what size (AH) battery should I get for 2x19km commute???

[callagga]

Hi,

I'm about to buy batteries for a 36V 20A brushless geared system (http://www.ebike.biz/bmc.htm) and I'm interested in recommendations for what size / type of batteries to get. The ride I have is 2 x 19km commute (i.e. 38km total in the day). I plan to put reasonably substantial pedal effort in along the way on the flat & use batteries to keep up speed up the hills. I have several hills, but they aren't mountains. The options I'm pondering are:

(a) Battery Type - Lead Acid or "36V 10Ah LiFePO4 Ebike Battery" (latter from http://evpower.com.au/-Lithium-Ion-LiFePO4-Batteries-.html for AUS$399)?
(b) Capacity of battery - mainly a question for the sealed Lead Acid option (as the LiFePO4's are 10AH)? Basically I'm interested in going for the 10Ah LiFePO4's for weight, however if the 10AH isn't going to be enough then I'd consider the SLAs.
(c) Plan to Charge at Work or Not?

Question 1 - What sort of AmpHours (AH) do you think I'd be looking at for a round trip ride? I guess this will indicate whether the 10Ah LiFePO4 option would require a charge at work or not? What setup would you recommend?

Question 2 - If I plan to charge at work (not sure how much the 2nd charger would be though), what setup would you recommend?


Thanks

 

[dogman dan]

I like to use the figure of 1 ah of battery capacity per mile at full throttle. You'll go farther than that for sure, but that figure allows for weight difference, hills, wind, how you pedal, etc. If you are really heavy and the hill really steep, you won't be short that much. Based on that, a 10 ah lifepo4 should do it one way but it will be just a bit tight. A slower than full throttle ride would extend range. However, though it is not as pronounced as with lead batteries, the idea that it is good to discharge the battery at 1c or less and less than 100% depth of discharge still applies to lifepo4. It just lessens the chances of having problems and increases the chances of extremely long cycle life if you get more battery. A 15 ah lifpo4 would be good, a 20 ah better. In 36v even the 20 ah is very small and light, easy to carry. If you have budget issues, maybe buy a 10 ah, and then get another later to paralell connect it. The extra range of the 20 ah may allow you to go both ways without a charge if you have an issue with charging at work, like you leave early for some reason. One nice thing about a pair or paralell packs is you get to charge twice as fast, but a single pack means one less charger to mess with.

Sla's and hills don't mix well in my opinion, and big enough ones to reliably go 19 km are pretty heavy. I don't think 12 ah sla's would be big enough. You would discharge them 100% and soon range would drop a lot. Price per trip is better if you get a lifepo4 that goes 1000 cycles or more. We'll see if that really happens, I'm at about 300 cycles now myself. Though you don't mention it, nicads or nimh are also much better options than sla's.

 

[icecube57]

On a brushless geared on a 20 amp controller you should easily get two maybe three miles per AH if u hold the throttle just right. If i can get 35 miles out of 10 Ah going 20 to 25mph. A high quality 10Ah should do it or a 15AH will be a a wiser choice ...then you will have room to expand for a power hungry motor.

 

[callagga]

thanks icecube57, so at 2 to 3 miles per AH this would give me (with the lighter LiFePO4 10AH battery) from 32km to 48km. So there's a good change I can make the round trip if I'm careful, and then the fallback is to charge at work.

I've just been putting weights into a bag to compare the difference between the 4.2kg LiFePO4 and the 11kg SLA .... the difference is HUGE isn't it. I think I try to pay the extra for the LiFePO4 perhaps...

I'm guessing with the 10AH LiFePO4 if I wanted to in the future I could put another one in parallel to get 20AH worth?

 

[Dan K]

On a brushless geared on a 20 amp controller you should easily get two maybe three miles per AH if u hold the throttle just right. If i can get 35 miles out of 10 Ah going 20 to 25mph. A high quality 10Ah should do it or a 15AH will be a a wiser choice ...then you will have room to expand for a power hungry motor.

Can you describe the setup you're using to get 35 miles @ 20-25MPH from a 10Ah battery? 10Ah @ what voltage? How hard are you pedaling? Hills? What geared motor? Bike setup, tire size, PSI?

Thanks,

Dan

 

[Gregory]

Just be aware if/when you buy from Brett (solarbbq) who you linked to for the motor that there is a thread here on ES about recent issues with orders taking many, many months to be finalised.
I like him, I have dealt with him in the past with NO problem and I'm sure he'll manage to get back on top of things. His new website is looking good. Good luck

As for battery I'd forget SLA and with the weight you save maybe you could look at lifepo4 @ 48V instead?
If you don't think you can quite do your commute on 36V 10Ah, maybe consider that going from 36V (360Wh) to 48V (480Wh) with 10Ah cells is a 33% increase in Wh for only 4 extra cells, and you'll never regret the extra power.
A Watt's up/Cycle Analyst will be crucial to keep an eye on how much you're burning through.

 

[callagga]

ummm, I was trying to limit options I had to think about and its been 36V in my head for a while I'm not sure I've seen a good deal on 10AH 48V LiFePO4s (compared to the 36V). When I looked at the torque curves however I think I convinced myself that I only needed the 36V re hitting the speeds I was interested in.

Can you run it past me again why I'd get more distance with the same AH rating battery, but a 48V version instead of a 36V? I'm concerned (as you hinted at) I may be more likely to waste the extra power and get less distance no?

 

[Gregory]

Ha, sorry callagga that's the problem with opinions, everyone has one.

If your bike averages say 17Wh/km (what Justin averaged across Canada?) then with all other factors (particularly top speed) being equal (with the 48V you'd have to limit yourself to maybe 75% throttle for the comparison) you could expect 21km from 36 V 10Ah 360 Wh battery or 28km from the 480Wh 48V. But as you say it's human nature to just give the throttle that extra twist if you have the extra power on tap.

So my opinion is
a) LiFePO4
b) for lead you'll want to limit current draw to 2C and under 80%DOD to get 500 cycles so that's maybe 36V 18Ah batteries (19kg) just to get one way. LifePO4 you still want that extra headroom so 10Ah is still pushing it.
c) SLA you have to recharge at work, LiFePO4 will depend on your budget or size constraints.

PS I hear Rod at EV Power is excellent to deal with and firmly believe cost shouldn't be the be all and end all. But have you tried sending Headway an email direct to see if they can cut out the middle man for batteries?

 

[morph999]

DON'T BUY FROM EBIKE.BIZ....READ THE COMPLAINTS...YOU WON'T GET YOUR STUFF FOR 12 MONTHS...OR MAYBE NOT AT ALL !!!!

 

[morph999]

have you thought about this 36v 18ah from ebikes.ca ?

http://ebikes.ca/store/photos/B3618MHR2-NX.jpg

Keep in mind that pingbattery is cheap but add about $150 for shipping and handling. If you get a 36v NIMH, you could always add a small 12v lead acid to make it 48v like what Dogman did.

19km is about 10 miles. Right? You could probably get by on a 48v 12ah NIMH. The 36v18ah NIMH would definitely be enough, though if you wanted to be on the safe side.

 

[icecube57]

On the trail that i ride. Its mostly level. If i feather the throttle just right i can maintain 20 to 25 mph consuming 5A to 10A peak. I dont even have to pedal cause i cant really pedal along. I do this on A Golden Motor at 48v and my cheap duck tape pack. Many trips i stay under 18wh a mile. Oh did i mention Im 290lbs. WOT yeah i consume about 1AH a mile.Especially if im commuting to work. But by backing off a lot you wil be surprise how fast you can go with so fewer amps. Just because i have a 30A controller doesnt mean i have to use it to it full potential.

 

[icecube57]

Get a Watts Up or Cycle Analyst. You may initially start laying on the throttle super heavy and draining the pack fast. The more you ride the more EV conscience you get and you begin to start learning how to hyper mile and squeeze every bit out. I may have been miss leading but I am not bloating my numbers. Its based on recreation riding where time and real world terrain arent factor. Even terrain no stop and go just blissful riding. Its fun to go fast and WOT yes it will be 0.75 to 1AH a mile if you have some where to be. If you change your route to more level roads and side streets it may be longer but you will be to keep your motor in that butter zone speed where the current falls to nothing and it will be more efficent luggin the motor at lower speeds uses alot of power.

 

[dogman dan]

When I talk range I talk wide open throtte, maybe uphill, maybe with the wind in your face. I ride in the real world ,by that I mean I don't ride only in good weather. It's a fairly long distance, 29 miles a day, so I have little interest in riding anything less than 20 mph or more if not uphill. It takes me an hour and a few minuites longer than a car ride, so I don't want to ride slow and have it take longer. It's very fun to play the how far can my battery take me game, but honestly, If I want to pedal that hard, I'll take my vintage roadbike out, after all, it's 45 pounds lighter than my ebike. Range, unlimited.

Seriously folks, a guy asks how much battery do I need. The only answer to give him is what it may take on the worst days. He's already heard how far can you go with the wind at your back , downhill, at 5 mph from many of the motor vendors. Go ahead with your calculations for the smallest possible battery, and get back with me in a few years and see who's battery lasted. The one that was 100% discharged every ride, or the one with a 70% discharge every ride? When I bought my 20 ah battery, I thought I had a pretty big reserve. A bit colder in the winter, and a seasonal wind direction change, and pretty soon I was barely making it. I had to get a more efficient motor to fix the problem.

I just don't see how telling a new member how efficient you are helps him. Sure it's nice to know what may be possible, but he needs to know the real deal on how much it could take too. When I bought my first motor, just about one year ago today, I actually thought I could ride 20 miles on the sla's in the kit. :lol:

Btw morph, I did not series connect two different chemistries and I never will. Paralell connecting two different chemistries is another thing. My 48v pack is two 24v nicad packs from ebikes ca. It got a bit expensive, but I did it so I'd have a battery with shelf life, and be able to run it at 24v on one bike, and 48v on others.

 

[biohazardman]

Hi,

I'm about to buy batteries for a 36V 20A brushless geared system (http://www.ebike.biz/bmc.htm) and I'm interested in recommendations for what size / type of batteries to get. The ride I have is 2 x 19km commute (i.e. 38km total in the day). I plan to put reasonably substantial pedal effort in along the way on the flat & use batteries to keep up speed up the hills. I have several hills, but they aren't mountains. The options I'm pondering are:

(a) Battery Type - Lead Acid or "36V 10Ah LiFePO4 Ebike Battery" (latter from http://evpower.com.au/-Lithium-Ion-LiFePO4-Batteries-.html for AUS$399)?
(b) Capacity of battery - mainly a question for the sealed Lead Acid option (as the LiFePO4's are 10AH)? Basically I'm interested in going for the 10Ah LiFePO4's for weight, however if the 10AH isn't going to be enough then I'd consider the SLAs.
(c) Plan to Charge at Work or Not?

Question 1 - What sort of AmpHours (AH) do you think I'd be looking at for a round trip ride? I guess this will indicate whether the 10Ah LiFePO4 option would require a charge at work or not? What setup would you recommend?


Question 2 - If I plan to charge at work (not sure how much the 2nd charger would be though), what setup would you recommend?


Thanks

I run 10ah of the Lifepo4 by Foxpower on a GM 36v motor. I have run this bike at both 36 and 48V. Total vehicle weight loaded with me 260lb I ran 18-20 mph with help on the hill on 36 volts and managed 18-20miles per charge pedaling maybe 10% of the time. About the same or a mile at most less on 48v at 20-22mph and I help less on the hills although I don't have to help at all. Some of the Packs will not give you the amperage needed to run your bike with a 10ah others will. Check the rated draw for what you need not the max, as you cannot run them there for any length of time. Take the time to research your choices closely it's an important decision. I have a123s for the next build way more amperage smaller and lighter than what I run now.

 

[Gordon]

I bought a 15ah lifepo battery for 4 mile round trip commute. Overkill but I'm glad I did. I don't have to mess with charging at work. I don't even have to charge every day. If I need to go out of my way and run a few errands on the way home I've got the reserve.

My point is; Go ahead and calculate how much battery you need and then add about 25% to it. In the long run you'll be glad you did.

I like Dogman's rounded off estimate of 1ah/mile. It's a good ballpark figure. You can do better with a lot of pedaling but some days you won't want to.

I also agree with everyone about sla batteries. Lot's of extra weight and short lifespan.

 

[Dan K]

One thing I didn't see mentioned, if it was my apologies: charging at work.

Why buy a 2nd charger? You're already going to have an e-bike with stuff everywhere, and probably a bag on a rack, or in the frame, at the very least a large saddle bag for tools, patch kits, co2, etc. Why not just carry the charger? I plan to carry my charger everywhere, and charge at work every day. Of course, with a 35 mile commute I don't have much of a choice, but still...

Also, as it's been pointed out, batteries last longer when not discharged as long. Topping off your batts at work is being kind to the batteries. The charger shouldn't be that big or heavy, I say carry it.

 

[callagga]

have you tried sending Headway an email direct to see if they can cut out the middle man for batteries?

Is that the name of the company Gregory? i.e. "Headway". Are they in Australia? Did a google on Headway and it was obvious. If you have a URL that would be great.

 

[callagga]

About the same or a mile at most less on 48v at 20-22mph

That's interesting. Some people are saying you should get more range with 48V over 36V, but you're showing in reality that's not really the case biohazardman then?

Can anyone clarify this. That is, why do some people suggest you could get more from the same AH rating battery, but a 48V version instead of a 36V? Is it the battery holds effectively more energy (i.e. power = V * I, so current would be the same in the two cases, but voltage is greater)

 

[callagga]

(thanks for all the advice/learnings so far guys)

Can I clarify my understanding re future expansion of a battery. Is it true to so with the 10AH LiFePO4 if I wanted to in the future I could put another one in parallel to get 20AH worth?

 

[Russell]

About the same or a mile at most less on 48v at 20-22mph

That's interesting. Some people are saying you should get more range with 48V over 36V, but you're showing in reality that's not really the case biohazardman then?

Can anyone clarify this. That is, why do some people suggest you could get more from the same AH rating battery, but a 48V version instead of a 36V? Is it the battery holds effectively more energy (i.e. power = V * I, so current would be the same in the two cases, but voltage is greater)

A 48V/10Ah battery stores more energy (480Wh) compared to a 36V/10Ah battery (360Wh). If you go the same speed with each pack you should consume roughly the same Wh/mi and go further on the 48V pack. However if for example you ride at 25 mph with the 48V pack just cuz you can instead of the 20 mph you rode with the 36V pack then you'd probably find you'd have less range with the 48V pack simply becasue it takes a LOT more energy per mile to go that few miles per hour faster.

-R

 

[Russell]

Is it true to so with the 10AH LiFePO4 if I wanted to in the future I could put another one in parallel to get 20AH worth?

Sure just add a schottky diode to the output of each to protect each pack from the other. Search the forum for "schottky diode" for more info.

-R

 

[dogman dan]

Back to chargers, they like to go poof. So unless you like waiting to have another shipped, a 2nd charger is a good idea. I am able to keep my 4 amp one at work for a faster recharge, and use one of two that I keep at home at night. I had a couple fall apart from carrying, so if you do carry, don't put em in a basket or whatever to bounce around. Your controller is built a lot sturdier so it doesn't fall apart, but on chargers, I have had shorts happen because parts moved around in there. In that case there was a little circuit board in there that stood on flimsy wires above the main board. A bit of shaking and it got moved to where the supporting wires shorted out on the board. The other one had both the in and out cords break where the wires were soldered. I've learned not to trust these cheap chargers much, so I keep spares around.

 

[icecube57]

My 6 mile commute take 5-6AH out of my battery. I can use almost 17AH out of my battery. Thats three times what i need if i want to drain it to empty. My charger weighs less than a pound. I always carry a bookbag whenever I ride with tools and spare connectors even charger. I dont need to charge at work but i do anyway. Nothing like having a freshly charged pack when hopping on your bike. As long as its not big bulky and heavy carry it with you.

 

[dogman dan]

Yet another real world report in the ballpark of one amp hour per mile. I think it's a pretty realisitic number to use for 20-25 mph travel on most direct drive ebikes. Coasting more can of course ,really extend range on gearmotors.

 

[callagga]

Coasting more can of course ,really extend range on gearmotors.

based on the way you wrote this dogman it seems to indicate there a general consensus that for someone doing lots of "coasting" (freewheeling) that the geared brushless hub motors stand out for this?