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Load Test of a New Backpack Electrofisher

Rarely does a new model electrofisher hit the market, so it is fortunate to be able to evaluate it in some respects. The first backpack electrofisher we bought at a federal fish hatchery for capturing possible mussel host fish was an Appalachian Aquatics AA-24. It had multiple voltage ranges, but the waveform was fixed at 120 Hz pulsed direct current with a duty cycle that varied slightly with load from about 73 to 80 percent. Despite the fixed frequency and duty cycle, it captured fish well. It was sturdily made, and I understand those units are still operating after 15 years of service. One day, we had the opportunity to use the AA-24 at the same stream as an ETS ABP-3 and a Smith-Root LR-24. As I recall, the ambient water conductivity was about 40 μS/cm, so we set each unit to 400 volts and began shocking. All three units successfully captured small stream fish, and we saw in this short comparison no real differences in fish catch among the three units.

Appalachian Aquatics, owned by Bart Carter, became Aqua Shock Solutions, owned by Anthony Strokoff. I think the AA-24, which later had a 12-volt battery, became the B1L under the new company. I tested one while I worked for the Fish and Wildlife Service and found it to be basically the same as our older AA-24, with a new name and with a 12-volt battery. Later, there was an A1L model which was replaced by the AS2 which is still made by Aqua Shock Solutions. Now you know that history.

The model tested for this blog is the new AP1. It is a 24-volt, 300-average-watt unit with independent controls for voltage, frequency and duty cycle. It has ten voltage ranges from 50 to 700 peak volts; frequency is continuously adjustable from 10 to 250 Hz; and duty cycle is continuously adjustable from 5 to 90 percent then to continuous direct current (100% duty cycle). Both controls are rotary dials, and the outputs are shown in one-unit increments (1 Hz and 1 %) on an LCD screen.  Output metering while shocking includes battery voltage and current, output average watts, frequency and duty cycle and a load (shocking) timer.  When the switch is not engaged, the meter output is the same except amp-hours used is displayed instead of output average watts.

Rear and both sides of the new AP1 backpack from Aqua Shock Solutions. Rear shows the display and the 24 volt battery. The right side (shown here on the left) has the cathode connection and the voltage control in steps of 50 or 100 volts. The left side has the anode connection, main power switch, annunciator (beeper) switch and the shocking timer reset. It also has the continuous controls for frequency and duty cycle.

Display while shocking: battery voltage and current draw, peak power output, output frequency, output duty cycle and shocking time.

Display when not shocking: Battery voltage and current draw, total amp hours used, frequency setting, duty cycle setting and  shocking time.

The first parameters checked were the accuracy of the frequency and duty cycle. This was done at a light load of 969 ohms resistance. This equates to about 27-30 μS/cm water conductivity. All testing was done using a ten-gallon aquarium with plate electrodes which could be moved to vary the resistance. High resistance equates to a light load (amps per volt) on the backpack. A Fluke 124B scopemeter was used as an independent measure of frequency, duty cycle, peak voltage and, in conjunction with a Fluke 80i-110s current probe, of peak current. The settings for these initial tests were 60 Hz and 15 percent duty cycle.

All output parameters were measured with a Fluke 124B scopemeter. Shown is the rectangular pulse produced by the AP1.

The frequency control was very smooth, and the meter reading was very accurate. The dashed line is the 1:1 line, and the open circles are the results from the Fluke scopemeter. The results above are for the light load of over 900 ohms. This test was performed later at a higher load of 20 ohms, corresponding to about 1300-1500 μS/cm conductivity, and the frequency results were of the same accuracy. To show the low and high load results on the same graph would mean one set of markers would cover the other.

The duty cycle control was also very smooth and accurate. The graph is for the results under the initial light load over 900 ohms resistance. The test was repeated at a higher load of 20 ohms, and the results were the same.

The next test was a check of voltage calibration. This was done at the initial light load and then twice more at less resistance.

At the light load, shown by open circles, the peak voltage followed the 1:1 line except for a very slight decrease below the line at the 700-volt setting. At an intermediate load of 127 ohms, which equates to about 200 to 230 μS/cm, peak voltage dropped below the line by 400 volts and dropped more by 500 volts (shown here by the open squares). The unit overloaded and shut off at the 600-volt setting. Those are typical results for load testing. These voltage calibration checks were done at 60 Hz with a 15% duty cycle. At a high load of 16 ohms, which equates to about 1600-1800 μS/cm, the peak voltage dropped very slightly below the line at about the 150-volt setting and somewhat more at the 200-volt setting. The unit overloaded and shut off at the 250-volt setting. Again, all of this is expected as one loads an electrofisher.

The next graph is a plot of peak power in watts versus resistance in ohms. From left to right, ascending diagonal lines are equal voltage lines, and descending diagonal lines are equal current lines. Voltage and current are both peak values. Don’t be overwhelmed by this graph. The first time I saw such a graph, it was too much to grasp. However, the graph is very informative. Focus first on the y-axis (power) and on the x-axis (resistance). Notice that resistance reads from right to left. You can think of that as water conductivity reading from left to right. Because I don’t know the resistance of the electrodes, I am not able to say with complete accuracy how resistance relates to conductivity, but the values presented above are close estimates based on measurements from other backpack electrodes. Backpack electrodes of different types and sizes may have different resistances, by design.

Let me explain a little more about this graph. Both power and resistance are on log scales. From the bottom right, each vertical line is another 4 ohms until it reaches 40 ohms, then each vertical line is 40 ohms, and so forth. Each horizontal line is 100 watts until it reaches 1,000 watts, then each line is 1,000 watts, and so forth. Voltage lines, from right to left, are 120 volts to 1000 volts. Current lines, from left to right, are 1 amp to 32 amps, doubling each time. This graph is used by electrical engineers to graphically solve Ohms Law and Joules Law.

The curved blue line is an estimate of fish catching threshold peak power across the resistance — think water conductivity — range. The black line is the peak power at a 15% duty cycle, the green line is at a 20% duty cycle, and the red line is at a 25% duty cycle. The white square at 16 ohms is 15% duty cycle at the 200-volt setting. The unit overloaded at 20% duty cycle at the 200-volt setting, but it did operate at 18% duty cycle at the 200-volt setting; that is the green circle. The three lines show consistent trends. At 4.7-4.8 ohms, the unit operated at 15% and 20% duty cycle but overloaded at 25% duty cycle, all at the 100-volt setting. The highest duty cycle at 4.7 ohms and the 100-volt setting was 23% (the red triangle). The maximum output at 4.6 ohms and a 5% duty cycle on the 200-volt setting was over 5300 peak watts (the orange diamond); that is 34 peak amps! At a 6% duty cycle, maximum power was 5000 peak watts.

I think the dip in peak power at 75 ohms was due to the change from the 400-volt setting to the 300-volt setting. The peak power likely would have been pretty level if there had been a 350-volt setting. Even with the dips at 75 ohms, there is plenty of excess power available for shocking fish. At a 25% duty cycle, the peak power at 75 ohms is about 2.5X the blue line fishing threshold. At a 15% duty cycle, the peak power is about 3X the blue line.

The unit performed well despite having large voltage steps. Anything above the blue line may be excess power, anyway. So far, I’d say it performed as a 300-avg-watt backpack; the low and high conductivity parameters will be the 700-volt line on the left and about 17 ohms or less on the right. An estimate of conductivity range, assuming the blue line is threshold, is a conductivity range of approximately 22 to 1700 μS/cm. To standardize the effective fishing field size across conductivity, i.e. to follow along the blue line, one would need to decrease voltage — and thus power — from the maximum values shown here.

The results shown above were from load tests conducted at 60 Hz. That is a common frequency for warmwater fish, as is 120 Hz. Trout are generally captured at or near 30 Hz to avoid fish injury. Therefore, load tests at the 16 ohms were conducted at 30, 60 and 120 Hz.

Maximum output of peak power was unchanged across the frequency range of 30 to 120 Hz. Peak power was highest for the lowest duty cycle setting, as expected. That a change in frequency did not affect peak power is an important confirmation of independent frequency control.

Let me summarize and provide some overall impressions. This appears to be a solid backpack unit which delivers 300 average watts of power if one can match the voltage range to the resistance. Frankly, I expected the maximum power versus resistance graph to be quite jagged because of the large voltage steps of 50 and 100 volts. To my surprise, max power was reasonably flat across a wide resistance range. It ran up the 700-volt diagonal line, as expected, and then continued across the top at an almost constant power all the way to the minimum resistance (4.6-4.8 ohms) which I could produce in a small aquarium. I don’t want to mention names or to preempt a paper on similar load testing, but let me say that similar testing with some other backpacks stopped at 20 ohms resistance. Only one other unit was tested to less than 4 ohms. What I’m saying here is that this unit compared very well versus some top brands made in this country. The only dip in power, at 75 ohms, was due to the voltage step from 400 to 300 volts. Again, this unit produced considerable excess power above the blue line successful fishing threshold at the 75-ohm dip, so that is no problem. One would reduce voltage to near the blue line when performing standardized fishing.

Below are some pros and cons of this unit. I was not able to field test the unit. As a retiree, it is illegal for me to go electrofishing without a collecting permit. My understanding is that biologists with the Great Smoky Mountain National Park have field tested this unit. Appalachian Aquatics was, and Aqua Shock Solutions is, in the East Tennessee area, and the units were designed for sampling in that area. Some of the streams there have low water conductivity.


300-average-watt backpack with independent controls for voltage, frequency and duty cycle. The frequency and duty cycle controls are very smooth, continuous and accurate. They read to the nearest unit.

Accurate metering for frequency, duty cycle and output in average watts. The cutoff was at 300 average watts.

Rectangular pulse shape with only a moderate droop which was most pronounced at about 250 volts. Otherwise, the pulse top was basically flat. The pulse droop seen here should be no issue for fishing.

Ten voltage ranges which should easily cover a wide conductivity range. My estimate is from 22 to about 1700 μS/cm, based on information from other units, but this should be validated with field testing.

Price. The AP1 lists for $5,450 which includes two lithium-ion phosphate 24-volt, 9.5 A-hr batteries, charger and complete customized pole electrode set.


Voltage is in steps instead of being continuously adjustable or adjustable in small steps such as the nearest 5 volts. The unit should fish well with its ten voltage ranges, but there is some lack of fine tuning with the coarse voltage steps.

Lack of peak metering for voltage and current. It does have an average watt reading, and one can divide that number by the duty cycle in proportion to estimate peak watts, but that is somewhat cumbersome in the field.


This appears to be a solid backpack electrofisher with impressive performance and power to spare over a wide range of water conductivity. It should compare well with all but one backpack on the market; that one is in a class by itself. That unit will be revealed in a paper on load testing four other backpacks. And there is one additional backpack that has a higher voltage capability and thus can operate in slightly lower water conductivity. My estimate is that this one will operate well down to about 22 μS/cm and perhaps to a little lower with a large anode loop.

Check the web site at www.aquashocksolutions.com for more details. This blog was written during the season of the Winter Olympics in South Korea. In that spirit, “The AP1 is a contender.”

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© 2015 Thread One Page. Imagery: Tom Rayner, Alan temple, Richard Pearson, Paul Godfrey, Roger Scott, John Rayner.