Preventing Failures:
The Problem
STO-P Solution
Back Up Power
Volume Quotes
Custom/Military Versions
Common Electrical System Faults:
Induced E.M.F.
Reverse Polarity
Land Transport


Written in 1993, this article described the original STO-P and it's use on Cruising Yachts. It was written for the NON-Technical user of marine electronics.


"Always make sure you turn off your electronic equipment when you start the engine....."   That's what the previous owner said when I bought the boat."  I don't think it's that much of a problem..." I said.

After 20 years of designing electronic systems I thought that my newly installed electrical system was as perfect as you could get on a boat. All of my instruments were brand new and very expensive ... so what could go wrong?


Not long after, my fancy and expensive Fishfinder packed up. A few curses and several hours of bench testing later I found the 'computer chip' that had failed. No causes were evident. No physical damage, no corrosion, no burned parts. It just failed for no reason.

A few months later it happened again! This time the power supply section of the Fishfinder burned up for no apparent reason. The cost to get it working again? About $275 for a new 'board'! But why did it fail? 'Solid state' electronics, i.e., transistors, diodes, integrated circuits and the like, should last a very long time. Twenty years, or more! Usually it's corrosion, or excessive heat that shortens the life of marine gear, but neither was the cause of the failure in this case. I checked with the Fishfinder manufacturer and was told they never had a problem like this - mine was the first one. (I didn't really believe that!)

One morning in a nice quiet anchorage there was a sudden knock on the hull and a frantic plea for help, "Come quickly. I've just blown up ALL of my electronics!" Black bag in hand, the 'electronic doctor' went to examine the stricken patients. Sure enough the Depth Sounder, Wind Speed Indicator, Electronic Log and Apparent Wind instruments were totally dead. After calming my friend, who by that time had tied an anchor around his neck and was heading for the rail, I learned that he was preparing to leave the dock when the accident happened. He had just started the engine when he noticed his instruments were off. All of the instruments had burned components in their power supply sections, so we concluded that something had gone wrong with his 12 volt system. The problem was traced to a faulty alternator voltage regulator which had failed and put a 'hefty jolt' into his instruments.

On another morning, the VHF radio blared: "Help! My brand new GPS just died". The GPS had been working fine and then all of a sudden it stopped. All of the waypoints including over 100 'secret' fishing spots were scrambled and totally useless. This suggested that something had altered the data in the GPS memory. It reminded me of problems I saw with computers when they had been hit with an AC Mains 'spike' or 'surge'. "What did you do?", I asked. "Just started the engine. But the GPS was OFF!" he said. Like many new pieces of equipment, this GPS has an ON/OFF 'button' that you press on the front panel. When you turn the GPS 'OFF' it is still connected to the 12 Volt power source. In fact, it is really 'asleep' and not 'Off' since some of the electronics inside the unit must keep checking to see when you press the 'ON' button again. The high voltage spikes generated by the engine's starter motor caused this failure and eventually destroyed the computer board in the GPS.


These were just a few of hundreds of incidents that we looked at over a period of four years. When we first started looking at 'why' marine electronics fail we assumed that corrosion would be the major cause. We were surprised when we discovered the real gremlins.


First, as the previous owner of my boat had hinted, high voltage spikes are generated when any electrical motor, and some other types of electrical equipment are turned on and off. (The terms Spikes, Surges, Transients, and the like, all refer to High Voltages that occur very suddenly, but last for a very brief period of time - much less than 1 second.) Usually the engine's starter motor or electric anchor winch is at fault. These generate positive and negative high voltage spikes and transients that can exceed several hundred volts!! But, we also measured high voltage spikes from water and bilge pumps, solenoids, small relays, clutches, AC inverters, Battery Chargers, and even an Electric Toilet! All of these ride along the 12 Volt DC line looking for someplace to go. Having a separate battery to start the engine or run the electric anchor winch helps. But it is no guarantee of avoiding those high voltage spikes which can travel back through the charging system to other battery banks even if you do have a battery isolator. In fact, these high voltage spikes are powerful enough to damage or destroy many battery isolators! And contrary to popular opinion batteries are not good 'spike suppressors'.


The second common electrical system problem is Overvoltage. Alternators and Voltage Regulators , when they fail, can put out 90 volts or more. Sometimes for less than a second, but long enough to destroy your electronics. The voltage regulator that had failed on my friend's yacht (and blew up all of the instruments) claimed it prevented 'Overvoltage' conditions. True enough until IT failed! And, if you should accidently turn your battery switch to the OFF position while charging with your alternator or wind generator, the overvoltage produced will almost certainly destroy your electronic gear! Outboard Engine charging systems and shore powered battery chargers are another big source of 'overvoltage' conditions.


Is your GPS at risk? Sorry, but the news is not very good. On a recent South Pacific cruise, we surveyed 40 cruising boats in Vanuatu (New Hebrides) to see what experiences offshore cruisers had with their GPS navigators. Twenty seven percent reported GPS equipment failures within the past 12 months! In some cases, boats had experienced two or more identical failures with the same unit. Each time they had to pack up the GPS, and send it off to the manufacturer or dealer - wondering if they would ever see it again. Sadly, many learned that their credit card accounts had been charged substantial amounts for 'non-warranty work'. It seems that if you destroy your GPS because of power problems on your boat the warranty may be VOID.

Because of these high failure rates, many cruising yachts are now carrying a 'spare' GPS! These are mostly of the 'handheld' variety that operate on standard dry cell batteries. Unfortunately, because the operating life of these batteries is so limited, most yachties plug the GPS into the boats 12 volt system. As soon as they did that, their GPS handhelds started to fail at the same high rate. Incidentally, we were constantly asked: 'Which is the best brand of GPS?' We did not see any difference in failure rates between different manufacturers. Despite the advertising rhetoric, all use virtually the same silicon technology - so this is not too surprising. High priced gear is just as vulnerable as the 'Cheapie'.

Some manufacturers are keenly aware of the problem and readily admit to their service technicians that power Spikes, Transients and Overvoltages are a real threat. But, others try to convey a false sense of security by saying their GPS units will operate over a wide range of voltages (up to 35 or 40 volts) - implying that they are immune to these problems- which they are not. But, the trend is now to exclude power induced damage on warranty coverage. So, if they think that a failure was caused by your electrical system, you may be in for a hefty non-warranty repair bill. Beware!


Why don't manufacturers design their equipment better? Having been both an electronic designer and the owner of an electronics company, let me share a few insights. In general, most manufacturers do try to build the best gear they can. But there are many pressures on their design engineers who must spend time making their black boxes 'better' than their competitor's by including more features. This usually entails the use of more IC and memory chips, squeezed into a smaller space, which makes the units more vulnerable to failure from spikes, transients and overvoltages.

The damage caused by Spikes and Transients is so insidious that even the most competent repair technician can miss it. Unless they have been trained by NASA or have worked in high-reliability military/aerospace programs most engineers have very little understanding of the transient-induced stresses that lead to semiconductor failure.

Transients are much like termites that eat their way through your house. You don't see the damage until one day the house collapses. If they are large enough and of sufficient duration, they will cause an immediate failure. But more often than not, Spikes and Transients 'chip away' at semiconductor junctions slowly destroying them until one day, in a weakened condition, the transistor or IC chip collapses. Unlike a house, we cannot inspect a transistor, diode or integrated circuit to see if damage is occurring. The only warning we have is when the equipment fails! And, the only way to prevent this is to keep spikes and transients out in the first place.

Sometimes we get clues that damage is occurring. A piece of equipment may start acting 'funny'. For example, your GPS may lose fixes, or your depth sounder may display some 'gibberish'. Then it starts working again. At first it will appear as a random incident and you put it out of mind as nothing to worry about. Then one day - without warning - total failure! When electronic equipment starts acting 'funny' be forewarned! There is always a cause!


So, what can we do about it? A simple 'fuse' or 'circuit breaker' may prevent fires, but they do nothing to protect against spikes, transients and overvoltages. It takes too long for them to 'react'. The damage is done by the time they 'protect' your equipment. Disconnecting the power to your equipment everytime you crank the engine or use the electric anchor winch is a good idea as long as you always remember to do it. But, this will NOT prevent damage from overvoltages, induced voltages, or spikes and transients caused by small motors like bilge and pressure water pumps.

A separate 'electronics' battery fed from the boats electrical system through a diode has often been suggested as a cure. This is good for low-voltage problems, but is ineffective as a spike and transient suppressor. And, it will be damaged by overvoltages. As it turned out, identifying the problem was easier than solving it. We tried all of the conventional 'cures'. Filters, first. They're cheap! But, little has changed with them since World War II and they were generally ineffective. We tried 'MOV's' - the devices used in AC mains surge suppressors - again with disappointing results. We tried capacitors, zener diodes, special IC regulators, switching power supplies, and much more. All rejected for various technical reasons.


In the end we realized that no one technology was suited to the task and that we would have to 'purpose build' a totally new device that was specifically designed for 12 and 24 volt battery powered environments. The result is 'STO-P'(tm) short for 'Spike, Transient, Overvoltage Protector'. It is placed between the power source and the equipment to be protected, constantly monitoring the battery line. STO-P provides an instant barrier to any spikes, transients (surges) and Overvoltages that may appear. We also put in filtering to help remove induced E.M.F. (generated by nearby lightning strikes, or onboard SSB transmitters) and noise generated by instruments on your d.c. power system.

STO-P's are easily installed in a power panel or any out of the way place. One STO-P will protect many pieces of electronic equipment - you don't need a separate STO-P for each unit! The 10 amp version will protect most of the electronics on a typical boat: GPS, Fishfinder, Satnav, Depth Sounder, Electronic Log, Knotmeter, Radar, Autopilot electronics, Wind Speed Meter, Apparent Wind Indicator and perhaps one or two other instruments. It will even protect your laptop computer if you have one!

As for its performance, we subjected STO-P to thousands of hours of testing both in the lab and on the water. On an oscilloscope, we can watch 200+ volt 'spikes' going into the 'STO-P' but the only thing coming out is nice clean DC. But, the most important test of all is how well does it work on your boat! STO-P's were originally tested on more than 100 vessels . These ranged from fishing runabouts and cruising yachts, to megabuck launches. The failure rates for electronic gear, especially GPS', dropped dramatically to a few percent - a remarkable improvement over the 27 percent failure rate mentioned earlier!

My recommendation? I'm biased, of course, but honestly you must seriously consider the damaging effects that spikes, transients and overvoltages will have on your marine electronics. 'STO-P' is the perfect answer - and I would not leave the dock without one!


This article was written in 1993 and kicked off the demand for STO-P. Over the years, it has become an indispensable component of 12/24 volt electrical systems where reliability is a must. Today (mid 1999) thousands are in use worldwide in virtually every d.c. powered application. STO-P is one of those products that came out of a real world need to solve a problem.

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