The Car Conversion Experts

Battery Management

Batteries are often a major part of the expense in your electric car conversion. In order to get the best life out of your batteries, it is important to take care of them. Discharging and overcharging can both cause wear on batteries, especially if there is no way of knowing the state of charge for each cell. The car relies on it's energy from a large number of battery cells and if only one of these fails, you will have problems, the least of these would be not being able to get home.

A battery management system is an electronic that manages the battery system and helps to keep cells balanced, stops the cells being overcharge and stops a full discharge from happening.

Why do you need A Battery Management System?

Without an active battery management system cells can have varying capacity over a period of time meaning some cells could be low on capacity while others in the same pack can be high, as the current is drawn from these cells the low cells will go below a critically low voltage state and fail completely in worse case scenarios. The difference between a fully charged cell and flat one is only .5 of a volt! 90% of the capacity is in that .5V range. So a GOOD quality Battery Management system is important for good vehicle range and to manage the state of charge accurately. 

 

There are 2 types of BMS. we supply Australian made Batrium Brand and US-made Orion Brand. Both considered first-tier quality.

 

Passive BMS works while charging, so as any cell reaches its full state of charge a cell monitor will alert the BMS which in turn sends signals to the charger to reduce the rate of charging. The cell monitor then takes on any excess current for that cell and uses it to heat resistors so that cell is kept at its max cell voltage. As more cells reach full capacity they too are held at that voltage until ALL cells are the same and balanced. So every charge is a fully balanced charge. The benefit is that the system works well especially on smaller packs and is cost-effective. 

 

Active BMS does similar but in a centralised module. There each cell has wires connecting the cell to the BMS. As the cells are charging again the BMS will hold the full cells at the set voltage however excess current is shifted to low cells, not burnt off as heat. This style will shift current at a higher rate than the passive BMS and also balances the cells as they discharge, meaning as you drive current is shifted from higher cells to lower cells so an even discharge rate is achieved. This type of system in the case of the Orion brand can be used for DC fast charging in some cases. The benefit is a better control of input current, More efficient, best balancing as it balances continually and generally considered the best option. Of course this comes at a price and is much more expensive. 

 

Both systems have a great number of options and flexibility, we will help you to work out your particular needs in order to help you decide on the best BMS for you. 

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