why are comercial EV's all 48volts?

[monster]

both the G-wiz and the NICE mega are both 48v why is this when we electric bikers are all running 72v systems? i figured that a 200v system would be best for easy charging from mains 240v. whats the minimum watt hours you would want for a small EV car?

 

[Link]

Parts, probably. Anything over about 72V makes finding suitable parts difficult. Really, the only good commercially available controller that will go over 100V is the Zilla, which costs over $2000 (I think). Batteries are probably easier to deal with, too.

And in theory, there shouldn't be any particular disadvantages to running lower voltages. In reality, however, we get crap like ohmic heating.

And I would want at LEAST 2kWh. Bigger ones will have a minimum of 10kWh. That motorcycle on Electric motorsport (the one they don't make anymore) had like 8kWh on it. Didn't last long at the speeds that thing went, though 8).

 

[vanilla ice]

Its harder to hurt yourself with 48v. Maybe that has something to do with it. I'd like to think not, but with the litigiousness of the peeps these days..

 

[monster]

i reckon i could out accelerate a G-wiz on my electirc bike 72v, 20 amp

 

[fechter]

Once you exceed around 100v, the performance of the available transistors drops significantly. Safety might be another reason. There might be loads of additional safety requirements for systems over 48v.

 

[Toorbough ULL-Zeveigh]

It would be for UL & other safety certification is my guess.
Anything over 50V is considered potentially lethal shock hazard & would require another layer of expense for electrical safety testing that the manufacturer would have to cough up.
Under 50V is generally rubber stamp approval.

 

[Drunkskunk]

you can pretty easily get a bike up to its legal limit with 48V, and since 48V componants are a military standard, its easy enough to find curcuit componants that can handle it. 72 volts isn't a standard for anything but EVs, and there aren't that many in the world.

 

[monster]

so how would you people design an electric car if you were gonna make one tomorrow? i'ld go for dual hacked X5's with 50amp controllers and 90v each. im familiar with crystalyte stuff but i'm not sure its the best for e-cars though.

 

[Drunkskunk]

Well consider that an original 60's era Mini, or an MG midgit had 40 horsepower, with the ones in the 70's having 60HP. That translates to roughly 30 kilowatts peak for the low end modles. You could probably run them on 15k to 20 kilowatt rated motors, since they would pull 30-40Kw while accelerating.
if you didn't care for acceleration, or hill climbing much, you could probably get away with a 10Kw motor on a small enough car.

a couple of hacked 5X motors might give 2k each, constant. probably a little less, but we'll call it 4 kilowatts total. or 6 horse power. that would be good for a smaller sized motor bike, or something like a Berkeley B65 roadster.

 

[Link]

+ one of these.

= 640,000 watts peak.

That's over 850 hp.

 

[monster]

i thought an X5 could handle 5kw? ebike.ca are selling 50amp controllers surely they could do 5kw and two of those would be 10kw.

 

[Drunkskunk]

Sure, they can do 5000 watts while accelerating, but at peak power, what they can maintain at full speed, its around 2k.

 

[monster]

oh

 

[TylerDurden]

48V takes advantage of a wide range of supplies, not the least of which are motors available off-the-shelf; for golfcarts, forklifts, motorized pallet-trucks... esp. 36V motors which can tolerate a bit of overvolting @ 48V for higher rpm.

 

[safe]

Less than 48 volts - Shock - You Live

More than 48 volts - Shock - You Die

 

[TylerDurden]

In general you don't feel shocks unless your body voltage is above about 3000-4000 V. Getting out of a car, about 8000-10000 V is not uncommon. In general the likelihood of achieving a certain body voltage decreases as the voltage increases, so voltages of a few hundred volts are "normal", and a few thousand volts not uncommon, but tens of thousands of volts are more unusual.

http://electrostaticsolutions.blogspot.com/2006/01/what-is-average-static-shock-in-volts.html

 

[Link]

Tell me about it. Damn car shocks me almost every time I get out and touch the door. My friend also shocked me unexpectedly twice in a row, so I slapped him.

And while static discharges like that are common, the lack power. Even small ones will discharge in the hundreds of amps range, but only perhaps for a few microseconds.

Less than 48 volts - Shock - You Live

More than 48 volts - Shock - You Die

Nah. I've touched 48V or higher lines before. Bit of a surprise, but not life threatening. Maybe break your arm, though.

BTW, did you know old people have a higher resistance value than younger ones? :|

EDIT: Hey, 123rd post. Neat.

 

[TylerDurden]

BTW, did you know old people have a higher resistance value than younger ones?

Yes, but if you put 'em in a tank of pickle-brine for a week, they conduct pretty good. (but smell pretty bad)

 

[JRP3]

I always thought it was amperage that killed you more so than voltage.

 

[Link]

I always thought it was amperage that killed you more so than voltage.

Yup. It makes your heart go into an arrhythmia. But, it takes a bit of voltage to actually get the amperage through you.

BTW, did you know old people have a higher resistance value than younger ones?

Yes, but if you put 'em in a tank of pickle-brine for a week, they conduct pretty good. (but smell pretty bad)

I would imagine so, but what a waste of perfectly good pickle brine .

 

[monster]

but when i touch the +ve and -ve terminals of my 72v bike i never get a shock?

 

[fechter]

The resistance of your skin is apparently high enough to limit the current to an inperceptable level. Not everybody has the same skin resistance. If you measure with an impedance meter, most humans are about 10k ohms across dry skin. Could be as high as 100k ohms. If you poke into the skin with a needle, it drops to around 1k. Water will lower it too. If you know the body resistance, and the voltage, you can do ohm's law and calculate the current. You will start to feel a shock somewhere around a few milliamps. Over 10ma gets into the potentially lethal range.

 

[Drunkskunk]

I guess it depends on the person. I've worked on a few cattle fences, and they're between 12,000 and 24,000 VDC. Most are around 1 amp or less. when they shock you, you know it. But they aren't lethal. I've helped repair a couple, and its often easier to work on them Live, instead of constantly making the treck back and forth from the power sorce to the field, to test it as you go. sometimes that can be a couple mile walk each way. If you're around them enough, you get were you don't pay much attention when they zap you.

Taser guns are another wounderfull DC voltage device. 90,000 to 240,000 volts DC, at .1 amps. Now I ain't been shot with a taser yet, but I've been hit with one of the hand held stunners. Someone brought one to a party once, and we had fun playing taser tag. Easy to tell who was "out"

On the flip side of this, My professor, in a lecture on electrical safety, showed us a film about a cold war erra device, what consisted of 2 hearing aid batteries hidden in a ring. it had 2 needles for electrides, and when used, could stop a mans heart. it would have been about 6 volts, at 0.01Amps

I guess the point is, there ain't no such thing as "Safe" But Electricty doesn't need to be feared, either.

 

[Link]

Not everybody has the same skin resistance. If you measure with an impedance meter, most humans are about 10k ohms across dry skin. Could be as high as 100k ohms.

But across what length of skin? If I just touch the probes of my multimeter, I get about 1M ohm from hand to hand. Squeezing hard gets about 600k ohm. I can't seem to get a proper wet reading, because my slightly screwed up electrodes have a bit of copper exposed, and if there is any moisture on my skin, it causes a bit of a chemical reaction. This produces a voltage differential and I end up with a negative resistance value.

Taser guns are another wounderfull DC voltage device. 90,000 to 240,000 volts DC, at .1 amps. Now I ain't been shot with a taser yet, but I've been hit with one of the hand held stunners. Someone brought one to a party once, and we had fun playing taser tag. Easy to tell who was "out"

On the flip side of this, My professor, in a lecture on electrical safety, showed us a film about a cold war erra device, what consisted of 2 hearing aid batteries hidden in a ring. it had 2 needles for electrides, and when used, could stop a mans heart. it would have been about 6 volts, at 0.01Amps

I guess the point is, there ain't no such thing as "Safe" But Electricty doesn't need to be feared, either.

Since when are stun guns DC? I thought they were AC. That's why you spazzed out when you got hit. Or are they pulsed DC?

If it's that low power, you would have to hit them pretty close to their heart, I would think.

I disagree. Safe is right over there, making a spreadsheet. Who's Electricity, and why does s/he need to be feared ?

 

[fechter]

I'm thinking of typical skin other than your fingertips.

You're right about a chemical reaction screwing up the readings with a regular ohmmeter. You behave like a battery and throw off the dc readings.

With electric fences and stun guns, the current is pulsed dc. If the pulse is short enough, it is unlikely to stop your heart.