On Wed, 31 Oct 2012 23:39:12 -0400, "Existential Angst"
Basically your alternator charges at its maximum current into a
discharged battery. If you connect two discharged batteries it doesn't
"short out" it just keeps right on producing its maximum current. You
need to look up what your alternator can put out on a continuous basis
with whatever cooling it has without overheating.
If you have, for example, a 60 amp alternator then the alternator will
put out its maximum 60 amps without damage.... assuming of course that
it doesn't overheat.
Your best bet would be to have a look at some of the yachting or RV
installations where a guy has, say a 6 - 700 AH battery bank and a
single alternator to charge it. Or perhaps have a look at Trojan
Battery's site, they have a lot of information about deep-cycle
On Wed, 31 Oct 2012 23:39:12 -0400, "Existential Angst"
First, make sure you use a Deep Cycle battery or batteries for your
inverter bank in the trunk. And it's best if you make a sealed
battery box that is vented to the outside of the trunk top and bottom
- Batteries have Sulfuric Acid inside them and release Hydrogen Gas
when they charge, best to get that outside the car. The little Scoop
Vents and 3" hose from a boating supply will work well for that.
It is NOT recommended, but if you use two 12V Batteries in Parallel,
they must be a matched pair in brand, model, and manufacturing date.
Otherwise one battery with the better connections and/or lower
internal resistance takes all the load and does all the work - then
it shorts out and kills everything. This is bad.
If you need more than 105 AH capacity, it is far better to get two 6V
Deep Cycle Golf Cart batteries (some Costco's stock them) and you wire
them in Series - (-) of #1 to chassis ground, (+) of #1 to (-) of #2,
(+) of #2 to Alternator and Loads. That will give you around 200
amp-hours with GC2 batteries.
DO NOT try running a large inverter off the starting battery - unless
you have a huge alternator that can supply most of the load and you
have the engine running at above 2,000 RPM to get full output, or you
WILL wreck the starting battery by running it down deep.
Second, the regular car battery WILL need recharging after you start
the engine - that was a 250A load you just put on it for 3 to 5
seconds running the starter motor. And since the alternator doesn't
put out full current below about 2000 RPM the battery is supporting
the loads whenever you are sitting at a stoplight at night.
The alternator will not "Short Out" - it tries to put out 13.8V up
till it runs out of current and then the voltage drops to what it can
produce - until it starts to overheat and it cuts itself back. Once
the batteries get charged the current will drop off, and the voltage
will come up to the 13.8V "float charge" level.
Stuff in as much alternator as you can under the hood, so it isn't
hitting that thermal limiter much - lots of cars have optional
heavy-duty alternators available that drop right in and give you a 20A
to 50A bump in output. And you need a heavier cable from the
alternator to the isolator.
If you want more than 120A to 140A output there are new aftermarket
alternators available from several makers, but they aren't cheap. Go
to a smart person running an Auto Electric Shop - they'll know where
to get you rebuilt truck alternators far cheaper, and they'll last
just as long. Sometimes they can put the Truck alternator innards in
a Car alternator case that fits your car.
Or they put in a Leece-Neville where the rectifier diode stack and
regulator are in a separate external box - this is needed on Vans used
as ambulances, where there just isn't any space under that Doghouse
for a physically bigger alternator. They stick the rectifier under the
Install a Diode Battery Charge Isolator - and be sure to wire the
fourth stud voltage sense lead back to the alternator (follow the
instructions) so the alternator voltage regulator sees the 0.5V drop
through the diodes and adjusts itself up to compensate accordingly.
Most alternators have the external sense lead - If the car maker
leaves that terminal disconnected (normal cars) it uses the Output
wire as the reference source. But if the regulator sees voltage on
that sense line, it switches to that as the voltage reference.
--<< Bruce >>--
How much juice can a truck alternator put out? Big Rigs?? I'll bet big rig
alts (with the attached apartment in the back) are good for 500 A.
Overall, I'm realizing this inverter thing isn't a super-practical idear ito
It could dull the pain a bit, but not much else. I'm still going to
experiment with this, bec that would just be one application of my setup,
but too many pieces of the puzzle don't quite fit right.
Good info, tho.
You certainly wont get proper cooling without adequate airflow and the
designers were almost certainly counting on vehicle speed to provide a
good part of that.
IMHO this application would REQUIRE an external alternator controller
(available commercially) with a temperature sensor on the alternator
housing and probably a ducted in cooling air feed to the rear housing.
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
Good points, more big bummers.
The devil is in the details, and what initially seemed like a slam-dunk
no-brainer has become quite problematic.
I'm looking to replace my (stolen) BlackMax with a tri-fuel -- just bite the
bullet, and go thru all the sound-proofing, plumbing, and electrics to the
panel. And put a chain on it...
I'm still going to fool around with a big-ish inverter, just to see what can
be made of it.
A good fraction of the Sandy victims will not have power 'til Nov 11 or
so.... holy shit....
And more salt-in-wound:
Linemen from other states have arrived, to a massive gas shortage, and
are essentially immobile.... it just never ends.
On Fri, 2 Nov 2012 00:17:42 -0400, "Existential Angst"
250 amp is pretty standard. The units Leece Neville/Presolite builds
for fire trucks are 270 amp. (Series 4800 and 4900)
The AVi 160 used in school busses is a 210 amp unit.
Their largest unit is 325 amps (2270 or 2272 series)
Never seen or heard of a 500 amp alternator for vehicle use.
On Fri, 02 Nov 2012 14:21:16 -0400, firstname.lastname@example.org wrote:
That's about the biggest *practical* unit I've seen also. They put
those on the Semis when they used to plaster them with 500 marker
lights and they were all incandescent.
Oh, and they did use the 300A ones on the new Disneyland Parking Lot
Trams - a tractor with a Cat 3208T on Natural Gas, and a string of 7
passenger trailers with overhead lighting in all the cars. Just a
little bit of alternator load...
Now that they've gone to LED's it cut the power draw by about 75%, and
they can get by with the normal factory-option 'heavy' alternator in
the 200A range.
The best way to make an Inverter Rig like that for your house is to
get a larger gasoline engine, like perhaps a 13-HP to 18-HP Briggs
with the flyweight speed governor for generator set use, find a sheave
to fit the crankshaft, and couple that to a truck alternator and a big
deep-cycle battery - preferably two GC-2 Golf Cart batteries in
The governor part is very important, you can't chance setting the
throttle by hand - if the belt snaps and the load dumps from the
alternator you can overspeed the engine and blow it up. The air-vane
governor on a Lawnmower-duty engine will work kinda sorta, but they'll
'hunt' and 'surge' on you while working. But most small car engines
that you would repurpose into a prime mover don't have any sort of
governor built in at all - you have to add one.
For small overnight loads you can run off the batteries, but you want
the engine running before you crank up the microwave oven, or start
charging your cellphones and Laptop battery.
Put it on a cart with wheels, add a pair of 4/0 Truck-sized Jumper
Cables (and a 300A or 500A circuit breaker in case of an "Oopsie!"),
and you can boost-charge and start almost anything from a Semi to a
D-9 Dozer to a Liebherr mining dump-truck or a Locomotive.
Note that when the engines get really huge they are often 24V
electrical systems. Or they have an Air-Starter, and you need a
gas-engine air compressor on a cart to give them a jump-start.
--<< Bruce >>--
I'd like to see the rectifier and regulator for a 500 amp unit!
When we got the latest rig (E One built on a commercial chassis with no
electrical upgrades!) I stuck a spare LN unit I had on it.
The original dept was always complaining that the low voltage alarm
would go off and they had to rev up the engine to bring it up (which is
SOP in most departments anyway, even the big units don't put out enough
at idle to power all the lights on the new rigs)
Only real problem I had was the crappy wiring that I replaced with heavy
duty stuff. Just bugs me to see low grade crap on an emergency vehicle.
After reading through your posts.
Use the Nissan for charging. It has a 100 amp unit compared to the Fit's
Those numbers are NOT idle numbers, they are at 2,500 rpm. They drop
down a LOT at idle.
If you plan on 50% discharge you don't want auto batteries, you will
have to use deep cycle marine units. Auto batteries won't handle deep
discharges very long before they fail.
Best solution would be to put the batteries in a box in the garage or a
shed (NOT IN THE HOUSE UNLESS YOU BUILD AN EXTERIOR VENTED ENCLOSURE!)
Mount the inverter nearby and use copper buss bars to feed the inverter.
Then use common jumper cables from the car to the batteries to charge
them. Also hook up a good battery maintainer and a solar panel and you
would have reliable long term power. You could add batteries as needed,
OR replace them with much larger industrial units like fork truck batteries.
As to how many batteries an alternator will handle, it all depends on
how discharged they are. The curve on a typical alternator is pretty
steep. They are designed to charge a low battery FAST, then as the
battery comes up to charge it takes less power so the alternator works
less. This isn't a problem most of the time because a battery in good
shape doesn't drop very far unless you leave the lights on or crank the
starter a lot.
Some interesting info on batteries and power here:
Heh, Thevenin's Theorem is not taught in any "first college class", you
AND, if you can cite a single relevancy of Thevenin's theorem to charging
batteries -- aside from the detail of mismatched batteries -- I'll blow you
in any venue you choose. No one is asking for equivalent circuits here.
You remind me of the asshole who brings up relativity in the middle of
billiard ball collision problem.
Your pathetically feeble attempt at deceit notwithstanding, I was
quite certain, as you've provided proof positive, that both the
concept and the point would far out reach your miniscule grasp.
Deceit?? YOU brought up Thevenins theorem, and YOU can't show how it
The ball is still in your delusional court:
Show me and everyone else exactly how you would apply Thevenin's/Norton's
theorems to the discussion at hand. Show me and everyone else exactly what
insights into this discussion these theorems would provide in the context of
this thread, what contribution..
I'll answer it for you: NONE.
But, I could be wrong. So show us.
But, really, you just wanted to theorem-name-drop, flap your dick around.
Like I said, if you can provide ONE instance where these theorems contribute
one iota to the discussion, I'll blow you.
No, I will not further spoonfeed you, nor am I in the least
interested in what you conspicuously consider to be an offer
which someone of your miscreant ilk couldn't muster a refusal.
You're truly a pretentious, addlepated bore highly reminiscent
of Monty Python's Black Knight. Here's a hint, with apologies
to Will Rogers, when you find yourself in a hole, stop digging.
On Wed, 31 Oct 2012 23:39:12 -0400, "Existential Angst"
I just did a couple quick calc's and here's what I got. Assuming a
regular setup first with the battery sitting at 12.5 volts, which is
reasonably well charged, and with an internal resistance of 0.08 ohms.
V=IR, doing the math gives you 25 amps if the alternator spins fast
enough to put out 14.5 volts while it's charging the battery. That's
based on the 2volt difference between the battery voltage and the
alternator voltage. Add a second battery with the same state of
charge at 12.5v and the parallel resistance value calc's to 0.04 and
the math gives you 50 amps from the alternator.
If the two batteries were down to 12.0 volts, which is a fair
discharge level, you get a final value for both batteries charging of
62.5 amps. If those assumptions are in the ballpark it doesn't seem
to me that adding a second battery that's 50% discharged would be that
big a deal IF charging the batteries was the only thing going on. If
you are driving around and using 30 amps to run the car, stereo, AC
system then you are pulling over 90 amps and I suspect most standard
alternators don't like cranking out that much power for very long.
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