Range dissapointment

[Morgen 3Eman]

Hi Folks,

I finally ran my battery down to low voltage cutoff, and the total milage was 13....

I made an effort to drive the Morgen to minimize the range; went fast all the time, climbed a steep hill several times on each outing, full throttle acceleration ,  and such.  But I was hoping to get closer to 20 miles.  My next test step is to drive it sensibly all the time and see what those results are.  I knew in my heart that the weight was going to drastically affect the range,  but hope springs eternal in the human heart. 

But  I sure smiled a lot while killing the battery:)

I would like to have advice on how to treat the battery.  Is it a good/bad idea to completely discharge the battery?  Should it be kept fully charged as much as possible? Recharge after every outing, or only at some discharge level?   I have no experience with modern battery care, and I want this to be as reliable as possible.  So please share your experience and knowledge to help make me smarter.  ( the Web has already made me taller and better looking)

TTFN,
Dennis

[Pwd]

Hi Dennis

Welcome to the world of batteries. What battery are you using? What are the specs on it?

Typically with a lithium based battery you don't want to discharge past 80%. This is how I killed the life of my battery; I used to discharge it past the LVC (low voltage cut off). My advice is charge frequently, so yes keep fully charged unless you are storing for an extended period of time.

[Morgen 3Eman]

Thanks for your reply.   I have a 48 V 12AH GM LiFePo battery.  So charging it after every run is the best plan?   I don't really plan any long drives with it, so that would be no problem.

If the real output voltage starts at 58 Volts, are you suggesting I don't discharge it below about 46 volts? 

TTFN,
Dennis

[Pwd]

No problem,

so you say you have a GM LifePO battery; if it is for sure 48V12AH then it is not the LifePO version but the LiMn2O4 (Lithium Manganese) version. If it is for sure a LifePO 48V then it is the 48V10ah (GM doesn't make a 12aH LifePO battery). Either way, charging it after every run is a safe bet. The GM batteries have a Battery Management System built in that will automatically cut-out power when it reaches too low of a voltage to prevent damage.

Best practice would be to avoid ever hitting the cut-off limit (voltage varies depending if you have the LifePO or the LiMn). The mistake I made with my LiMn was draining it frequently and turning it back on after the battery cut-off from low voltage. My LiMn 48V12aH still works but the range has suffered because of this. Technically this is repairable by replacing the cells that are damaged, if you are able to solder and like to fix things. The GM LifePO batteries are significantly better than the GM LiMn batteries; the cycle life is longer which means you can get more charges out of them. I've learned alot about batteries in the past year; but I am still learning; so definitly do some more research if you are interested.

I know the feeling; the battery is the most expensive component to the GM kit; its sad to see the range go down hill.

[Morgen 3Eman]

Sorry,you're right, it is 10 AH rated, not 12.   The analog voltmeter I have on my dashboard does a great job of acting as a "fuel gauge", as it reads full scale on a fresh charge, and zero just before battery cutout, so I'll be using that to keep me out of the danger zone you mentioned.   

I have been concerned about the weight from the beginning of this project.  I'm going to start by making the fenders from carbon fiber, as the ones that are appropriate for the design weigh 5 lbs each in steel.   I'll evaluate the pain of composite making, and then decide where to go.  One part of me wants to form the chassis out of polycarbonate and carbon fiber, but I really want to get back to oil painting, which is my real passion.  My previous experiences with composites have been successful, but not as much fun as hitting a sheet of steel with hammers.....

Thanks again,
Dennis

[truly_bent]

Hi Dennis.

I'm running a 20AH LiFeP04 and have not yet run it down to cutoff, but the distances I'm getting may give you some help with benchmarking.

I've made two trips (among many) out to a nearby town, which is 31 kilometers (19.2 miles) out. The first time I let the motor do all the work and it cost 8 AH (3.9 km/AH). Yesterday morning I went again, but this time decided to put some physical effort in. I also kept the driving speed (not the downhill yahoo! speed) below 40kph (24.8mph) and the same trip cost 6 AH (5.1 km/AH).

I'm not watching voltage, although I have that info available on the Cycle Analyst, but amps and amp hours. If you're getting 13 miles (20.9 kilometers) for your 10 AH, then that benchmark of 2.09 km/AH is almost half of what I'm getting under similar circumstances. Granted, your Morgan is heavier, but is your total load twice my total load? I'm a pretty hefty boy at 230 pounds and the recumbent is no lightweight either.

What occurred to me is the difference in the size of our batteries. First off, as you know, it's a 30A motor. I have my controller limited to 35A, but I've never noticed my amp draw higher than 28A. I'm pretty sure the GM battery packs are rated at 2C. In your case, 2C equals 20 amps. If your motor is drawing anything like mine, then you're often drawing beyond that 2C nominal rating. I'm no battery expert, but I suspect this may be causing a more rapid depletion and consequently the shorter than expected range.

I look forward to seeing more pics of the Morgan. Great project...

[REV Bikes]

I am running an MP2 front wheel on a schwinn corvette cruiser with a 3 speed hub.
I ride like I stole it on long rides including hills too steep to pedal without power assistance.
I use a LiFPo4 10AH battery from GM.
I continually get 3km per AH at full power settings.
If I scale back the continuous and peak ampage so that the maximum watts are 760-800, then I get 4km per AH
If I tow a trailer with 30 to 50kg in it, I'll get closer to 2.2km per AH.
I weigh 80kg and I pedal on the uphill parts of my ride.
Hope that helps.

Oh yeah, on a dyno pulling 350watts at full power settings, I have clocked 70km on my 10AH battery