Can you explain amp-hours?

[capslock118]

I feel like this is a 'after july 4th weekend and I have less brain cells now then I had before' kind of a thing.

My battery, when fully charged, is rated for 105 Ah at a 20 hour rate.

Does this mean I can draw 105 amps continuously for 20 hours before the battery is fully depleted to 10.5 volts?

Let's say I had one device that drew exactly 105 amps at 12 volts - I guess that could be a microwave - I can run that microwave for 20 hours?

or - if I consumed 105 amps for 1 hour I would have depleted the battery?

I feel the latter is correct...

 

[lkrasner]

Re: Can you explain amp-hours?

All batteries can be given a ratting of amp hours, if a battery is 1 amp hour it can provide a steady current of 1 amp for 1 hour. If it is rated for 105 amp hours, it can provide 105 amps for one hour.

 

[Pez Vela]

Re: Can you explain amp-hours?

No one has ever successfully explained the amp-hour rating of a battery. Einstein attempted it, but he gave up and came up with his theory of relativity instead. Nonetheless, I will give it a try. Your battery is rated to allow you to draw just a tad more than 5 amps per hour, at an even rate, for 20 hours, after which it will be depleted.

 

[capslock118]

Re: Can you explain amp-hours?

if a battery is 1 amp hour it can provide a steady current of 1 amp for 1 hour. If it is rated for 105 amp hours, it can provide 105 amps for one hour.

Your battery is rated to allow you to draw just a tad more than 5 amps per hour, at an even rate, for 20 hours, after which it will be depleted.

Excellent.

Now, how does CCA / MCA fit in with this?

Let's say my battery is 50% depleted, meaning there is about 52 Ah left to work with. My battery is rated 800 CCA / 1000 MCA.

If the battery is 50% depleted, does this imply the CCA and MCA is also cut in half? In other words 400 CCA / 500 MCA respectively?

Or, is CCA/MCA concerned more with the remaining voltage in the battery?

 

[dingbat]

Re: Can you explain amp-hours?

Temperture has a big effect on a battery performance.

Cold cranking amperes (CCA) is the amount of current a battery can provide at 0 ?F (−18 ?C) for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery).

Marine cold cranking amperes (MCA) is the same except when measured at 32?F (0?C).

Unless your operating your boat in these temps, it means nothing.

About amp hours, they are rated till death. I realtiy, you only have 60% of that number if you want your battery to survive to live another day.

 

[kahuna123]

Re: Can you explain amp-hours?

http://www.odysseyfactory.com/faq.html#3

 

[capslock118]

Re: Can you explain amp-hours?

Cold cranking amperes (CCA) is the amount of current a battery can provide at 0 ?F (−18 ?C) for 30 seconds and maintain at least 1.2 volts per cell (7.2 volts for a 12 volt battery).

Interesting; so ignoring temp for a minute (I understand it does play a big part though ) if my engine requires 500 MCA and my battery is rated for 1000 MCA, then the battery could in theory provide 1 minute of juice before it dies. That's a long time for an engine not to start .

Thanks kahuna123 for that link.

great information; thank you.