48v battery gauge on 44,4v battery (done)

[UBMag]

I just tried out Grin`s version of the eZee Battery Gauge with "CA-plug" controller interface. Its a good little product with its basic configurability (although simple), and I can so far recommend it (for its purpos). The bike is built for a non-tech-savy person, so wanted to keep it simple, and a little less pricy (thus no real CA unit).

The challenge is that I have built a 44,4v pack with 12S Bms for it (since I only had 12 new 10Ah pouches, that I do not know anything about). Now the tricky part, in my eyes, is to get the gauge indication about right battery-status. The guage can be programmed for either 36 or 48v packs. What is the best/viable solution in modifying the indication?

* Have a (%-constant) step-up DC-DC in front of the gauge (-set to 48v operation)
* Have a (%-constant) step-down DC-DC in front of the gauge (-set to 36v operation)
* Or open the thing up, take pictures, and ask you guys which resistor to change?

Thank you

 

[Raged]

why don't you just get a simple 0-100v digital led display voltmeter and plug it into the CA DP plug pins 1 and 2 :

Pin 1 is +ve and pin 2 is gnd.

 

[UBMag]

why don't you just get a simple 0-100v digital led display voltmeter and plug it into the CA DP plug pins 1 and 2 :

Pin 1 is +ve and pin 2 is gnd.

Not A bad idea, but want to keep it as clean as possible, so want to find a way to configure the unit (if possible).

 

[UBMag]

* Second thought: Since The Battery Gauge is a "active" device in that it regulates the controller A-output based on the shunt reading threw the CA-plug: will this voltage modification interupt its behavior or communication with the controller too? I guess the communication-voltage is at 5v both for the controller and Display, so that should(?) be ok. But what about the shunt value? If I am not mistaken, this value is unaffected by voltage, since it is in affect a ampermeter? hm.....

edit: Deleted stupid idea

 

[UBMag]

edit: Deleted

 

[UBMag]

Ok. I think I got the answer for the tiny voltage divider circuit i need... Im learning by doing here, so PLEASE correct me if I am wrong (so I do not fry anything testing it)

V(in): 44,4 volt (-from the CA-plug on the controller on 12S pack)
V(out): 37 volt (-to the eZee Battery Gauge set for 36v operation)
R(1): 1480 ohm resistor (7,4v / 0,005A / 0,037W)
R(2): 7400 ohm resistor (37v / 0,005A / 0,037W)

If the eZee gauge is taking 10mA @ 37v, this should add up to 20mA in total, and work ok (....I think?) When fully charged 50,4 V pack, this should give the eZee 42 V, showing full battery "correctly"...

 

[UBMag]

Solved.
(10k resistor + pot) = adjustable voltage divider...

 

[friendly1uk]

I have wanted to use a divider to drop my 44 down for a 36 meter. However, the meter not only watches that 44v, it also uses it. If it's load is not consistent the meter would be wrong.

 

[UBMag]

I have wanted to use a divider to drop my 44 down for a 36 meter. However, the meter not only watches that 44v, it also uses it. If it's load is not consistent the meter would be wrong.

Yes, I found that out to. Why I went for the trimpot instead of fixed resistors. (Just added a 10k ohm r between the pot and ground, to be sure not to fry the controller output by turning the pot to the max). Since I do not know the exact resistance of the gauge during operation, I am doing a trial'n'error test with different pot adjustments. So far it seems to be about 750 ohm on r1 and 14250 on r2 (for this particular device). The gauge seems to be using more or less unchanged current during operation though

Edit: battery level drops like always under motor load due to normal sag (but I think this device might also have an internal clock that limits this effect, compared to analog gauge)