DIY Electric Car Forums banner

1 - 20 of 108 Posts

·
Premium Member
Joined
·
103 Posts
Discussion Starter #1
Is there a post on this wiki or in the main forum comparing the pros and cons of AC motors vs DC motors?
Thanks everyone!
 

·
Administrator
Joined
·
6,137 Posts
Hi DrGee

DC means series wound with brushes (there are some sepex but very rare)
Old school technology - you can get oodles of power cheap but you can't get re-gen
Cheap and cheerful and powerful - but unsophisticated

AC - as in new AC - expensive and wimpy

AC as in taken from a crashed EV
Definitely the best - sophisticated powerful and you get re-gen
BUT you either have to nut out all the CANBUS stuff - or else replace the "electronic brain"
 

·
Registered
Joined
·
1,124 Posts
Specifically, what type of AC motors are you considering.

Like, if you want to do basic research, you can probably do that on your own.

If you're having trouble deciding between a few things you've looked into, that's where the forums are helpful.

I presume you don't want a technological review, you just want to know from a DIY perspective, why would you choose one over the other?

AC:
- More expensive.
- More expensive controllers.
- More complicated.
- Can use regen braking (adds 5% to your range, saves you from a $50 brake job every 5 years).
- Easily reversed/transmissionless.
- Generally, OEM salvage are fairly beefy motors and a complete solution.

DC:
- Dirt cheap, used you pay $200 scrap value.
- Cheaper controllers.
- Dead simple.
- Can't use regen braking (technically can, but no one does and no controller uses it).
- Brushes eventually wear out after years and need replacing.
- Reversing is a bit of a chore mechanically with most controllers, usually you'd keep the car's original transmission to do that.

I wouldn't go purchasing a new AC motor or anything other than an AC motor from a wrecked OEM vehicle.
 

·
Premium Member
Joined
·
103 Posts
Discussion Starter #6
Great stuff guys, thanks so much!
A bit disappointed that DC motors don't do reverse easily - I was hoping to get rid of the transmission in my proposed ev build.
I can do without regen. I love the concept, but it's a bit too much complexity for a little gain.
Once again, this forum is the best!
 

·
Administrator
Joined
·
6,137 Posts
Hi
DC motors do do reverse - that is how my car works

But it's not as simple as reversing the wires - you need to reverse either the field coils or the armature

The simple way is to use a "reversing contactor" - every forklift has one!
 

·
Premium Member
Joined
·
103 Posts
Discussion Starter #8
Aha.. a DC motor with a reversing contactor - this looks like the way forward for me ( excuse the pun)
 

·
Registered
Joined
·
136 Posts
just a few comments after going through several DC motors, They can be gotten cheap, great power capability and they work well but make sure that you don't:

design poorly or gear poorly as you will overload/heat the motor (AC motor is sophisticated enough to protect itself from overheating.)

ever hill hold or accelerate while creeping backward or have a less knowledgable driver drive the car ever. (AC motor is more bullet-proof, no brushes to burn up)

I have Hpevs AC motor that I really like. not much increase in range from regen but saves the brakes and the resulting brake dust pollution.

The Orion BMS talks to the 1238 AC controller and when a cell gets too low, power is cut slowly to the motor ensuring that you don't over discharge cells. (This feature is probably available for dc controllers with a BMS so equipped.)

I am not an engineer but have driven and upgraded EVs for 20+ years.
 

·
Administrator
Joined
·
6,137 Posts
design poorly or gear poorly as you will overload/heat the motor (AC motor is sophisticated enough to protect itself from overheating.)

.
As a cynical engineer I wonder if the aftermarket AC motors protect themselves from being overheated by "sophisticated" means
Or just by being so wimpy that they are protected that way!

If I limited the current on my forklift motor to match the power on the Hpevs AC motor then it would never overheat!
 

·
Premium Member
Joined
·
103 Posts
Discussion Starter #11
Leaving the motor aside for a moment and shifting to the gearbox.. Is keeping a 4x4 automatic transmission feasible in an ev conversion? Emphasis on "automatic". If it's a sensible option, I'll keep the gearbox & use only one large motor instead of my plan to use two smaller ones.
 

·
Registered
Joined
·
4,914 Posts
Leaving the motor aside for a moment and shifting to the gearbox.. Is keeping a 4x4 automatic transmission feasible in an ev conversion? Emphasis on "automatic". If it's a sensible option, I'll keep the gearbox & use only one large motor instead of my plan to use two smaller ones.
That really doesn't have much to do with AC versus DC... why not put everything about your build in one build thread in All EV Conversions and Builds?

A reference source (not a place for discussion) from the DIY EV Wiki > EV Information section:
Automatic Transmissions in EVs
 

·
Premium Member
Joined
·
103 Posts
Discussion Starter #13
Leaving the motor aside for a moment and shifting to the gearbox.. Is keeping a 4x4 automatic transmission feasible in an ev conversion? Emphasis on "automatic". If it's a sensible option, I'll keep the gearbox & use only one large motor instead of my plan to use two smaller ones.
That really doesn't have much to do with AC versus DC... why not put everything about your build in one build thread in All EV Conversions and Builds?

A reference source (not a place for discussion) from the DIY EV Wiki > EV Information section:
Automatic Transmissions in EVs
Thanks so much Brian!
 

·
Registered
Joined
·
1,773 Posts
Hi DrGee

DC means series wound with brushes (there are some sepex but very rare)
Old school technology - you can get oodles of power cheap but you can't get re-gen
Cheap and cheerful and powerful - but unsophisticated

That is not entirely accurate. I am no fan of DC motors, but SEPEX motors are found in all three the major golf cart manufactures, and crosses over into their PTV and NEV lines as well. Secondly every one of those SEPEX do regen. In the golf cart world Series use to be default, but not today. EZGO is th eonly one who uses AC motors for their high end stuff, but Fleet line and consumer carts are SEPEX.




AC - as in new AC - expensive and wimpy

Expensive yes, wimpy not so much IMO. Again my experience is with racing golf carts, but HPEV AC15 motor smokes any DC motors has to offer. The AC15 develops 70 foot-pounds of Torque from 0 to 5500 RPM (71 HP Peak) and rated 16 HP continuous at 8000 RPM. Not wimpy in golf cart world and is the most powerful motor available for golf carts and NEVs. None of the DC motors made for golf carts can even come close. With a 17:1 transmission is roughly 1200 foot-pounds of torque applied to the wheels on a vehicle that weighs less than 800 pounds. Not many ICE vehicles have that power to weight ratio.
 

·
Registered
Joined
·
4,914 Posts
DC means series wound with brushes (there are some sepex but very rare)
Old school technology - you can get oodles of power cheap but you can't get re-gen
I am no fan of DC motors, but SEPEX motors are found in all three the major golf cart manufactures, and crosses over into their PTV and NEV lines as well. Secondly every one of those SEPEX do regen.
There seems to be an assumption in this forum that all DC motors are salvaged from old forklift trucks or purchased from a supplier or two who specialize in motors that look like refurbished old forklift truck motors. If you assume that, then they nearly all have series field windings. The commonly used controllers are for these motors, so they cannot handle SepEx motors.

Since the series winding configuration is the only reason that "forklift" motors are not suitable for regen (because the field cannot be controlled), it makes sense that motors with separately excited field windings are routinely used for regenerative braking.
 

·
Administrator
Joined
·
6,137 Posts
There seems to be an assumption in this forum that all DC motors are salvaged from old forklift trucks or purchased from a supplier or two who specialize in motors that look like refurbished old forklift truck motors.
It's the size - for a car you want at least a 9 inch motor which will be about 60 kg

I'm using an 11 inch 102 kg motor

As far as I know Golf Carts all use much smaller motors

Which makes perfect sense as they are intermittent use in lightweight vehicles at low speeds while Fork lifts are heavier with much more intensive use
 

·
Registered
Joined
·
1,773 Posts
There seems to be an assumption in this forum that all DC motors are salvaged from old forklift trucks or purchased from a supplier or two who specialize in motors that look like refurbished old forklift truck motors. If you assume that, then they nearly all have series field windings. The commonly used controllers are for these motors, so they cannot handle SepEx motors.

Brian I do not disagree with anything you are saying. Series wound is the right choice for a Fork Lift where low RPM torque is priority over speed. Speed is priority for today golf carts because the three major manufactures also off basically the same vehicle for NEV, LSV and PTV options which means lift the speed limits in the controller along with added DOT requirements to make the Licensed Street Legal. They cannot do that with Series motors.

OTOH there is a crowd in the custom Golf Cart World that insist on using Series wound motors, and there is a large after market motor offerings like from D&D Motors, Admiral, and FSIP to name a few. This crowd is the work horse crowd where the cart is used to haul heavy material, pull trailers, rock climbers, hunting, and swamp buggies. Series motors work best for that where Torque at low rpms are required and speed is not an issue as 10 to 20 mph is more than fast enough for them. Nor do they need a cart to hold speed going up hills. Then there is the other crowd that wants speed and that crowd uses either SEPEX, or if it can be afforded the best of both worlds torque and speed using AC induction motors.

As a fun factoid the worlds fastest golf cart is faster than most ICE manufactured vehicles including sports model. Plum quick motors holds the World Record fastest golf cart. Clocked the 1/4 mile in 12.241 seconds @ 118.76 mph.


Video Link Here
 

·
Registered
Joined
·
1,124 Posts
Since the series winding configuration is the only reason that "forklift" motors are not suitable for regen (because the field cannot be controlled), it makes sense that motors with separately excited field windings are routinely used for regenerative braking.
Except that, mechanically speaking, 99% of forklift motors actually are SepEx, in that, they have all 4 terminals (both field and armature winding ends) independent and accessible. Because almost all forklifts are electrically reversed and have emergency "plug" breaking by reversing the field.

A true Series-Wound motor would only have 2 terminals.

...

That said, to be usefully controlled SepEx usually have thinner wire gauge on the field windings IIRC because they're not simply forcefed the same current as the armature, so, everyone's right in that sense.

Also true that almost no series-wound controllers would ever make any use of the 4 accessible terminals except to mechanically switch them for reversing. They never vary the power levels to them independently, even though they could.
 

·
Premium Member
Joined
·
103 Posts
Discussion Starter #19
Is there relatively simple formula for calculating what type of forklift motor to convert to power a car?
For example, if the motor is rated at 6 hp & 36V DC, can you expect 24hp from it if you power it up to 144V?
Also, when it comes to range, is there any advantage in AC over DC apart from the ability to use regen?
Thanks guys!
 

·
Registered
Joined
·
1,124 Posts
Is there relatively simple formula for calculating what type of forklift motor to convert to power a car?
Almost all electrical limits are thermal.

As in, what you have to worry about is heat buildup. If you add fan or liquid cooling, you can demand far more from the motors. I'm sure there's a theoretical maximum, or at least massively diminishing returns for magnetic reasons eventually, but not in the ranges you'd see people using.

Go look up other builds, but, general rule of thumb, I don't think I've seen anyone even flinch at doing 2x the voltage, 3x is common. Duncan's running his at like, 8x for sprints.

For example, if the motor is rated at 6 hp & 36V DC, can you expect 24hp from it if you power it up to 144V?
Power is the product of Voltage x Amps.

But Amps is the result of Voltage / Resistance, and resistance in the motor isn't changing.

So when you double the Voltage you double the power for that reason, but you also double it again because the Voltage doubles the Amps that will flow.

As you quadrupled the Voltage from 36v to 144v, whatever the Amps that were flowing would (or could) also be quadroupled. 4x from Volts and 4x from Amps is 16x total, so, 96 horsepower.

This of course, as long as you pick a controller that can handle that Voltage, and, not safety limit or blow up at that much current.

750 watts per horsepower so that 6hp motor is actually just rated for 125 amps. You'll be shoving 500 amps through it.
 
1 - 20 of 108 Posts
Top