Aotema review - Watts used

[ekingsting]

Got a Killawatt meter a little over a month ago so I charted my Aotema watt usage by monitoring the charger watts used. The usage in not as acurate as a CA meter but the results are close enough for now.

[Russell]

Are you making any correction to account for the efficiency of the battery charger?

-R

[kevo]

Charger watts have more to do with your battery, charger than your Aotema hub - right?

[ekingsting]

The only correction I made was to subtract 5watts x hours on charger from total killwatt reading. the reason is that when battery is fully charged the charger consumes 5watts an hour. Not scientific I know but I have no idea as to the efficiency of the charger. Also my watts used on short rides are influenced by steep hills to my home which is on side of mountain.

And yes watts consumed during charging would not be exactly what Aotema hub uses but with the correction I made I feel it gives me an idea of how far, or fast I can go with 48v12a sla. And also a way to monitor the health of batts.

Any idea on what the effienency rate of the average 3amp 3stage 48v charger?

[Russell]

Ballpark efficiency guess around 80% for the charger which if I remember correctly is what my SLA charger is.

A Watt's-Up meter is a much better choice of course. You don't have to mount it in view if you don't want just in your battery supply line somewhere. You don't even have to carry it along just place it between your charger and battery when recharging.

-R

[ekingsting]

Russell, do you think i should reduce the wattage used by 20% for my future charting to more reflect actual motor consumption?
Upgraded batteries are next on my list so a watt meter wil have to wait - you know, 2 kids (son just started college, ouch), a wife and business is real slow- not much money left for me nowadays. Thank God I have my ebike so I can get away from it all for an hour or two for just 2 or 3 cents.

[Russell]

Yes reducing your killawatt numbers by 20% would get you closer to the actual power your ebike is consuming.

-R

[ekingsting]

Here is the watt usage chart for my last 100 miles adjusted for charger effiencency of 80%. So it appears that overall I am averaging about 20 t0 21 watts per mile at 14 to 15mph average with light pedaling. No pedal assist and aotema uses about 45 watts per mile.

[Kevin]

I'm a newbie to electronics. I have the same motor as you. My battery is 36V 20amps. So how do I calculate how many watts my battery should be able to supply? Do I sound like a moron? Is this really simple algebra?

[Gregory]

ekingsting there are some very cheap ($25) watts up clones on Hobbycity, seems like great value, price of a few cups of coffee.

I'm a newbie to electronics. I have the same motor as you. My battery is 36V 20amps. So how do I calculate how many watts my battery should be able to supply? Do I sound like a moron? Is this really simple algebra?

That depends on battery chemistry - what C rate the battery can discharge at reasonably.
Volts x Amps = Watts

eg If you have cheap 36 V 20 Ah LiFePO4 that can do 2C you can safely draw a max continuous 40Amps (2C x 20Ah).
So you could draw 36V x 40 A = 1440 W.
LiPo can do much higher C rates so supply higher watts.

Remember what a battery can PEAK discharge is very different to what battery, BMS, controller or motor may be able to handle for sustained periods, which is why watt ratings are generally understated by manufacturers. Ping rates his 36V20Ah battery for 800W which looks conservative, but will go easy on the pack (it's rated at only 1C continuous, 2C Peak).
Not sure if there is a rule but I consider Peak is 10sec to 1 minute, burst is 1 sec.


Volts x Amp hours = Watt Hours, which if you know how many Wh you use can estimate run time. You have 720 Wh (less if you run lead acid batteries which sag). If you average 15 Wh per kilometre you might go 48 km.