quick question about dc/dc charger for lifepo4

[burronazul]

Hi,
This is my first post, I hope I am not braking any rules.

I own a Prius and I am looking to add a second battery to it. I am planning on hacking into the built in 60w solar panel, and add an mppt charger, 100ah Lifepo4 battery, and dc/dc charger with voltage sensitivity or a relay to only charge from the alternator when the car is on.

I already got an MPPT charger from amazon. 10ah ( more than enough for the 60w panel}. Battery I can either buy, or build from cells. However, the dc/dc charger is becoming a problem. I want to keep my setup as economic as posible. I built a van and got the renogy 50amp charger, thst is MPPT and dc/dc, while also maintains my main battery charged. it is what i need, but for the prius project I was looking to get something smaller and way cheaper.
every dc/dc charger I have looked at is either too expensive, or does not provide the 14.6v for lifepo4. I was also looking at a dc converter to bump the voltage from 13.4a (alternator) to 14.6. however, it will not provide a charging profile)

questions are
why are mppt chargers $10, and dc chsrgers $80?

is there a small dc chager someone recommends? preferably 20amps, but i can probably do 10a or less.

 

[sunshine_eggo]

Hi,
This is my first post, I hope I am not braking any rules.

I own a Prius and I am looking to add a second battery to it.

Why?

I am planning on hacking into the built in 60w solar panel,

Just make sure you don't compromise the cooling system. The Gen3 cook their batteries due to a horribly designed cooling system.

and add an mppt charger, 100ah Lifepo4 battery, and dc/dc charger with voltage sensitivity or a relay to only charge from the alternator when the car is on.

Your car doesn't have an alternator. You have no belt driven devices of any kind as your car has no belt.

I already got an MPPT charger from amazon. 10ah ( more than enough for the 60w panel}.

See comment below.

Battery I can either buy, or build from cells. However, the dc/dc charger is becoming a problem. I want to keep my setup as economic as posible. I built a van and got the renogy 50amp charger, thst is MPPT and dc/dc, while also maintains my main battery charged. it is what i need, but for the prius project I was looking to get something smaller and way cheaper.
every dc/dc charger I have looked at is either too expensive, or does not provide the 14.6v for lifepo4. I was also looking at a dc converter to bump the voltage from 13.4a (alternator) to 14.6. however, it will not provide a charging profile)

LFP can achieve full charge at 13.8V. It just takes a little longer. MOST batteries (especially when new and imbalanced) won't tolerate 14.6V because one or more cells hits high voltage, and the BMS cuts off charging.

questions are
why are mppt chargers $10

Because you didn't buy a MPPT charger. You bought a fake PWM charger labeled as an MPPT.

There are 8-40V to 13.8V 10A converters on amazon. I've used one to float lead acid batteries. it would be useful for DC-DC charging, but you would need to devise a cut-off.

 

[burronazul]

the comment on violating the rules go to posting in the wrong section. I have bern criticized before for that. I created an account and posted on the first section I saw ?

this is what I got for MMPT, is it fake then?



I have a Prius 4 2010, the solar panel is only connected to a fan as far as I understand.

 

[sunshine_eggo]

the comment on violating the rules go to posting in the wrong section. I have bern criticized before for that. I created an account and posted on the first section I saw ?

I was asking why you want to add 12V capacity.

this is what I got for MMPT, is it fake then?

Actually, no. I haven't seen that one. Most of your $20-30 MPPT are fake like this one:

https://www.amazon.com/Controller-Battery-Intelligent-Regulator-Display/dp/B0BLVMC2JS

I have a Prius 4 2010, the solar panel is only connected to a fan as far as I understand.

Yep. The 4 is trim level. All Gen3 (2010-2015) are identical "under the hood."

 

[burronazul]

i want keep a 12v fridge when I travel. also charge phones and thing like that while the car is off. I figure that at 40wh thst the fridge consumes (and cycling on/off) a 100amp hour should last for a few hours. the panel shoukd charge some, and running the car will do the rest. I shoukd also be able to jump start the car from the second battery.

so, is there any dc/dc charger available? I don't need much, even 10ah should do it.

 

[mikefitz]

dc/dc charger with voltage sensitivity

Try,

https://www.amazon.com/Victron-Orion-TR-Isolated-Charger-Supply/dp/B0851TPKV7/ref=sr_1_1?crid=2MZYYOV0HXK0V&keywords=Victron+orion+tri+smart+12+12+18&qid=1701644479&sprefix=victron+orion+tri+smart+12+12+18%2Caps%2C184&sr=8-1

The unit is a charger so will terminate charge correctly. The unit has programmable voltage levels for cut in and cut out and control inputs for override if needed. The link is for the 18 amp version, a 30 amp unit is also available.

14.6v for lifepo4

The Victron default is 14.2 volts, adequate for lithium.

 

[burronazul]

well, if I am buying that I rather get the renogy 30a cd/dc charger. it has mmpt, dc/dc and priorizes my starter battery over the house battery. it solves all my problems and it goes for $170 to $200. My question was directed as trying to get my setup as cost effective as possible. I figured a 100ah battery for about $200, $20 for the mmpt, and was trying to get the dc charging for about $20 to $40. Obviously it is not possible.

thank anywa6.

 

[burronazul]

I ended up returning the mmpt charger. it said on the box "made in the PRC"... Not sure why they are avoiding explicitly writing china on it, but I rather don't deal with it?