New Guy.....needs advice - Enclosed Cargo Trailer Conversion - SOLAR

[ClearwaterMexico]

I am converting a 20 x 7 x 7 all aluminum enclosed trailer into a travel trailer, with an 8000 btu Midea AC unit, 120 vac electric water heater, large apartment size Bosch refrigerator, diesel heater.....I will be very AC centric, no propane

Approx - 2000 watt PV on the roof
30 amp shore power
2000 watt honda generator
I have 24 - 280 ah prismatic cells
I was planning on putting 16 cells into a 24 volt bank, to supply power to a 3000 watt Victron Inverter
And 8 cells into a 12 volt bank for the regular dc loads, fans, lights etc......i was going to charge this bank using a Victron 120 vac - 12 volt battery charger

Is this the best use of these cells?
I can add more if needed?
Your thoughts please

 

[FilterGuy]

I am converting a 20 x 7 x 7 all aluminum enclosed trailer into a travel trailer, with an 8000 btu Midea AC unit, 120 vac electric water heater, large apartment size Bosch refrigerator, diesel heater.....I will be very AC centric, no propane

Approx - 2000 watt PV on the roof
30 amp shore power
2000 watt honda generator
I have 24 - 280 ah prismatic cells
I was planning on putting 16 cells into a 24 volt bank, to supply power to a 3000 watt Victron Inverter
And 8 cells into a 12 volt bank for the regular dc loads, fans, lights etc......i was going to charge this bank using a Victron 120 vac - 12 volt battery charger

Is this the best use of these cells?
I can add more if needed?
Your thoughts please

That sounds like a *lot* of energy usage. Have you done any kind of energy analysis to see if the 2K panels are enough? I use this spreadsheet to do the analysis:

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

 

[ClearwaterMexico]

Thank you for your input....it is the most I can fit on the roof, my hope is that by using a DC to DC charger, we can charge the batteries while driving. My real question is about my method of using the lithium cells i have

I have 24 - 280 ah prismatic cells
I was planning on putting 16 cells into a 24 volt bank, to supply power to a 3000 watt Victron Inverter
And 8 cells into a 12 volt bank for the regular dc loads, fans, lights etc......i was going to charge this bank using a Victron 120 vac - 12 volt battery charger

Is this the best use of these cells?
I can add more if needed?
Your thoughts please

 

[Short_Shot]

I am converting a 20 x 7 x 7 all aluminum enclosed trailer into a travel trailer, with an 8000 btu Midea AC unit, 120 vac electric water heater, large apartment size Bosch refrigerator, diesel heater.....I will be very AC centric, no propane

Approx - 2000 watt PV on the roof
30 amp shore power
2000 watt honda generator
I have 24 - 280 ah prismatic cells
I was planning on putting 16 cells into a 24 volt bank, to supply power to a 3000 watt Victron Inverter
And 8 cells into a 12 volt bank for the regular dc loads, fans, lights etc......i was going to charge this bank using a Victron 120 vac - 12 volt battery charger

Is this the best use of these cells?
I can add more if needed?
Your thoughts please

You'd be better off putting all of those cells into a 24v pack and just getting a 24 to 12v dc to dc converter.

And if I were you I'd run 2 to 3 inches of insulation for a trailer that large to get away with only 8k btu.

 

[FilterGuy]

I was planning on putting 16 cells into a 24 volt bank, to supply power to a 3000 watt Victron Inverter

If you are going to have 16 cells for the 'large' bank, you might want to consider wiring them for 48volt.

And 8 cells into a 12 volt bank for the regular dc loads, fans, lights etc......i was going to charge this bank using a Victron 120 vac - 12 volt battery charger

That seems like a very inefficent way to go. Charger->large battery->inverter->Charger->Small Battery->12-volt loads. There are power losses at each step so the total loss could get pretty big.

Do you have an estimate for the power and energy needed for your 12 volt? I would seriously think about using a buck converter from the large battery to the 12V loads. Since that would free up 8 cells, you could either do a 3P 24V or buy 4 more cells and do a 2P 48V for a single battery bank.

 

[ClearwaterMexico]

Thanks....yes the trailer will be fully insulated with closed cell foam, 1.5 inches in the walls, 2.5 inches in the ceiling and 3 inches underneath. The roof will be totally shaded by the solar panels....the windows and doors will be made from double pane acrylic glazing, for increased insulation properties above glass.

How can I arrange the 24 - lithium cells into a single 24 volt bank? Can you share how they should be wired? what kind of BMS would i need?

THANKS

 

[ClearwaterMexico]

If you are going to have 16 cells for the 'large' bank, you might want to consider wiring them for 48volt.

That seems like a very inefficent way to go. Charger->large battery->inverter->Charger->Small Battery->12-volt loads. There are power losses at each step so the total loss could get pretty big.

Do you have an estimate for the power and energy needed for your 12 volt? I would seriously think about using a buck converter from the large battery to the 12V loads. Since that would free up 8 cells, you could either do a 3P 24V or buy 4 more cells and do a 2P 48V for a single battery bank.

thank uuu is there a specific bmw for a 3p 24 volt? BTW, i already purchased a 24 v inverter. Can you share how to wire the 24 cells to accommodate this?

 

[FilterGuy]

thank uuu is there a specific bmw for a 3p 24 volt? BTW, i already purchased a 24 v inverter. Can you share how to wire the 24 cells to accommodate this

Here are a couple of 3P8S cell layouts you could use:
EDIT: Corrected first layout in image below



Each of the groupings of 3 parallel cells is seen as a single cell to the BMS.

The advantage of these layouts is simplicity.

Alternatively, you could build 3 Separate batteries (8S3P), each with it's own BMS and then wire the 3 Batteries in parallel.

EDIT: Corrected image to show 8S3P (It incorrectly showed 4S3P before)


The advantage of doing 3 separate batteries is that you can use lower powered BMSs.


Note: It does not cover 3P layouts, but you might want to review this resource. If you understand what this resource is saying, extrapolating to 3P will be easy.

Cell Configurations for 12V 24V and 48V LiFePo4 Batteries

This short deck shows 1P and 2P cell configurations for 12V, 24V & 48V LiFePO4 batteries. To get the deck, click on the orange button at the top of this page. Note: Reviews, Comments and corrections are welcome Document Revision History...

diysolarforum.com

As far as what BMS to use..... we would have to know a more about the DC loads. However, we can do some guesses to show how to calculate the total load the BMS will need to handle:
* We know you will have a 3000W inverter. Assuming a 90% efficiency, you will need 3000/.9 = 3333W from the battery. That works out to 3333/24V= 139A when the battery is low.
* Just as an example, lets assume the DC loads need 20A and the buck converter is 90% efficient. That means you will need 20/.9=22A for the DC loads.

Between the Inverter and the DC loads, the BMS would need to handle up to 139A + 22A = ~161A.

You might have a challenge finding a FET based BMS that can handle that much current. As such, if you want to use FET based BMSs you may want to consider doing the 3 separate batteries and 3 separate BMSs (8S3P). (Each BMS only has to handle 1/3 of the current). If this is the rout you go I would recommend the JBD 8S 100A BMS. (@OverkillSolar sells them or you can find them on Alix).

Alternatively, you could use the Electrocus SBMS0 and let it directly control your Inverter and Buck converter. However, for this to work well, you really need to go with the expensive Victron Multiplus inverters.

 

[hidiyguy]

First, congratulations. I did a small 6x12 conversion a few years ago and hope to do a larger one in the future. I agree with what others have indicated, that separating 8 cells into a separate 12V pack doesn't seem to be the best use of that capacity. Your other large consumers (AC, water heater, etc) would be a better use for that additional capacity, at the slight expense (efficiency loss) of using a stepdown converter to power your 12V items--which should be a pretty small load assuming use of LED lighting.

If you are documenting your build, please post a link as I'd be interesting in following it.

 

[FilterGuy]

Note: I goofed up the images in post 8 above. They are corrected in the post and here they are again

 

[ClearwaterMexico]

thank you all