12 volt control panel

[(unknown)]

Recycling some dumpster finds. The aluminum chassis was behind a local electronic manufacturer along with the panel underneath it. This picture shows the front with the 5x12 inch heatsink that has 3 50 amp bridges mounted on the back.

The inside showing the insulated terminal block for the positive wires at the top of the 3 bridge rectifiers. On the left are 8 heatsinks with 4 ,023 ohm 25 watt resistors on each one. The plan is to series 16 of the resistors then put the 2 strings in parallel. I should end up with .184 ohms at 800 watts which is going to be overkill for the small 12 volt axial I am building (200-300 watts).

Plans are to use the dumpload for the solar panels also which are 90 watts. This box plus my Xantrex C60 charge controller which I plan on using in diversion mode will be the heart of my 12 volt system for house lights and maybe enough power to run the corn stove in the winter.

[jimjjnn]

WOW!!!

Terrific job.  Lots of heatsink for the bridges too and room to add a computer fan if need be. Definitely plenty of dump load for 300+ watts.

Waiting to see your "Bird" up and flying too along with the completed setup, batteries, controller, etc.

[Old F]

I rate that dumpster dive a 10.0  : )

What a find !

Old F

[SamoaPower]

Neat find Mary!

I'd suggest that you wire the resistors all in series. Your .184 Ohms will have a peak current of almost 80 Amps through the C60 at 14.4 volts.

For your sources, 40 Amps would seem adequate and of course, you would still have the 800 Watts dissipation capability.

[Mary B]

True, I was thinking of that. My other thought was to keep 1/2 disconnected as a spare to be switched in when needed (like a resistor failure).

[richhagen]

Your C60 will not handle 80 amps even for a short time period.  Check your manual, this has come up before, but I think the maximum current when used as a dump load controller is less than 60 amps.  I would configure the resistors to limit the dump load to dump well under the specified maximum current when operating as a dump load controller.  In your case that probably means placing one string of resistors in series.  Rich Hagen  

[richhagen]

Ok, I just checked the specifications from an on-line vendor.  It looks like it is supposed to be able to handle 60 amps controlling a diversion load.  I still would limit the current well below that amount, especially since you have a smaller power input from your generator.  Rich

Copied from vendor site:

Electrical Specifications

Voltage Configurations: 12 and 24 VDC

Maximum PV Open Circuit Array Voltage: 55 VDC

Charging/Load Current (@ 25C): 60 amps DC

Maximum Peak Current: 85 amps

Maximum Voltage Drop through controller: 0.30 volts

Typical Operating Consumption: 15 ma

Recommended Breaker Size: 60 amps rated 1000% continuous duty

Recommended Wire Size: #6 AWG rated at 90 degrees C

Lead Acid Battery Settings: Adjustable

NiCad Battery Settings: Adjustable

Load Control Mode: Low Voltage Reconnect-Adjustable (sticker provided with unit) all models. User selectable manual or automatic reconnection - includes warning flash before disconnect and provides a "grace" period.

General specifications

Specified Temperature Range: 32-104 degree F (0-40 degree C)

Enclosure Type: Indoor, ventilated, powder-coated steel with 3/4" and 1" knockouts

Dimensions (HxWxD): 10"x5"x2.5" (25.4 x 12.7 x 6.35cm)

Mounting: Vertical Wall Mount

Weight (Controller only): 3.0 lbs (1.4 kg)

Weight (Shipping): 3.5 lbs (1.6 kg)

Warranty: Two years against defects in workmanship and materials

[ghurd]

My current thinking is the load shouldn't be a whole lot larger than the maximum input.

Resistor failure will be far less likely if they are dumping well below their rated watts.

How did you fasten the resistors to the heat sinks?

G-

[Mary B]

Drilled and tapped 64 6-32 holes :-) lots of fun. Heatsink compound under each resistor to aid heat transfer. Heatsinks could be a tad bigger but I had 10 of that size (3x5) on hand from another dumpster dive. They were brand new in a box.

[Mary B]

Here is a better view of the dump load.

Wiring is only #12 but for that short of a run it shouldn't be an issue.

[s4w2099]

hey, if you are still winding the stator I would recommend you to wind it to 24 volts. Ive been a die hard 12V user but now I am starting to realize the downpits of this design.

You will need heavy wire  from the mill to the batteries. I was loosing 400Watts of power due to resistance loss. My tower is only 10ft tall so you figure.... I am now using 4ga wire from the mill to the batteries and its a little better. I will never ever make a 12V system.

The panels you can series them to get 24V.

Just some advice.

[Mary B]

I am going to run the wild AC from the tower to the house, will cut down on a lot of the resistive losses. This is just backup to my 12 volt house lighting and extra backup for the corn stove. Only going to have 5' blades on this one. The 2 meter blades are going to be 24 volt or maybe even 48, going to really depend on what I can scrounge for batteries.

[s4w2099]

sure you will get even more losses if you rectify at the top of the tower. I was rectifying at the bottom, next to  the batteries and still was loosing 400Watts.

I still would not recommend it but if you have a very strong reason to stay with 12V then so be it.

Good luck with you project.

:-)

[Mary B]

easy access to RV flouro lights is one reason. And other low voltage lights like track lighting for my kitchen. This is just to get my feet wet before I tackle something larger and more expensive. Lighting is one of my big energy users outside of the appliances so that is the first item I am tackling. Water heater, washer/dryer, and fridge are next on my target list.