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custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 19517

You can always stick in a diode over the coil too, to suppress voltage spikes and EMI.
The problem happens when the switch drops out with voltage contained in the coil.
It can tend to fly back up the switching positive feed.
Many smaller relays have them in-built.
HD relays rarely do, but you can fit externally easily enough anyway and the coils on these are typically about only about 300mA.

For the instance of the OP’s purpose a Durite VSR would be fine.
We all do things differently, but the voltage drop on cranking is something to bear in mind.
If it kicks in once alternator charging voltage is achieved that’s ideal.
But voltage can vary even due to ambient temp and VSR’s can vary on their switching voltages. That can vary for lots of reasons. Diesels Lives Matter. ⛽️🛢️👨‍🔧🧰⚙️
And if You Love the Country, then we’re on the same side ~
I got’ love for Britain, I got’ British pride’. 🇬🇧

13th Sep 2019 6:02pm

sako243

Member Since: 08 Jul 2014
Location: Wales
Posts: 1185

1994 Defender 110 300 Tdi CSW Alpine White

Bear in mind that the diode across the coil will only suppress fly-back voltages on the circuit activating the relay. Not any fly-back generated from the contactor suddenly disconnecting any load.

You'll also need a diode rated for >~5W (at least a peak rating) given P=VI=14*0.3=4.2W. Ed
82 Hotspur Sandringham 6x6
95 Defender 110 300Tdi

13th Sep 2019 6:22pm

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 19517

Diesels Lives Matter. ⛽️🛢️👨‍🔧🧰⚙️
And if You Love the Country, then we’re on the same side ~
I got’ love for Britain, I got’ British pride’. 🇬🇧

13th Sep 2019 8:11pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5413

2006 Defender 110 Td5 USW Zermatt Silver

I’ve fitted Durite VSR to three Land Rovers now, and never had an issue with them. Very simple to install and require not maintenance or operation.

Joins batteries at 13.3v
Disconnects at 12.6v
They also have a 5 second delay in operation so won’t keep flicking on and off.

If, which I never have, needed to jump start myself I would just join my batteries physically as they are next to each other.

https://www.simplysplitcharge.co.uk/0-727-...-charge-vw

14th Sep 2019 8:06am

windy81

Member Since: 14 Mar 2018
Location: North Wales
Posts: 311

why not get a battery to battery charger like those offered by Ctek. Much better IMO due to the charging profiles offered by Ctek, which enables the battery to be fully charged correctly. Leisure batteries don't charge that well from the alternator.

14th Sep 2019 10:25am

Gilloverland

Member Since: 12 Nov 2017
Location: Yorkshire
Posts: 61

Bit of a price difference though !

14th Sep 2019 2:27pm

windy81

Member Since: 14 Mar 2018
Location: North Wales
Posts: 311

Its a proper job though, and you can add solar or whatever if need be

14th Sep 2019 4:39pm

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