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Battery Sizing

1oddtech

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May 22, 2020
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Central Va.
Just left chit chat and found this forum. I'm "wanting" to build a 2 seater UTV sized EV with 4 frame mounted independent motors driving portal boxes on the end of independent suspension. Found some lightweight axial high power motors (50 hp each continuous 81 HP peak iirc) and high voltage controllers but trying to calculate battery sizing to give a decent day of trail riding has been difficult. Discuss
 
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$$$.

What type of trail riding? Speed, range, terrain, and %time active are going to play a huge roll.

How heavy are you expecting without batteries?

What voltage are the motors and controllers?

What sort of steering?

Any estimate of the power demands for stuff like cooling, lights, etc.?

Are you going to run peak power on all motors simultaneously or will there be something controlling max combined power?


General principal is:
motor voltage / battery voltage = number of batteries in series
Peak current / battery capacity and c-rate gives parallel
Pack capacity / battery capacity= parallel
Max of the two parallel values is the number to use.
 
On the east coast is mostly slow trail riding so the motors would probably only be putting out 25-30 hp each with a giggle switch for wide open. Liquid cooled motors and controllers with a central main cpu. I'm thinking 400v to improve efficiency and reduce amperage. Electric power steering rack with the ability to lock the rack and "skid steer". This is all still in the very preliminary stages of design and by the time I get around to actually doing it electric performance UTV's will be already out. As far as weight I have no clue. Most utv's now are around 2k lbs so around that weight maybe 2500¿
 
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These are the motors I was looking at due to power density, size and IP65 liquid cooled rating

188 (60kW | 100Nm) - EMRAX

Axial flux motor / generator; up to 52 kW, up to 90 Nm; size 188 x 77 mm; weight 7 kg; air (IP21) / combined (IP21) / liquid (IP65) cooled.
emrax.com emrax.com
 
Have you looked at the new electric Polaris General I think it is. Supposedly 110hp. Just thinking it may give you a starting point for batterey info.

2023 Polaris RANGER XP Kinetic UTV

The all-electric 2023 RANGER XP Kinetic is the world’s most capable, most durable, and highest performing electric UTV. The all-new electric powertrain boasts uncompromised capability and unrivaled durability.
www.polaris.com www.polaris.com
 
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JohnnyJ said:
Have you seen Rich Rebuilds SXS series on youtube? Might get ideas on battery size from there.
Click to expand...
I had heard about that and thought it was a new model machine being released so maybe the market isn't as close as I thought. Thank you
 
Tesla's battery efficiency is claimed to be about 0.25-0.4 kwh/mile. That's a car that in ICE config would probably get 30-35mpg.
Class 4 bus (think 15 passenger E450) is about 0.9-1.2 kwh/mile. ICE equivalent there is 6ish mpg.
I'd think an off-road play toy is closer to the E450 efficiency, so I'd lean towards those numbers when figuring out battery sizing.
On the plus side, 100 miles is a lot of trail riding, on the minus side, 40kwh of battery is about 600lb.
 
ScottRS said:
Tesla's battery efficiency is claimed to be about 0.25-0.4 kwh/mile. That's a car that in ICE config would probably get 30-35mpg.
Class 4 bus (think 15 passenger E450) is about 0.9-1.2 kwh/mile. ICE equivalent there is 6ish mpg.
I'd think an off-road play toy is closer to the E450 efficiency, so I'd lean towards those numbers when figuring out battery sizing.
On the plus side, 100 miles is a lot of trail riding, on the minus side, 40kwh of battery is about 600lb.
Click to expand...
40kwh is what the Polaris uses and claims 80 mile range with 110hp
 
1oddtech said:
These are the motors I was looking at due to power density, size and IP65 liquid cooled rating

188 (60kW | 100Nm) - EMRAX

Axial flux motor / generator; up to 52 kW, up to 90 Nm; size 188 x 77 mm; weight 7 kg; air (IP21) / combined (IP21) / liquid (IP65) cooled.
emrax.com emrax.com
Click to expand...
Do you know which controllers you in plan to use?

The 188s turn pretty fast. You're going to need more reduction than most portals have.

Some data on past and current off-road EVs
The new hybrid Wrangler (5100 lbs) has 17.3 Kwh, about 15 usable, and a range of 20 miles in town. TFLoffroad found it got 4ish miles going up Red Cone pass before the motor kicked on. Once we account for the 5.6 Kwh that went it took to take that 5000 lbs up 3000 ft, that leaves us with 2.5 kwh/mile trail riding.

TonyK had 6.7 Kwh and could get 4 miles of southwest crawling. I have found one other electric buggy, that gets 4 hours of eastern wheeling out of 16-18 kwh battery. An EV Samurai over on PBB gets a couple hours hours out of 13.3 Kwh. He believes it can do the Rubicon in one charge, but takes a generator and charges it just to be safe. Also says that wheeling in low range he averages 25 A or 2.4 kw draw. With his 96 V pack, that puts him at 5-6 hours. That makes me believe that 25 A is the average when moving and not over the entire ride.
Click to expand...
 
Peak power is around 6500 rpms so I would need roughly a 10:1 reduction so yes I would need some reduction between the motor and CV's. Also looking at Sevcon/Borg Warner controllers. I want everything liquid cooled.
 
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