[want33s]

Someone posted a diagram showing how to wire up a relay for thalternator sense wire a while ago..
I think it was NissVit..... I've looked and looked but can't find it... Anyone got a link?

[royce]

no but it would look like this

pin 30, from battery
pin 87 to sense pin on alt
pin 85 standard sense wire (comes on with ignition)
pin 86 to earth

you are just switching direct from teh battery volatge into the alt

[want33s]

royce wrote:

no but it would look like this

pin 30, from battery
pin 87 to sense pin on alt
pin 85 standard sense wire (comes on with ignition)
pin 86 to earth

you are just switching direct from teh battery volatge into the alt

Cheers Royce.... That's how I thought it would be but wanted to confirm it.

[Ben_Sierra]

Can someone explain the reason for hooking a relay up in there?

[want33s]

Ben_Sierra wrote:

Can someone explain the reason for hooking a relay up in there?

To correctly charge the battery the alternator needs to know its voltage but Sierra wiring being what it is, the sense wire actually reads a lower voltage than what is in the battery so the alt can overcharge it.
The relay setup tells the alt exactly what voltage is in the battery.

[royce]

depending on what voltage you end up with at the battery sometimes it can be better to leave it how it is as well, a lot of batteries wont fully charge at normal battery voltage so the extra kick helps em along and prevents sulfating, the downside is they boil more so you need to top them up more

[want33s]

I just hooked up a Redarc dual batt controller that has a fault code function built into the LED on it...
It was flashing twice indicating an OVER VOLTAGE .. It shuts down at 15.5V according to the book but it's actually 15.25V..
The voltage at the battery while running was 15.2-15.5V. I connected the sense wire direct to the battery and the voltage dropped to 14.8V instantly and the Redarc unit cut in and worked.

Now I just have to hook up a relay for the sense wire and an over-ride button for the Redarc unit.

[Ben_Sierra]

If its just about voltage drop through the crappy Sierra wiring wouldn't it be far easier and just as effective to replace the original sense wire with a thicker one?

[royce]

Technically yes but its a poor design, the sense wire in one way or another would go from battery positive > across to passenger firewall loom > back to fuse box > up to ignition switch > back to fuse box > back over to passenger firewall loom > back over to teh alternator, so even with new cable youll see drops through minute corrosion in each connector and other items along the line drawing power and causing drop

Just like you fit relays to lights to make the power path as short as possible with the least interferance from other items this gives the most accurate reading possible