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Battery voltage charge/discharge curves | 18 comments (18 topical, editorial)

Re: Battery voltage charge/discharge curves (3.00 / 0) (#3)
by frackers (g8ecj at *nospam* gilks dot org) on Wed Aug 13th, 2008 at 02:45:44 AM MST
(User Info) http://www.gilks.org

The batteries have arrived as promised - the supplier took the half dozen recycled truck batteries that I'd finished off in exchange for the delivery charge - he's happy and so am I :-)

They are all sitting, fully charged, at 6.39 to 6.41 volts so I'm going to set my dump load voltage to 6.75 volts per battery (27 volts rather than the 28 I was going to use). On the discharge side of the equation, I'm again going to err on the side of caution and cut out at 23 volts. I'll keep an eye on the specific gravity over a few days/weeks and see what happens.

Thanks for confirming my suspicion that I can't really use voltage, especially if charging at a high current. Guess I'll have to build the proper charge monitor/load-controller by counting amp-hours in and out of the battery bank. Got most of the bits, I've just got to clear the decks of all the other projects which may take a while with spring just round the corner!!

Cheers
Robin - Down Under (or are you Up Over)
[ Parent ]

Re: Battery voltage charge/discharge curves (3.00 / 0) (#5)
by Flux on Wed Aug 13th, 2008 at 03:00:25 AM MST
(User Info)

I think 27v will do as float but you will need to equalise regularly if you keep it that low. Keep an idea on the sg. ( I would give them a good equalising charge now and check the sg at the end for future reference)

The table that Damon gave is about as useful as I have seen, but you really need to have figures related to charge and discharge current for your capacity of battery. The voltages change a lot and "significant current" is pretty vague.

The Ah meter is the best solution but even that is far from easy unless your charge and discharge currents don't vary much. If they do then you need Peukert as well as a general figure for efficiency. Again the big issue is a reference and the only thing you can reasonably use is full charge ( after equalising probably). If you can get an Ah meter to track sg you have about cracked it.

Even sg is not foolproof unless you gas enough occasionally to stir the electrolyte and avoid stratification. If you just use 27v without gassing it will eventually stratify.

Flux

[ Parent ]

Battery voltage charge/discharge curves | 18 comments (18 topical, 0 editorial)

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