Alternator Positive Wire Sizing

[goboatingnow]

Originally Posted by Maine Sail

Dave,

Really? If you have a 1/2/BOTH, as the vast majority of boats do, and sent a sense wire to the start battery at 12.6V- 12.72V (full) and you turn on the regulator which is trying to get to 14.4V to 14.8V it will simply full field the alt.

This will be fine and dandy if the bank being charged is in bulk and can take more current than the alt can push to raise the voltage to absorption level but once it gets to that point the voltage of the non-sensed bank will keep on climbing because the reg is still thinking the bank is at 12.6V and it is feeding the alt full or near full field..

I have seen it both ways and the reg could care less whether the banks is sitting at 12.7V or 12.1V it still pushes the field very hard and won't stop because it has no voltage to limit because it thinks it is not there yet....

I know you are smart with this stuff so perhaps I am missing what you are trying to convey?

, I was addressing the negativity around diode splitters and voltage drop

Maybe I got my English mixed up, I was referring to using diode splitters and sensing from one battery, not 1-2-both switching

In my view 1-2-both switching has no place in charging circuits , it has ( an arguable but weak ) use in supply side switching

Dave

[goboatingnow]

Originally Posted by Pelorus32

And here I was thinking we were dealing with a DC circuit.

We are , impedance has a resistive and a reactive component at DC the reactive component is zero, but only in theory as all circuits have AC characteristics due to pulse activity.

Dave

[hellosailor]

A lot of "stock" is done because it is cheap and someone can get away with it.

10AWG or even 10SAE wiring from the alternator to the battery is actually normal in the auto industry as well, SAE wire gauge being even smaller (# for #) than AWG wire. It works, it can safely carry more than 55 amps, the problem is that it causes voltage drop which causes the alternator to work harder, the engine to work harder, the batteries to suffer as well. So by all means, if you have a whole seven or even ten feet of wire? Replace it with a cable that has "zero" voltage drop at 55A. Since it is only "half" the circuit...I'm not sure how to properly calculate that but I'd say #2AWG is already so little voltage drop that it doesn't pay to go any heavier than that. www.genuinedealz.com is a good source for proper fully tinned wire, and they'll put proper crimp lugs on it for you as well. (Memo, check out the negative battery cabling at the same time.)

"Don't run the alternator +ve to the starter - going direct to the battery is the better way." Again, someone could get away with it. Wiring was and is often done "point to point" in order to use less wire so you may find almost anything. DO beware that on an older boat, the wire from the alternator to the starter was often "fusible link wire" where the entire wire is designed to burn and blow like a fuse. That's considered a fire hazard these days, even when a fiberglass sleeve has been put over it. Part of the logic is that if you run from the alternator to the starter, that's the heaviest load, so the heaviest wire, and then you continue onwards with lighter wire, saving money twice. See, the engineers don't want to damage their slide rules by using them as clubs, but the accountants have all those sharp pencils, cheaper by the dozen, so you know who wins that war.

Most automotive type (internally regulated) alternators did have a voltage sense wire, and some didn't need the sense wire, they can "read" the battery in between output pulses, over the same main output wire. The problem on a boat is that as soon as you put in two batteries and a switch, where do you put that *one* battery sense lead? So there's more kludging done.

Once you decide on the fixes you want, you'll be spending a lot less money on batteries and doing a lot less engine time to charge them.

[Maine Sail]

Originally Posted by goboatingnow

, I was addressing the negativity around diode splitters and voltage drop

Maybe I got my English mixed up, I was referring to using diode splitters and sensing from one battery, not 1-2-both switching

In my view 1-2-both switching has no place in charging circuits , it has ( an arguable but weak ) use in supply side switching

Dave

Ah that clears it up!! I tend to like the 1/2/BOTH as a use/supply side switch, lots of redundancy, but much prefer charge sources direct wired to the bank with proper OCP..

If I am starting from scratch I prefer ON/OFFS with an emergency parallel. Problem is most boats are already fitted with a 1/2/BOTH and sometimes the surgery required to convert to two or three switches or another brand is not worth it to the customer. A 1/2/BOTH more adequately wired and used as a simple on/off is easy and, its already there.

[pbiJim]

Originally Posted by Maine Sail

Dave,

Really? If you have a 1/2/BOTH, as the vast majority of boats do, and sent a sense wire to the start battery at 12.6V- 12.72V (full) and you turn on the regulator which is trying to get to 14.4V to 14.8V it will simply full field the alt.

This will be fine and dandy if the bank being charged is in bulk and can take more current than the alt can push to raise the voltage to absorption level but once it gets to that point the voltage of the non-sensed bank will keep on climbing because the reg is still thinking the bank is at 12.6V and it is feeding the alt full or near full field..

I have seen it both ways and the reg could care less whether the banks is sitting at 12.7V or 12.1V it still pushes the field very hard and won't stop because it has no voltage to limit because it thinks it is not there yet....

I know you are smart with this stuff so perhaps I am missing what you are trying to convey?

I believe this to be a completely accurate description of reality.

[pbiJim]

Originally Posted by goboatingnow

A large battery bank essentially controls the terminal voltage as its by far the lowest impedance compared to the output impedance of the alternator. In bulk phase the impedance is so low that irrespective the alternator does not regulate anything.

As the battery changes its effective impedance rises and hence the charger gains more control over the terminal voltage , but only within a narrow range and attempting to exceed a particular max voltage will cause large currents to flow , which will suppress alternator voltage etc.

Dave

Dave, I am trying really hard to fight back the urge to post back to you, something you posted to me recently & simply say that this post is quite frankly rubbish. I am having a very hard time making sense of what you wrote here.

At best, I can try to take away from this that you are trying to say that a battery is a voltage source & an alternator is a current source & because the battery is bigger, it will overpower the alternator & take control of the voltage.

You seem to fully discount the effect of the voltage regulator. You seem to want to ignore the fact that the alternator can put out current for an infinite period of time but the battery cannot accept more & more current for an infinite period of time. If a full field alternator is pushing amps into a battery non-stop as fast as it can, then the battery will overcharge & fail, no? Sure, a large battery bank will survive longer than a small one will under this type of abuse, but not all that long. A few hours of full field operation is enough to kill any bank of batteries on any boat that I've been on. Most battery banks that I have seen would be in an adverse condition in well under an hour.

Please explain this to me better if I am misunderstanding you.

Thanks,
Jim

[pbiJim]

Originally Posted by goboatingnow

, I was addressing the negativity around diode splitters and voltage drop

Maybe I got my English mixed up, I was referring to using diode splitters and sensing from one battery, not 1-2-both switching
Dave

I wish that I had read this before I posted my last post. I now see where the problem came from. I see that that your comments regarding my previous post assumed that the batteries were wired differently than had been described. I had described 1-2-both switching & you responded with comments that assumed we were talking about diode isolated banks. We were talking about two very different circuits. We were talking about apples & bananas. That is why our descriptions of what would & would not work were so completely opposed.

I still do not see where you are taking the effect of the voltage regulator into proper account. I also do not see how a sense wire on one bank will allow proper charging of both in your chosen circuit. Perhaps I am not properly visualizing your wiring arrangement. I expect that the diode voltage drops will still cause imbalanced charging. If you could perhaps post a schematic drawing of the circuit you envision, that might help me to understand you better.

Thanks,
Jim

[David M]

Originally Posted by goboatingnow

A large battery bank essentially controls the terminal voltage as its by far the lowest impedance compared to the output impedance of the alternator. In bulk phase the impedance is so low that irrespective the alternator does not regulate anything.

As the battery changes its effective impedance rises and hence the charger gains more control over the terminal voltage , but only within a narrow range and attempting to exceed a particular max voltage will cause large currents to flow , which will suppress alternator voltage etc.

Dave

No, when charging the alternators voltage regulator controls the DC system voltage....period. The amount of current produced by the alternator is determined by the system load and batteries charge state in order to keep the voltage at a high enough level primarily to charge the batteries.

If the voltage regulator has no effect on DC system voltage when in bulk phase then try removing it or cut the voltage sensor wire and see what happens. Yes I understand that there can be a period of time when the load in amps is greater than what the alternator can produce.

[Maine Sail]

Originally Posted by David M

If the voltage regulator has no effect on DC system voltage when in bulk phase then try removing it

The effect it has is to full filed the alt. It is not regulating voltage at this point.. If you disconnect the field wire the alt shuts down.

Originally Posted by David M

or cut the voltage sensor wire and see what happens.

If you cut the volt sense wire the reg still produces full field in bulk (unless of course like the MC-614 it won't work it the VS wire is disconnected). If the bank comes up to absorption voltage without the sense wire the bank will simply over charge because it has nothing sense or regulate to and it thinks the banks voltage is still low and this would send the reg into full field..

Originally Posted by David M

Yes I understand that there can be a period of time when the load in amps is greater than what the alternator can produce.

It's called bulk. With our LiFePO4 bank my alt & reg are almost always in bulk (until the last 15 min or so). In bulk the bank is not yet at the target voltage or limiting voltage for the reg to "limit".

Despite Balmar muddying the waters with terms like "bulk 1" & "bulk 2" voltages, bulk is generally considered the period of time before you have attained the regulators limiting voltage.

I have long gone back and forth with Rick etc. at Balmar that these should be absorption #1 and absorption #2 but marketing wins...

Throw larger current at a low bank and it comes up to a limiting voltage much faster than a bank with a small charging current. In bulk the battery determines the terminal voltage for its state of charge and how much current it is taking. In absorption the regulator limits the voltage but the battery determines the current accepted at that voltage.

[David M]

Originally Posted by Maine Sail

The effect it has is to full filed the alt. It is not regulating voltage at this point.. If you disconnect the field wire the alt shuts down.



If you cut the volt sense wire the reg still produces full field in bulk (unless of course like the MC-614 it won't work it the VS wire is disconnected). If the bank comes up to absorption voltage without the sense wire the bank will simply over charge because it has nothing sense or regulate to and it thinks the banks voltage is still low and this would send the reg into full field..




It's called bulk. With our LiFePO4 bank my alt & reg are almost always in bulk (until the last 15 min or so). In bulk the bank is not yet at the target voltage or limiting voltage for the reg to "limit".

Despite Balmar muddying the waters with terms like "bulk 1" & "bulk 2" voltages, bulk is generally considered the period of time before you have attained the regulators limiting voltage.

I have long gone back and forth with Rick etc. at Balmar that these should be absorption #1 and absorption #2 but marketing wins...

Throw larger current at a low bank and it comes up to a limiting voltage much faster than a bank with a small charging current. In bulk the battery determines the terminal voltage for its state of charge and how much current it is taking. In absorption the regulator limits the voltage but the battery determines the current accepted at that voltage.

Yup.

[pbiJim]

Since we seem to have a few people here that actually understand these systems well enough, I'll throw in an extra little tidbit of background theory, just for academic purposes.

The voltage regulator on a traditional alternator, is not actually a voltage regulator. It is actually a voltage sensing current regulator, technically speaking.

An alternator is actually a current source, not a voltage source. If you disconnect the load from the output of an alternator, the output voltage will shoot sky high as the alternator attempts to find a high enough voltage to push out the current that it wants to deliver. This very high voltage is often enough to surpass the PIV rating of the components in the regulator & fry it.

The amount of current that the alternator wants to deliver is determined by the amount of current that exists in its field coil in conjunction with its RPM. The current in the field coil is what actually gets controlled by the "voltage regulator". The regulator senses the voltage at the test point (which can be internal or external to the regulator) & based on that voltage, it either increases or decreases the current in the field. When this current (0 to full field generation capacity) is applied across a load (load = battery, lights, radio, etc) then the combination of the current & the load impedance interact with each other to form a voltage according to ohm's law of V=IR. This voltage is sensed by the regulator, which then adjusts the field current to influence the alternator output current to balance the system voltage at it's target value. This all happens many times in a fraction of a second, over & over again to maintain a balance that you see as a constant voltage. In very old systems, like on a 1940's vintage truck that I once owned, the regulator was actually a bank of 3 relays with 3 different resistor banks. This crude system made a lot of noise & was a bit erratic, but it did work. Today's transistorized regulators are much smoother & more reliable.

For now, I'll leave out the part about how the transistors inside the regulator get biases & stabilized in order to produce the desired field current & I'll leave out the part about how an alternator actually produces AC that is then converted to DC by the rectifier bridge.

[hellosailor]

Jim, I think the reality of alternators is more complex than that simply due to the hundreds of different designs out there.

I was looking askance at a Japanese car (Hitachi or Denso alternator) that was putting out 14.5 volts in the winter cold but "mysteriously" dropped to 14.0 in high heat but I'm now told Hitachi and perhaps others are somehow doing heat compensation, even though they have no external temperature sensor, and one would think the heat they generate overwhelms any ambient sensing they can do. Damfino, I won't ask Hitachi, they don't like to talk to civilians.

The shop manuals for them indicate loose voltage regulation, from 13.8 to 14.4 depending on engine speed and ignoring battery condition. As opposed to the classic Delcotrons, which put out a very precise 14.3-14.4 and only vary the pulse frequency they put it out with. So it seems like there's a bunch of alternator engineers with different ideas about how to skin cats, and that's just for internal regulators. What "we" civilians see with mutlimeters that are pretending to read clean DC...and the effects of system voltage being pulled or limited by other constraints rather than by intentional control...
Makes it hard to tell what are the "causes" and what are the "effects".

[pbiJim]

Originally Posted by hellosailor

Jim, I think the reality of alternators is more complex than that simply due to the hundreds of different designs out there.

This is true & this is why I spoke of "The voltage regulator on a traditional alternator".

More modern alternators have regulators that work on a variety of proprietary principals. The most complex ones that I have been told about will occasionally send out a voltage spike & analyze the resulting current response to sense the condition of the battery, then provide a calibrated sequence of positive & negative currents in order to charge the battery faster.

This system of quickly alternating charge/discharge cycles makes little sense to me intuitively & I don't have a useful working knowledge of it, so I really can't describe it in proper detail.

Proponents of this system claim that it charges batteries faster & prolongs their lifespan. I haven't seen hard empirical data to prove or disprove those claims. That stuff is still black magic to me. I only have a working knowledge of the more classic systems.

[scoobert]

Originally Posted by Pelorus32

G'day Gurus,

This may have been covered somewhere but I've searched and can't find it.

I'm rewiring the charging system on our boat. It currently uses an old Victron diode system to separate the batteries. The house battery never sees more than 13.2V on charge and of course you can guess what happens to the house battery. It's only 120AH but our needs are very modest.

I'm replacing the Victron with a CTek D250S Dual and a SmartPass. I already have them to hand and I've seen them doing a good job elsewhere...so that's not the question

The boat is powered by a 3GM30 with the standard 55A alternator.

The sparky who wired the boat took the positive feed from the alternator across the boat for about 6 feet to a shunt, using 10 AWG wire. From the other side of the shunt it goes to the live side of the starting battery switch again using 10 AWG for about 2 feet. This is instead of a short run from the alternator to the battery +ve on the starter according to the Yanmar wiring diagram.

Unless I'm mistaken all charging current is travelling over that 10 AWG wire for a considerable distance.

I reckon that wire is much, much too small for the job at hand. For various reasons the location of the shunt is probably the best compromise. So what I intend to do is to beef up that wire substantially. Am I missing something here and is that 10 AWG wire enough or am I right in wanting to upsize it and if so what size would you recommend - I'd rather be over than under in size.

All battery cables (to the switches and to the starter etc) are bigger than 2 AWG - I would guess 0 AWG and I have made up all leads for the new interconnects using 2 AWG...except for the lead from the alternator.

I'd appreciate views on sizing please.

Also if anyone knows the size of that +ve stud on the standard Yanmar alternator I'd be grateful. I'm away from the boat during the week and forgot to check.

i would not go smaller then 8AWG. but then i always up-size.

[hellosailor]

Jim-
Even "modern" versus "traditional" is up for grabs. My 68 Ford had one of those "box of resistors on the firewall" pieces of junk. The nice thing is, it was easy to adjust or replace. My 72 Chevy had one of the fancy Delcotrons, which was ages more advanced than my 85 Riceburner. And I'm trying to remember...I think it was a Marchal/Motorola combination that we found and replaced with a Delcotron on a boat ten years ago. Now, THAT old thing was outright scary, I don't know where it came from but the batteries were much happier to see it go.
Getting rid of the external voltage sense wire makes sense. You know, "hardware costs money". And more money to assemble it. Once you go to digital controls and you can pause the output, query the battery, and make adjustments in microseconds...sure, that makes sense to me. Of course it has to make diagnostics harder and no doubt the damned things are going to find invisible and insidious ways to fail...but I can respect the principle.
Of course Delco tried to put spike protection into a line of alternators about ten years ago also, and then found out the hard way that the protection would fail and take out the alternator, more often than anything else.
"OOpsie."