With lithium do we actually need a dedicated starter battery?

[seaexplorer]

You've piqued my interest with these LTO SCiB cells.
I've wanted to get rid of my lead acid starter batteries for a long time.

I have a 4.5L John Deere Diesel with 24v starter on my port side (starboard side removed and replaced with 48v 50kW Molabo inboard electric powered by 105kWh LFP 48v bank).

I already have 2 independent battery banks (24v & 48v) and will also have a 12v 100ah LFP for 12v backup so I really don't need the starter batteries for anything other than starting the diesel.

Currently I have the 2x 24v 100Ah LA banks still in place charged by a Victron Isolated DC-DC Converter / Charger in engine room from my 24v Victron LFP bank at front of boat (via another Victron DC-DC converter). It is a big boat so the cable run from the house LFPs to the engine is over 25m.

I think that if I replaced all 4 LAs with 12 LTO 2.3v SCiBs then I could keep the same config and lose over 100kg of lead at the rear (which is significant on a performance cat).

You mentioned them not needing a BMS only a balancer. What do you suggest?

Alternatively I could charge them parallel with my Victron 24v LFP bank but would need to run another thick cable to the rear

What do you think?

[Mal Reynolds]

Originally Posted by CaptainRivet

Depends on cell quality, deviation and C-rate used.
Without BMS 4S in general yes, 8s for several month yes, 16S weeks. In 8 and 16S the closer you go to its approach C-rate the less time without BMS.
Sure in emergency case always.

For clarity, I assume you are thinking about cell balancing here. Yes, LFP should be balanced periodically, the period being driven by number of cells in series and C rate in and out. HVC, LVC, HTC, LTC can all be managed easily manually as long as the boat is attended. I did this for 20,000 miles.

It should be noted that not all BMS's actively cell balance.

The broader point is, even if a BMS fails, you can easily bypass it and get to port. Or just carry a spare.

[tsenator]

What happens if there is a nearby lightning strike and the ‘emp’ knocks out the Lithium BMS ? Then you’re not getting anything out of your lithium batteries . But with lead acid one could still turn over their engine and have navigation and lights. I was sailing and there was a nearby lightning strike maybe 50 -100 yards away and it knocked out my radar and over the next few days I realized it knocked out a few more things like my water tank monitor and battery “echo charger”. It’s nice to have some Lead Acid in an emergency to keep basic “electrical needs” going.

I guess if if was a homemade lithium battery bank you could rip out the BMS and bypass it and just wire the individual cells of a battery in an emergency. But that’s not an easy fix and if they are off the shelf Lithium batteries trying to do that would be even more difficult and potentially dangerous. Having that one Lead Acid is a nice quick and efficient backup

[Ionlydream]

Originally Posted by CaptainRivet

With LFP and the tight monitoring and massive current capabilities do we really need a dedicated starter…a LFP house at 2.8V can easily start the engine several times…a depleted AGM can‘t.

Where did a seperate starter actually come from:
Simple answer a lead battery is either
1) a deep cycle for storage, that cannot deliver high current otherwise you destroy it or
2) a starter that can deliver short terms high current but you destroy it if you take constantly current off.
Additional the leads needed to be always full to have full CCA or current capabilities, at a lower SOC they are much worse and if not charged full die very quick. Add to that Peukert effect means the more current you pull the more weak the lead gets and voltage sags deep cause devil cycle more current….
Additional monitoring a lead is still not a secure method to know it’s ok as eg a dry lead still shows the full voltage but as soon as you put a load it collapses.

With lithium this is all completely different.
Already most 100AH LFP can start an engine, 200AH LFP house can easily start your engines, if then BMS is the limiting factor.
A LFP is very tightly monitored and every second you know exactly the real!!! state of your battery.
Conclusion:
There is absolutely no reason not to start from your lithium house bank your engine…it’s actually beneficial as the house is normally that big in AH that it’s kindergarten for the cells to do, means you are at 0.1 till 0.3C and wear on the starter is much less as enough current capabilities and no significant sag in voltage. House is always in use so you know it will 1000% start your engine and you have no surprise of a dry dead starter that collapses when you put a load on

Redundancy:
A lead lives a short live (300cycles max) and is unreliable in monitoring, sure you need redundancy in having a starter that just does this job.

A lithium lives much longer 2000-8000cycles and has a reliable monitoring.
A lithium bank consist of several single batteries in parallel so you already have redundancy.
For a costal sailor which are mostly the small boats too and space is a premium that hybrid LFP house has enough redundancy and reliability compared to a lead setup and as you are close to shore and in the really unlikely event you get fast help if needed

For bluewater cruiser or boats often far way from coast still redundancy is good and senseful requirement but having sitting around a starter that 98% of time does nothing, you don’t know if it really works if you need it and is of no added value then just sitting around waiting to be ever used.

is it not time to modernize and change these concepts as the reason there was seperate starter and house bats is completely gone with lithium.
My clear answer is yes it makes sense and is long overdue.

A much better approach is a buffer battery as redundancy:
It’s much better to have a hybrid starter house bank and a buffer battery (LTO or LFP or AGM) which by default is always full (or near full depending on how you set BMS if LFP) and that isolates and serves as independent power source for our nav equipment at navstation and helm.
that buffer battery is always in use, so you know it’s working and always full or the SOC you target. besides being small AH if LTO or eg Winston cells or an LFP starter bat it is still able to start engine in emergency case, so you have your redundancy and know your redundancy works if needed.

To me much better setup, cheaper, simpler and solves a lot of issues you have with a dedicated starter.
No need for a lead starter ever again.

There is a small thing that you seem to have overlooked, that would be the generator/alternator on the motor. If you are directly connecting LFP batteries to it the resistance of the LFPs is low and if the are low on power they will burn out your generator. Silver that and maybe a 2 battery system, both dual duty, switch back and forth might work

[Goodxcharly]

Yo really don’t need one. Just a waste of money and another system to fail. My car only has one battery.
If you have a hard starting engine somethings wrong and needs to be fixed.
4 - 6 volt house batteries will easily start my engine. 30 hp Universal. Takes all of 3 seconds.
When I bought my boat it didn’t have a start battery and I always thought it should. Now, 3 years later, I’m in the camp that it doesn’t need one. The boat is 22 years old without a start battery.

[mcon12000]

For what’s its worth after reading some of this thread.

I utilize a 24v lifepo4 house bank and a 12v LA (Victron Gel) sub bank. The sub banks 12v loads are actually handled by two 24v/12v 30 amp DC to DC charger's and unless the house bank goes offline the sub bank batteries remain at 100% SOC . One of the DC chargers is enough to cover
almost all the 12v loads I only have two for redundancy.

My 38hp Beta can be started off of the 12v sub bank and it’s setup this way currently. I haven’t made a final decision on whether this is ideal or if the dedicated start battery is more appropriate.

The reason I say this? Well I’ve already been down the road of a dedicated start battery which was charged via a DC to DC charger (Victron) with no direct connection to the alternator. This setup left me stranded after an engine issue in the Atlantic as it showed it was charging my start battery but was actually NOT charging that battery and after 36 hours of sailing I had a decimated starter battery.

My setup at the moment has two 50 amp Victron Buck Boosts terminating on both the 12v LA sub bank and the 24v house bank. This is “better” as there are two robust charging sources for the sub/start bank one from the engine and one from the house. This sub bank also has one dedicated 110w solar panel for maintaining the sub bank in storage when I shutdown the primary bank. This would also work on a dedicated start battery but I felt having a way of powering the boats 12v systems continuously at night via the alternator in the event of a primary bank failure was a better choice.

There are many many ways to get the redundancy and simplicity and it’s been my experience that it’s very case specific and past experiences will have a huge influence.

[OneBoatman]

Once upon a time there were both sailing vessels and motoryachts cruising and sailing the World's oceans before there were LFP batteries. Most every one of them had engines they needed to start from time to time and were using LA batteries. Somehow, they managed to make it back to land.

[newhaul]

Originally Posted by tsenator

What happens if there is a nearby lightning strike and the ‘emp’ knocks out the Lithium BMS ? Then you’re not getting anything out of your lithium batteries . But with lead acid one could still turn over their engine and have navigation and lights. I was sailing and there was a nearby lightning strike maybe 50 -100 yards away and it knocked out my radar and over the next few days I realized it knocked out a few more things like my water tank monitor and battery “echo charger”. It’s nice to have some Lead Acid in an emergency to keep basic “electrical needs” going.

I guess if if was a homemade lithium battery bank you could rip out the BMS and bypass it and just wire the individual cells of a battery in an emergency. But that’s not an easy fix and if they are off the shelf Lithium batteries trying to do that would be even more difficult and potentially dangerous. Having that one Lead Acid is a nice quick and efficient backup

In a diy bank it's a really simple thing to bypass the bms . All you need is to connect the bms main input directly to the ground buss. I intend to actually install a locked switch to do just that . That bypasses the bms in an emergency.

[newhaul]

Originally Posted by Goodxcharly

Yo really don’t need one. Just a waste of money and another system to fail. My car only has one battery.
If you have a hard starting engine somethings wrong and needs to be fixed.
4 - 6 volt house batteries will easily start my engine. 30 hp Universal. Takes all of 3 seconds.
When I bought my boat it didn’t have a start battery and I always thought it should. Now, 3 years later, I’m in the camp that it doesn’t need one. The boat is 22 years old without a start battery.

Your 4 6 volt FLA batteries are a start bank as well as a house bank .

[GreenWave]

Originally Posted by Ionlydream

There is a small thing that you seem to have overlooked, that would be the generator/alternator on the motor. If you are directly connecting LFP batteries to it the resistance of the LFPs is low and if the are low on power they will burn out your generator. Silver that and maybe a 2 battery system, both dual duty, switch back and forth might work

Plenty of ways to ameliorate your concern. The have done it.

[tsenator]

Originally Posted by seaexplorer

All lithium batteries can be used without a BMS in an emergency (like if lightning fries the BMS).

Only for DYI self built Lithium batteries (or the few that have an External BMS).

Most drop in Lithium batteries are sealed and would be a major bitch ripping open and overriding the BMS.

[cram]

So much potential bad advise in this topic without specifying the conditions or use cases assumed when making a recommendation.

Day sailing vs cruising have very different energy needs. A 27 footer with a small outboard and no refrigeration vs a 42' cruising boat drawing 120 Ah have very different design requirements.

Unless one invests in modern lithium cells and smart alternator regulators that can communicate directly with each other to avoid inadvertent disconnects, the safe and reliable approach still stands. Alternator charges start battery (flooded, AGM) and the house lithium is charged from DC-DC chargers.

Facts:

Most BMS are not designed for the very short current spike that occurs when the starter is engaged.

The vast majority of alternators will get burned out if directly connected to a large lithium bank.

Sometimes I wonder if people commenting on design are actually out there cruising or just armchair quarterbacks.

Want to learn something about electrical standards for boats? Read the ABYC or EC standards. Watch the entire PY Systems youtube series... https://www.youtube.com/user/PacificYachtSystems

[cram]

Originally Posted by Goodxcharly

Yo really don’t need one. Just a waste of money and another system to fail. My car only has one battery.
If you have a hard starting engine somethings wrong and needs to be fixed.
4 - 6 volt house batteries will easily start my engine. 30 hp Universal. Takes all of 3 seconds.
When I bought my boat it didn’t have a start battery and I always thought it should. Now, 3 years later, I’m in the camp that it doesn’t need one. The boat is 22 years old without a start battery.

Hardly a basis of comparison. Your car doesn't consume 100 Ah daily when not in use.... so any recommendation would have to be based on the vessel size, it's systems and how it's used.

Most small sport boats only have a start battery. Which is fine, since it's only used to start the engine and electrical loads only exist while the engine is running. Wakesurf boats usually have a start and house battery to power the stereo (and multiple high power audio amps) while not under way.

Any recommendation really needs to be accompanied by a description of the vessel, it's systems and how it's used.

[CaptainRivet]

Originally Posted by s/v Jedi

I would do that. I mean it’s just a buffer to aid the dc-dc chargers. Where can I buy them in the US?

https://batteryhookup.com/products/2...prismatic-cell


18$ per cell and never cycled.

[sinnerman]

Why carry a reserve parachute if the main chute opens 99.9% of the time??

(One less chutes = less weight & less complexity...).

My two cents

cheers