Lithium main bank for engine starting.

[Gybe Ho]

Would it be possible to eliminate the lead acid starting battery on a new canal boat with large lithium battery bank?

 

I understand the original need for dedicated starting batteries i.e. many thin plates to create 100s of crank amps plus an isolated reserve battery for the all too common case of a crashed domestic battery voltage. These problems do not apply to lithium.

 

Consider an 800Ah lithium domestic bank. I expect this would generate enough amps to fire up a 40hp cold main engine and with computerized oversight of battery charge, a flat domestic bank should be a thing of the past.

 

So why not run a pair of fat cables from the main lithium bank to the starter motor? Has this been done before?

[matty40s]

You have to ask yourself "Why has no-one done this before?"....then join the Facebook 12v group and find out.

Jumping from a domestic bank to get you out of a hole is an accepted temporary fix, making it a permanent feature is unwise.

[Gybe Ho]

1 minute ago, matty40s said:

You have to ask yourself "Why has no-one done this before?"....then join the Facebook 12v group and find out.

Jumping from a domestic bank to get you out of a hole is an accepted temporary fix, making it a permanent feature is unwise.

 

We can be thankful that Columbus did not follow your advice and ask the Catholic Church if the world was flat.

 

2 minutes ago, matty40s said:

making it a permanent feature is unwise.

 

 

Since this is the crux of my question, could you expand on this assertion?

[BEngo]

Most LiFePO4 batteries are discharge current limited by the built in Battery Management System.  Typically the current limit is 100 or 200 A.  If the BMS allows ( usually identical)  additional parallel batteries then the discharge limit can be doubled or trebled or even quadrupled..

After that it depends on whether your starter draw is low enough to be accepted by the battery(s).

 

Running the BMS at max current is quite risky.  Typically the BMS depends on a lot of fairly small FET in parallel  each handling a part of the total current.  If one fails the rest cannot handle the current, and fail too, without the BMS cutting the discharge.

Of course if you built your own Li battery and used contactors to control discharge or used an RET BMS then things will be different.

 

N

[dmr]

Yes, with suitable batteries you could do this......but why?

A LA starter costs £100ish, lasts 7+ years and does its job well with zero maintenance.

 

With liveaboard boating redundancy is a priority and keeping starter and domestic circuits separate is key to this and has been done this way by various means for years.

Clever technology can not replace redundancy, almost the opposite.

Maybe an illness or family crisis will lead to a discharged domestic bank....last thing you want is to come home from hospital and be unable to start the engine in mid winter.

[MtB]

6 minutes ago, dmr said:

Yes, with suitable batteries you could do this......but why?

 

One emerging reason might be to avoid mixing battery chemistries in order to comply with comprehensive insurance conditions. 

[dmr]

2 minutes ago, MtB said:

 

One emerging reason might be to avoid mixing battery chemistries in order to comply with comprehensive insurance conditions. 

But the fundamental concept is that they are totally separate circuits so not mixed.

As BEngo says, there are potential risks with high current lithiums, plus its normal not to fuse the starter circuit which is another safety issue.

[Gybe Ho]

4 minutes ago, dmr said:

A LA starter costs £100ish, lasts 7+ years and does its job well with zero maintenance.

 

 

Judging by the number of lengthy forum discussion threads that include the phrase "maybe the VSR has failed", I am not confident starter batteries are zero maintenance. Simplification should increase reliability and reduce engine bay clutter.

 

11 minutes ago, dmr said:

last thing you want is to come home from hospital and be unable to start the engine in mid winter.

 

 

There are enough battery management widgets in the Victron range to eliminate that risk.

[MtB]

3 minutes ago, dmr said:

But the fundamental concept is that they are totally separate circuits so not mixed.

 

But does not a VSR parallel them once in a while? 

[dmr]

8 minutes ago, MtB said:

 

But does not a VSR parallel them once in a while? 

 

You are right, a diode splitter is better from that aspect but otherwise less good. A VSR might be acceptable as it is not a permanent connection.

A modern boat will have separate start and domestic alternators so there can be no connection at all if reqquired, but ifs its desired to use the starter alternator to help charge the domestics then the new Victron DC-DC charger is the way to go   and GybeHo likes technology 😀

[Gybe Ho]

41 minutes ago, BEngo said:

Running the BMS at max current is quite risky.  Typically the BMS depends on a lot of fairly small FET in parallel  each handling a part of the total current.  If one fails the rest cannot handle the current, and fail too, without the BMS cutting the discharge.

 

 

After reading this who would consider building a serial hybrid narrowboat 😀

 

Some further reading suggests that a narrow boat starter motor will draw 2kW at max load, that would be well under what an 800Ah or 9.6kW lithium bank could deliver.

Edited October 5 by Gybe Ho

[IanD]

6 minutes ago, dmr said:

 

You are right, a diode splitter is better from that aspect but otherwise less good. A VSR might be acceptable as it is not a permanent connection.

A modern boat will have separate start and domestic alternators so there can be no connection at all if reqquired, but ifs its desired to use the starter alternator to help charge the domestics then the new Victron DC-DC charger is the way to go   and GybeHo likes technology 😀

 

Since the manufacturer's data sheets for LFP cells/batteries say they must not be connected in parallel with batteries with a different chemistry, VSRs do this some of the time, and (most? all?) insurers now say that LFP batteries must be installed according to the manufacturers recommendations for cover to be valid, this suggests that using a VSR between LA and LFP would mean no insurance cover.

 

1 minute ago, Gybe Ho said:

 

After reading this who would consider building a serial hybrid narrowboat 😀

 

Some further reading suggests that a narrow boat start motor will draw 2kW at max load, that would be well under what an 800Ah or 9.6kW lithium bank could deliver.

 

Someone who has a battery bank designed to supply enough current without any such problems? 🙂 

Edited October 5 by IanD

[Tony Brooks]

30 minutes ago, MtB said:

 

One emerging reason might be to avoid mixing battery chemistries in order to comply with comprehensive insurance conditions. 

 

But that is simply solved - at a cost. Charge the start battery from the alternator/solar/charger and use a B to B to charge the lithium. A B to B is not like a VSR, or long wire, it is not a direct conenction.

[IanD]

3 minutes ago, Tony Brooks said:

 

But that is simply solved - at a cost. Charge the start battery from the alternator/solar/charger and use a B to B to charge the lithium. A B to B is not like a VSR, or long wire, it is not a direct conenction.

If the domestic LFP bank is the big one, it would be better to have the charging sources connected to it and use the B2B to top up the starter battery -- this avoid the need for a high-current B2B with associated losses.

 

That assumes an extenally controlled alternator (e.g. Wakespeed, Zeus...) -- a normal alternator would have to connect to the LA, then you need a bidirectional B2B. Which is supposed to be coming for the Victron Orion XS, but isn't there yet... 😉 

Edited October 5 by IanD

[Tony Brooks]

Just now, IanD said:

If the domestic LFP bank is the big one, it would be better to have the charging sources connected to it and use the B2B to top up the starter battery -- this avoid the need for a high-current B2B with associated losses.

 

That assumes an extenally controlled alternator (e.g. Wakespeed, Zeus...) -- a normal alternator would have to connect to the LA, then you need a bidirectional B2B. Which is supposed to be coming for the Victron Orion XS, but isn't there yet... 😉 

 

Totally agree on all counts, but at present it seems what I said would be the easiest and cheapest "proper" option because it keeps the existing alternator regulator. The available technology is moving fast so goodness knows how this will be solved in the near future

[MtB]

3 minutes ago, IanD said:

If the domestic LFP bank is the big one, it would be better to have the charging sources connected to it and use the B2B to top up the starter battery -- this avoid the need for a high-current B2B with associated losses.

 

That assumes an extenally controlled alternator (e.g. Wakespeed, Zeus...) -- a normal alternator would have to connect to the LA, then you need a bidirectional B2B. Which is supposed to be coming for the Victron Orion XS, but isn't there yet... 😉 

 

 

 

The main reason for all these awkard technical solutions seems to be to avoid breaching the conditions of comprehensive insurance. 

 

Third party insurance seems to make no such demands. 

 

 

 

 

 

 

 

 

[IanD]

5 minutes ago, MtB said:

 

The main reason for all these awkard technical solutions seems to be to avoid breaching the conditions of comprehensive insurance. 

 

Third party insurance seems to make no such demands. 

 

 

Probably true, but you'd need to check the small print to be sure.

 

I'd have thought the main reason was to stop either LA or LFP dying an early death, since their charging requirements are very different... 😉

[David Mack]

Don't most modern boat engines have twin alternators? In which case its easy to keep the lithium domestic and LA starter battery systems completely separate. Add in a small dedicated solar panel and controller to top up the starter battery, with the main solar bank connected to the domestics, and that should provide pretty much what is wanted by both boater and insurer.

[MtB]

Just now, David Mack said:

Don't most modern boat engines have twin alternators?

 

 

Um.... not all boats on the canals are modern boats with modern engines! 

 

 

[David Mack]

Just now, MtB said:

 

 

Um.... not all boats on the canals are modern boats with modern engines! 

 

 

I know - mine included!  But I assume that vast majority of new boats have twin alternators.

[MtB]

3 minutes ago, David Mack said:

I know - mine included!  

 

Yes I was wondering if you'd noticed! 🤣

[Gybe Ho]

24 minutes ago, David Mack said:

Don't most modern boat engines have twin alternators? In which case its easy to keep the lithium domestic and LA starter battery systems completely separate. Add in a small dedicated solar panel and controller to top up the starter battery, with the main solar bank connected to the domestics, and that should provide pretty much what is wanted by both boater and insurer.

 

Indeed, yet another reason to ditch the LA start battery entirely. Why waste the output of the second alternative on the minimal recharge requirement of the starter battery.

[IanD]

2 hours ago, David Mack said:

Don't most modern boat engines have twin alternators? In which case its easy to keep the lithium domestic and LA starter battery systems completely separate. Add in a small dedicated solar panel and controller to top up the starter battery, with the main solar bank connected to the domestics, and that should provide pretty much what is wanted by both boater and insurer.

 

Yes they do -- but if you want to use one to charge LFP it really needs an expensive (£700?) external controller to provide the required charge voltage/current and protect the alternator, and few boats have these.

Edited October 5 by IanD
charge!

[dmr]

1 hour ago, Gybe Ho said:

 

Indeed, yet another reason to ditch the LA start battery entirely. Why waste the output of the second alternative on the minimal recharge requirement of the starter battery.

 

This is the reeason for the voltage sensitive relay on modern twin alternator boats, loads of stuff about this on this forum if you can make the search work.

[Alan de Enfield]

2 hours ago, IanD said:

 

Yes they do -- but if you want to use one to change LFP it really needs an expensive (£700?) external controller to provide the required charge voltage/current and protect the alternator, and few boats have these.

 

And folks still say that 'lithiums' are just plug and play replacements. 

(Not you - you clearly make the point that 'work is needed' to convert from LA)