Input on 24V system for cargo trailer conversion design appreciated!

[AmyG]

I've been lurking and learning here for a while (can't say enough about how helpful the resources and posts on this Forum have been), so here goes my first post. I would appreciate any input you might have on this 24V system for my cargo trailer conversion. I already have the Renogy panels and one of the charge controllers and would like to reuse them - otherwise am totally open to suggestions about choice of equipment. I plan to use the 2 Renogy panels for a portable ground array that will run on its own SCC, which will also serve as a backup SCC for the roof array, so will be wired/fused accordingly.

For my AC loads, I anticipate using the inverter only for short (< 30 min) periods to run kitchen appliances at < 1800 watts or to charge batteries for power tools.

I do have a couple specific questions:

1) Should the wires and fuses for the battery bank and inverter be sized based on continuous or surge amps from the inverter? I chose the former, and understand from other posts that the BMS on the SOKs should handle the surge amps okay, but couldn't find a consistent answer on this.

2) Are there best practices for wiring a system that has both 24V and 12V appliances? Is it okay to wire a buck converter off of a 24V fuse block?

Thank you! Amy

 

[Cajunwolf]

I love the schematic, nicely laid out, well-labeled, and easy to follow. At a glance, it looks good to me. The AIMS 12/24-volt, that's for charging via alternator while driving?
(1) Yeah, I would too.
(2) I can't see a reason why you can't, but someone else might. That's really similar to the system I'm working on for my 28-foot RV.

 

[John Frum]

I do have a couple specific questions:

1) Should the wires and fuses for the battery bank and inverter be sized based on continuous or surge amps from the inverter? I chose the former, and understand from other posts that the BMS on the SOKs should handle the surge amps okay, but couldn't find a consistent answer on this.

Your high frequency inverter's surge rating duration is ~20 milli-seconds and is only significant to the marketing department.
2000 ac watts / .85 conversion factor / 24 volts = 98.039215686 service amps
98.039215686 service amps / .8 fuse headroom = 122.549019608 fault amps
I suggest 4 awg wire with a 150 amp fuse.
Ideally class-t for the AIC(arc interrupt capacity)

2) Are there best practices for wiring a system that has both 24V and 12V appliances?

Not really.

Is it okay to wire a buck converter off of a 24V fuse block?

Your buck converter is rated for 20 amps so the 24 volt draw will be...
10 amps @ 24 volts / .9 conversion factor / .8 fuse headroom = 13.888888889 so you can easily run it off a branch position on the blue sea fuse block.

The branches can be up to 30 amps and the fuse-block is rated for 100 amps aggregate.

 

[John Frum]

Actually since you have signifcant dc loads you should up the main wire to 2 awg with a 200 amp fuse.

 

[Cajunwolf]

As for the choice of equipment, what's your budget, tier 1 or working-class?

 

[John Frum]

Maxx air really should make a 24 volt version of their product.

 

[rmaddy]

A few comments:

Keep in mind that if you load up the inverter close to 2000W and several of the 24V or 12V DC loads are going (fridge, charging the laptop, fans, some lights, etc) then you could easily be pulling more than the 120A the 2AWG wire is good for. 1AWG might be better.

30A per circuit on the 24V fuse box is serious overkill. Most of those items at 24V will be much smaller. Keep in mind that the 8AWG is only good for 40A total. If everything you might have on at once (including the 12V converter) is more than 40A then you should use bigger wire (and appropriate fuse).

Powering the 24V-12V converter through the 24V fuse box is doable. I connected mine to the bus bars separately with its own fuse. Either approach can work if everything is sized correctly.

Question for you - what devices are you planning to use for the laptop and USB that works with 24V?

 

[AmyG]

I love the schematic, nicely laid out, well-labeled, and easy to follow. At a glance, it looks good to me. The AIMS 12/24-volt, that's for charging via alternator while driving?

Thank you! The charger is for shore power, which will only rarely be used. I plan to use the trailer for ~ 3-4 months at a time, mostly boondocking in the desert SW US.

 

[AmyG]

Your high frequency inverter's surge rating duration is ~20 milli-seconds and is only significant to the marketing department.
2000 ac watts / .85 conversion factor / 24 volts = 98.039215686 service amps
98.039215686 service amps / .8 fuse headroom = 122.549019608 fault amps
I suggest 4 awg wire with a 150 amp fuse.
Ideally class-t for the AIC(arc interrupt capacity)

Not really.

Your buck converter is rated for 20 amps so the 24 volt draw will be...
10 amps @ 24 volts / .9 conversion factor / .8 fuse headroom = 13.888888889 so you can easily run it off a branch position on the blue sea fuse block.

The branches can be up to 30 amps and the fuse-block is rated for 100 amps aggregate.

Thank you! I will change the wire and fuse sizes as you suggested. I assume the class T fuse should replace the terminal fuse on the battery terminal?

 

[AmyG]

As for the choice of equipment, what's your budget, tier 1 or working-class?

Working class for now (hence the Renogy SCC) but in a couple years I plan to do a cabin build, so would like to learn from the trailer system in order to make good decisions about the cabin system.

 

[AmyG]

A few comments:

Keep in mind that if you load up the inverter close to 2000W and several of the 24V or 12V DC loads are going (fridge, charging the laptop, fans, some lights, etc) then you could easily be pulling more than the 120A the 2AWG wire is good for. 1AWG might be better.

30A per circuit on the 24V fuse box is serious overkill. Most of those items at 24V will be much smaller. Keep in mind that the 8AWG is only good for 40A total. If everything you might have on at once (including the 12V converter) is more than 40A then you should use bigger wire (and appropriate fuse).

Powering the 24V-12V converter through the 24V fuse box is doable. I connected mine to the bus bars separately with its own fuse. Either approach can work if everything is sized correctly.

Question for you - what devices are you planning to use for the laptop and USB that works with 24V?

Yes, I thought about the total load on the battery, and wondered if I should size the wire based on what the BMS is expected to deliver vs what the max loads might be if I ran everything at once. Realistically, I don't expect to come close to running all the loads at once, but can certainly up the wire size from the battery to 1AWG to make sure.

For the laptop/USB charging, I purchased the Coolgear 75W Dual Port USB Charger that should deliver 60W USB-C for the laptop as well as 15W for standard USB. Hoping it works although it doesn't specify input voltage above 24V.

Thank you for your input! Amy

 

[John Frum]

Just noticed a snag.
The BMS in those batteries in only rated for 100 amps continuous.
As it stands that is the bottleneck of the system.
The easy fix is to run 4 of them configured as 2s2p.

SOK Battery

SK12V100,SK12V206,SK12V206H,SK24V100,SK48V100

www.sokbattery.com

 

[Cajunwolf]

Just noticed a snag.
The BMS in those batteries in only rated for 100 amps continuous.
As it stands that is the bottleneck of the system.
The easy fix is to run 4 of them configured as 2s2p.

SOK Battery

SK12V100,SK12V206,SK12V206H,SK24V100,SK48V100

www.sokbattery.com

Yeah, I agree, but she's going nowhere near a 100 amp load from her posts.

 

[AmyG]

Just noticed a snag.
The BMS in those batteries in only rated for 100 amps continuous.
As it stands that is the bottleneck of the system.
The easy fix is to run 4 of them configured as 2s2p.

SOK Battery

SK12V100,SK12V206,SK12V206H,SK24V100,SK48V100

www.sokbattery.com

I thought about that, and actually have another iteration of the design in 12V with the batteries in parallel with a slightly over-paneled system. However, there are several posts on the Forum about the SOKs being able to discharge 150A continuous, and since I'll be careful about the loads I use at one time, and anything near 100A total will be short term, I thought I could probably get away with it. Bad idea maybe?

 

[John Frum]

I thought about that, and actually have another iteration of the design in 12V with the batteries in parallel with a slightly over-paneled system. However, there are several posts on the Forum about the SOKs being able to discharge 150A continuous, and since I'll be careful about the loads I use at one time, and anything near 100A total will be short term, I thought I could probably get away with it. Bad idea maybe?

If the bms can do 150 continous I guess its ok.

 

[John Frum]

Yeah, I agree, but she's going nowhere near a 100 amp load from her posts.

Its my policy to design for the full continuous load of the inverter.
If the dc loads are significant I add some margin for those.

 

[Cajunwolf]

I thought about that, and actually have another iteration of the design in 12V with the batteries in parallel with a slightly over-paneled system. However, there are several posts on the Forum about the SOKs being able to discharge 150A continuous, and since I'll be careful about the loads I use at one time, and anything near 100A total will be short term, I thought I could probably get away with it. Bad idea maybe?

You seem to have a handle on things and know the limitation of your system. If you feel good about it, then go with that.

 

[AmyG]

Thanks everyone for your input!

 

[Cajunwolf]

Thanks everyone for your input!

You'll get to critique mine as well pretty soon. I need to get my RV going in the next three months or sooner because I want to head up to Utah. My oldest son and grandson want to do a little Jeeping, WJ's, my tow vehicle. I went with the Giandel 24-volt 4kw inverter to run my AC.

 

[AmyG]

You'll get to critique mine as well pretty soon. I need to get my RV going in the next three months or sooner because I want to head up to Utah. My oldest son and grandson want to do a little Jeeping, WJ's, my tow vehicle. I went with the Giandel 24-volt 4kw inverter to run my AC.

That's funny cuz I'm trying to get my trailer done enough in the next 3 weeks to head down to warmer temps in Utah and New Mexico - have an off grid property at 9600 ft in CO and it finally turned into winter here so I need to order some stuff and then finish installation someplace with less snow. I moved up here from Baton Rouge a year ago, so really appreciate the advice from a Cajun

I'll try to post a "show me your setup" thread once I have it all done.