Measuring remaining charge

[jumpjack]

I found this generic log for a battery powering a brushless motor:


It reveals what I thought, i.e. that "charge indicator" on my scooter "lies", as it can't properly show remaining charge; indeed the indicator goes down as much as the motor effort is higher (i.e. each time I accelerate or drive over a slope). So how could I build an affordable charge/range indicator?

[Ypedal]

Get a Cycle Analyst..

never look back.

edit : you can get the less expensive doc wattson , Watt's up meter, turnigy gizmo, etc... but none of them compare to the CA .. nto by a long shot.

the CA has a handlebar mount, waterproof, has speedo meter, works up to 100v, etc etc etc.. just a better mouse trap.

[jumpjack]

Which type of current do such devices measure?
I tried measuring current coming from my LiFePo4 battery, and at the beginning I didn't succeed... then I figured out why: my battery produces an ALTERNATE current!
How is this possibile?!?
I know there is some electronic inside the battery (I saw it), but I thought it was the equalizer! Why in the world should I see alternate current coming out from a battery? Is there any similar graph available around? I'll try posting mine later.

[Pure]

Which type of current do such devices measure?
I tried measuring current coming from my LiFePo4 battery, and at the beginning I didn't succeed... then I figured out why: my battery produces an ALTERNATE current!

Try again, I can assure you you are mistaken. The electronics you are seeing are probably some form of BMS.

Technically there is no way to measure how much charge is left in a pack. We monitor how much was put in and how much is taken out. This tells us what is left. But there is no way of sticking a meter to a battery an saying "yep it's still got 12Ah in it.

[jumpjack]

My weird graphs:



Current sensor is not yet calibrated, I just have values between 0 and 1023.
TENSIONE = VOLTAGE
VELOCITA = SPEED (km/h)

[noahpodolefsky]

all those dips are voltage sag. battery voltage drops whenever there is a load (when there is current being drawn). more load = more voltage sag.

if you can measure current, then you can multiply current * time to get charge used (in Ah). Subtract that from your fully charged battery capacity and you have a decent estimate of remaining charge. That's basically what a CA does.

[Alan B]

The Cycle Analyst uses a shunt to measure current, and it does it frequently. It then adds the little intervals of current into amp-hours. Rather like a fuel flowmeter. It also presents other useful readouts like speed, voltage, power, distance traveled this charge, distance total odometer, charge cycles, watt hours, watt hours per mile, or kilometers if you prefer, etc. It can also be used to limit current, maximum speed, or make the throttle control current instead of speed.

See http://www.ebikes.ca for further info.