Fitting an auxiliary heater

[STP]

Hi all, I'm considering fitting the PTC auxiliary heater using part number 1K0963235F, the dumb version. I have manual heating and no AC, I don't need help on wiring or control, I'll make that myself as a separate controller type device - but my question is, does the air blower rad have a place for the PTC unit to physically slot into?

It would be ideal if there's already a mounting position it would slide into and bolt into place. Any help or info would be much appreciated. I don't want to jerry rig it into place.

I'll build a DC controller with a fused 100A supply and block it from turning on until the engine is running and a 30 second timer is elapsed for example, shutting it off when the coolant hits a certain temperature.

[Javito]

I couldn't tell you 100% cause mine has AC but it's pretty easy to check.

There's a plastic cover held be 3 screws. If you remove that you should see the slot for the ptc heater.

Mine was almost exactly like this: https://www.golfmkv.com/forums/index.ph ... ll.106960/

I'm curious about your DC controller. What kind of board would you use?

[STP]

Thanks Javito, that is an excellent page! Just what I needed.

Ok on the controller side, there is a straightforward solution and a more complex one.

First I could use a 100A contactor, 12V DC coil model or a solid state relay (SSR) of the same capacity, and a simple fused cable to the heater from the battery via a 80A or 100A master fuse (there are actually spare 80A ones on my front fuse module but would likely use a separate one) and 16mm DI (double insulated) CSA cables, short-circuit proof type we use in industrial control panels, with a dedicated bolted ground cable of the same cross section. The live would pass through the contactor or relay and the control signal to the trigger (SSR) or the coil (contactor) would be fed from a simple switch or a timer relay & switch.

A smarter version would use a mini PLC (programmable logic controller) - there are a few available which operate on 12-24V and could be programmed to respond to various inputs such as ignition on, coolant temp (sensor on a hose or the radiator shell) and a press button to trigger the cycle, shutting off after a predetermined time or if the engine reaches 60 degrees C first for example, and small enough to hide easily.

Allen Bradley make a Micro810 which is a great little PLC for which the programming software is free, called "Connected Components Workbench", and there's also a few German models in RS which are 12V powered and all have 8A relay outputs, which is great for switching the main relay/contactor/SSR to power the PTC heater. We could also add a thermal switch to detect the surface temperature of the PTC and cut it off at a certain point so it doesn't get too hot, by interrupting the control signal.

I'd also block it from coming on if the internal fan is off or fails to run. That only requires a sense wire from the fan motor live side to determine it is on, so the heater can't operate if there's no fan running to take the heat away.

If going the SSR route and PLC, I could modulate the SSR signal from the PLC output to reduce the average current to the heater elements and control the actual temperature it produces. Feedback can be from a simple J type thermocouple to the PLC on an analogue input. That way I can have two non latching buttons to give low power and high power to the heater as required, and a main switch for isolation.

This means the high current circuit is only handled by the contactor or the SSR, everything else works on the control circuit side of less than 1 amp. I'd mount the controls on a plate fitted in the little storage area where the ashtray used to be (already removed my ashtray as I've no need of it)

Would be nice to get the alternative cubby hole part for vans which came with no ashtray at all of course.

[Javito]

Sounds fun, I like it.

Wouldn't you be able to use something cheap like an Arduino instead?

[STP]

Well, an Arduino would work too in a way but it's I/O is only rated at 3.3v or 5v so not much use to switch relays or SSRs which are usually 24v or 12v. A PLC is readymade for this stuff and ultra reliable. I have access to a lot of those - so even though I literally have dozens of ESP32s, Arduino boards, CYDs, I'd rather use a hardened industrial controller for this stuff.

But you never know, I might fall back to one of those micro controllers - it would need a separate power board to control the relays where a PLC doesn't. I'll see how this pans out. Will likely test the heater on the bench first so will report back on progress. I'll do a thread on it as a separate item.

To be fair if you didn't want a complex or expensive solution then a switch, a couple of relays and a fuse will do, all suitably rated of course. One relay to be triggered when the internal fan is running (and blocking the main one if it's not running) and the main one to fire up the heater.