Battery Switch Wiring Questions

[thesaintlyone]

Probably the mess of the old system that caused it was a problem as it was a mess which it won't be

 

[lpdsn]

Probably the mess of the old system that caused it was a problem as it was a mess which it won't be

Take care then. Messing up with the small 12V wiring might just cause a bit of smoke or a small fire. 12V won't electrocute you, but if a mistake is made when messing around with the battery wiring a considerable amount of energy can be released in a very short time. I recently saw a poster that described, for example, an open ended spanner as a fuse of 2,000A (slow blow).

 

[thesaintlyone]

Battery switch = isolator switch.

The benefits of three switches include, one switch turns on the domestics, one turns on the engine battery, the 3rd is your emergency switch, you turn it on if the engine battery is flat and you can start the engine using the domestic battery, for instance. If the engine battery failed due to internal shorting you can turn it off and turn the emergency switch on, using the domestic battery for everything.

The Blue Sea switch is very similar in use, except that you cannot isolate the faulty battery, you'd need to disconnect it. It is, however, a million times better than the 1-2-both switch that you have now.

Cables sizes : Positive cables from engine battery to isolator and from isolator to starter, domestic battery to isolator all 35mm. Negative cable from battery to battery and batteries to engine all 35mm. If using three switches, interconnecting cables 35mm.

Negative from domestic battery to busbar and from isolator to busbar/fuse panel, VSR to batteries or isolators* at least 10mm.

* Technically, the VSR can be connected to the positive terminals of each battery or to the battery terminals of the isolators, whichever is easiest/requires the shortest cables.

If fitting the Blue Sea switch, the wiring diagram you posted is almost correct. I would connect the VSR to the battery terminals of the switch (very short cables) and put the fuses in the battery cables, next to the batteries. That said, there are cases where there is no point in fusing the battery cables. If they are located in an area where they cannot short there is little point fusing them. (Awaiting flaming).

What Cable size would you recomend from battery to VSR Looking to buy a pre fused cable on ebay will probably connect it to the Positive terminals of the batteries as to the switch would require 4ft cables what Fuse Ampage is required

Looking to buy something like this

http://www.ebay.co.uk/itm/240-AMP-I...hash=item465f062edc:m:mjRfO-h27D9uRa3kDHTcy4g

Regards

 

[PaulRainbow]

What Cable size would you recomend from battery to VSR Looking to buy a pre fused cable on ebay will probably connect it to the Positive terminals of the batteries as to the switch would require 4ft cables what Fuse Ampage is required

Looking to buy something like this

http://www.ebay.co.uk/itm/240-AMP-I...hash=item465f062edc:m:mjRfO-h27D9uRa3kDHTcy4g

Regards

Assuming that if using the Victron Cyrix you won't be using the start assist feature, you need cable sized for your charging systems. So making another assumption that you won't be generating more than about 70 amps i would use 10mm thin wall cable. You then need a fuse to (a) protect the 10mm cable and (b) protect the VSR, the VSR is rated at 120a and the cable at 70a, so your fuse would be 70a max. In reality, your charging output will be much less than that, so you can fit a much smaller fuse. The cable and fuse you linked to are much too big. I have a 30 amp blade fuse and it has never blown. If you have an alternator with a very high output, fit a bigger fuse (no bigger than the 70a max).

Fit the VSR close to the engine battery and if there is nothing for the cable to short out on, fit a single fuse close to the domestic battery.