ISDN batterygo BG-8S

geoff57

10 kW
Joined
Apr 25, 2007
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752
Location
England
I found this a while back on hobbyking it is unavailable at the moment but banggood and aliexpress both have them in stock.
It has a battery balancing function available similar to the battery medic that has been out for years but it is a lot more accurate.
It does not have a discharge and balance function like on the battery medic but we cant have everything.
I opened on up to see how the balance function worked with a mind to putting it on steroids so to speak, I found inside there were a bank of 8 680 ohm 1206 SMD resistors, one for each cell I presume.
Lifting the resistors has not been too difficult what I need to know is what size and wattage of resistor to replace the resistors with to speed up the balancing process. My guess would be a 3 watt metal film through hole resistor, but what resistance would be required?

geoff
 
What are the transistors that switch those resistors rated for?

If they can't handle the higher current (and heat), they'll fail after the resistors are changed allowing the higher current to flow.


Note that the resistors (and transistors) will generate more heat at the higher current; if there isn't enough heat dissipation/ventilation then surrounding components may be damaged over time, including the PCB.

Regarding the resistance value, you'd calculate that based on the amount of balancing current you want to shunt around the cell, at whatever voltage that will be happening at.

If the present resistors are 680ohm, what is the balancing current rated to be? Then you can use algebra to divide the new current by the old one and use that ratio to multiply the old resistance to get the new one.

Regarding the wattage of the resistor required, you'd need to know how many watts of heat it will generate. Current thru the resistor times the voltage across the resistor will give you that. Voltage across the resistor is current thru the resistor times the resistance.
 
Hi
Since posting the initial post I have been testing the BG-8s With various sizes of battery I’ve used both 18650 and turnigy lipo, From 1000 mA hours to 26 ah. The small batteries balanced in 1/2 an hour the 25 took a day.
I can live with those times my reasoning for wanting to change the resistor was due to the time the old battery medic took but it seems this balance I got device is a lot quicker.
Geoff
 
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