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

[Jorma]

I am replacing my Volvo 115 A alternator with Balmar AT-200 with MC-614. I am planning to run the VSR (single sense) from house bank to starter battery. All the chargers (alternator, shore power) will be feeding the house bank.The technician is proposing that we’ll have a main switch that cuts the connection between the house bank and alternator.

I am concerned about the mishap of somebody accidentally turning the main switch off when the engine running and blowing the diodes.

There are at least three ways I know to build the system

1) Use a switch with AFD (alternator field disconnect)
I have read somewhere that the alternators are somewhat self exciting when running, so that the AFD would not help (?)

2) Connect the house bank to alternator with no off-switch

3) Special product from Balmar :
Spike Protector (RSP-12) Fused diodes will fail prior to alternator diode damage

How have you solved this issue on your boat?

[Fuss]

This is how I did it.... get yourself a 200a Diode Splitter and this will stop power flowing to the alternator when the engine is off and there is then no way to make a mistake and blow the alternator.
Then, wire a bridge wire between the 2 output diodes so they share the load of 200 amps between them.
Now wire a switch from the input diode to one of the output diodes and switch this on when running the motor and you will remove the diode voltage drop problem.
The advantage of this is that you get all the advantages of not having live power at the alternator with no disadvantages of diode voltage drop and no possibility of damaging your alternator.

[Jorma]

Nice idea Fuss! Have to consider it. Many advantages.

I talked to Balmar support (great service as always) and got one more idea. That is using an AFD switch, but cutting the brown ignition wire instead of blue field wire. The advantage is that when reconnecting it will be smoother on the alternator.

They also told that the AT-200 is not self exciting. So ADF switch with ignition or field wire will be fine - cutting the output quickly enough.

[DeepFrz]

Another idea. Run the alternator directly to the main power bus, or directly to the house battery post with a fuse near the battery/power bus. Switch your main power panel.

I suggest you take a look at the current thread on rewiring and follow the links that Stu. posted.

[skipmac]

Originally Posted by DeepFrz

Another idea. Run the alternator directly to the main power bus, or directly to the house battery post with a fuse near the battery/power bus. Switch your main power panel.

I suggest you take a look at the current thread on rewiring and follow the links that Stu. posted.

Simplest solution, solves the problem. This is how I wired my system.

[Rusty123]

I used a blue seas key operated on off switch as an alternator service disconnect (which I think is what you're talking about). I had to slightly modify the keyway with a dremel to allow the key to be removed with the switch closed (it's designed to be removed with the switch open), but now I can just remove the key to avoid anyone absentmindedly opening the switch with the engine running.

Plus, the switch is installed on the bulkhead in the engine compartment near the alternator, which isn't really accessible underway, unlike most of the other electrical system switches, which are located in the battery compartment.

[FionaJC]

I have a starer battery and two 110Ah batteries for domestic. My alternator has an Adverc for regulation to maximise charging efficiency. I then have a VSR (Voltage sensitive realay) When the starter is re-charged, usually two minutes the VSR joins the doestic to the circuit and charges them all. I have a battery monitor by NASA marine watching over them and an overide switch to join them together if I need more power to start. Works beautifully.

[sailcrazy]

My 85amp main engine alternator is wired through a 90amp c/b directly to the main house battery bus (which gets the power back to each of the 3 house batteries for recharging). I do not have an On/Off sw; the system has worked perfectly since 2009. I also have a Balmer Duo-Charge connected to the house bank bus bar feeding the islolated start battery (1-way power flow) so my start battery is always charged up. and there is a paralleling sw if I ever needed to tie the 2 battery banks together.

[skipmac]

From much research and from previous experience with other setups it seems clear that the best way to wire charging to house and start batteries is to connect the charging sources (all charging sources: alternators, AC charger, solar, wind) directly to the house batteries (with a fuse or CB) and charge the start battery with a device like the Yandina Combiner, Duocharge, Echocharge, etc.

The reasons.

1. Alternator output is connected directly to the batteries so can never be accidentally switched off.

2. The house batteries are the ones that need the most charge since starting (in all normal circumstances) uses very little charge from the start battery.

3. A voltage controlled combiner will automatically charge the start battery any time there is charging voltage in the circuit so the start battery will always be charged.

4. The combiner will automatically disconnect the start battery when there is not a charging voltage present so the start battery will never be accidentally discharged.

5. Connecting the charging sources to the start battery then charging the house bank through a combiner can cause problems overloading the combiner if the house bank is drawing too much current.

6. Still very simple to add a switch or another way to bring the house batteries in for starting if needed.

7. This setup is the most KISS, foolproof method, does not rely on remembering to change a switch or turn on/off anything on the boat.

[S/V Alchemy]

Originally Posted by skipmac

From much research and from previous experience with other setups it seems clear that the best way to wire charging to house and start batteries is to connect the charging sources (all charging sources: alternators, AC charger, solar, wind) directly to the house batteries (with a fuse or CB) and charge the start battery with a device like the Yandina Combiner, Duocharge, Echocharge, etc.

The reasons.

1. Alternator output is connected directly to the batteries so can never be accidentally switched off.

2. The house batteries are the ones that need the most charge since starting (in all normal circumstances) uses very little charge from the start battery.

3. A voltage controlled combiner will automatically charge the start battery any time there is charging voltage in the circuit so the start battery will always be charged.

4. The combiner will automatically disconnect the start battery when there is not a charging voltage present so the start battery will never be accidentally discharged.

5. Connecting the charging sources to the start battery then charging the house bank through a combiner can cause problems overloading the combiner if the house bank is drawing too much current.

6. Still very simple to add a switch or another way to bring the house batteries in for starting if needed.

7. This setup is the most KISS, foolproof method, does not rely on remembering to change a switch or turn on/off anything on the boat.

Agreed. The "switch" should be between starter or house banks. With some sort of echocharger/ACR, your starter banks are kept close to 100% at all times and can be used as an emergency house bank should you need to work on that. Another advantage is that a greater proportion of renewable amps can be "captured" and put to use in the starter bank.

[Maine Sail]

Originally Posted by Jorma

The technician is proposing that we’ll have a main switch that cuts the connection between the house bank and alternator.

I am concerned about the mishap of somebody accidentally turning the main switch off when the engine running and blowing the diodes.


How have you solved this issue on your boat?

Your technician is correct and this switch is called a Service Technician Disconnect Switch.

Mishaps are easily managed by switch location but an AFD switch can add to the redundancy.

The switch should be placed in the engine bay/engine room, close to the alternator and clearly labeled "SERVICE TECH USE ONLY"

This switch should not be visible to normal occupants but a service tech should be able to kill all DC power to the motor when servicing it..

[skipmac]

Originally Posted by Maine Sail

Your technician is correct and this switch is called a Service Technician Disconnect Switch.

Mishaps are easily managed by switch location but an AFD switch can add to the redundancy.

The switch should be placed in the engine bay/engine room, close to the alternator and clearly labeled "SERVICE TECH USE ONLY"

This switch should not be visible to normal occupants but a service tech should be able to kill all DC power to the motor when servicing it..

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

[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.

[Maine Sail]

Originally Posted by skipmac

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

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...

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.

[Maine Sail]

Originally Posted by Jorma

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.

If it did not blow you'd have a hell of a lot more to worry about than blown diodes, like a boat fire....

An alternator fuse should be sized at 130% to 150% of the alternators output rating. If the is sized correctly, I prefer the 150% end of the spectrum, there will never be a case where the alt can blow the fuse unless the wire shorted and even then the alt did not blow the fuse the battery bank did... In that case, see sentence #1...

An alternator is a current limited device only ever capable of its rating or perhaps 105% +/- of its rating. A properly sized fuse will not blow unless it needed to.