Giant - battery meter discrepancy

[Chris the Sheep]

Hi - I've got a 2013 Giant Twist Esprit Power, which has a hub motor and a single 36V 10AH battery on top of the rack. This morning after riding to work there's a discrepancy between the two battery meters which has me a bit worried!

There's a meter on the display / control unit which shows up to five bars, and on arrival at work (10-mile journey) it was still showing all five. This isn't unusual, but there was a bit of a headwind this morning so I was surprised; but I turned it off and on again, and now it showed four bars, exactly what I'd expect.

However, I then checked the meter on the battery - one of those where you press a button and, again, it shows up to five bars. This usually reads lower than the control unit, typically by one bar, but this morning it's only showing one bar, which is flashing.

Does anyone know which reading I should trust? The bike's performing exactly as normal, but it's a long way home if the battery goes flat.

Also - is there some sort of reset / calibration for the battery meter?

For info, it was last charged on Monday evening, and took about three hours as usual. It's had around 100 - 150 charge cycles.

Cheers

 

[trex]

you know you've done 10 miles with a little headwind - the battery should be 60% full. Rule of thumb is 10WH/mile on flat roads if you pedal lightly, 15WH per mile on throttle alone.
The meters are not a reliable indicator. They show current battery voltage, they drop when you are riding and go back up when you stop. Their indication when you stop is better because they relate to how much is left in the battery.
The first bar goes off with about 60% capacity remaining, the second bar goes off with about 20% remaining.

 

[flecc]

The battery meter would normally be the most accurate, but it may be faulty of course.

Giant on the Panasonic powered models often had smart meters in the battery and these can drift out of register. The change sounds rather sudden, but it's just possible you have this type of meter. Resetting these can only be done by using the bike to run the battery to as empty as possible, then recharging to full. Running to empty resets the zero point for the meter to measure from.

Some expert advice is to do this ever 30 or so full charges, but mostly just doing it when absolutely necessary is best.

I'd say risk using the bike to run the battery lower since it seems to be performing ok and see if that partially corrects the battery meter readout once it's content has dropped. If it does you are on the right lines so do a full reset as described. If it doesn't correct from one flashing light but does your next journey ok, then it's the meter circuit in the battery that's faulty.

If you don't want to risk it on your work run, perhaps you could do a spare time run circling very local routes and staying close to home to see how it goes.

 

[Chris the Sheep]

Thanks for the suggestions - assuming I get home OK it looks like Easter's going to be a good time to run the battery right down - I live in Blackpool so can just go up and down the prom for as long as it takes. I'll feedback how it goes; the worry for me, as flecc suggests, is that it's happened so suddenly.

Cheers

 

[Chris the Sheep]

Quick update - I rode home with no problems, with quite a vicious headwind at times; the battery meter on the control unit went down to three bars as I'd expect, so it looks like it's just the meter on the battery itself. Will discharge it and see what happens.

 

[Chris the Sheep]

...and the final update. I ran the bike until flat this morning, then put the battery on charge - and the meter now seems to be working! So thanks for the advice.

However - I've since noticed that the plastic membrane around the button on the battery meter has split, so it may be that water's got in. I'll tape it over as I don't need it anway.

 

[flecc]

That's good Chris, I didn't think it would be anything serious or terminal.

 

[drsolly]

I think these "blobmeters" are not good enough. They're measuring the voltage, but since they can only show one to five blobs, you don't really get a good idea of what's going on.

I added an LED voltmeter.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=261411957582

It's mounted on my handlebarrs, and connected to the same connectors as the blobmeter, and mounted with duct tape, so it's very easy to connect and mount. It tells me the voltage of the battery, and actual number! And when the motor is running, it shows me the lower voltage that the current draw causes.

I'm using 8S Lipos, so I can see my "freshly charged" voltage of 33.6 volts, and watch as that gradually falls; at about 26 volts, the battery is empty.