K1 -- VW Solar Panel -- Controller Help

[KEN-101]

Hello folks,

Have a new 2.3SLA battery I'm trying to charge for the K1. Here the problem I'm having. The battery started out at about 9.6V and is now at 12.10V or so after charging for several days on and off.

The VW panel reads about 20V in full sun. When connected to Don Brown's low power controller, it drops to 12.75V (full sun). I have a few panels and tried them all....same results. Even paralleled two.

The controller will cut-off around 14.0V. Needless to say, this one will never make it to cut-off. I'm wondering if there is a problem with the controller. Don says the panel connection point at the controller should read about 15V.

I don't have a current limiting supply to test the controller the way the instruction sheet suggests.

Any thoughts appreciated,

Thanks....Ken...W2GIW
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[G3VVT]

 
In a message dated 06/11/06 09:06:10 GMT Standard Time,  
[hidden email] writes:

The VW panel reads about 20V in full sun. When connected to Don Brown's  low
power controller, it drops to 12.75V (full sun). I have a few panels and  
tried them all....same results. Even paralleled two.




:-----------------------------------------------------------------------------
---------------------------
 
Hi Ken,
 
I would think the VW panels are too puny to provide sufficeint power to  
fully charge a battery as they were designed only to trickle charge an auto  
battery in transit.
 
The 20V you describe out of the solar panel is the open circuit voltage.  
Most 12V solar panels depending on type will give 17V to 21V under these  
circumstances. However, when you connect it to a battery, the voltage will fall  to
the charge voltage of the battery depending on it's current state of charge.  
Disconnect the controller and connect the panel direct to the battery if you  
want to check for sure. With most types of controllers the effect will be the  
same in that the readings will be identical less the current needed to run the
 controller.
 
Unless you get hold of some solar panels with the necessary capacity the  
result is going to be the same in that you can only trickle charge the  
batteries. Apart from long term float charging where the controllers would only  come
into use after a long period of charge. For most cases with low power solar  
panels a controller is not needed unless the panel does not have a series diode  
fitted. Many more of the VW solar panels in parallel or a larger solar
panel(s)  to increase the power is the only answer if you need to use this facility
in  real terms. The VW solar panels will most probably have series isolation
diodes  fitted to prevent discharge of the auto battery back through the solar
panel at  night or when not insolated sufficiently
 
As a quick test to see what your panel is capable of, remove the solar  panel
from circuit and place a current meter directly across the solar panel  
terminals. The current reading will be limited to the available capacity of the  
panel. This is how we checked the 15kW solar arrays at the workplace when they  
were originally commissioned. These were built up from about 200 of the 75W  
solar panels arranged in series/banks to provide the necessary voltage/current  
capacity and each individual one had to be tested to ensured that it met  
specification. Was not unusual to see 120A going into the 7500Ah 48V battery  
plant in the morning sun. For that we really did require multiple solar  
controllers of sturdy proportions!
 
Regards,
Bob, G3VVT
(ex civilian desert rat)
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[Don Brown-4]

Hi

I have tested my controller with a VW panel and a 2.8 amp hour battery. This
setup WILL fully charge the battery and the controller will start cycling
with the panel in full sun, but if the battery is discharged it may take
several days to bring the battery up to full charge. The VW panels are very
low power about 3 watts at best or about 180 mA. It would require over 14
hours of full sun on the panel to charge a discharged 2.35 amp hour battery.
If the panel is not perpendicular to the sun the output will be lower and
would require even longer to charge the battery.

You may have a battery with a bad cell. You may want to try charging it with
a battery charger designed for gel cells or connect it to a power supply set
to 13.8-14.5 with a limiting resistor of about 5-10 ohms at 10 watts. If the
terminal voltage of the battery will not come up to 13.8 or higher the
battery is most likely bad.

You do not need a current limiting supply to test the controller. Any power
supply with an output of 15 to 25 volts will work in place of the solar
panel if you install a limiting resistor in series with the power supply of
about 5-10 ohms and about 5-10 watts.

If you have any variable power supply that can be adjusted from 13.0 to 14.2
volts you can follow the instructions supplied with my controller to check
the operation of the controller. The current required for this test is only
about 20 mA so any type of variable power supply should work.

If you still cannot get the controller to work send it back to me and I will
test it for proper operation and repair or replace it if required

Thanks

Don Brown
KD5NDB

19132 Falls Creek Drive
Flint, Texas 75762




----- Original Message -----
From: "KEN" <[hidden email]>
To: "elecraft" <[hidden email]>
Sent: Sunday, November 05, 2006 9:42 AM
Subject: [Elecraft] K1 -- VW Solar Panel -- Controller Help


Hello folks,

Have a new 2.3SLA battery I'm trying to charge for the K1. Here the problem
I'm having. The battery started out at about 9.6V and is now at 12.10V or so
after charging for several days on and off.

The VW panel reads about 20V in full sun. When connected to Don Brown's low
power controller, it drops to 12.75V (full sun). I have a few panels and
tried them all....same results. Even paralleled two.

The controller will cut-off around 14.0V. Needless to say, this one will
never make it to cut-off. I'm wondering if there is a problem with the
controller. Don says the panel connection point at the controller should
read about 15V.

I don't have a current limiting supply to test the controller the way the
instruction sheet suggests.

Any thoughts appreciated,

Thanks....Ken...W2GIW
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