Lithium house batteries : Lead acid engine battery

Poey50

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I know. It's the reason for the original question (not put very clearly).
So, what is the solution?

Either get someone competent to design and install your system or you need to start from scratch and do your research. I spent 18 months reading everything I could. I and others have sketched out some approaches which I hope highlight for you more issues than your main question addresses. I give references in the opening post of this long thread. 270ah DIY LiFePO4 build
 

jac

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Is the “Join” switch your engine start contingency in case the starter battery fails. (Mine was)
If so, also worth considering that issue - AIUI, Lithium are not suitable for engine start so if your engine start battery does fail, what would you do?.
 

William_H

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Not knowing much about LFP. However I would suggest OP set up the LA battery in a standard manner alternator to battery. As said the switch to connect batteries should be disconnected. This assuming you also had a VSR is to provide jump start for engine. (which also should be disconnected)
So you need a charge system for LFP running from the alternator /battery system. A diode will isolate the batteries. The charge controller for LFP should manage charge control. This assumes that alternator when running produces enough voltage ie14v to supply LFP controller to charge LFP. If not enough voltage then you will need a BtoB charger to boost voltage to that needed. If charging LFP/ controller directly from alternator via diode you will also need some current limit to protect the alternator/LA battery.
If you want jump start ability then you would need a diode for isolation and some current limiting from the LFP so some recharge and contribution from LFP without expecting LFP to provide all starter current. (depending on LFP current capability) (all via your now redundant battery parallel switch.) just a few thoughts ol'will
 

pauldowrick

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Is the “Join” switch your engine start contingency in case the starter battery fails. (Mine was)
If so, also worth considering that issue - AIUI, Lithium are not suitable for engine start so if your engine start battery does fail, what would you do?.
yes it is
 

Moodysailor

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geem is talking about a reasonably common solution which avoids the expense of a new alternator, external regulator and probably a serpentine belt upgrade. It may have a role to play for those who are mainly using solar (or mains) and may be content for the alternator to make a relatively modest contribution. A 30 amp B2b is commonly used and as long as the alternator is say 60 amp or above this should work OK or at least up to a point. They do run hot and switch on an off to cope with heat so 30amps is a theoretical maximum. The advantage of this system is that should the BMS disconnect the house bank the voltage spike should be contained by the start battery protecting the alternator diodes. It doesn't however necessarily have a bad affect on the start battery - it is no different to a car battery regularly receiving 14+ volts since it will only take what it needs to stay topped up.

However, as you say (Paul Rainbow has made a similar point) I agree that this method gives up on the enormous advantage of LFP which is the ability to take charge very quickly and therefore, unlike lead acid, makes full and efficient use of the engine/alternator. Given how costly LFP is I think the single chance to do it right shouldn't be given up easily and, in the end, that is the way that I did it and haven't regretted it for a moment.

There is a third approach which is to keep a lead acid battery permanently in parallel with the LFP - this has its own complications because of the different charging profile between the two chemistries but it does solve some risks associated with sudden disconnect.

All these solutions can protect the system - with additions - against sudden BMS disconnect. However the use of drop-in batteries for all systems begs this three part question which needs to be addressed for any marine system. Apologies for repetition. You are crossing a busy shipping lane at night under engine using AIS, nav lights, and VHF. 1. How will you know if your house bank is about to be isolated? 2. What will be the consequences? 3. How will you mitigate the problems? How or whether you answer those questions determines the safety of the LFP system at sea.

Thank you :) (y)
 

Poey50

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Companies marketing drop-in LFP batteries for boats and the sailing mags that carry the advertising have a poor record of conveying a balanced picture of the pros and cons. So this, from Pacific Yacht Systems, is a welcome exception. I appreciate that the OP is not planning on using drop-ins but the issues of sudden disconnect have wide relevance for marine installations.

 
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geem

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I'm curious on this solution as it sounds elegant, so apologies if I get this wrong but isn't it preferable to have the alternator charge the lithium bank, as that way it can take in a very high current? I get that a separate alternator regulator may be preferable, but it seems to me that having a B2B charger defeats part of the benefit of lithium as the charge would be limited by either the capacity of the B2B, or the capacity of the LA bank - which is not preferable as the LA doesn't really like heavy charge/discharge cycles.

Or am I completely wrong? Thanks for your time, I'm learning about lithium setups so am curios as this was one of the areas where I deemed we would need to invest quite a bit of money.
I guess it comes down to how you use your boat. If you have a large solar array as a liveaboard then the alternator is rarely ever used as a means of battery charging. Spending weeks at anchor the alternator and diesel engine don't get any use. If this is the case an expensive alternator, serpentine belt assembly and alternator external regulator are not good value for money.
A B2B charger at £250 is not too unaffordable for the rare occasions the engine is ran
 

Poey50

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I guess it comes down to how you use your boat. If you have a large solar array as a liveaboard then the alternator is rarely ever used as a means of battery charging. Spending weeks at anchor the alternator and diesel engine don't get any use. If this is the case an expensive alternator, serpentine belt assembly and alternator external regulator are not good value for money.
A B2B charger at £250 is not too unaffordable for the rare occasions the engine is ran

The correct take, I think. LFP is also far better at harvesting available solar energy than lead acid.
 

Poey50

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Having hopefully encouraged the OP to think about the bigger questions than the one he started with, I will now address it. I have a three switch set-up. The emergency linking switch gives me three emergency options. The one I will never use is the emergency parallel option. That leaves me with two useful options.

1. With the LFP isolated for any reason, to run any essential loads from the engine battery.

2. With the engine battery isolated for any reason, to start the engine with the LFP. This is not the strong suit for LFP since it requires a short burst of high current and may exceed the capacity of those BMSs which carry the current rather than those that operate external relays. Some people do use LFP regularly for starting but I'm not sure its the best way of getting a long life from your investment even if the BMS and relays are up to it. But for an emergency, if it's possible? Yes.

However, both of the above are very unlikely so they are last ditch options. Charging of the LFP is limited by the external regulator. Should this fail then a voltage sensitive relay will safely switch off the alternator before high voltage disconnect levels on the BMS are reached. However a BMS can disconnect for both high and low voltage and if high or low voltage parameters are exceeded for any cell. So I have a Victron BMV712 which gives a first audible warning if parameters are neared. If this is missed then the external relay of the BMV712 is set up is connected to a siren giving a loud warning of imminent disconnect. If the BMS does disconnect because of high voltage then only the charge circuit is disconnected and loads are unaffected. If the BMS disconnects for low voltage the charge circuit is unaffected. So the worst case scenario needing emergency option 1 above is if there is a high or low temperature disconnect and of these only the high temperature one is remotely likely since I don't sail in near frozen conditions.. And because I have both a Victron monitor and information via Bluetooth from my BMS I can check on all cells parameters as well as pack voltage and state of charge easily from my phone. Like all LFP obsessives I always know what my battery is doing.

Over the top? Possibly, but I've addressed the three-part crossing a shipping lane at night question.

And there are even safer systems where the BMS directly controls all charging from cell-level information. Why is this safer? Because my charging controls operate on the voltage of the combined pack. My alternator charging ceases at 13.8 volts and two progressively louder warnings start above these pack voltage settings. But a BMS protects the individual cells and therefore disconnects when any cell is in danger of exceeding a safe parameter. You often see recommendations that it is fine to charge to 14.4 volts on a nominal 12 volt pack. For a standard pack consisting of 4 cells in series this is equivalent to 3.6 volts per cell which is below the 3.65 volts figure when a cell is considered full. So you might think that a high voltage cut-off of 3.7 volts per cell would be safe to charge to 14.4 volts. But consider a pack that has gone well out of balance with the cells at these voltages 3.59v, 3.59v, 3.50v and 3.7v. This will give a pack voltage of 14.38 volts. So the charging will not shut down before the high voltage disconnect. Cell-level control is safer.

The obvious solutions are to keep the cells well balanced and to keep the target charging pack voltage low enough to avoid rogue cells triggering a disconnect but high enough for the balancing function of the BMS to kick in. So my charging ends at 13.8 volts and my balancing begins at 3.4 volts per cell (13.6v for pack). Those using drop-ins where the cells have not been charged high enough to balance regularly enough and where they have no access to the cellular information are most at risk of high voltage disconnect. Manufacturers often manage this by setting much higher disconnect voltages. But if this allows cells to be charged too much and too regularly above 3.65 volt then irreversible lithium plating will set in reducing capacity. The US explosion in the use of LFP on boats has not resulted in boats burned to the waterline as some predicted, instead there are a lot of people who have discovered their expensive batteries have permanently and mysteriously lost capacity.

I hope anyone getting this far who thought that LFP might be straightforward is beginning to think again. As Jeff Cote says on the video "nothing is easy".
 
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Richard10002

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I'm curious on this solution as it sounds elegant, so apologies if I get this wrong but isn't it preferable to have the alternator charge the lithium bank, as that way it can take in a very high current? I get that a separate alternator regulator may be preferable, but it seems to me that having a B2B charger defeats part of the benefit of lithium as the charge would be limited by either the capacity of the B2B, or the capacity of the LA bank - which is not preferable as the LA doesn't really like heavy charge/discharge cycles.

Or am I completely wrong? Thanks for your time, I'm learning about lithium setups so am curios as this was one of the areas where I deemed we would need to invest quite a bit of money.

i don’t know if it’s been said but, if you charge lithiums direct from the alternator, they will take whatever is offered, and the alternator will run continuously at “full” power, overheat, and fail with a puff of smoke. It doesn’t do this when charging LA batteries because, as they get full, they draw less amps.

This is why there is a search for a way of charging lithiums from the alternator, avoiding the above.

The B2B is one way of doing this, by reducing the power drawn from the alternator. A 30A B2B will only draw about 30A from the alternator, so a 60A alternator would only be running at about half capacity in this case. With a B2B, I don’t think the LA bank gets much charge, merely acting as a conduit to the lithiums, (or whatever is on the other end of the B2B)

There seems to be a recommendation that an alternator be capable of double the continuous draw in order to be safe, (I think Sterling talk about 30% extra power, but some comment suggests that this is risky).
 

pvb

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i don’t know if it’s been said but, if you charge lithiums direct from the alternator, they will take whatever is offered, and the alternator will run continuously at “full” power, overheat, and fail with a puff of smoke. It doesn’t do this when charging LA batteries because, as they get full, they draw less amps.

This is why there is a search for a way of charging lithiums from the alternator, avoiding the above.

The B2B is one way of doing this, by reducing the power drawn from the alternator. A 30A B2B will only draw about 30A from the alternator, so a 60A alternator would only be running at about half capacity in this case. With a B2B, I don’t think the LA bank gets much charge, merely acting as a conduit to the lithiums, (or whatever is on the other end of the B2B)

There seems to be a recommendation that an alternator be capable of double the continuous draw in order to be safe, (I think Sterling talk about 30% extra power, but some comment suggests that this is risky).

An alternator running at "full power" shouldn't necessarily overheat and die, they're designed to run at full power. However, there are alternator regulators which include temperature compensation.
 

Pete7

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The correct take, I think. LFP is also far better at harvesting available solar energy than lead acid.

Indeed, when you see 18 out of a possible maximum 20A going into the battery all the way up to full means the battery does charge far more quickly compared to our previous lead acid batteries. If its raining and we don't reach 100% well so what? the LFP will be quite happy at 80%. and that's enough to see us through a couple of poor weather.

We have a Victron DC>DC charger (25-30A output) to go between the engine battery and the LFP, but have only used it I think 3 times during our 3 week summer cruise this year, mainly because we didn't have sun or couldn't be certain of it later.

Whilst we can't make use of the very fast charge rate only having a 60A alternator, we haven't felt the need is there in real world use.
 

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Pete7

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An alternator running at "full power" shouldn't necessarily overheat and die, they're designed to run at full power. However, there are alternator regulators which include temperature compensation.

No, ordinary car type alternators fitted as standard to many small yacht engines are not rated to 100%. They are designed as cheap dumb alternators to charge a car starter battery and run the radio, windscreen wipers and lights. Not charge hundreds of Ah of house batteries. There is also an issue of alternator speed may be too low if you are only motoring slowly for the power being extracted.

 

Poey50

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The question of what alternator and whether external regulation is needed is a hot (sorry) topic on the Lithium Batteries on a Boat Facebook Group. Some people seem to make it work with those alternators that have some temperature compensation. The majority experience however seems to be that of alternator melting and a switch to Balmars and external regulation. Those who make it work are always among the most experienced. As with all things LFP, successful variation from standard practice depends on really understanding your system and working around the limitations.
 
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pvb

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No, ordinary car type alternators fitted as standard to many small yacht engines are not rated to 100%. They are designed as cheap dumb alternators to charge a car starter battery and run the radio, windscreen wipers and lights. Not charge hundreds of Ah of house batteries. There is also an issue of alternator speed may be too low if you are only motoring slowly for the power being extracted.

All alternators are rated for max continuous output at specified temperatures.

You can't have an alternator speed too low for the power being extracted, because the available power is dependent on the speed. You can't extract more than is available.
 

pvb

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Are you talking from experience here?

People like Sterling Power disagree with you. Did you watch the video btw?

Yes, and ended up specifying a Prestolite Leece-Neville alternator on my last boat, to charge a 660Ah domestic bank. It worked fine, didn't melt at all.

Now, how about my question to you about the fact that you can't extract more power from an alternator than is available?
 

Poey50

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Anyone wishing to research the alternator issue for LFP will find a useful section about 3/4 of the way down this repeatedly quoted Rod Collins article. Navigate to the section heading "Alternator Considerations for LiFePO4". The whole article is, in my view, essential reading for anyone seriously considering LFP.

LiFePO4 Batteries On Boats - Marine How To
 
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gregcope

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Indeed, when you see 18 out of a possible maximum 20A going into the battery all the way up to full means the battery does charge far more quickly compared to our previous lead acid batteries. If its raining and we don't reach 100% well so what? the LFP will be quite happy at 80%. and that's enough to see us through a couple of poor weather.

We have a Victron DC>DC charger (25-30A output) to go between the engine battery and the LFP, but have only used it I think 3 times during our 3 week summer cruise this year, mainly because we didn't have sun or couldn't be certain of it later.

Whilst we can't make use of the very fast charge rate only having a 60A alternator, we haven't felt the need is there in real world use.

Which BMS is that?
 

geem

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Yes, and ended up specifying a Prestolite Leece-Neville alternator on my last boat, to charge a 660Ah domestic bank. It worked fine, didn't melt at all.

Now, how about my question to you about the fact that you can't extract more power from an alternator than is available?
We have the same Prestolite Leece Neville manufactured alternator. It is a standard fit on my Perkins M92B engine. To get more volts out of it (24v boat, 60amp output at 24v) we installed a Sterling smart reg. This has battery temperature sensing. It did raise the voltage under bulk charging but the inbuilt temperature sensor would cut out the external reg fairly quickly. We persevered with it but it really didn't add a lot of charging capability due to the time spent switch off by the temperature sensor. I tried disconnecting the temperature probe for a while and it worked fine. After a few weeks, out of interest, I removed the alternator and stripped it down. The windings were black. It still worked but clearly had been running very hot. I installed the spare alternator with nice shiny copper windings and didn't bother reconnecting the Sterling reg. Clearly driving this normal alternators hard and hot does have consequences.
It makes sense that Balmar heavy duty alternators are equipped with oversized cooling fans as well as other more robust solutions.
 
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