Charging LiFePO4 from 12V

[dwh]

That Victron DC-DC is not optimum for this application. It's intended to be a constant voltage power supply for things like radios. Once you set the output voltage, there it stays. It you set it to say 14.6v, then it's going to supply 14.6v even when the battery is full, which you don't want. It's also only good for 9a.

The "special charge regimen" of LiFePo is a bit of a red herring and a bit of a myth. Look at the specs for the solar controller you linked that Bioenno sells and claims is special for LiFePo. Bulk/absorb to 14.4v and float at 13.8v. That's an off the shelf Chinese charge controller for lead-acid with a Bioenno sticker on it or I'll eat my hat.

BUT... it will work just fine for charging a LiFePo.

The "proper" charge routine for LiFePo is "charge to a specified voltage then unplug the charger because you're done".

But there are pretty much no chargers that do that. BattleBorn says their LiFePo has a full charge resting voltage of 13.6v. So if you use a charge routine like "bulk to 14.6v then float at 13.6v or less", it'll work just fine.

 

[DiploStrat]

...
The "proper" charge routine for LiFePo is "charge to a specified voltage then unplug the charger because you're done".

But there are pretty much no chargers that do that. BattleBorn says their LiFePo has a full charge resting voltage of 13.6v. So if you use a charge routine like "bulk to 14.6v then float at 13.6v or less", it'll work just fine.

Ding! Ding! A winner. While betting hats, I suspect that, after having spent a ton of change designing chargers that do the bulk/absorb/float dance, the manufacturers will simply reprogram their float stage to be lower than the resting stage of a lithium battery. The same thing that you can do on some of the Sterling units. (Or let REDARC do it for you.)

Ironically, some of the old gel profiles might work rather well, right out of the box.

And again, this is more of an issue for solar, which is on all the time, than it is for your alternator, which only runs about six hours a day.

 

[dwh]

Damaging a LiFePo by float charging is something to worry about if it's connected to a shore charger 24/7/365.

With alternator it's only going to happen for a few hours while driving true, but with solar it's going to stop when the sun goes down.

So IMHO it's not a serious issue either way.


And to address another question...

BattleBorn says their BMS does NOT prevent overcharging. It will interrupt if the current or voltage exceed certain values, but otherwise no. Basically the BMS is a smart, auto-resetting breaker + cell balancing.

I would assume that Bioenno's BMS works basically the same way.

 

[DiploStrat]

... but with solar it's going to stop when the sun goes down.

So IMHO it's not a serious issue either way. ...

I had forgotten about the sun setting! And, with most of us, the big electrical loads come in the evening - cooking, etc. so the battery voltage is going to hammered in any case. The kill-your-batteries-by-floating is mostly a problem with open lead acid sitting on city power for months, e.g. the starter batteries of an emergency generator. (And I once had to manage 150 of 'em!)

... BattleBorn says their BMS does NOT prevent overcharging. It will interrupt if the current or voltage exceed certain values, but otherwise no. Basically the BMS is a smart, auto-resetting breaker + cell balancing. ...

Friend of mine field tested this (quite by accident) with Starkpower batteries and that is exactly what happened. When the voltage got too low, the BMS disconnected the batteries before they could be harmed.

 

[dreadlocks]

My BattleBorn at full charge shows 0.00A input, the BMS seems like it interrupts further charge.. but I still disconnect the battery when its on shore power for any considerable time.

 

[dwh]

Well that 0.0a could be due to supply voltage potential vs. battery voltage. For example if the battery is at 13.6v and the charger drops to 13.2v float - no amps will flow toward the battery. Can't say for sure due to lack of info.

As to the BattleBorn BMS, what their guy told us was:

"Basically, the charging switches will open if one of the following is detected: one cell exceeds a prescribed high voltage, the cell temperatures exceed 140F, the MOSFET temperatures exceed 170F, the charging current exceeds 200A for 0.5s, or 100A for 30 seconds."

So unless they've changed how it works since he told us that...

 

[feltyellow]

I think this is the boost converter "soul" was using, or a very similar one,
https://www.amazon.com/DROK-Converter-Controller-Stabilizer-Automotive/dp/B01E283VYM

I actually bought one for another part of my project (undervoltage solar panel) and while I think it will work the quality is not inspiring.

I think the "epic pwr gate" is probably a reasonable choice if you don't have another charger. The sterling might be great but no electronics with capacitors can be expected to "last decades".

 

[feltyellow]

Here's another $145 DC-DC lithium charger with boost (but I can't tell if it is available in the US),
https://www.ivt-hirschau.de/product_info.php?products_id=853

 

[john61ct]

The quality that makes a charge source suitable for lithium

besides good overcurrent protection

is the ability to allow the user to custom adjust setpoints. The best ones are designed for lead, which is NP.

Ideally using a shunt to measure trailing amps, and the ability to "just stop", Float = none, but those are very rare.

Every device I have seen claiming "lithium compatibility" has the voltage set way too high for longevity.

_______

I am not an irrational fanboi wrt Sterling's products but they have got a great reputation in the marine electrics world for build quality and excellent customer support, including after warranty service - try that with Mastervolt or Xantrex

But if anyone comes across any other DC-DC B2B charger that has setpoint adjustability, please let me know.

 

[Alloy]

I did't read the whole thread. I apologize if this has been mentioned

FLA degredation is reduced the longer/more often is at 100% SOC. This is not the same with Lithium that degrades faster when the SOC is above 80%

 

[Meatpuppet]

When I got my new SUV, I found out the smart alternator varies from 12.8 volts to 14.6. I built a homemade “20mm ammo can battery box” that is ugly as sin, but it works.

I am using a Victron Energy Orion-TR 12/12-18A (220W) Isolated DC-DC converter regulated to 14.6 volts, feeding a West Mountain Radio Epic PWRGate (MPPT Charge Controller/UPS Power Supply/Battery Charger) which in turn charges a Bioenneo 50 amp/hr LifePo4.

I plug it in to a cigarette port in the back of my SUV. I have never blown a fuse since the PWRGate has a user selectable charge current limit to 2 amp, 5 amp or 10 amp and user selectable charge profiles for Lead-Acid, AGM and LiFePo4. A bonus is the MPPT solar charge controller built in.

Ugly but it works.

 

[pdxfrogdog]

When I got my new SUV, I found out the smart alternator varies from 12.8 volts to 14.6. I built a homemade “20mm ammo can battery box” that is ugly as sin, but it works.

I am using a Victron Energy Orion-TR 12/12-18A (220W) Isolated DC-DC converter regulated to 14.6 volts, feeding a West Mountain Radio Epic PWRGate (MPPT Charge Controller/UPS Power Supply/Battery Charger) which in turn charges a Bioenneo 50 amp/hr LifePo4.

I plug it in to a cigarette port in the back of my SUV. I have never blown a fuse since the PWRGate has a user selectable charge current limit to 2 amp, 5 amp or 10 amp and user selectable charge profiles for Lead-Acid, AGM and LiFePo4. A bonus is the MPPT solar charge controller built in.

Ugly but it works.

I'm thinking of doing something similar to add DC/DC charging capability to my custom battery box. The box has a 100AH Battle Born LiFePO4 battery and a Victron 75/15 MPPT controller built in and it often sits in the back of my jeep, but ultimately I designed it to be portable (its a FrontRunner wolf pack box). I only have 8AWG wire to the rear of the jeep, so just plugging the box to charge direct off alternator seemed like a bad move... not to mention I prefer the programmable profile I set in the MPPT controller.

I had been wondering if adding a Victron Orion-TR 12/24-10 (switched to vehicle ignition) and feeding the 24v output into my MPPT controller would be viable. It's good to hear that someone else is doing something similar. The reason to up convert to 24v is because the MPPT needs to see +5V over battery voltage before starting the charge program. I don't really care about efficiency loss because it's all being powered off alternator anyway. Major downside seems to be limiting the MPPT input to 10A at 24V but that's not the end of the world either. Here is the concept:

[12v alternator] ---> [Orion-TR 12/24-10] --(24v)--> [MPPT 75/15] --(13.8v)--> [12v LiFePO4]

 

[luthj]

As mentioned, most alternators output something around 14V, which is perfectly fine for charging Lithium packs. No need for expensive or complicated charging schemes, a simple relay works great.

 

[DiploStrat]

As mentioned, most alternators output something around 14V, which is perfectly fine for charging Lithium packs. No need for expensive or complicated charging schemes, a simple relay works great.

AMEN! (Now, if I had stock in CTEK, Sterling, or REDARC … )

 

[pdxfrogdog]

As mentioned, most alternators output something around 14V, which is perfectly fine for charging Lithium packs. No need for expensive or complicated charging schemes, a simple relay works great.

In my case, the complicated charging scheme is because I feel it's prudent to regulate the current that the lithium battery might pull. I only have 8AWG from alternator to rear circuit bus, 12AWG from solar input of battery box to on-board MPPT.