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Old 18-07-2013, 07:59   #16
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Re: Alternator Positive Wire Sizing

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Originally Posted by Maine Sail View Post
I find this sort of installation simply unacceptable for the 2.5K he paid the yard to "fix" his charging issues, but I see it all the time. I quite often see in excess of 1V of drop in charging circuits. This results in batteries so sulfated in just a couple of years that they are well beyond saving. Getting the voltage to a proper level can drastically improve the situation and greatly increase battery life. The vast majority of boats I work on are mooring sailed also so there is no shore power charging during the season. An improperly installed & wired and set up alternator & circuit can lead to destroyed batteries if fairly short order under these circumstances....
The problem with owners with amp hungry sailing boats is that most of their charging systems are not optimised for sailing boats (short motor/charging runs).

If you tell them that they have to supply every possible amp that the batteries will accept when charging, charge the batteries up fully once a week, rip out the unsized untidy wiring and replace the car alternator with a real one etc. They dont want to hear that.

Paying 2.5k for an inadequate solution says alot about the owner as well as the yard.

Messy wiring, undercharged batteries, paying too much for a poor solution, owner doesn't understand the importance, generally given wrong advice... normal.

Tidy wiring, properly charged and maintained batteries, work done by an electrically competant person, owner understands the importance.... abnormal.
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Old 18-07-2013, 08:52   #17
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Re: Alternator Positive Wire Sizing

Going back as far as a 1977 jeep that I used to have, the Delco alternator on that had a sensing wire on the regulator that would pick up the voltage at the battery itself, or wherever else in the electrical system you attached the sense wire & then the regulator would compensate the alternator output to produce the desired voltage after any existing drop due to the charge wire, connectors, etc.

Are these types of regulators with sensing wires not used in boats these days?
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Old 18-07-2013, 09:02   #18
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Re: Alternator Positive Wire Sizing

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Going back as far as a 1977 jeep that I used to have, the Delco alternator on that had a sensing wire on the regulator that would pick up the voltage at the battery itself, or wherever else in the electrical system you attached the sense wire & then the regulator would compensate the alternator output to produce the desired voltage after any existing drop due to the charge wire, connectors, etc.

Are these types of regulators with sensing wires not used in boats these days?
They are used in boats and some factory alts do have this capability. Many factory alts however don't have this capability without physically digging into the alt. Bank sensing can't be used in all installations especially with a 1/2/BOTH or charge directing switch which can move the charge current from bank to bank. You can't sense one bank and then move the charge current to the other bank or it will send the voltage through the roof on the bank not being sensed, but being charged. I find and fix this wiring mishap often as well. You would need to sense the "C" terminal of the batt switch, not always ideal, or direct wire to the house bank and use a combiner or B2B device to charge the other bank.
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Old 18-07-2013, 09:34   #19
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Re: Alternator Positive Wire Sizing

Ah, so then in the case that you have multiple battery banks that are independently switched & you do not have independent charging systems on each bank, you can't use a sense wire because depending on the position of the switch, you might end up sensing an area that you are not charging (which would be very bad indeed). In this case, you run heavy wires to minimize the drops so that you can get the best possible performance out of the self sensing alternator that you are forced to use.

That's the part that I was missing. Got it now. Thanks for sorting me out on that aspect of the situation.

If you did have a regulator with a sense wire, I would think that you would still be able to run the sense wire as far as the battery switch post where the charging wire connects & at least get some improvement that way. You might also choose to wire the sense wire into a resistor network that would lie to the regulator a little & artificially increase the alternator output to compensate for known voltage drops in the system that might be created by things like diodes. If you don't have a sense wire system, then I guess you are stuck running heavy wires & hoping for the best.

Thank you for the explanations.
Jim
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Old 18-07-2013, 09:45   #20
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Re: Alternator Positive Wire Sizing

Hang on,

if you battery sense the starter battery ( being the most charged battery), but charge the domestics, all you do is set the maximum regulated voltage at the starter level, ie teh absorption value, this would handle any wire drops or diode drops in either wire ( in general).

Its not perfect, but it would work

Dave
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Old 18-07-2013, 10:04   #21
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Re: Alternator Positive Wire Sizing

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Hang on,

if you battery sense the starter battery ( being the most charged battery), but charge the domestics, all you do is set the maximum regulated voltage at the starter level, ie teh absorption value, this would handle any wire drops or diode drops in either wire ( in general).

Its not perfect, but it would work

Dave
If the starter battery & the domestic battery are isolated by the battery switch not being set to both, & you charge the domestic battery with the sense wire on the start battery, then the regulator will only see flat, not-charging, battery voltage from the start battery at the sense wire & the regulator will then continually increase the alternator's output voltage in an attempt to see a proper charging voltage at the sense wire, which would result in a voltage runaway situation & a severe over-voltage condition at the domestic battery, no?
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Old 18-07-2013, 10:06   #22
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Re: Alternator Positive Wire Sizing

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...I regularly wire high capacity alts with 1/0 or 2/0 wire...Most marine alts can still be fried by a load disconnect. A few auto style alts use avalanche diodes but I don't know any marine units that do. Still if an alt is direct wired to the bank it should ideally be fused for the ampacity of the wire and as close to the battery as possible..
Maine ail

With a standard 55amp alternator, the connector at the back for the battery wire is a #8 stud. If you use say, 1awg cable, how do you attach it to the alternator? The slugs are only available for 1/4 inch upwards.
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Old 18-07-2013, 10:16   #23
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Re: Alternator Positive Wire Sizing

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Originally Posted by pbiJim View Post
If the starter battery & the domestic battery are isolated by the battery switch not being set to both, & you charge the domestic battery with the sense wire on the start battery, then the regulator will only see flat, not-charging, battery voltage from the start battery at the sense wire & the regulator will then continually increase the alternator's output voltage in an attempt to see a proper charging voltage at the sense wire, which would result in a severe over-voltage situation at the domestic battery, no?
NO,

whats likely to happen is that the regulator will have a lower output becuase the alternator thinks the battery is charged, but since you are charging the stater battery , does this really matter.?

alternators like all charging sources, dont set the the output voltage, teh battery in general determines that. all it does is regulate to that voltage

dave
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Old 18-07-2013, 10:20   #24
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Re: Alternator Positive Wire Sizing

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Maine ail

With a standard 55amp alternator, the connector at the back for the battery wire is a #8 stud. If you use say, 1awg cable, how do you attach it to the alternator? The slugs are only available for 1/4 inch upwards.
MaineSail did say high capacity alts, not the standard internally regulated 55 amp alt
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Old 18-07-2013, 10:51   #25
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Re: Alternator Positive Wire Sizing

For an 8 foot run at 55 amps with a 3% drop, you want 6 AWG wire. Anything larger would be overkill and anything smaller would create an unacceptable voltage drop.

The West Advisor: Marine Wire

Ancor sells a #6 AWG ring terminal with a #10 hole. I wouldn't worry about the size difference of putting a #10 hole onto a #8 stud. Tighten it down with a stainless steel nylock or double nut it so that it does not shake loose. You might also want to put a little corrosion block or Tef-Gel on the ring terminal.

http://www.marinco.com/product/ring-...ylon-insulated
http://www.marinco.com/product/heavy-duty-lugs

Having a shunt on your alternator output is a great idea. Knowing how much current your alternator is producing can tell you a number of things...since an alternator grounds through its frame. A shunt on the positive side is the most convenient way of knowing your alternators output. It works fine for analog current meters. For digital meters you need to install a converter which "fools" the digital meter into "thinking" it is on the negative side of the circuit.
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Old 18-07-2013, 10:54   #26
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Re: Alternator Positive Wire Sizing

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NO,

whats likely to happen is that the regulator will have a lower output becuase the alternator thinks the battery is charged, but since you are charging the stater battery , does this really matter.?

alternators like all charging sources, dont set the the output voltage, teh battery in general determines that. all it does is regulate to that voltage

dave
As I understand it, the battery doesn't set the voltage, the voltage regulator does. As I understand it, the voltage regulator adjusts the output voltage of the alternator to be higher than the battery voltage so that the battery will accept current from the alternator & take a charge. Is that not the way that it works in the systems that you are familiar with?

Also, in the example that I gave, the battery switch is not set to both, so therefore you are either charging one bank or the other. In the event that you are charging the domestic battery, that is not sensed, I believe that there would be a big problem, no?
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Old 18-07-2013, 11:42   #27
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Re: Alternator Positive Wire Sizing

Correct, the alternator voltage regulator controls the DC system voltage when charging. When not charging the battery determines the DC system voltage...assuming nothing else is charging the DC system like a battery charger.

Set up your house and start batteries with a battery combiner so that charging to both is automated. This way you do not have to keep moving battery switches in order to keep both your house and start banks charged. If just makes things easier and prevents you from having to remember to move the battery switches. You can always bypass the the combiner if it fails...which they do on occasion.
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Old 18-07-2013, 12:39   #28
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Re: Alternator Positive Wire Sizing

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Originally Posted by goboatingnow View Post
NO,

whats likely to happen is that the regulator will have a lower output becuase the alternator thinks the battery is charged, but since you are charging the stater battery , does this really matter.?

alternators like all charging sources, dont set the the output voltage, teh battery in general determines that. all it does is regulate to that voltage

dave
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?
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Old 18-07-2013, 16:58   #29
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Correct, the alternator voltage regulator controls the DC system voltage when charging. When not charging the battery determines the DC system voltage...assuming nothing else is charging the DC system like a battery charger.

Set up your house and start batteries with a battery combiner so that charging to both is automated. This way you do not have to keep moving battery switches in order to keep both your house and start banks charged. If just makes things easier and prevents you from having to remember to move the battery switches. You can always bypass the the combiner if it fails...which they do on occasion.
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
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Old 18-07-2013, 17:12   #30
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Re: Alternator Positive Wire Sizing

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