Lithium battery install, lead-acid starter with DC-DC. Where to put solar?

[PaulRainbow]

It might be interesting if insurance companies start requesting compliance with ISO or ABYC. This set up of mixed chemistries won't comply with either standard.

I'm aware of that, hence the "experimental". I wanted to see for myself what would happen, rather than the doom and gloom claims from some internet sites. It doesn't do what they say. I've been using it for year now with no adverse effects. The only negative thing i've found is that with the alternators connected to the LA batteries i don't get much charging, because the LA are already charged. If i removed the alternator charging and fitted a DC-DC charger between the engine batteries and the LFP bank that fixes the charging issue. At the moment they provide dark ship syndrome and give me an alternate way of starting the engines, however, i'll be removing them soon and fitting DC-DC chargers for charging. I'll be fitting two additional key switches in the main electrical panel to operate two contactors, one will parallel the load circuits and the other will bypass the BMS. For emergency starting, turn both keys on, start the engines, turn them both back off. In the event of a dark ship, isolate the LFP bank (from a key switch in the main panel (already fitted)) and turn the parallel key on.

 

[Sea Change]

I'm a bit late to this one but just wanted to say, just charge the lithium from the solar, and don't worry about the lead acid, unless you're going months between engine starts.

We live aboard full time and our engine/windlass batteries have no charging except the alternator. It's never failed to start. We sometimes spend a few weeks anchored in the same place without running the engine.
If I was worried that the engine battery was getting low, I'd just hook up a battery charger running off the inverter, which draws from the lithium. But I've never had to even think about that.

 

[JT14]

I'm a bit late to this one but just wanted to say, just charge the lithium from the solar, and don't worry about the lead acid, unless you're going months between engine starts.

We live aboard full time and our engine/windlass batteries have no charging except the alternator. It's never failed to start. We sometimes spend a few weeks anchored in the same place without running the engine.
If I was worried that the engine battery was getting low, I'd just hook up a battery charger running off the inverter, which draws from the lithium. But I've never had to even think about that.

Even simpler! Here's my response to an earlier question:

We have sailed over 15,000 nautical miles now without trickle charging the starter battery. Charging has only been via alternator when engine running, no problems.

It seems we can go head with our installation and worry (or not) about regeneration in the future. A small panel to trickle charge, or inverter charging looks to be the best options.

Thanks to all for the advice !

 

[tomaz_slo]

I'm a bit late to this one but just wanted to say, just charge the lithium from the solar, and don't worry about the lead acid, unless you're going months between engine starts.

My proposal for long periods between engine starts: charge the lithium from the solar and put Schottky diode in series with 20W bulb between both + terminals of lithium and lead acid.

 

[Rhylsailer99]

I'm installing a single Renogy 300ah Lithium battery (with internal BMS) as the house bank on our Rival 32. Starter battery will remain as the 100ah lead-acid, with a Renogy 40A DC-DC charger between the starter and house bank. Engine alternator puts out 40A, with output regulated to 20A on the DC-DC so as not to burn the alternator out when engine is running.

We are a long-distance cruising boat, and rely on our solar panels for regeneration, therefore the low output from alternator is not too much of a concern as we spend most of our time sailing. Potentially in the future we will upgrade to a Balmar system, when the wallet allows.

Solar: We have 3 x 100W panels. Each panel has an individual MPPT, two of which are Victron (and programmable to Lithium) and one is a cheaper unit that cannot be programmed.

I'd like the starter battery to be trickle fed so when we turn the key we have a full suite of cranking amps. This lead to our thinking about MPPT placement in this setup, to gain the best regeneration potential for both banks.

Option 1: We could put all the solar MPPT's on to a common bus which feeds the starter battery, with the DC-DC charger on the same bus. The thinking here is that once the starter battery reaches 13.2V, the DC-DC will kick in and start feeding the lithium house bank. This seems simple enough, but will the internal resistance of the lead acid reduce efficiency to the lithium?

Option 2: Two 100W panels are wired to the lithium house bank, with the other 100W feeding the starter battery. This is the simplest solution I think, but we do stand to lose the extra charging capacity from the 100W panel that is reserved just for the starter battery. 3 panels take up a lot of space on our small boat and to not gain their maximum output into the lithium bank would be frustrating.

Option 3: One Victron MPPT to lithium, with two 100W wired in parallel. The other Victron MPPT with a single 100W wired to lithium. Buy a new, small panel of 20W ish, to trickle charge the starter battery with the last MPPT.

Space is a at a premium right now, and adding another panel somewhere would be tricky - but that's the only downside of Option 3.

Finally, for option 2 & 3 - when the starter reaches 13.2V, and DC-DC starts feeding the lithium bank - will this trigger the lithium MPPT's to stop charging, or can the lithium accept multiple charging sources in these cases?

Thanks in advance for your input and experience!

I have a duel solar charger that puts a trickle.charge in the starter battery when needed.

 

[billcole]

My proposal for long periods between engine starts: charge the lithium from the solar and put Schottky diode in series with 20W bulb between both + terminals of lithium and lead acid.

That's what I was thinking, but would it even need to be a Shottky? Since the lithium is slightly higher voltage than LA the 0.6V drop of a standard silicone diode would still feed about 13.6 V to trickle charge the starter battery.

 

[Phil_boat]

I haven’t read through everything but what about one of these?

It will trickle charge your engine battery from the house bank. I think it’s compatible with the voltages of differing battery chemistry.

Sterling Battery-Battery Maintainer 12V-12V, 3A

 

[tomaz_slo]

That's what I was thinking, but would it even need to be a Shottky? Since the lithium is slightly higher voltage than LA the 0.6V drop of a standard silicone diode would still feed about 13.6 V to trickle charge the starter battery.

During off season time you should keep LiFePO4 between 20%-80% SOC for longer life time of the battery. On the other hand LA should be full. That is the reason why Schottky.

 

[geem]

During off season time you should keep LiFePO4 between 20%-80% SOC for longer life time of the battery. On the other hand LA should be full. That is the reason why Schottky.

The recommendations for storing lifepo4 during the off season are lower than 80%. Lifepo4 will last the longest if it is at an average of 50% SOC. The recommendation is to store at 60% with no charge. Assume up to 3% loss of SOC per month will give you are SOC of approximately 40% after the layup period. This averages out at 50% SOC over the 6 month layup period

 

[Sea Change]

The recommendations for storing lifepo4 during the off season are lower than 80%. Lifepo4 will last the longest if it is at an average of 50% SOC. The recommendation is to store at 60% with no charge. Assume up to 3% loss of SOC per month will give you are SOC of approximately 40% after the layup period. This averages out at 50% SOC over the 6 month layup period

Is that 3% self discharge for the cells on their own? I assume you do the same as me and disconnect the BMS when putting the batteries in storage.
What would self discharge be like for a 'drop in' battery where you cannot disconnect the BMS?

 

[lustyd]

Is that 3% self discharge for the cells on their own? I assume you do the same as me and disconnect the BMS when putting the batteries in storage.
What would self discharge be like for a 'drop in' battery where you cannot disconnect the BMS?

Negligible. I left mine for a month and it didn’t drop at all so unless leaving it long long term I wouldn’t give it a second thought. Ours has now spent the year at mostly 98% with occasional weeks where it drops as we’re full time cruising. No appreciable difference in performance when we do discharge it.


Much of the talk about lithium is theoretical, it performs far better in the real world than people would have you believe.

 

[geem]

Is that 3% self discharge for the cells on their own? I assume you do the same as me and disconnect the BMS when putting the batteries in storage.
What would self discharge be like for a 'drop in' battery where you cannot disconnect the BMS?

The 3% is the likely maximum for cells with no bms discharge. Some drops in go into hibernation mode when not used.

 

[geem]

Negligible. I left mine for a month and it didn’t drop at all so unless leaving it long long term I wouldn’t give it a second thought. Ours has now spent the year at mostly 98% with occasional weeks where it drops as we’re full time cruising. No appreciable difference in performance when we do discharge it.


Much of the talk about lithium is theoretical, it performs far better in the real world than people would have you believe.

How did you measure the SOC?

 

[lustyd]

How did you measure the SOC?

No way to really other than using it and then charging it. Ultimately none of this is that important, as you’ll know having used them in the real world.

Our Fogstar has BMS as well as the Victron shunt so we can see how much juice goes back in.

 

[geem]

No way to really other than using it and then charging it. Ultimately none of this is that important, as you’ll know having used them in the real world.

Our Fogstar has BMS as well as the Victron shunt so we can see how much juice goes back in.

It hard to measure self discharge. If the battery is isolated from the bms, you measure nothing.

 

[lustyd]

It hard to measure self discharge. If the battery is isolated from the bms, you measure nothing.

Yes that’s what I was saying. It makes no difference though, the battery would be fine and they’re now relatively cheap even if the life is shortened by a year or so out of the twenty it will probably last.
People on forums overthink this stuff, in the real world lithium is quite happy and continues to work.

 

[PaulRainbow]

Yes that’s what I was saying. It makes no difference though, the battery would be fine and they’re now relatively cheap even if the life is shortened by a year or so out of the twenty it will probably last.
People on forums overthink this stuff, in the real world lithium is quite happy and continues to work.

Spend half of your day monitoring the batteries, tinkering with settings to keep them at the absolute optimum to get 20 years of of them, or keeping an eye on them and using settings that are reasonable, giving a good balance for longevity with minimal inconvenience, but only getting 18 years out of them.

Hmmm, let me think.......

 

[geem]

Yes that’s what I was saying. It makes no difference though, the battery would be fine and they’re now relatively cheap even if the life is shortened by a year or so out of the twenty it will probably last.
People on forums overthink this stuff, in the real world lithium is quite happy and continues to work.

You are right, but best practise is still best practice.
I know of boats on their second sets of lithium. One guy left his connected to solar for 18 months over covid in a hot boat in the Caribbean. 100% charged and high temperature killed them.
Another boat batteries died at 5 years because they were in the engine room. The engine room was always hot as the generator needed to run at least twice per day. No solar.
Keep them at 50% and hot is better than 100% and hot. 50% SOC and 20degC and they will last far longer

 

[lustyd]

Im not saying don’t follow best practice, just if you leave them for a few months and they had reasonable charge they’ll be fine if you disconnect them.
That said, the idea of laying up a boat for six months is so alien to me I probably shouldn’t even comment. We’ve only just left Scotland and it was a beautiful day yesterday despite most boats in the area already out of the water.

 

[geem]

Im not saying don’t follow best practice, just if you leave them for a few months and they had reasonable charge they’ll be fine if you disconnect them.
That said, the idea of laying up a boat for six months is so alien to me I probably shouldn’t even comment. We’ve only just left Scotland and it was a beautiful day yesterday despite most boats in the area already out of the water.

We have only just started. Launched in July. No plans to lay up until 2027. That will only be 3 months