Yamaha Outboard Charging Circuit - Help needed

[Travesso]

Hey guys,

I have a 2004 F100 Yammy 4 stroke and have been doing some serious troubleshooting of late, trying to figure out some issues I've had starting the engine. I'm running 2 x Supercharge Allrounder 80Ah 650CCA batteries on an isolator and have recently had the startermotor refurbished with a new brush plate assembly and the commutator cleaned up nice and shiny.

I located a significant voltage drop over the original Yamaha high tension leads and replaced with new 4 gauge leads. (The original Yamaha HTs had significant corrosion on the copper for over 2 foot from the end of the cable!)

Anyway, long story short the electrical system from engine to batteries has been completely rewired and the engine starts a treat with the batteries fully charged. The issue is, I dont believe my engine is correctly charging the batteries. I drove the boat yesterday at wide open throttle for about 10 minutes and the volt meter on the Yammy gauges never got over 13.2v and generally sat at 13.0v.

My understanding is that the charge voltage should be regulated at between 13.6v and 14.8v depending on RPM. So I'm not convinced that my alternator / rectifier / regulator system is up to scratch. Any ideas on where to look at first? I can confirm that the voltage at the engine is now the same as the voltage at the batteries / gauges so I'm not getting a big drop in the HT leads any more. Any help would be much apprecated!

Cheers,
Trav

[FNQCairns]

A wild stab based solely on my personal observation over the years is never trust original equipment volt meters, never sit on full throttle for that long but that is another subject and finally that it is best to check for the difference in charge V charging ie check the state of charge of the battery static then check the output once running all with a multimeter or trusted gauge because it has been checked for accuracy.

You can also partly flatten the batterys before the test as this will give a better indication of what charge the alternator is capable of providing.

Hope someone can help more.

cheers fnq

[Travesso]

Thanks FNQ,

The 10 minutes may have been a bit of an exaggeration but I take your point :)

I agree definitely on the accuracy of the original volt meters, however I was on the boat alone and I'm sure nobody would have liked to see me at the stern with a multimeter and nobody at the helm! ;D haha... I have verified the voltage on the gauge previously using a DMM and it was pretty much spot on. I also had the internal voltage overlay on my HDS 5 sounder which was reading the same +/- 0.2v.

As I actually used the boat as the "limo" for my sister and her husband to arrive at their wedding reception, I couldn't really take any chances with partially discharging the batteries beforehand! :D In fact I actually had 4 batteries on board just in case...

Cheers,
Trav

[oldboot]

firstly.....what is the charge capacity of your motor......how many amps will it deliver....and what is the specified charge voltage?

typicaly outboard motors have relativly small charging systems in comparison to cars........12 to 15 amps is not an unusual maximum charge current....if it is a small motor is could be as low as 8 or 5 amps.
You realy need to know for sure, before you get any expectations.
The bro'inlaws 30HP merc pushes 15 amps, my 60HP everude pushes 12 amps, another member on here has a 75 everude that only pushes 8 amps.

you potentialy have 160AH of battery connected..............if you have any sort of discharge state it may take a bit more than 10 minutes to return to full charge.

you should not have to run at WOT to get a decent charge rate.....you should be kicking out a decent rate ( near capacity) at 3000 to 3500 RPM...........even at idle you should be getting some charging happening and if the battery isn't discharged much you should be back up to voltage in a short time.

Have you baught the factory manual yet?

I recon the best place to chek this is at home with the leg in a bucket........bunnings have a big black rectangular tub for about $50 which is just the ticket.

Have you tried charging one battery only, at atime.

If you have access to a DC clamp meter you could confirm the current going to the battery.

cheers

[PADDLES]

hey trav, have you checked all the basics? (this will have no influence on the output voltage of your motor but will affect your batteries charging correctly) ie. wire brush the battery terminals, sand the inside of the connecting lugs, grease them once installed, check your main isolator switch for corroded contacts. that voltage does sound a little low for charging if your voltmeter is reading correctly. check it at home (with the motor running in a bag or with muffs) with a multimeter, the rev's shouldn't make too much difference if the regulator/rectifier is doing it's job properly.

[Jarrah Jack]

There is a site in the US called marine engine.com which is full of yamaha fanatics and a huge backlog of answered questions should the problem require even deeper fishing around.

Cheers

[Travesso]

Thanks guys for all the replies. I will clarify a few things in the hope that I can find a solution:

Oldboot, the motor is a 100hp and the Yammy specs say it has a 20A alternator.
The charge current does not go any higher than 13.2v at any point in the rev range from 800rpm idle to 6000rpm WOT. I have kept the batteries fully charged (particularly prior to this weekend! ;) ) by use of a Jaycar 16A charger as recommended in another thread here, and by a solar panel that has a 5A regulator with reverse current protection hard wired direct to both batteries. After rewiring everything from the motor forward, I'm not convinced my alternator is charging at all! :(

Paddles, all terminals have been re-terminated with new lugs when I replaced all the wiring. Inox grease has been used after tightening the nylock nuts on the terminal posts and I even used those little washers that cut into the terminal! I checked the voltage with a DMM on the ear muffs and there was no change in voltage between the motor off and the motor at idle to about 1200-1500rpm. (I wont go above that on earmuffs as I dont want the motor to overrun).

Jarra Jack, I will check out that marineengine.com site, thanks. I have always had a good read on the iboat forums in the US and learnt a great deal from that one so hopefully marineengine.com might have some answers for me. Iboats has a regulator check on one of its threads that I will be trying when I can next get down to the boat... I'd just hate to replace the rectifier / regulator and find that the alternator stator or something else was the problem! These things get bloody expensive!

Any other tips on where I should be looking would be much appreciated, thanks guys!

Cheers,
Trav

[PADDLES]

sounds like you've got the basics sorted trav. if the voltage is not changing from not running to stopped, i'd definitely be getting the alternator/regulator checked by either a yamaha techo or auto electrician, i would think the voltage should be a smidge higher to charge batteries. is there any fuse or protective device on the output of the alternator, can the alternator output voltage be checked whilst disconnected? (ie. open circuit) there'll be guys on here that know heaps more about alternators than i do, but i have a feeling there's issues with the regulator when it's open circuited.

[oldboot]

DO NOT... repeat ..DO NOT run any outboard motor that has a charging circuit connected without a battery connected.....it is almost guaranteed to snot the regulator and or rectifier.

Most outboard motors( except the realy big ones) run permanent magnet, magneto type charging circuits....without a load connected the charging coils can produce very high (hundreds of volts) voltages that will snot any electronics connected.

here is a basic test procedure.
leave the boat and battery sitting unmolested for some time.....at least a few hours.....this will let the battery settle to a "resting state".

measure the terminal voltage at the battery......should be around 12 to 12.5 volts...a bit lower or higher maybee

put the leg in a tub or fit the muffs...tub is best because with the leg in water you can reasonably give it a little rev....and you can run in a tub quite happily for half an hour and the neibours wont get pissed.....it is so much quieter.

start the motor and check the battery terminal voltage.....depending on how quickly you get there....it may be a little lower from the cranking... but the battery voltage should slowly increase....if the charging circuit is working it should soon be over 13 volts......over time it should increase to the maximum charging voltage which will vary depending on charging system.

Remember almost all sounders have the ability to display battery voltage and reasonably accurately.....as long as the battery that the sounder is powered from is connected to the charging system.

now if the charging circuit isn't working the battery will seem to recover from the cranking...but..it will not go above the original voltage tested.

as I said before.. don't expect too much of these charging systems....they are generaly quite small in comparison to cars......even the smallest cars have a 40 amp charging system.

definitely buy the manual.....it will give you all the details you need and should give test procedures for the regulator out of circuit..

cheers

[Travesso]

Oldboot,

Yep no worries, I've heard that the no battery thing is a no-go. Thanks heaps mate, I will try your test method this afternoon and see what I get :) I have ordered the Seloc Manual today from a book store in the states... $42 delivered express international air mail :) A lot better than $74 in a bookshop here! Only problem is the wait that I have to receive it! However, thanks heaps for the tips on how to diagnose whether I am getting any charge at all! It will give me a good heading in the right direction anyway! I will update on how I go...

Cheers,
Trav

[Travesso]

Ok, after diagnostics last night, I have also determined that my starter motor is not up to scratch either! Even after getting a full new brush plate last week. :'( However, that is another matter...

Testing the batteries at rest (after a few days isolated except for a solar charger)
Battery 1: 13.18V
Battery 2: 13.18V

Due to my starter difficulties, I was not able to start the motor on one battery, so battery 1 got a bit more draw than battery 2 as I tried battery 1 then switched to 1+2 to start it. So, after starting:
Battery 1:12.92V
Battery 2: 13.04V

With the motor running at idle (800RPM) and the isolator set back to battery 1 (on 1+2 the charge rate was negligible and I noticed no increase in voltage), I observed the voltage increasing on battery 1 from the 12.92V gradually, back up to about 13.04V at a rate of about 0.01V every 5 seconds. Even after running for 10 minutes the charge rate never really changed, just plodded along like that, putting 0.01v back in every 5 seconds or so.

I checked the voltages at the engine to make sure the new HT leads and terminals didn't have problems and the voltages and charge rates were identical. Increasing the revs to 2500RPM had minimal effect on the voltage, and only slightly increased the rate that the 0.01V was being added to the batteries (0.01V per 2-3 seconds).

I switched the motor off with the volt meter connected and observed the voltage drop from 13.01V to 12.97V at the motor. So it appears my magneto/rectifier/regulator is providing only 0.04V to charge my batteries?? This seems far too low to me... What do you guys think? My understanding was that when you kick the engine over, the voltage should jump up from the 12V or so to about 13.6V and when you rev the engine toward WOT it should increase up to the regulated 14.8V?

PS: the starter is off and headed back to the autoelectrician today to test the windings and plates in the armature. However this is a side issue and does not directly relate to my charging concerns (with the exception of the bad starter draining my batteries when I try to crank the engine! :()

[FNQCairns]

Do you have the old analogue rpm gauge, does it work? It can be indicator of charging problems on some engines, Can you fit a flat battery (say 12v) to number 2 , then switch to it. IMO it's hard to assume what's going on for certain at the battery until the differential is large and the alternator/regulator knows this and decides to do something about it..or not.

My old yam on full battery's doesn't fully behave like you say yours should and it so far is working fine, i know this because I have tested it with a flat battery as my testing was done at the battery.

cheers fnq

[oldboot]

trav mate you have made some errors in your method.......because the batteries are on the solar charger.....they are not at rest... but anyway.
Having batteries at rest makes it all look better because you will start with a lower voltage and the spread of figures will be wider.

You can not make assumptions from your charging voltages the way you are...the charging voltage will only rise as fast as the battery lets it......we do not know the age or condition of the batteries so we can not make assumptions.

it is the current that charges the battery......the voltage is a side show....important but still a sideshow.

the charging system is applying SOME charge.....that is the only conclusion we can safely draw.

we do not know the charging capacity of the motor..so we cant make assumptions.

as for the starter motor.....have you tested it with a known good battery

If you want to test the charging system you will need to get some means of measuring the current......a DC clamp meter is your only real option......and you need to know the chargong capacity of your motor.
Even better a set of charge curves would be good.

have you had your batteries tested?

try this it isnt great bit it might give an indication................charge the batteries with a known good charger.....disconnect from everything.....measure the voltage.....over the next hour or so the voltage will drop till the battery is at rest....12 to 12.5 volt ..ish.....over the next couple of days....the voltage should not drop much at all.....a good marine battery should hold its resting voltage ... more or less for a couple of weeks... more or less...if the resting voltage drops significantly over a couple of days.....the battery is sus.

better still take the batteeries down to the autolec and get him to test them with a battery tester.

or.... put them in the car and see how they crank that in comparison to the battery that belongs there.....if it is a normal pasenger car....85AH will be bigger than what is there so they should do better.

If you hadn't gathered I'm sus of the batteries.

remember....small charging system....large battery........so much we don't know.
lets not jump at conclusions.

cheers

[Travesso]

Thanks FNQ, I will try a flat battery and see what happens...

Oldboot,

I concede the fact that the solar charger could possibly be still trickling the batteries however I started testing the boat about an hour after dark, I would have thought it would have settled by then... maybe not!

Both batteries I am using were purchased new in May 2009 from Bias... Funny you mention it though because the auto electrician who is looking at the starter today reckons there is nothing wrong with the starter and is suggesting that I bought dud batteries :o The engine manual says it requires a battery with 70Ah and 430CCA minimum. These batteries are 80Ah and 650CCA. Surely I couldnt have got 2 duds?!

My Yamaha manual specifications indicates "Alternator output for battery DC: 20.0A" I dont have a clamp meter, only a standard DMM so I'm not sure on checking the charge current output unfortunately :(

Yeah I agree, I think the next step is to get the auto electrician to test my batteries. I'll be really peeved if they are stuffed, considering I spent nearly $400 on them only a couple of months ago! On the same token I'll be happy if the problem is as simple as that! I have my doubts however.... :-/

[oldboot]

If it has a 20 amp charging capacity. and requires a 70 AH battery .. I gather it is a reasonable sized motor.......the manual says "alternator".....does this machine have a seperate alternator or a charging coil under the flywheel?

Does the manual state a maximum charging voltage.......It may only charge at 13.8V or such like a normal car..........there realy is no standard voltage.
13.6, 13.8, 14.2, 14.5, 14.8, 15 volts......they are all to be found and there might be small differences but they make a big difference if you are looking at behaviour and have an incorrect expectation.



Need the manual..... there is no substitute for accurate information.


have you tried substituting the car battery........both ways.

And the number of times I have heard people say....It cant be, such and such, its new........when you have a problem you just cant assume that anything isn't faulty.

cheers

[Jarrah Jack]

Old Boot hasn't been thanked so many times for nothing.

Just been reading my seloc manual on diagnostics and its brilliant so really its just time to get the starter fixed and sit back and wait for the manual to arrive. Mine took just a bit over a week from the same place I'm guessing.

[Travesso]

I gather it is a reasonable sized motor.......

Yeah like I said previously, its a 100 horsies.

I've tried 4 different batteries, all freshly charged so I doubt the batteries are the problem... I will get the new batteries tested though just to make sure.

Jarrah Jack, I've ordered my Seloc manual from Betterworldbooks.com and unfortunately received an email this morning saying the shipping would be delayed and the book would be sent from a third party supplier... so who knows how long it will take...? ::)

Will hopefully get some news on the starter shortly...

Cheers,
Trav

[Travesso]

Got the starter motor back from the auto electrician. According to them the armature has nothing wrong with it and after they replaced the brushes last time, it is working like new when provided with a solid 12V supply. They believe the fault must be elsewhere in the wiring... So the whole boat is heading down in the morning... Hopefully I dont have a charging issue at all and I just have some dodgy (original :P )wiring that they can find that fixes the starting problem.

I'll update tomorrow... once they have looked it over.

Cheers,

Trav

[oldboot]

I am always happy to help where I can, I have learned so much from this and other forums over the years..... expect to contribute in return......I hope others feel the same.... cheers

[Travesso]

Ok... As for my starting issues, after some more diagnostics, it appears that I am experiencing excessive resistance through either my negative leads/terminals or my battery switch. At the batteries, when cranking the starter, the voltage drops from 12.9v to about 11ish. At the starter motor, the voltage is dropping from 12.9v to as little as 2v! :o When I remove the battery switch and connect the negative and positive leads from the engine directly to either battery, the starter cranks the motor perfectly and the voltage at the starter drops to around 9V during cranking... Might need a new battery switch or re-terminate my negative leads (or both!)

On the plus side, I know there is nothing wrong with my batteries (tested by the auto electrician) and I can confidently start the motor no matter where I am. :)

The charging circuit is an issue that I will put on the back burner for the time being but I will definitely try hooking a flat battery up and switching over to it and see what the rectifier/regulator does :) Cheers for all the tips guys, I will get to the bottom of this yet!

[FNQCairns]

Looks like you nailed it..the whole lot! with your dodgee switch charging should work fine after the resistance is decreased i would guess but testing will tell all.

i decided against anything complicated here and simply carry a known good battery with me every time also a piece of rope to pull start if ever needed, still one day when the lights go in i may need to fit a house battery but plan to keep it all super simple with a solenoid insted of a switch..had too many problems with them over the years.

cheers fnq

[Travesso]

Yeah I can see myself dropping the coin on one of those BEP isolator / vsr panels to replace my battery switch... I guess my "Heavy Duty" $30 switch just cant cut it out in the elements... ah... Bring On Another Thousand ::)

[Jarrah Jack]

I think that when that manual finally arrives you'll be able to confidently use a multimeter around all the electrics to do your own trouble shooting from now on.

Cheers

[Travesso]

My manual still hasnt arrived but I did a bit of diagnostics this morning to determine the cause of my starting issues... with the batteries under the centre console (7m total circuit length pos+neg) the motor wouldnt start. I have new 4AWG cables (21mm2). So assuming the cables are too small, I put the same battery on 2 x 1m long 6AWG cables right beside the motor and it fired up no problem.

When I checked the voltages at the starter motor and the drop during starting, I was only getting about 7-8v during cranking at the starter with the batteries under the console. I hooked up another 6 gauge cable on the positive side (in parallel) and the voltage went up to about 9v at the starter and it kicked over. Just saw my dad's mate who is an industrial electrician and he is going to give me 2 x 50mm2 @ 4m length cables to try. If they give me the amps I need with minimal voltage drop over that length I will be ripping out the new 21mm2 cable and replacing it!

Hopefully a lower resistivity cable will assist my charging too and all my problems will go away! (Could it be that easy?? ;)) I will report back tomorrow after I try the new cables...

[oldboot]

I'd be thinking terminations being the problem rather than the size of the cable.

starting high compression race car engines with the battery in the boot 5 meters of cable and chasis earth return seems to be no problem.

if you are crimping up new cables... spray the bare ends with lanox or similar before crimping... then wipe down the cable & lug with solvent and apply glue lined heat shrink.....spray all bolts and mating surfaces with before bolting up.

cheers

[finga]

Mate, have you tested each termination yet?
I would be curious to find where exactly the problem is before pulling it all apart.

Easiest way to test each place where the cable ends and something else takes it place ie battery connection or lug or battery switch is to put your voltmeter across the 2 ends of the join ie one lead in the cable and the other on the battery clamp or one lead on the battery clamp and the other pushed into the battery terminal or one lead on the common terminal of your battery switch and the other on the battery 1 and 2 terminal.
If you get a reading when you apply a load ie try to start the motor then there is the faulty connection.
Make sense?? Hope so. If not please say so.
It surprising where dodgy connections happen :)

Personally I crimp and solder each termination and then the resin cored heat shrink it. But that's just me...and never had a problem that I know about. :)

[Travesso]

I agree, my first suspicions lied in the terminals and connections too! So we have just last week re-terminaled all leads and connections. All are clean, using those cutting washers between lug and terminal. All terminals were crimped, soldered, heatshrunk and then wrapped in self amalgamating tape to be sure.

I have tested the voltage drop through the connections as you describe finga and there is nothing in particular that stands out on any connection, yet the overall cable drops 3-4v under cranking load. The test cable isnt costing me anything so it is worth a shot anyway, I'll pick it up this arvo and test it out and post back... :)

PS: My mate who used to do the fitout on Seafarers said that for all battery wiring they used to use 0 AWG wiring, particularly when they needed to locate the batteries remotely to the engine for weight distribution purposes.

If you do a ohms law calc for voltage drop over a cable, assuming a 3.5m (one way) wire length and 150A current draw for the starter at 12VDC you would need a 1/0AWG (50mm2) wire to get around a 3% voltage drop over that distance. Lets see if the theory turns out in practice... Will post back tomorrow :)

[ifishcq1]

Bloody hell Trav
see what happens when you do it right
hope it gets solved soon and the headaches are over
all the best mate
s & c and the fur kids

[Jarrah Jack]

That manual should have turned up easily by now. I ordered mine through that marine engine website. Time to fire off a few emails. Hope you get it soon.

[oldboot]

yeh this crimp and solder argument will always continue....& recently replaced the battery cables on the new tub...........quite a bit of the cable had black wire disease.....I chopped and stripped the cable to see the extent of the corrosion.......it had gone a couple of meters up the cable.

however the dense part of the crimp.....I cut the crimps apart.... was still clean......the old crimps were done with the " old style nipple crusher" crimp tool that just thumped a big dint in the lug........the new hex crimp tools used with the correct size crimps for the wire... should perform better................. I still maintain that soldering a properly made crimp is not an improvement....it introduces a corrosive eliment ( the flux)... and a properly made crimp should be air tight and near to welded.......add some low viscosity corrosion inhibitor like lanox......should do the trick,

OH and tinned battery cable is the go too... I used #2 b&s... which works out to about 32mm2

cheers

[Travesso]

Whooohooo!! the new leads work a treat! :) they are 1/0 AWG (so about 50mm2) and have been professionally crimped and heatshrunk. I also used self amalgamating tape to seal up the terminals properly too.

Due to the size (about 16mm OD each lead) I had to cut a bit out of the yamaha outboard cable grommet but everything has gone in snug again without undue pressure on the fuel or pitot pipes.

The overall length is slightly longer than my old cables too but when i checked the voltage drop at the starter last night it was well less than a volt, compared to the old cable dropping 4v!

Looks like Im back in business... I will check out how the engine charges through these new cables... hopefully no more nervous anticipation when reaching for the ignition key when 25km offshore! ;D

PS: good one Scotty! I do miss the charm of bashing the battery terminals with a shifter to get it started!! :P

[oldboot]

and the important lesson here is.

you only have 12 volts......you only have to lose a couple of those to be in trouble.

you have to be 20 times more fussy about cable size and connection quality than a household electrician.

cheers

[finga]

and the important lesson here is.

you only have 12 volts......you only have to lose a couple of those to be in trouble.

you have to be 20 times more fussy about cable size and connection quality than a household electrician.

cheers
Sorry for saying so but CRAP!! >:(
I know. I'm a licensed sparky used to working in voltages up to 132kV and if you have a bad connection or undersized cable in even a domestic residence you'll know about it.
We have for more stringent testing procedures to make sure joints are correct (especially in the earthing side of things) and far stiffer penalties if undersized cable is used.
A bad joint or undersized cable can burn a house down to say the least.

[oldboot]

not crap at all.......simple maths and ohms law.

even in the earthing system by 240v regs you are allowed a total of a couple of ohms by the time you run from your earth common, thru the house wiring, the extension cord and the appliance cord...there will be at least that in the active and neutral lines... and that does not account for contact resistance in the plugs switches and breaker.


so how does your 12volt system cope with 4 ohms in the circuit...... you only need to be drawing 1 amp to be short 4 volts.

the mains electrical system has been robust enough to sustain a legeslated 10 volt drop in power supply voltage... check it out the power supply is now officialy 230 volts not 240volts


20 times less voltage means 20 times more current to do the same work and therefore the cables need to have proportionaly less ( 20 times less) resistance.

try this.......take your insulation tester set to the low ohms range and start looking at contact resistances thru some standard 240V (sorry 230V) switch gear and plug ware....particularly if it has a bit of age......half an ohm here an ohm there.

sure the requirement for workmanship remains the same....and the consiquences will be different.......... but the need for a low resistance path is more important the lowerer the voltage gets.

cheers

[finga]

not crap at all.......simple maths and ohms law.

even in the earthing system by 240v regs you are allowed a total of a couple of ohms by the time you run from your earth common, thru the house wiring, the extension cord and the appliance cord...there will be at least that in the active and neutral lines... and that does not account for contact resistance in the plugs switches and breaker.


so how does your 12volt system cope with 4 ohms in the circuit...... you only need to be drawing 1 amp to be short 4 volts.

the mains electrical system has been robust enough to sustain a legeslated 10 volt drop in power supply voltage... check it out the power supply is now officialy 230 volts not 240volts


20 times less voltage means 20 times more current to do the same work and therefore the cables need to have proportionaly less ( 20 times less) resistance.

try this.......take your insulation tester set to the low ohms range and start looking at contact resistances thru some standard 240V (sorry 230V) switch gear and plug ware....particularly if it has a bit of age......half an ohm here an ohm there.

sure the requirement for workmanship remains the same....and the consiquences will be different.......... but the need for a low resistance path is more important the lowerer the voltage gets.

cheers
Sometimes maths and basic electrical principles are not all that's important or considered.
That's why an electrical fitter/mechanic based apprenticeship takes about 4 years not 30 minutes in a physics class in high school.

But if basic maths is to be considered try another angle.
Consider the 2v drop on the 12v system as a percentage.
That will give you a voltage drop of close to 17%
Voltage drop on a 240 (or yes, more accurately 230v as per AS 60038) system is deemed to be a maximum of 5% of the nominal supply voltage whether it be single phase or 3 (not the quoted legislated 10 volts...it's actually a higher figure in reality) as per AS 3000:2007 clause 3.6.2 so if a 17% voltage drops occurs something is really wrong and if that problem was circuit design then the person who designed it could be in deep do-do if if the voltage drop is due to a fault present then things are not going to work too well, especially items that use a bit of current.

Very low resistance readings are very evident, and regulated, in main stream house wiring, and especially so, where high currents are used as resistance figures in home are more accurately, and more typically, worked out as an impedance figure or earth fault-loop impedance.
True, some total circuit resistances can be as low as a couple of ohms but each total impedance reading needs, and is, to be assessed on it's own merits.
Some examples of low resistance joints needed in single phase (230v) wiring:
In clause 5.4.6.3 of AS 3000 "Earthing of parts of structural metalwork, including conductive building materials, may be effected by the connection of a protective earthing conductor of appropriate size at one point of the metalwork provided that the resistance between the earth bar and any part required to be earthed
does not exceed 0.5 Ω."
Or clause 5.5.1.4 states "The resistance of the main earthing conductor, measured between the main earthing terminal/connection or bar and the earth electrode, including the connection to the earth electrode, shall be not more than 0.5 Ω."
Or if you consider a current of 200A at the nominal voltage of 230V (roughly the current in a 12v starter motor as in this thread) the total earth fault-loop impedance is a whopping 0.29 ohms.
That is the total impedance allowable for that circuit. (as referenced from AS 3017:2007 table 3.1)

I will not start on bad connections in power point or extension cord plugs and sockets because we all know what happens to them eventually. They burn. It has happened to all of us especially if a high current user ie jug, heater or welder is used..and that resistance may only be a couple of ohms.

So if a 2 ohm joint exists in a 12volt system things might not work too well.
A 2 ohm joint in a simple 230/240volt AC installation could mean someone could die or something might burn if a fault occurs so there could be arguments on which will be deemed more critical/important to the statement "the need for a low resistance path is more important the lowerer the voltage gets."

There is more to been an electrician then the ability to make something work.
.

[finga]

As a side note clause 20.9.2 of AS/ACIF S009:2006 states in a note "If required, the termination within the ferrule of a cable lug may be filled with solder after crimping to exclude moisture." so does that mean the corrosive effects of flux mentioned previously is not as critical as the exclusion of moisture to the joint in cables over 2.5mm or 4mm in size?

[oldboot]

Oh come on finga...all I am trying to point out is that in 12 volt systems low circuit resistance is an important issue..... joints need to be good, cables need to be of adequate size..........much bigger than the untrained person would be used to seeing in the houshold wiring they are familiar with............a matter and concept that people consistently fail to grasp.

the vast majority of 240V wiring is done by trained people.......on the other hand a considerable amount of 12V wiring is done by untrained & unlicenced people.

hopefully those reading this will understand that like for like..... a 12 volt system... carries 20 times the current than houshold mains, therfore the circuit resistance needs to be proportionaly lower......20 times lower.

If a battery fails to charge, a engine fails to start and the radio fails to transmit.....a poor connection in a 12 volt system can just as easily kill someone or a whole boat full.

as for the reference to S009 correct me if I am wrong but that is the communication cabling standard and that crimp lug would only be on a land bassed communications earth....the cable & lug would not typicaly be exposed to salt water or vibration ( in fact most likly it would be high and dry within a comunications enclosure, service duct or switch room) and nor should it be carrying heavy currents under normal circumstances .......additionaly those cables would typicaly be heavy stranded cables, not fine stranded cables we use in battery circuits..........heavy stranded cables do not pack and conform as well as fine stranded cables.

Additionaly S009 permits a great many things that would not be permissable in electrical wiring and prohibits a great many things that would be normal practice in elecrtical wiring.
for example, double insulation is not factored in communications wiring... this alone changes many things.

cheers