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Concerns about powering DC loads in a 24V system

barbtalon

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Jul 29, 2021
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Hi! This is my first post on the forum, looking forward to interacting with y'all.

I'm currently designing a 24V LiFePO4 system for my van. It will be my first system. My question in this post is about the design of the DC loads.

So from my positive busbar will come my 24V DC line. From this line there will be three splits, one going to a 24V fuse box, one going to a 24/12 V DC buck converter, and one going to a 24/19 V DC Buck converter.

From the 24/12 line will be a 12V fuse box. From the 24/19 line will be just one load, my laptop. I plan to use my laptop quite a bit, and it's the only 19V load I have.

My questions are, how sound does this design sound to y'all out there? I'm concerned about the reliability of these buck converters, particularly the one to my laptop. Do I need extra overvoltage protection? Inrush current protection? I've heard the MPPT might see this circuit as a short on startup due to low resistance. I'd prefer to power my laptop via a DC step down instead of the inverter to reduce inefficiency.
 
Here is the 24/12 V converter I'm looking at:


And the variable voltage DROK I'll use as the 24/19:

If it helps I use that exact buck from drok and it works well for me in my solar generator I use at work. I use the regulator to power my laptop and unitary controllers for programming if they don't have power in the field yet. I have used this arrangement for a few years now and it has been fine.
 
I would put a power switch inline with both of them - When you're not using 12 or 19 volts, these units will still be drawing some idle current, so the ability to switch them off might be advisable

Don
 
Add fuses on both the input and output. Electronics tend to fail hard short. I don't trust Chinese electronics.
Inline automotive blade fuses would work.
inline fuses
 
If it helps I use that exact buck from drok and it works well for me in my solar generator I use at work. I use the regulator to power my laptop and unitary controllers for programming if they don't have power in the field yet. I have used this arrangement for a few years now and it has been fine.
I almost went that route. I did find a 90W DC-DC 12v-20v laptop charger for Lenovo on amazon. Small and totally enclosed brick, with cigarette lighter plug and lenovo connector. Also saw many for 19V laptops.
Lenovo 12v car charger
universal 65w car charger
 
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I have multiple Lenovo laptops and a Dell or two. I use the 120v output from the inverter, along with the standard laptop power supply cord/brick. It works fine and is a simple solution.

If you don't plan to use an inverter at all then I can see why you would look to the 24v-19v option.
 
I have multiple Lenovo laptops and a Dell or two. I use the 120v output from the inverter, along with the standard laptop power supply cord/brick. It works fine and is a simple solution.

If you don't plan to use an inverter at all then I can see why you would look to the 24v-19v option.
Inverters to 110v brick is not efficient. 12v to 19v boost is far more efficient. It can make a world of difference when camping on solar. Especially for cloudy days.
 
Inverters to 110v brick is not efficient. 12v to 19v boost is far more efficient. It can make a world of difference when camping on solar. Especially for cloudy days.

You're right, it's not efficient. But it's simple. I have enough battery and solar that I don't worry about the state of charge until I've had clouds for four days, which is almost unheard of in the Rocky Mountains.
 
Here is the 24/12 V converter I'm looking at:


And the variable voltage DROK I'll use as the 24/19:

I've heard nothing but good things about the drok converters here. I'm using 2 small (3a) drok regulated converters to go from 24-12. They provide the juice for my bms' to control protection circuits with.
 
I've heard nothing but good things about the drok converters here. I'm using 2 small (3a) drok regulated converters to go from 24-12. They provide the juice for my bms' to control protection circuits with.
I used a DROK 12v - 13.8v 15A boost to keep my campers batteries topped up from the tow vehicle.
The campers is sold. The replacement has LiFePO4 batteries, which can take some charge at 13.8v, so I might do it again.
 
Fwiw, I also have used the Lenovo 12v to 19v power supply. It did get warm, and it made an odd ticking noise, if I recall, but it worked fine, and never failed.
 
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Any chance the laptop can be powered by USB C? 12v to USB C seems like it’s more future proof than 19v. Maybe it’d be a good reason to upgrade the laptop.

just a thought
 
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