Blown Battery Fuse- Overcharging AGM 4D

[Schatzi]

Maine: A couple of years ago, I had the Promariner battery charger go up and replaced it with a new one. I noticed some battery life issue (didn’t seem to last as long at anchor between charges) and purchased a Victron monitor (3/2012) from you (Thanks!). Last fall my FWD 4D heated up (very hot), so I replaced all the batteries with new East Penn AGM’s. Since then, I have never received the amp hrs in the house bank that I thought I should have, and the SOC has never matched up with the voltage since Victron installation. Last week, I took the batteries back to East Penn to be tested and was told they were good (except one was overcharged and one needed charge-they should have been the same voltage??). This weekend found a blown 300 amp fuse on the positive side of my FWD battery. Must have been blown for a long while. This allowed the forward battery to be overcharged (don’t know how?) through the negative and the AFT battery was not getting up to full charge and was doing all the discharging while we were at anchorage. I moved the AFT fuse forward and temporarily bypassed the AFT fuse and all is well. SOC is correct, Amp Hrs are better, and both batteries are the same voltage.
My question is: Once I replace the JJN-300 fuse, how do I know if one blows again before the battery gets overcharged? Is there a better way to wire the batteries, so I can’t overcharge a battery if a fuse blows? Would some kind of blown fuse indicator work (if so, what do you recommend)? FYI.. 2/0 awg battery cables are approx. 12-15’ and the battery charger is on all week, while the boat is in the slip. I have attached the schematic for the charging system. The only change is the negatives from the battery go to the Victron shunt and then to the Neg Bus. Thanks in advance!!

 

[Maine Sail]

Maine: A couple of years ago, I had the Promariner battery charger go up and replaced it with a new one. I noticed some battery life issue (didn’t seem to last as long at anchor between charges) and purchased a Victron monitor (3/2012) from you (Thanks!). Last fall my FWD 4D heated up (very hot), so I replaced all the batteries with new East Penn AGM’s. Since then, I have never received the amp hrs in the house bank that I thought I should have, and the SOC has never matched up with the voltage since Victron installation. Last week, I took the batteries back to East Penn to be tested and was told they were good (except one was overcharged and one needed charge-they should have been the same voltage??). This weekend found a blown 300 amp fuse on the positive side of my FWD battery. Must have been blown for a long while. This allowed the forward battery to be overcharged (don’t know how?) through the negative and the AFT battery was not getting up to full charge and was doing all the discharging while we were at anchorage. I moved the AFT fuse forward and temporarily bypassed the AFT fuse and all is well. SOC is correct, Amp Hrs are better, and both batteries are the same voltage.
My question is: Once I replace the JJN-300 fuse, how do I know if one blows again before the battery gets overcharged? Is there a better way to wire the batteries, so I can’t overcharge a battery if a fuse blows? Would some kind of blown fuse indicator work (if so, what do you recommend)? FYI.. 2/0 awg battery cables are approx. 12-15’ and the battery charger is on all week, while the boat is in the slip. I have attached the schematic for the charging system. The only change is the negatives from the battery go to the Victron shunt and then to the Neg Bus. Thanks in advance!!

None of this makes much sense but this is what I read.....

* You were not receiving the Ah's because you only had half your programmed bank.

* How far apart are the forward and aft battery? If they are close to each other and the wire can be "protected" then one bank fuse should be sufficient. If they are far apart then you will need two fuses to protect the wire..

* I would much rather see the fwd and aft batts wired in parallel on the neg side, like the pos side, then the loads taken from opposite batteries. Meaning all neg connections feed to fwd battery and all pos connections to aft battery. This will help keep them balanced. It is likely you are creating an imbalance the way they are wired.

* I am at a loss as to how you blew a 300A fuse without a dead short unless it was defective. You could have blown it when the ProMariner went up and never noticed. If the fwd battery heated up you could have developed an internal short and also blew the fuse though this is unlikely as these shorts start out as small drains and kill the bank well before you'd trip a 300A fuse..

* You can't over charge the fwd battery with a blown fuse. This is impossible unless the wiring diagram does not match the drawing. If that fuse blows you have no charging and an open circuit. If you are over charging one battery with the charger, then all batteries will be over charging.