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5 Posts
Discussion Starter · #1 ·
Howdy all,

A newbie to the EV world, though I have been following the tech a bit over the years. Typically an old car guy, I've "restored/restomod" a number of ICE cars - ('67 Mustang, 50 Jeepster, 49 Jeepster, 54 Singer, 47 Dodge, and 2 CJ2a's)

Recently I was doing the last Jeep CJ2a, and when I purchased the tub the lady said she had "other parts" if I want them. Well, the "other parts" turned out to be an almost complete CJ2a - frame, springs, tub, transmission; everything but the engine and differentials/axles.

Well, rather than do CJ2a #3, I'm thinking of doing CJ2aEV. I've only seen 3 other Jeeps converted on the forum and other online sources. (an MB, CJ5 and CJ7)

So here's the scenario:

Your skill level with auto mechanics and fabrication
- Minimal, weekend warrior with an excellent mechanic friend. I can do more than most but wouldn't say I'm skilled. Still very much an apprentice. Regarding fabrication, similar. Been welding for about 3 years now - lamps, fences, tables. Mostly 16-1/4" mild steel via MIG. Flux on the odd occasion when convenient. Some Oxy/Acet experience, but not much. I have an Oxy setup as well as Lincoln 120v MIG

The range you are hoping to get (how many miles/charge)
- I currently drive my CJ every day, but local errands. Maybe 20 miles total. I would like to have the capability to get 100 or so miles if practical. I'm in LA so it would be nice to have the occasional road trip to Palm Springs, Santa Barbara, San Diego. As said, I do want something relatively practical.

What level of performance you are hoping to get
- The CJ's weren't meant to go more than 65 or so, and "off the line" performance is a non-issue. Freeway capable would be good. It's actually something I can't do safely today with the ICE.

How much money you are willing to put into your project
- Not looking to spend a ton, but reasonable as to what these projects cost. I'm thinking of starting slow on the batteries and adding battery banks as the other bank allows. I know this will add some challenges. I can and will spend accordingly.

What parts you've already considered, if any.
- What I am thinking, based on scouring the forums, youtubes, and other searches over the past few weeks is the following:

Motor - DC forklift motor - 48v or 72v if I can get one. AC-35 or 50 is an option as well, but I think going to an AC system will bump my costs up.
Controller - Most seem to be using Curtis. Thinking running the system at 96-120v and 500amp? No idea. Thoughts, inputs and suggestion highly recommended on this one.
DC-DC - Not too particular. There's not much electrical in these other than the basics so I don't need anything fancy (30a)
Charger - No idea
Battery - Probably LifePO4 but curious how hard (vs labor intensive) an 18650 bank would be.
BMS - Still trying to figure out what's what and how they work. I know what they do, but 3s, 4s, 96s, etc is getting me cross-eyed. Particularly when comparing LifePO to 18650

What I need help with:

I know the DC motors give you more torque compared to AC. My concern is the transmission gearing already provides a lot of torque. From what I understand I'd want less torque and more volts since I have plenty of gearing to handle RPM and Torque concerns

Since I don't have diffs and axles, that does give me some flexibility -
I don't need to run 4wd so I can put in any rear-end I want (I have a spare Ford 9" but it's too wide and would look odd)
I can get standard diff/axles but then I'm back up to the torque question as the diffs are 5.33.

Thanks in advance for the help and advice. I look forward to this project. A whole new world.

5 Posts
Discussion Starter · #3 ·
From what I've read on the forum. It's been stated many times in many threads. If I am wrong please correct me. As I said in my post, I'm new to this and learning.

In most forums it's okay to be wrong. What I've noticed here is the members tend to get off on flaming other folks versus giving helpful advice and counselling.

I am hoping to get some useful feedback on my ideas, as well as suggestions on how to do it better and what I may have missed.

If I am wrong, perhaps a comment of why I am wrong and how I may be misguided is more productive.

8,170 Posts
I know the DC motors give you more torque compared to AC.
From what I've read on the forum. It's been stated many times in many threads.
I think you're seeing other people's impressions, based on rumour and driving impressions rather than fact. I've never seen a dynamometer test result for a DIY-built electric car, and even an acceleration test result is rare... let alone tests of the same car with two different motors for comparison.

One problem is that there is not just one size and rating of motor, so what DC motor do you compare to what AC motor?

A brushed DC motor and a synchronous (ignore induction for the moment) AC motor are really very similar: there is a rotor winding field and a stator winding field and their interaction to provide torque. In both cases, torque is a function of the rotor radius and the field strength, and the field strength depends on the number of turns of winding and the current through them, and how much magnetic flux the "iron" of the motor can handle. So if you're comparing, you could compare by:
  • torque for a given mass of motor
  • torque for a given current and voltage
  • torque for a given power, even if a different combination of current and voltage
All of those will vary even between DC motors. Maximum torque for a given motor will depend on what the user decides is allowable for current. Getting any useful data for any DC motor will be difficult, because most are salvaged and used far outside of rated conditions, and the rest are built by companies that don't even have the equipment to test them properly.

To illustrate part of the comparison problem, here are three specs for the same motor (an induction motor, but the manufacturer provides some specs), with the same supply voltage to the same controller:
  • AC-50 continuous without cooling: 28 lb-ft of torque at 190 amps and 3000 rpm (unknown voltage under 96V)
  • AC-50 continuous with fan cooling: 96 volts gives 50 lb-ft of torque at 360 amps and 4000 rpm (unknown voltage under 96V)
  • AC-50 peak:121 to 110 lb-ft of torque at 655 amps and 0-3500 rpm (likely 96V)
Unfortunately, all those currents are from the battery to the controller, not into the motor, which is nonsense but that's all that HPEVS provides. Still... what numbers do you use, and are they comparable to other motors in the comparison?

DC motor ratings from NetGain are based on a really primitive friction brake test, and are presumably all peak values that can't be sustained. A WarP 9 is listed at higher torque than any of those AC-50 values, but lower speed, and hundreds of amps.

Motors from serious and reputable manufacturers (e.g. HVH motors from BorgWarner, formerly Remy) are typically provided with much more useful specifications, but those motors are priced out of range for almost all DIY builds. The same manufacturers don't make brushed DC motors (so you can't get comparable specs), because there is no market for them; even forklifts don't use them anymore.
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