LiFePO4 (Lithium) and Lead Acid Hybrid Arrangement

[RogerIvy]

Just for interest (I found it interesting anyway).
I recently helped a boat owner debug a charging issue.

He has a 300AH LiFePO4 battery with Eve cells and a Daly 150A BMS. A Daly 150A can accept a charge of 50% of its capacity, so 75A in this case.
He has the LiFePO4 battery connected to a small bank of Lead Acid batteries (in parallel of course). I’m not sure how many Lead batteries.
The hybrid battery bank is connected to one of two alternators (this is quite common on boats). Direct connection, no DC-DC.

The LiFePO4 was around 20% or less SOC when he installed it.

His problem kicked in when he started the engine. The charge MOSFET would turn off after a second or two. After he stopped the engine it would turn back on.
I asked for him to check the Daly app to see what current was flowing into the LiFePO4 battery.
The answer: just under 130A
So the BMS was protecting itself (Correctly so).
I asked what current was flowing into the LiFePO4 battery when engine turned off.
The answer: 70A

So the LifePO4 was receiving 70A + 60A = 130A (from Lead Acid and Alternator respectively).

Interestingly these hybrid arrangements are encouraged on boats. I think it may have started when one person wrote an article about the merits of such a hybrid system. Just to be clear I’m talking about the leisure batteries only, not the starter battery.
I recently had one guy call me to buy one of our batteries for his boat to connect in parallel to his Lead Acids. He said in the boating world the idea is to “buffer” the LiFePO4 with Lead Acid. Hmmm. Not needed. He also said that when the LiFePO4 runs out the leads can charge it (even at the expense of damaging the leads). When full, the LiFePO4 would charge the leads when everything was at rest which he said was a good thing. In the end he decided against a hybrid arrangement. To keep it simple I gave him two good reasons to not use a hybrid arrangement:
1. You would potentially damage the Lead Acids unless you installed a Battery Protect when the LiFePO4 was depleted
2. Your Lead Acids would bleed power from the LiFePO4 when at rest for no real gain

Anyway - hope you find this interesting.
Anyone out there run on a hybrid battery arrangement?

 

[autorouter]

You'd probably get the same problem with two LiFePO4 batteries if one was 100% and the other was 20%, and you connected them together. The BMS would cut off because the current while equalising the charges would be over the 75A limit. You need to start off with the lithium and lead-acid batteries in the same state of charge, ideally both 100%, before they are connected. Once equalised, the problem goes away.

 

[RogerIvy]

You'd probably get the same problem with two LiFePO4 batteries if one was 100% and the other was 20%, and you connected them together. The BMS would cut off because the current while equalising the charges would be over the 75A limit. You need to start off with the lithium and lead-acid batteries in the same state of charge, ideally both 100%, before they are connected. Once equalised, the problem goes away.

Agree the problem goes away (of the excessive charging current), but I still don’t see any real advantage to a hybrid arrangement.

 

[Hoovie]

Some questions ....

Just for interest (I found it interesting anyway).
I recently helped a boat owner debug a charging issue.

He has a 300AH LiFePO4 battery with Eve cells and a Daly 150A BMS. A Daly 150A can accept a charge of 50% of its capacity, so 75A in this case.
He has the LiFePO4 battery connected to a small bank of Lead Acid batteries (in parallel of course). I’m not sure how many Lead batteries.
The hybrid battery bank is connected to one of two alternators (this is quite common on boats). Direct connection, no DC-DC.

The LiFePO4 was around 20% or less SOC when he installed it.

His problem kicked in when he started the engine. The charge MOSFET would turn off after a second or two. After he stopped the engine it would turn back on.
I asked for him to check the Daly app to see what current was flowing into the LiFePO4 battery.
The answer: just under 130A
So the BMS was protecting itself (Correctly so).
I asked what current was flowing into the LiFePO4 battery when engine turned off.
The answer: 70A

So the LifePO4 was receiving 70A + 60A = 130A (from Lead Acid and Alternator respectively).

How exactly is the Lithium battery receiving 70A from the Lead Acid battery? I find that a little hard to believe and in normal use just is not going to happen. His issue is not about having a hybrid type of setup but adding in a battery that quite significantly depleted and with, TBH, a pretty rubbish BMS setup (a 300Ah Lithium with an absolute maximum 75A charge? that is just pants).

Interestingly these hybrid arrangements are encouraged on boats. I think it may have started when one person wrote an article about the merits of such a hybrid system. Just to be clear I’m talking about the leisure batteries only, not the starter battery.
I recently had one guy call me to buy one of our batteries for his boat to connect in parallel to his Lead Acids. He said in the boating world the idea is to “buffer” the LiFePO4 with Lead Acid. Hmmm. Not needed. He also said that when the LiFePO4 runs out the leads can charge it (even at the expense of damaging the leads).

I doubt he understood the concept correctly. That is NOT how a Hybrid battery setup would, or should, or even could, work.

When full, the LiFePO4 would charge the leads when everything was at rest which he said was a good thing. In the end he decided against a hybrid arrangement. To keep it simple I gave him two good reasons to not use a hybrid arrangement:
1. You would potentially damage the Lead Acids unless you installed a Battery Protect when the LiFePO4 was depleted
2. Your Lead Acids would bleed power from the LiFePO4 when at rest for no real gain

Anyway - hope you find this interesting.

Interesting, but not correct.

Anyone out there run on a hybrid battery arrangement?

Yes. I do. Not on a boat, but in my Motorhome and I don't have any of the "problems" you claim happen in a Hybrid arrangement.
However I certainly also don't have a Lithium Battery with such a restrictive BMS.

Here is an unfortunately quite busy chart that shows both the Lithium Battery and the Lead Battery in a Hybrid arrangment, with their respective SOCs and Current Flow.
Lithium - Orange = SOC, Red = Current; Lead - Blue = SOC, Green = Current. Note the scales vary, so bear that in mind when comparing...
Hybrid Battery by David, on Flickr
You can see the Lithium goes below 10%, so quite a bit lower than your 20% observation and although the Lead is pretty charged (over 90%) there is none of this mega current flow from Lead to Lithium you seem to think happens.
Yes, there is a small trickle effect from Lead to Lithium in 'quiet periods', just as there is from Lithium to Lead when the Lithium is high, but that is very small and is just noise in effect as the current transferred stays within the Hybrid battery bank and the actual wastage is a very small percentage of that trickle.


There are a number of advantages with a Hybrid setup over 100% Lithium. Cost is a major one undoubtedly (my 300AH of Lead Carbon batteries, which I can discharge down to 30% quite safely, were 3/4 of the price of one of my 100AH Lithium batteries to give an example), but there are also technical advantages and my own belief and experience suggests that a Lithium/Lead Hybrid configuration overall is both superior to a purely Lead Acid based battery bank AND a purely Lithium based battery bank regardless of the cost.

If you are interested, you can have a read of some of the research on using a Lithium + Lead Carbon Hybrid setup here - https://www.wildebus.com/hybrid-battery-bank-introduction/ - None of this was "lab based" and theory, note, but actual installation of a Hybrid setup and empirical evidence and observation over an extended period.

 

[autorouter]

The theory is something like this. Most people use a certain amount of charge regularly every day, but like to have a reserve for unforseen circumstances and spells of bad weather etc.

Lithium is ideal for regular daily usage, and it doesn't degrade if it is never fully charged, like a lead-acid would. Lead-acid is ideal for keeping fully charged until it is needed, then charged up again to 100% ready for next time.

You could have two sets of batteries, lithium and LA, and a sophisticated electronic control system that responded to loads, prioritising the lithium until it is low, then bringing in the lead-acid as a backup. When charging was available, it would fill up the LA first, then fill up the lithium, to ensure the LA was always fully charged.

It turns out that if you just connect the lithium and LA batteries in parallel, that is exactly what happens, no sophisticated electronic control unit needed. The voltages are just right between lithium and LA for this to happen.

You can have a small lithium and a large LA, like the Hymer hybrid system. Or a 50/50 arrangement like a lot of narrowboats have. Or any ratio you want, really.

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[bigtwin]

I’ve just found this thread as a result of it being linked from a more recent thread.

He said in the boating world the idea is to “buffer” the LiFePO4 with Lead Acid. Hmmm. Not needed.

He is mistaken. The idea is that the lead acid acts as a buffer (if you like) for the alternator when the LiFePO4 is disconnected from the alternator when it becomes fully charged.

He also said that when the LiFePO4 runs out the leads can charge it (even at the expense of damaging the leads).

Again, he is mistaken. If the LiFePO4 becomes ‘discharged’ its voltage has simply fallen to the same level as the lead battery and they both feed any connected loads.

When full, the LiFePO4 would charge the leads when everything was at rest which he said was a good thing.

He got that bit right. But it'd be more accurate to say the LiFePO4 keeps the lead battery on float (just where lead acid batteries like to be).

1. You would potentially damage the Lead Acids unless you installed a Battery Protect when the LiFePO4 was depleted

I don’t understand why you believe the lead acid batteries would be damaged. Provided that you don't attempt to connected a fully discharged LiFePO4 to a fully charged lead acid battery then no significant current flow would occur.

Your Lead Acids would bleed power from the LiFePO4 when at rest for no real gain

The lead acid batteries would accept a float charge to keep them in their happy place with minimal impact on the LiFePO4. Remember, they’re both connected to whatever charge sources exist on the system.

Anyone out there run on a hybrid battery arrangement?

Yes, I ran such a system on our narrowboat.

You need to start off with the lithium and lead-acid batteries in the same state of charge, ideally both 100%, before they are connected.

Indeed, this prevents the LiFePO4 from initially sucking available charge out of the lead.

Agree the problem goes away (of the excessive charging current), but I still don’t see any real advantage to a hybrid arrangement.

The key advantage is that it allows folks to adopt the benefits available from LiFePO4 (quick charging and being content at SoC <100%) for minimal cost outlay. Narrowboaters can spend 6 - 8 hrs/day running their engines to charge their lead banks and the fast charge capabilities of LiFePO4 means that they can cut their engine running times to an hour or two per day.

I doubt he understood the concept correctly. That is NOT how a Hybrid battery setup would, or should, or even could, work.

He clearly didn’t understand the technicalities of the arrangement.

Most people use a certain amount of charge regularly every day, but like to have a reserve for unforseen circumstances and spells of bad weather etc.

Indeed and a lead/LiFePO4 hybrid delivers exactly that arrangement.

Lithium is ideal for regular daily usage, and it doesn't degrade if it is never fully charged, like a lead-acid would. Lead-acid is ideal for keeping fully charged until it is needed, then charged up again to 100% ready for next time.

Spot on.

Ian

 

[jongood]

Ive been running Hybrid on my Motorhome for the past 18 months, My chassis electrics are 24v so I have a separate 12v alternator that runs the hab batteries. I have 1x 200ah LifePo4 with a programmable BMS and an old but healthy 220ah gel in parallel. I also have 600w of solar and a bluetooth shunt. I simply bolted the LifePo4 battery in where the other Gel used to sit. I had already replaced by mains charger because the 20 years old originals were very inefficient.

I'm under the impression that the programmable BMS is important because they set it up slightly differently. However I met a French Guy with an identical Clou had just installed a LifePo4 as his only LB and the only change he had made was to change the original mains charger.

I find it works pretty well. I rarely need to use the mains charger , I'm not often plugged in, we like using electric kettle ( 800w), Toaster, Microwave, remoska, induction hob etc. The only issue I have with it is that I don't always get the full charge from my 12v alternator, but thats usually only a problem in UK winter because at other times the solar sorts it out. My theory is that because of the difference in resistances the power gets sucked out of the LifePo4 first but then when I start driving the alternator thinks that because the voltage is so high that only a float charge is required. I have wondered whether a manually switched B2B from the 24v would sort this out but its not often a problem.

I'm tagging you Lenny HB and Raul RogerIvy because I think you may be interested to comment. I'm sure there are plenty of others but hopefully anyone interested will see it.

 

[jongood]

Just to add that I did consider just going LifePo4 connecting a 24/12v B2b and ditching the 12v Alternator but I then have the complication of altering the D+ etc. Although I have since discovered where the feed from the 12v alternator goes.

 

[Jim]

Lead-acid batteries. I have fond memories of them. Victorian technology still working well today. Long lived, little real maintenance, but can be a pain to maintain if hard to reach. In one RV I had 7 x 100Ah in a line across the chassis rails, easy to maintain; but I don't miss them. They were so heavy, took ages to charge, if they ever did.

Can someone explain to me why I would want to keep a lead acid battery in my motorhome setup in some complicated hybrid setup? I just can't see a scenario where I wouldn't benefit from swapping every Victorian LA battery out for LiFePO4 . Please enlighten me, thanks.

 

[bigtwin]

Can someone explain to me why I would want to keep a lead acid battery in my motorhome setup in some complicated hybrid setup? I just can't see a scenario where I wouldn't benefit from swapping every Victorian LA battery out for LiFePO4 . Please enlighten me, thanks.

If you’re prepared to change, potentially all of, your charge sources then there’s no need to.

If, however, you’re on a tight budget then adopting a hybrid arrangement means that you do not have to change any of your charge sources.

One of the beauties of the hybrid arrangement is that it isn’t a complicated setup; you simply add the LiFePO4 in parallel with the lead acid. It couldn’t be simpler.

You get all the benefits of LiFePO4 without all the disadvantages of lead.

Ian

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[AdrianChen]

Just for interest (I found it interesting anyway).
I recently helped a boat owner debug a charging issue.

He has a 300AH LiFePO4 battery with Eve cells and a Daly 150A BMS. A Daly 150A can accept a charge of 50% of its capacity, so 75A in this case.
He has the LiFePO4 battery connected to a small bank of Lead Acid batteries (in parallel of course). I’m not sure how many Lead batteries.
The hybrid battery bank is connected to one of two alternators (this is quite common on boats). Direct connection, no DC-DC.

The LiFePO4 was around 20% or less SOC when he installed it.

His problem kicked in when he started the engine. The charge MOSFET would turn off after a second or two. After he stopped the engine it would turn back on.
I asked for him to check the Daly app to see what current was flowing into the LiFePO4 battery.
The answer: just under 130A
So the BMS was protecting itself (Correctly so).
I asked what current was flowing into the LiFePO4 battery when engine turned off.
The answer: 70A

So the LifePO4 was receiving 70A + 60A = 130A (from Lead Acid and Alternator respectively).

Interestingly these hybrid arrangements are encouraged on boats. I think it may have started when one person wrote an article about the merits of such a hybrid system. Just to be clear I’m talking about the leisure batteries only, not the starter battery.
I recently had one guy call me to buy one of our batteries for his boat to connect in parallel to his Lead Acids. He said in the boating world the idea is to “buffer” the LiFePO4 with Lead Acid. Hmmm. Not needed. He also said that when the LiFePO4 runs out the leads can charge it (even at the expense of damaging the leads). When full, the LiFePO4 would charge the leads when everything was at rest which he said was a good thing. In the end he decided against a hybrid arrangement. To keep it simple I gave him two good reasons to not use a hybrid arrangement:
1. You would potentially damage the Lead Acids unless you installed a Battery Protect when the LiFePO4 was depleted
2. Your Lead Acids would bleed power from the LiFePO4 when at rest for no real gain

Anyway - hope you find this interesting.
Anyone out there run on a hybrid battery arrangement?

I remember when the Lithium interest started in yachts, and the early adopters started finding out the hard way about how best to install charge and protect them, and the considerable cost.

As you say it is quite common on boats to have twin alternators on a small(ish) sailboat auxiliary engines. especially on boats with 12v engine and 24v domestics.

Equally because back in time alternators putting out 200amp 12v were rare and expensive, or big school bus jobbies requiring custom bracketry and pullies, it was a pain in the neck getting a single large alternator, twins were often more effective - Yanmar and Volvo often wouldn't warranty engines with DIY installs because of the additional side loads on the main bearings being unknown.

The first hybrids installs I read about were done as a means of protecting the alternator from frying its diodes when the lithium battery disconnected from its charge, there would be a LA battery to protect it. As well as offsetting the then very high cost of Lithium at the time, and retaining the value of the existing domestic bank if it was in good nick.

Now of course Lithium is much cheaper (my first quote for a 780AH all lithium domestic bank with twin alternator was a £30,000 extra cost back in 2012) and more intelligent alternator regulators such as Wakespeed and MV Alpha can be used which turn the alternator field current off when the battery is full, thus protecting from blown diodes.

So our last boat was 24v lithium for domestics, 24v lead acid banks for the thrusters and 12v LA for the engine and 12v LA for the instruments, with twin alternators one connected to the 12v start battery and the other 24v connected to the domestic, then 24/24v B2B chargers to top up the Thruster banks and 24/12v for the instrument batt. Hybrid to an extent, but it was thought Lithium was not a good (Cost?) choice for thrusters (400amps at 24v?)

But those guys that overcame those issues with their ingenuity and determination established principles that will take years to die out! In the boat building (not narrowboats, know nowt about them) industry I never came across any interest in offering hybrids, just at a point in time folk started choosing Lithium installs over LA as the cost came down, and the demand for more electrical gadgetry went up. So I think it is the retrofit guys, many with a significant sunk cost in their current LA system who favour this approach.

Hymer still offer a hybrid system I believe, a freind has that option, and there are some folk on here using them. So it can be done successfully.

I guess your two observations will be answered by someone - I've read of Shotkey Diodes and Arduino controls etc, all far to clever for me to understand.

I think with technology for most folk it is best if it is in the background, like with your car when you start the engine you don't need to think about the multitude of computers etc runing the engine, heating lights etc. Hence using "systems" from providers like Victron/MV/Renogy is popular with installers and DIY, its as simple as it can be especially the so called portable solar generators thingies.

PS In our van we swapped out the Gels for Lithium, to increase the capacity to maximum(ish) in the available space, and cope with a modest 3000VA invertor, couldn't see any reason/benefit to re-using the gels

 

[eddie]

Lead-acid batteries. I have fond memories of them. Victorian technology still working well today. Long lived, little real maintenance, but can be a pain to maintain if hard to reach. In one RV I had 7 x 100Ah in a line across the chassis rails, easy to maintain; but I don't miss them. They were so heavy, took ages to charge, if they ever did.

Can someone explain to me why I would want to keep a lead acid battery in my motorhome setup in some complicated hybrid setup? I just can't see a scenario where I wouldn't benefit from swapping every Victorian LA battery out for LiFePO4 . Please enlighten me, thanks.

Baffles me too, along with classic car restoration, ham radio and train spotting

 

[bigtwin]

The only issue I have with it is that I don't always get the full charge from my 12v alternator,

Is that because the engine run times are too short Jon or are you saying that the system isn’t charging the LiFePO4 correctly?

Ian

 

[eddie]

You get all the benefits of LiFePO4 without all the disadvantages of lead.

Ian

You don’t get all the benefits.

Replace a 100 amp lead acid with a 100amp Lithium you pretty much halve the weight, for twice as much usable power

Using my camper’s set up, I have a 120amp B2B so my recharge time is incredible, a piggy backed lithium onto a lead acid battery could never achieve anything like that

Another big thing is the ability to see exactly what the system is doing via Bluetooth, again, you’ll still be in the dark as to what the lead Acid battery is up to

I’m not saying that it doesn’t improve the situation of a lead Acid setup, I’ve really not bothered to look too much into it as it wasn’t something I was prepared to do commercially and to be fair, wasn’t what my paying customers enquired about, but you can’t say “All the benefits lol”

I guess the analogy is Alloy wheels look good and are lighter and improve the overall look of the motorhome, but if you can’t afford it plastic wheel trims are ‘exactly the same’

 

[Pausim]

An interesting discussion and I can see some cost advantages where there are existing good LA batteries and where charge sources might need changing. In the motorhome context I am not sure about the relevance of the buffer arrangement to protect the alternator where there is already a LA engine battery in parallel with the leisure battery when the engine is running. The risk of over working the alternator with LiFePO4 batteries is often used as an argument for adding a B2B into the system. Does the addition of a hybrid parallel LiFePO4 battery not increase the risk of overworking the alternator not protect it?

It seems to me that the cost advantage of a hybrid arrangement must be changing as LiFePO4 batteries get cheaper. When I bought my LiFePO4 battery 6 years ago the cost was about £10 per Ah but it is now less than £4 per Ah. The use of smart alternators is also taking some of the advantage out of hybrid systems, in newer motorhomes a B2B is essential and the split charge arrangement has to be dumped (doesn’t apply to boats). I would also expect modern chargers to have LiFePO4 profiles.

Times are changing and I am glad that I no longer need to use Victorian technology for my leisure batteries.

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[bigtwin]

You don’t get all the benefits.

You’re right, you don’t.

but you can’t say “All the benefits lol”

You’re right, I can’t.

You get all the benefits of LiFePO4 without all the disadvantages of lead.

Edited to be more accurate.

Of all the things I had you down as, a pederast wasn’t one of them.

Ian

 

[Cush]

i think a more appropriate analogy is “a Tesla compared to a Prius”. Still some old technology involved in the Prius, both get you there, you get the benefit from whatever lithium you install in both, Tesla does it a lot faster for a lot more money.

 

[Cush]

In the motorhome context I am not sure about the relevance of the buffer arrangement to protect the alternator where there is already a LA engine battery in parallel with the leisure battery when the engine is running

That is the current thinking. If one does have the space for the lead but not the money to change it too then it does give a little extra capacity and “keeps” the lights on if you happen to over-discharge or break the lithium. A bit of a contingency. The model has been lifted from boats with 2 alternators therefore 1 LA had to be left in the hab side system. They also use a “long wire” method to increase the voltage drop from alternator to battery and protect the alternator from over heating. I understand that this also drops the charging amps to the battery so it takes a little longer. Another compromise but it all works for them. They are certainly creative thinkers.

am glad that I no longer need to use Victorian technology for my leisure batteries.

Unfortunately some of us do .

 

[jongood]

i think a more appropriate analogy is “a Tesla compared to a Prius”. Still some old technology involved in the Prius, both get you there, you get the benefit from whatever lithium you install in both, Tesla does it a lot faster for a lot more money.

Although Ive seen a lot of Priuses being used as taxis. Not seen many Bev taxis.

 

[jongood]

Is that because the engine run times are too short Jon or are you saying that the system isn’t charging the LiFePO4 correctly?

Ian

No Ian. initial charge is 30a ( according to the shunt) but drops down to half that pretty quickly (65a alternator doing nothing else asfaik) I reckon the LifePo4's are holding the voltage up which is fooling the alternator.

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[jongood]

Lead-acid batteries. I have fond memories of them. Victorian technology still working well today. Long lived, little real maintenance, but can be a pain to maintain if hard to reach. In one RV I had 7 x 100Ah in a line across the chassis rails, easy to maintain; but I don't miss them. They were so heavy, took ages to charge, if they ever did.

Can someone explain to me why I would want to keep a lead acid battery in my motorhome setup in some complicated hybrid setup? I just can't see a scenario where I wouldn't benefit from swapping every Victorian LA battery out for LiFePO4 . Please enlighten me, thanks.

For me, it was reluctance to change the whole system on a 20 year old Mh with a lot of gadgets on it and 2 voltages going on. Retaining the 2 alternators also gives me an element of redundancy.

 

[AdrianChen]

The only issue I have with it is that I don't always get the full charge from my 12v alternator, but thats usually only a problem in UK winter because at other times the solar sorts it out. My theory is that because of the difference in resistances the power gets sucked out of the LifePo4 first but then when I start driving the alternator thinks that because the voltage is so high that only a float charge is required. I have wondered whether a manually switched B2B from the 24v would sort this out but its not often a problem.

Most Non smart alternators only output a constant voltage, unless there is a smart regulator installed. Older alternators can be regulated as low as 13.8v and more modern ones 14.2v, and smart up to 15.?v. Some alternators regulators used to be +/-0.3v in their spec so not great. But they were only intended to maintain a start battery and run the wipers etc, not whack 100amps into a hungry lithium

Some when they get hot start reducing the output voltage as a means to reduce the acceptance rate of the intended LA battery so allowing them to cool down. So unless you monitor it the whole time it's difficult to predict what the output voltage really is when its working hard, and I guess that effect increases as it ages, and or the fan belt slips a little.

If it ever goes pop then it will be a good time to sort it as I doubt it makes a huge difference?

 

[bigtwin]

Using my camper’s set up, I have a 120amp B2B so my recharge time is incredible,

I guess you missed this bit:

If, however, you’re on a tight budget then adopting a hybrid arrangement means that you do not have to change any of your charge sources.

a piggy backed lithium onto a lead acid battery could never achieve anything like that

On boats with 185A alternators, it’s perfectly possible to achieve what your B2B does. One size rarely fits all.

you’ll still be in the dark as to what the lead Acid battery is up to

Yes, one of the inherent drawbacks of lead but this issue becomes somewhat immaterial on most hybrid setups as the leads are rarely called upon to do anything. As a hangover from the old LA battery monitoring obsession, many use their shunt just to monitor the LA batteries but they soon realise that they needn’t worry about the LA batteries as they just sit there in there happy place being gently float charged.

I guess the analogy is Alloy wheels look good and are lighter and improve the overall look of the motorhome, but if you can’t afford it plastic wheel trims are ‘exactly the same’

Sometimes (see below) those on a limited budget might opt for a Mini, rather than a Rolls-Royce, as their personal transport solution. They’d draw their own conclusions if they were castigated by the RR owner for their choice.

If, however, you’re on a tight budget then adopting a hybrid arrangement means that you do not have to change any of your charge sources.

As I said earlier, there is no one size fits all. By all means go for the RR solution if your budget permits it but that doesn’t mean that other solutions aren’t equally as effective.

Ian

 

[eddie]

You’re right, you don’t.


You’re right, I can’t.


Edited to be more accurate.

Of all the things I had you down as, a pederast wasn’t one of them.

Ian

 

[bigtwin]

Does the addition of a hybrid parallel LiFePO4 battery not increase the risk of overworking the alternator not protect it?

It does, and this is the main caution (to monitor both the current output and the peak temperature of the alternator) advised when adopting the arrangement. In most instances the temperature is fine but in some instances fitting a longer alternator cable is necessary to reduce the current being drawn.

The protection element referred to is associated with the alternator having a continued load on it when the LiFePO4 is disconnected from the alternator when it reaches full charge. If there was no load in the system, a voltage spike would kill the alternator.

They also use a “long wire” method to increase the voltage drop from alternator to battery and protect the alternator from over heating. I understand that this also drops the charging amps to the battery so it takes a little longer. Another compromise but it all works for them. They are certainly creative thinkers.

The primary purpose of the long lead is to limit the current to no more than about 2/3 of the alternator’s rated output (and hence to limit the peak temperature of the alternator). Clearly, how much current can be delivered is dependent on the installed alternator but most boat alternators are capable of delivering a hefty enough charge that exceeds the output of most of the commonly fitted B2Bs (Victron are finally producing a B2B with a 50A output).

Ian

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[Lenny HB]

Ive been running Hybrid on my Motorhome for the past 18 months, My chassis electrics are 24v so I have a separate 12v alternator that runs the hab batteries. I have 1x 200ah LifePo4 with a programmable BMS and an old but healthy 220ah gel in parallel. I also have 600w of solar and a bluetooth shunt. I simply bolted the LifePo4 battery in where the other Gel used to sit. I had already replaced by mains charger because the 20 years old originals were very inefficient.

I'm under the impression that the programmable BMS is important because they set it up slightly differently. However I met a French Guy with an identical Clou had just installed a LifePo4 as his only LB and the only change he had made was to change the original mains charger.

I find it works pretty well. I rarely need to use the mains charger , I'm not often plugged in, we like using electric kettle ( 800w), Toaster, Microwave, remoska, induction hob etc. The only issue I have with it is that I don't always get the full charge from my 12v alternator, but thats usually only a problem in UK winter because at other times the solar sorts it out. My theory is that because of the difference in resistances the power gets sucked out of the LifePo4 first but then when I start driving the alternator thinks that because the voltage is so high that only a float charge is required. I have wondered whether a manually switched B2B from the 24v would sort this out but its not often a problem.

I'm tagging you Lenny HB and Raul RogerIvy because I think you may be interested to comment. I'm sure there are plenty of others but hopefully anyone interested will see it.

I don't really know much about Hybrid systems apart from that's what Hymer do if you order Lithium.
I really don't see much point in it on a Motorhome, why you would want to lug 50kg or more of lead around for very little advantage.

If you are still using your 20 year old Gels they will not be helping, when Gels get very old they take ages to charge I assume their internal resistance increases.

If it was me I would ditch the Gels, fit a B2B with decent size cabling then you would be able to charge the Lithium properly at a decent rate . I suspect the reason your alternator & Lithium are surviving is down to long runs of undersize cables.

 

[autorouter]

The protection element referred to is associated with the alternator having a continued load on it when the LiFePO4 is disconnected from the alternator when it reaches full charge. If there was no load in the system, a voltage spike would kill the alternator.

This is the same with motorhomes, but as mentioned the lead-acid starter battery is is always connected so it's less of a problem. That's why it's not a good idea to modify the wire from the alternator to starter battery, and why all alternator charging is taken from the starter battery terminal, after that wire.

If for some reason that wire goes open-circuit, the voltage on the alternator can jump to 60V or so for several seconds. This is written into the specifications for any electrical device that is connected to vehicle electrics - it has to be able to withstand 60V for several seconds. Critical items like engine control and ABS have to show they will still work 100% at that voltage, other items like radio etc just have to show they will not be damaged by it.

The most common reason for the alternator-starter battery loop to go open-circuit is the earth strap on the negative return path, so keeping that in good condition is a good idea.

 

[jongood]

If you are still using your 20 year old Gels they will not be helping, when Gels get very old they take ages to charge I assume their internal resistance increases.


If I disconnect the gel it doesnt make any difference.

If it was me I would ditch the Gels, fit a B2B with decent size cabling then you would be able to charge the Lithium properly at a decent rate . I suspect the reason your alternator & Lithium are surviving is down to long runs of undersize cables.

Ultimately I may well do this but at the moment it works pretty well as long as there's a bit of sun around - so another good excuse to go South ( not that I really need one ). I'm being a bit lazy really just don't fancy the hassle of tracing the cables. I don't think cable size is an issue as everything I can see is fairly meaty and labelled ( in german)