4 Questions: 377 amp alternator charging LiPo system

[dwh]

Yea, but even if Sterling no longer has a problem with it, feeding that kind of voltage straight to the battery via split-charge relay...

 

[Rando]

Before I call Blue Sea or BB, see if there is common agreement with the quotes above. I may use some or most of these recommendations.
But Post 23, I need a specific referral for a “A B2B with a lithium charge profile”. Thanks for all the advice.

Before buying a DC-DC charger (and you would need a huge one for $$$ to support the charge rates you are looking for), hook your batteries up to the alternator with an ammeter in the circuit and see what happens. There is a lot of arm chair engineering going on here, but I really don't think there will be an issue.

Luthj is pretty much spot on in his analysis - there is a common electrical component used to limit current, the resistor. These are very cheap components, but luckily you will already have one in the form of your cables and fuses. As safety measure, if the Rds of the MOSFETS in the BattleBorne really is 17mOhm, then you would be dropping nearly a volt there at 50A, so you may never reach 50A even without your wire losses.

 

[luthj]

The BB BMS issue is not very likely to come into play unless you are exceeding .5C for 2 hours or so. Say discharge at 0.5C for 1.5hrs, and then immediately start charging at 0.5C+. Some back of the napkin math has the battery hitting the overtemp limit in warm weather with that kind of loading.

 

[dwh]

Look at the OP. He's assuming a full recharge in 3 hours or less. And with a split-charge relay and plenty of alternator, he could easily exceed C*.5 on a pair of those batteries for more than a couple hours.

 

[mrfoamy]

I assumed that the greatest charge would be in the first 30 minutes, then diminishing over the following period. If that is the case then I don't understand the 2 hour comments and heat issues I see discussed. Make sense?

 

[mrfoamy]

And I was trying to be humourous with the simultaneous A/C and induction comment. Just noting the potential with the factory alternators.

 

[DiploStrat]

I assumed that the greatest charge would be in the first 30 minutes, then diminishing over the following period. If that is the case then I don't understand the 2 hour comments and heat issues I see discussed. Make sense?

Some real world numbers taken from an e-mail. 100Ah LiFePO4 battery, discharged until the BMS shut it down.

Connected to a Chevrolet with 2x125A alternators. Connection by classic jumper cables. The jumpers were disconnected periodically when they got hot enough to melt the insulation. Took about one hour to restore a about 100Ah. That is, the last number was written down about an hour after the first numbers.

Left number is voltage at the battery terminals, the amp number is from an ammeter clamped on the jumper. Right voltage was taken at the truck battery terminals.

Some of the numbers I took down are:

LiFePo 10v 160A

LiFePo 13.3A 120A

LiFePo 13.8v 106A lead 14.3V

LiFePo 13.9V 96A lead 14.4v

LiFePo 14.0v 83A lead 14.48v

LiFePo 14.1v 65A lead 14.48v

LiFePo 14.3v 46A lead 14.7v

LiFePo 14.5v 31A lead 14.7v

LiFePo 14.6v 20A lead 14.8v

LiFePo 14.7v 11.6A lead 14.8v

LiFePo 14.9v 0A lead 14.8v​

You will note that the amp rates remain higher, longer than with lead acid.

 

[mrfoamy]

Hmmm, so are you confirming my suspicion that the greatest load would be in the early period of charging? I'm only looking at amperage.

 

[DiploStrat]

Hmmm, so are you confirming my suspicion that the greatest load would be in the early period of charging? I'm only looking at amperage.

Not a suspicion, but simply the way that batteries work.

One thing to note is the sudden jump in battery voltage with no reduction in charge rate. You would not see that with lead acid. The differences between this chart and the chart that you would see with lead acid are:

-- The amp rate would drop faster, thus reducing the load on the alternator

-- It would take much longer to reach a full charge, increasing the danger of only partial charging,

-- The changes in voltage and amp flow would not have the sharp knees of LiFiPO4, but would be more gradual.

There are several folk on this forum who have gone to LiFePO4; I suspect that all will report similar results.

But this small experiment, done in the parking lot of a battery manufacturer's plant, gives a good indication of why people want to go to LiFePO4. Not to mention the others:

-- Weight

-- Steadier amp output/less voltage drop

-- More cycles

-- And the biggie: no danger of damage due to partial discharge.

 

[john61ct]

For LFP longevity you don't want a charge rate higher than .5C anyway.

That means recharging in under 2 hours.

If your super fancy heat-managing alternator setup (you do have that right? I think not)

**really can** output 200A continuously

(I think not)

(is your top priority to capture all that energy? why?)

Then install a bank over 400Ah in size, not piddly drop-in junk but a proper prismatic bank.

______
With regard to voltage, for longevity

normal daily cycling should just stop at 3.45Vpc, or 13.8V for 4S. Maybe 14V would be OK at such high current rates, long as you do "just stop", no CV Absorption time.

The Sterling BB series is what is needed here, **not** any product that someone stuck a "Lithium" label on and gives you zero adjustability.

To handle 200+ actual charging amps (really?) then you need to stack four of them, since Charles has not yet released the higher-than-60A models.

That is the only practical safe and reliable way to give the bank what it needs to last a long time, **and** to protect the alt setup from LFP's rapaciously large CAR / current demand.

Which yes is maintained very high up the SoC curve, the whole reason it is brilliant compared to lead, which requires 5-7 hours to get back to 100% Full.

 

[john61ct]

Your discharge rate will be limited to that .5C as well, so even a 400Ah bank will be too small to consider big loads like aircon or electric heat-producing appliances

 

[mrfoamy]

Before buying a DC-DC charger (and you would need a huge one for $$$ to support the charge rates you are looking for), hook your batteries up to the alternator with an ammeter in the circuit and see what happens. There is a lot of arm chair engineering going on here, but I really don't think there will be an issue.

"Armchair engineering". I am an empiricist so I'll proceed with several recommendations from here...THANKS everyone.

 

[RichieFromBoston]

Battle born batteries have issues with continuous currents over 0.5C, I would size your wiring to restrict charging current to that level. This is due to the solid-state relay they use for the internal BMS. It has a fairly high resistance and suffers from spot heating under heavy loading or charging.

good to know just bought a reLIon lithium instaed of BB for that very reason