Guide for LIFEPO4 wiring

[T1 Terry]

Originally Posted by Letterkenny

So how do you charge the lot with a battery charger then? Or do you need a second one?

If you connect the battery charger to the same terminals on the battery isolator that come from the alternator, the system will work the same as it would with alternator charging.
With the isolator there is no need for an ignition switch wire to the DC to DC because as soon as the alternator stops turning, the current to the battery isolator stops and the diode in the start battery output blocks any current flowing back to the DC to DC charger. This way, there is nothing to switch on if a mains charger is connected to the battery isolator input terminal and the common negative point for all the charging devices and batteries.

T1 Terry

[T1 Terry]

Originally Posted by Oceanride007

Was thinking between LA & LFP, that will be safe.
Don't mind getting DC2DC but not sure how it is switched off, does it boost voltage?, will it discharge LA battery if Engine shut down and Therefore Alternator is off.
And why not a "AND" Function, temperature NC switch, Alternator charging, and a Diode. ie 3 switches in series. Instead of DC2DC charger.

The isolation part I've answered in the last post. There is nothing wrong with adding and/or gates other than complexity. Unless you fully understand the electronic path and related contactors or "ideal relays", tracking down a problem in the middle of the big blue would be near to impossible. The DC to DC takes that confussion/mystery out of the equation, it either works or doesn't work. If it doesn't work then a work around can be used, otherwise it's a fit and forget part of the system, it just does what it should do when it should do it. Way too many better things to do that micro-manage a house power system .... even if that is just sitting back in the sunshine enjoying a cool drink .....

T1 Terry

[SailRN]

Lithium batteries typically have a Battery Management System (BMS) which do disconnect the batteries.


See

https://www.youtube.com/watch?v=jgoIocPgOug

And a good read: https://marinehowto.com/lifepo4-batteries-on-boats/


An excerpt:


The alternator for the Volvo MD2030 with 300 Amps lfp 14.6 max lasted a few hours. I believe BMS was switching on to off I to keep the lfp voltage to safe measure? Boat service replace alternator and it happens the second time? I now read your story on lfp and it explain to me why.”
Unfortunately the reader above learned the hard way. Ask yourself what happens when your alternator is in bulk charge, supplying all the current it can, and the internal BMS decides to “open circuit” or disconnect the battery from the boat? I’ll help out a bit here.
A) The alternator diodes, unless avalanche style, (rare in many existing marine alternators) but all Balmar alternators now use them, can be blown and the alternator can be rendered non-operable. Two years ago I did exactly this. Using the alternator test bench here at CMI the alternator was running at full bore charging an LFP battery. The “system” I set up had a .3A dummy load on, light bulb, to simulate a depth sounder. With the alternator running at full bore I disconnected the battery, just as an internal sealed BMS would do to protect the LFP cells. Poof went the alternator diodes and the light bulb! Worse yet the voltage transient I recorded on the “load bus” (think your navigation electronics) using a Fluke 289 was 87.2V. Ouch. Even if your alternator uses avalanche diodes, like Balmar’s do, the voltage at which they begin to protect the alternator is far too high for the vessels load bus equipment so you still need a way to protect against a load dump.


This might be helpful too:

https://www.youtube.com/watch?v=dzU_pQFa19s

[Letterkenny]

Thanks for the info. There’s a couple 300ah batteries I’m debating getting from Amazon, some of which have been recommended here. On the one hand, I’m hesitant to change out my 240ah lead acid house bank since it’s brand news. On the other hand. I get power anxiety (as a coastal cruiser only) still so would be nice to have almost 300ah useable space vs 120ah or less.

[T1 Terry]

Originally Posted by Letterkenny

Thanks for the info. There’s a couple 300ah batteries I’m debating getting from Amazon, some of which have been recommended here. On the one hand, I’m hesitant to change out my 240ah lead acid house bank since it’s brand news. On the other hand. I get power anxiety (as a coastal cruiser only) still so would be nice to have almost 300ah useable space vs 120ah or less.

Can you use the new lead acid batteries as start batteries? You might be able to find a sale for the near new lead acid batteries to someone who isn't prepared to go down the lithium path just yet ....

T1 Terry

[Pete7]

Originally Posted by Letterkenny

Thanks for the info. There’s a couple 300ah batteries I’m debating getting from Amazon, some of which have been recommended here. On the one hand, I’m hesitant to change out my 240ah lead acid house bank since it’s brand news. On the other hand. I get power anxiety (as a coastal cruiser only) still so would be nice to have almost 300ah useable space vs 120ah or less.

Understood, then how about a hybrid system with the LA and LFP combined into a single house bank? Like you I didn't want to throw away two nearly new FLA batteries.

The advantage is the LFP does all the work and the LA just sits there most of the time. However, if the LFP suddenly disconnects then you still have power still available for chart plotter, VHF lights etc. The other thing I do is when I leave the boat disconnect the LFP completely, so the solar just charges the LA battery. This means the bilge pump is still in auto mode should it ever be needed but stops the LFP from being float charged constantly. Since the solar is more than able to maintain the LA on float when I connect them back again next time on board they are a similar voltage so no big sparks or rush of current between them.

The DC>DC charger is switched off with the software app most of the time as solar is more than capable of charging the house bank. However, in the even of several days of rain it's there if needed. The DC>DC chargers like victron or Sterling can be stacked btw, so you can have two or more.

Pete

[Letterkenny]

Originally Posted by Pete7

Understood, then how about a hybrid system with the LA and LFP combined into a single house bank? Like you I didn't want to throw away two nearly new FLA batteries.

The advantage is the LFP does all the work and the LA just sits there most of the time. However, if the LFP suddenly disconnects then you still have power still available for chart plotter, VHF lights etc. The other thing I do is when I leave the boat disconnect the LFP completely, so the solar just charges the LA battery. This means the bilge pump is still in auto mode should it ever be needed but stops the LFP from being float charged constantly. Since the solar is more than able to maintain the LA on float when I connect them back again next time on board they are a similar voltage so no big sparks or rush of current between them.

The DC>DC charger is switched off with the software app most of the time as solar is more than capable of charging the house bank. However, in the even of several days of rain it's there if needed. The DC>DC chargers like victron or Sterling can be stacked btw, so you can have two or more.

Pete

Could be an ideal approach. I’ll need to check space once we get the boat in.

[T1 Terry]

The thing to keep in mind, the lead acid batteries will be a constant parasitic load on the LFP battery, so you need to keep this in mind when planning battery capacity and charging requirements, the losses the lead acid batteries add to the system must be counted as part of the load.

As long as you have a form of charging that is not 24/7, such as solar, there really isn't a need to disconnect between the battery packs. The lead acid will act as a load over night so the LFP battery will be pulled down below float voltage, so it will go through a charge cycle every day. It will make the lead acid batteries last a lot longer, they will virtually be UPS batteries where they stay constantly fully charged.

T1 Terry

[Letterkenny]

Having the boat for a couple months now makes this seem a lot easier. Plan is to remove the wires from the alternator and battery charger from the house bank terminal and then just add a DC to DC from the starter terminal to the house terminal. I believe a common negative is fine, correct?

[Oceanride007]

In general yes, some vessels however do switch the negative when starting as well as the positive.

When I did mine, I didn't need a DC to DC because on the few times I paralleled the batteries the Alternator high current was not enough to warm the stator temperature very high anyway (like 60deg).