this post was submitted on 24 Jul 2023
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I replaced 12x 12v batteries in my UPS stack this weekend and ONLY insta-welded two connectors. (lemmy.world)
submitted 1 year ago* (last edited 1 year ago) by BobsAccountant to c/selfhosted
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I see this as an absolute win. Be careful, folks. Just because it's DC doesn't mean it won't cause serious damage.

Edit for Clarification: When done correctly, the batteries should not arc. My problem is I did not wire the array correctly the first and a-hem second times. It only cost me one battery, which is a lot cheaper than a trip to an American ER.

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[–] geekworking 5 points 1 year ago (1 children)

UPS batteries are really dangerous because you cannot turn them off. They are also high enough voltage and current to harm you through arc flash and burns.

The other thing with small UPS batteries is that there are usually multiple batteries. There are fuses between the battery string and the circuit board but not between each battery in the string.

OP may have connected batteries wrong or he put a new battery in a string with a shorted/dead battery.

Whenever you are going to string multiple batteries together always disconnect batteries and check voltage on each separate battery to make sure that they are the same or very close in voltage. If different charge to the same level. Any difference in voltage between the cells will cause current flow that can cause a fire hazard.

[–] BobsAccountant 2 points 1 year ago

It was the former. This unit had 8 12v batteries VERY snuggly placed within it. I didn't pay attention to all the leads and their locations when dissembling the old batteries. I'm professional IT and hubris was nearly the end of me.

[–] [email protected] 3 points 1 year ago (2 children)

Hm I have not heard about such an issue so far but I also don't have as many UPS as you.

I see you holding a red cable which could be +. When I switch UPS batteries, I do it the same way as it's recommended for car batteries to avoid sparks/arcs. Remove - (black) first, as it won't spark/arc. Then remove + (red) as it can't get a circuit closed any more, so also no spark/arc.

When plugging a car battery in, it's the other way around. + (red) goes in first and only then you connect - (black) to avoid spark/arc for both connectors again that way.

[–] [email protected] 12 points 1 year ago (2 children)

Either polarity will arc the same, the reason on cars for doing negative first is because you're supposed to attach it to the frame, so a spark doesn't set off any hydrogen in the battery and cause an explosion.

[–] [email protected] 2 points 1 year ago (1 children)

Additionally, if you where to drop a clamp or touch something by accident, it is most likely to contact negative, as that is the whole chassis. If you adhere to this order and drop the negative clamp, it will most likely just reconnect to negative. If you drop the positive clamp on the negative chassis nothing happens anymore, as you broke the circuit beforehand.

[–] [email protected] 2 points 1 year ago

That's a good point as well.

[–] [email protected] 2 points 1 year ago

The frame is already grounded negatively. so if you remove red and happen to touch red post while leaning on metal car you make a circuit. so you pull negative first so even if you touch red it can't travel back to the battery

[–] BobsAccountant 7 points 1 year ago* (last edited 1 year ago)

Oh no. Half of this post is me making fun of myself. Mistakes were made. When you have a large array of batteries, it's important to wire them up correctly when replacing them. I definitely closed the circuit on some of the batteries when I shouldn't have.

I see how it could be confusing, and in the spirit of sending the correct message, I have added a clarifying edit.

[–] [email protected] 1 points 1 year ago (1 children)

Replaced the batteries?

I'm in the process of topping up the water in mine intending to refresh them... but you've made me think... I need to check them for deadshorts / opencircuit

And I thought you'd burnt a horrible groove in your finger!

[–] BobsAccountant 1 points 1 year ago

Yeah these are the small, closed cell 12v batteries. Just make sure you have the circuit open until the very last step. Additionally, if you have an array of batteries, make sure you're paying attention to their configuration.

[–] [email protected] 1 points 1 year ago

At first I thought you accidentally welded it to your hand lol

[–] [email protected] 1 points 1 year ago (2 children)

Who needs fuses anyway.

[–] BobsAccountant 1 points 1 year ago

Where we're going, we don't need have fuses.