Hunter 38 Lithium Ideas

[mpearce]

I have a 2005 Hunter 38…time to replace my 12v house bank that is currently 4 X 205Amph 6v Trojan batteries. I’m looking for advice on how to work lithium batteries into the mix. Do you have schematics of potential set ups available?
I’m wondering if/how the solenoid on the charging switch panel comes into play between the house and start battery banks. I’m aware that the alternator needs protection with a regulator and looking for practical solutions that others may have employed.

 

[Johann]

This is a great plan:

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The solenoid/combiner is replaced by the Orion XS.

 

[jssailem]

Watt Cycle is marketing some 100AHr that are nearly drop-in units. You will need proper charging capabilities to optimize their use. I just bought 3. They include the BMS and a Bluetooth interface at $175 per battery. I received a notice that they are promoting on sale the same battery without the Bluetooth connection for $159.
I have no connection to this resource.

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[heritage]

You might want to buy your batteries right away. Tariffs on Chinese goods, or even the threat of tariffs, will more than likely drive up the prices.

 

[Johann]

You might want to buy your batteries right away. Tariffs on Chinese goods, or even the threat of tariffs, will more than likely drive up the prices.

That and also prices will go up as excess inventory sells off. China apparently made a ton of cells for the EV market that never took off.

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[marcham]

I did this exactly on my H380 last winter.
You have a decision to make: connect the alternator output to the house battery or to the start battery?

If the alternator goes to the start battery, you'll need one or two DC-DC chargers (at least 50A of charging output). If you connect the alternator to the house battery, you just need a small DC-DC converter (18 amp) if you move the windlass feed from the start to the house battery.
This assumes that you have an external alternator regulator and you know how to program it for lithium (over-charge would cause your battery BMS to disconnect and fry the alternator!).

I created an always ON charging bus bar for the MPPT controllers and for the pair of DC-DC converters. This goes to a Victron Lynx battery distribution (easily modified with just a few bolts to hold fuses). The Lynx goes to: DC charging bus bar, inverter and HOUSE battery switch. There is a disconnect to the line going to the inverter. A Victron smartshunt is attached to the negative input of the Lynx to track voltages and power. Batteries and inverter are protected by 300A class T fuses. DC charging distribution bus uses MRMF fuses.

Took me 3-4 evenings to rewire everything including the 2 new DC buses ... the bulk of the work is crimping and heat shrinking! Fine tuning the external regulator probably took another 30-40 minutes under way (fine tuning behavior to better respond to load changes from the DC-DC converters).

This fall I plan to move the alternator to the house side. This will require moving only 3 wires and a new Mega fuse, reconfiguring the DC-DC converter program for AGM and reprogramming the ARS-5 regulator for lithium. The Cerbo GX will have a relay to shut down the regulator when the battery has achieve 100% for 15 minutes.

My advise is to do a complete electrical survey of your boat. Study the DC wiring schematic in the owner's manual, ensure it matches how your boat is currently configured and start labelling cables that aren't attached to the DC panel. Draw it out and from there you can determine what's required to go to lithium. Your combiner will have to go!.

Previously I had 400 Ah of AGM, now I have 420 Ah of lithium and can spend about 4-5 days at anchor with no sun to power the 200W of solar panels. Overall, this is a way better system than AGM. For one, the voltage is higher (13-13.5 instead of 12-12.5) so some devices draw less current. Two is you can use 80% of the capacity (although I've rarely gone below 50% with daily solar top ups. 400A Lithium = 640 Ah of AGM, saves a lot of weight and frees up compartments for storage. In an emergency if the start battery were to die, I would move one DC cable about 12 inches to connect to the wire going to the starter (no combine switch).

I bought SOK batteries last year. Based on the current market, I'd go with a single Epoch battery with Victron comms (connects to the Cerbo BX). 12V 460Ah LiFePO4 Battery | Group 8D Size, IP67, Heated, Bluetooth & Victron Comms



I've attached my current diagram.

 

[heritage]

Looks good Marcham, except shouldn't the class T fuse be placed where the two lithium house batteries are paralleled instead of near the inverter?

 

[marcham]

I have class T fuse about 12 inches from the lithium batteries, then the 2/0 cable goes to the Victron Lynx (6 feet away). Each circuit in the Lynx has an appropriately sized Maxi fused (based on wire size and loads). From the Lynx , a 2/0 cable goes to the inverter (4 feet away). As the inverter can produce DC, it must also be fused as close as practicable. This T-Class fuse is 12inches from the inverter r DC positive post.

So loads of protection! BMS protects the cells. Battery main fuse protects that cable run to the Lynx distributor. Lynx distributor is fused for the smaller cables exiting (2 gauge for DC panel with 125A fuse, 2/0 for the inverter with 300A fuse, 2 gauge going to the always ON charging bus bar with 125A fuse. I have room to expand the Lynx with 2 other terminals (one internal and one off to the side).

 

[Tin Kicker]

Engine alternator output should always go to the start battery which should be kept lead AGM due to the potentially high discharge rate when the start motor engages. Keep that side of the system as simple as possible.

There are various types of isolation devices to put between the house and start batteries. I have the solar connected to the house side.

 

[Hayden Watson]

You will get a ton of opinions on this issue so as with any info found on the internet, you will need to filter through the comments to see what will work best for you, your boat and your needs and that includes the following.

When I went through this process about 3 years ago, my research found that there are two primary camps.

• You should never send the alternator power to the LFP batteries.
• You should definitely send the alternator power to the LFP batteries.

It is hard to reconcile these two diametrically opposed opinions but both are true depending on the rest of the boats systems are.

IF your boat has a simple internally regulated low-output alternator, you would be better off in the first camp and have the alternator go to the start battery. Then charge the LFP from a B2B charger which will limit the amount of power that the alternator needs to produce so that it will not burn up.

IF your boat has a high-output alternator with an external regulator that can reduce the power output if the alternator gets too hot, you would be better off in the second camp and have the alternator go to the LFP battery to maximize the power you can get from the engine. Some in this camp like to charge the start battery from a B2B charger which will allow the charge regime to be tailored to each battery chemistry. I personally do not like this method because it has the alternator connected only to the LFP with no dump load for when the BMS shuts of charging as it should. If the cells are a bit too far out of balance so that the battery cannot get to the regulator's absorption voltage setpoint, the BMS will not allow any charge to reach the battery and this will cause a voltage spike in the alternator. [the dreaded Diode BOOM].

On my boat, I get around this by having the start and house loads totally isolated from each other. The alternator [a 250A large frame Denso hairpin] is controlled by a Zeus regulator that limits the max output to 190A and monitors the alternator case temperature and limits it to 200ºF. This high current is then sent to an ArgoFET battery isolator which sends the current to both the LFP house and AGM start batteries when the alternator output voltage is greater than the battery voltage. The Zeus absorption voltage is set at 14.1v which works well for both the LFP and AGM.

 

[Tin Kicker]

If it if you are going to start an engine with lithium batteries, the #1 biggest consideration is what happens when you push the start button. That’s an inrush current that even for a little 2gm Yanmar can reach 150 amps. Most boats have a single start battery and this can far exceed the discharge rate of the less expensive lithiums.

 

[marcham]

My 3JH3 (40 Hp) starts fine with my AGM 10Ah motorcycle battery (in my RIB)... it's CCA is 170 I believe. The issue with Lithium and a starter is inrush current may trip the BMS. I haven't tried mine, but we have a member in our club that was able to start (very easily) with 2x Epoch 12V 400Ah batteries in parallel. Some smaller lithiums are purpose built for start application with a high rated discharge BMS.

5 years ago, the recommendation from alternator and regulator manufacturers was to charge the start AGM and then use multiple DC-DC chargers for the lithium bank. That has since changed with better equipment, software and greater confidence in LIFEPO4 in a marine environment. By connecting the alternator (equipped with a modern regulator such as wakespeed 500 or Electromaax Pro X), they can easily be configured to taper down the current once the cells are balancing (usually 14-14.4, depends on your BMS). AGM is easy. Put in the battery, set the charger and regulator to AGM and you're done. Lithium is trickier. I would never use the default settings as charge recommendations can vary greatly between manufacturers. SOK wants 14.4-14.6, whereas Epoch wants. There is a huge advantage of having a Lifepo4 that is networked to your Cerbo GX as it can direct other systems (Inverter, regulator) to taper down the charge and can shut down charging sources before the BMS kicks-in.

If the charge voltage for a lifepo4 is too low, it will take a long time to balance the cells and could result in an overcharge (BMS shutdown). On the other hand, exceeding the max voltage will also trigger the BMS to shut the battery down. With an alternator running, this could destroy the diodes.... Different BMS have different voltages to start balancing, some as low as 14, others need 14.4 v.

 

[Hayden Watson]

If the voltage for a lifepo4 is too low, it will take a long time to balance the cells and could result in an overcharge (BMS shutdown). On the other hand, exceeding the max voltage will also trigger the BMS to shut the battery down. With an alternator running, this could destroy the diodes....

Dirty little secret. With most of the batteries that recommend 14.4v - 14.6v are using their BMS as a charge controller. In order to get to 14.6v, the cells must be perfectly balanced at 3.65v each with 0.000v difference. That does not happen no matter how good the cells are. Even with a 5mv imbalance, you will only get to 14.585v and then it will trip. What they are doing is having you charge the battery until the BMS trips and then letting it passive balance in the tripped condition while your battery charger supplies the loads to the house.

I personally would never charge any LFP to more than 14.2v and if the cells are a bit imbalanced, I would go lower until I was able to get them closer.

 

[jssailem]

I personally would never charge any LFP to more than 14.2v and if the cells are a bit imbalanced, I would go lower until I was able to get them closer.

Along with what Hayden has described, I recently observed this behavior in the BMS's for my 3 new 100Ahr batteries. They were shipped with the batteries partially charged. I did my first charge-up in my garage.
Here are the last BMS screens from this process.

The BMS reports the state of charge when I unpack the batteries.


Here is the state of charge after the first full charge sequence.


I named the batteries 1-2-&3 so that I can distinguish them. Batteries 1 & 2 were resting for 24 hours. Battery 3 had just finished it's charge.