36v packs to power off grid trailer

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ShartsN'Sparks   1 µW

1 µW
Posts: 3
Joined: Oct 28 2019 5:47am

36v packs to power off grid trailer

Post by ShartsN'Sparks » May 15 2021 9:19am

Hi all! I know there are some big brains in here and I plan to pickem! Lol. Looking for actual survival advice, please be respectful.
Here's what I have : around 10kwh worth of good LG 36v 18650 packs(10s6p) with standalone BMS I plan to use for charging purposes only and it will accept 5a each 10s6p setup. I do have a load of surge strips and 2.9 chargers that's part of the proprietary system used with the packs. Each is a little over 500wh, but we'll call it .5kwh/ea for easy math.. I also have a window type ac that I've shown to draw around 11 amps at startup.
Here's what I want to do : I live in the Southwest with many days over 100°f, I plan on converting a cheap enclosed trailer (Like a LooK trailer type) around 14×8 that I'm going to insulate well, I want to be creative with my power supply location to insure it gets to reap some of its own reward so it's cabinet should be kept somewhere around 70°. I have access to other appliances and it's obviously the AC that I'm most concerned with but may running small fridge and television at most together with the AC unit. I also plan to get an easy start for the air conditioner and plan on reducing the current draw by at least a third & adding solar help, and finally eu2000i type generator if absolutely necessary. I know the solar at least, may factor in to my inverter/charge controller selection.. I always like to over engineer, so I'm not necessarily wanting to incorporate that in at the moment I would like to know that my battery wall could keep the AC running for at least four or five hours without any issue.
What is the most efficient means of inverting the power from DC to AC and what is the least expensive and last but certainly not least what is the most reliable?
I was looking at a 4000 Watt RMS/8000 w peak, 36v dc/ac pure sine inverter on eBay/Amazon looks a lot like an audio amplifier as opposed to the almost round tube setup of the other inverter that's of similar ratings and I'm sure that the more flat thinner case unit has a better time dissipating heat but perhaps some of you have had experience with these or potentially I'm even going down the wrong road and there's a better way to do it rather than a pure sine wave inverter? Time is also of the essence so shipping from outside of the US is not a possibility at this time.
Thanks in advance for your help and I apologize for any typos or grammatical errors.. I lose my train of thought if I don't use talk to text. :confused:

john61ct   100 GW

100 GW
Posts: 7832
Joined: Dec 18 2018 2:06pm

Re: 36v packs to power off grid trailer

Post by john61ct » May 16 2021 11:49am

IMO the only lithium chemistry suitable for mobile House bank use is LFP.

The li-ion chemistries at 3.6 - 3.7Vnominal are way too prone to fires, "thermal runaway" for use anywhere near human habitation, much less within a small mobile living space.

ShartsN'Sparks   1 µW

1 µW
Posts: 3
Joined: Oct 28 2019 5:47am

Re: 36v packs to power off grid trailer

Post by ShartsN'Sparks » Jun 11 2021 1:45am

Ok, I can accept that. I really don't have any experience along those lines, so I'm sure given the circumstances you're right in the regard it's best not to take any risks given it's a home. I do use these packs for EVERYTHING I currently build, I would think the abuse I put them through would at least make for a short life but I think the stigma of yesterday's li ion still plagues it today, despite having a much better construction. I build my scooter batteries by splitting the battery packs from 10s6p to 20s3p & have retired rentals that will do 40mph on 6.5" hubs. All stock parts other than driver cap bumped to 100v. I obviously have to bypass stock BMS for output and CFW patch to forgive the overvolt. Everything I read, said it wasn't possible with this setup.. I also live in an extreme environment, Phoenix stays well over 100°f for 6-8mos a year, my oldest one is approaching one year since modding with no issues and is absolutely amazing! The crazy part is, range is actually extended if cruising at the stock 36v top speed(18mph). I purposely left stock 14ga wiring to limit current from the source/regen and I will admit it does get warm enough to feel through the deck sometimes, I've yet to have any issues. Is it the constant drain for extended periods that has you concerned?

john61ct   100 GW

100 GW
Posts: 7832
Joined: Dec 18 2018 2:06pm

Re: 36v packs to power off grid trailer

Post by john61ct » Jun 11 2021 7:14am

The fact that random thermal runaway becomes exponentially more likely as they age

Boom bad!

Proactive replacement at 75-80% SoH would reduce the risk, but many don't even know how to do cap testing.

Timed CC loading is more precise than using a coulomb counter.

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