‘Fessing up. My dubious LiFePo install.

[fredrussell]

So first things first. I’m not in any way advising anyone to follow my lead here - just thought it might result in an interesting discussion.

So, A year ago I installed a 100 amp hour LiFePo battery on my small (VW T5) campervan. It charges from the vehicle alternator in winter and from a roof-mounted 200 watt solar panel in the sunnier months. On the alternator charging setup there is no B2B charger, just a 100A rated VSR connected to the LiFePo battery by 6mm cable. At the VSR end AND at the LiFePo end of this cable there is a 40amp fast blow midi fuse. Alternator is standard 90 amp one. LiFePo battery itself has a 200 amp ANL fuse.

So in effect this is a ‘drop in’ lithium battery install - by that I mean the only thing added other than the LiFePo was the ANL fuse. Everything else in that setup was there when leisure battery was a 110 amp lead acid type.

But here’s the interesting thing. After installing the LiFePo I deliberately flattened it to the point where the BMS switched it off. Then I started the engine and let the alternator charge it. No solar input. The maximum charge current I saw was 30 amps. Starter battery is good and healthy, and I would have thought that after a minute or two from starting (van always starts instantly) all charge would have been going to LiFePo. I’ve read that realistically the max output of an alternator is half (or a bit above that) it’s rated output so 45 to 50 amps, so in this instance it would seem that the LiFePo was not sucking the life out of the alternator. After ten minutes charge current dropped to circa 20 amps.

The reason I’m posting this is it’s often said on here that, given half a chance, a lithium battery will damage an alternator by pushing the latter to its output limit, but that doesn’t seem to be happening here. Many boat engines have alternators bigger than the 90amp one in my van - Yanmar fit 120 amp ones as standard on their two cylinder and above engines.

When my current lead acid house batteries in boat die, I’ll replace them with a self built LiFePo battery, and charging setup will be done ‘by the book’ as obviously you can’t just walk away from a burning boat, and, as already stated, I’m DEFINITELY NOT suggesting anyone do as I’ve done - DON’T! - but I’m interested to here what the panel thinks.

 

[lustyd]

How high were the engine revs? These need to be high to get more output.

Lithium doesn't "pull" from the alternator to kill it, it just accepts charge quickly, allowing the alternator to overheat and kill itself, but there are various factors involved in that. If you can cool it (much easier in a van) then in theory it could be fine.

 

[Sea Change]

The 6mm² cable might be introducing enough resistance to restrict the charging rate.

 

[MikeBz]

If the alternator regulator is 13.8V that might explain it? That’s not much above float voltage a 12V LifePo4 battery.

 

[fredrussell]

Engine revs were between idle and 2k - made some difference but not hugely noticeable.

Cable size good for 50a I believe. I felt the cable and alternator itself - cable had no discernible heat to it, alternator was warm, as you would expect but not hot enough that you couldn’t keep your hand on it. I don’t have a laser temp gun so can’t give any useful figures I’m afraid.

Alternator charges at 14.4v if memory serves, certainly not less than that.

I did wonder if BMS is not acting correctly re charge current. LiFePo is a cheap’n’cheerful Ecoworthy one. I’m aware there are many better regarded brands but when you look at reviews and comments online they’re positive on the whole. Latest ones have Bluetooth, but still no heating.

 

[sawduster]

I have a 100ah DC House Lifepo4 battery, which I think is just a rebadged Ecoworthy battery. 115A alternator to SLA started to 60A DC-DC charger and I've never seen more than 45A on the battery monitor with it more typically being 30-35A, even when deeply discharged. I think it's probably just a cheap battery with a BMS limit of some sort but I'm not bothered enough to open it up to find out what's in there.

 

[thinwater]

Lithium iron phosphate batteries are abbreviated LiFePO4.

Li is lithium
Fe is iron
P is phosphorous
O is oxygen

It does sort of matter, because Po is Polonium, which is both very rare and very radioactive. Chemical engineer.

(phosphate is the PO4 ion)

 

[Neeves]

Your battery has a built in BMS? - I assume the BMS characteristics are defined - what are they. When your battery is fully charged its BMS should shut off the charging regime has this happened? when you checked the charging current, and it was lower than expected, was the Lithium battery fully charged?

 

[William_H]

My guess is that OP set up is working well.
An alternator when worked hard may deteriorate but essentially when overloaded by current drain it will just fail to produce regulated voltage. This point is dictated by alternator RPM and rating of alternator.
As said also I think the wiring from alternator to battery is current limiting by it's resistance. (both pos and neg return)
ol'will

 

[geem]

Some modern vehicle alternators are temperature sensed. They will regulated output based on alternator winding temperature. It is likely that your alternator has this feature. Some yachts have Hatachi alternators with this feature. They have been able to install lithium with direct alternator charging and suffered no ill effects. Another fudge is to install a lithium battery on a very long cable such that you create a high resistance connection to the lithium. This will have the affect of reducing output to the lithium.

 

[Moodysailor]

There is a very good reason why it is unanimously stated to use a B2B charger on a mixed chemistry installtion and not a VSR. The 'horror stories' are what insurers are picking up on and why it is hard to get insurance for self-installations. Please don't make it harder than it already is!
As mentioned, the cable is under-sized for the installation, there are also a few other variables, therefore not easy to put a finger on the cause - does your T5 have a smart alternator? You could have high resistance caused by the cable size and total length or a poor connection. The BMS may have regulated the charge current (unlikely).
I am not a proper expert on electric motors and charging systems (an alternator is just a motor in reverse), but I know enough to know that a non-smart alternator can put out max (or close to) current, when the conditions are right - i.e. when the rpm is high enough and the battery charge state is low enough. The current will drop off when everything gets hot, and it it can't cool itself well enough (e.g. not enough ventilation in an engine bay and a painted alternator), it will overheat. This is why a properly rated B2B charger is needed as the alternator will kill itself trying to 'satisfy' the LiFePO4 battery otherwise.

 

[geem]

There is a very good reason why it is unanimously stated to use a B2B charger on a mixed chemistry installtion and not a VSR. The 'horror stories' are what insurers are picking up on and why it is hard to get insurance for self-installations. Please don't make it harder than it already is!
As mentioned, the cable is under-sized for the installation, there are also a few other variables, therefore not easy to put a finger on the cause - does your T5 have a smart alternator? You could have high resistance caused by the cable size and total length or a poor connection. The BMS may have regulated the charge current (unlikely).
I am not a proper expert on electric motors and charging systems (an alternator is just a motor in reverse), but I know enough to know that a non-smart alternator can put out max (or close to) current, when the conditions are right - i.e. when the rpm is high enough and the battery charge state is low enough. The current will drop off when everything gets hot, and it it can't cool itself well enough (e.g. not enough ventilation in an engine bay and a painted alternator), it will overheat. This is why a properly rated B2B charger is needed as the alternator will kill itself trying to 'satisfy' the LiFePO4 battery otherwise.

But it's not doing that. The under sized wire will be creating a high resistance, therefore limiting current flow. If this is all that is making it work, it's not a great engineering solution, but it works. I wouldn't do it myself. I would use a DC/DC charger. I wouldn't be happy using the bms to switch off as I don't want my cells at 3.65v each. The BMS is a cell protection device, not a charge control device. It switches the charging off when the voltage is hitting the upper limit for the cell safety. The cells are into the absolute upper limit of the knuckle, enduring maximum stress. I would rather my cells got an easier life and last many years

 

[Moodysailor]

But it's not doing that. The under sized wire will be creating a high resistance, therefore limiting current flow. If this is all that is making it work, it's not a great engineering solution, but it works. I wouldn't do it myself. I would use a DC/DC charger. I wouldn't be happy using the bms to switch off as I don't want my cells at 3.65v each. The BMS is a cell protection device, not a charge control device. It switches the charging off when the voltage is hitting the upper limit for the cell safety. The cells are into the absolute upper limit of the knuckle, enduring maximum stress. I would rather my cells got an easier life and last many years

Hi, i'm not sure if we are in agreement or not?

"As mentioned, the cable is under-sized for the installation, there are also a few other variables, therefore not easy to put a finger on the cause - does your T5 have a smart alternator? You could have high resistance caused by the cable size and total length or a poor connection. The BMS may have regulated the charge current (unlikely)."

 

[PaulRainbow]

I have 280Ah @24V of Lithium, connected in parallel to 220Ah @ 24V of lead acid. Both 60A, 24V alternators are connected to the LA batteries, all loads are connected to the Lithium bank. No B2B. All are correctly fused and connected using appropriate cables. The cables to the LA bank are the same as they were originally.

Why ?

1) Experimental reasons.
2) Gives a backup if the BMS shuts down (not really a big worry)
3) I need a 2nd way of starting a pair of 7 litre diesel in the event of flat engine batteries.

Been running like this since last September, results are interesting and give no cause for concern thus far. Biggest surprise has been how little the current is from the alternators.

Testing continues. I have 2 DC-DC chargers sitting in a box ready to install when i've finished.

Oh, don't try this at home.

 

[lustyd]

The under sized wire will be creating a high resistance, therefore limiting current flow

Limiting current to the battery, but importantly that current is still flowing from the alternator. It’s pedantic, I know, but I thought worth pointing out since it explains why long thin wires aren’t a good solution.

 

[rotrax]

I have 280Ah @24V of Lithium, connected in parallel to 220Ah @ 24V of lead acid. Both 60A, 24V alternators are connected to the LA batteries, all loads are connected to the Lithium bank. No B2B. All are correctly fused and connected using appropriate cables. The cables to the LA bank are the same as they were originally.

Why ?

1) Experimental reasons.
2) Gives a backup if the BMS shuts down (not really a big worry)
3) I need a 2nd way of starting a pair of 7 litre diesel in the event of flat engine batteries.

Been running like this since last September, results are interesting and give no cause for concern thus far. Biggest surprise has been how little the current is from the alternators.

Testing continues. I have 2 DC-DC chargers sitting in a box ready to install when i've finished.

Oh, don't try this at home.

Interesting Paul.

A fellow club member of our NZ club had a mixed bank. The potential horror stories were all around the club, spread by an ex NZ Electricity boffin which put many off trying Li Fo Po.

In practice, on the water, all was well. He never had a problem and his alternator output was never too high. The Li Fo Po were connected in parallel to his LA batteries. At 12v though.

Just like yours.........................................

 

[simonfraser]

I have 280Ah @24V of Lithium, connected in parallel to 220Ah @ 24V of lead acid. Both 60A, 24V alternators are connected to the LA batteries, all loads are connected to the Lithium bank. No B2B. All are correctly fused and connected using appropriate cables. The cables to the LA bank are the same as they were originally.

Why ?

1) Experimental reasons.
2) Gives a backup if the BMS shuts down (not really a big worry)
3) I need a 2nd way of starting a pair of 7 litre diesel in the event of flat engine batteries.

Been running like this since last September, results are interesting and give no cause for concern thus far. Biggest surprise has been how little the current is from the alternators.

Testing continues. I have 2 DC-DC chargers sitting in a box ready to install when i've finished.

Oh, don't try this at home.

why install the DC2DC if it works well without ?

 

[fredrussell]

…As mentioned, the cable is under-sized for the installation, there are also a few other variables, therefore not easy to put a finger on the cause - does your T5 have a smart alternator? You could have high resistance caused by the cable size and total length or a poor connection. The BMS may have regulated the charge current (unlikely).
I am not a proper expert on electric motors and charging systems (an alternator is just a motor in reverse), but I know enough to know that a non-smart alternator can put out max (or close to) current, when the conditions are right - i.e. when the rpm is high enough and the battery charge state is low enough. The current will drop off when everything gets hot, and it it can't cool itself well enough (e.g. not enough ventilation in an engine bay and a painted alternator), it will overheat. This is why a properly rated B2B charger is needed as the alternator will kill itself trying to 'satisfy' the LiFePO4 battery otherwise.

All well and good. Don’t disagree with any of that. So why is my alternator not dead after a year of this bodgery - and i accept that’s what it is, but I have an inquisitive mind, and my ‘research’ prior to trying this, suggested that in the real world the most you can expect from a bog standard alternator is half its max rated output. The fact that neither 40 amp fuse has blown would back this up.

I’m not trying to reinvent the wheel here, I’m just putting something up for discussion. I’ve stated clearly and repeatedly that this is not the way to do things.

 

[Neeves]

I’m not trying to reinvent the wheel here, I’m just putting something up for discussion. I’ve stated clearly and repeatedly that this is not the way to do things.

Actually I suspect many or us, or a healthy few, test the accepted norm....because we are inquisitive. A few of us then post here, and quite often get shot down in flames and burdened with the contempt. Sometimes the norm is incorrect.

Courageous of you to post the thread.

Jonathan

 

[Moodysailor]

All well and good. Don’t disagree with any of that. So why is my alternator not dead after a year of this bodgery - and i accept that’s what it is, but I have an inquisitive mind, and my ‘research’ prior to trying this, suggested that in the real world the most you can expect from a bog standard alternator is half its max rated output. The fact that neither 40 amp fuse has blown would back this up.

I’m not trying to reinvent the wheel here, I’m just putting something up for discussion. I’ve stated clearly and repeatedly that this is not the way to do things.

I have no idea, and it's a good question.

If it's a smart alternator, maybe it reduced the output. Maybe it's absolutely fine and 'conventional wisdom' is wrong (it wouldn't be the first time).

I have seen alternators cook from being overloaded, that isn't unique to LiFePO4 though, so maybe yours is