Hiding battery in airbox / Lithium batteries

[yaktackler]

I am using a very small Shorai battery tucked under the seat (LFX14a1-BS12) It is small enough to fit in the air filter if you wanted to. I was concerned at first if it would crank the bike on cold mornings. I live in Minnesota. It has been a champ so far. Event on those cold 30 degree mornings

[Donkey Hotey]

Originally Posted by Jon-Lars

Consider what happens when the bike accelerates and decelerates.

The battery's momentum is applied to the structure in the direction of that acceleration. You are side loading those threads, with the length of the shaft acting as a lever.

The cut threads are notch points that focus the force, and the base plate attachment gives the lever a fulcrum point.

If what you described were even remotely true, rubber and woven hold-down straps would have to be magic.

The battery is in a pocket. There is a friction component keeping the battery located within that pocket. The ONLY thing the bolts have to do is keep downward pressure on the battery and it ain't going anywhere--same as straps.

Rocking the battery exerts a lifting force and only the tiniest of bending forces. Those bending loads are negligible until long after the battery has translated enough to leave the tray. It's not going anywhere.

My biggest worry in that installation would be engine vibration being transmitted directly into the dangling lead plates in the battery. That's a sure-fire way to destroy a battery.

[Jon-Lars]

Originally Posted by Donkey Hotey

If what you described were even remotely true, rubber and woven hold-down straps would have to be magic.

The battery is in a pocket. There is a friction component keeping the battery located within that pocket. The ONLY thing the bolts have to do is keep downward pressure on the battery and it ain't going anywhere--same as straps.

Rocking the battery exerts a lifting force and only the tiniest of bending forces. Those bending loads are negligible until long after the battery has translated enough to leave the tray. It's not going anywhere.

My biggest worry in that installation would be engine vibration being transmitted directly into the dangling lead plates in the battery. That's a sure-fire way to destroy a battery.

Draw a simple force diagram of the design we are talking about. ANY side loading on those threads is a problem.

[bmweuro]

Originally Posted by Donkey Hotey

If what you described were even remotely true, rubber and woven hold-down straps would have to be magic.

The battery is in a pocket. There is a friction component keeping the battery located within that pocket. The ONLY thing the bolts have to do is keep downward pressure on the battery and it ain't going anywhere--same as straps.

Rocking the battery exerts a lifting force and only the tiniest of bending forces. Those bending loads are negligible until long after the battery has translated enough to leave the tray. It's not going anywhere.

My biggest worry in that installation would be engine vibration being transmitted directly into the dangling lead plates in the battery. That's a sure-fire way to destroy a battery.

I agree with you. Some early BMW's were solid mounted batteries and some had very small rubber bumpers for the battery to rest on. Realize that people that are doing these sort of modifications are not riding the bikes 1000's of miles a week or a month so the chance of any of this becoming an issue is slim to none.

[halflive]

Originally Posted by bmweuro

It is. 70-79 models and 80-95 models

I hope the production model is made with a larger radius?
All corners of this aluminum plate are cracked. A good rule of thumb is to use a radius 3x aluminum thickness. At least for 6000 or 3000 T3 or T4.

[Donkey Hotey]

Originally Posted by Jon-Lars

Draw a simple force diagram of the design we are talking about.

I'm not going to draw free-body diagrams for you. If you can't figure out that the shear is being taken out between the battery and the tray, no diagram will convince you. Yes, the battery's CG is above that mounting plane but, rocking of the battery turns into a large vertical translation with only the tiniest lateral translation. If the nuts are tight, that lateral translation is zero.

This is how people can have a $100K seat of Nastran and get hyper-accurate, yet incorrect results.

Perhaps explain how a rubber strap over the same tray would hold the same battery in place? The rubber strap has no meaningful resistance to bending. Is it magical, non-bending rubber?

[boxerkuh]

Love the discussion. I have spend a great deal of research on this matter. I am not wanting to subject my daily rider to early burn out so I am keeping the airbox in place. What I have done so far is shaped 2 US license plates by hammering them and enclosing the current batter box. That allowed me to remove the side covers and to have a "custom" look. The "hammering" procedure was a workout and an experience in off self, one plate I did on concrete and the other on wood. It's different. When I change the rear subframe to a /5 short I will hang the battery underneath the seat in a custom box. It will be out of the way, it will be an open look, which will work well.

Bottom line for you will be "What do YOU like" and what you can afford. Making it yourself might be the cheapest way, but all the suggestions given to you will work and are different....even the one you don't like from Boxer Metal under the frame (BTW: I considered it, but was not willing to sacrifice the centerstand).

My brother runs a Lithium battery on his 2010 K 1200GT and he loves it... technology...


Compromise....it is what it is.... compromise....

[Big Bamboo]

Originally Posted by Sutherngintelmen

Here's some data

OK, I tried to read that whole thing, really I did, but I see only specs on cold weather starting. Does anyone know how well the lithium batteries handle heat?

[bmweuro]

Originally Posted by halflive

I hope the production model is made with a larger radius?
All corners of this aluminum plate are cracked. A good rule of thumb is to use a radius 3x aluminum thickness. At least for 6000 or 3000 T3 or T4.

All corners of this aluminum plate are cracked?

[Jon-Lars]

Originally Posted by Donkey Hotey

Perhaps explain how a rubber strap over the same tray would hold the same battery in place? The rubber strap has no meaningful resistance to bending. Is it magical, non-bending rubber?

I am only concerned about the mounting of the bolt to the base. It's fixed on one end, weakened by the cut threads, and highly stressed. There is no way to alleviate the side load with the threaded end fixed that way.

[boxerkuh]

We live in South Carolina and have aweful Summers. My brothers bike is K bike with a full fairing and it is in the middle of the thing. I would say, that you are good to go with summer concerns. Should not be an issue....

[WRC51]

This is in an old BMW, I dont think the force from from the engine will rock that battery too much.

[DiabloADV]

Yeah...if mine accelerates (or brakes) hard enough to snap the battery mounts off, I will be the happiest airhead around.

Those mounts aren't going anywhere. Just because you can come up with a conjectural scenario for failure doesn't mean the actual scenario will lead to failure.

[Jon-Lars]

Originally Posted by DiabloADV

Yeah...if mine accelerates (or brakes) hard enough to snap the battery mounts off, I will be the happiest airhead around.

Those mounts aren't going anywhere. Just because you can come up with a conjectural scenario for failure doesn't mean the actual scenario will lead to failure.

Of course not.
Poor design leads to an increased chance of failure, not a guarantee of failure.
The failure mode I have in mind isn' sudden but rather eventual cracking and separation after subject to vibration and off-axis excessive loading.

[MotoKaw]

Fiberglass cover -

http://www.boxercafe.com/startercover.htm