches will open if one of the following is detected:
- one cell exceeds a prescribed high voltage
- the cell temperatures exceed 140F,
- the MOSFET temperatures exceed 170F,
- the charging current exceeds 200A for 0.5s, or 100A for 30 seconds.
- one cell falls below a low voltage threshold,
- the cell temperatures exceed 140F,
- the MOSFET temperatures exceed 170F,
- the cell temperatures fall below 25F (deadband at 30F),
- the discharging current exceeds 200A for 0.5s, or 100A for 30 seconds.
You can see that if the system is well balanced and kept at moderate temperatures then they will not cut out.
Finally, the reason I chose drop in batteries is on the one hand when I looked at systems that used an external BMS the expense of refactoring my positive bus into a charge side and a load side so I could put in the cut out solenoids created a wiring bill that increased the cost of the project by 50 to 100% while on the other hand when I looked closely at a quality drop in battery like Batttleborn that has a reasonable sustained output capacity I couldn’t find a downside. The drop in system was simpler and with little downside.
