How to protect the alternator-house bank connection AFD switch?

[skipmac]

Originally Posted by Maine Sail

If you have any bank in excess of 800CCA or 100Ah it is a requirement anyway, if you want to meet the minimum safety standards. Not installing a battery switch, for a cranking bank, even on small boats with CCA sub 800, is just poor form...

Isn't it amazing how many "requirements" are just good common sense as well.

Originally Posted by Maine Sail

Wiring an alternator service disconnect switch is not a "requirement" but is a best practice. If the alt feeds direct to a battery bank or its bus then it needs over-current protection at the battery end.

Everything connected to my batteries goes to Blue Seas MRBF terminal fuse blocks, including the starter cables. I love those things.

[Maine Sail]

Originally Posted by skipmac

Isn't it amazing how many "requirements" are just good common sense as well.

And sometimes no matter how much you fight and kick and scream the electrical committee, creating the standards, can't seem to do the right thing.. Oh but this boat "meets" ABYC standards.....



This boat had four 8 year old junior sailing program sailors on it seconds before it erupted into flames. I was on-site when it erupted because my daughter is one of those sailors and I was there to pick her up from sailing camp.

The cause? Electrical fire! It was caused by a short in the 8GA outboard motor wire. A single Group 24 battery, that did not require a battery switch, nor did it require overcurrent protection, because it was a cranking circuit, caused this fire and complete destruction of a 15' Boston Whaler. It almost burned a few kids too.

Sometimes the standards are far too weak and this is why I always say they are the "minimum requirements".......

Originally Posted by skipmac

Everything connected to my batteries goes to Blue Seas MRBF terminal fuse blocks, including the starter cables. I love those things.

And everyone of the 15 - 17 chase boats in this junior program fleet now are fused. Not a single nuisance trip in thousands and thousands of motor starts.. Sometimes exceptions (cranking battery conductors) are just plain dangerous..

[a64pilot]

Originally Posted by skipmac

I also like to put a switch between the start battery and the starter in case the solenoid hangs.

On my boat I believe that would be the 1,2,ALL, OFF. Switch?

[Fuss]

Apart from the fusing, 2 very important points...

1 - It is not good to have no way of isolating the alternator from the battery.

2 - It is not good to have a switch in common use that potentially can isolate the alternator from the battery.

This is why I recommended the diode splitter method.

[Maine Sail]

Originally Posted by Fuss

Apart from the fusing, 2 very important points...

1 - It is not good to have no way of isolating the alternator from the battery.

Yep this is why you install a service tech disconnect switch, in the engine room.

Originally Posted by Fuss

2 - It is not good to have a switch in common use that potentially can isolate the alternator from the battery.

Again this is why placement of the switch is important. It will be left in the ON position 99.9% of the time and out of site of any "common use" areas.

Originally Posted by Fuss

This is why I recommended the diode splitter method.

I have seen far too many failures of diode isolators over the years. Because they are in the path of the alternator they often take out the alternator when they fail. People often assume they are dead nuts reliable, but not always. I have one sitting in the scrap box in my shop that has physically melted the potting epoxy due to heating.

They also induce voltage drop, creating waste heat and less charge efficiency. This voltage drop needs correction via the volt sensing circuit. Not all alternators can externally sense. The vast majority of diode isolators I see, about 75-80%, are not wired for voltage drop corrections. This leads to banks being murdered in huge numbers due to chronic under charging. The voltage drop across the diodes also leads to turtle paced charging of the house bank. Not only are you under absorbing the batteries, which is really, really, really bad for them, but you are also charging them slower and you can not drive nearly as much energy into them, in the short charging run times cruising sailors have come to expect..

In late bulk & early absorption it can also cause one bank to see excessive charge voltages because the VD across the diodes is not static or fixed, as far too many boat owners often assume it is. The VD across the diode is current dependent. It normally ranges from a low of about 0.6V to 1.1V, depending upon the amperage across the diode, and it can go even higher..

I measured one that was dropping 1.37V between the input and output stud. It was too hot to touch after running the vessels inverter for 20 minutes while making water. The owner called me in to find out what the "burning smell" was when they were running the inverter.. At the 94A the alt was pumping out this equated to a 126W loss in heating the isolator. At the voltage I measured this at, 13.3V, this meant a loss of about 9.5A of energy from the alternators output being wasted. Why pass your alternator current though anything creating inefficiencies, when all it needs to do is be directly wired to the bank that needs the current most?

If the house bank is requiring a 1V correction across the diode, plus 0.4V for the wire drop, the start battery would only be seeing a 0.6V drop and thus it is now getting over voltaged in the late stages of bulk and during early absorption.

Diode isolators are almost always incorrectly installed and located closer to the alternator rather than closer to the batteries. This leads to additional voltage drops in the system wiring that need correction. Best case, to treat all banks fairly, is to sense the input stud and keep the output wiring large and "pig tail" short.

The other big issue is that you now have an installed isolating or charge directing device that won't work with other "smart" charge sources that require a 12V signal to boot safely. On top of the isolator, you're now adding a combiner, Echo type charger, battery to battery chargers etc. in order to have all banks charged automatically from all charge sources..

[Rusty123]

Just wanted to point back to my post above (#6) as another way of minimizing risk of inadvertent disconnection of alternator.

[skipmac]

Originally Posted by a64pilot

On my boat I believe that would be the 1,2,ALL, OFF. Switch?

If it's wired like my boat then yes it is.

[smac999]

Originally Posted by skipmac

I also like to put a switch between the start battery and the starter in case the solenoid hangs.

Of course. Every boat needs an engine switch and it can't be in engine room. But accessible outside somewhere incase of engine room fire

[smac999]

Originally Posted by Jorma

Thank you all for comments and directions to go.

The original question was how to protect the alternator - house bank connection. I’ve learned so far from the above:

1. During normal cruising, it is not a huge risk to have battery voltage on the alternator, when the engine is not running (a simple alt-house bat connection OK).

2. A “service switch” (Service Technician Disconnect Switch- thanks MS) is needed to cut that voltage when doing service. It can be in a hidden place as not used every day. After the service you must remember to close the switch before starting the engine. So hard to protect from human error! An AFD switch would help though (cutting field or ignition of the regulator).

3.There is still the fuse to worry about. If it blows when alternator running, the diodes will have a hard time once again. There might be some dual circuit CB that cuts the field as the CB cuts the main circuit (alt to bat). I admit that worrying about the fuse might come closer to OCD than common good boat care.

Unless you are servicing or removing the actual alternator itself there is no reason to cut power. Just boot / protect the alt post. I just run them to mrbf fuses. It takes 15 secs to remove the fuse. Likly only done once every few years if ever. No switch to turn off by mistake.

Starting engine with switch off will do no harm. It just won't. charge. Big difference from shutting down an alt already charging.

Alternator fuses (and chargers). Are fused at 150%. So if you have a 100a alt you use a 150a fuse. The Alt will never blow that fuse. Only if the alt wire shorts badly to ground. If that happens, the alt diodes will probably blow before or as the fuse blows anyways. So strap / protect the wires as well as fuse them.

[john61ct]

There are times with very HO alt setups on relatively low-HP engines, a depleted bank of high-acceptance chemistry will significantly reduce the output available to propulsion.

Not usually an issue just motoring along in open water, but maneuvering near shore or in an emergency, you may want the ability to kill field current from a spot in reach of the helm.

[Stu Jackson]

Originally Posted by john61ct

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Not usually an issue just motoring along in open water, but maneuvering near shore or in an emergency, you may want the ability to kill field current from a spot in reach of the helm.

Wouldn't that simply be the ignition switch (key)? Mine turns the power to the external regulator off.

[Jorma]

Originally Posted by smac999

Starting engine with switch off will do no harm. It just won't. charge. Big difference from shutting down an alt already charging.

This is a little bit confusing. Think a regulator that is hooked to the house battery (power-in; nro 2 in MC-614) as is the sensing wire. I would think that the alt will start pushing current with no place to go if the service switch is open when staring the engine. Is there some kind safety feature in Balmar MC-614 that would prevent it?

If you connect the power input (nro 2) on the alternator side of service switch it would not start the regulator when the engine is fired as the regulator receives no power with service switch open. Would this be a good idea for the connecting the power-input cable of the reg? Perhaps also the sensing wire as it would react to the rising voltage.

[Bleemus]

Wire alternator directly to house bank and use an ACR and you shouldnt have to worry about diodes anymore. Many charter boats are no longer built with the old 1-2-Both-Off switches. They have the Blue Seas Off-On-Combine switch or similar with ACR or Echo type relays. Idiot proof.

[john61ct]

Originally Posted by Stu Jackson

Wouldn't that simply be the ignition switch (key)? Mine turns the power to the external regulator off.

I'm talking about turning off alt power output, removing all its load from the pulley / belts while the propulsion engine is running to give all available engine HP to propulsion when needed.

An AFD-feature bank switch has this built in, but may not be mounted at the helm.

[smac999]

Originally Posted by Jorma

This is a little bit confusing. Think a regulator that is hooked to the house battery (power-in; nro 2 in MC-614) as is the sensing wire. I would think that the alt will start pushing current with no place to go if the service switch is open when staring the engine. Is there some kind safety feature in Balmar MC-614 that would prevent it?

If you connect the power input (nro 2) on the alternator side of service switch it would not start the regulator when the engine is fired as the regulator receives no power with service switch open. Would this be a good idea for the connecting the power-input cable of the reg? Perhaps also the sensing wire as it would react to the rising voltage.

There is no current produced if it has no where to go

Different then shutting off current after it is already flowing.

Though having the reg power from that switch would be a good idea. Not the sense or ign. The power.