Re: Battery charging circuit

From: Ross Herbert (rherber1SPAMEX_at_bigpond.net.au)
Date: 10/19/04 

Date: Tue, 19 Oct 2004 03:56:49 GMT

On Mon, 18 Oct 2004 05:56:40 -0700, "Watson A.Name - \"Watt Sun, the
Dark Remover\"" <NOSPAM@dslextreme.com> wrote:

|
|"Ross Herbert" <rherber1SPAMEX@bigpond.net.au> wrote in message
|news:ptr6n0hbnfpbro61itov63eqrupmuc6nnr@4ax.com...
|> You are starting from the wrong end...
|>
|> You need to determine the charging requirements of the 165V battery
|> itself before anything else. Only then can you determine what is
|> required of your charging circuitry and design it accordingly. The
|> fact that you want to use a 12V (nominal), 80W solar panel as the
|> charging source simply because that is what you have on hand is not
|> the way to go about the problem. Once you know what the charging
|> requirements of the battery are you can then determine how many solar
|> panels you will require in order to charge a 12V,24V or 48V battery to
|> power a suitable dc - ac inverter/rectifier/charging arrangement.
|
|I don't buy that at all. Firs off, he doesn't need to know the charging
|requuirements of the 165V battery because it can charge at anywhere up
|to hundreds of amps for short periods. And he will never be able to buy
|enough solar cells to do that, let alone the next problem.

A logical approach would need to balance the time it takes to charge
the 165V battery in the time space determined by the OP's time frame,
so he does need to know the charging requirements. He might require
the battery to be charged in 4 hrs or less, since he is talking about
solar charging, and the weather conditions would have some bearing on
whether that is possible. The fact that he may need more than one
panel is therefore dependant upon this time frame.

|
|And the next problem is that the solar cells will put out anywhere from
|max to min to zero depending on the time of day, and the weather,
|cloudy, overcast, etc. So he needs a converter that can handle a large
|variation in input power. Why should he need an intermediate battery,
|12V, etc. to charge? That's just a waste of efficiecny.

Exactly.... However, a nominal 12V, 80W panel can deliver a max of
around 6.8A peak and that will vary up and down depending on weather
conditions. One thing you can be sure of is that for 60 - 70% of the
year the maximum output of the panel will never be achieved, therefore
some consideration will be necessary to increase input capacity to
whatever converter is used in order to raise the actual output above
the theoretical maximum.

|
|What he needs is a converter that monitors the input voltage to see if
|it drops below a threshold, as long as it stays at about 12V, pull as
|much current from the solar cells as it can. Then monitor the output
|voltage to make sure it doesn't go much above 200V, so that if the
|converter is not plugged into the battery, it shuts down.

I agree. It would be wonderful to design a 12V > 165V converter to run
directly off solar panels such that it could accurately control the
charging in the required time frame while at the same time taking into
account the variable input voltage. I think this is not the best
method since the panel might not be able to get started on cloudy
days. If a battery is used it can be storing charge at all times when
charging of the 165V battery is not being undertaken so that when
required it will start charging immediately and it will also smooth
out the peaks and troughs in the panel output. The very same converter
you suggest is just what you would need even with a battery although
the input voltage monitoring might not be so important depending on
the battery capacity.

|
|What I would do is start with a standard Dc-Dc converter like those used
|for running tube equipment off 12V. Add an overvoltage monitor to the
|output, and under voltage to the input. And fuses, of course.
|
|And he can put a large capacitor across the solar cell, to hold enough
|charge to run the converter for a second or two. If the converter
|charges in spurts, that's okay, too.

Yep, this would work. However, what do you do when you desperately
must have the 165V battery charged right now and the weather is such
that only brief periods of sunshine were available during the daytime?
At least with a panel storage battery already fully charged you could
dump most of the stored capacity into the 165V battery via the
charging converter.

I know who's system would work best and it wouldn't be yours.

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