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Need help determining my amph hours
By shaniac, Section Controls Posted on Fri Aug 8th, 2008 at 07:21:34 PM MST
I Need help determining my amph hours please

Based on your guys advice, I am trying to set up a used Trimetric i just bought, and I am trying to determine the amp hours of my battery bank.
I have 8 L16s, two groups of four running at 24V. Interstate says the amp hour rating is 375 and the Trimetric manual suggest using 60% of that. (because manufacturer specs are optimistic.)
The manual states:
(snip)
The battery capacity of a set of batteries in series and parallel can be computed if
the capacity (in amp -hours) of each individual battery in the system is known. There are two simple rules: If several
batteries are connected in series, the capacity of the series string is equal to the value (amp -hours) of the least capacity
battery in the series. (This is like a chain whose strength is determined by its weakest link.) After figuring this for each
series string you have, if the battery system has several series strings which are placed in parallel, then add up the
capacity of each series string to get the total for the system.
(un-snip)
So if I understand this correctly each of my two 24V strings has an amp our rating of 375. Then I multiply that by 2 for the two banks in parallel. (750)
Then I take 60% of that to compensate for optimistic specs. So I should have an amp hour rate of 450 for my 8 L16s.
Is this correct or am I confused?
Thanks for your help everyone. Now and over the years.

Need help determining my amph hours | 5 comments (5 topical, 0 editorial)

Re: Need help determining my amph hours (3.00 / 0) (#1)
by Bruce S (bruce(dot)stahl <at>gmail (dot)(com)) on Fri Aug 8th, 2008 at 01:36:13 PM MST
(User Info)

If the two strings are of equal ratings, then they add up.
I don't think I would discount the total amount to 60% though. For charging reason, the system need to know to total amount.
So you are correct in thinking that the total amount would be 750.

Hope this helps;
Bruce S

Re: Need help determining my amph hours (3.00 / 0) (#2)
by shaniac on Fri Aug 8th, 2008 at 02:32:17 PM MST
(User Info)

Thanks so much, here is what the manual says about reducing the amp hours by a percentage. Your thoughts please.

(snip)
Choosing battery capacity: The "battery capacity" means the number of amp -hours that your battery system holds when
it is full. A value of battery capacity should usually be selected that is equal or lower than the actual capacity. It's
recommended that you use a conservative (low) value for the TriMetric--50-75% of their factory rated value--
considering that the stated capacity numbers for batteries tend to be optimistic. They are also usually measured at 77
degrees F, and capacity will decrease somewhat at lower temperatures. Furthermore, they are rated from when they are
completely and utterly charged, which probably won't happen often in a real system.
(un-snip)

[ Parent ]

Re: Need help determining my amph hours (3.00 / 0) (#4)
by bob g on Sat Aug 9th, 2008 at 09:40:07 AM MST
(User Info)

that final comment really bothers me

"Furthermore, they are rated from when they are
completely and utterly charged, which probably won't happen often in a real system."

if you cannot provide for a "complete and utterly charged"

you have no business with batteries, unless you expect to get dramatically less lifespan out of them.

in my opinion of course :)

bob g

[ Parent ]

Re: Need help determining my amph hours (3.00 / 0) (#5)
by TomW on Sat Aug 9th, 2008 at 09:45:31 AM MST
(User Info)

bob;

Darned good point.

You gotta cook em occasionally and keep them full as much as possible or suffer drastic reduction in capacity and lifespan.

Tom

"Education consists mainly of what we have unlearned."--Mark Twain
[ Parent ]

Re: Need help determining my amph hours (3.00 / 0) (#3)
by electronbaby (roy<at>windsine.org) on Fri Aug 8th, 2008 at 05:25:53 PM MST
(User Info) http://www.windsine.org

The 60% discount would be so that you could go by the "gas gauge". All this does, is simply give you a % of remaining energy in the bank. If you discount it by 60%, then you can use 100% of the displayed capacity before you have serious problems (really only the top 40% of bank capacity).

This is a little misleading if you are not familiar with how battery banks should be sized, but totally doable for the average consumer. If it was me, I would not discharge more than 30% (or less). The batteries will thank you by staying alive for a long time.

(PS: make sure you know the difference in bank capacity with regard to temperature).
Have Fun!! RoyR KB2UHF

Need help determining my amph hours | 5 comments (5 topical, 0 editorial)

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