# Working on an EV dangerous due to High Voltage ?



## dragonsgate (May 19, 2012)

That is why we disconnect everything before we start work on our electric vehicles no matter what the voltage. Even when working on an ice car it is often recommended that the 12 volt battery be disconnected. For example…I was replacing a rusted out header in my Land Cruiser and unhooked the battery. Sure enough as I was working the header down between the engine and frame when the header rubbed across the starter. While not deadly it could have cause a lot of sparks and some other damage. So always even for the simplest job disconnect the batteries on your EV. If I doesn’t out and out kill you it could cause a nasty shock and burn your skin real bad. Then there is the problem of explaining how you burned down your house.


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## skooler (Mar 26, 2011)

Yep, maintenance switch is a must!

I'd be lying if i said I hadn't had a few minor shocks.....


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## Ziggythewiz (May 16, 2010)

I think I'm up to 100 or 2 shocks...and a couple molten lead events.

It's only dangerous if you use bad practices, get too comfortable, and don't think things through.

Use a maintenence disconnect, insulated tools, wear gloves, and think about what you're doing. Wish I could say I regularly did more than 2 of those.


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## Sunking (Aug 10, 2009)

It can be very dangerous, to fatal especially DC because it locks or paralyzes the muscles.


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## ricklearned (Mar 3, 2012)

Lipo Louis said:


> I wonder how dangerous is 350v dc to human ?
> 
> Everybody would try to avoid touching 350v I think, but there is a good change of making a mistake and touch both polarity by accident. How dangerous is that ?


It is the amps that are dangerous. With AC we feel the shock of higher voltage more but DC is trickier since you could put two fingers across that much DC and not feel much unless your hands were wet. I would not recommend two hands since that would take the potential load across your chest. 

An example of a low voltage DC accident occured one time when I was working on assembling a pack of 1850's for an upgrade for an 18v battery pack for my Dewalt power tools. I inadvertantly shorted two of the tabs and they got red hot very quickly and gave me a serious 3rd degree burn on my thumb which was trying to separate them. Gloves and insulated tools are important safety items for even the simplest of projects


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## Lipo Louis (Oct 29, 2012)

A 12v battery won't shock anyone, but I meant, how dangerous is 350v ? Will you survive that ?

I am busy with ebikes for several years and if you keep working on batteries etc sooner or later you will make a mistake and burn some wires or connector, I'm very very careful but since we are humans there is always a change to do something wrong, I don't feel anything from 75 V DC.

So I don't mean how dangerous is it when dropping some tools to an open battery pack, I just would like to know what if you touch the + and - of 350V DC

I will disconnect the power when working on the EV ofcourse.


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## Sunking (Aug 10, 2009)

ricklearned said:


> It is the amps that are dangerous. With AC we feel the shock of higher voltage more


Sorry but that is only half truth. 170 volt DC is just as painful as 120 VAC (170 volt peak). 

Current is what kills but it takes voltage to push current and it makes no difference if it is AC or DC as both are regulated by Ohm's Law. AC will generate just as much heat (power aka watts) as DC will. Here is a little video clip of an AC spark

http://www.youtube.com/watch?v=4bBvmPRqfmo


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## dtbaker (Jan 5, 2008)

Lipo Louis said:


> A 12v battery won't shock anyone, but I meant, how dangerous is 350v ? Will you survive that ?


if you have a 'good contact', i.e. wet hands, metal wrenches, etc. especially through both hands (heart) you will die.... so, yes, serious.

anything over about 80vDC can kill you pretty quick once the muscles contract and you can't let go. so, even a partial pack can kill you if you happen to touch across terminals with enough series voltage.

be careful!

...I wear thin gloves that have a non-conductive foam coating on fingers almost all the time I work on the car in addition to being very delibrearte around the high-voltage connections. Added benefit in the garage is that they are warm in the garage in the winter, still have 'touch'. 

check out: 118019 Ansell® HyFlex® 11-801 Grey and Black Nitrile Coated
$48/dozen from magidglove.com


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## subcooledheatpump (Mar 5, 2012)

Yes it takes voltage to push current. Current kills but current never happens withouth voltage (except for in superconductors) thats ohms law.
The resistance of the human body varies, but it may take up to 2 kV to push a lethal current through some. I would advise against testing it though
I have been shocked from 340 vdc before and walked away from it. It certainly doesn't feel good but I'm still here. It would help to note that I only got shocked on one hand. Had I been using both hands and had the current flowed through both arms I could have been in serious trouble. 

Just as I've heard it said before, try not to use both hands when you know something with that kind of voltage is live. The best advice though has already been posted. disconnect everything before working. The safest voltage is zero.


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## Sunking (Aug 10, 2009)

There is one other serious issue when working with batteries, even at low voltage. Arc Flash from a short circuit especially around the battery terminals where there is no over current protection. Even a 12 volt car battery can vaporize a wrench, ring on your finger, or wrist watch. This is one reasons why the HVDC is not bonded (referenced to the vehicle frame) and allowed to float. Contrary to popular belief grounded systems are dangerous.


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## Qer (May 7, 2008)

As little as 10uA (with the voltage need as low as 3mV) can actually kill you.

http://en.wikipedia.org/wiki/Microshock
http://van.physics.illinois.edu/qa/listing.php?id=6793

Although it's rather unlikely you'll succeed killing yourself with 10uA without the help of a heart surgeon it kinda shows how much the skin of our bodies insulate us and thus improve our chances to survive electrocution.

I've personally experienced 230Vac through the arms and chest and, well, even though I have had more unpleasant moments in my life I think it easily makes it to my personal top 10 in most pain experienced. I survived (obviously) and I expect the main reason for that was because I was dry. Had I done the same mistake outside in rain or in a bath tub I'd say my odds would've been noticeably lower.

So can you survive 350Vdc? Sure. I know people that has survived a few kV. Can you die from 350Vdc? Of course. If you're wet, if the skin is punctured by the wire or some other factor lowers the resistance the risk will increase dramatically.

Simplest solution is to just don't electrocute yourself. It's bad for you.


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## Ace_bridger (Nov 22, 2011)

Yep, very dangerous and you must ensure that you avoid completing the circuit with any part of your anatomy!

Use insulated tools and work one handed where possible. Avoid working on your car outdoors in the rain and if in doubt get help from a competent friend.


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## ricklearned (Mar 3, 2012)

Sunking said:


> It can be very dangerous, to fatal especially DC because it locks or paralyzes the muscles.


Yes, and AC can fibrillate the heart. Imagine the surprise to our vascular system when our heart starts going at 60 hz instead of 75 beats per minute.


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## mizlplix (May 1, 2011)

When the electric chair was being developed for use in executions, AC and DC both were tried.

They both were tested. Both killed people, but AC was chosen overall because the frequency could be varied during the execution and provided a more widespread damage to the body. 

Miz


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## Tesseract (Sep 27, 2008)

mizlplix said:


> When the electric chair was being developed for use in executions, AC and DC both were tried.
> 
> They both were tested. Both killed people, but AC was chosen overall because the frequency could be varied during the execution and provided a more widespread damage to the body.
> 
> Miz


Sometimes I wonder about you, Miz... 

More seriously... I have experienced an electrical shock from ~340VDC and I can tell you that it Really F'in Hurts. I also tend to have very dry and somewhat calloused skin on my hands, which helps keeps the current to the sub-lethal range whenever I am shocked (which is not often, mind you). If you have "clammy" hands, though, you can easily be killed by 300VDC. The resistance across my body when my fingers are dry is around 20M; if I moisten my fingers the resistance drops to 2M. When dry the current through my body will be in the hundreds of uA range; when wet the current increases into the mA range, and that is potentially lethal.

I understand from experience that it is not always practical to follow the rule that you keep one hand in your pocket when working on live circuits (though you can be damn sure that rule is almost habit for me!), so I suggest putting on thin latex or nitrile gloves. Not exactly "electrician grade" dielectric, but every bit helps.


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## sirwattsalot (Aug 27, 2012)

That could be the last mistake you ever make. Always disconnect the negitive battery connection as well as the positive. If the chassis is ground, disconnect negative first. Rubber gloves should be worn and treat everything you touch as hot.


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## mk4gti (May 6, 2011)

sirwattsalot said:


> If the chassis is ground, disconnect negative first.


Not sure if you meant HV ground, but chassis should never be tied to the HV battery pack.


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## ricklearned (Mar 3, 2012)

Sunking said:


> Sorry but that is only half truth. 170 volt DC is just as painful as 120 VAC (170 volt peak).
> 
> Current is what kills but it takes voltage to push current and it makes no difference if it is AC or DC ..........


Yes, that is a more complete statement.

Let me pose a question about safe disconnect practices. I currently have a disconnect before my controller. All my other devices such as shunts and voltage connections for meters and charger are downstream (between disconnect and battery) and therefore hot when the disconnect is open. I often work on these and I have several high voltage leads to instruments in my dash.
My question is, shouldn't I reinstall the disconnect as close to the pack as possible? My disconnect opens both positive and negative legs of the pack.
BTW, this thread has convinced me that I should rearrange the disconnect, but other responses might be helpful to others.


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## dragonsgate (May 19, 2012)

I unplug at the neg end of the battery pack and have release in the middle of the pack. I also disconnect the ground to the contactor to avoid it being inadvertently engaged by the 12 volt system. Whenever I am working on the vehicle I am constantly checking things for voltage with the meter before I touch it. One of the few things I agreed with in the navy was when working on electricity you fist broke the connection put a notice on the box and posted a man next to it to make sure no on messed with it while you were working. You Can’t be Too Safe.


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## Ziggythewiz (May 16, 2010)

Safety devices should be as close to the power source as possible. That includes fuses, disconnects, and contactors if possible. Obviously the larger the item the more difficult it is to locate it near the battery pack, so contactor(s) usually end up by the controller instead.

I have several HV leads going to gauges on the dash, each fused at the battery terminal.

***Note for lead acid builds: Switching devices should not be placed in (or too near) a lead acid battery box.


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## ricklearned (Mar 3, 2012)

dragonsgate said:


> I unplug at the neg end of the battery pack and have release in the middle of the pack...... You Can’t be Too Safe.


That leads to another question. With certain BMS systems a mid pack disconnect can expose the BMS boards to total pack voltage if a load is applied. I guess the workaround for a mid pack disconnect is to also disconnect the two halves of of the BMS boards or have a way to make sure a load does not get applied as mentioned above by disconnecting 12v tocontactor. Do those seem reasonable?


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## ricklearned (Mar 3, 2012)

Ziggythewiz said:


> Safety devices should be as close to the power source as possible. That includes fuses, disconnects, and contactors if possible. Obviously the larger the item the more difficult it is to locate it near the battery pack, so contactor(s) usually end up by the controller instead.
> 
> I have several HV leads going to gauges on the dash, each fused at the battery terminal.


Do the fuses affect the accuracy of the guages?


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## Ziggythewiz (May 16, 2010)

ricklearned said:


> Do the fuses affect the accuracy of the guages?


Hard to say. For most I don't think it could matter as they're cheap DVMs anyway, but that could affect my JLDs. Will have to test that and get back to you. 

I somehow turned a 6' wire into a fuse for an impromptu 4th o July celebration so I added fuses to every connection after that.


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