[DeTomaso] Alternator found

Fri Sep 14 08:52:22 EDT 2012

I rebuilt my tractor this past summer. I put a disconnect so if the
tractor sits for a long time I can disconnect the battery.

When I got done with the build I failed to secure the alternator cable; it
was still loose. By the end of the mowing the battery smelled funny and
the amp meter showed it overcharging.

I got a voltmeter out to check and the battery voltage was a little high.
I disconnected the battery cutoff to check the voltage and it jumped to
40-90 volts. I turned the battery cutoff back on then tried to move the
tractor back to the shop. It died before I got it there.

It took me a little bit to unwind the chain of events but the loose wire
on the alternator took out the voltage regulator which began to overcharge
the battery. When I disconnected the battery there was nothing to absorb
the high voltage and it then took out the Pertronix.

> If your circuit breaker releases you will be running the alternator
> without a battery. This is normally considered a big no-no with
> alternators. Generators will tolerate that but they're a different kind
> of machine.
>
> Tomas
>
> <-----Ursprungligt Meddelande----->
> From: David D Fisher [fisher95020 at yahoo.com]
> Sent: 14/9/2012 12:47:48 AM
> To: Brian Dudley; John Buckman
> Cc: detomaso at realbig.com
> Subject: Re: [DeTomaso] Alternator found
>
> In the end I think I will put a 4 gauge cable from the Alt to the fuse
> box and install one of these resetable circuit breakers on the ammeter
> circuit in the event that circuit ever gets up to 70Amps.
>
> Seems like that should put an end to the worries, keep the stock look
> and has the bonus of cutting off all battery power with a push button.
> I suppose it makes for a lightweight theft deterrent too if you want to
> kill power to the ignition bus.
>
> http://www.amazon.com/Bussmann-Hi-Amp-Circuit-Breaker-Amps/dp/B0024JKT9W
> /ref=pd_luc_sim_03_01_t_lh
>
>
> David
>
>
> ________________________________
> From: Brian Dudley <bd8134 at gmail.com>
> To: John Buckman <jb841 at cox.net>
> Cc: David D Fisher <fisher95020 at yahoo.com>; "detomaso at realbig.com"
> <detomaso at realbig.com>
> Sent: Thursday, September 13, 2012 1:13 PM
> Subject: Re: [DeTomaso] Alternator found
>
> On Sep 13, 2012, at 3:42 PM, John Buckman <jb841 at cox.net> wrote:
>
>> David,
>>
>>> Sorry if this had been hashed over many times before...
>>
>>
>>>>> No problem.  It's good to review from time to time.
>>
>>> LET'S SEE IF I HAVE THIS CORRECT...
>>
>>
>>> 1) Run a 4 or 2 AWG wire on the 9' run from the Alt to the Fuse
> block.  This is the most likely wire to overheat as it will carry the
> full Alt output in the times when both the battery is low and the
> consumers are on full blast.
>>
>>
>>>>> Any increase in wire size helps.
>
> I ran a new 4ga wire as above.
> I have added Jon Haas's fuse panel and ignition relay which all feed
> off where the 4ga joins the old 8ga which feeds the amp meter then to
> the battery.
>>
>>> 2) Live with the 8 AWG from the fuse block to the Ammeter but clean
> the terminals, put copper and star washers on and tighten up well.  Per
> SOBill's note and the wiring diagrams, this circuit only sees the
> current going to and from the battery.
>>
>>
>>>>> Just remember that with a low battery and very few consumer on,
> most of the alt's current will be going back to the battery via that 8
> AWG wire.
>>
>
> A 150 Amp alternator may put out 100 Amp at idle and would be too much
> if using any of the alternator to battery wiring, including most
> likely the amp meter.  Better to use a 125 or 105 Amp alternator which
> may put out 85 or 75 Amp at idle. You would still need to replace the
> "9 foot" wire at minimum.
> Using a larger pulley on a large output alternator could also work if
> not wired as a 1-wire.
>>> Assuming a dead battery and all consumers on, the Alt is working at
> full tilt, sending (for sake of argument) 150A down the wire to the fuse
> block.  From there the current splits with part of it going off to run
> consumers (through numerous wires) and part going through the ammeter to
> try and charge the battery.  Only part of the current is going through
> the ammeter circuit and can probably live with 8AWG.
>>
>>>>> Yes (see previous comment).
> If large output alternator you could have trouble.
>
>>> 3) Given that the starter circuit does not go through the ammeter, we
> dont have to worry about it.
>>
>>>>> Correct.
> If you decided to use a high output alternator (>130A) and replaced
> the wire from alt to battery, with the size of wires going to amp
> meter etc, it might be best to go to a volt meter or go without. A
> simpler way is to just run the alt wire straight to the feed on the
> starter solenoid and make everything easier.
>>
>>> 4) This still leaves 2 potential fire hazard cases.  The first is
> when your battery is dead and your alternator is trying to push whatever
> the battery will take through the ammeter circuit.  I'm not enough of a
> battery charging expert to know, but I am guessing this could be
> hundreds of amps, probably about the same as the battery is capable of
> delivering.
>>
>>>>> The alt won't produce more than its rated current (+/- a small
> percent), and the battery (when low) will take all that it can get.
>>
> This is where you need to be careful. If you have a 100 - 125 Amp
> alternator with upgraded cables, if you do not increase your engine
> speed over idle and you wait until your amp meter has moved down from
> being pegged at +75, you might be ok.
> A higher amperage alternator (with >95 Amp idle), decreasing the
> alternator pulley size, not increasing wire size or increasing engine
> revs while battery is discharged could cause wiring problems.
>>> Note, that it doesnt matter if your consumers are on - they are on a
> seperate circuit, but it could be fatal if you are trying to boost
> someone else from your dead battery as the alternator is now trying to
> both charge your battery and the other guys, all through the ammeter
> circuit.  Soution here: Never boost with the  Alt on (engine running) .
>>
>>>>> If the engine is running on the donor car (and its alt is working),
> then the donor car's alt will be trying to charge the dead battery.
> When the car (with the dead battery) is started, both alts will be
> trying to charge the dead battery.
>>
>
> I would think you would be better off starting your car before jumping
> starting another. Keep your car at idle and watch the amp meter. If
> you have an alternator with <95 Amp output at idle with upgraded wire,
> it should be okay for a short duration.
> Starting your car after jump starting another could drain your battery
> and require you to idle for a while until the amp meter dropped to a
> reasonable level.
>>> 2nd hazard case, (which could happen with either a hi output or low
> output alternator).  Your alternator is not producing at all, and you
> have all consumers on.  You bought a nice hi output battery and it is
> now trying to power all the consumers through the Ammeter circuit
> because the Alt is doing nothing.  It you added a lot of consumers
> (fans, etc) this current need might exceed the Ammeter wiring.
>>
>>>>> Correct.  If possible, turn off some of the consumers.
>>
>>> Seems like these last two cases are fairly remote, but one would have
> to be aware of them.
>>
>>>>> Correct, but they do happen.
>>
>> John
>>
>>
>>
>>
>>
>>
>> On Sep 13, 2012, at 9:37 AM, David D Fisher wrote:
>>
>>> John,
>>>
>>> I echo Chucks comments... good info.
>>>
>>> Sorry if this had been hashed over many times before...
>>>
>>>
>>>
>>> I guess if one was to design the wiring upgrade based on a pareto of
> likely failures you might do the following (for a later car)...
>>>
>>> LET'S SEE IF I HAVE THIS CORRECT...
>>>
>>> 1) Run a 4 or 2 AWG wire on the 9' run from the Alt to the Fuse
> block.  This is the most likely wire to overheat as it will carry the
> full Alt output in the times when both the battery is low and the
> consumers are on full blast.
>>>
>>> 2) Live with the 8 AWG from the fuse block to the Ammeter but clean
> the terminals, put copper and star washers on and tighten up well.  Per
> SOBill's note and the wiring diagrams, this circuit only sees the
> current going to and from the battery.
>>>
>>> Assuming a dead battery and all consumers on, the Alt is working at
> full tilt, sending (for sake of argument) 150A down the wire to the fuse
> block.  From there the current splits with part of it going off to run
> consumers (through numerous wires) and part going through the ammeter to
> try and charge the battery.  Only part of the current is going through
> the ammeter circuit and can probably live with 8AWG.
>>>
>>> 3) Given that the starter circuit does not go through the ammeter, we
> dont have to worry about it.
>>>
>>> 4) This still leaves 2 potential fire hazard cases.  The first is
> when your battery is dead and your alternator is trying to push whatever
> the battery will take through the ammeter circuit.  I'm not enough of a
> battery charging expert to know, but I am guessing this could be
> hundreds of amps, probably about the same as the battery is capable of
> delivering. Note, that it doesnt matter if your consumers are on - they
> are on a seperate circuit, but it could be fatal if you are trying to
> boost someone else from your dead battery as the alternator is now
> trying to both charge your battery and the other guys, all through the
> ammeter circuit.  Soution here: Never boost with the  Alt on (engine
> running) .
>>>
>>> 2nd hazard case, (which could happen with either a hi output or low
> output alternator).  Your alternator is not producing at all, and you
> have all consumers on.  You bought a nice hi output battery and it is
> now trying to power all the consumers through the Ammeter circuit
> because the Alt is doing nothing.  It you added a lot of consumers
> (fans, etc) this current need might exceed the Ammeter wiring.  Of
> course this isnt going to last long as your battery will soon be dead.
> Seems like these last two cases are fairly remote, but one would have to
> be aware of them.
>>>
>>>
>>> Thoughts?
>>>
>>> David
>>>
>>> From: John Buckman <jb841 at cox.net>
>>> To: detomaso at realbig.com
>>> Sent: Thursday, September 13, 2012 8:39 AM
>>> Subject: [DeTomaso] Alternator found
>>>
>>> Anyone care to guess how long the run is from the alternator through
> the ammeter and to the battery?
>>>
>>>
>>>>>> Early cars:  ~25'  Alt to ammeter to starter soleno
>>>>>> Later cars:  ~20'  Alt to ammeter to battery.
>>>
>>>>>> The tap (splice) for the fuse panel, ignition switch, and
> headlight switch is ~9' from the alternator.
>>>
>>>>>> The original ammeter wires (at least on the early cars) were 8
> AWG.
>>>
>>>>>> One must remember that, when sizing wires, heat generation /
> dissipation can be a major concern.
>>> The more current (amps) that passes through a given size wire, the
> more heat is generated, and the more
>>> heat that is generated, the more the resistance (in that wire)
> increases, and as the wire's resistance increases,
>>> so does the voltage drop.
>>>
>>> Selecting a wire with a higher insulation temp rating is always a
> good idea, but NOT a good idea if you are
>>> selecting that wire size based upon a given current (amps) at that
> (high) temp.  Wires in bundles have a much
>>> slower heat dissipation rate than a wire that is run by itself.
>>>
>>> Tefzel (aircraft) wire is an excellent choice, although expensive.
> It can withstand 200* C (392* F).
>>>
>>> John
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>>
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