Air date: February 21, 2012
On a previous show, Dwight Escalera (Executive Marine Services) gave us a primer on some of the new battery technologies that are entering the marine market, and explained how they differ from lead-acid batteries. On this show, we go into more detail about installation procedures to ensure that safety hazards are eliminated and battery advantages are maximized.
Lithium-ion batteries came on the market in the 70s, but only became viable for marine uses in the 90s when larger sizes became available. At the same time, new problems arose in terms of heat and fire hazards.
The problem is that lithium, the metal, is very reactive. The batteries do perform well as long as they are kept within safe operating parameters, and that’s where the problems come in because people think, “A battery is a battery,” and they don’t realize that they need one with a battery-management system that can actively make changes.
It’s important that the BMS be included within the system, and that it be a management system, not a monitoring system. The BMS will manage each individual cell and will compare the cells to make decisions about discharge and recharge.
When batteries are in a bank, there are more cells in the system, and the BMS has to be able to analyze all those cells, or else each battery has to have its own BMS. (In a lead acid battery, there may be difference, but they can be averaged out, except in rare cases.) With Lithium Ion, it’s very easily done to create an unsafe condition, especially when recharging or discharging, so it’s important to have a BMS monitoring both high and low voltages.
In the installation, you would have to install a relay to allow the BMS to entirely disconnect the battery or the bank to let things settle down before you reach an unsafe situation. The relay should be normally open, and require electric power to close the relay, i.e. a deadman’s switch. The master relay must be included in the installation of the batteries, and that needs to be controlled by the BMS.
In addition, we still need to include overcurrent protection to prevent boat fires. Overcurrent protection at the source of power in many cases could have prevented those fires, and with lithium batteries there are tremendous current flows, thousands of amps, and that becomes another problem.
Fuses and circuit breakers will open if ratings are exceeded, but Amperage Interrupt Circuit (AIC) gives you a number that tells you what a circuit breaker can withstand and still operate. But with Lithium batteries, you can provide thousands of amps in a surge and that circuit breaker will exceed its rating, but there’s so much current that you could literally weld it closed.
So, in selecting a circuit breaker, you need to be sure you have the trip rating as well as the proper AIC rating. This will ensure that mater overcurrent protection will still perform its function.
In installing these new batteries, you also need to be concerned about location. The batteries produce gas that is heavier than air, and these gasses are also explosive. If they exceed levels, and they are not vented properly, they can create a “bomb” inside the battery case, unless the gasses can be controlled in the safe matter.
The concerns about BMS and overcurrent protection then need to be combined with concerns about actual voltage on the boat. We need to be especially careful about charging voltages. There are DC-to-DC chargers now that can be connected into existing lead-acid systems, and they can be used to charge lithium batteries as well. But, the two types of batteries still need to be kept separate. Be sure you do not have the old battery parallel switch. You need a switch that goes to either lithium or lead acid, not both, because you need to be able to change the voltage.
It would be best if the charger would controlled by the BMS so you won’t exceed any of the safe parameters.
Again, if you are using a DC-to-DC charger, you can control either the lead-acid bank or the lithium battery bank. You just need to make sure they are kept completely separate. The drawback is that you lose the advantage of lithium’s high charging rates when you run it through a DC-to-DC chargers because your system will be limited by the maximum available for the lead-acid bank.
The wiring, too, much be completely separate, and there needs to be overcurrent protection at the source of power on both sides. You must select the batteries by what you are using them for, i.e. engine start or house bank.
Another important point is that when you reach the low-voltage level, you have to stop using the battery. Again, this is different from lead-acid batteries. With lithium, the BMS will sense an unsafe situation and turn the batteries off. In that case, you’ll want to be able to switch to a second bank, or just keep an eye on the charge level so you don’t get close to that situation.
Again, that’s something else that people just have to become aware of. Even if everything is installed correctly, the end user will still have a learning curve.
Will these batteries save money? You will have to change-out wiring, but the actual performance shows lithium can last 10 times longer than lead-acid batteries. (Similarly, the purchase price may also have a factor of 10.) A lead-acid battery may last 8 years, but lithium might last 50 to 80 years. When the purchase cost comes down, there will be no hesitation.
ABYC is still working on a paper describing concerns and best practices. The manufacturers are also being very good about providing information. The problems are coming in when people want to be do-it-yourselfers and are buying lithium batteries online without complete BMS systems. Anyone working with these products needs to become educated about these batteries themselves.
