Heating & Cooling (Cabin, not the Drivetrain)

Since in EVs it's much more important to think about energy efficiency, and there is no large source of engine heat avaliable, an overhaul of the cabin heating/AC is needed. Fortunately, the main traction batteries are an easy source of high voltage DC power, which can be used to supply power-hungry heating/cooling.

Heating:
There are a few viable approaches. There is nowhere near enough energy wasted as heat by the drivetrain components to warm the cabin even a little bit, so additional heating/AC is normally required. Remember that any high voltage wiring in the car needs care taken to ensure that it's safe, fused and with DC rated contactors to disconnect it. Standard mains-voltage rated AC relays are completely inadequate and will weld closed on their first operation if you're unlucky. Here are a few options;

• Reuse the stock heater core and plumb in a HVDC electric fluid-heater (powered from the main traction battery pack, so high voltage)
• Replace the stock heater core with a HVDC electric heating element ( i.e. cut a hole in the heater core and install a ceramic heating element )
• Use an air-source heat pump (very expensive, but more energy efficient. New EVs such as the Tesla Model 3 now use heat-pumps)

It is a good idea to supplement the main heater (required for windscreen clearing) with heated seats & a heated steering wheel retrofit, as these are a much smaller drain on the battery. (Heated seats on full power could be 60W, an air heater might be anything up to 3000-4000W.)

Cooling:
It is not sensible to attach any mechanical loads onto the drivetrain (alternator, A/C compressor etc) as these are generally far less efficient than directly drawing power from the car's electrical system, especially since the main battery pack has high voltage to drive heaters/compressors etc.

Therefore if you want to maintain or install an air conditioning system, you need to replace the A/C compressor with an electric model. The most cost effective source of these is finding parts from scrapped EVs. These components are expensive however, and usually need some degree of signal spoofing, or replacement control systems to control them, as they come from modern cars and have CAN signalling everywhere.

Fortunately for most of us driving an MGF/TF, any time the weather's warm enough to need AC, we'll pop the roof down... Avoid the complexity of designing a replacement AC system and get the wind in your hair at the same time!

Useful info.

I have just a few thoughts.

1) Will a heated windscreen use less power than a blower?
These are available for the F/TF and mine clears condensation or ice really quickly.
2) If a blower is required a cheapish hair dryer style could be used for the MOT.

3) A/C helps clear the windscreen of moisture quicker, especially beneficial in a soft top.
4) As the F/TF A/C compressor pump is in the engine bay efficiencies can be had by installing an electric compressor at the front.

1) I had no idea that they were avaliable - a heated windscreen would indeed clear a windscreen faster than a blower
2) Not sure that a blower is needed specifically - but it's pretty easy to hook up a heating element.

For those with higher spec cars than mine, it might make sense to keep the AC. The key thing to remember is that it's not going to be good for pure EV range to run any AC compressor or power hungry air heater for that much of the journey. If it's a decision between getting home cold or having range anxiety because you have the heater on full blast, it's an obvious choice for me - I'll put a pair of gloves and a coat on and get home.

As for adding an air heater, the most cost-effective option seems to me to be a DIY modification to the heater matrix. I've attached a couple of pictures of what i've done - half an hour with a grinder and some pliers ripping apart the old matrix (I ordered a spare as I intend to use the heater matrix as a radiator for the drivetrain parts...) and a dismantled £15 1500W ceramic PTC heater. That can be run directly off my battery voltage (my system will be a 380VDC system, so higher than mains voltage, but the heater won't break, just run more strongly). I can run the wiring out of the old water hose connections to keep it neat The Ceramic PTC heaters self-regulate, so it makes controlling them far easier than other solutions - the faster the blower runs, the more power the heater will draw and the hotter the airflow will be.

With my MGF EV conversion, I retained the original heater core and pipes, as I really did not want to dismantle dash to get to heater core. I bought a water heater tank (HV) from friend second-hand and behind firewall, plumbed this into existing water heater pipes. to turn-on I used the demister button which has never been used on my soft-top. Heater works really well and heats up the cabin like traditional MGF heater. But really the best thing I installed was heated seat kit off ebay, it draws very little power and warms up your behind nice and quick, some photos below.