PTC (Auxiliary) Heater for Quicker Heating in Winter

[vindaloo]

...It's getting a fair bit cooler now... and It's only gonna get colder.. You must be tempted to hook it straight up on to a power source, (with a decent fuse & switch of course)?? Can just have the switch in the drivers side glove box or something until you get in installed properly.. no need to hack the dash about.

Controlling it manually, Just to see how effective it is and enjoy it now it's in it's OEM position.. I've gotta admit, If I start using my car on winter mornings again I'd seriously consider this, though hooking into the switched live feed rather than the permanent would be the clever way to do it... It'd only take one forgetful morning to end up with a VERY flat battery at the end of the day.

Would have to be a fairly meaty relay, I'd have thought. It's rated at 80 amps! Short of a Dr frankenstein "wall mounted" switch, I doubt a mere switch would do the job.

At the OP, might be worth trying a more international approach in tracking down the PTC loom.

J.

[Benjiman]

Would have to be a fairly meaty relay, I'd have thought. It's rated at 80 amps! Short of a Dr frankenstein "wall mounted" switch, I doubt a mere switch would do the job.

Any low current switch could be used - that's the beauty of a relay! No 'Egor, it's alive!' moments as you turn on the heat though!

150a 12v relay - a little overkill but surprisingly small: Height;45mm, Width;63mm, Depth;40mm

http://uk.farnell.com/te-connectivity/v23132a2001b100/relay-high-current-150a-12v/dp/9659048

[Rob.]

Actually, using the ignition switching feed to trigger the relay.. but with a manual switch in line as well, to turn it off once the engines up to temp, would be quite clever.. cuz it would mean you couldn't physically leave it switched on with the key out..

[Rob.]

Annual BUMP!

To add to my last comment.. A timed circuit, in line from the ignition circuit could be a good solution.. retaining the manual switch for permanent off in warmer months..

[piggoy]

I thought I would ressurect this old thread. BUMP!!

 

Whilst I sat in the car (mk1 vrs) yesterday I was shivering uncontrollably waiting for the clattering diesel engine the heat up and demist the windows. The experience inspired me to remember this post from several years ago where I realised that nothing ever came of it. What if we could retrofit the PTC heater from the VW Polo??

 

We are already aware from the previous posts that the Polo part (6Q0963235) will fit into the hot air assembly. The problem is that the Fabia has no connection in the wiring harness for the heater. This is annoying since the EU spec diesel Fabia was fitted with the heater. So the bottom line is that we need to provide our own electronic control.

 

The electrical connection to the heater is very simple. It is three input wires (red, black and white) and one earth return (brown). The three input wires are connected to three individual heating elements within the assembly therefore allowing a three level control system. These inputs are electronically switched to a 12V supply by the ECU depending on coolant temperature, internal temperature and alternator load. Obviously we won't be able to tap into this level of control. However I feel we can devise a simple relay switched circuit to connect the heating elements from the Terminal 30 connection block (permanent 12V supply).

 

The relay needs to be operated by a timed circuit to ensure that the heater is not operating continuously. We need to ensure that the heater can only be operated when the engine is running. We also want the driver to control whether or not it switches on. What signal can we tap into?? The best signal we can tap into is the indication LED on the rear heated window switch. We can convert the switch to operate both the rear heated window and the PTC heater whilst satisfying all the requirments above. This should be a neat solution, as best as "OEM style" we can get.

 

Am I missing anything? Answers on a postcard please :-) I'll post some circuit diagrams soon.

[Breezy_Pete]

This is a nice idea.  Suitably thick wiring (directly from battery fusebox, I should think), suitably fused and protected from physical damage, and you're onto a winner here.

A nice feature would be a low-voltage inhibit, which would stop it working if the battery/alternator voltage was below a certain level.  A fairly simple comparator circuit?

[piggoy]

This is a nice idea.  Suitably thick wiring (directly from battery fusebox, I should think), suitably fused and protected from physical damage, and you're onto a winner here.

A nice feature would be a low-voltage inhibit, which would stop it working if the battery/alternator voltage was below a certain level.  A fairly simple comparator circuit?

That's a good idea, and a fairly simple comparator circuit like you describe. I think the problem is how to calibrate it - what voltage is too low? And what do you use as a reference?

 

Another problem I foresee is whether or not the fan should be running when the heater is powered. Would the heater be at risk of overheating if the fan is not running? Would we also need a fan operation detection as a safety feature? Looking at the circuit diagram in the Haynes manual I cannot find an obvious signal to use. The fan switch/dial is simply a variable resistor connecting the fan to the 12V supply.

Edited 7 November, 2014 by piggoy

[Breezy_Pete]

I guess your voltage reference would be (say) a 2V reference, generated by a dedicated chip, then you'd divide the battery/alt voltage down by the necessary ratio for the comparison.  The battery voltage is never gonna go low enough that the 2V reference can't be generated.

 

Don't think the fan working/not would be critical.  The beauty of the PTC heater is, it can't get above a certain temperature, as its resistance just goes up in a self-limiting way.

[piggoy]

Here's my circuit diagram - edited from the trusty Haynes Manual. No copyright warnings please.

 

 

Edited 7 November, 2014 by piggoy

[coskev]

Would be a nice thing to have

 

But I've never had trouble with my VRS warming up in all honesty,1 mile down the road and I'm getting warm air through the vents.

[Breezy_Pete]

Your circuit looks OK, except do we know how much current the pin 6c/2 is able to supply?  If it's only driving an LED at the moment, it may only be good for a handful of milliamps, which may not be enough to drive a relay coil. Unless you know what device is supplying that current within the Convenience ECU (or whatever it's called), and know its current capability, you risk blowing that output, I think.

Why not splice your relay coil into the White wire off pin 5c/4 that feeds the actual rear screen element?

[piggoy]

Your circuit looks OK, except do we know how much current the pin 6c/2 is able to supply?  If it's only driving an LED at the moment, it may only be good for a handful of milliamps, which may not be enough to drive a relay coil. Unless you know what device is supplying that current within the Convenience ECU (or whatever it's called), and know its current capability, you risk blowing that output, I think.

Why not splice your relay coil into the White wire off pin 5c/4 that feeds the actual rear screen element?

That's a good point Wino, thanks. I chose the LED signal 6c/2 since I know it is easily acessible, just behind the switch in the dash. I'm not sure how accessible 5c/4 is without looking. The other option is use 6c/2 to switch a N-channel FET which drives the relay coil.

 

I need to find out how much current the PTC heater draws. Luckily I have access to a 200A low voltage supply at work. I'll connect it up and find out next week. I'm hoping the total draw is less than 100A, otherwise the relay will be expensive and the cables hefty!

[piggoy]

Would be a nice thing to have

 

But I've never had trouble with my VRS warming up in all honesty,1 mile down the road and I'm getting warm air through the vents.

Do you not wait for the warm air to demist the windows before driving 1 mile down the road lol?

[Breezy_Pete]

I'd be reasonably confident that its steady-state current draw would be a fair bit under 100A, but it will depend on how much air is being blown through it by the fan if used.  More airflow will keep it cooler, so it'll take more current; so ideally put it in front of a strong fan while you're measuring, to get a worst case figure.

[piggoy]

I'd be reasonably confident that its steady-state current draw would be a fair bit under 100A, but it will depend on how much air is being blown through it by the fan if used.  More airflow will keep it cooler, so it'll take more current; so ideally put it in front of a strong fan while you're measuring, to get a worst case figure.

Good call Wino. I'll also make sure I test it at 14.5V, I presume more representative of the system voltage when the engine is running. I'll work on a schemtic for the comparator circuit. Can't be more than a couple of op amps and a few resisitors.

[coskev]

Do you not wait for the warm air to demist the windows before driving 1 mile down the road lol?

Rarely get mist on the inside, perhaps you have a water leak somehere so your interior is damp and causing windows to mist?

[Breezy_Pete]

Nice guide to PTCs and their applications, for those interested, here.

[dieselV6]

For anyone considering this mod on Fabia 2/Roomster, a word of warning. There is some ECU now under the heater matrix, fixed to the floor with a long bolt (bolt welded to floor, nut on top) so removing heater matrix is a dash out job after all. Fabia 1 does not have that ECU so the job is as per Elsawin manual.

 

I bought the heater for my Roomster, and after 2 attempts to open the heater matrix housing (and/or remove the ECU underneath) I gave up and sold it on Ebay.

Total current for Fabia heater is 80A, and before abandoning the project I planned to use 1 section coming up together with the rear window heater, and 2 further sections using a short timer (2min-3min) and a separate button. You need serious gauge wiring straight to battery, and put a screw in 80A - 100A fuse at the battery. And of course a heavy duty relay, I'd use at least 40A/section.

[piggoy]

Nice guide to PTCs and their applications, for those interested, here.

Thanks Wino. What's the risk of damaging the alternator with excessive current draw? The alternator in my vRS is rated at 90A (according to sticker) and is fused at 175A. We are expecting this PTC heater to draw up to 100A (certainly I will install a 100A rated fuse and relay to power it). My basic understanding is that whatever remaining current the alternator cannot provide is provided by the battery instead. There is a risk the battery could go flat rather quickly assuming a high load situation on a cold dark morning - PTC heater + headlights + windscreen wipers + fans + loud stereo + discharged battery following starter motor cranking etc. Any advice would be gratefully appreciated.

[Breezy_Pete]

No danger at all to the alternator, it will give what it can, which will be much less than 90A at idle revs I think.  As you say, whatever else the heater wants, it will take from the battery.  The only risk is low voltage due to battery discharge, affecting other systems.  This is why I suggested an inhibit/cut-out based on system voltage. Then you can fit and forget.

 

Do your measurements first, confirm dieselV6's 80A figure; I suspect this may only be what it pulls at first when it's cold, not its steady-state operating current. That 80A draw may only last two seconds, which means the necessary cabling & fusing may not be as heavy as you think, but the relay(s) should be specced for the very highest current that can occur, even transiently.  Use the cables that come with the heater as a guide to what you need to use, but go up one size as a margin of safety and to minimise voltage drop.  May be cheaper/easier/safer to use 3 separate cables with 3 separate fuses and relays, so everything can be lower-rated, to each element within the overall heater package.

 

Try to find the Skoda wiring diagram, to see how they do it w.r.t. fusing and so on.  I'll have a look at info I've got, which is limited, but it may be there, I've not looked.

 

Here you go: linky

 

Seems you can have 1/3, 2/3 or all three elements working depending on when the black/blue and black/brown wires are pulled down by the main ECU. (The two wires finishing in square boxes labelled 46 & 45 go to pins 21 & 22 respectively of connector T81a on device J248 which is the "Diesel Direct Injection Control Unit". I assume this is the main engine ECU, judging by that description.)

[piggoy]

No danger at all to the alternator, it will give what it can, which will be much less than 90A at idle revs I think.  As you say, whatever else the heater wants, it will take from the battery.  The only risk is low voltage due to battery discharge, affecting other systems.  This is why I suggested an inhibit/cut-out based on system voltage. Then you can fit and forget.

 

Do your measurements first, confirm dieselV6's 80A figure; I suspect this may only be what it pulls at first when it's cold, not its steady-state operating current. That 80A draw may only last two seconds, which means the necessary cabling & fusing may not be as heavy as you think, but the relay(s) should be specced for the very highest current that can occur, even transiently.  Use the cables that come with the heater as a guide to what you need to use, but go up one size as a margin of safety and to minimise voltage drop.  May be cheaper/easier/safer to use 3 separate cables with 3 separate fuses and relays, so everything can be lower-rated, to each element within the overall heater package.

 

Try to find the Skoda wiring diagram, to see how they do it w.r.t. fusing and so on.  I'll have a look at info I've got, which is limited, but it may be there, I've not looked.

 

Here you go: linky

 

Seems you can have 1/3, 2/3 or all three elements working depending on when the black/blue and black/brown wires are pulled down by the main ECU. (The two wires finishing in square boxes labelled 46 & 45 go to pins 21 & 22 respectively of connector T81a on device J248 which is the "Diesel Direct Injection Control Unit". I assume this is the main engine ECU, judging by that description.)

Many thanks Wino. Originally I considered connecting directly to the battery but according to the diagram the heater supply is connected to terminal 30 junction which is fused 110A from the battery. This would be easier from the point of view of the wiring meaning I don't have to run a wire into the engine bay. However do you think cars with the heater fitted would have an uprated terminal 30 fuse greater than 110A? Thanks for your help. Here is my comparator circuit. It uses LM317 as a 2V reference. It's designed to trigger the relay when Vs>12v.

Edited 10 November, 2014 by piggoy

[Breezy_Pete]

Your circuit looks good, except I think you have swapped over the positions of the 60 & 100 Ohm resistors. It should be easy to test/tweak/debug anyway. 12.5V might be a more conservative minimum to set, but again, easily tweaked up or down if required. Replace one of the resistors in each pair with a little trimpot, then you have some adjustment . :sun:

 

As far as where you get the feed from, I expect there are some different fuse values fitted depending on options, so whatever fuse is feeding the point where you take your feed from, increase it by the amount your heater is taking.

 

Why not do this in stages? Try to get one of the three elements in the heater working as intended first, then expand it to further sections as confidence grows?

[vindaloo]

Oh dear, I'm wondering bad thoughts... Like whether it's possible/practical or advisable to add a water cooled EGR to an earlier model. :(

[piggoy]

Oh dear, I'm wondering bad thoughts... Like whether it's possible/practical or advisable to add a water cooled EGR to an earlier model. :(

A bit off topic....why would you want to fit the BLT EGR to the ASZ engine?? Most people on this forum curse the darn things :-)

[Phil-E]

That would be my only concern that having it wired up manually it will just draw the max current it can. When originally fitted it will only draw what the alternator is able to supply after supplying all the other bits.

 

I think I'm going to get a 240v coolant heater... although the convinience of a PTC heater would be great. No idea how caparable the install is on a MK2 Octavi to a MK1 Fabia. Probably completely different.

 

Oh dear, I'm wondering bad thoughts... Like whether it's possible/practical or advisable to add a water cooled EGR to an earlier model. :(

 

My car has an EGR cooler. It must make some difference but doesn't seam much quicker compared to our Cordoba PD130 we had.

 

The work involved would likely outweigh any small benefit.

 

The other option would be something like this:
 

Coolant flange with 2 glow plugs in it.

 

Phil