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nonemoreunknown t1_j6c68vi wrote

Reply to comment by Hattix in Share: DIY A 12.8V 120Ah LiFePO4 Battery For My Travel Trailer(AGM Battery Replacement) by QH-Technology

Voltage is less important than amperage. 20mA can paralyze your lungs and cause defib. 2A will stop your heart. These are 100Ah cells, they are capable of putting off lethal current.

Edit: Rather than respond to so many people individually, I'll do so with an edit.

First, thanks for many well thought out responses. My response was intentionally kept short because I didn't want to go as in depth as some of you did, I was just laying down for bed when I saw the comment and felt it was important enough to make a response.

Next, a lot of different scenarios were used in the responses: AC/DC, the assumption of dry sky, and the assumption that everything was done right during assembly. I didn't make assumptions, only pointed out that 12V can be lethal. Likely? No. Possible? Yes. So safety first, and I applaud the OP for pointed that out.

Lastly, to those responses that were personal attacks: You don't know me and you don't know what I've been through. I have worked in electrical fields all my life from an Avionics Electrician, oil equipment calibration, to semiconductors. Yes, I know Ohms Law. Yes, I know what Amp Hours are. Again, I kept my response brief because I think it's safer to remind people that low voltage can still be dangerous in the wrong situations.

And I feel it's better to make a blanket statement like "voltage is less important than amperage" rather that "12V is safe".

So, I'm sorry for not being more detailed in my response. But ya'll are quite hurtful, so I guess I'll go back to lurking.

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Hattix t1_j6c8til wrote

You don't seem to understand what current (or atrial fibrillation, but that's another topic) or current capacity is.

Current is pushed through a resistance by a voltage, at the most basic level. The resistance of unbroken dry human skin is 100 kohms. This does vary, but 100 k is a decent ballpark when working out safety. I've just measured the resistance across my body with two probes to get 1.2 mega-ohms, but we'll use 100 k.

Using the very simple equation I = V/R we get:

I = 12/100000 = 0.00012 A = 0.12 mA. = 120 uA

So no, they are not capable of lethal current (and "it's the current not the volts" is only true for AC or where the voltage changes rapidly, it gets far more complicated than that, to the point where you can put five amps through someone without harm). Your "capable of lethal current" is four orders of magnitude out. That's somewhat like saying a pencil is the same size as the moon.

A "100Ah" rating tells you the duration for which a current can be maintained, it is a measure of capacity, not capability. In our case, it could maintain that 120 microamps across your arms for a few years. You'd probably get very bored. A capacity rating doesn't tell you anything about how much current you can pull at any one time.

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penguiin_ t1_j6cn3sy wrote

stop perpetuating this dumb phrase without understanding it

you would have to have 2 metal stakes piercing your chest with battery leads hooked up to them to deliver the current where it would stop your heart. ugh

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trundlinggrundle t1_j6d258u wrote

Roughly 50v is required to overcome the resistance of dry skin. Unless you're putting 12v electrical contacts directly across your heart, inside your chest, you'll be fine. Think of current as a volume of water, and voltage as a pump that pushes it though pipes.

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Hinote21 t1_j6d3yjm wrote

Not that I ever thought about this before but this must be why it's totally safe to stick a 9V battery on your tongue. Not that I ever did that... Multiple times... In middle school...

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SatanLifeProTips t1_j6dn4eb wrote

This. Unless you are making out with your battery, 12v is incredibly safe unless you arc come metal across the contacts. Doing a more powerful PV system right these days means stepping up to 48V and even that is pretty safe to handle with bare dry (not wet) hands. Maybe thin skinned baby hands will feel it? Caloused man hands don’t give 2 shits.

My solar PV array is 48v. A lot of the electric forklifts I work on are 48. It’s fine. Electrical Code changes at 60V and then you need to take it more seriously.

And if you don’t feel like fucking around spot welding a battery pack you can buy off the shelf LFP batteries that are a drop in replacement for lead acid including the BMS baked right into a plastic shell. They even look like a lead battery but are 1/3 the weight. Motorcycle versions even have a low battery protection system and will shut off at 20% life left when the bike is parked. Press a button on the battery and it wakes right up again.

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wut3va t1_j6cqfbi wrote

Ohms law says they can't. Your skin is about 100,000 ohms. 12.8 / 100,000 = 0.000128 or 0.128 mA.

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fkenthrowaway t1_j6cv2zq wrote

imagine being so confident about something you know nothing about. Incredible

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nonemoreunknown t1_j6d8m7j wrote

Imagine using this stock response to a stranger on the internet you know nothing about. Hurtful.

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steveatari t1_j6jw09e wrote

Thanks for replying. No need to take it to personal. Thanks for striking up the further conversation and once again reminding most laymen that they're are technically other things to consider beyond voltage

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