Another wiring question re: Link 1000

[John]

I am planning out the wiring for the Link 1000 I bought. The schematic shows one wire running from the positive of the start battery to the control panel of the Link 1000 and two running from the positive of the house bank to the Link 1000 control panel. Is there any reason I can't run these wires from the posts on the battery selector switch to which the cables from these batteries run? This would mean a run of about 6-12" vs. 8-10' of this wire. I realize there may be a small voltage drop from the battery to the switch through the battery cable, but it seems to me that this would be less than any drop that happens in the #18 wire that would run the same distance directly to the batteries. Also, since it would run directly to the post of the switch, it would in effect be connected directly to the cable, meaning that the position of the battery switch wouldn't matter. Am I right about this, or is there something I'm missing?

Attached is a link to the owners manual for the Link 1000, for anybody who wants to look at it. If you scroll down to p. 12 in the manual, you will find the schematic.

 

[Don12364]

Nope!

John,
One wire to each battery positive is the voltage measuring connection and it really needs to go directly to the battery to avoid any voltage drops along the wiring from battery post to battery switch etc. It is vital that the Link reads the battery voltage accurately because it does all its decision making regarding the state of charge based on the voltage it sees.
For info the other wire to the house battery is only the power supply to the Link and it needs to be permanently 'ON' to measure the amps in and out of the battery, including when the battery switches are off and nobody is aboard.

BTW make sure to fit an in line fuse on each wire close to each battery post as these wires are always on and not protected by the boat's master switches etc.

 

[John]

Just to make clear...

Don, thanks for the explanation. Maybe this doesn't change anything, but you comment that the power supply needs to be on, regardless of the battery switch position. However, if I ran the wire to the back of the switch, to the post that the battery cable connects to the switch, it would always be "on" even if the switch is off. Maybe this doesn't make any difference as far as your explanation, though, and I should run these wires directly to the batteries anyway.

Also, thanks for the reminder about the fuses. The schematic makes that clear also.

 

[Don12364]

Yes

John,
You are quite correct insofar as the power supply is concerned; but I figured that whilst you would already need to run two wires to the positive battery posts then a third on the same route would be little extra trouble and make the installation easier for a future owner/electrician to understand. At least that is what I did on my H376 with the Link unit.
Regards,