No Frame Ground! Electric Golf Carts and such systems

[CobyRupert]

From what I understand, it is to eliminate a short circuit path for these higher voltages.
In a ICE auto, when I touch the 12VDC+ terminal and the grounded frame with my (say) 1000ohm body, I'm only passing (12V/1000Ohm=) 12mA. I'd get three times that if I touch a 48VDC+ terminal and a grounded frame, but I get nothing because there is no path back to the negative terminal.

Same if a screwdriver or ratchet accidently touches the frame and a positive terminal. With a floating ground (or floating negative terminal, however you want to think about it; i.e. an isolated negative) there will be no metal melting flash. Like one commenter said: "You're one slip from making/being an arc welder".

...but, isn't that true with 12 volts also, so what's the big difference with 48 volts. It's only 3 times the current.

 

[k0ua]

From what I understand, it is to eliminate a short circuit path for these higher voltages.
In a ICE auto, when I touch the 12VDC+ terminal and the grounded frame with my (say) 1000ohm body, I'm only passing (12V/1000Ohm=) 12mA. I'd get three times that if I touch a 48VDC+ terminal and a grounded frame, but I get nothing because there is no path back to the negative terminal.

Same if a screwdriver or ratchet accidently touches the frame and a positive terminal. With a floating ground (or floating negative terminal, however you want to think about it; i.e. an isolated negative) there will be no metal melting flash. Like one commenter said: "You're one slip from making/being an arc welder".

...but, isn't that true with 12 volts also, so what's the big difference with 48 volts. It's only 3 times the current.

actually 4 times... I have worked around 48 volts most of my adult life, and you can feel it if and when you "complete the circuit". Especially if your sweaty, you can really feel it. 4 times the voltage, 4 times the current for a given resistance, and more likely to cause a problem if the path is thru your heart.

 

[Industrial Toys]

I have visions of that movie with the Die hard guy (I think) hung up hand cuffed with some car batteries and wet sponges near by. But apparently 48 volt is still not considered dangerous to the touch. So I am just guessing, it is not a life safety issue.

A friend had a brand new diesel GM pick-up, many years ago that suffered some kind of a major short circuit. Much got melted away includng the parking brake cables.

I am guessing it has more to do with the potential for a high current short circuit. IF that is the case, then fusing my little radio project at a mere 15 or 20 amps shouldn't be a big risk.

 

[k0ua]

48 volts is not dangerous to the touch with dry skin. Sweaty salty skin is another matter.. It is iffy, but it might be possible to get enough current flow to cause fibrillation. You only need about 50 milliamps (.050 amps) to get the job done. I think companies don't want to risk it.

As you point out a high current short circuit can be a disaster. Hot molten metal and hydrogen outgassing... Yeah not a pretty picture.

 

[Industrial Toys]

On the other side of the coin. How many people have compromised the safety of their electric carts in adding something? With ridiculous warning labels everywhere, would it not be prudent to have such a message on such a vehicle? IF it were in fact an issue. In this case, we are speaking JD. Does anyone have more safety labels? Soon, I'm guessing they will have safety lables indicating the possible absense of a safety label.

NOT a word about grounding in the service manual either.

Very, very strange.

 

[k0ua]

My thoughts on the companies reasoning is just a guess, I don't really have any hard data on the matter.

 

[Luke'sScreenName]

No, it is not grounded and I don't know why.

But it is a neat UTV, so powerful it will climb a tree!

View attachment 470383

View attachment 470384

Looks like it had to pee!

 

[Xfaxman]

Looks like it had to pee!

That is funny. :laughing:

I'll have to get a picture of it backed it up the tree, so it has it's hind leg hiked.

 

[joefromga]

It's for safety to keep the frame from becoming part of the loop and if it failed it keeps you from becoming the return path.

48v is indeed dangerous especially when backed by 6 current monster batteries.

It's also to protect the speed controller in that situation and other circuits in the cart or buggy.

There are warning labels about not grounding the frame. Gas carts don't have this problem but all electric carts do.

 

[joefromga]

You can also make a ground plane that's isolated from the frame out of sheet metal and then wired back to your converters negative wire. It would probably be better than using a frame grounded roll bar.