What amp 12-12/ dc dc charger?

[Traveler2017]

We have 780 watts of solar on our motorhome with 150 amp epever SCC & 4000 watt inverter. We are going to replace the two SLA batteries with one 280 Ah LifePo4 lithium battery. We have a 115 amp alternator (as per Ford dealer based on VIN #). We want to go with a Victron DC/DC charger between the alternator and the lithium battery, but unsure as to what would be the optimum amp charger. We want to be able to charge the battery while we are traveling without frying the alternator. This would be more of a trickle/top off charge rather than charging from a depleted battery.

 

[Samsonite801]

I like the Victron gear a lot..

Something like this maybe (can parallel multiple units if more amps is desired):

Orion-Tr Smart DC-DC Charger Non-Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...

www.victronenergy.com

Renogy makes DC-DC LFP battery chargers for vehicles as well..

30a should be just fine. If you wanted to have more, like when vehicle AC and other accessories aren't turned on, you could have a second charger in parallel, and turn off the second one when the car has less surplus power available. So it could have the capacity to run 30a or 60a...

You could run the car with all accessories turned on, then put an amp probe (amp clamp meter) on the alternator to see how many amps it is running at max, and decide how much surplus delta you have there, and turn off some loads like blower motors down, AC off, and see how much extra you have for the two operating charge capacities.

You could also put a dash mount amp meter on the alternator output wire to help decide on the fly how many amps are available for your house battery charging too.

 

[12vDC]

what @Samsonite801 said for sure
and/or
upgrade your alternator, get whichever charger(s) you like and not worry about it.

my 2016 van comes with either a 180A or option 220A alternator. but it currently has a 280A. i was using the Sterling60A but after adding a solar panel i “downgraded” to a 30A victron.

apples/oranges but i dont think 115A leaves a lot of wiggle room.

 

[DeniseAck]

According to Renogy FAQs... "As a general rule, a 75-200AH battery bank will require a 25-amp dual battery charger. If you have higher capacity needs, then a 40-amp dual battery charger may be more suitable." The 30-amp dual charger (solar and alternator) is $199 and the 50Amp is $10 more

Shop DC to DC Battery Charger Products | Renogy

Chage up your Renogy battery with one of our intuitive Renogy DC to DC Battery Chargers, Get affordable dc battery charger price now. 10% off: Renogy10off

www.renogy.com

 

[DeniseAck]

read this site as well... https://faroutride.com/van-electrical-sizing/#alternator

 

[RV8R]

I recently added a Kisae 1250 into my Van’s electrical system & love it;

DMT1250 – Kisae Technology Inc

You can custom set the;

Voltage “Volts”
Charge Current “Amps”. 50 Amps Max
Other Charge Profile Stuff

Note; You can set the Amps from 5 to 50 max in 5 amp increments !! ? ,,, This way you can utilize your existing alternator, or increase the max amps later if you upgrade your alternator ?





It is a DC2DC & also a Solar MPPT ( I only use it as a DC2DC ).

FLA, AGM, & LFP

https://www.kisaepower.com/wp-content/uploads/2020/04/AbsoCharger_Manual_DMT12V_24V-Series_Rev-D_190612_Print.pdf

This was the screenshot the other day from my Victron BM 712 Smart;

 

[mikefitz]

We have a 115 amp alternator

At low engine speed tha available alternator current will be less than 115 amps, perhaps in the region of 75 amps. Taking into account vehicle battery charging and running vehicle systems, lights, heater, air con , it would be a good idea to limit DC to DC curent to lower than 40 amps. The Victron Otion Tri Smart at 30 amp output pulls around 35 amps from the vehicle, this would seem a suitable choise.

 

[Traveler2017]

Thank you all for all of the information, it is greatly appreciated. We've decided to go with the Victron 12/12 30amp unit. This forum is great. thanks again.

 

[12vDC]

At low engine speed tha available alternator current will be less than 115 amps, perhaps in the region of 75 amps. Taking into account vehicle battery charging and running vehicle systems, lights, heater, air con , it would be a good idea to limit DC to DC curent to lower than 40 amps. The Victron Otion Tri Smart at 30 amp output pulls around 35 amps from the vehicle, this would seem a suitable choise.

it is possible to pull 35A, it will not continuously do that.

the amount of current it will actually provide depends on battery SOC and mostly how well ventilated the heatsinks are. much of the inefficiency is lost to heat.