Exactly Watt IsThe What Meter Telling Me?

[Fessernohair]

I just went over 100 miles on my new Rad Rover 5 and have a newbie question: What, exactly, is the watt meter telling me? Is it the power going to the motor from the battery at that particular instant expressed in watts per hour?

If so, does it mean I theoretically could expect two hours of battery life from my 672 watt battery at a watt meter reading of 336?

 

[legsofbeer]

The watt display is telling you your instantaneous power consumption. 1 watt is 1 amp of electricity at 1 volt. So on your nominally 48v battery, if you're drawing 350 watts (PAS 3) you're pulling 7.3 amps from the battery. If you ride nonstop at PAS3 for an hour, you will drain your battery by roughly* 350 watt-hours.

does it mean I theoretically could expect two hours of battery life from my 672 watt battery at a watt meter reading of 336?

Your battery is 672 watt-hour battery. So yes, you roughly* get that. But...

*roughly, because your battery voltage drops as you use it. So your PAS3 might give you 370 watts on a full charge (where your battery is reading about 54.2 volts), and steadily drops to 280 watts just before the voltage drops to near 40 volts and the battery management system cuts you off to save the battery from damage. Be advised on the radrover 4 at least, the bar meter on the display is wildly optimistic. Assume once a steady 60% is showing you really have 40-50% of the range left, and at 20% you'd better be within 5 miles of home and using PAS 2 or 3. Once you figure out the bike's range on flat ground at various PAS levels, your odometer becomes your best range remaining indicator.

 

[Fessernohair]

Thanks! Exactly what I needed to know. My first 100 miles has mostly been doing just what you suggest—experimenting with various grades, surfaces, and PAS settings. I’m in SW Colorado now so have had lots of paved and gravel roads averaging close to 200 feet vertical per mile. Next week in relatively flat Texas to check out the contrast.

 

[AHicks]

I use the watt meter as a guide to how efficiently I'm riding the bike. Object being to keep that number as low as possible. Coordinate your speed, the gear your in, and the PAS level using that meter as a guide for maximum range.

Kinda like using a vacuum gauge on a car if you've been around long enough to have had something like that in your experience.

 

[legsofbeer]

experimenting with various grades, surfaces, and PAS settings.

Cold temperature is a factor, too. I see less range when the temps are below 50 degrees, but haven't done that enough to quantify it. Got no info on high temp (80+ degrees) usage, save the professor from Nova Scotia's advice that discharging the battery at higher temps tends to shorten the battery's useful lifespan a bit more than middle temp usage, but not as badly as charging it at higher temps (that's the big no-no).

 

[Fessernohair]

Again, excellent information and advice. Please keep it coming.

 

[legsofbeer]

Last bits of info. These numbers come from when my battery was new, 800 miles or less. My daily commute is 5 miles each way on pavement with one 400 foot up and down hill each way. On PAS 4 or 5 I got the advertised 25 mile minimum. I don't use PAS 4 enough to break that out. PAS 3, got 35 miles, though the last 2-3 miles were iffy. PAS 2 used for 5 days straight, got 55 miles, rode the battery to cutoff on the 5th day to see what would happen and how far it would go.

Maximizing range: Don't touch that throttle. It is really, really hard to reliably apply an intermediate power amount such as 300w with the twist throttle; even if you get it right you hit a bump and your hand moves 1mm and now you're at 550-750w. In my impression, 5 minutes at PAS 5 (750w) drains the battery more than 10 minutes at PAS 3 (375w). When coasting to an intersection where you have to stop and you're cycling the pedals to gear down, pull a brake lever a little bit so the motor doesn't kick on. Pump up those tires to near max pressure; squishy tires are fun and necessary in some terrain, but they suck for mileage.

Also, when my rear kenda juggernaut (not a bad tire) wore out, I replaced it with a slick, resulting in about 10-12% faster cruising speed for same cadence in PAS 3. This doesn't directly translate to 10% greater range, since I burn the battery more getting up to cruising speed and my urban biking has lots of stops, but it helps since you get to your destination sooner.