Please check my math

[dougnutz]

So according to my CA I have used 355AH in about 900 miles. This got me thinking, how much does that cost. I know it's cheap, but I am curious...

If 355 ah used at about 48V = 17040 Watt hours
and 1kwh on my electic bill is $.10
then
17kwh= $1.70 ?? is that right? it seems too low

I know there is some percentage of loss charging the battery so if the battery has output 17kwh then it has taken more than that to charge it. I have no idea how much loss the charger has.

So I have two questions. Is my math correct? If not please set me straight.

Does anyone know how to calculate the effenciency of a a battery charger? Even an aproximation would be fine.

 

[icecube57]

Sounds right to me.

 

[Ykick]

So according to my CA I have used 355AH in about 900 miles. This got me thinking, how much does that cost. I know it's cheap, but I am curious...

If 355 ah used at about 48V = 17040 Watt hours
and 1kwh on my electic bill is $.10
then
17kwh= $1.70 ?? is that right? it seems too low

I know there is some percentage of loss charging the battery so if the battery has output 17kwh then it has taken more than that to charge it. I have no idea how much loss the charger has.

So I have two questions. Is my math correct? If not please set me straight.

Does anyone know how to calculate the effenciency of a a battery charger? Even an aproximation would be fine.

Pretty close to kwh consumed IMO. $.10 kwh seems low as NYC is actually closer to $.30kwh due to their billing of supply, delivery, taxes, priviledge of being their customer, etc.

I'll dig out the Kill-a-Watt meter again and check what the Meanwell is pulling from my outlet. I did it months' ago and don't quote me but 'think it was only about/roughly 20% more than using the bike consumption measurement? But since you're thinking along these lines and I would love to bitch about the high cost of electricity in my area(s), I'll gather and post some numbers from my charging outlet this week.

 

[dogman dan]

I found my 48v 15 ah pingbattery completely discharged will take just under 1 kwh of 110 v to charge it. So a close enough to call it 15 cents a charge. And close enough to call it a penny an ah charged. My E rate is closer to 15 cents a kwh.


Since I don't always discharge the thing all the way, a dime a ride is pretty close. 20 cents of power gets me to work and back, 30 miles round trip. Even a moped would take a dollar to go 30 miles.

Justin tracked his power used at the CA across canada. Not counting the losses in the charger, but he came up with about 5 bucks to cross the continent. I suppose that in reality, he may have used 7 bucks counting the charger losses. Those that harp that pedal bikes are the most efficient transport, try pedaling across canada on 7 bucks of food.

 

[dougnutz]

I live in Wa and electricity is super cheap here due to the abundance of hydro power from damns. There are two basic rates on the bill peek (.10) and off peek (.08) plus a bunch of supplemental fee's that drive it up about another cent. I just took .10 to make the math easy

I think I can get a rough idea of how much power the charger is using by looking at the current draw (with an inductive amp probe) and then timming how long it takes to charge the battery. If the current draw is stable (I have no idea if it is) then I should be able to get an aproximation of how much power was used.

But even if the charger wastes 50% of the power it's still super cheap. 900 miles at 170 cents= .18 cents per mile or about 1 cent for 5 miles.

Truely this makes me smile

 

[SamTexas]

If 355 ah used at about 48V = 17040 Watt hours
and 1kwh on my electic bill is $.10
then
17kwh= $1.70 ?? is that right? it seems too low

Nothing wrong with the calculation. Charging efficiency is around 80%, so 17kwh/0.8 is 21kwh on the electric bill. For a REAL (legal) electric bicyle, the electricity (fuel) cost is truly too insignificant to worry about. The real operating cost is in battery degradation.

Edit: miscalculation

 

[dogman dan]

Right. I calculate my 30 mile round trip at three bucks. 20 cents for the electricity, and about a buck per cycle for the battery if you get 500. 50 cents per cycle if you get 1000.

FWIW bike costs vary widely. Cheap wallbikes need replacement at 3-4 thousand miles or less. You literally wear out the frame. By the second thou, it gets really rubbery. But a 1000 dollar bike may go 20,000 miles. Tires become a suprisingly big expense over 10,000 miles. I tend to damage em before the tread actually wears out.

We've had huge rates for most of my life thanks to nuklar power. Thank god the power plant is way out in AZ. Upwind, but at least we have time to bug out

 

[dougnutz]

Nothing wrong with the calculation. Charging efficiency is around 80%, so 355/0.8 is 444 kwh on the electric bill. For a REAL (legal) electric bicyle, the electricity (fuel) cost is truly too insignificant to worry about. The real operating cost is in battery degradation.

Ya I was only trying to figure out "fuel" costs. True operating cost will be much harder to estimate but I'll give it a try. as you mentioned the battery is probably the fastest wearing item since it will probably only last me two years. The bike itself wears out, as does riding gear, lights, tires, tubes, etc, etc. In the past I have spent about $120 bucks a year maintaining my bike and gear. The electric bike is new to me and carries a few added expenses but most of them should be one time expenses. Such as the hub motor. While it's not truely a one time expense they seem to last many years.

It seems like the bike and electric parts could be depreciated over 5 years and the battery over 2 years to get an estimate. If my bike and kit (sans battery) should last 5 years (total guess)
Thats $700/5 = $140 per year.
The battery was about $650 and should be good for about 2 years ( another guess)
Which makes the battery cost $325 per year
now add electricity cost $7.50
Add basic maintenance cost and gear replacement $120 per year for a grand total of $592.50 per year for "operating expense"


I commute about 16 miles a day 5 days a week 50 weeks a year (4000 miles/year)this brings my average cost to just under $.15 a mile (592.50/4000). Compared to a car which I believe the average for a car is closer to $.70 per mile these days. Not counting the purchase price and payment.

The bigest factor here is the life of the battery followed by the life of the bike and kit. The Kit will probably last longer than 5 years but I wouldn't be surprised to need to replace the battery after two years.

still $600 per year compared to $2800 (plus car payment) still makes me smile.

Oh and I didn't subtract the gym membership that I don't need. Or the health benifits, etc, etc...

 

[Ykick]

Cost of energy is so negligeable it's hardly worth the trouble. But, it's never a bad idea to know what somebody is charging you for energy and for that you need to know how much you used.

Turnigy power meter performing DC honors and the Kill-a-Watt taking care of AC supply side I started charging my 12S2P Flightmax pack.

peak DC output - 320W, peak AC input - 372W for about 14% loss.

by the end of charge cycle I recorded:

DC .279kwh, AC .320kwh for about 13% loss.

Basically, safe to add 15% to what you see going into your battery. My feeble memory rounded it up to 20% but I tend to estimate "worst cases" in order to achieve widest margin of range.

 

[SamTexas]

I commute about 16 miles a day 5 days a week 50 weeks a year (4000 miles/year)this brings my average cost to just under $.15 a mile (592.50/4000). Compared to a car which I believe the average for a car is closer to $.70 per mile these days. Not counting the purchase price and payment.

The ebike operating cost looks reasonable (just a little on the high side). The $.70/mi for the average car is also right, but that INCLUDES EVERYTHING (purchase, depreciation, fuel, insurance....)

 

[John in CR]

My high power bikes are comparatively real electricity hogs at 50wh/mile or more, but even only 60 or 70% efficient charging results in a ridiculously low electricity cost. Until 5-10 year service lives for our battery packs become a proven reality, the battery cost is the primary cost of operation. Sure the electricity cost is fun to brag about to the unknowing, and is a great ebike factoid to promote our cause, but we need factor in amortization of our batteries to arrive at true cost.

 

[dogman dan]

His math comes out just about what I figured on mine. .15 per mile for the ebike. Interestingly, a 150 cc cheap chinese scooter came up about the same. Cars can be cheaper than 70 cents, but you have to buy lucky on the used car market to do it, and not buy insurance for the car other than liability. My 1 ton truck is a full dollar a mile, even though it cost only $3500 to purchase. 1 tire for the beast is $250.

Riding the bus is only about 7 cents a mile, but the same 15 mile trip takes 90 min. While the ebike takes 50 min. Miss the bus, and you wait a full hour to catch the next one. Real convenient.

Re the batteries, I now have 200 cycles on my year old pingbattery, and my three year old ping has an estimated 600. I think 800 cycles is a pretty reasonable expectation for a commuter to base a calculation on. So 5.4 cents per mile if your battery lasts three years, 750 15 mile cycles. Not too bad compared to the cost of a car engine.

I like to look at it another way. If I drive the car, it's 15 bucks out of my pocket, and if I ride it's only 3. Ride 3 days and I'm 36 bucks closer that week to the point where the ebike ride is nearly free (to the weekly budget), just like a car that is paid off. Carry that further though. every day I ride the ebike is one day longer before I have to bite the bullet and buy that expensive repair for the car, or even replace it. In a way, that doubles the daily take for riding to 24 bucks a day to ride the bike. Not bad, 12 bucks an hour to do what I love to do anyway.

On the other hand, I'd have to ride an awful lot to pay in full for the ebike addiction. I have 6 ebikes up and running at the moment. 8) But even so, it's cheap entertainment compared to hot air balloons, skiing, or weekends at the lake. What I really love is that the weekends are no longer spent bolting new parts to the car constantly.

 

[SamTexas]

What I really love is that the weekends are no longer spent bolting new parts to the car constantly.

Instead that time is now spent on checking individual cells' voltage, on cells' rebalancing, on electrical connections' inspection, on fretting over batteries life, remaining capacity... That's just a wild guess on my part. How far off am I, dogman?

 

[dogman dan]

About as far off as china dude. :lol: But I do spend hours and hours riding ebikes, never worrying much about my batteries other than turning for home in time to grab a different battery before overdischarging. Then let a motor cool off while I get a drink, and roar out the door for more riding on the nearby dirt singletracks. By sunday though, I may be fiddling endlessly removing hundreds of mesquite thorns from tires, straightening that bent wheel, or just recovering from having way too much fun for a 53 year old body.

Yeah I spend some time fiddling with batteries. I must be worrying about my pings that I commute daily on at least annually. Once a year or so I'll actually put the CA on the bike and see how they are doing. Or I'll ride with the CA because I want maximum range on a day I plan to go 70 miles or so.

I spend a lot of time on the lipo. It's amazing how time consuming lipo gets when a Hobby King box arrives every month. Each shipment requires a few cycles where your watch the voltages and balance till you are satisfied with their performance. Then an afternoon of pairing them in 10 ah paralell blocks if desired. After that, it's ride- charge , ride- charge, Since I charge with lipo chargers, I'll go ahead an spend an extra 30 seconds to balance charge em about monthly.

I do have a cellog 8, and do spend a few minuites scrutinizing every lipo pack I have occasionally. On race day!

I will admit, I do spend a lot of weekend time on bikes. I now have two commuters, a trike, a beach cruiser, a dirt bike, and a racing bike in running order ready to ride. That took time. For a few years vendors were sending me free motors for destruction testing in hot climate. That took time. In all that fiddling around though, I never remember one time that I had to repair an ebike weekly, but I sure have had that experience with cars. Building an Ebike from scratch or even repairing a toasted motor is a snap compared to an engine rebuild, or even a simple CV replacement.

 

[Ykick]

For about a year, I've commuted 6 days per week using Hobby King Lipo and my routine is that I come home, disconnect plug to controller, connect Meanwell with inline power meter to the battery pack, check resting voltage and if it total voltage looks somewhat normal (and no LVC alarms triggered during the ride) I start charging. Hour or two later my pack is ready for another trip. My connections take all of 30 seconds requiring NO parallel/series swapping, etc.

If something doesn't look right regarding resting pack voltage of course I'll dig a little deeper and check individual cells to make sure everything's reasonably balanced but that's an exception rather than the norm.

And yes, I spend some time paying attention to my Lipo bricks but no more than checking spokes, tire pressure and/or making a brake adjustment. It's like any other critical component - 'simply embrace how it functions while educating my mind...

 

[dogman dan]

Here's a short vid for Sam. It shows how I do shallow discharges when I am fiddling around with new lipo, breaking it in.

http://www.youtube.com/watch?v=yOY8tvj9i3E

I sure hate all that time I spend fiddling around with my lipo.

 

[SamTexas]

Here's a short vid for Sam. It shows how I do shallow discharges when I am fiddling around with new lipo, breaking it in.

http://www.youtube.com/watch?v=yOY8tvj9i3E

I sure hate all that time I spend fiddling around with my lipo.

Thanks dogman. I have been building small packs of different chemistry batteries (Lithium 18650, NiCd and NiMh). I tested them with light bulbs most of the time, and sometime with my scooter. Without a doubt, Lithium 18650 is the most rewarding to work with because of its higher energy density and higher discharge rate. I'm not brave nor patient nor careful enough to play with LiPo.

 

[Zenid]

Does anyone know how to calculate the effenciency of a a battery charger? Even an aproximation would be fine.

Get one of those plug-in adaptor/energy meters, like this:
http://www.maplin.co.uk/plug-in-power-energy-and-cosub2-sub-meter-286534
That way you can measure exactly how much power your charger has used for a single charge operation. That will give you a more realistic measure of what it's costing you.