Nuts and Volts - November 2011

www.nutsvolts.com/index.php?/magazine/article/november2011_QA

in detail, it may be possible to write a program to accomplish the desired result. From your questions, I sense that you do not know how this circuit works and I cannot help you with that.

SOLAR CONTROLLER

QI have only received a couple issues of Nuts & Volts and enjoy your Q & A section. Therefore, I

MAILBAG

Dear Russell: Re: Leak Noise Correlator, July ‘ 11, page 22: With regards to Howard Epstein’s question regarding a “Leak Noise Correlator,” you might want to check your definition of velocity (V). Using V = D/T, the quantity T1 + T2 becomes D1/V + D2/V, and that becomes the constant K = (D1 + D2)/V or D/V, the known quantity.

∆T = T1 - T2 = D1/V - D2/V = D1/V - D2/V + D2/V - D2/V; cleverly add zero then regroup the terms, = D1/V + D2/V - 2D2/V = K - 2D2/V In a similar fashion as above, by adding zero in the form of (D1/V - D1/V), we get: = 2D1/V - K Simple algebra gives the two relations: D1 = (K - ∆T)V/2 and D2 = (K + ∆T)V/2

— Ken Meier

24 November 2011

Response: Thanks for the

■ FIGURE 4.

thought you might be able to help me with a simple circuit I need to fabricate.

Here is my situation: I have two solar panels on the roof of my van camper to keep the batteries charged. A problem developed in the ignition switch that put 4 ohms to ground on the + side of the batteries.

Since I wasn’t using the van, I didn’t notice the batteries going down. Eventually, what apparently

feedback, Ken. If I had plugged some numbers in, I would have discovered my error in the beginning! I wonder how many were aware that I started off with the wrong premise? You were the only one to let me know of the error and I appreciate the opportunity to let the readers know that the math was wrong.

Dear Russell: Re: Transistor Replacement Needed, August ‘ 11, page 22: I love your column but found a major error in the theory of operation for “Transistor Replacement Needed”.

The International Rectifier B2M was a popular circa 1966 hobbyist photovoltaic (solar) cell and not a photoresistor. The germanium transistor is merely used as a “common emitter,” albeit one requiring a lower base voltage than a silicon transistor to turn it on.

R1 and C1 are simply a snubber to protect the transistor from back EMF transients when the coil is de-energized.

Workarounds to allow a silicon

happened was the batteries became so low they drew more current than the controller could handle.

The solar panels are putting out 19V but, the controller was putting 0V into the batteries. The controller is a SOLAR COMMANDER SERIES IV model FM16C made by Kyocera Solar, Inc., Kyoto, Japan which they no longer manufacture or repair.

This controller is quite complicated with five LEDs, a screen that shows voltage, and a pushbutton to show amps. I don’t believe I need such a sophisticated device.

Back when I was working in electronics — almost 50 years ago — we used tubes, not these tiny little components the size of a grain of rice that I have no idea what they are.

What say you? Am I a hopeless case or could you develop a controller that would suffice for my application? I wish to keep two 12V vehicle batteries charged. I can still read a schematic, more or less.

— Denis Kellogg

AI checked the Harbor Freight website; it has a 15 watt solar panel. Two of them would be more than

transistor to be used include using a second B2M in series to provide a higher drive voltage, or returning the grounded end of the original cell instead to the tap of a voltage divider between B+ and ground so that the cell voltage adds to the tap voltage. The drawback would be a constant low current drain on the battery due to the divider.

Better yet would be to replace the B2M as well, by using a common phototransistor along with a suitable current limiting transistor between base and B+, with a second resistor between base and ground to ensure that the transistor remains off when the light level is below the desired turn-on threshold.

Relays with ultra-sensitive 4,000Ω coils (~ 20 mW) are also quite expensive and difficult to find. There’s no reason other than battery life why a far more economical normal sensitivity relay couldn’t be used.