[DeTomaso] Alternator found

Fri Sep 14 15:07:41 EDT 2012

I did a little more research on this.  According to tech support on the Alt I bought (Powermaster),  the proposed setup should be fine.   What the Alt does not like is a circuit breaker or shut off switch that cuts it off while its spinning.   If its spinning away, cranking out amps and you break the circuit, the field voltage goes skyward and things melt down.  This is probably why the racers disconnect switches include a resistor for the alt circuit to flow current through while the Alt winds down. 

In my case all the consumers are still connected to the Alternater even if the Ammeter circuit breaker blows, so the current draw from the consumers should keep the Alt from frying until the breaker is reset.   At at minimum, the Alt will be powering the ignition circuit.  Tech support confirmed this should be fine.    

It does beg the question of what happens when you turn off the ignition and the battery circuit is still open - this could create a second while the engine stops spinning and the Alt has nothing to dump power into, although its pretty likely the cooling fans are or some other consumer is still on.  I guess to be absolutely safe, one could lean on the horn while turning off the ignition... assuming you had realized the battery circuit has blown :-)

Net, net,  probably a reasonable compromise while applying a safety circuit against dash metldown and fire.   

David

________________________________
 From: Tomas Gunnarsson <guson at home.se>
To: detomaso at realbig.com 
Sent: Thursday, September 13, 2012 11:38 PM
Subject: Re: [DeTomaso] Alternator found

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
>> _______________________________________________
>>
>> Detomaso Forum Managed by POCA
>>
>> Archive Search Engine Now Available at
http://www.realbig.com/detomaso/
>>
>> DeTomaso mailing list
>> DeTomaso at list.realbig.com
>> http://list.realbig.com/mailman/listinfo/detomaso
>>
>>
>
> _______________________________________________
>
> Detomaso Forum Managed by POCA
>
> Archive Search Engine Now Available at
http://www.realbig.com/detomaso/
>
> DeTomaso mailing list
> DeTomaso at list.realbig.com
> http://list.realbig.com/mailman/listinfo/detomaso
_______________________________________________

Detomaso Forum Managed by POCA

Archive Search Engine Now Available at http://www.realbig.com/detomaso/

DeTomaso mailing list
DeTomaso at list.realbig.com
http://list.realbig.com/mailman/listinfo/detomaso
.

_______________________________________________

Detomaso Forum Managed by POCA

Archive Search Engine Now Available at http://www.realbig.com/detomaso/

DeTomaso mailing list
DeTomaso at list.realbig.com
http://list.realbig.com/mailman/listinfo/detomaso