What size/type (if known)??Originally Posted by Spaniard_King
I don't know about the lightning theory.
Any burn marks on the boat or trailer??
They'd be pretty obvious to the eye. Well all the one's I've seen are pretty obvious
What size/type (if known)??
I don't know about the lightning theory.
Any burn marks on the boat or trailer??
They'd be pretty obvious to the eye. Well all the one's I've seen are pretty obvious
I intend on living for-ever....so far so good
Ok on the subject of how a fuse would not blow if +12 V was applies to the antenna shield.
If stray 12V from a wiring fault or other, became connected to the antenna shiled the circuit path would be from +12, thru the shield of the antenna connection, via the internal bonding between the antenna shield and the negative or 0V (black) connection thru the black wire and to OV battery.
Now... I know that earth potential rise is not going to happen in a small boat in the conventional trems.
BUT
If the radio was wired dired to the battery as many do.
AND
the negative supply or 0V cable going to the switch board was high resistance or open circuit.
AND
the antenna shield was connected directly or indirectly to something elses ground
the radio negative supply cable via the antenna shield may be providing the earth return for the entire switchboard load.
an example would be
marine two way directly connected to battery, ground plane antenna mounted on metal bow.
Metal cassed automotive spot light mounted on matal bow... yeh there are two wires going to the spot light 12V supply and earth... but the case is not isolated from the earth or negative connection.
so the radio will work fine, but because the earth return from the negative common is either bad or OC the entire load passes thru the radio negative wire.
A very similar situation to a MEN fault in 240V ac but different.
All hypothetical.
As far as it being a lightening strike........the damage does not look violent enough to me and with several gazillion volts the whole of the cable would be damaged.
I am sure the boat owner would have things to say about being struck by lightening if he survived.
That cable damage looks like a slow melt to me.
cheers
All of this is still intriguing me gentlemen.
The only source of a +12VDC supply to the radio is via the fuse. Why didn't it blow????? I'm assuming an alloy hull bonded to 0V.
If, as some are saying, the return wire was being used to carry a fault current, then why did the return wire only fail upstream of the plug???? The same current is flowing in the entire conductor.
If this was on a plate boat, was the hull bonded to 0V?
Gary, was there any sign of a fault or flashing in the plug itself? Did this customer have a problem with batteries going flat? To do that damage you would need a fault of greater than 3A and obviously it would be time dependant ie. the higher the current the less time it takes or a lower current over a long period of time. you can see where the heat has affected the coiled handset cable (given it that stained brown look), this has heated up over a long period of time to do that. You're customer was very lucky a fire didn't start.
This would have had you scratching your head in amazement.
Sometimes a picture is more useful. Attached is a very rough sketch of how the wire can blow and not the fuse. IF you look at the picture, the red arrow indicates convential current flow.
In the left picture, the unit functions as normal, and current flows from positive to negative.
In the second picture however, if power is applied to the coax shield, then current will flow from the coax shield to the negative wire, and the fuse is not part of the circuit.
The squigley wire in the power lead represents the fuse.
Hope that helps.
i'm picking up what you're putting down andy, but how do you get +12VDC onto the coax shield without it going through the fuse? are you suggesting that +12VDC from another device or busbar etc. has rubbed through the serving on the coax somewhere and energised the shield? that would make a circuit, but the question is still there, why did the return conductor only fail upstream of the plug????? i'm assuming that a fault onto the co-ax would have been picked up by gary, and considering that the replacement radio worked no problems i'd be thinking that the fault lies within the radio itself. if it was april the first i wouldn't have put it past someone to pull the piss and throw this problem on here to see what comments they could get
Welcome to the world of fault findingi'm picking up what you're putting down andy, but how do you get +12VDC onto the coax shield without it going through the fuse? are you suggesting that +12VDC from another device or busbar etc. has rubbed through the serving on the coax somewhere and energised the shield? yep, exactlythat would make a circuit,
but the question is still there, why did the return conductor only fail upstream of the plug????? There could be a few reasons. (1) the conductor on the burnt bit is smaller and they heat up a lot quicker then a bigger conductor and/or (2)the insulation is of a poorer heat rating and burn at a lower temperature.
i'm assuming that a fault onto the co-ax would have been picked up by gary, and considering that the replacement radio worked no problems i'd be thinking that the fault lies within the radio itself. if it was april the first i wouldn't have put it past someone to pull the piss and throw this problem on here to see what comments they could get
I intend on living for-ever....so far so good
Oldboots thery of some other using the radio as return is also valid and would cause the same problem, however this would require that the radio or antenna be grounded. Not sure if the radio in question has a seperate ground terminal or screw. Also not sure on what antenna was used on the boat, but if it were a grounded quarter wave then it is definatly possible.
has to be something internal to that radio if the replacement radio went back into the same wiring loom and worked....and still works......or are alien influences at work(which i suspect with everything electrical)!!
Andy
I have a Battery Q? I have a 60hp F/S Yammie with two batteries thru a battery switch the yammie runs perfect thru either battery however if you switch to both batteries at low revs <1000 rpm it hunts about 300 rpm switch back to either battery runs perfect. whats going on??
Thanks
BigE
My theory, having worked in this industry for a very long time would simply be that they have changed to another manufacturer, in Asia, and their QA is poor, and they have used a very shitty brand of capacitor on the Voltage conversion area of the circuit inside the radio, basically you need something like a simple switcher or similar to get probably 3.3v or perhaps 5v for the components, from the 12vdc thats coming in.. you will also need a tantalum capacitor as well, and there are a lot of flung dung capacitors out there now that aint what they seem to be
If men are from Mars, and women are from Venus, politicians must be from uranus ?
It confused...... no seriously........the voltage regulator probablay is confused.
It no longer has a direct relationship with one battery OR two batteries at the same state of charge......
have you checked the contact resistance of the battery switch in all positions.
cheers
I doubt it has anything to do with the radio. If it did the fuse would have blown well before the power cable.
Actually tantalum capacitors are not suitable for power supply bypassing as they dont like instantanious changes in voltage (dv/dt for the techo's).
I am going to have to pass this one on to someone else cause I have no idea. Sounds like some sort of loading issue on the regulator. I am not familiar with how the regulators work in boats.
I hate tantalum capacitors with a pashon......they were realy popular in the eighties.....I have yanked out my fair share of them.....lots of designers were seduced by their high frequency performance but failed to note things they would not tolerate.....like any level of reverse polarity... or heavy ripple.....
Modern conventional electros I reccon have made them obsolete.
I understand that most outboard charging curcuits are stator and permanent magnet arrangements with a rectifier followed by some sort of regulator....problay series pass... the charging capacity is also quite small in comparison to automotive expectations.
High current series pass regulators can be a bit difficult to design... it is quite possible that the reg can not handle the current demand of two batteries..... if the design is smart there may also be some over current protection involved.
so... tries to charge at higher than designed curennt...... revs fall due to more than designed load...... protection circuit cuts in...... load off revs rise.... repeat.
or
the charging curcuit may not run below say 500rpm...... additional load causes the motor to drop below 500rpm.... load off..... motor picks up.....alternator operates.... repeat.
The manual for my littel 30hp merc specifies a recomended battery size...the charging capacity of that motor is only 18amps......typical small car alternator is 45 amps....larger cars will go 55 to 90 amps.
Cars generaly regulate by controlling the field current in the alternator.....
consider a 30Hp motor is about the size of a small 400 motorbike.
Even a 90Hp motor is more like a motorbike than a car....would you expect a motorbike to charge two 90 ah batteries and still idle
cheers
As Oldboot has suggested check the resistances of all the switch contacts or check the voltages to the motor in all switch positions and both batteries if you have a good multi-meter.
Are the batteries the same size?
Sounds odd but check where the leads are going onto the battery switch.
I've seen this stuffed up on the odd occurrence.
Has this happened from the word go or did it just start all of a sudden like??
Lots of 60hp motors around charging two batteries with no adverse problems in the motor running.
It's not so diabolical as suggested above.
There is a problem there. It just has to be found.
I intend on living for-ever....so far so good
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