Battery Buying: 40Ah vs 60Ah

[freesiderxl]

I'm in the process of buying a battery to go with my:

Mars 3001 Motor (~5kw, continuous 100A, Peak 300) https://www.kellycontroller.com/mot/downloads/48VCW.pdf
Kelly KBL48301 48v Controller

I initially wanted a 48v 40Ah battery, but the sales person is suggesting the 48v 60Ah, stating that I wouldn't get the necessary power from a 40Ah battery.

I believed that Ah was the primary indicator for range, but did not effect top speed or acceleration.

He also suggested upgrading the BMS board to 120A, to accommodate the continuous 100A of my motor, which makes sense.

Is the sales person just trying to get me to buy a bigger battery, or will the additional Ah help take full advantage of the Motor and Controller?

Any Advice would be greatly appreciated.

 

[Ykick]

Seems like you need to understand C rating of batteries. Pulling 100-300A peak from 40AH is likely pushing the limit for most LiFePO4 chemistry. 'sounds to me like your saleman is shooting straight.

 

[Jethro56]

Depends on the C rate of the battery. If the battery is rated at 2C in other words 40AH discharges at 80amps or 60Ah discharges at 120 amps Then the 60Ah battery will have a much longer life. Need to find out what the "C" rating and cell construction is and post back.

 

[freesiderxl]

thanks for the replies, guys. i DO need to learn about C ratings, so thanks again.

the cells are a134 18650 cells, which a website states have a Continuous Discharge of 30C, with a Peak Discharge of 60C http://www.osnpower.com/productID/product_detail-9006013.html

The battery pack that I'm considering though, is from Conhis, which doesn't have the best reputation here.
http://www.conhismotor.com/ProductShow.asp?id=133

but to be honest, i really have no f*cking clue how to determine with certainty the battery's C rating.

i guess my discomfort with the salesman was really based on the fact that he's from Conhis, but i guess i should always learn the facts first before jumping to conclusions.

thanks guys.

 

[Jethro56]

The link to conhist shows a lifepo4 battery 48V 40aH with a 80 amp continous discharge. This would be a 2C battery... 80amps/40aH. This is typical of lifepo4 chemistry. Your orginal post stated a 100 amp requirement. So at 2C the battery needs to be 50Ah and above. The salesman appears to be sizing the battery correctly if 100 amps continous is the requirement. Maybe others can chime in on ConHis' quality.

 

[Ypedal]

Stop and learn before you spend money on stuff that will not work ! :wink:

First, the BMS, no matter what battery chemistry and capacity, you canot deliver to the motor more power than the BMS will allow, and most BMS's will not allow 100 amps, or even anything close to it..

2nd, the pack in your link from cohins, IF it's made with A123 cells, " could " work at 100 amps but the wires that exit that pack and the basic construction of it is not compatible with that Mars motor and Kelly controller...

==================

- What conditions will this motor/controller be used on ? .. a bicycle ? golf cart ? trike ?.. hills or flat land ?.. vehicle weight..

- Range, how far do you need to go on a charge ?

let's start there..

 

[Ykick]

Jethro sounds correct to me. For that kind of amperes RC Lipo nano would probably be best but you'd need to know even more than C rate to properly deal with that chemistry.

I bought 2qty motor/controller kit from ConHisMotor about a year ago when Barbara was rep - no problems with my order and the kits were very similar to 9C. I would never consider buying a battery pack from Chinese vendor though. Now I do cells/bricks from Hobby King but that's entirely different thing than a pack/charger. Ping seems to have a great rep from locals around here but no personal experience.

 

[freesiderxl]

Thanks for all the feedback.

This is for an electric motorcycle conversion, running on mostly flats, with an estimated bike weight of <200lbs/90kilos.

For range, the longer the better, so I guess I better cough up the extra dough for the 60Ah.

I was hoping that with my motor/controller/battery, I could maybe get a top speed of 60mph/~100kph and hopefully a range of around 40mi/~60kph. pipe dreams?

i read on another thread that Rule of Thumb: 10-20wh/km.

so...

60ah X 48V = 2880wh ... divided by 10-20wh= 144-288km.

(discounting weight, drag, etc)

but... this can't be right. Any advice would be much appreciated.

 

[Ypedal]

an electric bicycle ( 40 to 60 lbs ) with pedals being used gets around 10 wh/km ... at 30 km/h !!!

An electric motorcycle ( 200 lbs ) with no pedals and acceptable acceleration ( 100 amps + ) at 60 km/h = way more .. i would expect 50 or so wh/km or more..

 

[freesiderxl]

Thanks for the info. I think weight can be trimmed considerable, my running tally (w/o rider) is about 150lbs. I hope this can cap it at 50wh/km.

 

[dogman dan]

For a motorcycle, I'd be looking at 60- 100 ah battery. Your range will vanish with faster than moped speeds. It's pricy, and bulky, and part of the reason I went with bikes to start out. And ended up liking the bike enough to stick with it. Don't give up though, but get educated about battereries first and then get the budget and the build configuration adjusted to carry more battery. Lots of the larger EV's have been using Thundersky lifepo4. Perhaps the 80 ah bricks would work for you? Not a high c rate, but you'd have 160 amps peak with those.

Then perhaps you can get a controller that limits a bit lower than 300? Maybe you can get the vendor to program that controller to ramp down the amps when it gets over 150?

Forget bms for discharge at that amp level. You'll just have to monitor stuff manually. Some of the inexpensive stuff we are using with lipo will work for you though. You can easily rig a display to show the voltage at cell level with two cellogs from Hobby King. For charging, you could balance with a cheaper BMS, but it would take days to do it. So you will need to think a lot about how to charge that thing. Individual cell chargers may be the best way for balancing. Get the battery right though, and balancing may only be needed monthly or less. The rest of the time, if you have a good set of happy cells they will stay balanced enough for quite some time.

If you really want the top performance, and the 300 amps, then you need to go straight to a big pile of lipo or A123 lifepo4. $$$$. But with high c rate stuff, you could start with short range, and add capacity later as you can afford it. With lipo, you can get 300 amps in a tiny, and therefore inexpensive pack. Might be worth considering a small lipo battery to do the initial testing. 14s lipo = 48v lifepo4 which is 16 cells in series (16s).

 

[jimw1960]

For an E-motorcycle you might want to consider going to 72 volts or maybe even 96 volts system. You'd be able to get higher speeds with less current draw compared to a 48v system. I'm not sure what most folks do for charging and balancing on the high volts systems, though.

 

[freesiderxl]

Thanks everyone.

in the end, i'm not going to be buying from Conhis.

Their sales team are the rudest, most nonsensical people I've encountered. I figured with batteries, one could get 2 of the three: price-quality-service. i've seen some people happy with quality but not service, and vice versa. they've thoroughly proved that they have no interest in my business, so i guess back to looking for a supplier.

I've sent emails to Headway and Ping (the generic emails on their websites), but haven't heard back from them yet. Does anyone have up-to-date email for their current sales guys?

Any other recommendations? I'll keep trolling the forum for more suppliers too.

 

[dogman dan]

Again, ping isn't really in the buisness of supplying a battery for that kind of amps. The bms will only put out about 40 amps, because of 2c cells. He's got higher amp bms, but again, you really need to be thinking manual monitoring for that kind of controller amps. So no point in going to soft pack ping batteries when you could be getting nice hard shell thunderskies or similar, in 80 ah minimum.

Or go high discharge rate, like the 90c nano lipo at HK.

Or go ahead, and blow your dough, and we'll be happy to tell you told you so. I know, I'm just a bicycle doofus. But I've hung out here long enough to know big amps and bms sucks. Ask the guys that have built real motorcycles, dig in thier threads from the past, and you'll see.

Do charge with a bms, like a good lipo charger. fine. But don't bms your discharge with an inexpensive signalab bms.

Headways would work great, with a decent enough discharge rate. but a 40 ah pack of em will be very very very bulky using the round cell format.

Just one more time and I'll shut up. You want big bricks so you don't have to add 40 pounds of wire, connectors and nuts to the build. 60-100 ah blocks and as few connections as possible.