Wiring to the alternator for leisure battery

[Jambeers]

Hi, 

I'm trying to fit a leisure battery to my mk3 mondeo TDCI (53 reg).
All the battery wires, relay and fuses are fitted the only thing i'm left to do is get the trigger for the relay. 
I'd like to have it only live when the engine is running, so i was thinking of getting a wire from the alternator. 
I've looked in Haynes and i think a wire runs through a fuse in the fusebox in the engine bay.
Which brings me to my question,
Have has anyone tried wiring straight off the alternator before and if so got any pictures or tips?
Or can you think of a better line to run the trigger off? 
 

Cheers!
 

[al2052]

Why not use a auto sensing relay from a permanent live feed, the type used on caravan feeds which senses the rise in charging voltage to switch the feed on and switches off when engine stops, I used this way for years to charge my wifes mobility scooter in the boot.

[Jambeers]

11 hours ago, al2052 said:

Why not use a auto sensing relay from a permanent live feed, the type used on caravan feeds which senses the rise in charging voltage to switch the feed on and switches off when engine stops, I used this way for years to charge my wifes mobility scooter in the boot.

Yeh, in hindsight that would have been a better move, but I've already got/installed the kit with a normal relay and I've got to have it finished for Thursday.

I've got a couple of ideas atm:
1 - Trigger it off the second key position and have a switch so i can turn it off if i turn the engine off but want the AC or something on. Not the best solution but may do for now.
2 - I'm also tempted to make a latching circuit off key position 3 so it will only start after i've cranked the engine but i'm not sure if that could cause a problem when i start.
3 - Stick an arduino in the i can set timing etc but that may be a bit much for the little time i have left.

 

[al2052]

Sorry not familiar with MK3 Wiring/alternator having MK4 with smart charging, but in days past we used to manufacture standby gensets and one way we used to hold until running was to feed a relay from WL on the alternator which in days past used to feed the warning light, not sure if still fitted on latter days alternators, does the mk3 have a battery saver relay fitted ?

[iantt]

just get a voltage sensing relay and swap it for the existing normal relay, no extra wiring at all, cant see the issue?

[iantt]

Like this one

[al2052]

seems the obvious way

[Jambeers]

On 27/07/2016 at 10:16 PM, al2052 said:

seems the obvious way

Yeh, in hind sight i should have brought a sensing one. But they're about £40 to buy so ideally i'd use what i've got, i know it's not much but it would increase the cost of the job by 50% again. 

I was wondering if anyone had wired anything straight off the alternator / the battery charging circuit, if it was easy i'd give it a go, if not i'll look into a voltage sensing relay. 

 

 

On 26/07/2016 at 10:30 PM, al2052 said:

Sorry not familiar with MK3 Wiring/alternator having MK4 with smart charging, but in days past we used to manufacture standby gensets and one way we used to hold until running was to feed a relay from WL on the alternator which in days past used to feed the warning light, not sure if still fitted on latter days alternators, does the mk3 have a battery saver relay fitted ?

I'll look into warning light, thanks for the idea!
 

[al2052]

Your way over the top with your price for relay, quick look on fleabay the same one 30amp rating  I used at £12.69 post free, even if you find WL on alternator you will still need relay plus substantial wiring front to back, to me it makes sense and simpler to just use smart relay at that price,  no brainer.

http://www.ebay.co.uk/itm/TEC3M-12v-Charge-Relay-Splashproof-Holder-FREE-30Amp-DC-Multi-Purpose-Smart-/331929432759?hash=item4d488932b7:g:nTUAAOSwyQtV4ZIM

 

[al2052]

Just to Add, I fitted mine in a 4 x 4 plastic box with illuminated cigar lighter  socket fitted and flying lead with plug into rear socket in estate,, the mk4 estate rear socket stays alive all the while, I used a 12v/240 volt inverter to plug in the scooters mains charger at 24volt, and it worked well. this way I could virtually use anything i.e cool box or drill etc.

[Jambeers]

14 hours ago, al2052 said:

Your way over the top with your price for relay, quick look on fleabay the same one 30amp rating  I used at £12.69 post free, even if you find WL on alternator you will still need relay plus substantial wiring front to back, to me it makes sense and simpler to just use smart relay at that price,  no brainer.

http://www.ebay.co.uk/itm/TEC3M-12v-Charge-Relay-Splashproof-Holder-FREE-30Amp-DC-Multi-Purpose-Smart-/331929432759?hash=item4d488932b7:g:nTUAAOSwyQtV4ZIM

 

 

14 hours ago, al2052 said:

Just to Add, I fitted mine in a 4 x 4 plastic box with illuminated cigar lighter  socket fitted and flying lead with plug into rear socket in estate,, the mk4 estate rear socket stays alive all the while, I used a 12v/240 volt inverter to plug in the scooters mains charger at 24volt, and it worked well. this way I could virtually use anything i.e cool box or drill etc.

Thanks for the link, I didn't realise they were that cheap. I must be looking in the wrong places, i'll get one on order.

on a side note, out of interest i may still look into pulling signals off a warning light, if i do i'll post up the results. 

[Jambeers]

On 09/08/2016 at 0:45 PM, Jambeers said:

on a side note, out of interest i may still look into pulling signals off a warning light, if i do i'll post up the results. 

I felt i should give a bit of a an overview of my last weekend of trying to wire off the warning light. 

After referring to the haynes manual to find the colour codes of the wires from the battery charging circuit to the ECU my work began, i found the wires leading to the ECU and started measuring them with my DMM. no luck. I found one that was the battery voltage but not what i was looking for (i do have the wires i tested written down if anyone wants anymore info on what not to look at). 
So then the dash came apart to get to the instruments wiring, again after trying to find the battery warning light i had no luck. So dash back together and onto the last ditch attempt of looking for something useful in the engine bay. Battery out, fusebox up, again no luck. I may have been able to find a wire from the alternator but i didn't fancy hacking it apart to test them. 
So to summarise, 

On 25/07/2016 at 10:20 PM, al2052 said:

Why not use a auto sensing relay from a permanent live feed, the type used on caravan feeds which senses the rise in charging voltage to switch the feed on and switches off when engine stops, I used this way for years to charge my wifes mobility scooter in the boot.

After 3hrs wasted, I should have heeded your advice from the beginning. 

Thanks for the help!