How to choose battery selection switch-

[mitiempo]

Originally Posted by CharlieJ

@mitiempo #13


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.

I stand corrected.

[stormalong]

Originally Posted by mitiempo

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

This is correct. Unless you are running an electric cooker or microwave through an inverter. The switch should not get hot enough to matter. Wire size determines voltage drop. Smaller wire - greater resistance.

As I just said in another post: You should not crank your engine for more than a few seconds. The faster your engine starts the longer your starter motor will last. If you have it use preheat on a cold engine. Even if it is a hot day.

[MicHughV]

Squanderbucks is recommending [as do I] a Battery Selector Switch, c/w Alternator Field

what they say...

[bellrock]

The boat is 39 years old so I am assuming the cables are adequately sized.... since have never had a problem with them. I ordered the Blue Sea 9002e e-Series Battery Switch Selector w/Alternator Field Disconnect.

Thanks everyone.

[Squanderbucks]

Please read the article referenced by Jamme a few replys above. For this reason my two Bank system (Bank 1" Start" - 2 Group 31 and Bank 2 "House" - 2 8D ) uses Two of these switches interconnected.

By using two 1-2-1&2-Off switches you are able to fully isolate each Bank and still use them without juggling the switches all the time.
Rarely do I need to fiddle with the switches during regular operation. If replacing a battery set or if some problem arises with a set then they may be used to turn off a bank for change-out or system wiring repairs/upgrades.

Separate charging issues arise and there are several solutions often referenced on this site. But since my powerboat has twin engines - one alternator is connected to each bank and an onboard battery charger splits it's output to each bank and can regulate each independently.

With the boat running the battery charger is turned off and charging rely on the alternators. When docked the charger is on. There is a Balmar Digital Duo installed that allows Battery to Battery charging as a backup should one alternator fail but is normally turned off.

[Emouchet]

You should ditch any of those 1-2 switches. This is old thinking.

Use individual main battery switch for both Engine and service batteries.
So you have control for both your power circuit INDEPENDANTLY.

Then, on the charging side, use an automatic charging relay such as the Blue Sea SI-ACR.

Your service bank can be drain, and your startup battery will still be able to start the engine.

Those 1-2-All Switch are a killer, because you can be distracted and forget to switch it to the right position for charging/feeding power.

The SI-ACR does all this by himself. A joy to use. Install and forget...

[Shaneesprit]

Originally Posted by s/v Jedi

Take the nice and small 300A switch.

Yeah this will be fine, on larger engines (not pleasure craft) often 1000s of Amps at CCA but battery isolators only rated at 500A is quite normal. It’s not for opening under load or fault conditions.

[drdoyle]

I don't know if they are still made, but the Cole-hersey brand switches on my boat are very well made.

[Scubaseas]

Originally Posted by 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

Even with an ice cold engine with 24hp I doubt you would pull more than about 185 amps unless your starter is going bad. I.e. armature grounding to field. 120 to 150 amp would be my guess.