Night heating system electrical help needed

[cwilliams255]

Hi all, I'm a new member to forum but inherited a bongo from my Dad a few years ago when he moved to France. When I got it I wasn't sure I was going to like it but after about 5 minutes I was sold. Ripped out existing kitchen which had seen better days, insulated, fitted new floor, rewired, bought crash tested R&R bed etc.

I'm hoping to get everything completed soon and one of the big jobs left is heating. We'd love to use the bongo in all weather so this is a must for us. Given that the bongo already has a perfectly good heater matrix and fan in the rear my plan was to use a diesel water heater connected to the coolant loop. Now I've noticed a thread on here where someone managed this but details aren't all there. My biggest problem is the fact that mine has digital climate control and despite having a reasonable grasp of electrical circuits I don't fully understand how the motor speed is being varied. It has 12v input on +ve and then a transistor on the -ve unless on max power where relay opens a switch. I'd like to get the motor onto LB and seperate the existing circuit so was planning on using a DPDT switch. If I ignore the fact that mine has digital control I assume the motor is just like any other, lower input voltage = lower rpm - I want to run it at the same speed as the slowest fan setting. I've taken voltage readings all over the circuit and can't really tell how the digital controller is altering the fan speed. I could just get a great big resistor and try the motor and see what happens but I'd to understand what's going on first. The wiring diagram is here
http://www.g8dhe.net/bwm/bwmanualp.htm?1995/Page_88

Anyone able to point me in the right direction or should I just give up and buy an diesel air heater instead?

Thanks

[g8dhe]

If your thinking you can run the fans and a heating system (which would include the engine block itself) from 12 volts your going to be in for a dissapointment The fans are not designed for electrical efficiency as the vehicle power is normally supplied from the alternator not the batteries accept during starting. This is the reason that the diesel air heaters are rather popular if you need a warm/hot vehicle when stationery.

[cwilliams255]

That's a very good point and one which I had not considered. The relay that connects the circuit is rated at 20A, although when I directly connected rear motor to LB it ran at full speed and didn't blow a 15A fuse. I expect at minimum speed its current draw will be considerably less but probably not comparable to an air blown heater which seem to be 1-2A

The other option I considered was to completely remove the rear heater unit and replace it with a purpose built heater matrix but I'd lose the OEM vent integration without some creative thinking. Maybe I should just fit a small domestic radiator somewhere and be done with fans full stop

This is the thread that is of most interest viewtopic.php?f=3&t=71100 but no mention of power usage unfortunately.

[g8dhe]

Most people find an oil filled radiator powered from EHU quite acceptable, 0.5Kw to 0.8Kw seems fine, some prefer the instant heat of a blower heater, but not really viable for running overnight with the noise in a confined space.