Truma Ultra Heat System

[Grey13]

I was wondering if anyone has any IN DEPTH technical info regarding the system.
@ProfJohnL

The switch shows a heat setting variable between 1 and 9
The external switch selects wattage, 500, 1000, and 2000

Without looking I imagine that the relays on the board simply switch the two 1000 watt elements in different combinations,
In series for 2000 watts
In parallel for 500 watts
and only one on for 1000 watts

However I am looking for a wring diagram or detail diagram of the switch itself.
When adjusting between 1 and 9 what exactly is the output?
Is it a variable resistance or what?
A diagram and explanation of the whole system and how the 1 ~ 9 selection switch sets a control point and then where the thermocouple or other probe sits to measure the air temperature and work with that signal?

I see there is provision for an external air/room sensor:
What is that sensor T/C PT100 Thermister OR WHAT

How does that interact with the switch?

Any ideas.
Anyone welcome to comment.

 

[otherclive]

I just used to adjust the rotary switch until we had a comfortable heat setting. Once the temperature was stable I’d drop the power rating to a lower one as it reduced temperature fluctuations. Then set the fan to manual so the system was blowing gentle heat throughout the caravan.

I know this doesn’t answer your question for in depth technical details, but I found it such a simple and reliable system that in nine year usage on one caravan I never needed to delve deeper. In fact nor on a subsequent caravan either.

 

[Grey13]

I just used to adjust the rotary switch until we had a comfortable heat setting. Once the temperature was stable I’d drop the power rating to a lower one as it reduced temperature fluctuations. Then set the fan to manual so the system was blowing gentle heat throughout the caravan.

I know this doesn’t answer your question but I found it such a simple and reliable system that in nine year usage on one caravan I never needed to delve deeper.

I am going to add a proper temperature controller that will hold the temperature accurately. Second problem, the missus sleeps on the bed above the air pipe and always complains it's too hot while on my side it's cool. So going to lag that air pipe under her bed Ha ha

 

[otherclive]

I am going to add a proper temperature controller that will hold the temperature accurately. Second problem, the missus sleeps on the bed above the air pipe and always complains it's too hot while on my side it's cool. So going to lag that air pipe under her bed Ha ha

Perhaps a new missus? 🙈

 

[Dustydog]

Frankly Grey our little black dial is left at no 9. Too hot on 2000? We reduce the outer dialto 1000 and then 500. I’ve never really found the need for any further differentiation on temperature.
No one caravan I’ve had has the temperature sensor in the same place! That of course will make a big difference but one as you know you can choose .
Im sure rerouting the warm air pipe will help.
Or swap sides 😉
Like Clive I’m very sorry I can’t help you with the technical details but fully appreciate your desire for more knowledge.

 

[RogerL]

I recall a debate with Gary, of Arc Systems, where he explained that the best place for the "remote" temperature sensor was at the bottom of the Ultraheat unit where it sensed the cool air before it was heated and distributed.

As OC posted, I just adjusted the setting to a comfortable number, with a lower number at night - I set the fan control to auto in the day, which responded to changes in demand and minimum overnight to keep fan noise to a minimum.

 

[ProfJohnL]

Because of the way the heaters work, the way the controls are installed in a caravan varies so much that putting temperature values on the dial is asking for complaints. Its best to experiment and find by trial and error the dial position that suits your needs in your caravan.

Truma never published detail circuit or pcb information, What I know is based on repairing several of their products but good old structured fault finding and elimination processes. And I don't know enough about these later products to be able to give you a direct steer on their method of implementation, having retired from the leisure business som 25 years ago. In their twenty five year old designs I do know the used a carbon track resistor in the adjustment knob and an NTC thermistor as the temperature sensor, but I don't know the the specific characteristic such as its B value. I can't recall a single thermistor failing unless it had been physically damaged. They certainly won't be using dedicated temperature measurement grade thermocouples or platinum resistance units.

Do be careful when trying to implement a dedicated temperature controller. It entirely possible the hysteresis of off the shelf controllers might be too small and might lead to excessive PCB relay activity and early failure,

 

[gary]

I am going to add a proper temperature controller that will hold the temperature accurately. Second problem, the missus sleeps on the bed above the air pipe and always complains it's too hot while on my side it's cool. So going to lag that air pipe under her bed Ha ha

Original temp sensor is inside control switch so temp sensing depends where that's mounted, particularly where the back of the switch is and the heat or indeed cold its exposed to?!
So get yourself a 3.5mm mono jack plug + 600mm of lead and a 10k thermistor, (I used jack to jack 1200mm phono extension leads), simply plug this in the socket on control board, (that connects itself and disconnects original). Then its just a matter of attaching the sensor to the gas fires temp sensor in front of fire, after all, no one ever complains about gas fire not keeping an even temperature!!