How many electric horses does a car need?

[Desertprep]

I recall reading once that only about 40% of the horsepower from the engine actually gets to the wheels. So...if a car had 100 horsepower at the engine what size electric hub motors would you need to install (assume 1 in each of the four wheels) to equate what the car had before?

 

[TylerDurden]

1hp = ~750W

 

[Desertprep]

Thanks! But if a car engine puts out 80 horsepower but only 28 get to the wheels...does that mean an electric car with hub motors needs only 28 horsepower? Less? I have heard that the power ratings of engines and electric motors are different, that the car would actually need fewer horsepower than the 28.

 

[Link]

I'm not sure about the 40% figure. That would have to be a pretty crappy drivetrain. I think 85-95% is more on the mark.

But, you have to consider that the engine won't make its peak horsepower out of a very specific RPM range. The motors will.

Just a WAG, but I'd say you'd need about 50hp to match it if neither gets to top speed. But, horsepower is horsepower, and (drivetrain losses aside) the more powerful one WILL eventually catch up the the weaker one.

 

[fechter]

Perhaps 40% of the energy in the gasoline gets to the wheels. From the engine to the wheels should be much higher. The big difference is that an electric motor can make maximum torque at zero speed. This allows a much smaller electric motor to provide similar performance.
Cheap hub motors are usually around 85% efficient. Really expensive ones are up to 98%.

 

[knightmb]

It depends on a lot of factors, mainly terrain and how fast you want to go and how fast do you want to reach that top speed. Really, there is so much loss of energy for gasoline to mechanical conversion of energy you can't really put a simple static number on it. Some cars are better than others, some engines are better than others.

That's kind of why I've liked the simplicity of electric vehicles. You can put a meter on it and tell for certain how much power you are burning to get to X amount of speed instead of the millions of factors that can affect a gas engine and can't really be measured in real time everywhere.

100 HP electric would be about 100 X 745 = 74.5 KW of power. I'm not even sure the "rated" 166 HP in my SUV could really put out that much power if I hooked the engine to a dynamo. One thing I know about a lot of these HP ratings for engines, they are done in tests which I feel don't really reflect real world experience. They take the engine, hook it to some machines and test it in ideal conditions. They don't have to worry about AC, power steering pumps, electronics, lights, etc. So yeah, my engine might do 166HP at 4,000+ RPM, but what is it really after you strap on all the other stuff it has to power for the vehicle?

I would say 100HP (74.5 KW) electric is more than enough for any basic electric vehicle. It will make you go fast enough to get a speeding ticket (up or down hills), can carry plenty of people or cargo, and still have some left over to power your AC and radio. The best part is, you don't have to burn all 100HP everywhere you go. My gas vehicles, they burn engine sitting at a stoplight or just sitting in the drive through at a fast food joint. At least with an electric car the "down time" would be saved energy that isn't spinning my pistons around because they aren't allowed to stop without having to restart them again with *gasp* an electric motor.

 

[drewjet]

It's apples to oranges. You really can't compare the two. However, horsepower ratings are done at the wheels, so you need not worry about drivetrain losses.

IC are rated at max horsepower. Electric motors are rated at max continious power. Generally speaking an electric motor can take about 4 times it's max rating for a short period of time, and this will only be during accelearation. Therefore, if you get an electric motor rated at about 1/4 of the gas engine it is replacing you should be close in performance..

One of the easiest ways to decide if the power is suffecient is to see if someone else has done a conversion similar to what you want and then copy that. Austin EV is a great site for that kind of info.

 

[Deepkimchi]

About 25 to 30 hp.

There are plenty of sites to search on google: Use speed, air resistance, hp to search..

I would but the wife and kid won't be quiet and leave me alone..

 

[Desertprep]

Thanks! One of my reasons for pursuing this is that I live abroad and only return to the U.S every 2.5 years for about 5 months. Finding transportation is always a serious problem. I am thinking that an electric vehicle will store much more easily than a car with an ic and umpteen hundred moving parts that all have gaskets and lube points. My thought would be to buy a new battery pack when I return and sell it when I leave, probably for 60-75% of the cost of the battery pack. I know there are other considerations - interior oxidizing, a/c system leaking, etc but these, in my opinion, are minor. Also I have access to a 88 Dodge Caravan for almost free that looks like it's just askin' for a conversion. The 4 banger comes rated at 96 hp. In China here there are also millions of "bread vans", i.e. small vans that look a lot like a 68 vw van that can be had for cheap...the hub motors I have found so far have sizes more suitable to these vans....boy, I feel like a kid in a candy store! Now...if I only had money.....

 

[TylerDurden]

Thanks! One of my reasons for pursuing this is that I live abroad and only return to the U.S every 2.5 years for about 5 months.

What is the climate of the area in the US you return to?... EVs are not usually good cold-weather candidates.
:?

 

[Desertprep]

Good thought. I usually spend most of my time in Sacramento, CA If I were to go to a cold climate would some kind of battery warmer offset the cold climate effect? Or is there more than batteries to worry about? I have always thought that electric motors were more efficient at colder temperatures and became less efficient as the operating temp increased.

 

[TylerDurden]

The Caravan might be good!

Not too slippery, but light for a van and lighter still if you gut all the insulation and creature comforts. Finding lighter bench seats would also be a plus.


Motors like cold, batteries hate it.

 

[Desertprep]

Also, there were a bazillion of them made - lots of parts. I did a quick check and it seems it is easy to upgrade the suspension with a towing package to be able to hold more batteries

 

[TylerDurden]

http://www.evalbum.com/377

 

[Desertprep]

Nice job! Why do cars all seem to use AC motors? especially when batteries are always DC? There are sooooo many DC options now days....

 

[lawsonuw]

Good thought. I usually spend most of my time in Sacramento, CA If I were to go to a cold climate would some kind of battery warmer offset the cold climate effect? Or is there more than batteries to worry about? I have always thought that electric motors were more efficient at colder temperatures and became less efficient as the operating temp increased.

I think any issues EV's have with cold climates is primarily due to the need for cabin and battery heat during operation. Since EV's efficiently use the energy they cary, there is almost no "waste" heat available to heat the driver, thus most driver heat comes directly out of the EV's range. (there are ways around this for more $$) As far as I know, cold is just fine while storing batteries though.

Why do cars all seem to use AC motors? especially when batteries are always DC? There are sooooo many DC options now days....

There are a couple of reasons I can see. First, no brushes so the only wearing part in the motor is are the ball bearings and ball bearings last a LONNGGG time. The other thing going for AC motors (specifically AC Induction motors) is the torque-speed properties. Basically an AC induction motor makes it easier to convert a car by reducing the need for a multi-speed transmission.

Marty

 

[TylerDurden]

Cold is fine for storing batteries, but not so fine for getting the juice out when operating.

Cold sux when trying to defrost a windshield with a 12V hairdryer.

 

[ngocthach1130]

Cold sux when trying to defrost a windshield with a 12V hairdryer.

Words of true wisdom through personal experience?

Too bad we need to breath. Otherwise they sell those propane fueled outdoor heater that would work great. Maybe section off part of the cabin toward the rear to house the propane heater to heat some heat exchanger running into the driver's area? Might have to bolt it down though. Don't want to hit a pot hole and the propane tank shoot out flame at the car.

 

[Lowell]

Engine power vs true measured wheel HP is 75-80%. We have a Mustang AWD chassis dyno which measures horsepower via a load cell, and 300hp cars put down around 220whp. A 415hp Porsche 996TT shows ~325whp. My 1998 Pontiac Firefly 3cyl is rated 55hp at the crank, but only managed to get 33 of them to the ground. Fixed losses from the driveline and tires contribute to the lower reading.

 

[Drunkskunk]

Well, if you are willing to eliminate some top speed, and settle for something that can hit 55 max, then you don't need that 98 HP of the carivan. A manual transmission is good for about 85% of the engine power, but an automatic, Like the Ford C6 is lucky if it can deliver 60%, so depending on the Carivan's transmission (Chrysler Front wheel drive Autos are natoriously bad) you probaly only had 60-70 HP anyway.

You can cut that number in half, as I'm beting you won't need to haul a wife and 6 kids plus a weeks worth of luggage at freeway speeds, so 30-35 HP at the wheels should run it on gas, and since Electric makes max torque at zero RPM instead of at peak, you could almost cut that number in half again for electric. Lets call it 20 HP. Thats 15Kilowatts by my rough figures, but most builders on that Austin site seem to favor 20KW motors. probably because they run through transmissions at a 15 to 20% loss. All rough figures, but my numbers seem to be coming up with what others have done.


RVs use a propane heater that runs on a heat exchanger. should be easy enough to modify one to fit in the engine bay of a caravan.

and IIRC, the caravan has a nice flat floor from behind the driver seat all the way back, so adding batteries sould be easy.

 

[truckerzero]

my motorcycle makes 50hp at the crank and 40 at the wheel and has a top speed of 100mph and needs about 10 hp to do 60 so from what the one person said about continuous power of electric motor being 1/4 ice peak hp is a good referance point

 

[dogman dan]

Lots of things to consider here Pengyou. Horsepower ratings are apples to oranges comparison. A ten horse DC motor can produce hundreds of horsepower depending on the configuration of the voltage and amperage the controller sends the motor. From what I've seen on the web, most of the home conversions use as small as 8 horse motors for little cars like bugs, geos, festivas. Bigger vehicles like small vans and light trucks use motors that are still under 20 horses, but they produce a lot more than that the way they are used in a vehicle. Most home conversions use DC motors to keep it simple, just like we do with our e bikes. Factory ev's use AC motors for efficiency reasons, but run at deadly voltages like 300 volts so you don't just pop the hood and fool around on one of those if you want to live. What you convert will depend largely on what you need it to do, not on what vehicle is free. Cars with a bad engine are easy to buy cheap. If you are going to need only low speeds and short ranges like 45 mph and 20 mile range, a really good first project is to convert an old volkswagon. complete kits are avaliable really cheap and not having to tear the dashboard out of the car to do the wiring can be a real savings. The next easiest conversion seems to be a small pickup. In all cases they need to be standard shift, and I haven't seen that in a caravan that I've owned or looked at to buy. Some car models just weren't made with a stick. In genearal the more stuff a car has on it the more hard it is to get it all to work again after the convert. Bugs are ideal since they came with nothing to begin with. Allmost all parts are still avaliable for bugs from various mail order outfits. They just can't carry enough batteries to go very far. But a VW van could.

 

[lawsonuw]

When I replaced my tranny in my 1990 Plymouth voyager a few months ago my gear head friend who did most of it was tempting me with putting in a 5-speed manual. (it was just rusting in his garage. From another car, but he said it'd fit just fine) I'm pretty sure the 4-cylinder versions had manuals available. Also, I think a mini-van like mine would be an ideal conversion. With the fuel tank and exhaust gone it'd have a 10inch thick space 36in wide and about 72in long stretching from the front to rear axle with only a few ~3in tall floor beams to miss. Could fit one heck of a battery in that space. Aerodynamics are pretty bad on these old crates so getting good range is more expensive, the massive cargo space makes up for it some. Too bad my car is half rust by weight.

Anywho, manual tranny mini-vans DO exist but are rare.

Marty

 

[dogman dan]

I just know I hadn't owned or seen a stick in a minivan, and I've had a couple plymoth vans. One thing I learned reading all the car conversion blogs was that a lot of conversions suffer from poor donor vehicle choice. Extra metal is an anchor to carry around especially if the car is to run on lead batteries. People get stuck on the idea of a free donor vehicle when that is 5 or 10% of the cost of the project. Then they need an extra $2000 for enough batteries to haul the heavy, unsuitable car around. I saw one blog where a guy wanted to convert his F250 4wd truck. To get a 5 mile range he's gonna need enough batteries to take 5 geo metros that far. Put a load in the bed, and he won't make it around the block. The volkswagon conversions are soooo much less work to convert, and in the west they are still around to buy cheap. If Pengyou really needs the van space, fine, but the free electric car donor is often very expensive, especially if it does not fit needs. The number one need of EV's is to be lightweight. The minivans are light for vans, but still pretty heavy. I know, I've owned three of em, four if you count the VW.

 

[truckerzero]

from the research i did my choice would be a honda crx they are still around and kept alive by the tuner croud has the lowest cda of any car ive seen short of a honda insite are cheap to buy and are as light as a geo metro(1800 lbs) but in my opinion kind of high on the cool factor a pretty nice looking car for only 1800 lbs what does anyone else think of this choice