12v, 120ah inside cooler box to power car coolant heater

[Turponieminen]

Hi, i am asking for your thoughts and ideas about a battery build that i am planning to do.

I am planning to build 120ah 12v battery pack to power a inverter and 1000w car engine coolant heater/waterpump in the winter. (And trolling motor during summer)
My motto is cheap is beautiful

I already ordered the cells from Xuba Electronics, i am planning to use cheap BMS, to control a 200a 12v car relay. After BMS i am planning to use 12v weekly timer to activate the relay so relay power consumption is not a factor. In addition i plan to control the relay with a hallsensor/display unit that is able to perform its own overamp, undervoltage, etc. disconnects and display charge state and other information.
I am planning to house the cells inside a cooler box that hopefully maintains cells well above freezing temperatures overnight (10 hours or so).
Since there is no sun during winter, I ordered 50 amp adjustable voltage (11-14.8v) charger for the battery.
I plan to connect the battery to inverter/charger/trolling motor with 8mm bullet connectors (EC8), that is supposed to handle 190A

One concern of mine is that how does a cheap 10A BMS handle balancing when charged with this charger? I know balancing only occurs at near 100% soc, when the charging current has tapered down, but still, do these small resistors burn up, or do they only balance or absorb as much current that they are able to handle. I don't know so much about electronics.

I would appreciate your kind suggestions, ideas and comments...

edit: added links to parts that i am using or plan to use

 

[Craig]

Would need to see specs on BMS. I have not had much luck with the cheap ones but that does not mean a reliable one does not exist. Do you have a link?

 

[gnubie]

You can never tell with a cheapie but the resistors (or indeed just transistors) used to draw down the higher cells shouldn't pass excessive current if the voltage difference between the cells stays sane. A small cheapie BMS likely won't have good thermal design so general heating may be an issue.

 

[Turponieminen]

I plan something like this for BMS https://a.aliexpress.com/_mNA3Rxd

 

[gnubie]

Eyeballing it the resistors responsible for the balancing are 1W and rely on the copper on the PCB to get rid of heat. IMO, and I'm not a BMS expert so have that big grain of salt ready before continuing, it's going to struggle keeping your cells in check and if in a box is going to have heat issues.

 

[Turponieminen]

Eyeballing it the resistors responsible for the balancing are 1W and rely on the copper on the PCB to get rid of heat. IMO, and I'm not a BMS expert so have that big grain of salt ready before continuing, it's going to struggle keeping your cells in check and if in a box is going to have heat issues.

Thank you for the info. Do you or anyone have suggestion for better BMS hopefully under 20 €/$ ?During charging lid of the box can be opened if needed for heat dissipation.

 

[gnubie]

The problem I think you are going to run into is a low current, ie in that price range, BMS is going to be designed around a low charge rate and low amp hour cells too so won't be able to keep high amp hour cells with high charging current flowing through them in check.

Again said with a big grain of salt at hand.