Hello
I have 24 V battery bank on the catamaran. Serial pairs of 12V Victron Telecom batteries connected in parallel (4 pairs).
Last year one cell in one battery failed. It became 10 V battery instead of 12V. And all current form working pairs went to this defective 22V pair trying to charge it. Wires overheated and connections melted.
Replace with lithium batteries and BMS’s that communicate with your GX device, such as Victron’s next-generation smart lithium batteries. As for the overheated wires and melted insulation, that’s an installation problem. Your wiring needs to support your over-current protection devices. Use terminal fuses on each battery. I would suggest you find a reliable Victron dealer close to you and seek their assistance.
Per cell monitoring wont happen if you use 12v batteries.
However you could use a battery balancer for each string of batteries and use the alarm output to signal voltage deviation between the batteries.
Battery fuses for each battery string would be a good idea.
Agree with the above. Terminal fuses and more importantly cable that is more than adequate for the designed load so it hopefully doesn’t start a fire before you catch it!
With only a 400a fuse on one end of the bank, you have to assume that at any point in time any part of the rest of that circuit can/will experience that 400a. Depending on your charge/discharge rates you could have fused between batteries at say 150 or 200a and it would have popped as soon as the battery defected and everything would be happy till you realized you lost 25% of your capacity
400 A fuses came by design from the factory. I realized the danger of high currents between bank pairs just last year. No adequate protection at all. Termal breakers will help for sure
To “catch” the problem on time, I am thinking to buy new Victron battery balancers for each pair. If one battery in pair will fail, batteries will not be able to keep same voltage, and I will have an alarm on the dashboard from balancer build in alarm relay.
Is that schematic exactly how they had designed the system? Seems foolish to me to set it up like that when the cost difference is marginal to fuse each group separately
Even fusing each series group @200a rather than pairing them with a 400 may have helped prevent this. Personally that’s how I would, and have fused similar battery configurations. It’s a little more cost but the risk factor between 200 and 400amp worst case scenarios is worth it imo
Look, just battery - 24V. They care about rest of the system, functions, safety etc. But battery safety was neglected. I know many boats with same 24V architecture. Pairs of 12V. And no protection against each other. All Lithium ones have protection, but AGM - nobody care. I see it as safety hazard. Everybody should check their installations.
For sure I will look at MRBF. What will be proper Ampere rating for those fuses, if you can suggest formula?
My bank is 4 x (2 x 165Ah 12V) = 660Ah 24V
Yes, just a poorly designed system as far as safety is concerned, but maybe not entirely their fault as the drawing assumes a 24v battery not 2x 12v in series
How big is your inverter? That drawing calls for a 400a fuse to the battery bank and your original drawing shows a pair of 400a fuses (potential 800a on the line to the inverter). That’s ok if it’s a 10kw inverter and the wire size is appropriate, but if it’s only a 5kw and wiring sized accordingly for 5kw(as per the drawing) that side of the system isn’t protected either in its current configuration
24V 12V Factory A3.pdf (68.1 KB)
Here is original factory diagram, you can see two 24V batteries in each hull. In reality was delivered with two pairs of 12V+12V in one hull and two same pairs in other hull. As you can see, no protection by design between two hulls. And yes, 400A x2 fuses are too big. Factory inverter-charger was 2.5 kw, now I have 5kw Victron Quattro. I will need to reduce fuse amperage.
Many suggest MRBF Fuses, but I will need to have some kind of switch in line with them, to be able to disconnect broken pair of batteries. I was thinking MRCB Circuit Breakers, which can do both, protection and manual disconnect
So, question is: MRBF fuses plus switches or MRCB Circuit Breakers (Blue Sea 187-Series) ?
Should I keep properly sized fast acting ANL fuses in serial with thermal fuses at the point of connection to the system to protect from accidental shorts in the system?
Ok that is making a lot more sense why they have 400a fuses there, that’s the busbar feeder not direct to inverter. Although the wire size is smaller than I would personally use on a 400a circuit, that in itself is ok as your devices beyond the busbar are fused or breaker’d appropriately (for the original hardware installed).
The setup doesn’t offer any direct protection between hulls, though the main 400a would offer that bank-bank protection in the case I’ve a major overcurrent while still allowing both sides to remain energized and operable if one bank dropped out.
Again, the drawing is for a 24v battery so no other protection would be shown there. Unfortunately whoever did the installation and modification to this design neglected to install any protection
I have no experience with dc breakers so I’ll leave that up to someone else, though it seems a lot of guys on here are not a fan of them.
I also had problems with a similar configuration on a sailing boat with Telecom batteries connected in parallel (2 pairs). The result was not as dramatic as yours, but with the serial connection one of the batteries always suffers from undervoltage or overvoltage. Despite the balancer. The lifespan was shortened. After 3 years it was over.
My solution was 12 pieces of 2V OPzV batteries in series. They come in different sizes, but it always stays at 12 in the series. Now, after 5 years, the voltage difference of the individual cells is under 15mV
Yes, I was looking to OPzV, but usually OPzV cells are big. I have limited space in battery compartment, and basically stuck with telecom form factor. Victron has good looking Lithium NG 24V 300Ah, but they will not fit in battery space.
Interestingly, you mentioned, balancer did not help, what brand was it? I am planning to install Victron’s balancers for each pair. Will it work, what do you think?
Lithium batteries are a different world, but consider that 4 pairs of 12V batteries actually have 48 2V cells connected in serial and parallel, instead of 12 by OPzV in serial with only one fuse! In terms of volume, the 2V cells are 10% smaller than 12V batteries and can be installed in any position. The size of OPzV batteries I used is 65x198x592mm (385Ah) but this varies greatly from manufacturer to manufacturer. DoD goes up to 80%.
As for Balancers, they can only balance 1A. You had to install several in parallel to achieve a visible effect.
If you stick with 12V batteries, I would recommend connecting the midpoint of all pairs together (with fuses)
