Electric Cyclekart (bigwheel gokart) Motor and Battery Selection (HPM5000B)

[Evolknuj]

Greetings all!
I am building an electric cyclekart imitation of a 1935 Morgan F2 three wheeler. Basically an historically themed, small scale, big wheeled go kart. Here's my build thread if you're interested in more details: https://www.cyclekartclub.com/forum/custom-karts-forum.6/morgan-f2-threewheeler-electric-cyclecar.37863/

I've been reading and lurking on DIY EV sites while building, but I'm very near the point where I need to pull the trigger and order motor, controller, and battery and would appreciate advice.

Desired max speed on level ground:
35mph
Desired max range at what cruising speed.
15 miles at 25mph (with hills involved)
Preferred bike wheel size, or wheel size of bike you want to convert. Most common kits are for 26" wheels.
Rear drive wheel is 12" pitbike rim (overall diameter with street tire probably 8" greater)
Brake type of motor wheel. Disc or not.
Disk
Rider weight.
220 lbs rider + 30 lbs dog + ~250 lb chassis (guessing on chassis, trying to keep it light)
Terrain.
Hilly (hill country outside Austin TX)
Budget.
~$2000 for drivetrain: motor + controller + batteries + wires + throttle/switches

As you can see above, I don't have any great need for speed and likely it would scare the poop out of me to go over 30mph in my deathtrap. But I'll need enough power to go uphill, and want to be able to go faster than most golf carts.  It's a NEV, not highway machine.

I'm started by looking at the 3 and 5 kw kits from Goldenmotor. The 3kw model is certainly easy on the budget, however I have concerns that it would not provide satisfactory power. The 5kw kit would seem to give enough power.... if I can supply the current.

For the battery, hopefully the above would help inform those more experienced than I determine sizing.  I don't want to build my own from individual cells big-AA sized cells for my first foray into DIY EV (no spot welder for one), but understandably there aren't really a lot of prebuilt turnkey packs out there either... but GM has some.  I am strongly considering the Goldenmotor LFP-4830M, but I don't know if its max continuous discharge rate of 60A would be overly limiting. The motor and controller can handle a lot more it seems, so I would think being limited to 60A continuous might be a problem.... or might mean I wont stress the motor/controller combo and it'll last a lot better.  Any advice?  Suggestions for Li batteries for my application?

Thanks for reading (assuming you got here, sorry I'm long winded)!
Paul

[Bikemad]

Hi Paul andto the forum.

Check out this post for details on a similar project built by Dennis (Morgen 3Eman).

Unfortunately, Dennis has not been on the forum since his last post in July 2016, and his own website www.horsepowerportraits.com is no longer accessible, which makes me fear the worst. 

Alan
 

[Evolknuj]

Thanks Alan!
I'm about settled on the GM motor and controller, but still not really understanding the battery options.

If the total energy in a battery pack is kWh, and kWh = V x Ah... does that mean a 48v 30Ah battery would be equivalent in total energy to a 72v 20Ah battery?  48x30 == 72x20.

And would the 72v battery allow creating the same power at 50 A that would require 75 A at 48v?  72*50 == 48*75 == 3600

That all seems like simple obvious math... which means the GM 4830 battery which has a continuous discharge rating of 60A would only be able to power 48*60 == 2880 watts at perfect efficiency.  I.e. would be suitable for the full power range of the HPM3000 BLDC 3kw motor.  The HPM3000 is rated at 2-3kw, with peak up to 6kw.  If I used the HPM5000B 5kw rated motor, the 4830 battery would be unable to supply it with enough amps at 48v to really achieve its rating.

Again, that all seems like obvious math... am I missing anything?  Any recommendations for either 48v or 72v or even 96v batteries that would be better matched with the HPM5000B?  I'm leery of being underpowered due to vehicle (and driver, ahem) weight and the hills around here, even at low speeds.

[Evolknuj]

On other forums I've had 72V 40Ah A123 battery pack off ebay recommended -- very powerful, very high continuous amp discharge, easily could power the 5kw motor... but also heavy and doesn't have BMS, and adding BMS seems..... hard.

Any thoughts on using the LunaCycle 52v 25Ah, 90A continuous rated battery available here? https://lunacycle.com/52v-25ah-high-power-monster-battery-for-pedicab-or-ev-with-charger/?ctk=1ac5862e-bc96-4c13-8b92-8b1f8946147c
It seems like it would be a good turnkey solution for my build -- 48v * 90A == 4320 watts, so would be a good fit for the 5kw motor/controller combo (I think -- first time EV build!).

Is it dangerous to use a 14s (52v) battery with the Goldenmotor 48v motor/controller combo?

[Bikemad]

If the total energy in a battery pack is kWh, and kWh = V x Ah... does that mean a 48v 30Ah battery would be equivalent in total energy to a 72v 20Ah battery?  48x30 == 72x20.

And would the 72v battery allow creating the same power at 50 A that would require 75 A at 48v?  72*50 == 48*75 == 3600

That is correct.

That all seems like simple obvious math... which means the GM 4830 battery which has a continuous discharge rating of 60A would only be able to power 48*60 == 2880 watts at perfect efficiency.  I.e. would be suitable for the full power range of the HPM3000 BLDC 3kw motor.  The HPM3000 is rated at 2-3kw, with peak up to 6kw.  If I used the HPM5000B 5kw rated motor, the 4830 battery would be unable to supply it with enough amps at 48v to really achieve its rating.

Correct again, but if you used 2 battery packs in series and a 96V 5kW motor/controller you could then run it @ 5000 Watts continuously. 

Any thoughts on using the LunaCycle 52v 25Ah, 90A continuous rated battery available here? https://lunacycle.com/52v-25ah-high-power-monster-battery-for-pedicab-or-ev-with-charger/?ctk=1ac5862e-bc96-4c13-8b92-8b1f8946147c
It seems like it would be a good turnkey solution for my build -- 48v * 90A == 4320 watts, so would be a good fit for the 5kw motor/controller combo (I think -- first time EV build!).

Is it dangerous to use a 14s (52v) battery with the Goldenmotor 48v motor/controller combo?

I don't have any experience with LunaCycle batteries to know if their claims are correct, but hopefully the figures stated are genuine.

It is perfectly acceptable to run a 48V GM motor/controller from a 52V battery

I did not notice any mention of the number of expected charge cycles for the LunaCycle's 18650 Lithium Ion cells, but I would expect it to be a lot less than the stated >1000 stated for the GM LiFePO₄ cells.

I think that the LFP4830M GM battery's output of 90 Amps max and 60 Amps continuous should be more than enough for a vehicle geared for 35 mph max speed on the level.
You will need to calculate approximately how much power will be required to maintain the required 35 mph, and then make sure that the motor rpm is low enough at that speed to allow the required power to be produced, as the maximum available power output of an electric motor usually diminishes at higher rpm.

If you take a look at the Dynomometer data for the 48V 5kW motor, you can roughly estimate that the motor would need to be operating at full throttle below ~3700 rpm to draw ~90 Amps. And above 3900 rpm, the motor will be unable to draw more than 60 Amps.

I suggest that you brush up on your physics and maths and do some rough calculations to find out what torque, power and gear ratios etc. will be required, and what sort of inclines it will hopefully be able to cope with.

Alan
 

[Evolknuj]

Just following up to let anyone interested know that I did get the luna battery pack, and very happy with it so far.  Very nice and solid -- quality feels great even if I can't really verify how many charge cycle's it'll take etc.  I also finally got to the point where my Morgan can actually use it -- forward and reverse even!  See my cyclecartclub link above for more details including pics and video.  Installation (wires etc) still very rough, but I'll be working on that over time.

I haven't gone off my driveway yet, but very happy with the acceleration of the GM 5kw motor and controller so far.  We'll see if I run into any problems with hills or maintaining speed once I've double-checked all my bolts and really go on the road.

[Evolknuj]

Dangit.  Last weekend after taking a spin around the driveway I cleaned up the mess of saw dust and metal shavings in the garage.... and the 3-wheeler wouldn't start.  Multimeter verified voltage was available at the controller, but no reassuring "beeeep" of it turning on at all.  It had worked just fine 10 minutes prior, and hadn't been doing anything strenuous.  I tried it again a day later and still dead.  My son tried it a couple times and claimed it beeped once... but now doesnt.

How can I debug what's wrong?  I have the USB cable, but have never used it before -- is there a good guide to how to do diagnostics?  I'm not even sure where to get the software or if it only needs the USB cable hooked up or also needs to be connected to battery for diagnostics.

Help!