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high voltage batteries and wrenches


GlennWest
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Just a warning to everyone. I was mounting my fuses on my bstteries Thursday. Love those battery mount fuses by the way. I didn't tape the end of my 10mm wrench. Mistake. I shorted out and sparks flew. I was left with burnt finger and a melted wrench. No damage to batteries or fuses thankfully. A ratchet and socket would probably been safer also. Just wanted to share so someone else doesn't get a shock. lol

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When I first got my Calb LifePo4 cells about 6 years ago I had them all hooked up on a table where I was balancing them and testing them. Dropped the wrench. Holy S***. I happened to have a piece of wood nearby so I could very quickly knock the wrench away, but what a display. Really scared me. Whenever I mess with my batteries now it feels like a diffuse the bomb scene from Mission Impossible. Thank goodness my wife did not see it. I never said a word. The cell survived. 

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18 minutes ago, GlennWest said:

Mistake. I shorted out and sparks flew. I was left with burnt finger and a melted wrench.

That is exactly the reason that most of us who have technician backgrounds will recommend that you always lift the negative battery cable first when doing any work with a battery or battery bank. That won't prevent a tool shorting between battery terminals, but it will eliminate any sparks if your wrench should hit some part of the metal frame around the batteries. I might add that most of us were told the same thing but got more careful about actually doing so by having an experience such as yours. 🙄

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I have a half-inch socket with weld marks on it from when I was a teenager (40+yrs ago) and crossed terminals when removing a battery from a car.  That *shocking* experience has stayed with me and is front and center in my mind whenever working with high amperage DC current.  This 5 second real-life experience is much more immediate to me than my 4yr EE degree :)

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   Glenn, with the amount of stored energy you're talking about in your rig, or any rig for that matter even if it only had a 12 volt battery, a dead short with such a high current capacity conductor (like a metal wrench) MIGHT EASILY YIELD HUNDREDS OF AMPS of current flow, extreme high temperatures, and batteries can even explode %$##@!  That's why experienced mechanics or electricians advise removal of the ground connection, but you already knew that. In the past I've also made up wrenches with all but the business end well insulated.

 As far as any hazardous life threatening electrical shock, voltage of only 12 VDC (subject to energy capacity) isn't likely to produce the needed 30 to 50 milliamps of current flow in the heart area to be dangerous, while your 48 volts poses a higher risk.  

You're gonna be an ace electrician by the time this is all done 

Thanks for sharing, you may help someone out there.

John T

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9 hours ago, Kirk W said:

That is exactly the reason that most of us who have technician backgrounds will recommend that you always lift the negative battery cable first when doing any work with a battery or battery bank. That won't prevent a tool shorting between battery terminals, but it will eliminate any sparks if your wrench should hit some part of the metal frame around the batteries. I might add that most of us were told the same thing but got more careful about actually doing so by having an experience such as yours. 🙄

Trouble is that Glens batteries are made of 14 individual battery packs with exposed busbars joining them together. So you have positive and negative terminals all over the top of the batteries. Removing the final negative cable will not prevent you from a possible short if you lose control of your wrench.

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3 minutes ago, jcussen said:

 Removing the final negative cable will not prevent you from a possible short if you lose control of your wrench.

As one who does this type of work quite a bit, I have a dedicated set of the common tools I use and they are all taped up. They stay in my electrical bag. It is a good practice. And yes, I learned the hard way, like everyone else....

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When I was in college the local air force base donated a pallet full of surplus oil filled 400 volt capacitors to the electronics lab.  The instructor decided it would be a good object lesson to put them all in parallel, charge them up and then drop a wrench across the buss bars to demonstrate the dangers of a charged capacitor.

The wrench vaporized with a bang so loud the bomb squad was called out.

When his hearing and vision returned, he discovered he had misplaced the decimal point a few places when calculating the total capacitance on the pallet ... it was 4 farads, not 400 microfarads.

Edited by Lou Schneider
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4 hours ago, Jack Mayer said:

As one who does this type of work quite a bit, I have a dedicated set of the common tools I use and they are all taped up. They stay in my electrical bag. It is a good practice. And yes, I learned the hard way, like everyone else....

Me too, so far 9/16, 1/2., 7/16, and 3/8 and 10 mm.  Probably more in the future.

 

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12 hours ago, Ray,IN said:

I seem to remember it takes 48VDC to carry enough current to kill a human. We all know the results of lower voltage, some of us with scars as proof.

It isn't voltage that kills, but current. The current is determined by the body's resistance at the moment you receive the shock and that can vary widely depending on circumstances. While 12V isn't likely to kill you it can give you some really bad burns. The worst injuries that I have witnessed came from the sudden physical reaction to a shock causing the victim to jerk away and strike something sharp requiring stitches. 

Quote

It's The Current That Kills

Offhand it would seem that a shock of 10,000 volts would be more deadly than 100 volts. But this is not so! Individuals have been electrocuted by appliances using ordinary house currents of 110 volts and by electrical apparatus in industry using as little as 42 volts direct current. The real measure of shock's intensity lies in the amount of current (amperes) forced though the body, and not the voltage. Any electrical device used on a house wiring circuit can, under certain conditions, transmit a fatal current.

While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (0.1 to 0.2 amp) are lethal. Currents above 200 milliamps (0.2 amp), while producing severe burns and unconsciousness, do not usually cause death if the victim is given immediate attention. Resuscitation, consisting of artificial respiration, will usually revive the victim.

 

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8 hours ago, jcussen said:

Me too, so far 9/16, 1/2., 7/16, and 3/8 and 10 mm.  Probably more in the future.

 jc, those sizes cover most typical when attaching or removing battery cables. To take it even further, the best custom made wrenches I've seen are the extra deep offset box end that had one end cut off, the handle well insulated and not very long. Very little chance of accidental shorts using those. Of course, removing the ground first is wise.

 As far as electrocution, the most hazardous current is that which flows near the heart (causing fibrillation) and as I best recall (no warranty) as little as 30 to 50 milliamps can potentially cause lock on where the victim cant let go. We advised our electricians who insisted to "touch" an electrical device (NOT way to do it, use a non contact or other tester, but some were  stubborn lol) to bump their hand backwards up against the knuckles so if they received a shock and the muscles contracted their hand was less apt to grab ahold.  Those are reasons we taught the electricians in our shop where possible to only place one hand inside a panel to avoid any accidental current flow from one hand to the other past their heart. That's another reason why a GFCI device is designed to trip as low as 5 or 6 milliamps far below 30 to 50.

BE SAFE YALL  Electricity can kill although only 12 volts isn't so dangerous as say 40+ to 120 !!!!!!!!!!!!! 

John T  

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Good Neighbor Ray, Much of this reminds me of the chicken and egg dilemma, which came first chicken or egg, voltage or current  lol

It takes a sufficient Voltage difference to produce enough Current to electrocute a person, and that is determined by Ohms Law I = V/R. But that's NOT the end of the story. It also requires a Voltage source of sufficient Energy to be able to deliver X amps through X ohms of resistance absent a significant voltage drop. Imagine trying to start a car using eight 1.5 Volt D cells in series IT AINT GONNA HAPPEN, the voltage is adequate but NOT the energy. 

To be electrocuted its gonna first take a VOLTAGE source of sufficient ENERGY to cause enough CURRENT (I = V/R) to pass 30/50 or more milliamps of current near the heart. You're right, a VanDeGraff generator capable of extreme high voltage does not necessarily have enough energy to cause x amps of Current which also needs to pass near a persons heart to be hazardous !!!!!!!!!! 

High Voltage (of high energy) can be hazardous to your health...…………...

Are you and the motorhome we worked on still in Indiana or are you South now??????

John T

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On 12/29/2019 at 7:50 PM, jcussen said:

Trouble is that Glens batteries are made of 14 individual battery packs with exposed busbars joining them together. So you have positive and negative terminals all over the top of the batteries. Removing the final negative cable will not prevent you from a possible short if you lose control of your wrench.

So true. Taping tools would be the only protection and even then be easy to short out. 

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3 hours ago, GlennWest said:

So true. Taping tools would be the only protection and even then be easy to short out. 

Finished wiring my three 7kw battery packs and am now charging them. Might  cut some light plastic to lay over terminals.

Edited by jcussen
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I am yet to get my inverters. Got DC/DC converter in and wired, not hot yet though. Bussbars in and wired. 175 amp fuses in at each battery pak. Need shunt and inverters. If i had a way to charge my batteris I would hook up dc side. Had some unexpected exspenses this month and that was my inverter money plus double. Won't take long to get back though.

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7 minutes ago, GlennWest said:

That in the neighborhood of the solar I have planned on. Going to get Teton on line with just battery power and then solar.You didn't conside the 250 Midnite unit?

I did use the Midnite Solar 250's  because each string puts out 240 volts., They only handle 63 amps, so needed two. Do you think 5200 watts will fit on the roof even with no roof airs?

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16 hours ago, GlennWest said:

yes. I got up there with tape and accorrding to my measurements. Might could do more if cover entire roof. I planning on leaving a walkway. It would not be a big deal to remove a panel for maintance. 

If you want, you can stack panels on top of each other. Put one set of the pair on sliders and pull them out cantelivered over the side of the trailer when in a fixed place. For travel just push them back under. Make sure the bottom one comes out far enough not to be shadowed (much).

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