High Voltage Direct Current is LETHAL

[freemanjack]

I am getting slightly concerned about the lack of concern shown towards high voltages of direct current voltage. If you have ever taken a jolt off a 110v ac mains, you know it hurts like shit, 110v dc would have clamped to to the wires with a death grip, not only risking your life but potentially, considering the amperage's we are dealing with, risking the life of anyone trying to save you. 60vdc WILL BREACH DRY SKIN, 0.6-0.8A WILL KILL YOU, if you accidentally touch both wires of a 110vdc 10a driver you are in deep do do. My best advice, avoid this at all costs, if necessary, drive below 60v and drive parallel. Sod the extra expense and possible risk to your cob's, it ain't worth the risk.

 

[dandyrandy]

When I worked at Milacron many moons ago we generated our own 270 DC for cranes, mag Chuck's etc. We had a set of test leads that were hot to work on some of the stuff. We did a lot of dry cast iron machining. They would really explode when the dust would get in the reversing drum switch for the mag/demag!

 

[Shugglet]

Use common sense and youll be fine. (Well at least 30% of the users on this board should be fine) LOL

 

[dandyrandy]

I am getting slightly concerned about the lack of concern shown towards high voltages of direct current voltage. If you have ever taken a jolt off a 110v ac mains, you know it hurts like shit, 110v dc would have clamped to to the wires with a death grip, not only risking your life but potentially, considering the amperage's we are dealing with, risking the life of anyone trying to save you. 60vdc WILL BREACH DRY SKIN, 0.6-0.8A WILL KILL YOU, if you accidentally touch both wires of a 110vdc 10a driver you are in deep do do. My best advice, avoid this at all costs, if necessary, drive below 60v and drive parallel. Sod the extra expense and possible risk to your cob's, it ain't worth the risk.

The problem with parallel is if you have a cob that opens the others get the extra current.

 

[dandyrandy]

I run 3 veros for veg on one driver. I really need to put small fuses in series to prevent this.

 

[HalfBee]

Thanks @freemanjack for pointing this out.
With all the confused people trying to understand which driver to use for DIY it's important to mention.
I avoid this by using LDD buck drivers - one LDD • one COB - 48v max
Still will bite you, but much more comfortable to work with...

HalfBee

 

[freemanjack]

The problem with parallel is if you have a cob that opens the others get the extra current.

Agreed in theory, however, in practice, unless you are driving your forward current and junction temps to 9000, a single cob failing will do little but stress the cooling system on the remaining CoB, if it is one from a string of several cob's in parallel the increase in amps will be divided by the remaining cobs and providing it remains under the 200(ish)% max most brands will suffer, I suggest the hazards of high volts dc ain't worth it.

 

[dandyrandy]

Agreed in theory, however, in practice, unless you are driving your forward current and junction temps to 9000, a single cob failing will do little but stress the cooling system on the remaining CoB, if it is one from a string of several cob's in parallel the increase in amps will be divided by the remaining cobs and providing it remains under the 200(ish)% max most brands will suffer, I suggest the hazards of high volts dc ain't worth it.

I run three cobs at around 35 w each. If one opens they will distribute the 17 watts give or take to each left. As long as my cooling is ok.....

 

[goofy81]

Everything is becoming a little more dangerous now.
I recently installed 4 ceiling fans in my g'room and i have to remember to switch them off when doing any work.
Cables with aluminium angles get loose too, so i'm thinking of hot-glueing them in place.

Just have to be careful and do your cables as neatly as you can so it doesn't get in the way.

 

[CobKits]

The problem with parallel is if you have a cob that opens the others get the extra current.

not a risk if accounted for in design

 

[dandyrandy]

not a risk if accounted for in design

Agreed. Series I prefer.

 

[The Dawg]

You Only Live Once

 

[Bigfoot16]

I am getting slightly concerned about the lack of concern shown towards high voltages of direct current voltage

Depends on skin resistance for 10 amps to kill you. Although under the right circumstances 100mA can stop your heart. I am not sure it matters if it is AC or DC. The preferred method for electric chairs is AC with a wet sponge hat.

 

[freemanjack]

I run three cobs at around 35 w each. If one opens they will distribute the 17 watts give or take to each left. As long as my cooling is ok.....

precisely, well within a safe 150% drive current and providing you are a decent amount below 85c junction temp then yup, series is pointless and dangerous. If like us, yer running vero's or luxeons, junction temps up to 150c are within maximum permitted levels and both those cob's will suffer 180% forward current all day long and the only penalty will be a few percent off absolute luminous efficiency, but with a shitton more magic pixies (photon's), who gives a shit about maximum efficacy in the event of a single cob dying in a big array?

 

[Olive Drab Green]

Amperage is more important than voltage in determining lethality, I've been told. Not sure if that's the case, but that's what I've been told.

 

[freemanjack]

Depends on skin resistance for 10 amps to kill you. Although under the right circumstances 100mA can stop your heart. I am not sure it matters if it is AC or DC. The preferred method for electric chairs is AC with a wet sponge hat.

Funny you should mention that, I was going to reference 'westinghouseing' in my explanation of ac/dc adoption, well fuck it, i referenced it now, fill yer boots my yankee compadre's, it's your history a cockerknee thug is learnin yas;
http://www.smithsonianmag.com/ist/?next=/history/edison-vs-westinghouse-a-shocking-rivalry-102146036/

 

[Olive Drab Green]

Use common sense and youll be fine. (Well at least 30% of the users on this board should be fine) LOL

This.

I also want to point out, we're taking other risks than death, like decades of imprisonment, so you're dealing with a bunch of people who don't mind taking risks. Appreciate the concern, but I'm sure everything will be fine.

 

[freemanjack]

Amperage is more important than voltage in determining lethality, I've been told. Not sure if that's the case, but that's what I've been told.

less than 60vdc does not overcome skin resistance so is more or less safe at any amperage, 50v at 100a tickles if yer sweaty, as a welder i should know!! but make that 100vdc at 50a yer in an entirely different ballpark.

 

[freemanjack]

This.

I also want to point out, we're taking other risks than death, like decades of imprisonment, so you're dealing with a bunch of people who don't mind taking risks. Appreciate the concern, but I'm sure everything will be fine.

if that risk is accepted and adopted without first figuring if it is necessary then go have fun playing with the traffic on the nearest freeway!

 

[freemanjack]

I run 3 veros for veg on one driver. I really need to put small fuses in series to prevent this.

with vero's, unless yer driving 4.2a per cob @150c you won't, vero's are virtually bomb proof.