Battery Location. Your Opinion Matters!

rlewis

100 µW
Joined
Dec 21, 2018
Messages
8
Traditional downtube mount or seatpost tube mount?
 

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You're already in the right place for the battery, between the tires. I think the flat one may be marginally better due to slightly lower CoG.

Personally, I would go with the one that was the most convenient for ingress/egress
 
cal3thousand said:
You're already in the right place for the battery, between the tires. I think the flat one may be marginally better due to slightly lower CoG.

Personally, I would go with the one that was the most convenient for ingress/egress

+1 Lower center of gravity improves the handling a lot. Now correct me if I'm wrong, but in this frame, you can fit 2x battery case of this size (if you need so much power). In that case, I'd mount the lower one first (albight a bit higher on the downtube) and than the second one. And on a sidenote, I'd go for a suspended fork. Aluminium + no fork suspension + small tyres = bumpy ride, even with that seat tube suspension.
 
Thank you for your responses so far! I get the low center of gravity as a concept, but personally have no practical experience. So I appreciate your insite.

As an engineer, instinctively, I think vertical mount will provide a lower COG. Being that the weight y axis "lands" near the crankset.
 
Thank you for your responses so far! I get the low center of gravity as a concept, but personally have no practical experience. So I appreciate your insite.

As an engineer, instinctively, I think vertical mount will provide a marginally less COG. Being that the weight impact "lands" near the crank set.

From an ascetics perspective thoughts are welcome too.
 
Center of mass matters relative to the ground when at crawling speeds, and relative to the roll axis when underway. Fast motorcycles intentionally locate their mass high up and close to the F/R center of the bike. They change direction more easily that way.

For a cargo bike or a pedal bike, low weight distribution works best. Whether higher or lower works for you depends on your speed and riding style.
 
I like the downtube mount because more of the battery's weight rests against the cradle as opposed to the almost vertical position where I would surmise either the locking pin or the base of the cradle bears most of the weight.

I will admit not being familiar with the cradle for that particular battery so all of the above could be flawed.
 
Your bike looks like the one I past today, I was clocking in pretty fast to show him how fast DIY'ers go, his motor did not even protrude past the largest freewheel gear. I twisted the throttle just that bit extra when I realized the bike was juiced. My seat tube broke on the crappy Norco, its junked, I had to ride low-rider style. I prefer a battery mount of black gorilla duct tape, plastic zip ties and metal zip ties. Anything that looks too good, like your e-ride, grabs un-wanted attention, but it also acts as a camo flaged as well, I like how its all black on black, very well done! Have you scratched your that ride yet, its that first scratch that gets to you, just give it up, use duct tape! :wink:
 
Personally I would mount the battery as far forward as possible as you already have a fair bit of weight in the rear wheel, it won't make a huge difference on smooth roads but if you have to man handle the bike for storage or charging as I do then the less total weight of the rear makes a big difference. Also with too much weight at the back the ride will be very harsh on poor road surfaces. The only downside is that you will loose the water bottle mounts on the down tube if you need to carry any drink.
 
I like the last point of offsetting your rearward bias with some additional forward weight. Mount it on the downtube.
 
Were it me, I'd choose a mount location based almost entirely on where I want to mount my water bottles.

I have my substantial batteries mounted in almost the worst possible location based on the various handling theories. I have about 10 lbs of batteries mounted on each side of my rear rack (20 lbs total). The only thing that would make this position worse would be to mount them higher. But I put my 10=15 lb backpack up higher in my milk crate on top of my rack. And oh - I also have my rather heavy Meanwell charger, locks, and motor controller in the same general area. So how does my bike handle? I dunno - seems fine to me. I routinely cruise at 20-28 mph and go down steep hills at nearly 40 mph. I don't have stability or handling issues with my moderately powered (750-1000 watts) rear direct drive bike. The biggest issue I have is that the back end of my bike is very heavy and hard to lift given the heavy motor and batteries and other stuff.

To be clear, I'm not suggesting that you duplicate what I've done. My setup is hardly optimal. My point is that if my clearly non-optimal setup is workable, then the choice of down tube or seat tube for a lighter battery should probably be made for reasons other than handling - unless you are super persnickety about how your bike handles. And if that's the case, then try it both ways and pick the one that has the subtle benefits you want.
 
The lower it is the better.
The worst place is on the luggage rack of course but it is popular location of course because it is most lazy way
 
Ideal battery placement for a rear hub build has to be according to 3 factors: the weight of the battery, the weight of the hub, the speed that you ride.

You want to place the balance of the bike about the middle of its length. So, a heavy hub might force you to fit a very lightweight battery on the front, for an extreme example. Most are using a battery heavy enough that its best mount is inside the frame triangle. The down tube mount is common on factory built ebikes, for it is practical and good looking, considering the moderate speed and smallish battery of ´legal’ bikes.

The faster that you ride, the higher on the front you will like the battery weight, like the big gas tank of racing motorcycles. On the opposite, the slower and the most technical the ride, the lower center you will like the weight.
 
miro13car said:
The lower it is the better.
The worst place is on the luggage rack of course but it is popular location of course because it is most lazy way

Most lazy way? Hardly. Standard bottle/shark battery mounted to seat or down tube is about as simple/lazy as it gets.
Also, batteries disguised as luggage can have advantages if you are trying not to attract attention.
 
Thanks again for the feedback. I keep changing my mind... You guys are bringing up great points. Plan to drill and install a rivnut to anchor the battery good. First hole/scratch needs to be thought out. The battery is heavy for what it is. 52v 17.5ah 40a bms. Not a lighter weight version. So I want 3 fasteners holding the base.
I'm gravitating to the downtube and placing higher to accommodate a vertical water bottle. If I keep it low like the the first picture, I'll have no place for a water bottle at all.
 
I've mostly mounted my water bottle on top of the down tube mounted battery either directly or by a bracket from the seat tube bottle bracket holes. Mounting the controller tidily is usually the biggest challenge.
bottle 2 small jpg.jpg
bottle 1 small jpg.jpg
 
In my book luggage rack is for luggage, not battery.
You cannot cheat law of physics. Center of gravity low means stability
 
miro13car said:
In my book luggage rack is for luggage, not battery.
You cannot cheat law of physics. Center of gravity low means stability

And this is why everyone gets to customize their bike to suit their own preferences. In my book, a rack is a place to carry or attach stuff.

As for the physics of handling, please understand that when people mention "good handling" they do not necessarily mean "stability." It is more complicated than that. Standard bicycles have an inherently high center of gravity due to the person riding them. Nonetheless, they are very stable devices.

Also consider that one reason to keep added weight between the wheels is so that the bike has a lower polar moment of inertia and hence quicker and more nimble handling. That doesn't necessarily make the bike more stable, but for many types of riding it is a benefit. Others have mentioned the pros and cons of higher and lower centers of gravity and other aspects of weight distribution and how these things impact different kinds of riding. You might want to review those comments.
 
If you have a lot of power, I prefer the downtube. Both are low, but downtube is more forward.

Also, as stated above, when you hit a big pothole or land a jump, downtube mount seems like it would take force from that direction a little better
 
I have a wild idea after looking at the pics, make your battery look like an enlarged water bottle, for ultimate camouflage!

I know there are regular water bottles that are batteries, but there is not enough Wh in them to be of any good!

Have it look like this
2L (64oz) https://www.amazon.ca/Under-Armour-Insulated-Hydration-Bottle/dp/B00KBHO0V2/ref=sr_1_5?keywords=2L+water+bottles&qid=1555541800&s=sports&sr=1-5

Better yet, a thermos!
https://www.amazon.ca/iBaste-Stainless-Double-Layer-Capacity-Climbing/dp/B07G9WHFJJ/ref=sr_1_4?keywords=2L+thermos&qid=1555541867&s=sports&sr=1-4

Lunch Special 3L
https://www.amazon.ca/gp/product/B01M7QKEEE/ref=as_li_tf_tl?ie=UTF8&camp=15121&creative=330641&creativeASIN=B01M7QKEEE&linkCode=as2&tag=brca-50-gen-20

Kidding aside, all I'd do is get some sheet alum, somehow curve it round, and figure out how to stuff the maximum amount of 18650 in there, and place it on the downtube. Then make your own big THERMOS sticker for each side, making sure its readable!


RustyKipper said:
bottle 2 small jpg.jpg
bottle 1 small jpg.jpg
 
This was an Idea I was working on a while back, the carbon tubes carried the battery cells either side of the down tube and the water bottle was to hold the controller. I was hoping for a very stealth like silhouette, it would have been quite wide however.
 
Well, I'm going to disagree a bit with everybody. Because of the small size of all the batteries you show in the pictures, mount them anywhere you want. Seat tube, down tube, under the top tube, handlebars, rear rack, in a backpack, whatever.

But of course, always better to mount 8 pounds in the mid frame, if your bike has a frame triangle. But my point is that up to about 10 pounds is pretty tolerable, requiring only for the rider to make a slight change in riding position even on highly technical, or steep off road riding. My current off road ride has a Y frame, making a frame mount difficult. I carry 8 pounds of lipo on a seatpost rack that does not wiggle, and I'm just fine. In a RACE, I would not be winning, but I can ride dirt as hard as I ever do no problems.

15 pounds back there, problem for dirt, not too bad for street commute. Big battery, you need mid mount. This is why I built this frame. I wanted to carry up to 40 pounds of battery in the frame, fore and aft, but concentrating the weight nearest the seat post as possible. Finished cargo mixte..jpg

If you are making a street ride, and must carry a heavy battery, then split in half, and carried in panniers as low as possible works ok. As for width of a frame battery, I really think anything over 5 inches wide is for bikes you do not pedal. One 18650 wide is plenty narrow enough to pedal easily around, so a big triangle battery in the frame is the best bet for a large battery, if of course, your frame is that kind.
 
I once made the mistake of buying a set of Lifepo4 cells so I had to spread the weight around the frame in 3 battery boxes, 6 cells high up at the rear, 4 on the seat post and 2 under the down tube, unfortunately the ally frame would flex like it was made from rubber every time I hit a bump, with 18650 cells it would have been much better, even so the bms wiring was something special!
 

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This is where I'm leaning for battery, controller and water bottle. It's a good bit higher in the frame than I originally wanted, but is a compromise for water.
 

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rlewis said:
This is where I'm leaning for battery, controller and water bottle. It's a good bit higher in the frame than I originally wanted, but is a compromise for water.

Good choice. If you keep the water bottle full, then it's a similar center of gravity as with the battery placed lower, but without a bottle.
 
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