An eGas Gauge for My eBike

[rgsparber]

Trying to measure the remaining capacity in a Lithium-Ion battery is tricky. If the battery is not sourcing current, the voltage can give a good estimate for a given battery. All bets are off when current flows. The voltage will drop as the current rises and then go back up when the current falls.

A much more accurate, but not perfect, method is to record the current over time. The battery has an ampere-hour rating, so it is just a matter of knowing when the battery is fully charged and subtracting the ampere-hours as they pass by.

This is what my eGas Gauge does. The hardware consists of 3 resistors, 2 capacitors, a toggle switch, a piezoelectric beeper, 3 AA batteries, and a $1.50 computer system on a chip. The complexity is in the software but you don't have to build or pay for that.

If you are interested, please, click here.


Thanks,

Rick

[jdurand]

You can make the gauge self calibrating by integrating power in during charge and power out during discharge.

As long as you occasionally charge it to full, you can judge remaining battery service life too. So, have it e-mail you a warning to buy a new battery.

[rgsparber]

Each user has a different opinion of when they want to recharge the battery. I choose to refuel my car when it reaches 1/4 but my wife refills at 1/2. So we have different effective gas tank capacities. My circuit deals with this human factor.

If you simply integrate the current going in and coming out, it will eventually accumulate a lot of error.

Rick

[DIYer]

Thanks rgsparber! We've added your eGas Gauge to our Electronics category,
as well as to your builder page: rgsparber's Homemade Tools. Your receipt:

eGas Gauge by rgsparber

tags: gauge, battery

[rebuilder1954]

Very cool, as usual, Rick.

Nicely done!