batteries and controller in backpack?

[jason41987]

hey everyone.. i was looking to do an electric trike build for my parents recently, but ran into too many problems for the time being.. but id still like to atleast do one for myself.. i was looking for something i could use for commuting, and i had the idea.. with lithium cells being relatively light weight, and not needing many of them to get more than enough range at 30mph city speed... i had the idea of possibly using a backpack to carry th ebatteries, controller, and maybe a charger

the reason i had for this was largely a security reason, but it also seems it would be pretty convenient too to drop the backpack next to a power outlet and charge while youre at wherever youre going... and these are the most expensive parts of a conversion, so taking it indoors when youre done for the day seems like it would be a good idea... has anyone considered something like this?

 

[Philistine]

A lot of people do that, particularly with small conversions like BMXs etc. (where there is little room anyway to mount on the bike). For all the reasons you list, it is convenient. The nervous nelly types argue that you will have issues if the Lipo vents/flames in your backpack, but personally I think as long as you have put the batteries in a protective type of coverage to stop punctures if you crash, I think it is a fine idea. I was in the process of doing a BMX build and would have done the same thing myself.

One issue you might like to think about is depending on the speed wind of motor you are using and the controller you are using, you might have issues having the controller retained in the bag as it will get no airflow. For higher speed motors particularly when matched with smaller controllers (eg 12 Fet), then without airflow they can get pretty toasty. But if that becomes a problem you could just mount the controller on the bike to get airflow.

Best of luck.

 

[jason41987]

well, i wouldnt neccessarily have to use a pre-existing backpack though.. i could make one out of breathable, protective materials if i needed to for circulation or cooling.. maybe with a rigid internal structure, possibly with an exhaust fan.. however, im looking to take an inexpensive mountain bike with the front and rear suspension to convert... figured its best to have some kind of suspension when going at speeds faster than i could pedal,

30mph is all im shooting for as its the highest speed limit within the city limits here

 

[Drunkskunk]

A controller in a backpack is a bad idea. it needs airflow, and in the evernt of a crash, you would be tethered to the bike by the Phase, hall, and throttle wires, along with the brake wires and the CA, if you use one. Thats a crap load of connectors to hook up every time anyway.

The battery in the backpack is a debated idea. A few people use it and like it. Most people will tell you that its a bad idea because the weight is unweildy and will be anywhere from just annoying to dangerous. But test this idea for your self. Put 20lbs of junk in your backpack, tie the backpack to the seatpost with a thick rope to simulate the battery wires, and go try to ride your bike for an hour. If you aren't so completly anoyed with it that you want to throw the whole thing off a cliff, then it might work for you. My threshhold would be about 10 minutes before I'm ready to dump it in someone's flowerbed and just go home.

If you're an American, there are other points to consider. Imagine it's cold, you're wearing a ski mask. You need to stop off at the post office to buy stamps. You're in a hurry so you unhook your wire run in to the office. Some timid older lady sees you and calls 911, saying a man in a ski mask just ran into the post office wearing a backpack with wires sticking out.
The SWAT team and the bomb squad show up. Your backpack gets detonated on the 6 O'clock news.

Ok, Not all that likely to happen, but not unreasonable either.


If you really have to have it portable, get a detachable frame bag of some form.

 

[dogman dan]

Controller on the bike. ALWAYS getting some air. Waterproof boxes that still scoop air for cooling are possible. They won't take your controller, they'll take your whole bike. All the wiring on the bike going to the backpack would be an absolute nightmare. Bad enough the wire to the battery alone.

Backpacking the battery makes the most sense when the battery is that small and light. On the other hand, that small and light, why not just put it into a handlebar bag? To me, it's a catch 22. Climate matters, where I live a back pack makes you sweat waaaay too much 9 months of the year.

I've done the battery in a messenger bag many times, for a quick test. For me, the dangling wire is a pita. But I never rigged a really good permanent setup for it.

 

[pff7]

I like how you mentioned the advantage of batteries in backpack while bringing charger , can usually use outlets in most starbucks,ect. and could charge batteries while sipping coffee....(applies to US,unknown otherwise)

 

[dogman dan]

I've definitely broken some chargers carrying them on the bike, shaken to death.

Not so bad if you have FS bike, but carry a charge in a knapsack if you can, to minimize the shocks. Some can take it, others can't.

You can use silicone or potting compound to help shock proof a charger.

 

[pff7]

What about the 36 Volt Bosch Fat Pack charger I wonder....1 hour full charge,30 minute 80% charge? Then the Bosch batteries look not so big either?

 

[def215]

i actually have my batteries and controller in my backpack. since my battery is pretty small, 9ah 7s li-ion, it weighs in at around 10lbs. i have the heatsink of my controller sitting on the outside of the backpack for some air cooling, along with the on/off switch. my backpack battery was more for convenience, and not security reasons. since i take it to school sometimes, bringing the entire bike into class for charging is out of the question. taking just the backpack is no problem since i use it to carry my school books too. :wink: but if you are going to have a really big battery pack, it would probably better on the bike.

 

[iamsofunny]

I have 200ah of 100v Lipos in a plywood box mounted on my back using tie downs. Much better than the 8 deep cycle marine batteries I previously had to carry strapped to a pallet on my back during the early 90s when I worked as a DJ and acted as an extra in Ninja Turtle movies.
I had one problem whereby I would snag my legs on the battery cable so I switched to a wireless setup using Tesla coils.

 

[pff7]

At least detachable batteries so you can ccarry the batteries with you when you leave bike, put em in your backpack so you can recharge them without having to bring entire bike to wherever your power source is. Of course you would still need to bring charger also.

 

[motomech]

My Lipo gets kind of warm
Say, that's an idea, this winter I'm going to make a Lipo vest and put the controllers in pockets that cover my nipples :lol:

 

[pff7]

Ok I finally got this going, batteries on back of bike, in detachable carrying case. Black and red wires coming out of case through holes obviuosly meant for this(came with the yescomusa kit,pretty nifty in that 6 velcro straps connect it to the supplied rear mount bracket). Carry 5amp. power transformer(very light weight) plus the HK-E4 charger(so small you could literally put it in your shirt pocket) plus had to custom some wiring connections so didn't have to rip apart my battery connections ever time needing a charge, don't have to worry if I won't have enough juice for the return trip now, as long as I have access to a plug, and with so many people needing a plug for their laptops, usually you can find one. Only problem is that when charging and it's done charger chirps with a high beep. Kinda embarassing .....
I use 4 4s hardpacks, so charge them individually, but I think I could wire em up in parallel for charging, haven't got there yet..

 

[winkinatcha]

My Lipo gets kind of warm
Say, that's an idea, this winter I'm going to make a Lipo vest and put the controllers in pockets that cover my nipples :lol:

Ahahahaha! GOLD!