Difference between pages "Parallel Batteries" and "DIY-battery"

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(Created page with "There are two methods you can use to safely parallel batteries. ==Direct connection== To safely parallel batteries directly for more capacity, you must first ensure they are the same chemistry (lipo, li-ion, lifepo4, lead acid, etc) and the same voltage. Never attempt to directly connect batteries in parallel of different chemistries. It is also best if they have a 2 wire BMS (Charge and discharge through the same wires), since otherwise directly cross connecting th...")
 
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There are two methods you can use to safely parallel batteries.
'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.
Prerequisite software/knowledge (before building a pack)


==Direct connection==
Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.


To safely parallel batteries directly for more capacity, you must first ensure they are the same chemistry (lipo, li-ion, lifepo4, lead acid, etc) and the same voltage.  
You know how to use the [https://ebikewiki.com/index.php/Simulator|Grin simulator] - You need to know how much current your battery will be drawing.


Never attempt to directly connect batteries in parallel of different chemistries.
Ohm's law. Since we are not going into AC power, complex number/angle is not needed.  


It is also best if they have a 2 wire BMS (Charge and discharge through the same wires), since otherwise directly cross connecting them may defeat the overcharge protection.
Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batteryspace.com/prod-specs/11514.pdf LG M50LT datasheet, from batteryspace], [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]
 
By directly connecting the positive wires to each other and the negative wires of a 2 wire BMS, you can charge both batteries and discharge them through the same wires at the same time.
 
You must first however charge both batteries to the exact same voltage (fully charged is recommended as its easiest to reach) as directly connecting batteries of different charge states can cause huge currents to flow. Its best to verify with a DMM that they are the same voltage before connecting.
 
It is recommended to have an individual fuse or breaker for each battery, but not strictly required as the BMS should be able to disconnect the battery in event of over-current.
 
This means you can not directly connect a second battery in parallel as a backup unless its going to stay attached or only be attached when both batteries are fully charged. Use an A or B battery switch instead if you need to switch to a backup battery.  
 
==Diode connection==
 
By using high power diodes, you can ensure your one battery won't discharge into the other and can even connect different chemistries of battery or even different voltages, although they won't share the load if you do mix voltage/chemistries and you will need separate chargers.
 
The diodes need to be rated for higher then your max battery voltage and the full current you expect to draw, ideally much higher. This will make them rather large and likely require heat sinks. The diodes only need to be on the positive wires, directly connect the negatives.
 
You also need to use additional diode or separate connectors for charging. If you use diodes they will need to be rated for the full current of your charger and batteries.
 
Note that if you use diodes, your controller will no longer be able to recharge your battery and regen braking must be disabled.

Revision as of 08:31, 13 September 2023

Intent: This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery. Prerequisite software/knowledge (before building a pack)

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the simulator - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. LG M50LT datasheet, from batteryspace, Simplified datasheet of M50LT, courtesy of Batemo.de

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