Need Help Understanding Electrical System

[Huck]

I "borrowed" this from BattleBorn rep posted on AirStream forum. I highlighted most relevant points. I think this means I am OK on high temperature end.

Li-ion batteries operate based on the diffusion of Li-ion through an electrolyte. Since diffusion slows down in cold temperatures, there are some general limitations when it gets cold. When the internal battery temperature is freezing (32F) battery capacity falls to around 80-85% of full capacity. The capacity continues to fall to around 60% when the temperature falls to 0F. HOWEVER, the bigger problem occurs when you charge a Li-ion battery below freezing. The slow Li-ion transfer into the anode during charging could cause Li metal to plate the anode, and this could cause an internal short. The Battle Born battery has an internal protection mechanism that prevents charging when the internal temp falls below 25F, and reconnects when the temp rises above 30F. Discharge is always allowed at low temp.

The high temperature operation is not as restrictive. As long as the internal battery temperature stays below 170F (that is when the battery separator begins to melt), then you are OK. The Battle Born battery prevents charge and discharge when the internal battery temperature rises above 140F.

For long-term storage, the main thing is to avoid freezing of the electrolyte (sub-zero) and melting of the separator or thermal degradation of the MOSFETs on the battery management board at high temps. The acceptable temperature range is very wide. 0F to 100F is fine.

Battle Born LiFePO4 batteries - Page 3 - Airstream Forums

[buff30]

Powered by .... oh never mind

I thought you were going to say rainbows

The acceptable temperature range is very wide. 0F to 100F is fine.

Estimated Vehicle Interior Air Temperature v. Elapsed Time Elapsed time Outside Air Temperature
Deg (F) 70 75 80 85 90 95
0 minutes 70 75 80 85 90 95
10 minutes 89 94 99 104 109 114
20 minutes 99 104 109 114 119 124
30 minutes 104 109 114 119 124 129
40 minutes 108 113 118 123 128 133
50 minutes 111 116 121 126 131 136
60 minutes 113 118 123 128 133 138
> 1 hour 115 120 125 130 135 140
Courtesy Jan Null, CCM; Department of Geosciences, San Francisco State University

Looks like after 10 min at 85 deg you could be outside the recommend temp for the Battle Born battery. Sorry the table got wonky.

Maybe someone can make a temperature controlled battery box!

How about a temperature controlled van. My priority would be to finish the vans insulation. Use sun shields on the windows when parked. Install some rigid foam around the battery box. Install a vent fan such as this max air fan with a t-stat. Power the vent fan off the lifepo4 battery bank. It would come on automatically if the vans temp get to high.

https://www.etrailer.com/RV-Vents-an...00-07500K.html

If it was my money I would feel confident at this point that my investment in batteries would be protected. I would still keep an eye on the temperature of the battery bank though to ensure my plan was working. These are only my view on it and you are certainly free to do what you want with your money. If you have any more design questions I would be glad to assist.

[Huck]

I might find that my setup will run an air conditioner, but the air conditioner has to be in the van to keep the batteries cool!

Going to start tracking temperature in van to give me a baseline. Today it is about 10 degrees warmer in van than outside.

Don't know if there will be room for a roof fan after solar panels are installed. Still waiting for info on roof mounts for solar panels.

Also waiting for BB to call back to help me size MPPT charge controller and inverter.

Still have a bunch of things to figure out. Right now I am figuring out what it is I need to figure out.

[Huck]

I have a 5000 BTU air conditioner in my office, so I used that for testing. This was at a about 116v.

With just the fan running , a = .46 and w about 54.
With compressor running, a=5.0 and w about 560.

If the compressor runs for 40 minutes out of an hour, it works out to about 400 w/hr or 3.5 ah.

That would be about 35 a/h @ 12v (ignoring any loss).

Note: amps and watts are not an exact match because they were read off kill a watt and not calculated.

[buff30]

https://www.redarc.com.au/faq-tech-t...r-current-draw

If you figure 85% efficiency on your inverter divide your amps again by .85 to get the actual DC amps drawn by the inverter.

Your 200AH battery gives you 160 AH useable 80%DOD so I figure you are looking a three hours of run time if you start at 100% state of charge with no additions from solar or other sources. This is also not factoring in start up current if the compressor cycles. You didn't get a chance to measure that did you as it will be very important for your inverter selection. I did not factor in duty cycle as I have no idea of what that will be in your camper based on outside temp.

I got 5A * 116V = 580 watts /12.9VDC =44.96 amps DC/ .85 = 52.89 amps DC from the battery bank to run the AC.

[Huck]

Thanks Gene. I didn't see any spike when the compressor kicked in, so it must be of very short duration.

Where I anticipate using the AC is on the Outer Banks. I think with 800w, the batteries should be fully charged by 2 pm. At that point, I could run AC and batteries should stay charged. At some point in late afternoon, the AC would start to use more power than panels are supplying.

After 5 or 6 PM I wouldn't need the AC again until I'm ready to go to bed. Maybe 2 hours of AC and by then it should have cooled down outside into low 80' or high 70's. Fantastic fan and small fan near bed at that point.

I don't know if you have been to Outer Banks, but there is no shade at all in 3 of the 4 NPS campgrounds. Having a cool place to go mid afternoon is a necessity in July and August, especially if you get a little sunburned.

I've got a shade cloth I hope I can rig up someway to shade the trailer. The wind can get bad quick, so it's going to be a challenge.

[buff30]

I figured the kill-a-watt might not have the resolution to capture that. You would probably need a better meter to know for sure. Make sure you get a larg enough inverter. And remember that inverter will kick off a significant amount of heat when under that load. If it is in the air conditioned space it will be working against your cooling efforts. Let us know how it works out for you.

[buff30]

system sizing - DO IT YOURSELF SOLAR WAREHOUSE

According to this article you can expect 6 amps to reach your battery for every 100 watts of panels you have on an RV. And 30 amps total per day given 5 hours of peak per day. If I remember right you said you that the 600 watts on the van was going to charge the LiFePO4 and the 200 watts on the trailer were going to feed the Pb in the trailer. You will probably need to keep the 200 on the trailer to replace the power you will use out of that bank. So if you only use the 600 on the van for the LiFePO4 you can expect to replace 180 amps on that bank per day in ideal conditions. I think it will take you the entire day to recharge the batteries from your few hours of AC use from the night prior. I don't think you have enough solar recharge and run the AC. Have you considered adding 3 more 300 watt panels on a ground mount. For best results you could move the array to track the sun through out the day.

[Huck]

I was planning on only using the roof mounted 100w panel for trailer and using 100v portable panel on van for 700w total, expanding with another portable panel if needed.

Doesn't the MPPT controller charge batteries faster than PWM controller? I am hoping there is some advantage there. Even though there may only be 5 peak hours, I will still be storing a fair amount of amps for at least 4 more hours. About the only advantage of no shade is the solar panels will be in the sun all day.

I will be doing some testing when I finally get all the equipment. Battle Born is swamped and I haven't been able to talk to a tech yet, so I still haven't ordered charge controller and inverter. I also need to ask if I need a battery monitor or if all the info I need is available from charge controller.

[redbarron55]

You might want to consider using an AC with an inverter like my mini-split. No starting surge.

[buff30]

I believe you would still need to subtract the loss of the charge controller out of the last number I gave you. MPPT are around 92% efficient and PWM are about 80% efficient.

The battery monitor is the only way you will have an accurate picture of the amount of energy in your batteries.

Have you called AM Solar to discuss your plan? They are RV solar experts and they sell charge controllers. They have a lot of experience with LiFePO4 and running AC off batteries.

I am not a Solar expert, get the help of one.

[Huck]

Originally Posted by buff30

I believe you would still need to subtract the loss of the charge controller out of the last number I gave you. MPPT are around 92% efficient and PWM are about 80% efficient.

The battery monitor is the only way you will have an accurate picture of the amount of energy in your batteries.

Have you called AM Solar to discuss your plan? They are RV solar experts and they sell charge controllers. They have a lot of experience with LiFePO4 and running AC off batteries.

I am not a Solar expert, get the help of one.

I just ordered some roof mounts from am solar, but I wanted to get the charge controller and inverter from BB because 1) they have them on sale and 2) they come configured for bb batteries.