overcharge protection by shorting battery! HVC SHORTER

[flathill]

In a worse case situation where your charger and contactor fails
you just short the battery on purpose and blow the pack fuse preventing further charging

Ingeniously simple yet not intuitive
blow shite up to stop a big blow up

Tesla patent EP2448081 A2

instead of using a HVC breaker to stop the charge with FETs (that can fail short and keep charging the pack)
you create a short on purpose so the fuse blows

In this case the "HVC SHORTER" with FETS is only active when HVC is reached
(and in the unlikely event the fets fail short the fuse will still blow)

the next gen batteries are getting safer but you will always need overcharge protection
a pack can be designed to survive a couple cells failing but no pack can handle all the cells overcharging at the same time
this is why a high voltage cutoff is critical

 

[Farfle]

IIRC the term for that is called a crowbar circuit

 

[Ricky_nz]

IIRC the term for that is called a crowbar circuit

Yep Crowbar circuit. used for a long time on power supplies to avoid damaging loads with over voltage.
When used with a battery you would need to be very confident that the pack fusing is done right and can open the maximum current available from a short circuited pack and also it must be able to open under full pack voltage.

You would also have to ensure the fuse can be blown on even an old pack that has had its internal resistance grow higher over time.

If the fuse can't open for any reason then a crowbar just accelerates the damage.

 

[flathill]

Good points ricky
Maybe that is why telsa only uses it as the last resort if the two contactors also fail
But Even if the fuse didnt blow as long as the pack was draining faster than it was charging you would be better off since the cells would not overcharge
It may ruin the pack but I would not call this accelerating the damage
And the chance of the fuse blowing is pretty high so this is not likely
But good point to take pack aging into consideration when selecting the load resistor

overcharging could lead to all of the cells within the pack undergoing nearly simultaneous thermal runaway
Modern cells do not go thermal in any case other than overcharging for the most part

Would be intersting to know whether a contactor or solid state breaker would be more reliable than a crowbar with two fuses

In the future when you charge at 60C from your home fridge size sodium battery to mini 3d magnesium battery bombs you will want a crowbar
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As noted above, the OPD of the invention is not limited to the use of an IGBT. Other devices that meet the afore-described characteristics may also be used. For example, Fig. 9 shows an OPD 900 that utilizes a crowbar circuit to short out the battery pack when the voltage increases to a dangerous level. As shown, the Crowbar circuit interposed between the battery terminals consists of a zener diode 901, a silicon controlled rectifier (SCR) 903, a pair of resistors 905/907 and a capacitor 909, all rated to handle the desired trip voltage for the intended battery pack. Note that thyristor 903 may be replaced with a trisil or thyratron. The zener diode voltage is that of the trip voltage and therefore for a 100 series cell pack, each cell having a 4.2 volt maximum rating, the trip (i.e., trigger) voltage would be set at approximately 445 volts +/- 15 volts. When zener diode 901 reaches the trip voltage, current flows through the diode and triggers SCR 903, thereby shorting the battery and blowing the battery pack fuse. As in the embodiment shown in Fig. 8, the RC circuit is included to prevent noise or spikes from accidentally triggering the OPD. Also as in the prior embodiment, a heat sink (not shown) may be used to tune the I2t value of the device.

While one or more levels of overcharge protection are included in most systems utilizing rechargeable batteries, there is still a risk of an overcharging event occurring, for example due to the failure of both a charging circuit and a contactor. If such a failure were to occur in a system utilizing a large battery pack, overcharging could lead to all of the cells within the pack undergoing nearly simultaneous thermal runaway. While the collateral damage of such an event could be huge, if it were to occur in a safety sensitive application such as an electric vehicle, the consequences could be catastrophic. Accordingly, although the prior art discloses various systems that provide protection from an overcharging event, an additional layer of protection that is independent of the contactors and the charging circuit is desirable