# Backpack battery?



## Telewacker (Oct 5, 2005)

I'm thinking of converting my DH bike but there is no place to mount a battery on the frame. I've seen guys build batteries to carry in a backpack with an umbilical cord to connect to the motor but does anyone make a battery suitable for this?


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## fos'l (May 27, 2009)

There are all shapes and sizes of batteries that can be carried in a backpack, and companies that will produce a custom design. I'm not a fan, but batteries and quick-disconnect systems are available. Look at ebikesca, em3ev, Lunacycle and UPP, and others


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## Telewacker (Oct 5, 2005)

fos'l said:


> There are all shapes and sizes of batteries that can be carried in a backpack, and companies that will produce a custom design. I'm not a fan, but batteries and quick-disconnect systems are available. Look at ebikesca, em3ev, Lunacycle and UPP, and others


I found this on ebay. Seems like it might be suitable? 








UPP 52V 20AH Ebike Battery Waterproof PVC Lithium Battery Pack for 1000W 750W | eBay


1X 52V 20AH Lithium Battery with Built-in 30A BMS. Fit for Motor : 48V 500W 750W 1000W Motors ( can't exceed 1000W ). Battery shrink wrap with waterproof glue. Model: D034 PVC style Li-ion E-bike Battery.



www.ebay.com


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## fos'l (May 27, 2009)

Excellent price, and the one battery that I purchased from UPP was good. You might put 13 - 14 pounds in a backpack and ride around for awhile before purchasing.


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## Telewacker (Oct 5, 2005)

fos'l said:


> Excellent price, and the one battery that I purchased from UPP was good. You might put 13 - 14 pounds in a backpack and ride around for awhile before purchasing.


I've ridden with that much weight and more so no worries. It's my only option though as there is simply no place to put a battery on the frame.


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## _CJ (May 1, 2014)

I can't think of a worse place to carry weight, and I still run water bottles on my frame because of it. I'd suggest either building some sort of rack above the rear wheel, hanging it below the downtube, above the top tube, hell even in a handlebar bag, anything but in a backpack. Even better of course would be to just buy a pre-engineered eMTB and quit wasting your time with the e-frankenbike. Maybe even do one of those carbon frames on ebay that come with the Bafang motor and battery, then swap over all the parts from your downhill bike. There's a good Youtube series about doing that by Rob Rides, or something like that. I was tempted to build one like that myself, but the black Friday deal I got last year on a complete bike was just too sweet....and Black Friday is coming around again you know.


.


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## TwoTone (Jul 5, 2011)

Just a warning coming from the rc side of things. RC car racing rules require hard-cased batteries to prevent puncture and the resulting fire.
There is no way in hell I'd carry a softpack battery in a backpack on my body.


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## fos'l (May 27, 2009)

Look at endless sphere; there have been threads that discussed backpacks. You might get ideas about quick-release connectors or whatever.


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## KRob (Jan 13, 2004)

Telewacker said:


> I found this on ebay. Seems like it might be suitable?
> https://www.ebay.com/itm/UPP-52V-20...4-bd44-43c9-b6eb-d6d6022d0a75&redirect=mobile


Hmm. I wonder if this would work as a range extender for my Turbo Levo. Way cheaper than a stock battery for sure and small and easier to fit in a pack. What are the dangers of carrying a battery like this on your body?


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## Telewacker (Oct 5, 2005)

_CJ said:


> I can't think of a worse place to carry weight, and I still run water bottles on my frame because of it. I'd suggest either building some sort of rack above the rear wheel, hanging it below the downtube, above the top tube, hell even in a handlebar bag, anything but in a backpack. Even better of course would be to just buy a pre-engineered eMTB and quit wasting your time with the e-frankenbike. Maybe even do one of those carbon frames on ebay that come with the Bafang motor and battery, then swap over all the parts from your downhill bike. There's a good Youtube series about doing that by Rob Rides, or something like that. I was tempted to build one like that myself, but the black Friday deal I got last year on a complete bike was just too sweet....and Black Friday is coming around again you know.
> 
> 
> .


Couldn't disagree more. It's always better to carry excess weight unsprung. I've been riding with hydration packs for years and on expedition rides I've had over 20lbs including a 3 liter bladder.


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## TwoTone (Jul 5, 2011)

KRob said:


> Hmm. I wonder if this would work as a range extender for my Turbo Levo. Way cheaper than a stock battery for sure and small and easier to fit in a pack. What are the dangers of carrying a battery like this on your body?


You crash and puncture it and it catches fire. Enough of a risk that you won't find a single indoor RC track that will let you run soft-pack batteries.

Just a few examples and these are in buggies with suspension, now imagine 140+ pounds landing on one with a nice rock under it.


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## KRob (Jan 13, 2004)

TwoTone said:


> You crash and puncture it and it catches fire. Enough of a risk that you won't find a single indoor RC track that will let you run soft-pack batteries.
> 
> Just a few examples and these are in buggies with suspension, now imagine 140+ pounds landing on one with a nice rock under it.
> 
> ...


Yeah, that doesn't look good. I'll just have to remember not to crash.


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## _CJ (May 1, 2014)

Telewacker said:


> Couldn't disagree more. It's always better to carry excess weight unsprung. I've been riding with hydration packs for years and on expedition rides I've had over 20lbs including a 3 liter bladder.


FYI, "unsprung" would mean the weight was attached to the lower fork legs or rear triangle, and that's worst case scenario. Your body, the main frame, handlebars, seatpost, etc. is all "sprung weight" (supported by the suspension), which is where you want as much weight as possible. The higher the weight is mounted (including on your back) the worse it is for handling due to it's effect on center of gravity, not to mention the physical benefits of not carrying that weight with your body.


.


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## TwoTone (Jul 5, 2011)

_CJ said:


> FYI, "unsprung" would mean the weight was attached to the lower fork legs or rear triangle, and that's worst case scenario. Your body, the main frame, handlebars, seatpost, etc. is all "sprung weight" (supported by the suspension), which is where you want as much weight as possible. The higher the weight is mounted (including on your back) the worse it is for handling due to it's effect on center of gravity, not to mention the physical benefits of not carrying that weight with your body.
> 
> 
> .


🤫


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## Telewacker (Oct 5, 2005)

fos'l said:


> _CJ said:
> 
> 
> > FYI, "unsprung" would mean the weight was attached to the lower fork legs or rear triangle, and that's worst case scenario. Your body, the main frame, handlebars, seatpost, etc. is all "sprung weight" (supported by the suspension), which is where you want as much weight as possible. The higher the weight is mounted (including on your back) the worse it is for handling due to it's effect on center of gravity, not to mention the physical benefits of not carrying that weight with your body.
> ...


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## _CJ (May 1, 2014)

Good luck with that.


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## TwoTone (Jul 5, 2011)

_CJ said:


> Good luck with that.


Don't you love it when someone doesn't understand the concepts or terms they're using, but will go ahead and double down.


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## Telewacker (Oct 5, 2005)

TwoTone said:


> Don't you love it when someone doesn't understand the concepts or terms they're using, but will go ahead and double down.


Typical. I can't seem to avoid at least one of these types on any given thread.


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## TwoTone (Jul 5, 2011)

Telewacker said:


> Typical. I can't seem to avoid at least one of these types on any given thread.


Agreed. So please explain how carrying excess weight on your suspension is better than on the frame?
Just a hint, your belief is pretty much the opposite of any silly experts in motorsports, so I would really love to have the revolutionary theory explained to this pea-brain.
Enlighten away.


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## Telewacker (Oct 5, 2005)

TwoTone said:


> Agreed. So please explain how carrying excess weight on your suspension is better than on the frame?
> Just a hint, your belief is pretty much the opposite of any silly experts in motorsports, so I would really love to have the revolutionary theory explained to this pea-brain.
> Enlighten away.


Well pea brain the whole thrust of this thread was exploring the options of battery placement other than the frame. Because that was NOT an option. There is no place to put a battery on the bicycle. Period. I've seen riders in this case put battery packs in backpacks. My Turbo Levo has a battery in the downtube. My DH bike with it's complicated suspension and shock placement simply doesn't allow mounting a battery anywhere. I can fit a mid drive motor on it and carry the battery in a backpack and since I'm used to carrying a heavy hydration pack it seems like a workable solution for me. I suggest you step off the thread since you have nothing constructive to offer.


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## TwoTone (Jul 5, 2011)

Telewacker said:


> Well pea brain the whole thrust of this thread was exploring the options of battery placement other than the frame. Because that was NOT an option. There is no place to put a battery on the bicycle. Period. I've seen riders in this case put battery packs in backpacks. My Turbo Levo has a battery in the downtube. My DH bike with it's complicated suspension and shock placement simply doesn't allow mounting a battery anywhere. I can fit a mid drive motor on it and carry the battery in a backpack and since I'm used to carrying a heavy hydration pack it seems like a workable solution for me. I suggest you step off the thread since you have nothing constructive to offer.


So you're stepping back from this statement?


Telewacker said:


> Couldn't disagree more. It's always better to carry excess weight *unsprung*. I've been riding with hydration packs for years and on expedition rides I've had over 20lbs including a 3 liter bladder.



I offered constructive info, you just ignored it. You wanted to carry a fire starter in your backpack, I warned others why it's not a great idea.


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## Telewacker (Oct 5, 2005)

TwoTone said:


> So you're stepping back from this statement?
> 
> 
> 
> I offered constructive info, you just ignored it. You wanted to carry a fire starter in your backpack, I warned others why it's not a great idea.


Please show me the mountain biker who's burned up from a battery in a knapsack. I've got all day.


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## fos'l (May 27, 2009)

The major considerations are battery voltage, amp hours, shape and connector. There's at least one individual on endless sphere doing this. Start a thread (or check the ones there) to get started. Of course there will be detractors who say what happens if somebody shoots you in the back with a flaming arrow or whatever. Poppycock.


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## matt4x4 (Dec 21, 2013)

Backpack battery is bad but people do it. Just get a frame with lots of triangle space, or place battery on the top of the top tube, or rear rack, or backpack, or handlebar bags. Triangle is always the best, always.


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## TwoTone (Jul 5, 2011)

Telewacker said:


> Please show me the mountain biker who's burned up from a battery in a knapsack. I've got all day.


You do you man, if you've some facts share them, just cause you've never seen it posted still doesn't change the fact that it can happen. I glad your so confident that you'll never crash, I have and I've landed on my pack.
Try facts less emotion.


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## TwoTone (Jul 5, 2011)

fos'l said:


> The major considerations are battery voltage, amp hours, shape and connector. There's at least one individual on endless sphere doing this. Start a thread (or check the ones there) to get started. Of course there will be detractors who say what happens if somebody shoots you in the back with a flaming arrow or whatever. Poppycock.


Wow great argument. You seem much more knowledgeable about Lipos.


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## fos'l (May 27, 2009)

TwoTone said:


> Wow great argument. You seem much more knowledgeable about Lipos.


The point is that it's being done successfully, and since it's the only viable option, why come up with outlandish reasons not to do it? IMO, go to endless sphere and receive answers to questions from individuals who have actual experience, not contrarians.


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## TwoTone (Jul 5, 2011)

fos'l said:


> Looks like your sense of humor is as lame as your comments. The point is that it's being done successfully, and since it's the only option for the OP why come up with outlandish reasons not to do it.


Your opinion that's its outlandish doesn't make it a fact.
We've been using Lipos in the RC world for a very long time. Lipo fires aren't as uncommon as you think.


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## fos'l (May 27, 2009)

TwoTone said:


> Your opinion that's its outlandish doesn't make it a fact.
> We've been using Lipos in the RC world for a very long time. Lipo fires aren't as uncommon as you think.


The batteries for ebikes, while Lithium-based, are not the more energy dense and fragile "Lipos" employed in the RC world. These batteries, frequently designated "18650" (although they are being supplanted by a larger size), are preferred in almost all systems and much more stable than "Lipos". The end (at least for me).


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## WHALENARD (Feb 21, 2010)

The biggest factor in lipo instability is discharge rate (c-rate), which e-bikes have in stride. 

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