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SimonWH
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 Posted: Thu Mar 08, 2007 8:21 am Post subject: Ignition Relay
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Probably a question for Tim (fount of all electrickery knowledge!)
I want to fit a couple of power distribution blocks to the expedition truck. One will be perm live (but with a cut-off switch) the other will be live with ignition only.
What relay would I need to operate the ignition only circuit? Is it the same kind as a split charge system?
I want to run a live direct from the leisure batteries that only operates when the ignition is switched to the first position.
Cheers
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:)
Mud Obsessed
Joined: 06 Feb 2006
Odometer: 4337
Location: Norfolk
1995 Land Rover Defender
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| Posted: Thu Mar 08, 2007 2:39 pm Post subject: Re: Ignition Relay
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| Simon@Difflock wrote: | | Probably a question for Tim (fount of all electrickery knowledge!) |
This is just embarrassing 
I might have a couple of ideas here and there but I still have much to learn.
Anyway, back to your question.
Me, not being quite as bright as you seem to be suggesting, have read your question in a number of different ways...- If you want the relay engaged only when the engine is running then you will need something like a voltage sensitive relay (like the split charge relay).
- If you want the relay on in position-I and position-II then simply run a wire to operate the relay coil from the position-I contact. Be aware that on some key switches position-I goes dead when starting the engine (position III), but I don't know if the LR does this, but it could be solved with two diodes if it does.
- The next possibility is that you want the relay on in position I ONLY, ie off in all other positions - this could be done but may need a second control relay or some clever wiring of the relay coil to sneak an earth return from another source.
- For completeness, although I pretty sure this is not what you want, there is also this option: If you want it on only in position-II, even if the engine is not running, then pick up the relay drive from position II contact - same as the stop solenoid
You need to select a relay which will take your maximum current draw, but it is best not to over specify it too much as the relay needs some power to stay engaged and the more current the relay can switch the more power the coil is likely to need. The R70 relay on Vehicle Wiring Products web page might be suitable, although you can obtain similar relays from many sources.
--
Tim.
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-- Timothy Birt -- |
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mikeinatruck
Just got MTs
Joined: 02 Jun 2003
Odometer: 243
Location: Scotland
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| Posted: Sun Mar 11, 2007 12:46 am Post subject:
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If you want an ignition running trigger then take a spur from your alternator light, between light and alternator, to your relay. Then when the engine is running you will havea triggered relay.
of course if your alternator fails then you lose your feed.
Or use a relay in line with your oil pressure switch. I have this on mine for my fuel pump, you need a 5 pin relay though, this circuit then energises a second relay that comes from the battery to give you an engine running live.
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Got a V8 now....never bought so much fuel...... |
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Mud Obsessed
Joined: 06 Feb 2006
Odometer: 4337
Location: Norfolk
1995 Land Rover Defender
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| Posted: Sun Mar 11, 2007 6:26 am Post subject:
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| mikeinatruck wrote: | If you want an ignition running trigger then take a spur from your alternator light, between light and alternator, to your relay. Then when the engine is running you will havea triggered relay.
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This works with most alternators but I am aware of at least one where it can damage the regulator. You can't tell for certain which types are OK, without knowing the internal circuitry used inside the alternator regulator. For this reason alone I suggest using a voltage sensitive relay.
I have used the warning light to drive a a split charge system and it has another slight idiosyncrasy ... the engines revs need to be raised somewhat higher after starting before the alternator starts charging. This is due to some of the start-up current being 'stolen' by the split charge relay coil. Not really a problem as long as you know.
--
Tim.
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-- Timothy Birt -- |
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SimonWH
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| Posted: Sun Mar 11, 2007 10:05 am Post subject:
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When I fitted a split charge to our Transit camper using this method it killed the battery withing a couple of days. The alternator just wasn't charging anymore.
A bigger alternator cured it but that made it an expensive split charge system!
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