LifePo4 with a dedicated alternator.

[jongood]

As winter approaches again I m thinking about upgrading my 19 yo 440ah Gel to Life po4 again. My Gels are fine at 12v, but aren't liking the amount of mains we use so the voltage isn't holding long enough when the inverter is in use for longr periods.

My system is unusual because it has 2 alternators, 1 for the 12v leisure system and a 24v one for the vehicle requirements. I'm wondering whether I could safely charge a lithium battery straight off my existing 12v alternator as that would be its only job?

 

[Tombola]

Don't see why not..esp as it is dedicated ....Do you know what size your alternator is and how much lithium are you thinking of adding.
The alternator on mine used to throw up to 50amp into my lithium's .

Then also now and then I'm guessing you'd need a proper charge through all 3 stages with a dedicated charge profile

 

[bigtwin]

The answer to that Jon is YES.

The arrangement you have is identical to that of boats where many, myself included, have adopted what is known as a hybrid system.

The normal issue with using LiFePo4 batteries is that when the Lithium battery’s BMS disconnects itself from the alternator the alternator can be damaged by a spike. This can be overcome either by fitting dedicated electronickery (e.g. a DC to DC charger) or by retaining a lead acid battery (SLA) in parallel with the lithium (this is a hybrid system).

Unlike lead acids, lithiums will suck as much current from the alternator as it will deliver (hence the fast charge times for lithium). This can cause the alternator to run hot. On many boats, the output from the alternator is restricted by the size/length of the alternator cable. Where this is not the case, the problem is addressed by fitting a longer alternator cable (thereby increasing the circuit resistance). The hybrid approach means that it is not necessary to change other charge sources (e.g. solar, mains) as a lead acid battery is retained in the system.

Usually, combining battery types is considered to be a big no no. However, the characteristics of LiFePo4 and SLA are ideally matched in that the Lithium’s resting voltage sits slightly higher than the SLA and (with no charge sources inputting) will trickle charge the SLA. As soon as a load is connected the lithium will take the load (due to its higher resting voltage and it’s lower internal resistance) and only when the lithium has depleted to its BMS’s low voltage cut-off will the SLA contribute any power. This arrangement suits the two battery types perfectly as SLA prefers to be fully charged (and suffers when left is partial states of charge) and lithiums prefer not to be fully charged (controlled by the BMS when being charged) and will always be the first to supply a load.

It is imperative that the lithium has a configurable BMS and the supplier favoured by narrowboaters is from Life Batteries who will endure that batteries supplied have their BMS configured for a hybrid arrangement.

It might be worth you joining the Facebook group ‘12 volt boating group’ where you’ll find a wealth of information.
If you search the group you should fund a series of posts I made when I fitted my LiFePo4 batteries and tested/monitored my alternator while seeking to optimise the size/length of the alternator cable.

Ian

 

[Lenny HB]

You could probably get away with but depends on what batteries you fit & if fitting a large bank you could damage the alternator.
For peace of mind I would fit a B2B as not only will it give better control over the battery charging it will also protect the alternator.
With the amount you are going to be spending on the batteries what's the point of trying to do the installation on the cheap & putting the batteries and alternator at risk.

 

[funflair]

As winter approaches again I m thinking about upgrading my 19 yo 440ah Gel to Life po4 again. My Gels are fine at 12v, but aren't liking the amount of mains we use so the voltage isn't holding long enough when the inverter is in use for longr periods.

My system is unusual because it has 2 alternators, 1 for the 12v leisure system and a 24v one for the vehicle requirements. I'm wondering whether I could safely charge a lithium battery straight off my existing 12v alternator as that would be its only job?

I was going to say "not straight from the alternator" but then reading some above I could be wrong, I would worry that the batteries might suck the alternator dry and overheat it as Lenny suggests.

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[bigtwin]

With the amount you are going to be spending on the batteries what's the point of trying to do the installation on the cheap & putting the batteries and alternator at risk.

The hybrid arrangement is a much simpler (and hence more robust) arrangement than fitting a dc to dc charger. This approach presents a lower risk than adding more complex solutions that are seeking to achieve the same objective.

In a SLA system the Current output from the alternator is limited, primarily, by the internal resistance of the battery.
In a lithium setup the internal resistance is low and allows high current output from the alternator.
However, what matters is the circuit resistance and the current is easily limited by adding resistance to the circuit and there is no simpler (first principles, if you like I = V/R) method than increasing the resistance of the charging cable. In this case the current is, primarily, limited by the resistance of the alternator cable.

For some reason many folks believe that the more complex, and hence expensive, solution is the ‘better’ solution. Often that may well be the case but there is nothing simple, cheaper and safer than reverting to first principles and adding resistance to the circuit. In the boating world many are having difficulty in accepting what is known as ‘the long lead method’ but none of them have presented a coherent argument that explains why a first principles approach might be unsafe.

LiFePo4 requires a bit of a mindset change. Historically, resistance in a 12V dc circuit was the enemy of efficiency. However, when it comes to charging LiFePo4 resistance is your friend.

Ian

 

[bigtwin]

I was going to say "not straight from the alternator" but then reading some above I could be wrong, I would worry that the batteries might suck the alternator dry and overheat it as Lenny suggests.

Without putting measures in place it would.

In boating circles, many who have adopted the hybrid arrangement (necessary to protect the alternator on BMS disconnect of the lithiums) have found no need to add additional resistance in the charging circuit.
However some, myself included (my alternator cable was way oversized at 90mm2), had to change the alternator cable to adequately limit the current output (and hence temperature).

Ian

 

[Lenny HB]

I can see your point bigtwin about fitting a LA battery to help safeguard the alternator as Jon would have no other load on the alternator apart from the hab batteries. I still think it is worth fitting a B2B as then the LiFeP04 battery will receive a proper charge profile & not be relying on the BMS as a last resort.

 

[Pausim]

I would use a B2B, kinder to the battery and the alternator. LiFePO4 do not like overcharging. The BMS in my LiFePO4 battery will shut down to protect itself from over voltage but this is already way above the ideal charging voltage. The BMS doesn’t manage charging it just shuts the battery down if it senses a serious threat. If the BMS shuts down the cause needs to be identified and rectified and should not be part of the regular charging process.

 

[jongood]

The answer to that Jon is YES.

The arrangement you have is identical to that of boats where many, myself included, have adopted what is known as a hybrid system.

The normal issue with using LiFePo4 batteries is that when the Lithium battery’s BMS disconnects itself from the alternator the alternator can be damaged by a spike. This can be overcome either by fitting dedicated electronickery (e.g. a DC to DC charger) or by retaining a lead acid battery (SLA) in parallel with the lithium (this is a hybrid system).

Unlike lead acids, lithiums will suck as much current from the alternator as it will deliver (hence the fast charge times for lithium). This can cause the alternator to run hot. On many boats, the output from the alternator is restricted by the size/length of the alternator cable. Where this is not the case, the problem is addressed by fitting a longer alternator cable (thereby increasing the circuit resistance). The hybrid approach means that it is not necessary to change other charge sources (e.g. solar, mains) as a lead acid battery is retained in the system.

Usually, combining battery types is considered to be a big no no. However, the characteristics of LiFePo4 and SLA are ideally matched in that the Lithium’s resting voltage sits slightly higher than the SLA and (with no charge sources inputting) will trickle charge the SLA. As soon as a load is connected the lithium will take the load (due to its higher resting voltage and it’s lower internal resistance) and only when the lithium has depleted to its BMS’s low voltage cut-off will the SLA contribute any power. This arrangement suits the two battery types perfectly as SLA prefers to be fully charged (and suffers when left is partial states of charge) and lithiums prefer not to be fully charged (controlled by the BMS when being charged) and will always be the first to supply a load.

It is imperative that the lithium has a configurable BMS and the supplier favoured by narrowboaters is from Life Batteries who will endure that batteries supplied have their BMS configured for a hybrid arrangement.

It might be worth you joining the Facebook group ‘12 volt boating group’ where you’ll find a wealth of information.
If you search the group you should fund a series of posts I made when I fitted my LiFePo4 batteries and tested/monitored my alternator while seeking to optimise the size/length of the alternator cable.

Ian

thanks for this Ian. so just to be clear are you suggesting an Sla in parallel with a lithium?

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[bigtwin]

I still think it is worth fitting a B2B as then the LiFeP04 battery will receive a proper charge profile & not be relying on the BMS as a last resort.

Many do choose to fit a B2B but from what I’ve seen, they appear to substantially limit the current output (20 - 30 amps from recollection) on alternators rated at 150A plus. This seems to nullify the fast charging benefit of fitting lithiums.

This fast charge feature is a significant benefit to those who live on narrowboats. With SLA, they would typically run their engines for perhaps 6 - 8 hrs/day (perhaps longer) to charge their batteries (typically 500Ah bank sizes).
Adopting LiFePo4 with their fast charge capability allows them to fully charge their batteries typically within a couple of hours.

Ian

 

[Lenny HB]

Many do choose to fit a B2B but from what I’ve seen, they appear to substantially limit the current output (20 - 30 amps from recollection) on alternators rated at 150A plus. This seems to nullify the fast charging benefit of fitting lithiums.

Votronic make a 90 amp B2B. A lot of people save money by fitting a 30 amp B2B because a 60 amp one is twice the price.
On a Motorhome even with a 160 amp alternator you wouldn't want to be taking much more than 60 or 70 amps out of it as you need a fair bit of power for the rest of the system.

 

[bigtwin]

I would use a B2B, kinder to the battery and the alternator.

How is a B2B ‘kinder’ to the battery and alternator?

LiFePO4 do not like overcharging.

No, they don’t. That’s why it’s important to have a configurable Battery MANAGEMENT System.

What do you envisage that a B2B does in order to cease providing a charge to the batteries?

The BMS in my LiFePO4 battery will shut down to protect itself from over voltage but this is already way above the ideal charging voltage.

If that’s the case, it would seem that you don’t have a configurable BMS.

The BMS doesn’t manage charging it just shuts the battery down if it senses a serious threat.

Yes, the BMS will disconnect the charge source when either individual cell voltage, or battery voltage exceeds the thresholds defined in the BMS.

How do you characterise “a serious threat”?

If the BMS shuts down the cause needs to be identified and rectified and should not be part of the regular charging process.

If the BMS isolates the charging supply when you have added additional complexity between the charging source and the battery, it would rather suggest that the additional complexity is somewhat unreliable. The cable resistance in my charging circuit is somewhat foolproof as it is rated above the maximum alternator output current. This isn’t going to present my BMS with any serious threat.

Ian

 

[bigtwin]

On a Motorhome even with a 160 amp alternator you wouldn't want to be taking much more than 60 or 70 amps out of it as you need a fair bit of power for the rest of the system.

Agreed.

Ian

 

[bigtwin]

thanks for this Ian. so just to be clear are you suggesting an Sla in parallel with a lithium?

Yes.

Feel free to PM me if you’d like to have a telephone chat.

Ian

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[Pausim]

How is a B2B ‘kinder’ to the battery and alternator?

In my case I believe it provides the battery with a proper charging profile and prevents a hungry battery bank from over extending the the alternator. I wouldn’t be happy relying on cable resistance to manage either process.

No, they don’t. That’s why it’s important to have a configurable Battery MANAGEMENT System.

My battery does not have a configurable BMS and neither did any of the other off the shelf batteries I looked at.

What do you envisage that a B2B does in order to cease providing a charge to the batteries?

My B2B reduces the charge voltage from 14.6V to a maintenance charge of 13.8V which is much better for the battery once it is full.

If that’s the case, it would seem that you don’t have a configurable BMS.

I don’t.

I think our opinions differ because you are assuming most LiFePO4 batteries have a configurable BMS and I am assuming most don’t. Relion describe my BMS as a backstop, they also supply charging parameters which need to be incorporated into the external charging arrangements.

 

[bigtwin]

In my case I believe it provides the battery with a proper charging profile and prevents a hungry battery bank from over extending the the alternator. I wouldn’t be happy relying on cable resistance to manage either process.

For sure, a B2B will provide a more optimised charge profile than that directly from an alternator. However, it won’t provide any better, and arguably worse, alternator protection than current limiting resistance.

My battery does not have a configurable BMS and neither did any of the other off the shelf batteries I looked at.

Ahh, that explains a lot. Batteries from Life Batteries have fully configurable BMSs.

My B2B reduces the charge voltage from 14.6V to a maintenance charge of 13.8V which is much better for the battery once it is full.

When my batteries are full, the BMS disconnects the charge source while continuing to supply any loads that need servicing.

I think our opinions differ because you are assuming most LiFePO4 batteries have a configurable BMS and I am assuming most don’t. Relion describe my BMS as a backstop, they also supply charging parameters which need to be incorporated into the external charging arrangements.

Agreed.

I can highly recommend the batteries from Life Batteries. They are well spec’d and come with excellent customer service (both in pre-sales support and after-sales support).

Ian

 

[jongood]

Votronic make a 90 amp B2B. A lot of people save money by fitting a 30 amp B2B because a 60 amp one is twice the price.
On a Motorhome even with a 160 amp alternator you wouldn't want to be taking much more than 60 or 70 amps out of it as you need a fair bit of power for the rest of the system.

Fair enough but my system is different, I have 440ah of batteries my 12v alternator will produce about 60amps. if I were to fit a B2b it would have to be a 24v to 12v and ditch my 12v alternator, which seems a bit of a shame.

 

[Lenny HB]

Fair enough but my system is different, I have 440ah of batteries my 12v alternator will produce about 60amps. if I were to fit a B2b it would have to be a 24v to 12v and ditch my 12v alternator, which seems a bit of a shame.

Don't see why you can't use the 12v alternator.

 

[jongood]

Don't see why you can't use the 12v alternator.

connected straight to the B2b? doesn't seem right somehow.

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[bigtwin]

Fair enough but my system is different, I have 440ah of batteries my 12v alternator will produce about 60amps. if I were to fit a B2b it would have to be a 24v to 12v and ditch my 12v alternator, which seems a bit of a shame.

Many on narrowboats, effectively, derate their alternator as they can spend much of their running time at engine idle speed when the alternator cooling isn't as effective. I doubt that this would be the case with a MH.

I’d guess that you could aim for a 50 A output from your alternator. If you did, it’d be worth monitoring your alternator temperature to see how it copes.

The first graph below shows the performance of my NB alternator (110A) when I did a straight drop in without any change to my MASSIVE 95mm2 alternator cable and the second shows the change after fitting a smaller (and longer) alternator cable to throttle the alternator output current.

The increase in current output 15 mins into the test was as a result of switching on a 2kw kettle load supplied through the inverter to provide pretty much a worst case scenario and shows the alternator cable limiting the current output to about 78A.

Ian

 

[Lenny HB]

connected straight to the B2b? doesn't seem right somehow.

You could just fit a cheap car battery to give the alternator a constant load.

 

[jongood]

You could just fit a cheap car battery to give the alternator a constant load.

isnt that what Ian is suggesting?

 

[Lenny HB]

isnt that what Ian is suggesting?

He was suggesting doing that without a B2B I meant with a B2B.

 

[jongood]

thanks everyone, there's a lot to process here, so I'm going to try to get on the boat facebook thing and have a chat with life batteries.

Jon

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[Hoovie]

Just a comment on one of your points below ...

.....
Usually, combining battery types is considered to be a big no no. However, the characteristics of LiFePo4 and SLA are ideally matched in that the Lithium’s resting voltage sits slightly higher than the SLA and (with no charge sources inputting) will trickle charge the SLA. As soon as a load is connected the lithium will take the load (due to its higher resting voltage and it’s lower internal resistance) and only when the lithium has depleted to its BMS’s low voltage cut-off will the SLA contribute any power......

Ian

It is not quite as cut and dried as that. At a certain voltage point the Lead starts to contribute more and more, and that point is not the Lithiums low-voltage cut-off point.
The Lead can come on due to increased system load that causes a natural voltage sag in the system (in both Lead AND Lithium, although to differing levels) and as the Lithium gets to a lower state of charge the contribution from the Lead increases. And when the Lithium is in a high charged state it does just about everything - but even then, NOT everything. The Lead is not in a dormant state until the Lithium shuts down.

To illustrate this, some info at different states of charge of a Lead/Lithium Hybrid system, where there is a regular consistant load caused by the Inverter coming on to run a fridge compressor. Compressors have a high current surge (upto 20+ times the running current) and sometimes the system happens to capture that event, which is interesting as it helps reveal the Lead-Lithium relationship as can be seen in the middle graph.

Both Lead and Lithium at a high state of charge.

Even in normal running of the fridge, you can see the Lead is providing a small amount of power. And when the fridge stops, the Lithium puts most of that energy back (the little red blip between 18:45 and 19:00). But you see a much greater contribution on the spike captured between 20:00 and 20:15 - the Lead provides 11A at the point, while the Lithium does 15A (not the current scales are unfortunately different ). So a definate contribution of power from the Lead even at 13.2V (due to the voltage sag on the sudden high load).

Choosing the time when the Lithium is more depleted now.

The Lead State of Charge is still nearly 100% whilst the Lithium is down to 75%. The Lead remains at near enough the same SOC as the lithium does the little blip recharge to make up for the Leads contribution on load once the load is reduced, but again we can see the Lead is in use without a doubt.

And choosing a point where the Lithium is pretty low (but still active).

Now here the Lithium is down to 13.4% and when the fridge load is present, still both Lead and Lithium are providing power, but it is now the Lead doing most of the work. And interestingly, what is happening now when the load is reduced, the Lead is replenishing the Lithium to a degree (the reverse of earlier).
This means generally that the Lithium never drops below a certain state of charge and is always 'alive' just like the Lead is. The automatic relationship between Lead and Lithium means there is a natural plateau at which the lithium doesn't tend to go below (see below)

As far as charging the Hybrid System goes, I have all the chargers (70A Mains, 60A B2B and a pair of 20A MPPTs) all set on Lead profiles. The Lithium takes the Lions share (as can be seen above in the way the green line shoots up and hits 100% before the Lead), but invariably by the time the voltage gets to around 14.2V the Lithium is fully recharged and will not take more current - and ideally wants to be disconnected from any chargers, which is why I have it disconnect from the Hybrid system using a special microprocessor-controlled relay of my own specification and let the chargers continue to finish the Lead charging job (which is why you have them configured to suit Lead, as it is that that needs the multi-stage charging profiles).

If anyone wants to read a bit more on how the Lithium and Lead work together, I have a series of articles starting here - https://www.wildebus.com/hybrid-battery-bank-introduction/

 

[bigtwin]

Just a comment on one of your points below ...


It is not quite as cut and dried as that. At a certain voltage point the Lead starts to contribute more and more, and that point is not the Lithiums low-voltage cut-off point.
The Lead can come on due to increased system load that causes a natural voltage sag in the system (in both Lead AND Lithium, although to differing levels) and as the Lithium gets to a lower state of charge the contribution from the Lead increases. And when the Lithium is in a high charged state it does just about everything - but even then, NOT everything. The Lead is not in a dormant state until the Lithium shuts down.

To illustrate this, some info at different states of charge of a Lead/Lithium Hybrid system, where there is a regular consistant load caused by the Inverter coming on to run a fridge compressor. Compressors have a high current surge (upto 20+ times the running current) and sometimes the system happens to capture that event, which is interesting as it helps reveal the Lead-Lithium relationship as can be seen in the middle graph.

Both Lead and Lithium at a high state of charge.
View attachment 673581
Even in normal running of the fridge, you can see the Lead is providing a small amount of power. And when the fridge stops, the Lithium puts most of that energy back (the little red blip between 18:45 and 19:00). But you see a much greater contribution on the spike captured between 20:00 and 20:15 - the Lead provides 11A at the point, while the Lithium does 15A (not the current scales are unfortunately different ). So a definate contribution of power from the Lead even at 13.2V (due to the voltage sag on the sudden high load).

Choosing the time when the Lithium is more depleted now.
View attachment 673585
The Lead State of Charge is still nearly 100% whilst the Lithium is down to 75%. The Lead remains at near enough the same SOC as the lithium does the little blip recharge to make up for the Leads contribution on load once the load is reduced, but again we can see the Lead is in use without a doubt.

And choosing a point where the Lithium is pretty low (but still active).
View attachment 673586
Now here the Lithium is down to 13.4% and when the fridge load is present, still both Lead and Lithium are providing power, but it is now the Lead doing most of the work. And interestingly, what is happening now when the load is reduced, the Lead is replenishing the Lithium to a degree (the reverse of earlier).
This means generally that the Lithium never drops below a certain state of charge and is always 'alive' just like the Lead is. The automatic relationship between Lead and Lithium means there is a natural plateau at which the lithium doesn't tend to go below (see below)
View attachment 673611

As far as charging the Hybrid System goes, I have all the chargers (70A Mains, 60A B2B and a pair of 20A MPPTs) all set on Lead profiles. The Lithium takes the Lions share (as can be seen above in the way the green line shoots up and hits 100% before the Lead), but invariably by the time the voltage gets to around 14.2V the Lithium is fully recharged and will not take more current - and ideally wants to be disconnected from any chargers, which is why I have it disconnect from the Hybrid system using a special microprocessor-controlled relay of my own specification and let the chargers continue to finish the Lead charging job (which is why you have them configured to suit Lead, as it is that that needs the multi-stage charging profiles).

If anyone wants to read a bit more on how the Lithium and Lead work together, I have a series of articles starting here - https://www.wildebus.com/hybrid-battery-bank-introduction/

Yes, in practice, the lead will support the lithiums as required and, I guess, the extent of this will be related to the relative size of the lithium bank and the SLA bank and the particular load being serviced.

A great data set that you have there and I’ll have a read of the data in your hyperlink.

Thanks for posting.

Ian

 

[bigtwin]

Hoovie, just read the information in the hyperlink in your earlier post; great data logging and very informative.

Really shows how LiFePo4 and lead acid complement one another and mirrors the experience of boaters.

Ian

 

[Hoovie]

Hoovie, just read the information in the hyperlink in your earlier post; great data logging and very informative.

Really shows how LiFePo4 and lead acid complement one another and mirrors the experience of boaters.

Ian

bigtwin, this might be interesting to you. It shows the kind of point where the Lead side takes over from the Lithium in terms of its power contribution.
Handily, this time the current scales for Lead and Lithium are the same so much easier to compare (Victron is meant to be making them controllable eventually!).

 

[Bessy765]

This is what I get from my alternator when driving around 55 mph. 2019 Fiat 2.3 150 hp auto.I have 700 watts of solar, 2 x 100 amp Transporter Lithium and a 12/2000/80 Victron inverter charger. This is whilst running my Telair Freshjet 2200, there is no B2B fitted in the system, I am assured how this is set up one is not needed as the batteries approach fully charged the charging rate and voltage decrease. The installer warrants the whole system for 5 years and the batteries for 10. The only advice is not to run the engine stationary to just charge the batteries for more than 15 mins. 3 years and 17500 miles later all is fine.

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