How to "wire" a new tachometer to the alternator

[Dave Neptune]

Good advise

The voltage regulator controls the alternator which controls the output voltage, NOT THE BATTERIES.

The early and late A-4's were even shipped from the factory with a ballast resistor. Once you convert to an EI the resistor really becomes necessary for a happy coil as the "dwell" which charges the coil is a far longer elapsed time between pulses.

Neil and many others did a lot of work to get coil killing under control. That work has been verified many times over. My advise is to listen to him or Tom at Indigo.

The block will not work as a heat-sink as it is not in any real contact through the coil clamp.

Dave Neptune

[ndutton]

There's no adjustment, the internal regulator is a fixed voltage and must be replaced. Before tackling the project it's important to know how to retract and hold the brushes inside their holder to reassemble the alternator. If you don't you'll break the porcelain brush holder and create bigger problems with your new alternator. It involves a small retaining rod tool through a hole in the brush holder through the back of the alternator casing.

The first picture is the regulator, the second is the components inside the open alternator. While you'e in there we could talk about adding an AC tap but that ship has sailed, hasn't it? Let's get your alternator output voltage measured before we go off the deep end.

[ndutton]

It is very hard (lots of amps!) to charge a lead acid battery of any decent size to mid 14 volts is it not? That would require a pretty high current level to do that. I always
run with my two batteries "on" so "forcing" their voltages that high
is even harder. (My two cents.)

With an Atomic 4 you'll never get more than maybe 50 amps out of your alternator and that's only when you're at an elevated RPM and very depleted batteries (for shame!). Fully charged and at rest the batteries will get to around 12.8~13.0 volts and that's about it. I typically see between 10~15 amps charge current from my alternator, higher depending on my battery bank's State of Charge. My running engine accounts for at least 9 amps of that (ignition @3.4A, FWC pumps @4A, fuel pump @1.6A).

[bigoledave]

reply

Yes,,,I understand your comment. Thanks...but...
The "system voltage"..i,e, the volts measured at
the battery terminals in theory is identical when
there is no item drawing..or producing current in the system.

The ONLY way that voltage as measured at the battery
is different from that as measured at....the radio...the
lights...the alternator ...etc is in the condition where you
have resistors in the connections. If you have no resistors,
then you can only have different voltage MEASUREMENTS is
if the wire sizes are so low that you may measure voltages
from one end to the other of the wire (or there are very poor
contacts). So.....if you purchase a "battery connect cable" of
normal size (large diameter) and connected it from the
alternator + output terminal DIRECT to the battery (or high
current capacity switch) there will be a very small voltage drop
(millivolt range) or change when measuring this voltage. The
large wire is a super low ohm value resistor. There is no
way that the voltage drop from the ends of that cable can be
higher that millivolt levels unless the current flowing is extreeemely
high....ohms law of course. So......in my opinion, there is
no worry about high coil or other accessories voltages as the
roughly 30-40 amp currrent MAXIMUM charging energy is
being connected to a thick, normal "battery cable".I will
add a ballast resistor anyway given your experience with coil
failures as an insurance item (why not?) but still fail to understand
how the coil voltage can exceed the battery voltage given the
proper wire terminations are used and large wire is used .

What am I missing?

[ndutton]

First, you don't know yet what your alternator output voltage is so let's not get ahead of ourselves. You might not even need a ballast resistor.

Second, voltage drop can be significant due to insufficient wire gauge and circuit length. Typically boat wiring, especially old boat wiring, is a hot mess.

Third, think of a battery as a bucket of water filled and drained through a single hole at the bottom. It takes more pressure to push water into the bucket than the static pressure at the hole. If the pressure was the same the bucket would not fill, if it's less the bucket would drain. In this analogy, pressure = volts.

[bigoledave]

reply

Yes.....to your comments.

As you state..wires have to be "good". A battery
cable from the alternator is "very good" So the
voltage as measured at the alternator will
be extremely close to battery voltage. The poor condition
of miscellaneous wires and connections to accessories
can never cause a voltage rise....only a drop.

We can debate all day whether the "pressure" in your
bucket analogy is high enough to raise the voltage
of two, 100 amp hour batteries connected in parallel
to levels of almost 15 volts.

thanks for all your suggestions!

[joe_db]

We can debate all day whether the "pressure" in your
bucket analogy is high enough to raise the voltage
of two, 100 amp hour batteries connected in parallel
to levels of almost 15 volts.

thanks for all your suggestions!

No need to debate, I have seen it happen more than once. With full batteries you very much can exceed 15 volts. As a matter of fact, if I had wet batteries and kicked off an equalization cycle I would get to around 15.5-16 volts.

[bigoledave]

more info from the vendor---output voltage

"...Greetings....quick question on the alternator I purchased. Do you have any
specifications from the manufacturer regarding the maximum OUTPUT VOLTAGE
these units should have? I have heard that SOMETIMES, this exact alternator
MAY put out "too high" of a voltage. Any comments appreciated. Also do you
have any actual INSTRUCTIONS for hooking this up? Mine came with just
a small card. Thank you!!!!!!,.."

answer receivesd:

"...New message from: forklift-pro (2,109RED_STAR Star)
Regulator set point is 14.2 volts. The alternator is a one wire self excited unit. Hook up is just the Battery output post on alternator to positive terminal of battery and a good ground to the frame of alternator either by the mounting bracket or a ground wire to the tab with screw on the side of the alternator.

[bigoledave]

First test of new alternator

Ok..I finally got it running today.

It is wired in the simple "one wire" method. I have a
thick (6 ga?) wire connecting to the "bat' large terminal.
Ground is by the mounting bolts AND a short wire from
a ground terminal on the case of the alternator to the A4 block.
Waaay less wires and connectors than my old alternator/seperate
voltage regulator! (Great!)

I first tried using my old belt but since the slot in the versioning
bracket was very near the end I ordered a one inch shorter belt.
NO mods to anything was required and I was able to use all stock
parts.

I started it up and it took a second or so to see the ammeter make
a bigmove of about 30 amps. I had my battery switch on "all" and
both batteries I knew were not charged fully. I have two digital
voltmeters looking at system voltages. Charge voltage went up to
exactly 14.2 volts after running the engine at maybe 2k rpm for
3-4 minutes. I never saw the voltage ever rise above exactly 14,2 v.

So..all is good...but different than my old twp part charging system.
In the old system, charge voltage was never over I think 13.5 volts...
and the ammeter would drop down to a value of 2-5 amps pretty
quickly. With this NEW alternator, the voltage rises to 14.2..and
the charge CURRENT is staying up in the 15 amp range in my
brief first test. I am thinking that both batteries were "low"
or the new alternator just has a very different method of reducing
current than the old style components.

So....it all works....the charge VOLTAGE is not "too high" and I
am puzzled a bit about how the current is managed. Like I
mentioned in a previous post, with my "thick" wire connections,
I am convinced my battery voltages are nearly identical to the
voltage measured at the alternator output as well as anywhere
in my ignition system.

Hope this was informative...

[joe_db]

Current is not managed in your configuration, the alternator supplies 14.2 volts if it can and anything connected to it uses whatever current it will at that voltage.
Very few regulators actually manage current, most of the "smart" regulators are using various proxies for output. Wakespeed is the one current manufacturer that actually directly manages output current.