How to correctly wire 12v batteries

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K8Toledo

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#3034376 10-Feb-2023 10:43

Ge0rge: @K8Toledo - why are you allowing your battery to get down as low as that? A 12v AGM is essentially flat at around 10.50v. Taking it below that (and to be fair even as low as that) is just doing needless damage and significantly shortening its useful life.

Perhaps it's a typo, but I just can't see how it's of any use to you at 9v, let alone 3.

No typo.

Having lasted 9 years that particular battery was at the end of it's natural life. The voltage started dropping to 9V on a regular basis, most likely due to a bad plate.

K8Toledo

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#3034620 10-Feb-2023 15:01

SomeoneSomewhere:

12V 40A is equivalent to 24V 20A. It is usually best to think in Watts, not amps. Both are 480W.

With 12V 55 amp-hour, your battery bank would be either 12V 440Ah, or 24V 220Ah. In both cases, it would be 5280Wh.

EDIT: I didn't read the last post and missed the battery size...

This statement is totally incorrect. Power supply is measured in Amps not Watts.

Amps being current draw, the rated amperage of a PSU indicates the ability to supply that current without dropping voltage.

This mistake is particularly common when it comes to ATX 12V PSU's.

Jase2985

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#3034633 10-Feb-2023 15:22

K8Toledo:

SomeoneSomewhere:

12V 40A is equivalent to 24V 20A. It is usually best to think in Watts, not amps. Both are 480W.

This statement is totally incorrect. Power supply is measured in Amps not Watts.

its not totally incorrect, in fact its not incorrect at all its just a more helpful comparison. power is voltage x current, you have the voltage and the current so you know the power. when talking about 2 different voltages it can be useful to talk in watts, especially when talking to someone with lesser knowledge of the subject.

SomeoneSomewhere

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#3034746 10-Feb-2023 18:33

When designing systems where selection of a supply voltage is a factor, it is critical to think in terms of power, not current. 400A at 12VDC is very different to 400A at 11kV. If you need to move 50kW, you have a variety of voltage & current options and fixating on one is going to give you a bad outcome.

You want a 500Ah battery bank? It's going to make a big difference whether that's at 12V or 110V.

Amps being current draw, the rated amperage of a PSU indicates the ability to supply that current without dropping voltage.

Not necessarily. Many power supplies are thermally limited, and overloading will trigger a thermal trip, or perhaps lead to poor ripple or hard shutoff by protection - or, for a nice unit, an alarm being raised. Loss of regulation is only one option and in some cases (e.g. battery chargers and CC/CV LED drivers), it's entirely by design.

The ATX power supply issue is only that power available at 12V isn't necessarily the same as power available total. Selection based on power output is still entirely valid as, for example, you wouldn't consider your CPU's 120A load at 0.9V to require a 120A+ PSU - merely that it adds ~100W to the total load.

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