[Killzilla]

Hello all,

I have been making a custom reverse trike for personal use. A few specifications:

Design - Reverse Trike (2 Wh front and 1 Wh back which is my drive wheel)
GVW = 650 kg
Battery Pack = 48 V Lead Acid (12 x 4)
Ampere hour rating = 100 Ah or 200 Ah (varies)
Motor = 10 KW BLDC motor from Golden Motor
Final Drive Ratio = 1:10 or 1:5 (varies)

I wanted the vehicle to reach at least 80 km/hr or 50 mph, however with my 1:10 drive ratio @ 100 Ah I was only able to get to 26 mph and with 1:5 @ 200 Ah I was able to get to 31 mph (this with vehicle weight of 750 kg). Obviously I am not getting to the required top speed and I am looking at Lithium ion to provide that extra oomph to get me to my desired speed.

However my question is this, would it even make a difference?
Would a 48 V 60 Ah lithium ion give me more power? (or more Ah for the lithium ion) Based on my understanding there is too much sag because of the Lead Acid batteries and is not providing enough power for the motor. My calculation shows that the motor is only getting 6 KW of power from the lead acid. Which is why it isn't getting to it's required speed.

If anyone has any suggestions I would greatly appreciate it.

P.S. - I am on a very tight budget so can't go splurging beyond a certain limit.

 

[Killzilla]

The sag will depend on the particular battery. Some lead-acid will sag less than some Li. Trying to get 10kW from a 60Ah 48V Li battery puts you into 5C or 6C discharge territory.

Invest in a voltmeter and ammeter so you know what you're getting now.

major

I am thinking of buying a lithium ion battery of the LiNiMnCoO2 chemistry. The one I am looking at is a 48V 20 Ah rated battery (will use 3 or 4 in parallel). Here's the link for the battery I am looking at
http://www.cnchaowei.com/en/upload/BN4820CI.pdf

Would this battery be able to deliver a better performance than the lead acid batteries. The manufacturer of this battery has said not to discharge for than 1.2C. Are they being overly cautious with this number? I thought Lithium ions would allow for a higher discharge rate. Is it OK if I have a discharge rate of say 2-3C for 4-5 seconds at best?

 

[Killzilla]

1) What model controller are you using
I am using a golden motor 10 KW motor controller. And using the motor.
Here's the link to the motor and motor controller:
https://www.goldenmotor.com/

2) How much sag are you seeing now? That is, what is the voltage from the batteries under load?
The fully charged battery sags to 45-46 V

3) What is the discharge current now?
We see 100 Amps on our clamp meter

4) Any other instrumentation numbers; Max current under load, average current drawn, etc.
We have driven the vehicle on 100Ah Lead Acid battery for 70kms with 70% battery usage. The controller can take up to 250 Amps.

5) I have tried gear ratios of 1:10 and 1:5. 1:10 gave us the speed we were expecting (~around 40 km/hr). 1:5 should have theoretically given us around 90 km/hr but we barely went over 50 km/hr using 200 Ah. The moment it reaches 50+ km/hr the speed barely increases, and if it does, it does so at a very slow pace which isn't acceptable.

If you have any questions I'll be glad to answer them.

 

[Killzilla]

At 200 Amps and 45 Volts you have reached the limits of the controller and motor. There may be a thermal safety limit in the controller also to protect from meltdown. Take a look at the 48V motor curve and see if your speed and torque match up with that. What size tire and wheel are you running on the rear--need to know that to calculate road speed to motor speed.

Running a 600mm diameter wheel (roughly 23 inches). Motor operates at around 4000 rpm. According to the manufacturer of the motor it should be able to get to higher speeds, hence my concern regarding the lead acid causing issues.

 

[Killzilla]

Thanks Brian for taking the time in your reply and providing an insightful answer. It seems that the motor is simply not good enough to provide the necessary power. I have visited EVdrives.com and selected an entirely new set of motor and motor controller to work at 48 V.

Motor: http://www.evdrives.com/product_p/mot-me1602.htm

Motor Controller: http://www.evdrives.com/product_p/con-sr48400.htm

I am cutting back on my top speed expectations and settling for 50 mph (80 km/hr) as top speed. Also investing in a single speed transmission instead of the direct drive I had earlier to provide me the torque I require. The motor is rated at 6.4 KW @ 48V. In your estimation is this motor any good? The motor typically hovers around the 3500 mark unloaded. Would you say ME motors have better performance compared to Golden Motors?

And if you could recommend a motor that you think is good enough to sustain the performance requirements I am looking at. Somewhere in the range of $1000-$1200 for both motor and motor controller.

Thanks.

 

[Killzilla]

In order to understand better my motor's performance I asked Golden Motor for their 72V and 96V graphs to compare with the 48V motor's graph and performance. If anyone can help in making sense of it I'd greatly appreciate it. The graph is really convoluted and doesn't make complete sense to me. My question being that provided I go to a higher voltage system (72 or 96) would a GM motor do the needful or I'd still look into getting a forklift motor for my needs?

 

[Killzilla]

Thanks for your prompt reply. I feared that even changing the voltages won't make a massive difference. I will try getting the speed vs torque curve at the drive wheel and graph it out. That should give me a clearer idea.

 

[Killzilla]

Question regarding a new build.
Previously I used Lead Acid batteries (48V 200Ah) and got up to 30-35 mph. My motor was a 10 KW BLDC motor. I tried every possible gearing but was not able to reach my optimal speed of 50 mph. My assumption is that the battery pack simply cannot provide enough juice.

Therefore I am about to invest in a completely new drive train. I am looking at the AC-9 Motor (http://www.electricmotorsport.com/ac-9-kit.html) along with a Lithium ion battery pack, 48V 100 Ah (MnNiCo Composite Material + LiMn2O4 chemistry). This is my max budget that I can put into the vehicle.
Vehicle weight is 650 kgs with 2 passengers.