Leisure Battery to blame ?

[Hoovie]

I put a clamp monitor on my unit for 24hours. I found the initial start-up load was 15amp even with 6mm cables.

The startup load is not really affected by the gauge of cable. there may be some effect with some devices wanting a certain power due to a voltage drop with undersized cables but the current doesn't really tend to vary.

What I did notice was that as the unit ramped down the current dropped off but when the thermostat called for heat the current again went up to 10-12 amps. I found that the glow plug was kicking in each time and thus hammering the batteries. I cannot say if this was just on my unit, but I have heard of many people waking up with flat batteries after using the heaters over night.

Yup, makes sense if the heater needs to restart.

 

[Hoovie]

About 5½ amps at full power a bit less than 1 amp at min fan speed with a CP Plus controller and 1¼ amps with a classic controller.
With the way the Truma works by varying the fan speed relative to temperature an evenings consumption will vary depending on conditions,

I did a test on my Truma today. Didn't have the heater on, just had the fan set to the various settings for 15 minutes before going up to the next setting.

It looks like the Truma S3004 Fan uses significantly less power than the Truma Combi Fan.

Numbers logged on a minute-by-minute basis from the LOAD output of one of my Victron MPPT controllers that supplies all the Habitation 12V electrics and averaged.
Baseline current is from 12V devices that are powered (e.g. Amazon Echos, Router, Powered USB sockets).