On Tue, May 03, 2011 at 01:07:33PM -0400, [email protected] wrote:
>
> A postscript to my latest message describing Ahmet's Equalizer.
>
> I thought Ahmet was quite clear in his explanation of the device he had
> come up with. It was clear to me at least.
>
> "A very efficient DC/DC power converter (after a bulk charge with the
> engine or Honda 2000)
> takes the energy from one battery bank and slowly tops up the other house
> bank. Next day
> the process is repeated topping off or equalizing the other house bank"
It sounds like a reasonable idea - although you want to be aware that
you're trading a certain amount of battery life (by cycling the
batteries more than you would otherwise) as well as battery capacity
(since a fair amount of that capacity is now going to be used for this
job) for this ability. If you're already fully exercising your banks on
a daily basis, you'll need to add more batteries.
Also, unless I'm mistaken, this presumes that you're only going to draw
from one bank at a time - i.e., that you have at least double the
capacity that you use for your daily needs (a *highly* doubtful
assertion for most cruising boats.) Even if you do have that capacity,
the question is, which bank will you use for your daily energy needs? If
it's the one that you're charging from, then you'll be loading that bank
pretty heavily by pulling both what you need *and* the charge current
for the second bank (i.e., each bank will now need to be powerful enough
to supply your needs and to charge the other bank.) If, on the other
hand, you're going to draw from the one being charged, then that bank
will never get fully charged. Perhaps I'm failing to understand the
usage scenario here.
Next, this system will need a variety of sensors that would cut it off.
E.g., when the two banks are tied together via a "Both" setting on the
battery switch (this would short the input of the converter to the
output - perhaps not the most desirable scenario. :) You also probably
don't want this operating when the engine is running (maybe not - I'm
not very clear on that design goal) and maybe when there's a large load
on either one of the banks (you'd need a shunt for each bank, a pair of
comparators matched to the shunts, and some serious brain sweat put into
figuring out what "large" means in this case. It would be different for
each bank capacity/load combination.)
Overall, it doesn't sound like a big problem to build one, especially
since you can get good quality, high-current boost converters fairly
cheaply these days - no need to design or build them yourself, like you
had to in the 70s or early 80s. Again, the problem that I'm seeing is
that of usage, given the typical battery use on a cruising boat. I may
be wrong, but it seems like you'd be fussing with the thing all the
time, and having to make decisions about what to do with it on a daily
basis. That, in my experience, means that it just won't get used after
the first week or so.
Ben
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