How to choose battery selection switch-

[bellrock]

I have a sailboat with a 24 hp diesel motor..need to replace the 39 year old perko battery selector switch.

There are 2 battery banks,
1 ( house bank) is a set of 2 Duracell group 2 6 volt batteries wired in series.
230 amps @ 20 hours 230 cold cranking amps.

2.. ( starter) is a deep cycle AGM 12 volt, 545 cold cranking amps.

I am told that it is important to make sure that your battery selector switch is properly sized, but cannot find, after several hours of searching on line, including the perko, guest and blue sea sites, and guideline of what size switch is appropriate. For example, blue sea systems sells switches rated at
300 , 350,and 600 amp,

Can anyone point me to a guide or rule of thumb of what I should be purchasing? Electricity is not my strong point.. If I start the boat on "1 & 2", do I size it for the combined cranking amps of both sets of batteries.. size it for the higher rated cca, or what? Is there a downside ( other than cost) to having an oversized switch?

Thanks in advance! I'm a civil engineer, mainly cause I was failing my electrical course and bailed out.

[s/v Jedi]

Originally Posted by bellrock

I have a sailboat with a 24 hp diesel motor..need to replace the 39 year old perko battery selector switch.

There are 2 battery banks,
1 ( house bank) is a set of 2 Duracell group 2 6 volt batteries wired in series.
230 amps @ 20 hours 230 cold cranking amps.

2.. ( starter) is a deep cycle AGM 12 volt, 545 cold cranking amps.

I am told that it is important to make sure that your battery selector switch is properly sized, but cannot find, after several hours of searching on line, including the perko, guest and blue sea sites, and guideline of what size switch is appropriate. For example, blue sea systems sells switches rated at
300 , 350,and 600 amp,

Can anyone point me to a guide or rule of thumb of what I should be purchasing? Electricity is not my strong point.. If I start the boat on "1 & 2", do I size it for the combined cranking amps of both sets of batteries.. size it for the higher rated cca, or what? Is there a downside ( other than cost) to having an oversized switch?

Thanks in advance! I'm a civil engineer, mainly cause I was failing my electrical course and bailed out.

Take the nice and small 300A switch.

[smac999]

for engine starting I would take the normal size 350a one. it's easier to wire with more space then the 300a one. and it might fit in the existing hole. the 300a ones are tiny and hard to connect if more then a couple of wires.

all those switches are constant power rated. and likly rated double for ~30 secs. so they will handle 600-700a while cranking and most small engines will draw ~200-300a when starting

[Wotname]

The 300A Blue Seas switch has a 5 minute intermittent rating of 500A and a 30 second cranking rating of 900A. See https://www.bluesea.com/products/600...king_Key_-_Red and https://d2pyqm2yd3fw2i.cloudfront.ne...eb_version.pdf

The 350A Blue Seas switch has a 5 minute intermittent rating of 600A and 30 second cranking rating 1200A. See https://www.bluesea.com/products/110...witch_with_AFD

In your instance either one will do electrically speaking, choose the one which has the best physical footprint for your application. Physical sizes are shown on the website.

[stormalong]

This is my opinion. Do not sue me!

Don't buy Perko or Guest. I have disassembled a dead Perko. Cheapest piece of junk I have ever seen. Can't say I have seen a Guest taken apart but generally Guest products are poorly made.

Again, this is my opinion. Don't sue me.

[mitiempo]

Originally Posted by stormalong

This is my opinion. Do not sue me!

Don't buy Perko or Guest. I have disassembled a dead Perko. Cheapest piece of junk I have ever seen. Can't say I have seen a Guest taken apart but generally Guest products are poorly made.

Again, this is my opinion. Don't sue me.

I agree.

Blue Seas switches are the best choice. As posted above the 6000 series of smaller switches are fine but a 9000 series may be a better fit for the previous mount.

[Squanderbucks]

With your practice of combining the House and Start batteries for cranking and then switching to separate banks - I think you need to be sure and get a switch with alternator protection circuitry to allow this. Not all (mine don't) do and stating procedures need to be followed for what your equipment allows.

[GordMay]

Originally Posted by Squanderbucks

With your practice of combining the House and Start batteries for cranking and then switching to separate banks - I think you need to be sure and get a switch with alternator protection circuitry to allow this. Not all (mine don't) do and stating procedures need to be followed for what your equipment allows.

Squanderbucks is recommending [as do I] a Battery Selector Switch, c/w Alternator Field Disconnect [AFD]
See ➥ https://www.bluesea.com/resources/91
And ➥ https://www.bluesea.com/support/arti...witch_Position

Some Blue Sea Systems Battery Switches c/w AFD:
#3001 [600A Cont] ➥ https://www.bluesea.com/products/300...witch_with_AFD
#3003 [500A Cont.] ➥ https://www.bluesea.com/products/300...witch_with_AFD
#9002e [350A Cont] ➥ https://www.bluesea.com/products/900...witch_with_AFD

[bellrock]

Thanks to everyone for such sage advice.. I love this forum!

[Jamme]

A good read before installing a new 1-2-B selector: https://marinehowto.com/1-2-both-bat...onsiderations/

[MCOS]

Have you considered wiring your starter positive feed directly to the start battery through a solenoid and a battery cutoff switch before the solenoid. This provides a path to the starter independent of the selection switch.

Battery+ --- cutoff switch ---- solenoid ------ starter

There are cutoff switches available that mount to the battery terminal as well as ones that mount in line. Solenoid switch is usually mounted on your starter already.

[Bycrick]

When you look at the "continuous rating" of a battery switch, don’t forget the look at what the allowable heat rise is, and remember that some battery switches only handle their maximum rated current if you wire them with the largest possible wires. Apparently, they’re counting on the big wires as part of the heat sinking.

[mitiempo]

Originally Posted by Bycrick

When you look at the "continuous rating" of a battery switch, don’t forget the look at what the allowable heat rise is, and remember that some battery switches only handle their maximum rated current if you wire them with the largest possible wires. Apparently, they’re counting on the big wires as part of the heat sinking.

No, they are counting on the cables to handle the expected current.

[Bycrick]

You say banana, and I say banahna. If you don’t have big enough wires, the switch will get hot. It will likely stand less heat than the wire.

[CharlieJ]

@mitiempo #13

No, they are counting on the cables to handle the expected current.

The wire size and rating are interrelated and determined during the testing and certification of the battery switches. The wire size certainly is sized to ensure enough ampacity to handle the current and also to ensure that voltage drop requirements are met.

However, the battery switch ampacity is a function of the wire size used to act as a heat sink.