Why must the battery even be on the bike at all?

General Discussion about electric bicycles.
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Why must the battery even be on the bike at all?

Post by MikeFairbanks » Mar 14 2012 9:28pm

I'm sure I'm not the originator of this thought. If you have a geared hub motor plus controller on the bike, but have the battery in one of your backpack pockets with a telephone-style cord (spiral) to the controller, you could have a very light ebike.

Think it would work?

I do.
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Re: Why must the battery even be on the bike at all?

Post by amberwolf » Mar 14 2012 9:41pm

Been done a lot; various ES threads and builds show the benefits and problems of the approach. But it only makes the bike lighter when you are not on it riding. Plus it puts all the battery weight higher on the bike, and towards the rear. Then the backpack with weight swings back and forth on your back at a different phase than you do if you are pedallng or if the bike sways because of bumps or steering, et.c

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Re: Why must the battery even be on the bike at all?

Post by biohazardman » Mar 14 2012 9:52pm

Many have had or have batteries in backpacks. I use this methods for longer trips, 15+ miles, although I would not think of running with all my batteries in the backpack as it would weigh 15-20 lbs which is a bit much in my book. Half that weight seems to work well for me so I can double my range that way when I have the need. New pack soon to be built will weigh 16-18 pounds so I will rig it up in a trailer with the rest of my long distance, 75 mile, gear. I just use the 12ga noodle wire and Andersons for hook up. When I get off of the bike the Andersons disconnect as I pull on them when dismounting. The enclosure is built to take the impact if or should I say when I fall as it's been tested already. :shock:

Image
Last edited by biohazardman on Mar 14 2012 10:31pm, edited 1 time in total.
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Re: Why must the battery even be on the bike at all?

Post by ohzee » Mar 14 2012 9:52pm

IMO guys in school who are used to carrying back packs full of books would think a battery there is a good idea.

Being older I know Id rather enjoy the mobility of having the battery anywhere but on my body.

It does seem like a good idea in some situations , but for the me it seems like to much work.

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Re: Why must the battery even be on the bike at all?

Post by mvly » Mar 14 2012 10:13pm

I use to have battery in my backpack and after a few minutes ride, i was all tired and sore on my back. Now every battery goes on the bike.

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Re: Why must the battery even be on the bike at all?

Post by MadRhino » Mar 14 2012 10:27pm

If I follow your logic, if I carry my bike on my back, it weights nothing. :wink:

Your battery on your back only changes where the weight is, and not for the better IMO.

As a mountain rider, I abandoned the use of any back pack long ago, would it weight only 3 pounds. A rider is not in full control of his balance in a crash if he is wearing a back pack. I can't count how many times I saved my bones in a crash, with balance and agility.
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Re: Why must the battery even be on the bike at all?

Post by def215 » Mar 14 2012 10:32pm

ohzee wrote:IMO guys in school who are used to carrying back packs full of books would think a battery there is a good idea.
exactly why i opted for a backpack battery. :)
Image

my pack is about 10lbs, and long with my books, its not too bad. also, i did it for charging purposes because bikes arent allowed in the buildings at my school. all i need to do is find a receptacle and plug in for charging. :mrgreen:
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Re: Why must the battery even be on the bike at all?

Post by GrayKard » Mar 14 2012 10:33pm

That would be a good excuse to upgrade from SLA right? :D

I would recommend 500 watt hours as about all you want in there but it's possible to do more once you get used to the weight. A good fitting backpack that will hug your back and not shift is essential.

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Re: Why must the battery even be on the bike at all?

Post by Dauntless » Mar 15 2012 2:08am

Or then there's always the bendy battery.

http://news.discovery.com/tech/bendy-ba ... 20208.html
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Re: Why must the battery even be on the bike at all?

Post by LegendLength » Mar 15 2012 2:21am

You feel the weight on your muscles when carrying it whereas on the bike it carries it for you.

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Re: Why must the battery even be on the bike at all?

Post by neptronix » Mar 15 2012 2:27am

def215 wrote:Image
Looks like something they'd call the bomb squad on, hehe.

The higher up the weight, and the more weight, the tippier the handling gets. A backpack battery is good in some unique situations, but having the battery weight in the middle of the frame triangle ( well, if you have triangle space! ) is really the best place, IMHO. Feels very natural and balanced.
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Re: Why must the battery even be on the bike at all?

Post by Sacman » Mar 15 2012 2:43am

Lol... I got asked by police (with canine unit) to open my backpack full of LiFePO4 batteries on a commuter train before.

Everyone's eyes grew wide (thinking BOMB :shock: :shock: :shock: ) when I pulled out the packs and mess of wires. Fortunately my battery packs were actually labeled "Battery" so I was able to explain it easy enough. :mrgreen:

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Re: Why must the battery even be on the bike at all?

Post by dogman dan » Mar 15 2012 7:12am

That was a close one.

Backpack carry is fine for typical street riding, but not so good on the trails as said above.

I used to ski with a backpack all the time, even on the lifts. It was much harder to controll your balance, but could be tolerated once your skiing skill level got high enough. The deal was that I had to be able to ski with a 25 pound pack in order to have every thing I could need in an emergency when skiing in the wilderness. Out in the backcountry, only an idiot skied without enough gear to spend the night in a snowhole. It took a ton of practice to ski well with a pack.

Anyway, you could get used to it, but you weren't going to go slashing the moguls on the double blacks. The key thing was the right choice of backpack, and loading it to have the most weight possible down on your hips. Packs have really developed since the bad old days in the 70's. But you still can get junk backpacks designed only for students to carry books.

If you must carry some battery in a pack, spend a significant amount for a good one, designed for mouintaneers. Not a students book bag from walmart.

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Re: Why must the battery even be on the bike at all?

Post by lester12483 » Mar 15 2012 3:38pm

We tried the battery in the backpack and it works well for a light 36v 10ah pack. Anything heavier than that hurts your back.
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Re: Why must the battery even be on the bike at all?

Post by dogman dan » Mar 15 2012 3:53pm

It would with a cheap book bag. If you are serious about carrying in a backpack, do get a quality pack. A pack made for skiing or ice climbing is very different from packs made for day hikes.

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Re: Why must the battery even be on the bike at all?

Post by BATFINK » Mar 15 2012 5:41pm

I've got 2 of these rucksacks, the people's delete version and the megalopolis and both are solid and really comfortable with special straps to reinforce, I could easily carry 10kg in it and it wouldn't bother me.

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Re: Why must the battery even be on the bike at all?

Post by Phoebus » Mar 15 2012 6:07pm

I use a backpack battery for my trail riding. With a very firmly attached hard shell backpack, it doesn't move. With the battery under ~12lbs or so, I don't much notice it. Am rather happy with this setup, but will likely explore alternative mount options so that I can better compare.

I use this backpack. It protects the battery very well - have had many falls with no damage done to my LiFePO4 brick. This backpack also provides spine protection; it should make it less likely that the battery will snap my spine during a crash.

With the waist strap added, and the shoulder straps fastened tightly, the weight is distributed quite well and is comfortable.

http://www.boblbee.com/us/artiklar/kate ... k=219&acc=

Am also looking to swap over to NMC and shave a few lbs. Obviously LiPo in a backpack is a very bad idea.

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Re: Why must the battery even be on the bike at all?

Post by motorino magnet » Mar 15 2012 6:46pm

Sacman wrote:Lol... I got asked by police (with canine unit) to open my backpack full of LiFePO4 batteries on a commuter train before.

Everyone's eyes grew wide (thinking BOMB :shock: :shock: :shock: ) when I pulled out the packs and mess of wires. Fortunately my battery packs were actually labeled "Battery" so I was able to explain it easy enough. :mrgreen:

sad world we live-in....

you are looking like bomber because you have batteries in your backpack...that power your green e bike...


we are flocked as a people and a nation.

the" terrorists" won

who were the terrorists anyways...????

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Re: Why must the battery even be on the bike at all?

Post by John in CR » Mar 15 2012 6:56pm

While it may be fine for someone with a long commute, we found backpack batteries to really suck. Being tied to the bike and having to plug and unplug at multiple errand stops made it quite inconvenient. Plus battery mains should be as short as possible. My son and I still occasionally use a backpack battery, but just to carry extra capacity for especially long rides.

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Re: Why must the battery even be on the bike at all?

Post by rojitor » Mar 15 2012 7:08pm


I guess all of you remember the ego kits, they use backpacks.
I did it twice so far and i didn't like it much because it was a heavy lifepo4 nevertheless i think in some cases a light battery is ok on the back.

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Re: Why must the battery even be on the bike at all?

Post by GrayKard » Mar 15 2012 7:13pm

John in CR wrote:While it may be fine for someone with a long commute, we found backpack batteries to really suck. Being tied to the bike and having to plug and unplug at multiple errand stops made it quite inconvenient. Plus battery mains should be as short as possible. My son and I still occasionally use a backpack battery, but just to carry extra capacity for especially long rides.
2 more good reasons against backpacking it. It is quite annoying on multiple stops having to mess with wires both getting on and off. I did run pretty thick wires but the run is still way longer then it should be. If I was running high power I would probably be having problems with that.

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Re: Why must the battery even be on the bike at all?

Post by crossbreak » Mar 15 2012 7:24pm

I tried 36V and 10ah lipo. 15ah are also ok.

If you don't go further than 30km this will be ok for you.
The video is very promising. I you dont got for more than one kilowatt, everything is right :D

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Re: Why must the battery even be on the bike at all?

Post by Beachcruzer » Mar 16 2012 12:16am

I commuted for years on a road bike with anywhere from 10-20 pounds of stuff in a backpack. I don't think it affects handling that much. Remember the weight is on you; you can shift it just as you shift your body weight. This setup has advantages, especially in the stealth and don't-get-your-batteries-stolen categories. I prefer my batteries on the bike, but for some applications (smallish pack, road riding, lots of stops and parking the bike away from home or office) a backpack might be better.

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Re: Why must the battery even be on the bike at all?

Post by John in CR » Mar 16 2012 2:11am

The backpack weight is no big deal even for me, one of the least in shape guys on the forum. My issue is connecting with a wire long enough to conveniently get on and off the bike, but short enough to avoid getting entangled in anything. Imagine the fireworks potential of battery mains entangled in your wheel. :shock:

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Re: Why must the battery even be on the bike at all?

Post by Phoebus » Mar 16 2012 2:44am

I use a Dean connector from my battery to controller. This allows the cables to disconnect without placing any stress on the controller and battery elements.

The cable from my battery protrudes about 5" from the backpack. The cable from my controller, mounted on the top tube, is 36". I find this to be sufficiently long to permit me a very large range of motion without leading to inadvertent disconnects. The cable does still become disconnected - usually a result of brushing bushes. When this happens, the 36" controller cable has, thus far, dangled without incident until I grab it up and reconnect. Because my battery's cable is so short, only 5" protruding, I feel that my downside risks are somewhat managed.

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