New charger, new question

[SalingSue]

I recently bought a Victron AC to DC changer
The charger has a few modes, including normal and lithium

https://www.victronenergy.com/charge...ger-waterproof

My boat has two batteries, one AGM, one Lithium, both negatives bridged together and then grounded to the engine, one positive to battery switch position 1, the other to position 2

I hooked the charger up to the AC input line my OLD dual bank charger was hooked to

I hooked the negative DC charger output up to the AGM negative terminal

I hooked the positive DC charger output to the common on the battery switch.

My thinking is whatever position I have the switch I can use shore power to charge that battery (making the change on victronconnect from normal to lithium ofcourse)
PLUS I can have both batteries disengaged and use the "power supply" setting on the charger to feed my 12V systems while on shore power, independent of the batteries.

When charging the AGM, which is about 1yr old, but did get VERY discharged once, I am showing
14.4V on the victron app
14.15 at the common on the switch (with the negative probe on the AGMs neg terminal, same terminal the neg DC from the charger goes to)
14.09 at the AGM directly going off its terminals

The battery feels warm to the touch, no wire or switches feel warm, I am just running the charger but it is also powering the bilge pumps (which rarely run), a propane solenoid/alarm and a couple small indoor LED lights.

Does this sound right with the temp and the voltage differences as well as my method of using this onboard charger


Thank you!

[markcouz]

I can see no reason why your method of charging wouldn't work, PITA to manage but doable.

Some suggestions;

Don't use the charger as a power supply unless you are sure that your loads will never exceed the rating of your charger (you didn't mention which model you purchsed) rather always have a battery in parallel to cater for higher loads.

Switch off charger while switching batteries and changing battery source - will mean that you lose power momentarily while switching.

The voltage drop that you are seeing seems quite high, but as your charge current drops when battery approaches full charge the voltage drop will also reduce, meaning that you should still be able to fully charge at close to 14.4v.

Check all your connections and terminals to see if you can't reduce the volt drop that you are seeing.

[donradcliffe]

What is the purpose of your AGM battery? Is it wired directly to the starter motor, or though your battery switch?

How is your alternator wired? Through the switch (bad)?

Ditto for any solar panels.

[SalingSue]

Originally Posted by donradcliffe

What is the purpose of your AGM battery? Is it wired directly to the starter motor, or though your battery switch?

How is your alternator wired? Through the switch (bad)?

Ditto for any solar panels.

AGM is the start battery

Alternator through the switch as well as the Victron solar connected to the 330W LG solar.

[markcouz]

Wiring the alternator through the switch is a significant risk unless you have other protection mechanisms that you have not mentioned.

If the switch is operated while the alternator is producing power the voltage will rapidly escalate, at a minimum blowing the rectifier diodes, and possibly damaging electronic equipment connected to the common terminal of the switch.

Much safer for the alternator to be connected directly to the AGM which will act as a sink to limit voltage spikes from the alternator - if you want the alternator to charge the lithium you could switch to both depending on the charge profile of your lithium battery.

[DeValency]

Originally Posted by SalingSue

I recently bought a Victron AC to DC changer
The charger has a few modes, including normal and lithium

https://www.victronenergy.com/charge...ger-waterproof

My boat has two batteries, one AGM, one Lithium, both negatives bridged together and then grounded to the engine, one positive to battery switch position 1, the other to position 2

I hooked the charger up to the AC input line my OLD dual bank charger was hooked to

I hooked the negative DC charger output up to the AGM negative terminal

I hooked the positive DC charger output to the common on the battery switch.

My thinking is whatever position I have the switch I can use shore power to charge that battery (making the change on victronconnect from normal to lithium ofcourse)
PLUS I can have both batteries disengaged and use the "power supply" setting on the charger to feed my 12V systems while on shore power, independent of the batteries.

When charging the AGM, which is about 1yr old, but did get VERY discharged once, I am showing
14.4V on the victron app
14.15 at the common on the switch (with the negative probe on the AGMs neg terminal, same terminal the neg DC from the charger goes to)
14.09 at the AGM directly going off its terminals

The battery feels warm to the touch, no wire or switches feel warm, I am just running the charger but it is also powering the bilge pumps (which rarely run), a propane solenoid/alarm and a couple small indoor LED lights.

Does this sound right with the temp and the voltage differences as well as my method of using this onboard charger


Thank you!

When you want to charge two very different chemistry batteries, the charger should have two (or more) separate outputs with different charging patterns. As far as I can see, this Victron model has only one output. So not a good setup with your Lithium (is it LFP?) and AGM. If you still have the old working charger, you could connect the Victron to the Lithium only and continue using the old charger to the AGM.

Also, very important is to make sure the Lithium is not directly charged by the alternator without either an external regulator with power limiting or a DC to DC charger from the AGM to the Lithium, programmed to the Lithium charging pattern (basically and most important, limiting the current draw from the cranking battery and alternator way below the alternator rating (about 50%)