Ammonite
Well-known member
As a result of my other recent thread "Alternator Voltage / Replacement" I'm having a bit of a rethink when it comes to battery charging.
I currently have 2x 110amp SLA (House), 1 x 110amp SLA (Starter) and 1 x 120amp AGM (Thruster). All are 12v.
Alternator charging: I currently have a 60amp Alternator that appears to have been internally modified to output 14.8v with Battery sensing via a 1-2-Both switch meaning that when set to 2 only the house bank is sensed and if set to 1 only the starter bank is sensed. The alternator appears to be working but there is considerable heat damage / melting around the negative side of the rectifier plate. The output from the alternator goes directly to a 3 way low loss splitter (max 0.25v loss according to the manual) to each bank.
Engine off (no shore power): The starter and house bank are both charged via a wind generator which in practice I very really use. The house bank is also charged via an 80w solar panel and Victron smart controller. This works really well. The thruster battery is charged via a Cyrix VSR from the house bank which connects at 12.8v and disconnects at 13.8v.
Mains charger: I have a 20amp three output Sterling smart charge to charge each bank. This is set to the SLA profile. 14.4v max, 13.5v float.
Current issues:
Overcharging of the unsensed battery banks under engine. When the 1-2-Both is set to 2 it results in a steady 14.7/8v at the house bank but up to 15.2v at the others.
Undercharging of the thruster battery due to the mains charger having an SLA profile and the Cyrix VSR limiting the voltage to 13.8v.
Risk of Alternator damage in the event there is problem with battery sensing due to a duff battery etc
Solution: I am going to replace the heat damaged alternator with a Prestolite 70amp with a nominal output of 14.4v. If I keep the existing sensing arrangements this will result in 14.4v at the sensed battery and, based on what I'm seeing currently circa 14.8v at the others, which is ideal for the AGM but a bit high for an SLA, although it's reliant on what's happening with the sensed bank. This is all based on the sensing wire upping the voltage to account for the any load and losses through the splitter.
Add a Battery to battery charger for the Thruster to ensure that it has the correct AGM charging regime. This would then allow me to disconnect the Thruster battery from the alternator splitter and eliminate the overcharge risk. It would still use the mains charger SLA profile which is set to 14.4v with a 13.5v float. The mains charger is only used when in marinas and not on my regular mooring. Edit: on second thoughts this last bit won't be needed and I'll only need to charge the starter and house via the mains charger!
Switch the Cyrix so that it charges the starter battery from the house bank and remove the feed to the starter battery from the battery splitter. This would limit the charge to 13.8v under engine but it would still periodically charge the starter battery to 14.4v when using the mains charger. It would also remove the risk of over charging the starter battery due to the current sensing arrangements.
Remove the sense wire from the 1-2-Both switch and reinstate back onto the B+ terminal on the alternator. Remove the battery splitter which is now redundant. Connect the battery splitter input (from the AlternatorB+) back onto the starter motor solenoid where it would have originally been.
Apologies for the lengthy post but I'd appreciate your comments / other ideas. I have no plans to go down the li-on route due to a combination of cost and the current capacity being more than adequate for the type of sailing we do at the moment. Thanks
I currently have 2x 110amp SLA (House), 1 x 110amp SLA (Starter) and 1 x 120amp AGM (Thruster). All are 12v.
Alternator charging: I currently have a 60amp Alternator that appears to have been internally modified to output 14.8v with Battery sensing via a 1-2-Both switch meaning that when set to 2 only the house bank is sensed and if set to 1 only the starter bank is sensed. The alternator appears to be working but there is considerable heat damage / melting around the negative side of the rectifier plate. The output from the alternator goes directly to a 3 way low loss splitter (max 0.25v loss according to the manual) to each bank.
Engine off (no shore power): The starter and house bank are both charged via a wind generator which in practice I very really use. The house bank is also charged via an 80w solar panel and Victron smart controller. This works really well. The thruster battery is charged via a Cyrix VSR from the house bank which connects at 12.8v and disconnects at 13.8v.
Mains charger: I have a 20amp three output Sterling smart charge to charge each bank. This is set to the SLA profile. 14.4v max, 13.5v float.
Current issues:
Overcharging of the unsensed battery banks under engine. When the 1-2-Both is set to 2 it results in a steady 14.7/8v at the house bank but up to 15.2v at the others.
Undercharging of the thruster battery due to the mains charger having an SLA profile and the Cyrix VSR limiting the voltage to 13.8v.
Risk of Alternator damage in the event there is problem with battery sensing due to a duff battery etc
Solution: I am going to replace the heat damaged alternator with a Prestolite 70amp with a nominal output of 14.4v. If I keep the existing sensing arrangements this will result in 14.4v at the sensed battery and, based on what I'm seeing currently circa 14.8v at the others, which is ideal for the AGM but a bit high for an SLA, although it's reliant on what's happening with the sensed bank. This is all based on the sensing wire upping the voltage to account for the any load and losses through the splitter.
Add a Battery to battery charger for the Thruster to ensure that it has the correct AGM charging regime. This would then allow me to disconnect the Thruster battery from the alternator splitter and eliminate the overcharge risk. It would still use the mains charger SLA profile which is set to 14.4v with a 13.5v float. The mains charger is only used when in marinas and not on my regular mooring. Edit: on second thoughts this last bit won't be needed and I'll only need to charge the starter and house via the mains charger!
Switch the Cyrix so that it charges the starter battery from the house bank and remove the feed to the starter battery from the battery splitter. This would limit the charge to 13.8v under engine but it would still periodically charge the starter battery to 14.4v when using the mains charger. It would also remove the risk of over charging the starter battery due to the current sensing arrangements.
Remove the sense wire from the 1-2-Both switch and reinstate back onto the B+ terminal on the alternator. Remove the battery splitter which is now redundant. Connect the battery splitter input (from the AlternatorB+) back onto the starter motor solenoid where it would have originally been.
Apologies for the lengthy post but I'd appreciate your comments / other ideas. I have no plans to go down the li-on route due to a combination of cost and the current capacity being more than adequate for the type of sailing we do at the moment. Thanks
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