Scalable/Modular Battery Circut - Page 1
Forum section: electronics / beginners

author: fullbird
author_rank: Newbie
timestamp: September 18, 2025, 06:30:27 pm
content: Ok so I was wanting a good way to scale my battery's and move them from location to location. so my thought was to use 24v as main system DC voltage many readily available parts. also the process Yes may waste power but wanting to keep it to a minimum.so first of Basics and what i think id like to use.first off 24v system.so would like to use multiplusII as it can be paralleled from 2kva just add an inverter.next solar is 200watt-400watt using individual Victron 75-15 Mppts they can be paralleled and be redundant self contained per solar panel.now where the fun part begins the Battery.Currently have a JKBMS PB2A16S30P 300A. and 4 banks of 2 at 280ah a 304ah and 1 314ah. But been testing on small A123 cells and a cheap BMS.Transporting one pack is over 100lbs assembled and I'm a weak lil man. So what I was thinking was to design a Bus bar similar to what I've seen in VSDs but of course way different .so here goes my thought. each location has a full system, then I can just transport Cells to attach in parallel with current Packs. so to accomplish this the Cell would have to have a current limit In and Out for starters. so I could turn off the system attach the cells in parallel let them charge or discharge to a equal voltage the turn the system back on and Charge the system back up.SO what I've tried on a small scale works but low current is using a isolated dc to dc converter that can take 24v to an isolated 9v to a tp5000 that then charges at a limited 1-2amps per cell. then through a Current limiter like circuit appears similar to a lm314 the board I bought the chip is sanded off. but its just a cap 3 pin TO-220-3 and a power resistor and a led circuit that limits to 1amp. then I put a 1a PTC because I felt it was safer and if cells in parallel maybe it would help load share if one battery pulls to much. It does appear to work on a small scale.Biggest problem is low current. and isolated dc to dc converters are expensive.thought was to use the battery and some how a bi directional current limit circuit at about 5-10amps and maybe a ptc for safety? not really sure on the ptc part. Im sure everyone here will probably be like this Noob is gonna kill himselfLook forward to suggestions or solutions. may be just be like everyone else and parallel 24v battery's and be done but hey I may just do that. as I'm just playing with the fire.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: September 19, 2025, 05:33:17 pm
content: Quote from: fullbird on September 18, 2025, 06:30:27 pmYou can use a simple pre-charge method with relays. Each pack will have a fuse, BMS, pre-charge resistor, and main contactor. First, check that the pack and bus voltages are close. If the difference is small, close the pre-charge relay. Current flows through the resistor and equalizes voltages. Once the voltage difference is minimal, close the main contactor. The pack will now be connected for full current sharing. This will avoid uncontrolled surges and will be cost-effective. It needs operator discipline to check voltages first.

author: fullbird
author_rank: Newbie
timestamp: September 19, 2025, 06:57:25 pm
content: That makes sense for full pack Control contactors are easy to find. how would i figure out the Precharge resistor requirement for a battery