Alternator to battery wiring

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MilesnMiles
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Alternator to battery wiring

Post by MilesnMiles »

I’ve read a bunch of threads on this but could use some final advice. My 66 Cuda is not well protected from voltage surges.
The fusable link from bulkhead to starter solenoid has been replaced with a thick gauge wire.
The ammeter is still connected and working fine. At the moment.
Here’s my actual question; if I run a thick gauge fused wire from alternator live to battery live but leave the ammeter connected, will the ammeter still function correctly.
On my Roadrunner I disconnected the ammeter and connected the two lives. I then ran a fused live from alt to battrey and all was good.
I guess I’m really asking if my first option can retain the ammeter function as most voltage demand would use the new wire between alt and batt.
Any advice appreciated, don’t want a fire.

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Dave999
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Re: Alternator to battery wiring

Post by Dave999 »

currently :)

the ammeter has 2 wires to it

1) from battery
2) from alternator

that connect together via a circuit under the dash
from alt - ammeter
from ammeter --- circuit splice
from splice to battery.

two routes for power into the core of the cars electrical system so both or either supply can supply everything

you run on battery when starting and alternator when running...with excess current, dictated by the regulator, going right round via ammeter to the battery to charge it

if there is an imbalance it swings + or -
flat battery and running alternator = a big imbalance

hence if battery is flat the current from alternator runs through ammeter to the main car supply at the splice and to the battery. Then your ammeter shows + 30 and gets hot

and when starter motor running it chuggs down to -15 as you suck current out of the battery to run the starter

if battery is full the ammeter is normally the middle and little current flows through it 1-2 amp to keep battery happy
switch on headlamps and it will swing negative until the regulator spots the drain on the system and pumps up alternator current...the ammeter will slowly go back to the middle. it will be flowing more current but its within its capacity.

bypassing it with a wire from alternator + to the starter relay+ or the battery + means the ammeter is still in circuit but will not show current flow as the current takes the easy route via the new wire. not the route via the ammeter.
it can still be shorted out but it won't be because it overheats, melts its insulation, or the insulation on the wires to it

its a legit halfway house with the main benefit being you will not burn out your ammeter. as long as the wires are robustly bolted on and its not been overheated in the past. all should be all well and good.

if its already damaged, the liability of a short out still exists.

wire comes off melty
insulation between studs on ammeter and the metal back plane of the gauge pod melty melty

but that is so so much less likely to happen if it never flows much current. and it won't flow more than a few milliamps with your bypass plan.

i.e much less than when running a fully charged sensibly sized battery and your original spec 36 or 40 amp alternator hence much less risk.

if your car is un messed with you are in a safer position than in a modified car when running the standard set up
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

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Dave999
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Re: Alternator to battery wiring

Post by Dave999 »

the reason most ammeters fail is over specification on cold cranking amps for the battery

massive modern battery with huge capacity and low internal Resistance starts the car easy even when half flat and can then sink massive amperage when charging. ammeter stays longer pinned at + 30...over heats and melts

or

lets put a 60 amp alternator in a car with 40 amp wiring and add in loads of accessories and an electric fan that use all that current and suddenly the loom is a molten mess.

the studs on the ammeter pass through plastic washers to insulate them from the metal case or back frame of the pod
if they melt then it shorts out
they only melt if the get hot and they got hot for the reasons above

2 spiky washers either side of the cable and a nice tight nut means the wires should not come off if fitted correctly....
only chance of short is sticking you hand up there bending the wires... or a big spanner shorting them out or something metal falling into the dash

mine are on the ammeter
there is a blob of araldite/epoxy on the ends of the studs
and the lot is covered in insulating tape...

Dave
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

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MattH
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Re: Alternator to battery wiring

Post by MattH »

So running the second wire means it's safe but the ammeter will no longer give a reading with any meaning, is that right?

If so how can the ammeter be converted to a volt meter?

I am thinking for my Challenger as I have done the bypass so have an ammeter as a dash ornament only now.
Matt Hollingsworth - Vehicle Registrar
Panther Pink 73 Aussie Charger 265 Hemi 4 spd
Challenger Sam Posey Tribute car

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ScottyDave
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Re: Alternator to battery wiring

Post by ScottyDave »

MattH wrote:
Thu Sep 10, 20 8:26 am

If so how can the ammeter be converted to a volt meter?

I am thinking for my Challenger as I have done the bypass so have an ammeter as a dash ornament only now.

Mine's the same
73 Charger 318
MMA-130

MilesnMiles
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Re: Alternator to battery wiring

Post by MilesnMiles »

Thanks Dave, I’ve really missed your posts! Interesting and informative and clear :lol: !
Only one question. My car currently (pun intended) has no circuit protection in that there is no in line fusable link. It has been replaced with a big chunky wire from bulkhead connector to starter relay. (Terry pointed this out to me at the time I picked the car up).
What would you recommend to protect this circuit? I have a spare 8” 20 gauge fusable link on my shelf, but it looks quite small to me. Or should I use some sort of heavy duty slow burn fuse connected in line?

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Dave999
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Re: Alternator to battery wiring

Post by Dave999 »

Midi-link fuse and holder of about 40-45 amp blow rating and a 36 amp continuous rating 43 would be OK i guess for a 36 amp system

if you have the bigger alternator just apply rule of thumb slow blow rating of 15% more than the max output of the alternator and continuous within a few amps of max output

or standard fuse able link...does the same job

a circuit breaker will be £40-60, the fuse will be £5 and more reliable, no moving parts.
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

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ScottyDave
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Re: Alternator to battery wiring

Post by ScottyDave »

I'll be going the Midi link fuse route when I get to rewiring the front loom. Simple and easy replacement.
73 Charger 318
MMA-130

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Dave999
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Re: Alternator to battery wiring

Post by Dave999 »

Volt Meter measures a difference in voltage AROUND an item in a circuit or the whole circuit. its a none invasive piece of instrumentation.
Ammeter has to be IN the circuit. its a device in the actual circuit and as such must have nearly no resistance so it doesn't disrupt functions of the other components by using the current itself, it also needs to be rated higher than max current flow in order not to melt.

a car ammeter is really a milliamp meter with a bus bar inside most of the current through it bypasses the meter part via a precisely controlled low resistance short circuit, the bus or buffer or Shunt, while the rest swings the needle hence if the gauge parts fails the car still runs

Voltmeter has near infinite resistance (in context) if it allowed current through it it would not measure accurate volts
Ammeter is in circuit it has a resistance that tends toward infinitely small (in context) if it didn't it would have a voltage across it and it would mess up its own measure of current

volt meter measures the push from the battery or alternator by comparing before and after a thing that makes use of electrical energy, in our case the whole system.
ammeter measures the flow caused by the PUSH in relation to the FIGHT against the flow (resistance/ impiedence/ inductance) that the components in the circuit put up

Converting the actual electromechanical meter is not worthwhile it can be done but you have a centre scale meter and it involves massive resistors and messing about to a great extent

see here
https://www.niser.ac.in/sps/sites/defau ... -versa.pdf

replacement is the good option

you need a vintage looking pod mounted meter of appropriate size and pointer colour, in my case a modern VDO would work as my car has vintage Aussie VDO gauges. and id be looking for a face that is mounted with 2 small screws at a specific metric spacing to avoid drilling my cluster face with a tiny drill....if you have to the excess holes will be covered by your new decal...but still

it will need to be de mounted from its pod and the guts mounted where the ammeter goes
before you do that it is worth scanning the front of the ammeter and the front of the volt meter and taking it to a vinyl place to get a gauge face transfer made.... thus you can get ammeter style font and background and they can copy the volt meter scale on

once its all mounted and you applied your decal

you join the wires that used to go to the ammeter together and bind them up nice in loom tape and stick em some where safe in the depth of the dash

you connect 1 lead, the negative of the volt meter, the black wire, to earth/chassis i.e to the pod or dash mounting screws
you connect the red lead to any, and i mean any ignition switched 12 volt feed. suggest the switched end of the fuse box.

that way your volt meter always measures the difference between - battery post connected to the chassis and the 12 volt feed coming from the splice under the dash (i.e supplied from battery or alternator or both)

the meter needs to be a 0-16 or 20 volt meter as it will spend most of its time at 14.3 Volts. but don't get a 0-50 volt any granularity in what you measure is lost with an inappropriate scale

if its needle jiggles, in a really annoying way and looks LOW QUALITY as it fights to track what your mechanical voltage regulator is doing

get a small inductor from an electrical supply shop you are looking for a small iron ring with a coil of wire around it
put it in the red wire it will act as a voltage damper smoothing the movement of the needle on the scale
basically any voltage spike has to create a magnetic field before it hits the gauge which smooths things considerably
some experimentation might be necessary with this and the inductor needs to be 12- 15 volt rated current rating can be tiny as volt meter sinks next to no current. it has a massive resistance so does next to nothing in relation to flattening your battery....

the bulb used to illuminate it will use 10 times more energy than the meter itself.

Dave
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

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Dave999
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Re: Alternator to battery wiring

Post by Dave999 »

MattH wrote:
Thu Sep 10, 20 8:26 am
So running the second wire means it's safe but the ammeter will no longer give a reading with any meaning, is that right?

Yes indeed

you'd be hard pushed to see it move

Dave
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

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Dave999
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Re: Alternator to battery wiring

Post by Dave999 »

MilesnMiles wrote:
Thu Sep 10, 20 9:31 am
? I have a spare 8” 20 gauge fusable link on my shelf, but it looks quite small to me.
size makes no odds with this kind of thing its down to the alloy its made from and the narrowest point
combination of cross sectional area and the resistance of the wire.

the alloy dictates how that resistance behaves and how much the wire heats up at specific current levels.

its often a none linear relationship
fine at 36 amps hand hot, very hot at 40 burnt through at 41

they work well

if you did O'level or GCSE physics you did this experiment with griffin and George or philip harris power supply and a piece of constantan resistance wire.. linear over a wide range then it all goes to pot ....

then you branded your mates hand with the burnt end :)

"Mr Gray 0 -6 volts" not 16 volts......!" etc etc

Dave
David Gray. This year i am mainly In Twickenham, sometimes in Watford, often between the two but only between the hours of 07:00 -09:00 and 17:30-19:00

MilesnMiles
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Joined: Fri Nov 04, 05 8:40 pm
Location: Cornwall

Re: Alternator to battery wiring

Post by MilesnMiles »

Cheers Dave, I bypassed the ammeter today and I checked the main feed wire as it goes through the bulkhead. Signs of fire damage in the past, so I’m currently removing the damaged section and going for a midi fuse. Half way through the job along with fitting a new carb, alter wiring, battery cut off and all the usual stuff needed to make old Mopars safer from fires

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