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Old 09-15-2012, 05:47 PM   #1
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Another question regarding battery cables,etc...

Now that I have my new battery charger properly installed and all of the batteries happily charging....I have another question, or maybe two:

Is it highly advisable to have a battery switch between the charger and the battery bank on each leg?

Is it highly advisable to also have a fuse between the charger and the battery bank on each leg?

Or both???
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Old 09-15-2012, 06:14 PM   #2
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I don't see any value in the switch. You do need a fuse near the battery on the positive wire to the battery charger. That fuse should be matched to the size of the wire. For example if the wire is 10 gauge then the fuse should be 50 amps or less to protect the wire from a fault to ground.

If by leg you mean positive and negative wires, you only need to protect the positive wire. The negative will be protected when the positive blows.

On the subject of switches, it is good practise to have a main on/off battery switch that can disconnect the batteries in case of an electrical fire. Ideally it should be located outside of the engine room.

David
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Old 09-15-2012, 06:23 PM   #3
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Now that I have my new battery charger properly installed and all of the batteries happily charging....I have another question, or maybe two:

Is it highly advisable to have a battery switch between the charger and the battery bank on each leg?

Is it highly advisable to also have a fuse between the charger and the battery bank on each leg?

Or both???
If the battery charger was propely intalled, there will already be fuses within seven inches of each battery terminal and either internal fuses for each output on the charger or external fuses within seven inches of the charger connections.

You don't need a switch between the charger and the batteries, just turn the charger off if you don't want to charge the batteries.
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Old 09-16-2012, 08:22 PM   #4
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A fuse in the positive cable is not required on any cable that goes to an engine starter motor as per ABYC E-11.
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Old 09-18-2012, 08:42 AM   #5
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A fuse in the positive cable is not required on any cable that goes to an engine starter motor as per ABYC E-11.
While that is correct, it doesn't apply to this topic. Overcurrent protection is required in the battery charging conductors (at both ends).

Why at both ends? Because voltage (and current) can be supplied from either the charger or the batteries.
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Old 09-18-2012, 12:03 PM   #6
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Ron:

This issue gets debated from time to time. IMO there is no need to fuse a battery charger at its source, only at the battery end. Why?

The wire from the battery charger to the battery must be sized to handle the maximum current that the charger can supply. So if you have a 40 amp charger, the wire should be 10 gauge or larger and should have a 50 amp fuse at the battery.

If for some reason the wire shorted to ground, the battery fuse would blow. The charger would continue to supply power thrugh the ground fault but the wire could handle that current forever.

So the general rule is: size the wire for the current and protect the wire from overcurrent situations, in this case with a fuse at the battery.

David
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Old 09-18-2012, 12:08 PM   #7
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.Why at both ends? Because voltage (and current) can be supplied from either the charger or the batteries.
Ron, that is a very good and often overlooked point. It is also why when working on AC circuits it is important to turn off both the shore power or generator supply, but also the batteries feed to the inverter. Batteries can zap you on either side.

Edit: Just saw what David said. That is exactly the way my system is set up. There are fuses between the charger and the 3 battery banks.
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Old 09-18-2012, 12:50 PM   #8
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While that is correct, it doesn't apply to this topic. Overcurrent protection is required in the battery charging conductors (at both ends).

Why at both ends? Because voltage (and current) can be supplied from either the charger or the batteries.
It pertains to this topic as the issue of fuses was brought up in the port prior to mine.

I am ABYC Standards Certified and can tell you they definetly do not require fuses in any negative cable
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Old 09-19-2012, 06:01 AM   #9
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I am ABYC Standards Certified and can tell you they definetly do not require fuses in any negative cable

However many charge systems and SOC units require a shunt in the neg leg.

A shunt can be a fuse under some overload conditions..
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Old 09-19-2012, 06:46 AM   #10
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I am ABYC Standards Certified and can tell you they definetly do not require fuses in any negative cable

However many charge systems and SOC units require a shunt in the neg leg.

A shunt can be a fuse under some overload conditions..

Any metal can fuse under certain conditions but a shunt is not designed as a fuse.
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Old 09-19-2012, 08:33 AM   #11
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It pertains to this topic as the issue of fuses was brought up in the port prior to mine.

I am ABYC Standards Certified and can tell you they definetly do not require fuses in any negative cable
Of course fuses aren't required in a negative cable. I don't believe I or anyone else implied that.

I will try to be very clear and specific:

Overcurrent protection (fuse or circuit breaker) must be installed at both the charger and the battery ends of the positive conductor (that is what I meant in my previous post if it wasn't absolutely clear) between the two.

The reason for this is that both the charger and the battery are capable of supplying current to the conductor. If overcurrent protection is only installed at the charger end and there's fault in the conductor, current from the battery could overload the conductor and cause overheating or a fire.

If overcurrent protection is only installed at the battery end and there's fault in the conductor, current from the charger could overload the conductor and cause overheating or a fire.

Note: Many chrgers include output overcurrent protection in their design so if this is the case, the installer must only install protection at the battery end of each leg.
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Old 09-19-2012, 08:37 AM   #12
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I am ABYC Standards Certified and can tell you they definetly do not require fuses in any negative cable

However many charge systems and SOC units require a shunt in the neg leg.

A shunt can be a fuse under some overload conditions..
I have no idea what you are trying to convey here. Can you try again?
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Old 09-20-2012, 06:13 AM   #13
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I have no idea what you are trying to convey here. Can you try again?

The point is a large short , of say a starter cable could make a shunt into a fuse by accident.

This should be known to the folks attempting to get the boat going as another item to be checked.

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Old 09-20-2012, 09:33 AM   #14
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I have no idea what you are trying to convey here. Can you try again?

The point is a large short , of say a starter cable could make a shunt into a fuse by accident.

This should be known to the folks attempting to get the boat going as another item to be checked.

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Using that definition, any piece of wire could be considered a "fuse" because it could melt and break the circuit with enough current.

A "real" fuse is a device inserted into a circuit that's designed to melt and break continuity in a controlled manner at a specific current. In most fuses, steps are taken to control any heat, molten material, sparks, etc. and contain them within the device itself.
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Old 09-21-2012, 05:58 AM   #15
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"Using that definition, any piece of wire could be considered a "fuse" because it could melt and break the circuit with enough current."

That's how many car makers fuse many new cars."Fuseible link" AKA thin wire .

Normal wiring is supposed to be protected with some sort of over current device.

Starter circuits seldom are , except accidentally , my point on shunts.
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