[Elecraft] Re: Re solar controller

Wed Feb 11 09:03:00 2004

Hi

The controllers output is set by two 1% resistors. The threshold voltage =
can be changed by changing these resistors. Setting the threshold lower =
will not work very well and the battery may not charge. The 14.0 volt =
setting will result in a net charge of 13.8 volts because of the =
switching nature of this charger. 13.8 volts is the recommended float =
level for a 12 volt battery. With the charger operating as above the =
panel and charger can be connected to the battery indefinitely with no =
damage.=20

The maximum charge current specifications on these batteries assumes the =
current is constantly flowing. This controller switches on and off as =
needed so the average current is low when not needed to charge the =
battery and while charging the terminal voltage is not allowed to exceed =
14.0 volts. You can connect a large panel to a small battery and the =
controller will adapt to it by cutting the duty cycle to a very low =
rate. However it is better to match the solar panel size to the battery =
for best efficiency. I have found a rough rule of thumb of one to two =
watts per amp hour rating of the battery as a minimum. For example the =
2.9 amp hour battery in the K2 would need a 3-6 watt minimum panel =
depending on how much you wanted to use the K2. I have used a 3, 5 and =
35 watt panel to charge the K2 battery with the controller with equal =
success. I have also used the controller on a 100 amp hour battery with =
160 watts of panels running a K2/100 at 100 watts out on field day. A =
friend (W5EI) was running his K2/100 using an 80 watt panel and a 35 amp =
hour battery with one of my controllers. He was able to operate all day =
and night with this setup running about 50 watts CW with no other power =
required from any other source.=20

Don Brown
KD5NDB
  ----- Original Message -----=20
  From: [email protected]<mailto:[email protected]>=20
  To: [email protected]<mailto:[email protected]>=20
  Sent: Tuesday, February 10, 2004 8:55 PM
  Subject: Re solar controller

  Hi Don,
  I have a couple questions re your solar charger/controller.

  Is it possible to adjust the maximum output voltage to 12 or 13 volts =
instead of 14 volts?

  I have several solar panels made by Volkswagen for charging car =
batteries of new cars while enroute to dealers.  It is rated at 3.2 =
watts, but that is maximum and would often be less than that.  Does that =
present a problem?

  Thanks,

  72,

  Steve, N7SR

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