Charging the Start Battery

Charging our new Start Battery

Purchased a Duracell 12v AGM SL178 Battery to replace our 5.5 year old battery ( same make and model)

We found that our old battery was not being charged unless Shore Power was connected to the boat.

We had issues starting a few times recently and figured we should take the battery out of the equation.

The old battery will spend retirement in our Home Generator which has a long dead battery. Used the old Generator battery for the Core Charge recovery.

We need a reliable way to charge the start battery. Our House batteries ( 4 x Trojan 6v T105 Batteries in 2S2P configuration for 12v 450Ah.) and I decided to go for the Orion TR Smart 12 | 12  18 Isolated DC to DC Charger by Victron. 

Just adding to our Stable of Victron System equipment :)

The Orion can be used as either a Charger or as a Converter ( ie. stable DC output ) My plan is to use it to charge the Starter Battery from the House Battery. From everything I have read, it should only go into charge mode when the Input V ( House Battery V) is above a set limit ( set using the VictronConnect App ) and when the Starter Battery V is below a set limit ( again, set in the App )

So basically, this will mean that the charger will try to charge the start battery when the house battery voltage is above it's float value and if the Start battery is below it's Absorb value.

The House battery V goes up when it's being charged. ie. If the engine is running, the Multiplus is charging or if there is sufficient Solar to charge the House Battery. 

If that concept is incorrect, then there are other choices such as a manual switch to turn the Orion on, or the Engine Detection System override which would turn the charger on when the Alternator is running. 

Whichever method I end up using, it should involve keeping the existing Alternator to house Battery connection. I plan on upgrading our House Battery bank from Flooded Lead Acid to LiFePo4 batteries later this year/ early 2023. Their cost has dropped significantly in the past 5 months. Right now the Chin Batteries are looking good.

This diagram is modified version of the one in the Victron manual for the Orion.

This shows the Source ( Input ) supply being the House Battery and the Charged Battery being the Start Battery.

The Start battery is just a couple of feet away in a straight line, perhaps 6' around the bends from the other Victron Equipment. So I plan to install the Orion on the bulkhead adjacent to the Multiplus.

That will enable a short run of cable to the Positive Bus Bar and the Negative Bus Post, for the Input cables. The output will pass through the bulkhead adjacent to the Multiplus into the locker where the Start Battery is located.

I'll mount a 20Amp fuse on the +ve Bus Bar to the input of the Orion and a 20Amp fuse inline of the wire from the Orion to the Start Battery +ve.  The Start & House batteries share a common -ve. Victron don't make the 18Amp Orion in a Non-Isolated version and I understand that it's ok to join them, so there will be a wire from the -ve in and the -ve out to the -ve Bus post.

I'm curious to see if the Orion shows up in the Victron VRM if it does, then I should be able to view the charging history online. That would be cool too.

Ok, waiting on the arrival of the Orion, I have everything else. The max wire size for the unit is AWG6 

The Wiring calculator shows 14AWG but I'll use 10AWG.