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Installation of Lithium, DC Charger, AGM with a Boat Switch assistance

hcarmich

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Jul 12, 2022
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Hi. I am new to this Forum and appreciate any assistance regarding what I am trying to do.

Currently, my boat has two wet-cell batteries - one for starting and one for house. There is a Battery switch (I'll try to attach a picture of the switch in this post) that provides options (1, 2, ALL - off) for the current batteries. I also have a solar panel connected directly to the House battery through a MTTP controller.

My plan was to install a new AGM Starting battery and two Lithium house batteries (12 V) and since there are alternators from the engines I was planning on using a DC Charger/MTTP controller (Renogy) to protect the Lithiums. It all makes sense - until I introduce the current Battery switch into the mix.

I cannot figure out how to connect things, while at the same time not connecting the Alternator(s) to the Lithiums etc.

Any assistance on this is greatly appreciated. I have had the batteries (unopened box) well past the 30 day exchange period as I was thinking of exchanging for AGM's. Ideally, I would keep the Lithiums if I can figure this out.

Thank you!

Hugh
 

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There are several ways to handle it, but the easiest is to simply not have a switch. The alternator can charge the AGM battery. Solar the LiFePO4. DCDC will charge the LiFePO4 from the alternator. If you haven't bought it, I would get a separate MPPT and DCDC instead of the all in one. But if you already have it, the all in one should work.
You wouldn't be able to start from the LiFePO4 anyway, unless you have a more sophisticated install with a BMS and external contactors that can handle it. So, the switch is potentially a way to blow something up.
 
Thank you for the quick response. The challenge is - all of the DC house wiring leading to the switch is in place, so eliminating the switch means a bit of a challenge for my simple brain to reconnect things. I also have an AC charger in the mix that I forgot to mention in my initial post.

Replacing the current wet-cells with AGM for starting and two AGM for house - with the existing switch and current MTTP (BlueSky) is probably the simplest solution - but I really wanted the light weight and flexibility of Lithium. As I was saying - I don't know if they will even take them back or exchange.

Please confirm that based on the switch, Starting battery, DC charger, MTTP controller and AC charger that Lithiums cannot be introduced into the picture.

Thank you!

Hugh
 
Of course they can be introduced. The easiest way logistically would be to replace the switch with a fuse holder, or maybe 2. One for the AGM start battery, and one for the LiFePO4. Mount them right where the switch is currently so you don't have to re-run the wire.

Have you made a drawing of what you want to do? Start by doing that and post it here.
 
On your posted drawing, what are notes 2 and 3, and what are V1 and V2?
 
V1 and V2 from the diagram are voltmeters (supported by Note 2). Note three states dual engine models have a negative bonding cable.

Hugh
 
Where does the DC electrical panel connect? To the common terminal on the switch?
The simple way would be to eliminate the switch, have a fuse between the engine and AGM battery. And a second fuse between the DC panel and the LFP.
But draw it out.
 
Where does the DC electrical panel connect? To the common terminal on the switch?
The simple way would be to eliminate the switch, have a fuse between the engine and AGM battery. And a second fuse between the DC panel and the LFP.
But draw it out.
Good morning.

This is my biggest challenge with all of this. It seems that the switch provides selecting what battery - battery bank - is to be used to provide DC to the boat. Position 1 House, Position 2 Starting and ALL for both. There is a note on the switch stating not to change the position of the switch when the engines are running. This would indicate to me that the switch also selects which battery(s) the Alternator will charge when the engines are running.

I will look for additional illustrations of the wiring. I will also post a drawing that I thought would work - but I couldn't figure out how to get the lithiums connected up to system.

Thank you for your help here.
 
Hello I did a search, and I believe that this is way the switch is wired up. Does this help to figure out how to introduce lithiums into this?
 

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Yes, that is what I expected, but difficult to tell from the first drawing.
So, see how the DC panel and the engine both connect to the common terminal on the switch? Instead of that, simply connect the LFP battery to the DC panel, and the AGM battery. Then install the MPPT and DCDC controller as the instructions illustrate.
 
Yes, that is what I expected, but difficult to tell from the first drawing.
So, see how the DC panel and the engine both connect to the common terminal on the switch? Instead of that, simply connect the LFP battery to the DC panel, and the AGM battery. Then install the MPPT and DCDC controller as the instructions illustrate.
Good morning. I will write up what I think you are recommending and post for your review. Thank you again
 
Do you select #2 for start battery and switch to #1 battery for house after shut down?

Easiest way is to connect fused dc-dc to lithium at switch output, mppt directly to lithium.
When starting in #2 alternator charges AGM directly, dc-dc & solar charge lithium. When engine is off and you switch to #1, solar charges lithium. At this point "all" just becomes an emergency connection if one or the other battery is dead and not normally used.
 
Do you select #2 for start battery and switch to #1 battery for house after shut down?

Easiest way is to connect fused dc-dc to lithium at switch output, mppt directly to lithium.
When starting in #2 alternator charges AGM directly, dc-dc & solar charge lithium. When engine is off and you switch to #1, solar charges lithium. At this point "all" just becomes an emergency connection if one or the other battery is dead and not normally used.
Yes, When I am travelling, I switch to ALL prior to starting so that the Alternator is charging both Starting and House. When I arrive at destination, I switch to 1 (house) leaving 2 for starting purposes. My current MTTP is connected directly to house so when drawing down during the day (fridge etc) the solar keeps up to demand. In previous posts I have attached the back of the switch connections. For help, I have also included in this post a picture of an RV Dc to Dc connection that I would like to consider in my application - although I have this pesky battery switch. The DC charger also has MTTP. Any assistance in connecting this up is appreciated. I also have an AC charger in the mix (shore power)
 

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Hello again. Going forward, assuming I can figure out how to connect this (including the AC Charger) as you recommend, I would start in 2 - which as you point out would charge AGM and DC to DC would manage the lithiums - and charge if required. At destination I would switch to 1 and use house lithiums that will be charged with the DC to DC MTTP controller. What position would I switch to when on AC/Shore power?

There is a site that provides info about 1/2/ALL switches - https://marinehowto.com/1-2-both-battery-switch-considerations/

In the article it states the following that confuses me... please help if you can

Confusing Lingo:

START & HOUSE Banks – Like anything in the marine market the 1/2/B can develop it’s own levels of myth & lore. One of the most common misconceptions is that you have a Start Bank and House Bank. Sure, you can assign a switch position to HOUSE and START but they are really EVERYTHING banks. A “START” battery, by definition, is really dedicated to only starting an engine, no house loads.

If you wish to continually move the switch from 1 to 2 then 2 back to 1 etc. etc. it may feel like you have a START & HOUSE bank but you really don’t. In the #1 or #2 position each bank serves both starting and house purposes. Starting and House services cannot be isolated from one another with a 1/2/B unless you add another ON/OFF switch. It is for this reason that we refer to the banks, with a 1/2/B as HOUSE and START/RESERVE. This is still actually incorrect terminology, but a bit more accurate. As you read on you see more of what we mean by this. Technically, and accurately speaking, you have Bank 1 & 2 and each of those positions do both house and starting duties simultaneously.

Builder Blunders?​

The 1/2/B switch, as wired by most builders, becomes a Bank Selection and Charge Directing switch. This means what ever position you have the switch set to, is where your on-board energy comes from, and where the engines alternator sends its charge current.

What Bank Selection and Charge Directing Mean:

1/2/B Switch Set To;

Bank 1 =
DC loads are drawn from bank #1 and alternator charging goes to bank #1
Bank 2 = DC loads are drawn from bank #2 and alternator charging goes to bank #2
BOTH = DC loads are drawn from BOTH banks and alternator charging goes to BOTH banks
OFF = Both battery banks are isolated/OFF
 
I am no expert but presently if your start battery or alternator has a problem you can wait for solar charge your house then combine batteries and start your engines. If you have LiFePo4 house then combining batteries for emergency start is not straight forward due to the LiFePo4 BMS limits so you will need a work around for that added to your list. Very sorry I dont know the answer though.
 
I think I have answered my own question regarding what position for the switch for the AC charger. The batteries will be charged directly from the AC charger (not through the switch). My charger has settings for either AGM or Lithium per connection. I could therefore leave the switch in either 1 or 2. Any concerns based on the information I posted about the switch?
If you all agree that this will work - essentially avoiding the "All" position - anyone willing to assist with the drawing of the connections? thank you
 
Upon further reading about the switch from the posted link, I need to ensure the switch is in position 2 before starting the engines as per their statement "Bank 2 = DC loads are drawn from bank #2 and alternator charging goes to bank #2". Starting in Position 1 would be bad as the alternator would directly charge the lithiums "Bank 1 = DC loads are drawn from bank #1 and alternator charging goes to bank #1". Position "All" is also a bad idea. It would start the engines, but then the alternator would charge both AGM and lithium (bad idea). Sound right?
thanks!
 
Redarc are an alternative to Victron who do DC to DC chargers up 25A, 40A, 50A and LiFePo4 compatible and can set them up to only charge when it detects alternator higher voltage so when engines are off it will disconnect from our starter battery and stop charging even if you accidentally leave your switch combined. It does not allow current to flow from house to start.

If you wire your starter and alternator direct to your start battery you dont even need the switch, it becomes redundant, so no need to remember switch position all the time. My 4x4 had this set up to charge a dual 2nd battery but I did have an override solenoid to bypass for emergency start because both were AGM which you cant. And your AC charger with dual settings takes care of emergency start if you run it off your LiFePO4 via inverter to charge your start AGM, its just not instant you have to wait to charge your dead start AGM. Have your accessories wired only to your LiFePo4 battery.

I edited your pic. Blelue blob is DC DC charger.
1-2-BOTH-2.Label-Factory-Wiring-Final.png

By the way I have a blue seas 1-2-off switch (no combine) for something else but it is same bolt pattern as your switch so an easy swap. That would let you select which battery was providing power to your accessories panel but with a DC DC charger and engine running your LiFePo4 will always have a charge and you dont need a switch.
 
And a cheap low voltage beeper on your start battery so you get plenty of warning if you need to plug in your AC charger and give it a boost.
 
@hcarmich- thanks for the switch link. That has to be the best single article I've read on switches.

You have to remember that in this case you are not using the switch as designed.
It is being used as needed to mix two different technologies. Any time you do this there is greater responsibility for safety and user interaction. That said #2 position would be your normal position, switching to #1 on shut down, back to #2 for starting. Both would be only used if you drained your start battery. Keep in mind, if you forgot to switch to #2 for start, two lithium should give you
200-300 amps for starting, and your #2 battery won't be charging on the way home.
 
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