old fart forgeting how to wire

[divemaster1963]

Ok I have my Ghurd controller boxed up. now I what to ad a fan for the heatsink.

Question one.

should I wire the fan with the dump indicator light so it will come on with the dump?

question two.

should I use a thermostic switch attached to the heat sink to make the fan come on when the heat builds?

any help would be greatly greatly appreicated.

john

[ghurd]

Hey John,

What is the heat sink for?

The power fets need to be on separate heat sinks, but they sure do not need a heat sink that big!

More like this is plenty,

http://ghurd.info/images/DC/heat_sinks.jpg

If they are not on separate heat sinks, the loads are all connected together through the heat sink, and it will make the fets less reliable.

The fan could be connected to another fet, but it will most likely only twitch most of the time.

The dump load ammeter will mostly swing wild full scale, and very wildly.

It'll be about as smooth as a Red Squirrel after a gallon of StarBuck's espresso.

Each resistor will dump about 1.44A, so it's either 0A or 17A, and fast as a ticker tape machine.

G-

[ghurd]

Also.

The fan can not be driven directly from the controller circuit.

Very many added milliamps will make the circuit oscillate.

The fan takes too many amps for what the P-fet is rated. It will blow the P-fet.

G-

[divemaster1963]

Thanks Ghurd I was thinking that the fan would help with cooling . the heat sink is from a bunch of old computers that I had. I pulled all the heat sinks from then.

I will seperate the P-frets. I did not think about the linking the fan is rated at 12 volt .o12amps. I take it out. I have hundreds of heat sinks in the shop. I'll locate them on seperate one and isolate them from the metal housing. the amp meter is going to be tied to the solar panels only. they rated at only 45 watts. I just wanted everything together to minumize space in my shop. I just got my pole sections this weekend to get my tower up but rain has stoped the work again. If I have anymore questions I'll let you know.

Thanks again

john

[ghurd]

Separate the power N-fets on separate heat sinks.

The P channel fet (as opposed to N channel power fet) is the last little 3-legged black thing on the circuit board.

G-

[wooferhound]

I built a Two Stage dump controller using 2 of Ghurds circuits set to slightly different dump voltages. I hooked the fan to the Dump Power outputs through some isolating diodes with a large capacitor across the fan to keep it running through the slower dump pulses.

If any one of the 2 stages pulses a dump voltage to the resistors, it also pulses the capacitor through an isolation diode, which charges up a 10000mfd capacitor and can keep the fan running for about 5 or 8 seconds. The the diode isolates the capacitor from the resistors preventing the capacitor from discharging back through the resistors. The ghurd dump controller can be set for a wide histersis range and I have mine set for .01 volt. Set that way the controller can pulse dumps quite rapidly. It is rare to see it pulsing dumps more than 1 second apart. I usually see the dump pulses running faster than 10 times a second, but it can easy be so fast that the dump light appears to stay on continuously.

There has been some discussion about how bad it is to charge a capacitor Hard like this in the first few dump pulses that may be more than 5 seconds apart, but I have never heard of any actual problems doing this, plus this is a fairly high quality cap.

Here is a link to my dump controller that has a schematic showing the fan circuit clearly.

http://www.fieldlines.com/story/2008/7/13/211414/932

[divemaster1963]

sorry about that. big fingers small key board. went up instead of down to (n).:-)

yea I'm going to do that this weekend. It's suppose to rain again so cannot make it to my shop because of the now full creek bed. dang rain. but good wind.

[divemaster1963]

thanks woof

I have been looking for that story. dang problems locating things sense the change on the board. stuff just seemd to move by then self. sort of like my keys and wallet.