webasto diesel hot water system

[chris peiro]

hi all, i have a 2018 topaz with the diesel hot water system. it starts, lasts about 30 seconds then stops. switch it off wait and try again, lasts about 30 seconds then switch's off. The only time it works is when the car is running, or we have good solar. batteries read about 12.3v-12.5v and close to 14v with the car running. i have looked online but can't find anything about this fault. the batteries are about 2 years old and have solar hooked up when the van is not in use. anybody have this happen to them.

cheers chris

[Wetjala]

The problem is caused by using an incorrect gauge for the cable between the circuit breaker and the Webasto. When the Webasto first starts there is an inrush of current (~ 11Adc from memory) and due to the wrong cable being used a substantial voltage drop occurs over the length so when the voltage at the Webasto drops below 9Vdc the unit goes into fault lockout mode that can only be reset by removing the power from the Webasto for 10-15sec. It will enter the fault lockout mode a few milliseconds after start-up and then go through the shutdown cycle over the next 30 or so seconds which is what you have observed.

If the batteries are healthy and fully charged or another source like the car is connected then there will be enough charge available in the combined batteries to keep the voltage above the fault lockout threshold. New or strong, healthy and fully charged batteries in the van will suffice to mask the problem (wrong gauge cable used) but once the batteries age then a sudden high demand from them will cause the voltage to dip; how much they dip and how long it takes for them to recover is dependent on many factors (age, drain/charge usage to name two).

If you have a multimeter that can capture minimum and maximum voltages then measure the voltage at the connector on the Webasto that Track connect their cables to. Start the Webasto and then once the minimum voltage has been captured on the multimeter turn it off again. You will see a voltage <9Vdc. Then do the same at the CB where the 12Vdc is sourced for the Webasto circuit. You will see the voltage dip but it will not dip below 12Vdc. The cables used for powering the Webasto, both the 12Vdc and 0Vdc cables, will need to be replaced will heavier cable – that is with a larger cross-sectional area of the copper conductor. Aside from the losses across the length of the incorrectly spec'd cables installed by Track there is also likely to be losses across the power switch, crimp connections and connectors. How large these losses are and whether the crimps need to be redone or connectors replaced will need to be considered but you should see a significant improvement once the cables are replaced.

I have a 2016 Murranji with a Webasto heater which exhibits the same problem. I identified the cause earlier this year but due to other commitments have yet to spend time to rewire it myself. When I spotted the gauge of the cable that Track installed I was gob-smacked that it ever worked or that the cable hadn't burnt out! The gauge of the cable that should be used is dependent on three main factors: 1) the maximum current that it is likely to carry, 2) the overall length of the 12Vdc & 0Vdc cables and 3) how the cables are installed (in open air, insulated etc.) From this you can work out the gauge and then choose the next cable gauge (smaller number = broader cross-sectional area) to allow a safety margin.

(I have another issue with my T-Van that is also cable gauge related - the cable that powers to fridge in the front box is incorrectly sized as there is a >1Vdc drop from the battery to the fridge meaning that as the battery discharges the fridge will trip on low voltage cut-out much earlier than it should. Another job that's on my T-Van "fix" list!)

Good luck!

[Gumb]

I think your batteries could be on the way out too. I changed the Fullrivers in our 2017 Tvan after having similar issues with the fridge cutting out.

[Harry Lissimore]

I have replaced the 2 x FullRivers in my 2015 Topaz twice due to a similar problem.  The batteries seemed to lose their capacity after a while indicated by the voltage dropping too quickly from full charge preventing the slideout ARB fridge from working.  Even connecting larger wires straight from the batteries didn't help much at all.  The last 2 Fullrivers have lasted well, which I put down to not overly charging them.  I don't leave them charging at home, I don't charge them from the anderson plug from the car unless I have camped unpowered overnight and when on a powered site, I only have the 240V connected overnight and run all day just on solar. I have also heard that having Fullrivers charging without the batteries actively running something (like a fridge) is not good for them.  At home, I charge the batteries up about once a month for about 12 hours until charged.

[chris peiro]

thanks for the input guys, i have used it again and put the multi meter on it to check how low the volts dropped . only happens when the batteries are at about 12.5v ,anything above that and it works well. i might look into new lithium batteries soon..cheers chris

[Gumb]

I have replaced the 2 x FullRivers in my 2015 Topaz twice due to a similar problem.  The batteries seemed to lose their capacity after a while indicated by the voltage dropping too quickly from full charge preventing the slideout ARB fridge from working.  Even connecting larger wires straight from the batteries didn't help much at all.  The last 2 Fullrivers have lasted well, which I put down to not overly charging them.  I don't leave them charging at home, I don't charge them from the anderson plug from the car unless I have camped unpowered overnight and when on a powered site, I only have the 240V connected overnight and run all day just on solar. I have also heard that having Fullrivers charging without the batteries actively running something (like a fridge) is not good for them.  At home, I charge the batteries up about once a month for about 12 hours until charged.

That is correct battery management. The AGMs need to be cycled and not left on 240v charge when in storage like a lot of people do. I only charge mine every 2-3 months and I'll even put the fridge on for a couple of days just to give the batteries a cycle down before recharging again.

[theyabbyman]

The problem is caused by using an incorrect gauge for the cable between the circuit breaker and the Webasto. When the Webasto first starts there is an inrush of current (~ 11Adc from memory) and due to the wrong cable being used a substantial voltage drop occurs over the length so when the voltage at the Webasto drops below 9Vdc the unit goes into fault lockout mode that can only be reset by removing the power from the Webasto for 10-15sec. It will enter the fault lockout mode a few milliseconds after start-up and then go through the shutdown cycle over the next 30 or so seconds which is what you have observed.

If the batteries are healthy and fully charged or another source like the car is connected then there will be enough charge available in the combined batteries to keep the voltage above the fault lockout threshold. New or strong, healthy and fully charged batteries in the van will suffice to mask the problem (wrong gauge cable used) but once the batteries age then a sudden high demand from them will cause the voltage to dip; how much they dip and how long it takes for them to recover is dependent on many factors (age, drain/charge usage to name two).

If you have a multimeter that can capture minimum and maximum voltages then measure the voltage at the connector on the Webasto that Track connect their cables to. Start the Webasto and then once the minimum voltage has been captured on the multimeter turn it off again. You will see a voltage <9Vdc. Then do the same at the CB where the 12Vdc is sourced for the Webasto circuit. You will see the voltage dip but it will not dip below 12Vdc. The cables used for powering the Webasto, both the 12Vdc and 0Vdc cables, will need to be replaced will heavier cable – that is with a larger cross-sectional area of the copper conductor. Aside from the losses across the length of the incorrectly spec'd cables installed by Track there is also likely to be losses across the power switch, crimp connections and connectors. How large these losses are and whether the crimps need to be redone or connectors replaced will need to be considered but you should see a significant improvement once the cables are replaced.

I have a 2016 Murranji with a Webasto heater which exhibits the same problem. I identified the cause earlier this year but due to other commitments have yet to spend time to rewire it myself. When I spotted the gauge of the cable that Track installed I was gob-smacked that it ever worked or that the cable hadn't burnt out! The gauge of the cable that should be used is dependent on three main factors: 1) the maximum current that it is likely to carry, 2) the overall length of the 12Vdc & 0Vdc cables and 3) how the cables are installed (in open air, insulated etc.) From this you can work out the gauge and then choose the next cable gauge (smaller number = broader cross-sectional area) to allow a safety margin.

(I have another issue with my T-Van that is also cable gauge related - the cable that powers to fridge in the front box is incorrectly sized as there is a >1Vdc drop from the battery to the fridge meaning that as the battery discharges the fridge will trip on low voltage cut-out much earlier than it should. Another job that's on my T-Van "fix" list!)

Good luck!

Hi Wetjala,
I know it was a couple of years ago, however I'm experiencing a similar problem and I'm just wondering if you did replace the cables and was it a big job?
Thanks Yabbyman