LFP System Drawing

[tpbrady]

After solving the alternator issue (thanks for steering me to Romaine Electric), I completed my drawing of how I am going to switch from carbon foam batteries to LFP. I put this together to keep major wiring changes to a minimum. I elected not to connect the Wakespeed regulator to my Cerbo GX. It’s a long cable run and doesn’t give me anything I can’t get from the SmartShunt and Bluetooth app. I elected to charge the residual lead acid batteries with DC-DC chargers. The Firefly batteries will be stored for replacement of the 8D battery for the windlass and bow thruster. It’s 12 years old so due.

Please tell me if I am doing anything stupid, wrong, or if there is a better way.

Tom

 

[Jay N]

Hi Tom. Don't know if I can add anything helpful, the only thing I see in the schematic is that you should probably put 250A MRBF fuses on the LFP battery terminals, then have a 400A (or suitable) class T fuse after the bus.

So, WESTERLY replaced her 696Ah FireFly bank and cruised 2024 with (2) Epoch 300Ah batteries in parallel. I was very happy with the improvement in capacity. But I did keep the start battery (AGM) for starter/winch loads, so we only have two banks. Rather than the DC/DC chargers to the AGM banks, I just went with a legacy AC charger running off the alternator/inverter.

After a year of combining B1 and B2 when charging in order to guard against load dumps, I have decided the alternator is sufficiently protected by having (2) BMS's and an alternator protection device (APD). Monitoring the bank all summer indicated that max temps were about 94F, and charging voltage was well under any level that might cause a cell over voltage shutdown (The alternator charges to about 13.8v and 92% SOC when cruising). Epoch recommends charging to 100% and the charge termination threshold once per month, which I do with the AC charger set at 14.4v when on shore power.

Also, I wired a remote Blue Seas switch to the pilothouse where I can connect B2 (AGM) power very quickly if needed. And the regulator has remote pilothouse switches that turn the Balmar 618 regulator on/off, and force to float. When cruising on consecutive days, the alternator only charges to float (13.5v). Most of the time, the LFP bank cycled between 30% and 80%.

I know there are 20M ways to do this, and there are a lot of opinionated DIY'ers (like me), but I think you can install an LFP battery bank that is very safe, and simple (meaning non-victron/mastervolt).

See ya this summer. Jay N

 

[Bud]

After solving the alternator issue (thanks for steering me to Romaine Electric), I completed my drawing of how I am going to switch from carbon foam batteries to LFP. I put this together to keep major wiring changes to a minimum. I elected not to connect the Wakespeed regulator to my Cerbo GX. It’s a long cable run and doesn’t give me anything I can’t get from the SmartShunt and Bluetooth app. I elected to charge the residual lead acid batteries with DC-DC chargers. The Firefly batteries will be stored for replacement of the 8D battery for the windlass and bow thruster. It’s 12 years old so due.

Please tell me if I am doing anything stupid, wrong, or if there is a better way.

Tom

Looks good, A couple points for consideration. I assume from your drawing that your non LFP batteries are being charged by your engine(s) alternators and the LFP's charged via the two DC to DC chargers shown. Your two 60amp DC to DC chargers will not put out 120Amps combined, unless they communicate with each other and are programmed to do so. If they are not, then when you start your charging process for one of your non LFP batteries then the DC to DC charger starts charging the LFP's, the voltage on the LFP batteries will then increase,(hold that thought). When you now start charging your second bank of non LFP batteries the 2nd DC to DC charger comes online it will sense the higher charging voltage from the first DC to Dc charger and will just put out float charge voltage. This scenerio may vary somewhat with different conditions but the point is the first charger on will be doing the heavy lifting. Basicly your just using one DC to DC charger.

Bud

 

[twistedtree]

Looks good, A couple points for consideration. I assume from your drawing that your non LFP batteries are being charged by your engine(s) alternators and the LFP's charged via the two DC to DC chargers shown. Your two 60amp DC to DC chargers will not put out 120Amps combined, unless they communicate with each other and are programmed to do so. If they are not, then when you start your charging process for one of your non LFP batteries then the DC to DC charger starts charging the LFP's, the voltage on the LFP batteries will then increase,(hold that thought). When you now start charging your second bank of non LFP batteries the 2nd DC to DC charger comes online it will sense the higher charging voltage from the first DC to Dc charger and will just put out float charge voltage. This scenerio may vary somewhat with different conditions but the point is the first charger on will be doing the heavy lifting. Basicly your just using one DC to DC charger.

Bud

I think the DC/DC chargers charge the lead batteries, not the other way around.

 

[twistedtree]

After solving the alternator issue (thanks for steering me to Romaine Electric), I completed my drawing of how I am going to switch from carbon foam batteries to LFP. I put this together to keep major wiring changes to a minimum. I elected not to connect the Wakespeed regulator to my Cerbo GX. It’s a long cable run and doesn’t give me anything I can’t get from the SmartShunt and Bluetooth app. I elected to charge the residual lead acid batteries with DC-DC chargers. The Firefly batteries will be stored for replacement of the 8D battery for the windlass and bow thruster. It’s 12 years old so due.

Please tell me if I am doing anything stupid, wrong, or if there is a better way.

Tom

Looks good. One thing to consider would connecting terminal 2 of your 1-2-Off switch to the start bank. That would give you a quick way to switch house power over to the start bank in the event of some LFP shutdown or failure.

 

[tpbrady]

TT,

I didn’t think of connecting the start bank to port 2. I was planning on keeping the port side Firefly’s on port 2 but off. Periodically I would switch on the Firefly’s to top off the charge. My thought was while running, if the LFPs disconnected, the alternator would still be meeting the load and there wouldn’t be any adverse affect with the start battery connected to the Argo. If that isn’t the case, since my primary nav is on a laptop with a USB GPS as one input, I will still be able to operate for the few minutes it takes to switch batteries and power everything back up.

Tom

 

[Bud]

I think the DC/DC chargers charge the lead batteries, not the other way around.

Got it, then disregard comments,
Bud

 

[twistedtree]

TT,

I didn’t think of connecting the start bank to port 2. I was planning on keeping the port side Firefly’s on port 2 but off. Periodically I would switch on the Firefly’s to top off the charge. My thought was while running, if the LFPs disconnected, the alternator would still be meeting the load and there wouldn’t be any adverse affect with the start battery connected to the Argo. If that isn’t the case, since my primary nav is on a laptop with a USB GPS as one input, I will still be able to operate for the few minutes it takes to switch batteries and power everything back up.

Tom

Got it. Just trying to cover the "dark ship" scenario and have an easy backup. Your FireFly bank should accomplish that just fine.

 

[SteveK]

You have two 300Ah Vater each fused with 250 class T, to a bussbar and then a 300A MRBF. Do you even need that 300A fuse?

 

[tpbrady]

SteveK,

Since this is the only bank supplying the inverter and DC house loads, the theoretical maximum draw of the inverter is about 270 amps, that’s the purpose of the fuse. In that respect the ANL fuse is probably redundant since it is between the inverter and positive bus. In the past both port and starboard banks fed through the battery switch to the bus then to the inverter and beside the MRBFs on the batteries that was the only fuse in line with the inverter. I’ll keep it there until I decide on installing a third battery in the port box.

Tom