Simultaneous charging from MPPT and alternator

[krime777]

I have a medium van that I'm thinking about converting to a camper. Since it's pretty small and the space is limited I'm thinking of replacing the battery with a LiFePo4 and use it as a starting battery and a leisure one at the same time (keep only one battery in the car). Is there any issue if I connect a MPPT charger and the alternator to it at the same time ?
This is the type of battery I'm thinking about: https://www.aliexpress.com/item/4000944137004.html (probably the 100 or 150Ah one)
This is the type of inverter/MPPT charger I'm thinking about, which would also allow me to charge it from normal AC outlets: https://www.easunpower.com/products...-inverter-220v-hybrid-inverter-20a-ac-charger
... and I will get a 450W panel for the roof.
I don't need much power, will use only for 12V lighting/fan and charging phone/laptop.
PS.Yes, I am from Europe, need 220V

 

[damarshall7]

LiFePo4 batteries are not meant to replace LA starting batteries. What kind of amps does your starter pull and can the BMS of the LiFePo4 support those amperages?

You need a separate house LiFePo4 battery and a DC to DC charger to charge it with the alternator, if you alternator has enough output to support it. Research different products and you can find brands that play well with each other to keep your battery charged with the DC to DC charger and MPPT.

Head back to the drawing board and do some research. Victron products are spendy, but all work well with each other and the support is excellent. Join a FB group for DIY solar installs and you can glean the info and determine the best route for your needs.

 

[krime777]

LiFePo4 batteries are not meant to replace LA starting batteries. What kind of amps does your starter pull and can the BMS of the LiFePo4 support those amperages?

You need a separate house LiFePo4 battery and a DC to DC charger to charge it with the alternator, if you alternator has enough output to support it. Research different products and you can find brands that play well with each other to keep your battery charged with the DC to DC charger and MPPT.

Head back to the drawing board and do some research. Victron products are spendy, but all work well with each other and the support is excellent. Join a FB group for DIY solar installs and you can glean the info and determine the best route for your needs.

From what I saw that LiFePo4 battery in particular is designed to be a drop in replacement for the standard car battery.

 

[john61ct]

LFP cells have no problem at all even tiny Ah size cranking even huge diesel engines.

The issue is any circuitry between the cells not being designed to handle the high peak currents required, 600-800-1000+A

Most dropins are opaque in that regard

but yes if the assembler / seller states fit for purpose for Starter usage likely it is.

Of greater concern for me is the BMS and balancing functionality

suitability for connecting in series and/or parallel

as well as maximum amps rate continuous, charging and discharging.

You can get much higher quality cells, that can last for decades yourself, just need to do the research / get expert advice about BMS, the assembly process itself is not rocket science.

 

[jonyjoe101]

yes you can charge with alternator and mppt at the same time. The mppt will stop charging if the battery reaches 14.4 volts (while charging with alternator) . Since most drop in lifepo4 wont fully charge until 14.6 volts, charging constantly at 14.4 volts shouldnt be a problem since it will be charging at low amps.

 

[john61ct]

Not good for longevity.

Best is stop when a 4S LFP hits 13.8V

and in fact ideally only when loads are ready to soon start pulling it down, sitting at full for long is not healthy.

But many need to do that, or just don't care which of course is fine up to you

 

[Adam_Cole]

Maybe it can ’drop in’ as replacement. Who knows...?
Anyway, Be sure it has a low temperature function built into its BMS, or just dont use it if below freezing.

My understanding, and I could be wrong here…

LiFePO4 batteries can be safely charged between 0°C to 45°C meaning you can use the battery below freezing temps but if the batteries don’t have some type of heating system, they won’t take a charge if temps are below or above those numbers.
Low temp function in the BMS will just disconnect the BMS from the battery and not accept a charge until battery reaches above freezing levels.


Sent from my iPhone using Tapatalk

 

[john61ct]

The degree of damage from charging cold cells varies by C-rate and just how cold.

Just going from T-shirt weather to sweater weather can make a huge difference i
with high currents.

Do not charge at all getting down to freezing.

Discharging is not harmful, but power output is crippled