Alternator connected to starter WTH

[Wotname]

Originally Posted by transmitterdan

It also saves alternators. If the factory did not connect alternator to starter then alternator might not get connected to battery. Alternators can be destroyed if run disconnected from the battery. So this wire saves the factory some nuisance warranty claims for blown up alternators. It’s hard to run the starter without first connecting battery.

.......

Do you really think so? If so, please explain in detail how an alternator that is not connected to a load before starting will be destroyed after starting.

I suggest an alternator can only be damaged if it is disconnected while under load but I'm happy to educated further!

[RUSTYNAIL]

When an engine is designed and approved, it's designed more for an engine in a car or tractor. The alternator and wiring are expecting basic lighting and starting currents. As soon as a boat is sold, owners start adding more and more loads. Recharging the battery after starting should happen quickly, and the #8 wire shouldn't overheat during that quick recharge. Once you start adding constant loads over 75% of the alternator's max capacity, you are asking for trouble, and that's not what the engineers designed the wires for, especially in an engine room over one hundred degrees Fahrenheit, with no air flow. I upped my alternator size, and the wire to the starter positive terminal. The alternator charges the start battery first, and then about 20 seconds later charges the house bank through the ACR (Blue Seas) switch. I put an amp meter with a shunt in series with the ACR line to monitor the current flow. My solar panels charge the house bank and then the start battery, but the current is so little that it doesn't show on the 100 amp analog meter. I give my engine start battery, first priority.

[Charlie]

Originally Posted by olaf hart

Thanks for the schematic, what is the size of the fuse(e) on the house bank?

I now have an ~ 400 ah battery bank. The fuses are supposed to be sized for the smallest wire in the run. There were two existing 200 amp fuses. They never blew but I believe they were to small. I have to figure out the size of the wire. I think it is 2/0 which would require a 300 amp fuse. One thing I learned was that fuses are supposed to be on the load side of the power source.

Never stop learning in sailing. It's one of the things I like about sailing.

[mitiempo]

Originally Posted by Charlie

One thing I learned was that fuses are supposed to be on the load side of the power source.

Fuses should be within 7 inches of the positive post ideally per ABYC. The farther away from the positive post the more wire that is not protected.

A good solution is the Blue Seas terminal fuses which install directly on the battery post.
https://www.bluesea.com/products/519...k_-_30_to_300A

[transmitterdan]

Originally Posted by Wotname

Do you really think so? If so, please explain in detail how an alternator that is not connected to a load before starting will be destroyed after starting.

I suggest an alternator can only be damaged if it is disconnected while under load but I'm happy to educated further!

If the harness gives the alternator a field voltage from the key switch but no battery is connected the diodes will be blown.

[BlackHeron]

Originally Posted by mitiempo

A good solution is the Blue Seas terminal fuses which install directly on the battery post.
https://www.bluesea.com/products/519...k_-_30_to_300A

The BSS terminal fuse block is brilliant, with fuses available up to 300A, so there is no reason most boats can't have even the starter wire fused to protect that from short circuits to ground between the starter battery and
the starter motor.

My only quibble with the product is the wholly inadequate tiny rubber boot that comes with it. Why it doesn't enclose the terminal post of the battery itself is a mystery to me. Such larger boots can be purchased elsewhere, and that's what we have done on our installation.

A large starting battery and a 3/0 unfused wire shorting directly to ground will make one hell of a mess before the battery runs out of juice or the wire burns itself free. A loose metal tool or piece of equipment in the battery compartment or a loose floating ground wire that has become detached somehow on one end can be similarly dangerous.

Even in a covered and enclosed battery/electrical compartment all energized parts and terminals should be guarded from accidental contact to protect them when maintenance is being done, especially with flooded lead-acid batteries that need regular electrolyte level refilling.

[Wotname]

Originally Posted by transmitterdan

If the harness gives the alternator a field voltage from the key switch but no battery is connected the diodes will be blown.

????

You haven't really explained why the diodes will blow.

AFAIK, diodes usually fail from over heating or over voltage. Clearly they won't over heat with no load. Why would they over voltage in an internally regulated internally sensed alternator?

Still happy to be further educated!

[transmitterdan]

Originally Posted by Wotname

????

You haven't really explained why the diodes will blow.

AFAIK, diodes usually fail from over heating or over voltage. Clearly they won't over heat with no load. Why would they over voltage in an internally regulated internally sensed alternator?

Still happy to be further educated!

An alternator is fundamentally a current controlled current source in EE parlance. The output current is a function of field current and rotor speed. Ohms law says E=IxR. If R is infinite then E can go pretty high. The output voltage for even a small field current can exceed the diode breakdown voltage if there is zero ohm load. The battery is what limits the voltage output of an alternator and thus the diodes. No load + field current = broken diodes.

[RUSTYNAIL]

[QUOTE=Charlie;3159575]I now have an ~ 400 ah battery bank. The fuses are supposed to be sized for the smallest wire in the run. There were two existing 200 amp fuses. They never blew but I believe they were to small. I have to figure out the size of the wire. I think it is 2/0 which would require a 300 amp fuse. One thing I learned was that fuses are supposed to be on the load side of the power source.

The fuse protects the 2/0 cable from overheating, but just as importantly is protecting the load from overheating and catching on fire. If your biggest load is an inverter, check the manual for proper size fuse or circuit breaker. Example, if you have a 2,000 watt inverter, ballpark estimate is 2000 divided by 12 (volts) is 166 amps. That may be why you have a 200 amp fuse.
I put a 300 amp fuse in line with my starter, and it blew, so I went to a 400 amp fuse, for an 85 HP Perkins 4.236 with 3/0 cable.

[Wotname]

Originally Posted by transmitterdan

An alternator is fundamentally a current controlled current source in EE parlance. The output current is a function of field current and rotor speed. Ohms law says E=IxR. If R is infinite then E can go pretty high. The output voltage for even a small field current can exceed the diode breakdown voltage if there is zero ohm load. The battery is what limits the voltage output of an alternator and thus the diodes. No load + field current = broken diodes.

I suggest it is voltage controlled current source. The regulator internally senses the output voltage of the alternator (B+ terminal) and holds it at the regulated voltage. The alternator delivers whatever current (up to it's max rating) into whatever load. If a resistive load of say 14 ohms is connected to the output terminal in lieu of a battery, the alternator will provide ~14V at the output and ~1 amp into the load resistor. If 28 ohm load is used, the alternator will remain at ~14 V and deliver ~0.5 amps into the load. The load current has no effect on the output voltage. If R is open circuit, I = 0 and V remains at the voltage determined by the regulator sensing circuit which is connected internally to the B+ terminal.

No???

BTW, a zero ohm load is a short circuit, not an open circuit.

[transmitterdan]

In a word, no. What excites the alternator is the magnetic field. Magnetic fields are produced by current. The field current controls the output current. The average field voltage is simply the resistance of the field wire times the average current. Typically it is much less than 12V. Most “smart” regulators control field current by pulse width modulating the field coil. That’s how Balmar and many others do it. In the old days they used a series pass transistor and possibly as resistor which is wasteful of energy. So the field voltage varies wildly but the field current is pretty constant due to the high inductance of the field winding.

[BlackHeron]

Maximum fuse size is only partially determined by the wire size. but mostly it is sized to the load, and especially to a motor, to protect that.

The wire is sized to the designed load too, but a wire can be over-sized well beyond that to avoid voltage drop or other reasons such as ambient temperatures, bundling, or other factors requiring derating. Over-sizing the wire doesn't mean bumping up the fuse size too.

Fuse to the load, making sure that the wire is sized to the load as well. Fusing to the wire is a misapplication of the process.

In larger commercial motors we see separate fusing designed and sized to protect the wires as well as separate overload protection (often called heaters as the older style would actually heat up and melt to trip within the motor control centers) sized to protect each motor on the circuit from overload, of which there may be multiple motors tapped off of a 3-phase feeder. Overload here is most commonly caused by single-phasing (one leg of the three-phase goes down) low voltage conditions, or power-factor issues on site. Separate fusing for motors and feeders on a boat is probably pretty rare.

[Paul_Carroll]

Originally Posted by smac999

I think your laz switch is drawn wrong. Likly the stater comes from the common. And the Batteries go to 1 and 2. Otherwise it is very strange.

The alternator is normal. And fine if you have a stock 50-60a alt.

I concur. It looks like terminals 1 and Com on the Lazarette switch are reversed. If the point of the Lazarette switch is to allow the engine to be started off the House bank. As it is drawn, the alternator and starter can only ever get or deliver power to the House bank (in position 1). If the switch is moved to position 2, then the house bank is charging the engine battery, but the starter and alternator are completely disconnected. This would be bad as the alternator diodes would blow.

What is the intent of the switch in the lazarette? With that I might be able to offer a better way of wiring it. Also, do your switches not also have a "Both" mode? They still only have a 1, 2, Com terminals, but it is important for operating purposes.

As for the #8 wire, it is within spec, but just barely. As part of the rework, I would probably upgrade it.

[Wotname]

Originally Posted by transmitterdan

In a word, no. What excites the alternator is the magnetic field. Magnetic fields are produced by current. The field current controls the output current. The average field voltage is simply the resistance of the field wire times the average current. Typically it is much less than 12V. Most “smart” regulators control field current by pulse width modulating the field coil. That’s how Balmar and many others do it. In the old days they used a series pass transistor and possibly as resistor which is wasteful of energy. So the field voltage varies wildly but the field current is pretty constant due to the high inductance of the field winding.

The above does not explain how the output voltage is controlled. It explains how it is generated but not how the voltage is regulated. I have no issue with how the output voltage is generated, it is quite straightforward and I agree with your analysis above.

Let's stick to the original premise of a OEM engine fitted with a generic internally alternator. You posted that the diodes will be blown up if alternator output is disconnected before the engine is started. I disagree with this statement as I can't see why the output voltage would exceed the regulated voltage set point. Maybe I'm wrong but the regulator circuits I'm familiar with will not allow the output voltage to be greater than the set point (~14V).

At the heart of the issue is where the internal regulator senses the output voltage. If it senses it from anywhere else than the output terminal of the alternator, then I can see that the output voltage would keep rising if that terminal was open circuit. To what level, I don't know. I haven't seen such an alternator but of course, that doesn't mean they don't exist.

Attached are three different alternators all with internal regulators and although there are some differences, they all sense the output voltage internally from the B+ terminal and regulate the field current to maintain that set point. Although the other terminals vary from one to three, they work in the same manner using a zener diode to maintain the preset voltage. In all of these circuits, there is simply no requirement to have a battery connected to the B+ terminal before operation. The output voltage will rise to the set point and be held there by the regulator operation. It can't rise any higher because as soon as it does, the regulator removes the field current.

[cal40john]

Originally Posted by RUSTYNAIL

When an engine is designed and approved, it's designed more for an engine in a car or tractor. The alternator and wiring are expecting basic lighting and starting currents. As soon as a boat is sold, owners start adding more and more loads. Recharging the battery after starting should happen quickly, and the #8 wire shouldn't overheat during that quick recharge. Once you start adding constant loads over 75% of the alternator's max capacity, you are asking for trouble, and that's not what the engineers designed the wires for, especially in an engine room over one hundred degrees Fahrenheit, with no air flow. I upped my alternator size, and the wire to the starter positive terminal. The alternator charges the start battery first, and then about 20 seconds later charges the house bank through the ACR (Blue Seas) switch. I put an amp meter with a shunt in series with the ACR line to monitor the current flow. My solar panels charge the house bank and then the start battery, but the current is so little that it doesn't show on the 100 amp analog meter. I give my engine start battery, first priority.

Ancor wire #8 ampacity in engine space 68 amps. 1 foot of wire at 50 amps would be 30 mV drop, 0.2% voltage loss, 1.6 watts. The wire isn't going to cause a problem and won't overheat.

https://www.ancorproducts.com/en/res...onductor-sizes