Small Battery

[awol]

Have been thinking of reducing my overall bike weight.
My commute to work uses aprox 3.5ah according to my watt meter.
I have an idea of carrying a smaller 36V battery with about 4ah or 5ah for a one way trip but maybe with a higher C rating for about 20amp peak, then I would charge up for the next trip.
Is such a thing available and would this then be much smaller and lighter than even my bottle battery too?

 

[KirstinS]

Perhaps going the RC lipo route?

Two 5000mah 5s packs in series maybe ?

Best for energy density I believe but additional care required and risks involved

Hobbyking is the place for such things

 

[trex]

With Lithium Ion batteries, the recommended continuous current draw is 2C, that 8A-10A, and it will affects the bike's climbing ability.

 

[KirstinS]

Rc lipo won't have the c rating issue

 

[Deleted member 4366]

RC lipos from Hobbyking. I'd use the opportunity to go up to 12S (44v) for more speed and power.

 

[awol]

Both suggestions are pretty much exactly what I had in mind,great. I like the sound of the single block 12s, would I be able to wrap it in clingfilm/duck tape and velcro it straight on the crossbar even in the wet weather?
Being 20% more volts would the same journey use 20% more aH? so I then need to be looking at 4.5aH battery?
When you say 'risks' - I will be charging this at work so it is safe to do?
I guess the chargers also balances the battery? Could you suggest a cheapish one as I would need 2 of them and hobby king have loads I can't work out which is needed?
I am hoping I won't need to monitor voltage if I already know the battery is enough for 1 trip only but if it were to drop too low for whatever reason is that the whole thing dead?

 

[Deleted member 4366]

Lipos have to be monitored. You can use lipo alarms, which don't cost much.

I wouldn't recommend charging at work. It's safe enough, but it doesn't always look safe to others, who don't understand, and it's possible to make an incorrect connection that could result in a bang, which would be difficult to explain away. I missed the bit about charging at work. Maybe lipos aren't suitable then.

You don't need 20% more amp-hours because you already have 20% more watt-hours.

Most lipo chargers do up to 6S. You don't need two because you can charge two 6S packs at the same time by temporarily connecting them in parallel.

There's nothing to stop you installing a BMS to a lipo pack, which would make them plug-and-play, but you'd need good quality (expensive) packs and a reliable BMS.

 

[awol]

I still think it sounds a good option, I can get around the charging at work, carefully connecting etc. At worst I would have to buy a second pack and charge both at home but loose the size/weight benefit I wanted to achieve but still end up with a usable batteries anyway.
I will be velcro'ing it straight to my crossbar wrapped in ducktape, sound do-able?
Could you recommend which chargers are the ones to go for that, out of the hundreds available.

 

[Deleted member 4366]

My favourite is the BC168 because it charges through the balance leads. It's like 6 chargers in one box. Each cell is a treated like separate battery, so balancing is quick and efficient. Some cheap chargers struggle when the attery is unbalanced,

Lipos mustn't be dropped or punctured, so needprotection against that. I prefer the hard-packs, but you need three to get 12s at 1.5 kg for 5 aH:
http://www.hobbyking.co.uk/hobbyking/store/__26801__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack_UK_Warehouse_.html?strSearch=4s hard

 

[awol]

Ive just measured up the donor bike frame and the single block 12s will fit nice where I want it and a protective case will be easy enough to manufacture. It is 1.5kg lighter than my bottle battery and is much thinner.
I see the battery has 2 flat ribbon connectors, I take it these are the charging wires and I will get a 6s charger and charge one lead at a time as if it were 2 batteries ?
I will need 2 chargers because 1 will be at home, the other at work unless I carry it with me. Would one called a iMax B6 do, or one called a hobbyking eco six (2off BC168 is looking a bit expensive)
also I would set them to 4a charge if I have a 4aH battery or 5a if I have a 5aH one?
I will be monitoring my aH usage over a few months first using my MXUS and my backup motor to ensure I am carrying just enough capacity.
Thanks for the help on this

 

[Deleted member 4366]

the iMax ones are a bit hit and miss. I've had a couple misreading the voltages,so they don't balance properly. You need a 12v power supply too, which is what tends to limit your charge current. You can make one out of a PC or Playstation power supply. I usually charge at 0.2C. You can go much higher, but you only need to do that if you're in a hurry. You only need one charger. The BC168 comes with a balance board so you can charge three packs at the same time (IIRC). it can do 8 amps per channel.which is about 200w, if youhad a 20amp 12v power supply.

 

[amigafan2003]

Why is loosing 1.5kg from the bike a requirement? On an ebike, it doesn't make that much difference.

Besides, going on a diet for a week is a cheap way of losing 1.5kg ;-)

 

[awol]

Why is loosing 1.5kg from the bike a requirement? On an ebike, it doesn't make that much difference.

I am trying to pedal/cycle myself more but still have the motor there for the hills+headwinds (and the fun), and my current bike is a bit like pulling a truck up inclines, after riding a small/lighter normal bike which I want to motorize I decided to try and see how light I can keep it. It's more of an idea at the moment.

 

[awol]

I am putting d8veh's knowledge/experience in front of cost and ordering the recommended but slightly more expensive BC168 charger.
So project started and if all else fails I can still use the batteries+equip I end up with.

 

[awol]

I see BMSbattery have some new high C rating batteries now which may be a possible future replacement contender but at about twice the lipo price but plug&play usage and aprox 800 charge cycles and 2.4kg.
I am in the process of experimenting with a small lipo as a booster at the moment and it is going well so I believe they could be a possible contender for a future small full battery replacement. This is based on me getting used to handling/charging and cost/weight/size, however I don't know the number of charge cycles they last.
If I got 2x6s and more or less fully charged/emptied once a day, how many charge cycles do these lipo batteries on average last?

 

[cwah]

Lightest one are currently the NCR18650B at 3400mAH. But they are very expensive.

You can get the cheaper NCR18650A at 3100mAH (safer and cheaper), or even the NCR18650BD at 3200mAH (stronger and more expensive)


Let say you get the high discharge NCR18650BD, 20 cells would give you 36V6.4AH for about 1kg. Add wiring, bms and light enclosure and you have a fully functional battery of 1.3kg with 2.5C discharge (600W)