Building an EV motorcycle. Batteries: Need opinions. - Fuel Economy, Hypermiling, EcoModding News and Forum

TurnNBurn · 06-27-2013, 06:39 PM

I was on another forum (endless sphere) asking this, but I wanted some more unbiased opinions. I'm building an electric motorcycle (well, it's built). Motor is Mars ME0913 72v and the controller is an Alltrax 7245 (450 Amp)

My goals: 45 miles while maintaining an average speed of 45-55 MPH. I'd like to be able to do a few mile bursts of 65-70 MPH should I need to take it on the freeway.

I'm down to 3 battery choices: Lead-acid, LiFePO4, and LiPo.

On endless sphere everyone (literally EVERYONE) pointed me away from lead acid. It seems Lipo, with all of its dangers, was still a better option than lead acid. It seems everyone had their own views on which battery was better. LiFePO4 fans were against LiPo. Lipo fans were against LiFePO4 (because of size and cost). But it seems all were against lead acid, though I couldn't get a better reason other than "they're heavy". Which it's hard to argue against.

So lead acid: readily available, reasonably priced...but heavy. Is it worth it? The bike is a 1996 Honda CBR 600 and I can fit about 6 yellow optima batteries.

P-hack · 06-27-2013, 07:10 PM

I have also heard that lithium has far more recharge cycles, which if you keep the bike, more than make up for the extra cost after replacing a few lead packs.

TurnNBurn · 06-27-2013, 07:19 PM

Quote:

Originally Posted by P-hack

I have also heard that lithium has far more recharge cycles, which if you keep the bike, more than make up for the extra cost after replacing a few lead packs.

I do plan on keeping the bike, but at the same time I plan on upgrading it in the future. So I could save for better batteries and hopefully in a few years battery technology will improve.

P-hack · 06-27-2013, 07:37 PM

I'm entertaining building my own lithium pack from a large box of used computer batteries fyi. It involves things like building a battery tab welder out of a microwave transformer and sorting out an appropriate and affordable BMS and charger and dissecting the packs and matching the cells, ditching the bad ones. Lotta work, not sure I'm up for it, but the batteries themselves will be like $100 (or free if you are really good)

Daox · 06-27-2013, 10:25 PM

Life would be what I would go with. I don't know what kind of cycle life you get out of lipo but life is great. I've heard that most lipo also has a shelf life which isn't what you want if you are planning to keep it for a long time. I would also recommend just building it the way you want the first time around. It is very costly to redo things like a bms and charger.

I would definitely avoid lead. Its heavy, cycle life is horrible compared to lithium and it requires different charging profiles at the very least.

TurnNBurn · 06-27-2013, 11:45 PM

Grrr. I'm still captivated by lead acid. With lead acid there's no BMS required I thought. And I could get some good deep cycle batteries for $120 each and it'd only be about $720. if I go with Life, it's $1200 for the batteries plus another extra chunk for the BMS and chargers.

P-hack · 06-28-2013, 12:55 AM

which life and lipo batteries are you looking at and how many?

One other consideration is efficiency, higher loads affect lead far more than lithium due to the pukert effect. So weight, lifespan, efficiency, cost per mile, performance, how many reasons would you like?

Yes the charger/bms does add to the cost, but just so you know, you can trade convenience/time for cost there as well. If you have a suitable 3.7v charger (i.e. for one battery or collection in parallel) you can balance charge the whole pack by simply charging each battery one at a time. When you make/build a second one, it will take half as long, and could be controlled by a relatively simple box of chinese relays and a microcontroller.

Continuing to add 3.7v chargers gets inefficient though, as you take 120v down to 4ish volts several times, each at the same current that you could apply 72+ volts across the entire pack. Though you still have to monitor the individual voltages to prevent overcharging one of them.