voltage transient causing trouble

[FishingBuddy]

I have a 2001 Mercury 90 ELPTO on a 2001 Lund Mr. Pike 17. Everything seems to be working fine.

However, I have had two cell phone chargers die when connected to my 12V (cigarette lighter) power outlet. The outlet is working fine for my air pump and other devices.

I recently installed a new Lowrance HDS5 GPS/Sonar. I noticed that about 1 in 5 times I start the outboard that the HDS5 will reboot. This made me realize there must be a voltage transient that is occurring when I crank the motor. When I first plugged-in the phone chargers, they worked OK. Later they were dead. I wasn?t able to observe if they died when the outboard was being cranked.

I believe the transient to be in excess of 35V and beefy. I am the manufacturer of the two cell phone chargers that died. The chargers are designed to operate at a constant voltage of 32V, and are further designed to withstand (immunity) commonly specified vehicular transient waveforms (cranking, load dump, alternator whine, etc.). These are not cheap chargers.

I have an oscilloscope and can and will characterize the transient waveform. I only lack a flusher to get water to the outboard while testing. I am technically capable of tracking down the source of the transient. However, I am inexperienced with the Mercury outboard and whether the outboard or the (Lund) boat?s electrical system has any form of transient suppression built-in. So, I?m hoping to tap into any experience that the readers of this forum may have. For example, I don?t even know whether my Merc has a generator, an alternator, or a magneto. And, whether the starter motor has or hasn?t a separate solenoid, etc.

Perhaps:
1. I have a faulty component in the outboard. There will always be some level of transient when cranking the outboard, but the faulty component is making the transient larger than ?normal?. This is what I guess the matter to be, but the problem is masked because my motors starts right up and seems to be working just fine.
2. There is a component in the outboard designed to suppress this transient, but this component is missing or defective or out of circuit.
3. The transient is there, is not different from other motors/boats of the same type, but the equipment I have (Lowrance HDS5 & the cell phone charger) are particularly susceptible. I really doubt this to be the case.

If I do not have a faulty component in my motor, my obvious option is to install transient suppression componentry. Now, would the transient suppressor(s) be installed at the source or on the load side (i.e., at the 12V power outlet, and where the HDS5 is wired into the system)? I can imagine the solution being either way.

Thanks in advance for any comments.

 

[bruceb58]

Re: voltage transient causing trouble

It is not uncommon for sounders to reboot at start. This is normally due to a voltage drop however.

I can imagine a back EMF coming down the line when the starter motor stops. I would think you would have some protection diodes in your charger already for something like this.

 

[Silvertip]

Re: voltage transient causing trouble

There are essentially two electrical systems on a boat. 1) the engine electrical system consists of the alternator (a magnet and stator system), ignition system (magneto design), and the electrical harness going up front to the console. 2) the boat electrical system. The boat harness feeds 12 volts from the battery to the fuse/breaker panel. The common item in these two systems is the battery.

The engine electrical system sends 12 volts up the engine harness to the ignition switch and it powers the gauges and sends 12v back to the starter solenoid when the key is turned to START. The push to CHOKE function is also a back-feed to the engine. Other signals going up front are engine sensor outputs (water temp, oil related, and tachometer). All other gauges are not engine related. The voltmeter merely monitors "system" voltage and therefore provides an indication whether or not the battery is being charged or losing ground so to speak. The speedo is pitot driven and not electrical. The fuel gauge is boat related and driven by a restance device in the fuel tank. The boat electrical system is fed from the battery via the red and black leads (usually #8 or #10 gauge) to the fuse or breaker panel at the console with a system protection breaker or fuse at the battery. The engine obtains its power from the battery via the two large battery cables and the battery is charged via those two cables as well. A fuse or breaker in the engine bay protects the +12 volt feed to the gauges via the engine harness. Your engine has a 16A alternator and because its magneto driven, will run without a battery although that will certainly toast the rectifier/regulator. If you've done that accidentally or on purpose in the past, you probably found your issue.

In my view, there is nothing unique about a marine electrical system. Newer engines are regulated just like a car and in the case of EFI/DFI systems have ECU's that are nearly as sophisticated so regulation is equally important.

Since the failure of your chargers happens with the engine running (I will bet it is the engine start or stop function) I would begin my quest for an answer by verifying the integrity of the electrical connections at the battery. That doesn't mean "looking" at them. It means disassembly, making the terminals shiny clean and tightening them securely. Then repeat the process on the engine end. Then move to the boat harness leads both at the battery and the console fuse/breaker panel. The devices you say work ok are high current draw items and would likely exhibit a "hit" (although less noticeable) when you hit the key or turn it off just like your chargers. It is my opinion you have a faulty ground connection. Also, ground on a boat is at the negative terminal of the battery -- not the hull of the boat. Lastly, since the alternator is a stator, rectifier, regulator system, I would look for a loose ground or stator connection as an unloaded (unregulated) alternator can easily reach 35 volts on the output. Perhaps a bad diode(s) in the rectifier is to blame.

 

[FishingBuddy]

Re: voltage transient causing trouble

Hello Bruce,
Thanks for the reply.
When I scope the cranking, I should be able to see if it is voltage drop causing the sounder the reboot. I didn't know this was common. I'm a little less concerned now.

Yes, we do have a protection diode, and I have reviewed our data indicating that we can withstand pulses up through 50V. Over 50V, we have a fail-safe condition. Granted, this is testing with standardized waveforms. So, my transient must be in excess of 50V or have a longer dwell or both.

Now I'm wondering why the sounder and accessory power outlet aren't on my bank of trolling batteries (or, switched to either bank). I doubt any disturbances from the trolling motor would be so severe.

 

[bruceb58]

Re: voltage transient causing trouble

Where is the diode in the circuit? Is it right across the inputs? Is it basically set up as a back EMF diode or is it setup as a reverse polarity diode?

 

[FishingBuddy]

Re: voltage transient causing trouble

Thanks Silvertip!
Wow! A very informative reply. I'll be looking into all of this.

After I get it all figured out. I'll be sure to post the final result so the thread might be useful to someone in the future.

 

[FishingBuddy]

Re: voltage transient causing trouble

Bruce,
It's across the lines. It is not a reverse polarity diode, but is capable of withstanding reverse polarity.

 

[Silvertip]

Re: voltage transient causing trouble

You will likely want to scope the 12 volt supply. On a scope you will not see pure dc. Your engine has a 12 pole alternator producing 6 pulses per rev at the input to the rectifier. At whatever your idle rpm is you can do the math. The rectifier is full wave. I don't remember if that engine has the rectifier and regulator potted as an assembly or not. If they are separate units you have have a few more spots to scope. If not, you can only scope alternator output (AC) and regulator output.

 

[FishingBuddy]

Re: voltage transient causing trouble

Thanks again Silvertip. My scope is awesome so I'll get a very good idea of what's occuring. I just gotta get the motor flusher for my hose and wait for my wife to go shopping or something.

 

[jhebert]

Re: voltage transient causing trouble

Your 2001 Mercury outboard motor has a permanent magnet alternator. There typically is a full-wave bridge rectifier providing charging current.

It is quite typical that during engine cranking the battery voltage will sag from the load of the engine starter motor. If the battery voltage sags too much, it is typical that some electronic devices connected to the cranking battery will reboot due to low input voltage. A voltage sag to 8-volts may occur.

Developing high voltage transients is not as easy because the storage battery has a rather low impedance and is connected across the starter motor. When the solenoid drops out, the starter motor is disconnected from the battery. If there is energy stored in the magnetic field around the starter motor, when the field collapses it will induce current into the motor windings. However, since the starter motor is not connected to the battery any more, this transient cannot affect the battery.

It is much more likely that there will be a high-voltage transient if for some reason the battery becomes disconnected from the circuit. This can happen, for example, if the battery connection is intermittent. If the battery is momentarily disconnected from the circuit, the field of the starter motor collapses and generates a transient. If the solenoid holds in for just a fraction of a second, this transient can reach other components in the 12-volt distribution. Since the battery is not connected, it cannot help absorb the transient.

To better understand boat power generation, see

Boat Electrical Power Generation
by James W. Hebert
http://continuouswave.com/whaler/reference/electrical.html

For more on permanent magnet alternators, see

Permanent Magnet Alternators
by James W. Hebert
http://continuouswave.com/whaler/reference/PMA.html

 

[FishingBuddy]

Re: voltage transient causing trouble

thanks for those links James! I have bookmarked them

A battery certainly can suppress transients, but may be imperfect in doing so. Very fast transients can get by the battery and the battery may only dampen longer transients. We'll know more after I scope it.