Using boost converter for charging LiFePO4 from starter battery/alternator

[pawsen]

In the work wan(Peugeot Boxer), I have a 12V100Ah LiFePO4 battery box with inverter for charging power tools.
I would like to charge the battery box from the inverter.

Can I use this DC-DC Boost Converter(constant current) instead of more expensive LiFePO4 dc-dc chargers, like this LiTime 12V 40A DC-DC with MPTT. I don't have or plan to get any solar panels.

Specs fro the DC-DC boost converter
- Max. Output Power = 12V*30A = 360W
- Input Over-current Protection
- Lower Voltage Protection: Yes (V8 to 50V adjustable, self-recovery).
- Input Voltage: DC10V to 60V
- non-isolated boost power supply module
- Constant Current Range: 0.8A to 20A(+/-0.3A)
I gather it's a CC CV boost module with low voltage cutoff.

Are there any problems using the boost module, connecting it directly from the starter battery with proper fuses? I understand that the LiTime charger delivers 40A and I do not expect to get more than 20A continuous from the boost converter.
Does anyone have experiences with this, or similar, modules?

All the best,

 

[mikefitz]

anyone have experiences with this, or similar, modules?

Yes it lasted 15 seconds.

Recomend a 'real' charger, Victron Tr Smart,

Victron Orion-Tr Smart nicht isolierter DC-DC Wandler Ladegerät 360W-400W | eBay

Entdecken Sie Victron Orion-Tr Smart nicht isolierter DC-DC Wandler Ladegerät 360W-400W in der groÃen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!

www.ebay.de

 

[pawsen]

Yes it lasted 15 seconds.

Recomend a 'real' charger, Victron Tr Smart,

Victron Orion-Tr Smart nicht isolierter DC-DC Wandler Ladegerät 360W-400W | eBay

Entdecken Sie Victron Orion-Tr Smart nicht isolierter DC-DC Wandler Ladegerät 360W-400W in der groÃen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!

www.ebay.de

Ok, thanks for the link. Will you explain what/why it went wrong with the boost converter?

 

[meetyg]

I don't think you need a boost converter.
You should check to see what voltage your alternator outputs. Also, these boost converters will not stop charging your Lifepo4, so basically it will float charge the battery with the voltage you set. This is not healthy for Lifepo4 batteries and will degrade or damage them fairly quickly.

Most boost converters need some voltage difference between input and output voltage in order to work properly. So let's say your input voltage is 14v, and the minimum delta is 2v, you will have to set 16v as the output voltage, which if course is not suitable.

I would get a proper DC-DC converter made for this purpose. The Victron is one option but there are some cheaper options available (still a bit pricey).

 

[meetyg]

Yes it lasted 15 seconds.

Recomend a 'real' charger, Victron Tr Smart,

Victron Orion-Tr Smart nicht isolierter DC-DC Wandler Ladegerät 360W-400W | eBay

Entdecken Sie Victron Orion-Tr Smart nicht isolierter DC-DC Wandler Ladegerät 360W-400W in der groÃen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!

www.ebay.de

Let me guess what happend: Your Lifepo4 ground was connected to chassis ground, just like your starter battery, right?

I blew up a CC converter because of this. Only to find out that the negative MUST go through the converter, because there is a shunt resistor on the negative side, which gives feedback to the circuitry, so that it knows how much current is going out and throttles it accordingly.
If Lifepo4 battery negative is connected to chassis ground/negative, you are bypassing the negative side of the CC converter, so it thinks there is no current flowing, and ramps up current from input to output, untill it blows because of too much current.

I know Victron sells isolated and non-isolated versions of their DC-DC chargers. If a common ground is required, the non-isolated can be used (has 3 pins, one of them common ground, as opposed to 4 pins on the isolated).

 

[Dave in AZ]

Let me guess what happend: Your Lifepo4 ground was connected to chassis ground, just like your starter battery, right?

I blew up a CC converter because of this. Only to find out that the negative MUST go through the converter, because there is a shunt resistor on the negative side, which gives feedback to the circuitry, so that it knows how much current is going out and throttles it accordingly.
If Lifepo4 battery negative is connected to chassis ground/negative, you are bypassing the negative side of the CC converter, so it thinks there is no current flowing, and ramps up current from input to output, untill it blows because of too much current.

I know Victron sells isolated and non-isolated versions of their DC-DC chargers. If a common ground is required, the non-isolated can be used (has 3 pins, one of them common ground, as opposed to 4 pins on the isolated).

This. Non stop reports and reasons to spend $30 more and always run a negative cable and avoid chassis negative runs. But everyday, folks post up chassis negatives on small truck size setups that shouldn't use it...
Thx, good info.

 

[Dave911]

If your alternator can output enough voltage to charge your LIFEPO4, then you may not need a dc to dc converter.
But you will need an isolator so the LIFEPO4 battery doesn't discharge into the LA battery.
I have been doing this for 6+ months now and it works fine with an isolator. The relay type isolators are best for less voltage drop.
I have been buying them off Amazon for about $55 or so.
I have a 12 volt, 100ah battery setup this way in my car. It runs a refrigerator 24x7. I travel a lot. 5 days per week.
The LIFEPO4 battery can draw up to 25 amps or so after the car has been sitting for a while discharging the Lithium battery over the weekend, etc.
I ran a fused 10 gauge, 30amp feed to the isolator. It tied directly to the car battery.