I know 120V AC is pretty dangerous. Is having 12, 12VDC batteries in series just as dangerous?
[QUOTE=chiques;3497]I know 120V AC is pretty dangerous. Is having 12, 12VDC batteries in series just as dangerous?[/QUOTE]
I dont see why its not dangerous. It’s obviously not something to PLAY with. If you use the correct precautions, and be safe and smart about everything, there isn’t a thing to worry about.
Everything is dangerous… …
well, 144VDC never crosses 0V, so it constantly causes your muscles to contract… so you can’t let go.
Work safely, and consider a breaker to take the pack out of the contactor/controller/motor circuits.
Another thing, when you’re working on it, consider breaking the 144V at the 72V tap… that way, its only ever going to be 72V…
Anything over 50 volts is considered dangerous.
To be on the safe side, you should not be alone in the shop, while dealing with high voltage.
actually anything below 600V is considered low voltage… Its still enough to get zapped. My coworker got zapped the other day wiring the controller. The caps in the controller still had a charge, something like 160V on a full charged pack. It hurt, but it was a short burst. Just imagine if it was 144V constant! I have been zapped a few times on my motorcycle, 72V isn’t too bad, but you can feel it.
[QUOTE=chiques;3497]I know 120V AC is pretty dangerous. Is having 12, 12VDC batteries in series just as dangerous?[/QUOTE]
100ma across the heart will stop it or cause it to go into fibrillation. Your normal skin resistance is 1000 Ohms. If your skin is wet, or you are sweaty, or wearing any metal, or standing on a conductive surface, (concrete/metal ladder), your skin resistance may be far less than that <500ohms. In this situation 50 Volts (AC or DC) may kill you. With DC it can be harder to let go. Over 600 volts can depolarize your cellular membranes causing a delayed death up to 1 day after being shocked. Also causes permanent nerve damage and deep tissue burns. Burns and nerve damage can be caused by lower voltages especially if wearing metal jewelry. Use safety with all electrical power, remember you can’t turn off a battery. Get in the habit of using only one hand, this lessens the chance of current crossing the heart. Break your battery pack into <50 volt strings if possible, (use switches contactors, or removeable fuses). Stand on a rubber mat, (dry). Use electrical rated gloves when working on battery pack. cover all exposed metal on terminals and tool used for attaching cables. Also you can get flash burns from an arc if a battery is accidently short circuited. Be carefull; we are used to the hazards associated with Gasoline, High power electricity is new to some people. Both can be dangerous if careless. We know don’t smoke around gas, use ventilation for flammable vapors and carbon monoxde. Keep sources of sparks far away, keep fire extinguisher handly. Electricity has its own hazards also, and proceedures and precautions to use safely. There are numerous sources of electrical safety get familiar with them. Read up on white zombies plasma incident. Coat terminal bars with a non conductive coating wherever you can to minimize the chance of this happening to you.
A real good explanation above.
It’s just like any source of power, or power tool.
Think of all that could go wrong in every instance. Even the concept of fire - burns on contact, can do astronomical amounts of damage.
We quite simply need to learn all we can in order to understand and respect it.
The right work practices, proper clothing, the right tools. An electricians blanket, gloves, insulated tool should be at the top of our toolbox.
Design as many safeguards into your system as you can. Fuses, breakers, etc are of paramount importance. My 24 batteries, when it is all said and done will be wired in three separate strings, connected by contactors. Many have two contactors one on the pos and one on the neg lines. I have a total of four.
Once a dc arc gets started, it wants to keep going. AC reverses itself and crosses 0 volts 60 (or whatever the design frequency is) times a second.
My brother who runs a commercial power generating plant keeps admonishing me telling to be careful. He says "AC comes and goes. DC is forever.
I’m FAR from expert. But I have spent the last 8 or 9 months reading EVERYthing I’ve been able to lay my hands on. At this point I would say that I’m not paranoid; but based on what I think I understand, I’ve intentionally spent some extra dollars to include some extra safeguards.
All generalization aside, 144 volts (and lower as well as higher) is like any source of power. It is every bit as safe as we make it. So, hey! Be careful out there.
agree.
120V from the socket is ~170V peak to peak of the sinusoudal AC waveform, 120V is RMS voltage, but people have still died from electrocution from 120VAC.
144VDC is just as dangerous, if not more.
BE Careful, don’t touch + and - at the same time, period. And when you first start it up, do so with people away from the car. A plasma ball almost killed my father because another worker left a temperature probe in a High voltage high current DC drive system he was building, and it blew the door off and a ball of plasma went 20 feet into the air. Bubbled the paint on the wall. The arc didn’t want to stop.
No comments published ah.
Remeber that assume makes an ass out of u and me.
I assumed that the contactor was off because an electrician had taped it down 3 years ago after doing some wiring mods on my house.
Turns out he had taped it into the ON! position.
Found out while searching for the wiring inside the wall to instal the airconditioner whilst standing barefoot on wet grass.
240v AC.
New hairstyle for free.
Good point. Never Assume. Always double check. In industry when working with more than 1 person. Both are required to lock out all incoming sources of power with a lock that has their own name on it. Locks are not to be removed until all workers involved are clear of the machine and have agreed the machine repair is finished and it is safe to restore power. Also the power must be checked before work with a known good voltmeter that is tested before and after each voltage measurement to insure ALL sources of power have been disconnected. check against a known LIVE circuit to insure meter, (battery, leads, or electronics) haven’t malfunctioned during testing. Then check what you will be working on, THEN check the meter again. This saved my life once. I checked all the circuits and got zero volts, then turned around and tested a nearby outlet, instead of a steady 120VAC I got just a few flickers. I asked a co-worker for his meter and rechecked. One Circuit was still live. ohming my meter leads I found one had a broken wire inside the insulation. It only opened when flexed. Remember 100Volts will push 100 MA through a resisitance of 1000Ohms, (your normal skin resistance). 100MA may stop your heart. Have someone nearby that knows CPR. I always use a fuse and a switch inline even when just hooking up 1 battery for testing. You never know when you will need to turn something off in a hurry, (it is a bummer to have to go look for a wrench, “the right size”, to unscrew a lead off of a battery terminal while your arm is being chewed by a slipped belt, or a plasma ball is burning the flesh off of your face.
Great feedback everyone!
So bottom line: Even a kitchen fork can kill me if I’m not careful and take all precautions (e.g. don’t ice skate with the fork pushed against my throat 
). I just wanted to get a perspective to see how people treat these high voltage systems.
I’ll work on focusing on failsafe and maintenance safety designs.
Thanks alot!
I’m trying to learn what I can about safety for my newly-converted 72V system. I did not build this-- I bought it-- so I’m really ignorant about some of the items discussed in this thread.
My batteries are separated (6 in the front of the car, 6 in the back) but can anyone make a recommendation in layperson terms as to what I need to look for in my system to improve the safety? What about charging the system-- do I need to ventilate when it’s plugged in?
[QUOTE=Pressly;5839]I’m trying to learn what I can about safety for my newly-converted 72V system. I did not build this-- I bought it-- so I’m really ignorant about some of the items discussed in this thread.
My batteries are separated (6 in the front of the car, 6 in the back) but can anyone make a recommendation in layperson terms as to what I need to look for in my system to improve the safety? What about charging the system-- do I need to ventilate when it’s plugged in?[/QUOTE]
As a minimun I would suggest that you insure that both positive and negative are disconnected when the car is off. And that there is a manual disconnect and fuse inline. I also choose to separate my battery packs with a switch the the middle to cut the voltage in half when off.