Re: [Amel Yacht Owners] Re: Battery Compartment Explosion

Willem Kroes

Hi all Amel sailors,

Just a few comments about Lithium Ferro Phosphate (LFP) batteries. I installed this year early May 8  batteries at 12 V with 100 Ah capacity each in the existing Amel configuration forming a 24V bank with 400 Ah capacity. Dimensions of the batteries: 329*171*235mm; so a bit higher than the lead/acid Freedom batteries Amel installed. I had to cut 2 cm from the bar below the lid of the battery compartment. I did this on the upper side, so this change is only noticeable when you take measures. Other battery specifications:

·         nominal voltage = operating voltage 12,8V

·         charging voltage: 14,6V

·         internal impedance: < 150 mΩ

·         maximum continuous charge: current: 1C = 100A

·         maximum continuous discharge current: 1,5C = 150A

·         standard charge, constant current: 0,2C5A, constant voltage 14,6V and 0,02C cut off (by the BMS)

·         standard discharge, constant current 0,2 C5A, end voltage: 10.0V (cut off by the BMS)

·         operating temperature range: charge: 0 – 45, o C discharge:  -10 – 65 o C

·         can be wired in series up to 28V and unlimited in parallel

·         built-in Battery Management System (BMS) protects cells against excessively high and low voltages, high currents, short circuits and excessive heat and cold

·         automatic cell balancing by the BMS which reduces the charging rate in cells that have been topped off first, letting the rest of the cells catch up

·         battery holds its charge for up to a year without a load,; so no need for a trickle charger

The manufacturer in China claims that it is a ‘drop-in replacement’ for lead acid batteries. In my opinion, this claim is not correct. The reason for this is that it is important to keep charge and discharge currents within the parameters set for the batteries. For example: if you use the standard 55 or 100A alternators on the Super Maramu and leave the dock with almost full batteries, the current will go down when the batteries are above 98% and even more down, may be charging only 1 or 2 amps at 100%. A normal behaviour with lead acid batteries. But with LFP batteries the BMS will cut off the charge when the batteries are 100%. This will have the same effect as turning the ignition switch off with a running engine. It is likely that the diodes of the regulator of the alternator will not survive. So it is essential to have a regulator that turns off the charging current when the LFP-batteries are charged 100%.

Another possible problem is excessive heat of the alternator with the risk of burning. This, because the internal resistance of LFP-batteries is much lower than lead/acid batteries. On Aquarius this problem will be, I think, almost absent because there is a 100A alternator and a battery bank of 200 Ah. But if you stay with the same nominal battery bank of 400 Ah and you have the standard 55A alternator without any high temperature shut off feature installed, then the risk of burning your alternator will be present. The alternator will perform at maximum capacity for hours if the discharge rate of the batteries is considerable. With lead/acid batteries the normal discharge rate will be not much less than 65% and even after motoring 1 hour you will notice a considerable decrease of charging current. This is because the internal resistance of the battery bank goes up very quickly after being charged at 75% of its capacity. With LFP batteries you need a regulator that decreases or stops the charging current when the temperature of the alternator becomes too high.


Also the battery charger has to be programmed to match the new LFP-battery bank. Most modern chargers will do the job. On my boat ‘Kavanga’ SM#351 there is a Mastervolt Chargemaster 24/60 installed and this charger can be programmed to match the specifications of the LFP-battery bank with ease. The old backup 30A Dolphin can’t be programmed. The only thing is to set the internal dip switch to ‘gel-batteries’ and turn the ‘pot meter’ regulating the charging voltage to its maximum setting. Under normal conditions (discharging not more than 60%, the Dolphin will not start charging. But by switching the microwave on for a minute or so, voltage will drop under the level for activating the Dolphin. Once activated with this trick, the old Dolphin charger will continue with charging until the batteries reach around 98%. I suppose that placing two or three diodes in the measuring cable of the Dolphin, it will start charging if activated by the on/of switch on the 230V AC panel.

For the alternator I decided, being during the wintertime in the Netherlands and the boat in NW-Spain, to buy a new Prestolite 55A, 24 alternator and a Mastervolt dealer took out the internal regulator and connected in stead a Mastervolt Alpha Pro external regulator programmed for the LFP-batteries. The Alpha Pro has also a connection for a temperature sensor and this sensor is connected by a big hose clamp to the house of the Prestolite alternator. The Alpha Pro is programmed to cut the current when the alternator’s temperature rises over 115 o C.

The Mastervolt dealer also provided me with a scheme for the connections on board. The only problem turned out to be the relay for the activation of the Alpha Pro. This had to be a 24 V relay, not withstanding the engine is started by a 12V  starter. The reason is that the relay is also connected to the 24 V cable. The first installed 12V relay burned after 36 hours of engine running. After changing to a 24 relay the whole system worked perfectly during a several months of cruising.

This configuration ensures that under normal conditions the parameters of the LFP-battery bank of charging and discharging will not be exceeded. So the BMS cut off charging feature will not be activated. Nevertheless I also installed a Sterling alternator protector. It’s not expensive (around 55 euro) and will protect the alternator if the connection to the batteries is suddenly interrupted.

Finally the purchase of the LFP-batteries. These batteries are very expensive in Europe and what I heard, also in the USA. The Sterling company is selling the 100 Ah 12V LFP-battery (33 cm format) for £1200 each. So I spend some time looking at the Chinese Alibaba’s website for manufactures of LFP-batteries providing comparable specifications. It took some time, but in the end I found a company making these batteries with a CE certificate and selling these for a price around 400 US dollars each. With shipping cost, import duty and European VAT paid, the 8 batteries cost me around 4000 Euro in total. A lot of money compared to the price of 8 lead/acid marine batteries (1000-1200 Euro) in the Netherlands, but offering about half the weight, double usable amp hours, much faster charging and hopefully 5 to 8 times the life expectancy of traditional batteries.

After one  season I am very satisfied by the performance of the LFP-batteries. I can’t tell anything about the claim of the manufacturer that the batteries have a service life (not less than 85 á 90% of the nominal capacity) after 2000 cycles or more.  I hope this will turn out to be true.

Willem Kroes


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