Charge splitting diodes.

[JimC]

As a drift, to overcome the dangers of diodes blowing due to the removal of a load, would not a simple filament lamp across the alternator output suffice?

I think a better way to avoid blowing the alternator diodes by accidental load removal is to fit a substantial diode between the alternator output and the battery +ve terminal, with its anode going to the alternator. In my case I've wired the diode across the engine battery's isolating switch.

 

[Graham_Wright]

I think a better way to avoid blowing the alternator diodes by accidental load removal is to fit a substantial diode between the alternator output and the battery +ve terminal, with its anode going to the alternator. In my case I've wired the diode across the engine battery's isolating switch.

Why not just hard wire it? The diodes in the alternator will stop the back current.

 

[JimC]

Why not just hard wire it? The diodes in the alternator will stop the back current.

In my case because the boat was fitted with isolator switches for both batteries and removing the engine one would have left an unsightly hole in the panel! so I retained it but made it harmless by fitting the diode.

 

[halcyon]

Now;- how about the light?! Also should you fuse the output? That implies the fuse would blow for over-current……………thus causing the diodes to blow? So is it a no-win situation? Or would the lamp idea save the diodes?

What are we trying to do ?

If the alternator is wire to the service battery permanently, what is your worry.

Why not fit a VSR between the engine and service battery, if your worried the service battery is isolated, the alternator is still connected to the engine battery. If you loose an alternator the other will charge both banks. If the load is low, the alternator with the lower regulator setting will shut down.

Brian

 

[Graham_Wright]

What are we trying to do ?

If the alternator is wire to the service battery permanently, what is your worry.

Why not fit a VSR between the engine and service battery, if your worried the service battery is isolated, the alternator is still connected to the engine battery. If you loose an alternator the other will charge both banks. If the load is low, the alternator with the lower regulator setting will shut down.

Brian

There are two service batteries hence the need for a splitter.

 

[ghostlymoron]

There are two service batteries hence the need for a splitter.

Two service batteries can be wired in parallel and charged together using a VSR (or diodes).

 

[Graham_Wright]

Two service batteries can be wired in parallel and charged together using a VSR (or diodes).

Think that's what I said!

Not in parallel;- seen that on a charter boat. When one goes, t'other follows.

Guess you meant paralleled by the VSR. But diodes seem better in my case and I've just found some by Lucas in the "waiting to be fitted pile" in the garage.

 

[ghostlymoron]

Think that's what I said!

Not in parallel;- seen that on a charter boat. When one goes, t'other follows.

Guess you meant paralleled by the VSR. But diodes seem better in my case and I've just found some by Lucas in the "waiting to be fitted pile" in the garage.

Not sure of your setup but many boats have 2 battery banks, 1 is the 'start' battery solely for starting the engine, the other is the 'service' battery bank which is used for everything else - lights, instruments etc. The service battery bank can have any number of individual batteries connected in parallel to provide 12v.

 

[lw395]

Not sure of your setup but many boats have 2 battery banks, 1 is the 'start' battery solely for starting the engine, the other is the 'service' battery bank which is used for everything else - lights, instruments etc. The service battery bank can have any number of individual batteries connected in parallel to provide 12v.

Some boats have split service banks so the fridge can't take out the nav lights or gps etc, or so the windlass or thruster have dedicated batteries.

 

[Graham_Wright]

The service battery bank can have any number of individual batteries connected in parallel to provide 12v.

It is supposed to be bad practice as if one battery fails it will take the other(s) with it. We chartered in Greece and that is exactly what happened to the same set up.

 

[pvb]

It is supposed to be bad practice as if one battery fails it will take the other(s) with it. We chartered in Greece and that is exactly what happened to the same set up.

I don't think it's "bad practice", nor do the countless thousands of boatowners who have two or more domestic batteries connected in parallel (mine has 6 in parallel). It's practically essential if you want to run a heavy load such as an inverter. In the unlikely event that one battery develops a shorted cell, the voltage of the bank will drop, but the other batteries won't be ruined.

 

[halcyon]

I don't think it's "bad practice", nor do the countless thousands of boatowners who have two or more domestic batteries connected in parallel (mine has 6 in parallel). It's practically essential if you want to run a heavy load such as an inverter. In the unlikely event that one battery develops a shorted cell, the voltage of the bank will drop, but the other batteries won't be ruined.

Also worth remembering that each 12 volt battery, is made up of 6 batteries linked in series.

I've been designing charging systems now for 40 years, and it is only recently that this has come to light. I think it may lie in charging a bank with a faulty cell, this effects charge to the remainder, you get surface charge, little capacity , and shortened battery life. But it is down to battery maintenance, not battery layout.

Brian