3 hours ago, Tronx said:

Crossy's balancer  seems to be his only protection against over-discharge and over-charge. I agree that this is only a balancer, but it has features for battery protection.

 

I believe Crossy has added proper charge control to his BMS + battery pack and can now charge on the chargers limit instead of the BMS safety limit. If the pack is holding balance and the charger set correctly, for most of the time charging will stop before any BMS safety limit is reached.

 

He appears to have left the discharge point up to the BMS and although not recommended probably avoids reaching this often because of excess capacity in the pack.

 

There appears to some mix up between BMS and charge controller. To avoid confusion in the charging process the BMS and charge controller should be considered separately.

8 hours ago, maxpower said:

There appears to some mix up between BMS and charge controller. To avoid confusion in the charging process the BMS and charge controller should be considered separately.

Yup! Absolutely. A basic BMS consists of three functions.

1. When battery is charging (high voltage monitoring and disconnect if limit is reached).
2. When battery is discharging (low voltage monitoring and disconnect if limit is reached).
3. Cell balancing to distribute charge evenly between cells.

There are additional functions in some like temperature monitoring, state of health, state of charge and wireless connectivity for the curious. 

The BMS does not need to have anything to do with the charge controller. The charge controller is the beast which is used to set the maximum charge current/voltage.

Cell balancing does not need to be used. Balancing can be done by a separate external circuit however, information about each cell is gathered by some onboard cell balancers and made available via wireless connectivity for the curious. This can be useful for example, in the event of one cell underperforming.

Remember these?

 

 

Well, they've arrived.

 

For 113 Baht a pop I wasn't really expecting much but these things are CHEAP! 

 

So, like any engineer worth his salt Task A was to take the beast apart.

 

The first thing that was apparent was that there's no electronic driver in the box at the back, there's a 5 ohm 5W resistor as a current limiter. Whilst this does mean that PWM dimming works nicely it does make these rather inefficient. With a 12V supply they draw about 600mA (about 7.2W) of which 1.8W is wasted as heat in the resistor. That's 1.8W we can't afford in a solar powered system so the same driver as I used in the modified lights is going in.

 

The main body is an alloy die casting as thin as thin can be, but it does the job. The other parts are thin steel pressings. Cheap and light but effective.

 

Task B was to spray the metalwork black to match the existing units.