How to Integrate Safety into Charging System

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andrew's picture
Last seen: 14 years 2 months ago
Joined: Tuesday, November 28, 2006 - 17:21
Points: 1361
How to Integrate Safety into Charging System

This thread is to explore ideas on how to integrate safety systems to prevent fire or explosion in case of a charger, BMS, or battery failure during charging.

Chargers all have the potential to fail and not scale back current at the end-of-charge cycle. They may also fail to shut off if CC, and CV type. Fast chargers have much more potential to cause serious damage, explosion, or fire, especially when paired with Lithium chemistries.

BMS systems are critical for all lithium chemistries which can catch fire and explode if the BMS fails to prevent overcharge, or a short.

Batteries can be damaged by over discharge (most common), shock, overcharging, or undercharging. All of these cases can potentially cause fire or explosion. Over discharge can reverse a cell. Upon charging, that cell can quickly be overcharged vent explosive gas. Shock can cause internal shorting, leading to the battery to not come up to voltage, and the charger to stay in high current mode overcharging the rest of the cells and venting explosive gas. Undercharging can lead to sever cell unbalance over time, which can lead to over discharge of some cells. This can cause cell reversal. Additionally at end of life, battery cells can become severely unbalanced leading to cell reversal, and over charge of cell(s) with diminished capacity.

Cheap Safety Systems Everyone Should Have:
Smoke detector near batteries (cheap, easy to install, highly recommended)
Fire extinguisher (cheap, easy to install, highly recommended, works well in conjunction with smoke detector)
Timer to use in charger 120v circuit (highly recommended for fast charging)
Low amp fuse in charging circuit (not main high-power fuse, but separate fuse designed to specifically protect charging circuit, amp rating of charger max output)

More Expensive Safety Systems for Very Fast Charging and/or Lithium Chemistries
Temperature Sensor on each battery, or each cell if using dangerous lithium chemistry (independent from charger, used to cut power to charger if temp reaches a threshold. Not sure exactly how to do this yet.)
On-vehicle fire/explosion protection (Battery enclosure designed to protect from explosion/fire, battery cells isolated with fire-retarding paper, fire suppression)
Hydrogen detector near vehicle
Automatic fire suppression external to vehicle

Last seen: 6 years 2 months ago
Joined: Friday, December 1, 2006 - 09:01
Points: 712
Re: How to Integrate Safety into Charging System

The smoke detector is a good idea. Even if it was not controlling the charger, having a loud signal when it smells smoke inside the cowling would be a good thing, and simple to set up.

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