oscilloscope use to find spikes

[stevo]

this is a non landy question and related to a boat, I have changed the lay out of the dash on my boat cut a big hole in the dash and mounted a fishfinder/chartplotter in the dash had no room in the dash for the seven guages so went for a programable gauge that does the job of many.

but the problem is voltage spikes now my wiring for the dash is seperate from the motor wiring but the way wiring is done in boats with no ground to chassis probably does not help damping spikes.

I know a multimeter will not pick up spikes but need an ocilloscope jaycar has some cheap ones for $150 and I have made up a snubbing capicator with a diode and resistor wired in series to hopefully sort out the problem at the power bus bars and going to fit diodes across soleniods and the trim tab motors I suspect it is the bennet trim tab pump that is giving the spikes as when the boat is on the trailer and setting things up no problems, it is only when i am on the water that things go pear shaped and the trim tabs are the only extra thing working when I am in the water.

I want to do some before and after testing to see if what I have done gets rid of the spikes and where the problems are from what I have found out fishfinders are not to keen on spikes either the company I have bought the gauge from have been good it has been back three times the first two times to reload the software the third time to replace one of the micro computers they reckon it is picking up a spike on one of the inputs.

Will the cheap ocillascope do what I need it to do any advice would be greatfully recieved

[steveG]

Hi Stevo,
Sorry - cant answer your o'scope question, but thought you might be interested in this:
STO-P Power Fault Protectors (http://www.sto-p.com/pfp/pfp-articles.htm)
I'm guessing that there are other similar products out ther, so might be a better way to spend the $150 you were going to use for the scope.

Steve

[kaa45]

any circuit for digital electronics needs to be separate form any circuit running motors, switching power, etc. You need to look at the design of the wiring circuit, not try to track spikes. :(
A CRO won't help unless you know how to drive it.

[LOVEMYRANGIE]

A CRO won't help unless you know how to drive it.

Last time I drove a CRO, it was off a fence post with a shotgun! :p

[slug_burner]

Fish finders can cause a few problems as well. They need a bit of juice to generate the pulse and it is likely it is causing the supply to sag on each pulse or couple some of that pulse energy onto neighbouring circuits.

Nothing wrong with having to run a return wire for every circuit, better than relying on the chassis for a return path.

Part of the problem is that the battery is usually donw the back close to the motor to reduce the cost of the heavy cable run. This requires for you to run cables to the front of the boat to power all your bits and pieces as well as to connect to transducers and trim tabs etc. All those long legths of wire are acting as antennas to couple the noise or signals that are running on other cables.

Make sure you have a good healthy power run to your power consumers like your fishfinder, radar and transmitters. Give the pair of wires a couple of twists per foot to reduce the loop size. Physically seperate your signal cables from your power. Seperate the circuits that are giving you trouble until you find trhe ones that are not getting along with each other.

[stevo]

all the sounder cables run down one side of the boat and power down the other, heavy power cables go to the dash and connect to bus bars which supply power to radios, sounder, lights, gauge and now I think that the temp sender and trim tab for motor may have to have the earth seperate from the motor changing the temp sender to the two wire type and have the trim pot earth for the trim sender return back to the earth bus bar in dash.

Still will fit snubbing diodes to the soleniods and trim tab motor will look at the power fault protecter type of solution just need one that works as some are not worth th money.

[Dudley]

The biggest culprits in any low voltage DC system are the starter motor and/or the starter motor solenoid or any similar type of larger inductive load as they create spikes as soon as power is switched. There are snubber units available at electrical/electronic shops designed to over come this problem and are quite cheap and easy to fit. Hope this helps.

[stevo]

I have fitted something I made up across the power bus bars which should help and also fitted a DC DC converter from a mob that makes these things in WA for the marine industry (www.intervolt.com.au (http://www.intervolt.com.au)) which I have now running all the electronic stuff through.

Will be fitting diodes across the trim tab motors and soleniods and if there is still a problem will fit something to isolate one battery from the other till the motor is running and charging things.

Boats can keep you just as busy as your landy and I do really need to spend a weekend working on my disco at some stage!!

[Tombie]

Boats can keep you just as busy as your landy and I do really need to spend a weekend working on my disco at some stage!!

Can't they just!
I've been doing some work on mine lately too, and the Disco!

But you know the acronym for BOAT of course.
Bung
On
Another
Thousand $