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Update about wrench shorting out on battery


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Was putting my positive cables to one from each battery today. Noticed no spark or shunt light come on with first battery. Checked voltage and lower than should be. Checked for ground at bms to positive and zero volts. Bms fried. This had to happen when wrench shorted out. Battery pack at 49 volts. This is what all were before I bought the charger. The others  58v now. 

Edited by GlennWest
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  • GlennWest changed the title to Update about wrench shorting out on battery
13 hours ago, GlennWest said:

Was putting my positive cables to one from each battery today. Noticed no spark or shunt light come on with first battery.

That is the reason that most of us advocate always putting the negative cable to the frame ground back last and removing it first. If you do that you won't get the spark when a wrench slips. 

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This happened some time back. I posted about it. Taking negative off would not have helped. wrench shorted out on battery case. I had neglected taping the negative connection at the bms and it was touching the frame. So it sent 48+ volts to negative side of that bms. 

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Posted (edited)

I really need to move the bms to top of battery where I can get to them. That one farest from door is just about impossible to get at. That one that fried. I will have to disconnect the wall i built and lay battery packs down. I remember telling myself that bms ever fails I can't get ot it when layed that battery pack up. Just hadn't dawned on me to relocated the bms. An afterthought, with bms at top of battery and positive at top of battery is this not properly wired? I am sure the bms will equalize the cells though. I could extend the bms connection.

Edited by GlennWest
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2 hours ago, Kirk W said:

That is the reason that most of us advocate always putting the negative cable to the frame ground back last and removing it first. If you do that you won't get the spark when a wrench slips. 

This was a relatively simple and effective solution until the advent of solar, inverters and lithium batteries.   Most now suggest a battery cutoff switch.  This allows the wiring to be completed and then switched on after completing necessary functions such as precharging capacitors. 

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  • 1 month later...
On 8/8/2021 at 10:28 AM, Randyretired said:

This was a relatively simple and effective solution until the advent of solar, inverters and lithium batteries.   Most now suggest a battery cutoff switch.  This allows the wiring to be completed and then switched on after completing necessary functions such as precharging capacitors. 

re: what happened to Glenn; How would one install a battery cutoff between the positive cable/post and metal battery case?

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5 hours ago, Ray,IN said:

re: what happened to Glenn; How would one install a battery cutoff between the positive cable/post and metal battery case?

I turn off the BMS's.  A battery cutoff doesn't have to be on the positive side. However, you are right that when working on a battery there is inherent risk that cannot be avoided.

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I  have some wrenches kept in the battery compartment that are wrapped with electrical tape except for the box-ends, and I only have FLA batteries. I learned early-on to remove all rings and watches, in a flash things get very hot.

Thanks for the education Randy, I didn't know turning off a BMS cut off voltage.

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