auto electricians

what size fuse do you suggest?

John,
You say: "It's good practice to have a fuse right at the positive terminal of each battery and connect to the batteries through the fuses"

Why would you use a fuse between the 2 x batteries wired in parallel , I've never, ever seen this done on any 12v battery bank anywhere previously.

What type & size fuse would you recomend ?? (as Stewart has also asked)

Maîneÿ . . .

Stuart, Mainey,

There's a lot of energy in a battery, capable of doing damage and causing fire. It's not clear from Tuck's description whether the batteries are side by side, close together or maybe well separated. If they are sitting side by side as a battery bank, they could certainly be wired directly in parallel and a single fuse be used for the pair. If they are separated though, I'd fit a fuse to each battery as Peter has shown in his diagram.

What size fuse? Assuming these batteries are used only for "domestic" purposes, like running lights and a fridge, I'd use 20A or 30A, big enough to handle the load easily, small enough to prevent damage.

John

you said in your comment to put a fuse between batteries, you quoted 20-30 amp fuses, when your batteries go flat and are in need of a charge from the alternator, the alternatormay have the capacity to charge at 140 amps what happens to the flat battery?

Stuart,

Have you ever seen a 140A alternator pump 140A into a deep cycle battery??? The internal resistance of the battery, coupled with the wiring and switching resistance will ensure that it never happens. The alternator voltage is determined by feedback from the cranking battery, so will never rise high enough to force that sort of current into a deep cycle battery. (Of course, if it did, you'd need the fuse to protect the battery!)

I've used 20A or 30A fuses in that position for years. I also monitor charging current continuously. I've never seen more than 20A flow into my batteries.

Do you have a constructive comment to make? What would you recommend?

John

John,
I've this *question* for you, - What’s the value of having a 140 Amp alternator ???

You've said above: "I've used 20A or 30A fuses in that position for years. I also monitor charging current continuously. I've never seen more than 20A flow into my batteries"

You believe the maximum amperage produced by your 140 Amp alternator is just 20 Amps, this is obviously because it would 'blow' your 20 Amp fuse?

So according to your information, to have an alternator that can produce anything above 20 Amps is a complete waste of time, however I don’t believe Toyota & Nissan are aware of that information ?

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John, then you say: “The alternator voltage is determined by feedback from the *cranking* battery, so will never rise high enough to force that sort of current into a deep cycle battery”

What absolute rubbish, you obviously don’t understand the Deep Cycle battery is wired in parallel to the Cranking battery when it’s being charged.

Effectively these two batteries are in fact just one large single battery with the exact same voltage.

The alternator voltage is then determined by feedback from this one large battery, (Cranking and also Deep Cycle battery combination) not from just the Cranking battery at all.

Please keep information factual, I hope you will consider this as 'constructive comment' :-)

Maîneÿ . . .

Mainey,

I'm fed up with your ignorance and abuse. If you can't play nicely, go and play elsewhere.

I will not in future respond to your needling.

John