I have been using the Stancor 120-901 relays for many years in several
vans. It works fine. As for the voltages involved, keep in mind that it
is the relay coil voltage that they are talking about and depending on
how you power the coil the voltage can be quite a bit less that the
alternator output voltage.

Mark

pickle vanagon wrote:
> I know the stancor 120-901 relay is popular among listmembers for
> dual-battery setups, so I ordered one when I was preparing to do my big
> electrical project.
>
> I finally got around to looking at the detailed spec sheet, and see that the
> relay is rated for 12v of coil voltage, and is suited to take up to 10% more
> than that.  (The spec sheet is here:
> http://www.stancor.com/wrdstc/pdfs/Catalog_2006/Pg_052_53.pdf).   Of course,
> 10% more than that is just 13.2 volts, which is below what you'll see in
> your van when driving around.  In fact, at the bottom of the spec sheet,
> Stancor has printed the warning:
> "Note: Caution must be used in coil selection for use in 12 volt systems
> where battery charging may expose coil to continuous, higher-than-rated
> voltage. Stancor will not be responsible for consequences of misapplied
> solenoids."
>
> So, is this relay not such a good choice after all?
>
> On the other hand, it seems they have another relay (120-914) intended for
> automotive use and rated up to 15volts (its on the same spec sheet).  If I
> read the spec sheet, this will come online at 11.25 volts (75% of 15), which
> should be fine.  Maybe this is an acceptable choice?
>
> Thoughts?
> -Wes
>