[Elecraft] re: solar power

Fri Mar 21 08:34:00 2003

Hi

Bob is right on this. The controller kit I sell is a series mode controller
but uses a 45 amp P channel FET so it is turned on by pulling the gate to
ground. A switching supply is not required for this circuit so there is no
RF generated that may get into the receiver. The heat sink on my controller
is a small TO220 type and is really only needed if the panel is over 100
watts. The real limiting part in the design is the reverse current diodes
and I use 2 8 amp shottkey's in parallel. The controller IC has a precision
band gap reference and 2 precision comparators and I provide 1% metal film
resistors in the measuring circuit so there are no adjustments required.
There is also a LED that indicates when the panel is charging the battery
and when the battery is fully charged. The controller operates by connecting
the panel to the battery and monitoring the voltage. When the battery
voltage reaches 14.0 volts the panel is disconnected and a wait period
starts of about 4 seconds. At the end of the wait period the battery voltage
is checked again and if it is below about 13.8 volts the panel is
reconnected to the battery. The controller will maintain a 13.8 volt level
on the battery.

Don Brown
KD5NDB

----- Original Message -----
From: "Bob Lewis (AA4PB)" <[email protected]>
To: <[email protected]>
Sent: Friday, March 21, 2003 5:42 AM
Subject: Re: [Elecraft] re: solar power

> > Look at the heat sink on this controller!
>
> This is a shunt mode controller. During the times that the charge is
> not needed by the battery, the power generated by the solar panel is
> dissipated as heat in the controller. This does not really equate to
> wasted power because that power is not needed by the battery during
> the time it is being dissipated anyway and its essentially free from
> the sun. The biggest problem is simply getting rid of the heat.
>
> Series mode controllers "open" the circuit to the battery when
> charging is not needed therefore the series mode controllers don't
> generate so much heat. The problem with series mode controllers is
> that many designs require some sort of switching regulator to generate
> the higher voltages needed for the control circuit and this can
> generate RFI. Take a look at http://www.seslogic.com/microm+.html for
> a series mode charge controller that does not use a switching circuit
> and so does not generate RFI.
>
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