MUMM36 ZAMBONI Charging System

We have had our MUMM 36 race boat ZAMBONI since 2015.  

The battery electrical system consisted of two batteries: engine and house.  

Original batteries were standard 12V group 24 flooded lead acid batteries. 

There units were secured underneath the engine cowling in battery boxes:

Engine on left
Fuel tank on right

The engine and house batteries could be isolated with switches:

They could be combined with the center switch.  Worked well, very flexible.  We typically run with the batteries uncombined so that we can still start the engine to charge the house battery before combining the banks to charge.  In a pinch we could combine the engine/house for a longer run time, but risk not being able to start the motor.

The original batteries (age unknown) were not up to the task and were replaced with group 31 AGM batteries in 2016.  We found that we could run our house loads for about 8 hours before an alternator charge was required.

The standard alternator was the Yanmar supplied 35 amp unit.

The 105AH AGM house battery discharged to 40% (<12v) would take over 2 hours to recharge to 80%.
We were always running our house battery low on distance races.

This season, our 5 year old AGM batteries would not hold a charge anymore.  They would charge to 12.2V, then quickly discharge to under 11V in a couple of hours.

Since we needed to replace them before the Lake Ontario 300 race, we ordered a replacement Lithium Ion battery to replace the house battery.  LiFEPO4 batteries can be discharged safely and reliably to a 10-20% discharged rate which means we would have 900 watt hours of usable battery (vs ~500 watt hours) with the old AGM.

Lithium batteries will take as much charge as an alternator can deliver.  Alternators running full out can and will overheat and burn out.  To prevent this, you need to put a DC to DC charger controller to manage the charging of the lithium house bank.

We also needed a method to monitoring the state of charge of the house bank other than voltage.

I ended up purchasing a shunt AND a DC-DC Charger from Victron Energy.

We ordered the new lithium batteries in early May, but with Covid supply chain issues, we did not receive them in time, so we use two group AGM batteries that Michael had from his boat.

Here it is all installed secured with a plywood box that we fabricated:

The 3/4" plywood box also secured the batteries better.

Our original 35amp alternator was also pooched:

So I ordered a new 80amp alternator to replace it for $270:

The 80A alternator will run cooler and at lower RPMs than the old.

First run

Here is the wiring schematic:

Click for BIGGER

All new battery cables were done in AWG6 wire and mechanically crimped copper battery cable lugs.

The DC-DC Charger is a 12/12-30 Orion Smart TR unit from Victron Energy.  This unit connects up to the common negative (non isolated) ground and to the positive posts of the engine and start batteries.  It allows the house battery to be charged with 30amp max (360W) when it senses the engine battery is being charged with the alternator charge voltage over 14v.  

The DC-DC charger also allows a charge profile to suit the type of house battery being charged.  

The DC-DC charger also means we no longer have to combine the batteries with the battery switch to charge the house battery with the alternator!

The other problem this DC-DC charger solves is the fact that lithium batteries work until the internal battery management system shuts the battery down because of a low state charge.  This will toast a charging alternator in less than a second!

The DC-DC charger talks over Bluetooth to a Victron Connect phone app to monitor the charging.

Here you can see the Input voltage of 15.0V from the alternator and an Output voltage of 14.2V absorption charge to the lithium house bank.

The shunt is a Victron Energy SmartShunt 500A/50mV.  This unit installs on the negative side of the house battery and monitors all current going in/out.  It also connects to the engine and house batteries to monitor their voltage.
See the above schematic.

The smart shunt also talks over Bluetooth to the Victron Connect App:

The APP keeps track of the power in/out and accurately displays a percentage of charge.
In the above screenshot, the charger is bulk charging the lithium battery with almost 24A of current.

The SmartShunt is very useful for calculating loads and how long the house battery will last.
I have found that on an overnight race, with all instruments and nav lights on, we were using approximately 4A from the house battery and the 100AH lithium battery would last 16+ hours.   

To my surprise, charging a tablet and a couple of phones uses over 6A of power!

Here is a dive into the install of the lithium house battery that finally came in late August:

http://svstilltime.blogspot.com/2021/09/mumm36-zamboni-engine-lithium.html

All we had to do was change the charge profile with the APP.

We also ordered and received a lithium starter battery from Alberta Lithium:

https://www.ablithium.ca/products#!/13-2V-8ah-420-CCA-LiFePo4-starter-battery/p/285469327/category=80046389

This is a starter battery for motorcyles/ATVs and its 420CCA rating is more than enough to start the Yanmar engine.  Very small and only weighs 3 lbs (vs 70 lbs for the AGM).   I hooked it up temporarily and was able to start the Yanmar engine multiple times.  However, the battery connectors are different that what we have, so will look into permanently installing it next spring.