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Old 02-28-2016, 06:58 AM   #21
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" with an 80 amp red blue sea fuse holder inline."

So if the fuse goes , so does the alt?
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Old 02-28-2016, 07:11 AM   #22
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" with an 80 amp red blue sea fuse holder inline."

So if the fuse goes , so does the alt?
Fuses only blow at 125% of their power rating. I have read an alternator can not put out more than its rating without self destructing, so it might burn itself out before the fuse blows. The fuse is just in case the wire shorts, then battery amps would blow the fuse.

Don't know if the fuse goes , so does the alt, the alternators are 78 amp 12SI Delco one wire no external regulator. Since there is no separate wire sensing regulator to keep the field on, if the fuse blows all power is immediately cut to alternator.


I wired mine up this way since it keeps me ar anyone else from moving switches if engine is running and possibly killing the alternator.

I looked at circuit breakers for doing this, but already had one freebie Blue Sea fuse holder, so went with fuses, Just had to buy one fuse holder. You can buy 100 amp fuses for that fuse holder.
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Old 02-28-2016, 08:38 AM   #23
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the alternators are 78 amp 12SI Delco one wire no external regulator.

These are great , when used as created , to refill a start batt , and provide DC power to accessories, underway .

IF you want to charge house batts in a far shorter time , you will need to replace the internal Vregulator and wire in a 3 or 4 stage marine V regulator.

"Fuses only blow at 125% of their power rating.,"

That really depends on the fuse selected , some are instant at the rating , others are "slow blow".

A 200A fuse would give the same protection from a massive short , .
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Old 02-28-2016, 10:47 AM   #24
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the alternators are 78 amp 12SI Delco one wire no external regulator.

These are great , when used as created , to refill a start batt , and provide DC power to accessories, underway .

IF you want to charge house batts in a far shorter time , you will need to replace the internal Vregulator and wire in a 3 or 4 stage marine V regulator.

"Fuses only blow at 125% of their power rating.,"

That really depends on the fuse selected , some are instant at the rating , others are "slow blow".

A 200A fuse would give the same protection from a massive short , .
Yes it would. Mine are slow blow Maxi fuses from what I remember, like this
https://www.bluesea.com/products/cat...ses/MAXI_Fuses
.
Even at 2 times their rating, 10 seconds to blow.

The wire to the batteries is gauge 4. This helps keep the voltage higher. with an external regulator, voltage sensing is at the battery or buss which is good. With a one wire alternator, voltage sensing is at the alternator. When running for me it charges at about 14.6 vdc

I also have an Onan generator and a Raritan charger-converter. I don't have a lot of high power DC stuff. The Lectrasan is the biggest temporary draw. My electric horizontal windlass is AC powered. Inside is a Black and Decker 48vdc motor. AC is converted by a full wave bridge rectifier to DC. It has lots of gears inside, pulls about a foot per second and nothing stops it. I got it real cheap used, don't even know who made it. But I have seen this similar style on some older power boats. It is like a square white box with a single rope pulley and an on-off switch.

The big advantage of AC power is I can run a 16 gauge wire to the windlass. And for AC backup, I have a 3000 watt MSW inverter. Even so, my family mostly hauls in the anchor by hand.
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Old 02-28-2016, 06:46 PM   #25
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Fuses only blow at 125% of their power rating. I have read an alternator can not put out more than its rating without self destructing, so it might burn itself out before the fuse blows. The fuse is just in case the wire shorts, then battery amps would blow the fuse.

Don't know if the fuse goes , so does the alt, the alternators are 78 amp 12SI Delco one wire no external regulator. Since there is no separate wire sensing regulator to keep the field on, if the fuse blows all power is immediately cut to alternator.


I wired mine up this way since it keeps me ar anyone else from moving switches if engine is running and possibly killing the alternator.

I looked at circuit breakers for doing this, but already had one freebie Blue Sea fuse holder, so went with fuses, Just had to buy one fuse holder. You can buy 100 amp fuses for that fuse holder.
Alternator fuses should ideally be sized at 125-150% of the Max alt output rating. Balmar and others recommend 150%. The reason for this is that you don't really want to run an over current protection device at any more than about 80% of its rating, preferably less. Running a fuse at close to its rating also means more voltage drop across the fuse.

The fuse also goes at the battery end of the circuit not the alternator end. This is because the alt is a current limited device but a good sized bank can throw 15,000-20,000A into a dead short.

If a fuse trips in an alt circuit, or a switch is flipped resulting in an open circuit event, an extremely fast voltage transient occurs, faster than the regulator can react to, and it very often blows some or all of the alternators diodes.

The fuse is not really there to protect the alt it is there to protect the wire. However by sizing it too small it can eventually nuisance trip and potentially destroy the alt. When a fuse is constantly run at close to its rating it can eventually develop edge burn, a blackening of the edges of the thermal wire, the longer it goes on the higher the likelyhood it can nuisance trip.

Also many alternators, due to slight variances in manufacturing, can supply as much as 3-7% more than their rating upon cold start for short durations.
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Old 02-28-2016, 08:19 PM   #26
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I'm personally not a fan of fuses on the alternator charging cable. Too many chances of erroneous disconnection of the alt charge that would cause damage to the alternator diode. As it was explained to me, the over-current situation would be controlled by alt circuitry. I'm no alternator expert so if others out there know differently, I'd sure be interested in the facts.

I rewired my boat from the standard undersized wire going from the alt hot to the starter hot lug. This sent the charge current through the start cable-selector switch-battery cable-battery bank path. The undersized wire from the alternator reduces the charge current available at the battery. It also causes the selector switch to control charge plus load.

I like separate control of the charge and load circuits, so I wired my alts with large cable (#4 IIRC) directly from the alt to the battery. If I need to turn off the alt charge but not the engine, I can turn off my start switch on my legacy Perkins diesel without effect on the engine except for the hour meter and the stop solenoid. No harm to the alternator.

If I need to share the charge of one engine between two battery banks, I have a helm panel switch selectable Yandina 160A combiner plus manual Perko switches that can tie the banks together. When the Perkos are used to combine banks, the load and the charge circuits are switched together. The Perkos are located at the base of the fwd steps leading to the ER and fwd staterooms so I don't need to enter the ER to control the electricity.
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Old 02-28-2016, 10:23 PM   #27
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Originall ???. How can I damage my alternators ?. Simple question. A blown fuse on the output would do that. One wire or not, doesnt matter. The one wire Delco alternators are the most likely to be affected by this.
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Old 03-01-2016, 07:09 AM   #28
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In my situation, the fuse is close to the battery. Even though they are 78 amp alternators, I have never seen the ammeter go that high. They typically after cranking, run a charge from 30 to 40 amps and only for a minute or so. I could go with 100 amp fuses, that is the largest fuse that will fit that holder that I know of.

I have experience rebuilding these Delco alternators. I have about 4 spares.
My alternator wire goes from alternator to helm ammeter to fuse to battery lug in the battery switch.

OEM had run the output through ammeters up on the flybridge. That was a very long run, I cut them out of the circuit and rely on voltmeters for monitoring the power output both on lower and upper helm.

After pulling out the ammeters, to reuse the hole, I gutted the ammeter and put in a 3 wire digital volt meter. The third wire is a voltage sensing wire. Other 2 wires power the meter.




Created a black mask, then used some blue plastic to give led a bluer look.
Meter I pulled out of its case and hot glued to the old ammeter face.



The original SW ammeter case has 3 electrical connections built in. I was able to reuse them, so the internal wires from the LED gauge hook up inside the case., all the nuts work just like OEM.
New meter uses a ground, hot, voltage sense wire.
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Old 03-01-2016, 09:49 AM   #29
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My alternator wire goes from alternator to helm ammeter to fuse to battery lug in the battery switch.
Unless your ammeter has an external shunt, and uses voltage sensing shunt leads to the ammeter display, these dash mounted ammeters can induce lots of voltage drop in the B+ wire of the alt.

Voltage drop is quite possibly why you're only ever seeing a max of about 30-40A. If you're talking about a MAXI fuse holder for a 78A alt I would suggest a fuse with the correct AIC to be direct connected to a battery bank. The MAXI has a max AIC of 1000A which is not suffucuent for direct connection to a bank.

A 78A Delco can easily pump out 78A +/- if properly wired, and the bank can accept it. System voltage drop will have it hit the limit voltage and start current limiting considerably earlier. It's not uncommon to see an alt with bad voltage drop hit the voltage limit, at the alt end of the circuit, almost immediately. This limits how much current the battery will accept and we see low alternator output and longer charging times..

An MRBF terminal fuse holder & fuse can be mounted directly to the battery and would allow for a larger fuse. It also has an AIC rating of 10,000A that is appropriate for a battery bank connection.


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Old 03-01-2016, 11:10 AM   #30
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An MRBF terminal fuse holder & fuse can be mounted directly to the battery and would allow for a larger fuse. It also has an AIC rating of 10,000A that is appropriate for a battery bank connection.


That is what I used on my new bank to protect all the wires connected to the battery. Simple and effective.
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Old 03-01-2016, 12:27 PM   #31
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Unless your ammeter has an external shunt, and uses voltage sensing shunt leads to the ammeter display, these dash mounted ammeters can induce lots of voltage drop in the B+ wire of the alt.

Voltage drop is quite possibly why you're only ever seeing a max of about 30-40A. If you're talking about a MAXI fuse holder for a 78A alt I would suggest a fuse with the correct AIC to be direct connected to a battery bank. The MAXI has a max AIC of 1000A which is not suffucuent for direct connection to a bank.

A 78A Delco can easily pump out 78A +/- if properly wired, and the bank can accept it. System voltage drop will have it hit the limit voltage and start current limiting considerably earlier. It's not uncommon to see an alt with bad voltage drop hit the voltage limit, at the alt end of the circuit, almost immediately. This limits how much current the battery will accept and we see low alternator output and longer charging times..

An MRBF terminal fuse holder & fuse can be mounted directly to the battery and would allow for a larger fuse. It also has an AIC rating of 10,000A that is appropriate for a battery bank connection.


It is properly wired, a 4 gauge wire. I never see a super high draw since the batteries don't accept a huge charge and I do not have a huge amount of DC appliances. I know I have good grounds since I have good voltage coming from them. I have burned up a few drive belts in the past. One reason is I needed to modify the narrow pulley to use a 1/2 inch belt. Originally these motors used a Motorola 50 amp with external regulator. I put in the Delco since IMO, they are better than what I had.

I do not have the starters fused. I do have 3 fuses coming off the selector switches.
I have a 100 amp for the Lectrasan, a 150 amp for the house feeding the main DC buss, and 350 amp fast blow fuse feeding the 3000 watt inverter.
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Old 03-01-2016, 12:44 PM   #32
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Picture of the mod. I used a sawzall and sliced the pulley in half.
Then put hardened washer between each half. Pulley is a cast iron pulley, not stamped steel.

Hey, it works. Cheaper than buying a wider pulley, and I know how to do things.



Pulley runs true.
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