[Elecraft] Solar Controller Q&A

[Don Brown]

Hi

I have been getting a lot of questions about my Solar Controller Kit. This 
should answer most of them.

What is it and what does it do?

This is a small 2x3 circuit board that allows you to connect a solar panel 
to a 12 volt sealed lead acid or lead acid battery to keep it charged. The 
kit comes with instructions, application notes and all parts required to 
build the controller. The included circuit board is FR4 fiberglass with silk 
screen and solder mask. The kit does not include a box as most people build 
it into their battery box.

How much power can it handle?

The controller uses a 45 amp power fet to switch the solar panel on and off. 
The current that the controller can handle is limited by the shottkey 
blocking diodes. I use two of them in parallel rated at 8 amps each so 16 
amps is the maximum safe charging current. This equates to about a 200 watt 
panel

What size battery will work with the controller?

You can use almost any size battery with the controller although for best 
results the battery should be sized to the solar panel you are going to use. 
A rule of thumb is about 2 watts per amp hour has worked well for me 
although "your mileage may vary". For the K2's 2.9 amp hour internal battery 
a 5-10 watt panel would keep you on the air. For a K2/100 running 70-100 
watts a 110 amp hour battery and 100-150 watts of solar panels would work. I 
have used 2 35 watt panels and a 80 watt panel in parallel for 150 watts 
into a 110 amp hour sla battery.

Can I charge the K2 internal battery with the solar panel and controller?

Yes the internal battery can be charged as long as the charge controller is 
connected directly to the battery through a properly sized fuse. You cannot 
connect the controller to the normal K2 power connector. You will need to 
supply a connector on the K2 to connect the charge controller or build the 
controller into the K2 lid and install a connector for the solar panel.

Will it work with other types of batteries like NiCad's or NiMH?

No it is designed to work only with 12 volt LA or SLA batteries

Is there a 6 volt version?

Yes the instructions explain how to change the controller to 6 volts. I will 
supply the parts on request for 6 volts.

How does it compare with the MicroM+?

My controller functions exactly the same as the MicroM+ although I use a 
different IC and different circuit design. My controller is much simpler and 
includes a circuit to turn off the charge indicator LED when the solar panel 
is not outputting enough voltage to charge the battery. My controller will 
handle twice the current of the MicroM+ and because of the precision voltage 
reference in the IC it does not require any adjustments.

Does the controller generate any RF noise?

No this a purely analog switch circuit. It does not have any switching power 
supplies that generate RF noise

How much does it cost?

$30 check or money order. Sorry no credit cards or paypal

I only have 4 of these in stock but I am ordering the parts for more. I 
should have everything in about a week (need IC's and shottkey blocking 
diodes)

Thanks

Don Brown
KD5NDB

19132 Falls Creek Drive
Flint, Texas 75762