How are people charging Li/LA hybrid setups?

[Pete7]

Originally Posted by Ryban

Assuming your alternator is connected to your LA bank, do you ever find you need to charge your LFP batteries from the LA/Alternator side, and if so, how do you achieve this without the second DC-to-DC, or other complex schemes.

Alternator goes to the lead acid engine start battery. DC>DC connects the engine start battery to the LFP house bank. Early Spring and late Autumn we need 10% of the daily total from the alternator. Summer solar does everything directly to the LFP house bank. We don't need to back charge from the LFP house bank to the engine start battery.

For winter storage the LFP side of the hybrid house bank is isolated so the solar only charges the house lead acid battery. There is a jumper cable to connect and keep the engine start battery topped up.

[Ryban]

Originally Posted by Pete7

Alternator goes to the lead acid engine start battery. DC>DC connects the engine start battery to the LFP house bank.

Yeah I mistakenly asked the wrong question and meant to ask how you get power to the LA bank from the solar (since the MPPT chargers are configured for the LFP bank too).

The DIY solution mentioend above about using an ACR to join the systems only when the engine was running, but also measure the the temperatures, wasn't a bad one. It's something I probably would normally do -- but I also know from my other arduino projects that something unexpected almost always comes up, and it can be very hard to debug on a boat.

I think I'll probably just spend the extra $$ for the extra DC-to-DC charger and use a switch as I drew. I'm ok only getting 30-60A in either direction for my intented use of it.

[pbiJim]

Originally Posted by Ryban

Yeah I mistakenly asked the wrong question and meant to ask how you get power to the LA bank from the solar (since the MPPT chargers are configured for the LFP bank too). ...

My current preference is to install a second (smaller) solar controller to feed the start battery. It can be configured for the LA charge curve, since it will never charge the LI bank. These days, you can do that for like $100 or so.

I'm also a fan of keeping jumper cables on board in case I need to jump start or jump charge the start battery off the house bank in an emergency. Some people would advise installing an emergency bridge switch. I am lukewarm on that idea but may still consider it.

[Ryban]

Originally Posted by pbiJim

My current preference is to install a second (smaller) solar controller to feed the start battery. It can be configured for the LA charge curve, since it will never charge the LI bank. These days, you can do that for like $100 or so.

I'm also a fan of keeping jumper cables on board in case I need to jump start or jump charge the start battery off the house bank in an emergency. Some people would advise installing an emergency bridge switch. I am lukewarm on that idea but may still consider it.

That's not a bad idea either, though I don't know if in my case it will end up saving me a whole lot of complexity, since I want to retain the DC-to-DC to be able to charge the start bank off the LFP bank in situations where maybe there is no solar or at night in a crunch. But that's probably not something that will ever actually end up happening.

I also carry jumper cables for a lot of reasons, another of which is it that it lets you by-pass all your wiring in case you have a contact issue somewhere, or too much resistance in a wire for whatever reason, you can still get your engine started.

I updated my drawing to include the negative side to the bus and DC-to-DC chargers to also emphasize they're non-isolated.

[wholybee]

I have one of these on board. Mostly I use it as a power source to run the pump to inflate my dinghy. It is also useful on excursions to keep my phone/tablet charged for several days. But what it is made for, and works fine for, is starting the engine when the main battery is dead. It will easily start the large V8 cummins diesel in my brothers truck.

https://www.amazon.com/DBPOWER-18000...ef=sr_1_6?th=1

[Pete7]

You can't use an ACR because of the higher voltage of LFP, it will be permanently connected.

Why not just use a long wire and a battery switch? after all you are not going to be charging the LA from the LFP very often because using the engine will do that. Perhaps if you stop for more than a month. This is simple and cheap. the long wire and higher resistance of a LA start battery means only a gentle current will flow.

[Bowdrie]

Originally Posted by Ryban

I see a lot of talk about people keeping lead acid around for their start bank, and switching to LiFePO4 for the house bank, but I'm still a little confused on how people are charging these setups efficiently, given the different requirements of the chemistries.

Too many people mix apples and oranges and think they're getting pineapples.
Let the stock little internally regulated alternator do what it does best; charge the LA starting batts.
Mount a second big externally regulated alternator, (sometimes an off-engine mounting can work better,) and use it to charge the more exotic house batts.
Both batt systems get what they need without a lot of screwing around.

[rwidman]

Originally Posted by Ryban

I see a lot of talk about people keeping lead acid around for their start bank, and switching to LiFePO4 for the house bank, but I'm still a little confused on how people are charging these setups efficiently, given the different requirements of the chemistries.

Are people using DC-DC chargers for each bank, or manually switching between the banks to top up the start bank as needed?

Currently I have an ACR in my all lead acid setup so I never have to think about it, but I will be switching to Lithium soon.

I like the idea of just switching everything to Lithium, but people seem to have strong opinions about that.

I kept my AGM start battery, engine alternator and shore powered charger and bought a DC to DC charger to handle charging for the lithium house batteries.

This was the suggestion from the lithium battery company. It seems to work fine.

[rwidman]

Originally Posted by rwidman

I kept my AGM start battery, engine alternator and shore powered charger and bought a DC to DC charger to handle charging for the lithium house batteries.

This was the suggestion from the lithium battery company. It seems to work fine.

BTW: Remove the ACR. It is not needed, the DC to DC charger takes care of isolating the batteries when there is no charging voltage.

[Ryban]

The long wire and battery switch isn't a bad idea. Or even an appropriately sized resister. I just fear that I'll forget and leave the switch closed after the engine is turned off.

I wonder if there's a relay/ACR that can be easily configured with a timer, where it will automatically disconnect after a set duration.

[hjohnson]

Originally Posted by Ryban

I see a lot of talk about people keeping lead acid around for their start bank, and switching to LiFePO4 for the house bank, but I'm still a little confused on how people are charging these setups efficiently, given the different requirements of the chemistries.

Are people using DC-DC chargers for each bank, or manually switching between the banks to top up the start bank as needed?

Currently I have an ACR in my all lead acid setup so I never have to think about it, but I will be switching to Lithium soon.

I like the idea of just switching everything to Lithium, but people seem to have strong opinions about that.

I have a lithium house bank, and lead acid starter battery. All primary charging sources (inverter/charger, MPPTs, alternator) are connected to the lithium bank and managed by the BMS/Victron setup.

The lead acid battery is in turn charged/maintained by an 18A DC to DC charger. It spends its entire life on the float, so should last forever.

[Ryban]

I’ve been (over)thinking about this some more, and I’m considering swapping out the manual selection switch for which bank is providing power to the DC distribution bus with a remote battery switch. I could then use the BMS to trigger this switch in the event the LFP bank is about to be cut-off. I think this would be important in situations where the electric autopilot is doing its job, as interrupted power could be very unfortunate.

I think I could do this in a fairly straightforward way, but it’ll depend on which BMS I use and whether I want to do it through the VenusOS system.

[Bennyhill]

Concurring with all of the above posts, my variation was to charge the AGMs (three sets: Starter/Winch, Bow Thruster/Windlass, Auxiliary/Backup) from a beefy, 50A Victron Phoenix Smart 120v charger. This way, during winter layup, the Phoenix can keep the AGMs tip-top even if my bilge temp falls below 5°C, which shuts down the lithiums. And it just seemed to me to be cleaner than using a DC-DC charger: there is a clear, electrical and logistical separation between the power-hungry, motor-driving AGMs, which aside from the starter motor are not really mission-critical, and my electrically-independent lithium bank, which on an extended cruise is my life saver. So to clarify: charging the lithium House bank, I have a 250A Balmar scaled back through a Wakespeed regulator, with an additional ducted cooling fan on a thermostat; solar panels on the bimini thru a Victron MPPT charger; and the Victron MultiPlus inverter/charger when on shore power. Running off the MultiPlus inverter is the Phoenix charger for the AGM battery sets. In the marina, the Phoenix charges from shore power; once afloat, the Phoenix charges the AGMs by drawing from the 1,000Ah lithium bank via the inverter. For emergency situations, or simply for extra flexibility, I also wired in bypass cabling and switches, so if necessary, I can, say, start the engine from the lithium bank, or run the electronics and autopilot from the bow thruster's AGMs. What is crucially important, is to install only the best lithiums, with anything and everything charging them electronically Smart, which my research indicated had to be Victron throughout (and their new Ekrano CPU and integral display, controlling a Lynx BMS and distribution strip is as smart as it gets).

[gpeacock]

Ive spent years trying to sort out the best way to automate things and have yet to come up with a good solution.
Currently everything is connected to my house bank and I use my House bank to start my engine. Occasionally I manually combine my two banks using a selector switch to keep my small "spare FLA" bank topped up.
I've been lucky enough to survive 9 years with out my LiFePO4 bank safety contactor needing to kick off. In fact I've disabled HV cutoff for reasons below but I'd love to automatically combine my House and FLA bank while any charge source is active.
I even have an old Blue Sea ACR that would allow me to do Dreuge's elegant solution but here is the problem I have:
When my 160A (12V) alternators are pumping power in the voltage drop even with big cables is substantial through the Blue sea 1/2/All switch so I have the Balmar Voltage sense wire connected directly to my LiFePO4 bank (along with all my other charging sense wires). Kicking off the contactor with this setup would do two things: Fry the alternators, probably solar MPPT etc AND because the voltage sense wires are connected directly to the house bank the charging sources keep ramping up amps which causes the voltage to spike destroying more electrical systems on the boat...
How do people get around this issue? Just accept the voltage drop and connect the sense wires to the main Positive bus on the non battery side of the combiner? For me its almost a .3V drop when charging with big amps with with LiFePO4 is a problem...

[hjohnson]

Originally Posted by gpeacock

Ive spent years trying to sort out the best way to automate things and have yet to come up with a good solution.
Currently everything is connected to my house bank and I use my House bank to start my engine. Occasionally I manually combine my two banks using a selector switch to keep my small "spare FLA" bank topped up.
I've been lucky enough to survive 9 years with out my LiFePO4 bank safety contactor needing to kick off. In fact I've disabled HV cutoff for reasons below but I'd love to automatically combine my House and FLA bank while any charge source is active.
I even have an old Blue Sea ACR that would allow me to do Dreuge's elegant solution but here is the problem I have:
When my 160A (12V) alternators are pumping power in the voltage drop even with big cables is substantial through the Blue sea 1/2/All switch so I have the Balmar Voltage sense wire connected directly to my LiFePO4 bank (along with all my other charging sense wires). Kicking off the contactor with this setup would do two things: Fry the alternators, probably solar MPPT etc AND because the voltage sense wires are connected directly to the house bank the charging sources keep ramping up amps which causes the voltage to spike destroying more electrical systems on the boat...
How do people get around this issue? Just accept the voltage drop and connect the sense wires to the main Positive bus on the non battery side of the combiner? For me its almost a .3V drop when charging with big amps with with LiFePO4 is a problem...

I get around the issue by using a DC-DC charger to maintain my starter battery, which is a marine start FLA. No matter what my Lithium house bank is doing, the Lead Acid is spending its entire life happily sitting at 13.8v.

As far as the disconnect goes, that will never happen in my setup because the BMS will command the alternator off before it orders a disconnect. Yes, if I were to manually operate the contactor (it's a BlueSea RBS so I can manually do that) I could cause havoc, same with the service switch for the battery, but as long as I don't do that, we're good to go.