**Next message:**'AB7HI' Stephen Lee: "Re: Thanks to everyone!!!"**Previous message:**Stan Skelton: "Re: Cascade Info"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

Can anyone help me with a battery question?

I thought, and have read, that (lead acid, "stationary") batteries

deliver current to a load as follows:

First, take the amp hr. rating, which is AMPS X HOURS

Next, divide by the hours to get the amps delivered to the load during

that time. But by what time do you use here (to divide)?

So, for example, a "200 amp-hour" battery should deliver 25 amps for

8 hours -- OR -- 50 amps for only 4 hours.

But here's where the "stationary battery" manufacturers put in their

footnotes.

(The faster the battery is discharged, the lower its EFFECTIVE amp-

hour capacity.) Standard ratings ASSUME that the time for discharge

is 8 hours, when establishing the published amp-hour rating for any

particular battery.

The conclusion is that the 200 amp-hour battery will not deliver 50

amps for 4 hours; it delivers somewhat fewer than 50 amps.

Stationary batteries usually come with a chart that essentially

"de-rates" the "8 hr. AMP-HR" rating so you can find out how much

current to expect in a shorter (or longer) time period.

BUT. I read that gell cell batteries used by hams typically have

ratings of 4.5 to 7 amp-hour. If I use the 8 hour rule to get the

current delivered to my rig the answer makes little sense. A 7.5

amp-hour gell cell would give me about 930 ma. Now I know that guys

(and gals) take 7.5 ah batteries into the field and support QRP rigs

(that need about 3 amps on transmit). With only 900 ma expected,

the gell cell will be dead in no time.

Question: Is the assumed discharge time for establishing ratings of

small batteries standard? Or does it vary with the battery and the

manufacturer? If so, what is it? If not, what so I use?

Thanks for the info. Next we can discuss the assumed "end voltage"

for a gell cell when establishing the discharge time under a given

load. (But not now.) Whew!

72 de KR4GL

J. Foote

**Next message:**'AB7HI' Stephen Lee: "Re: Thanks to everyone!!!"**Previous message:**Stan Skelton: "Re: Cascade Info"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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