75 flashes! I hope you wore your welding goggles.
Charlie
On Fri, Sep 18, 2009 at 6:51 AM, Chuck Norcutt <
chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> I did some more testing with the old battery tonight and, regardless of
> its actual state of wellness it was able to deliver the goods. From a
> no load voltage measurement of 13.25 volts it was able to fire two Alien
> Bee B800 (360 watt seconds each) studio flash units at full power 75
> times with an ending no load voltage of 12.75 volts. I don't know how
> many more it might do. I just quit at 75. I would expect the upcoming
> shoot not to be more than 25 shots and at most at 50% power and more
> likely 25%. So the old battery is now capable of delivering all I need
> and much more.
>
> However, about half way through the inverter started chirping to
> complain about low battery voltage. I finally checked the specs on the
> inverter and found that the low voltage warning is issued at 10.5 volts
> so obviously the two lights (which, together, recycle in about 3 seconds
> from a full dump) are putting a large drain on the battery and drawing
> the voltage way down. The inverter shuts down at 10 volts but that
> hasn't happened yet.
>
> I think the Schumacher 1.5 amp charger/maintainer is much more a
> maintainer than a charger. It's designed to be mounted in the engine
> compartment of a truck or car and left on for months at a time. I think
> the maximum 12.85 no load volts I've been able to get out of it is
> deliberate to avoid any risk of overcharging. It's probably fine to
> keep the cells from falling too low but I think I'm going to have to put
> the cells on the 6 amp automotive charger to get the voltage up before
> use. That charger is no less than 43 years old. Anyone have a
> recommendation for an equivalent but modern low power charger.
> Something that can be, as Tim suggests, a bit more aggressive.
>
> Chuck Norcutt
>
>
>
> Tim Hughes wrote:
> > Chuck,
> > those numbers don't make a lot of sense.
> >
> > I have not followed this thread, but the least aggressive float charge
> > regime for any SLA (can float indefintely) is 2.25V/cell near end of
> > charge , so 13.5V for a "12V battery" . A more typical still
> > conservative charger can float for long periods at 2.3V/cell near end
> > of charge, or 13.8V for your battery. If you want to have any hope of
> > recovering sulphated cells and for cyclic applications,rejuvenation etc
> > 2.45V/cell or 14.4V, which is about what a car alternator is set to
> > charge at. A smart charger may charge at higher voltage
> > (2.45/cell) until current drops to a certain level and then drop back
> > to a less agressive long float regime, so it is possible that one of
> > your chargers does that, but you are reading the lower voltage in float
> > mode when it has already throttled back
> >
> > The cutoff voltage where the inverter stops operating is typically set
> > to somewhere between 1.5 and 2V a cell, depending on expected max
> > current of load, with 1.8V being a common value for moderate load (10.8V
> > cut off V for battery). 12.3V is way too high. I think what may be
> > happening is you have a sulphated battery and the internal battery
> > impedance is now so high, the voltage drops out at peak load to below
> > the cutoff point immediately, even though the battery is fully charged.
> > When you read voltage, it is oscillatiing between switching invertor on
> > and off giving a misleadingly V value.
> >
> > If you had a battery cycler with an aggressive charge regime and fully
> > discharged and charged the battery 10 or 20 times, you likely could
> > reduce impedance quite a bit and might get your bees flying a bit more.
> >
> > At 2.3V/cell it takes more than 20 hrs to fully charge most SLA's,if
> > you want to prevent your battery from slowly cycling down.
> >
> > There are a number of slightly different SLA technologies and some have
> > much higher self discharge than others (not good for occoasional use)
> > and also some have better recovery from abuse. Try cycling the batteries
> > using a light load like an 8W car indicator light. Be very careful to
> > set an alarm clock or something to be sure you don't overdischarge.
> >
> > Tim Hughes
> >
> >
> > --- On *Wed, 9/16/09, Chuck Norcutt /<chucknorcutt@xxxxxxxxxxxxxxxx>/*
> > wrote:
> >
> >
> > From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
> > Subject: Re: [OM] More on the 12 volt SLA battery
> > To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
> > Date: Wednesday, September 16, 2009, 7:48 PM
> >
> > Recall that this is just a little battery, only 12 amp hours. And
> the
> > inverter starts complaining about low voltage when the battery gets
> to
> > 12.6 volts. It can still keep on for quite a while but the chirping
> > from the inverter gets bothersome.
> >
> > Looking back on my 5 year old test notes I see that the Schumacher
> 1.5
> > amp battery charger/maintainer never got the battery over 12.85
> volts.
> > The 6 amp auto charger, however, it running them up to 13.5. That
> > should probably give me a lot of extra shooting life.
> >
> > Chuck Norcutt
> >
> >
> > Ken Norton wrote:
> > > Chuck, that number of full-dump flashes just doesn't seem right
> > to me. I
> > > know those inverters are pigs when it comes to "overhead" current
> > draw, so
> > > maybe you might be running into a time-based discharge pattern
> > when using
> > > the AB 800s.
> > > Of course, this is referring to "normal" usage, not your current
> > problem
> > > with a battery on life support.
> > >
> > > I do plan on seeing how much oomph my deep cycle marine battery
> > gives when
> > > powering a pair of monolights. I know it will keep a laptop
> > computer alive
> > > for 20+ hours. Hmm... Actually, now that I think of it, we got
> > at least 24
> > > computer hours (sometimes with two computers) and six hours of
> > 18w compact
> > > florescent runtime and the battery voltage was still about 10V
> > >
> > > AG
> > --
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