I'm still not sure about the live feed I've taken for my heated seats. I've been thinking about it quite a lot and have come to the conclusion it isn't suitable.

For those that don't know, I've taken the live feed from the fans fuse (25amp fuse) and then linked a wire direct from that to my fuse for the seats (15amp)

Since I've linked the two feeds together, I think if they both draw the max current at any time it could overload the wire and cause damage / possible fire.

The fan wire will be rated for 25amp hence the 25amp fuse. I've then added the heated seat wire which is 15amp so technically it has the potential to draw 40amp through a 25amp wire. Normally I wouldn't be worried thinking it would just blow a fuse, but since it's the main feed, it's before the fuses in the fuse box so technically doesn't have any fail safe, unless it has another fuse elsewhere, but I don't think they have fuses before the fuse box...

So I need to know where I can take a reliable switched live, or... How to make this one safer!

I'm thinking I can either...

A ) Add an inline fuse into the direct feed before the fuse box, so that should monitor both feeds at the same time. Stick to a 25amp fuse which the wire is suited for so if they both ever draw extra that will blow.

B ) Add an inline fuse into the link wire I've linked from the main feed in to the fuse box from the fans to the heated seat, that should ONLY monitor the heated seat link wire and blow that fuse if I rate it to 15amp for the seats.

Could you not take a new wire from one of the beefy terminals above the comfort module?

Also, unless I've read it wrong, wouldn't option B be just two 15A fuses in series, with the possibility of 40A on the earlier stretch still?

Edited 14 February, 201610 yr by wiredsoftware

Also, unless I've read it wrong, wouldn't option B be just two 15A fuses in series, with the possibility of 40A on the earlier stretch still?

No, the live feeds have no fuse (that I know of) so yes... The heated seats will have 2 x 15amp fuses but, one is for the live feed and other would be after the feed for faults with the seat etc, if you get me?

Could you not take a new wire from one of the beefy terminals above the comfort module?

Yeah, I'm sure they are more than capable of handling the extra wire for the heated seats, however they are all perminant live feeds, I tested them to find out.

Sounds like all you need to do is where you have joined the 2 feeds, fit a 15 amp fuse before you connect the heated seat wire, That way your protecting the heated seat wiring and the other 2 cables are still protected by their own fuse still

Hopefully these poor drawings will help you understand what's fuses and what isn't

And then what I think would help, obviously not both, that's plan A and plan B together

Edited 14 February, 201610 yr by hutchysrs50

I was going to suggest to use the beefy ones on the bus bar above the CCM as mentioned by wiredsoftware for the main feed to seats (via a 15amp fuse as per those wire diagrams I put on the other thread).

I'm not sure it matters that these are permanently live as the other feed to your seats is going to be a switched live.

 

You could always do a test wired as I mentioned above to see if they heat with the ignition off, if they do, then look at finding a heavy duty switched live.

Edited 14 February, 201610 yr by Bogwoppit

All the wires on the bus bar are perminant lives, if I wire them using that live the seats will perminantly be heated if the switch is left on any number other than zero, even if the engine is off and the cars locked up, they will still keep heating untill the battery is flat.

I've looked for switched lives (admittedly not for ages) and the best one I could come up with was the wire for the fans since I knew it uses high current, all the others are small thin wires.

All the other wires I tested that look thick enough are perminantly live when tested.

Use a relay to switch the beefy permanent live energised by a light duty switched live and put a 15A fuse inline with the relay contacts.

The bus bar is above the central electrics control unit, the CCM is above the clutch pedal.

But I'd just take a supply from the bus bar on the fuse box. There is normally a spade type terminal on the bar itself. Then use the ignition live to trigger a four pin relay. Pin 2 on the head lamp switch or the blue/red wire on the brake light switch are good ignition live sources.

Adding fuses at any point you show in your diagram won't help.

If you add the 25 before the fuse box, it'll blow if both are on (assuming together they draw a bit under 40). Adding a 15 between the two points on the fuse box doesn't help either, it just means two equal fuses on the same path.

The relay option would work quite well, run the heavy duty path of the relay through the 15a, and you can probably get away without an additional fuse for the low current side just using an existing switched live that is after some fuse already.

Edited 14 February, 201610 yr by wiredsoftware

I'm very slightly confused, but only because I've never wired up a relay before, not even sure how they work, I can guess though basically (Google will help!)

I'm close to accepting I'm out my depth and paying a specialist to wire this up for me.

So would this not be for a 3 pin relay?

Pin 1 - live feed in from bus bar

Pin 2 - live feed out to heated seats

Pin 3 - switched ignition live, which will be taken from pin 2 on the headlight switch

Adding fuses at any point you show in your diagram won't help.

If you add the 25 before the fuse box, it'll blow if both are on (assuming together they draw a bit under 40). Adding a 15 between the two points on the fuse box doesn't help either, it just means two equal fuses on the same path.

The relay option would work quite well, run the heavy duty path of the relay through the 15a, and you can probably get away without an additional fuse for the low current side just using an existing switched live that is after some fuse already.

Adding the 25amp fuse before the feed will do the job then, will stop any damage happening and blow the fuse if I switch everything on, if it is to much current it would just blow the fuse and stop any damage or a fire which I'm worried about.

Granted not ideal but safter for now

Ok, 4th pin is for an earth?

Found this on Google....

So....

Car battery (bus bar) will feed pin 30, I'll link them with a 15amp inline fuse

Ground pin 85 I'll link to the same earth as the seats above the fuse box on the metal part of the dash

Car ign pin 86 will come from the suggested wire from the light switch

To accessory pin 87 will go to the fuse box as a live feed for the seats

Yes. You want a four or five pin relay (if you get a 5 pin, just ignore pin 87a, don't need it for your job). 12v auto relays are generally rated for 30-40a so should work nicely.

Basically, they work by switching on a separate circuit when another circuit is on. Both circuits are separate and can work on different loads and voltages.

The type you'll get also make a characteristic click noise when they make the circuit, so you can test that you've got the low current side done correctly before you move the wires for the high current side if you wish by listening for this.

Incidentally you mention about putting 15a fuse inline. I'd go higher on this, say 25A as it is only there to protect the relay. If 24.99A is pulled through, the relay will be fine, the 15a in the fuse box will blow instead to protect the seats with no harm done, which will probably be easier to access!

Edited 14 February, 201610 yr by wiredsoftware

I guess I'll look into this then, spade connectors that just push into the relay pins ok?

Or...

http://www.ebay.co.uk/ulk/itm/121332727298

That says normally closed.

I'm Guessing I need "normally open"

My head is hurting now, going to reread it all tomorrow and see what's what!

Edited 14 February, 201610 yr by hutchysrs50

You can download a pdf from the Kufatec website for the Polo 9N, but you need to enter your invoice number

Assuming you can do this and translate it to english it could be worth a read as the Polo must be very similar:

 

https://www.kufatec.co.uk/shop/en/volkswagen/polo/polo-9n/seat-heating-harness-vw-polo-9n?tab=anleitung

 

Otherwise the relay option looks pretty good.

Edited 14 February, 201610 yr by Bogwoppit

Here's one with connector and integrated fuse:

http://www.ebay.co.uk/ulk/itm/291613194408

Fine to use spade connectors instead if you want, as long as you mount somewhere where they cannot move around and touch ground

Edited 15 February, 201610 yr by wiredsoftware

I've emailed them ragaurding the manual since I don't have the details to download it. Will see what they are soon hopefully.

Thanks for the link, I might end up purchasing it shortly.

The main thing with fuse selection, is to choose a fuse that will blow before the wire carrying the current gets hot enough to start a fire.  So the wire gauge is the thing that should determine the fuse size.  Car batteries can supply plenty of current into a shorted wire to overheat pretty much any wire.  

But if you look at my little drawing at the start of the thread, the live feed isn't fused (I'm guessing because it's a direct feed so can't fault, it's then fused then goes to whatever it powers, radio, fans, heated seats, so when they fault the fuse blows.

I've wired them up like this thinking it's quite rare for fans to draw max current, I can only assume they will draw 25amp if they go from completely off to bring put on speed 4 (since 4 is the only direct feed setting that doesn't rely on the fan speed resister... But that's a different thread!)

As long as you are using the same gauge as the fan is from battery to fuse box for the relay arrangement, you'll easily handle the seat heater loads, and the fuse will prevent any damage to your buttocks if the heater itself shorts.

I'd be using slightly thinner wire than the fans for wiring in the seats separate.

Since I'm cutting out the fans completely we can forget about them now basically, the fans will be wired back up, just how it left the factory.

The feed from the bus bar to the relay will be used by this with the 15A option: http://www.ebay.co.uk/ulk/itm/361480628153

The feed from the relay to the fuse box will use the shorter 6" wire that is provided in the seat kit from kufatec.

I assume you're putting that inline fuse somewhere you can access it if the seats overload? As it'll be probably be the one that pops, not the one in the fuse box (assuming you're talking about putting this on the high current circuit through the relay, if on the low side then ignore me!).

Edited 15 February, 201610 yr by wiredsoftware