Power spikes

[Rob_Webb]

I'm battling with a piece of marine electronic equipment - I won't say what type/manufacturer yet until they decide what to do - at which point I will name and shame or name and praise.

When the unit was 2yrs old the circuit board blew. They replaced it under warranty but advised that it could have been caused by power spikes because it was connected to the same battery as my anchor windlass.

So I took steps to change that which meant the said unit was now running off a battery that it shared only with the 12v fridge. Now, less than 18 months after the first repair it has blown the circuit board again.

This time they tell me that the fridge could have caused a power spike and as a result they have charged me over $600 to replace the circuit board.

My first question is can someone tell me whether they have heard of electronic equipment being damaged by sharing batteries with other equipment, especially mechanical stuff like windlass or fridge motors? Can the voltage seen at the 12V battery really spike up to a dangerous level? The advice I have received so far says it can only spike down not up.

Secondly, I regard this particualr unit as a 'premium' piece of kit frequently seen on round the world cruisers and racers. As such, I would expect it to be robust enough to surivive more than 18/24 months of light coastal cruising. And also to be designed to share its battery supply with other normal marine equipment including water pump motors and fridges. I can sort of buy the explanation that an anchor windlass could be a bit of a beast and should be isolated from other electrical stuff, maybe only sharing the engine start battery.

But surely my piece of kit has got some other kind of fault and I can't go on accepting that will need to fork out $600 every 18 months to keep it going. After all, if the electrical supply was so bad why doesn't it fail immediately?

Any thoughts?

 

[VicS]

I guess any inductive device such as a motor can/will produce a spike internally when the switch opens but I would not a have though it would affect other stuff in this way Any spike that did appear on the external wiring I would have thought would be absorbed by the battery anyway.

If the equipment is intended for use on small boats then it should tolerate this sort of thing or there should have been a warning about it as winch motors, pump motors, starter motors, fridges etc are bound to be on the circuits.

I would suggest you look at your battery charging. A defective alternator regulator with an intermittent fault causing short periods of high voltage could be to blame.

I once had something similar when an Autohelm was damaged but that was caused by running it with an outboard battery charging output connected but I'd forgotten to connect the battery. Burnt out the voltage stabiliser in the Autohelm. Nautech were so concerned that they managed to contact me at work!

 

[ga1135]

Have you add a fuse between the power supply & your equipment (in addition to the auto circuit breaker in your system)? In this case, it will blow the fuse first and disconnect the electricity supply to avoid damage to the instrument.

Usually it will have a recommended fuse value (e.g. 1-5A) in the user/installation manual.

 

[Rob_Webb]

Yes there is a small fuse in the + supply to the unit but I can't remember what rating.

 

[ga1135]

Just experience for sharing.

My Silver Nexus Server was once out of order and unable to drive the chain of display units connected. Finally it was discovered that the contacts of the pins connecting the mother board and the in/out put terminals were deformed after 12 years of service. I just re-solder the contact points myself and everything work again.

Don't know if such situation would happen in other brand's instruments.

 

[john_morris_uk]

[ QUOTE ]
Have you add a fuse between the power supply & your equipment (in addition to the auto circuit breaker in your system)? In this case, it will blow the fuse first and disconnect the electricity supply to avoid damage to the instrument.

Usually it will have a recommended fuse value (e.g. 1-5A) in the user/installation manual.

[/ QUOTE ]A good idea and obviously good practice, but a fuse is unlikely to do anything about voltage transients from inductive loads. For instance (and off subject slightly and making a broad sweeping sort of statement) there is no wire fuse that will prevent a silicon device in thermal runaway self destroying. In a lab I worked in once, we described some of the delicate transistors as the quickest fuses known to man. In thermal runaway they blew quicker than a quick thing on a quick day. Anyway what I am saying is that fuses don't generally blow on transients unless they're mahoosive ones, and even then the electronics will have already cooked.

However that is not the issue hereas its fairly easy to protect against voltage transients. Most electronic equipment has some crude protection built in as a norm. (Capacitors across the supply etc). I smell a ratty sort of smell in their weasle words (mixing the metaphors now). The fridge 'might ' be the culprit, but you would need a good engineer to diagnose what is going on with any certainty. Even then, random faults and occasional failures are the curse of diagnostics.

 

[halcyon]

[ QUOTE ]
When the unit was 2yrs old the circuit board blew.

[/ QUOTE ]

When you say it blew, what happened to the board, i.e. did it burn out, blow chips apart, or did it just stop working ?

Brian

 

[DavidNB]

Relays can often cause spikes, have seen them wreck alternators, easy fixed with a power diode across the coil terminals. Your windlass might have one to take the load off the switch.

 

[JKay]

I had the same from "Garmin"they replaced it even though out of warranty /forums/images/graemlins/grin.gif
Cheers Joe

 

[Rob_Webb]

When I say 'blew' it just stopped driving the motor although the display was unchanged. The term 'blew' was the verdict from the agent.

 

[jfkal]

Sounds like an excuse. Should not happen unless something wrong with your alternator or you had a lightning strike.

 

[VicS]

[ QUOTE ]
unless something wrong with your alternator .....

[/ QUOTE ] Hence my earlier suggestion that it might be a regulator fault.

 

[halcyon]

The problem here is we do not know what failed. Could be a power MOSFET, could be the driver stage, or logic / micro, either would have a differant type of fault to cause failure. Added to this is 18 / 24 months use between failures, and differant batteries to supply power. All indicating a non standard situation, or one that is very very rare.

So without all the info an answer is not possible.

Should it fail no, but you cannot cover all bases, and extremeor odd circumstances can do funny things.

Should you pay?, unless they can say you did this, and caused this, no.

If they cannot say what caused it, then a token material cost for repair would be fair, but I doubt I would inpose it for customer relations and good name.

Have a moan at them

Brian