Thread: MHEV DC to DC Converter Failures

My D350 L405 was only producing 60-70A near the end of 2x20km drives today.

Originally Posted by Graeme

My D350 L405 was only producing 60-70A near the end of 2x20km drives today.

Hi Graeme, did you by any chance note the voltages during your trips?

No, I didn't. My previous voltages were taken from a display not visible when driving and I didn't think to have the IIDtool display the converter's o/p voltage, assuming that it can. I'll try again.

I didn't get to check right at start-up but after a few minutes idling while on a phone call the current was briefly up to 117A then down to 80-90A for the 1st km or so before settling to around 60A. The converter supply voltage from the IIDtool was 14.8V for a few moments initially before dropping to 14.5V where it stayed for the 8km drive. I stopped a couple of times to check my display in my rear side window which showed 14.3V every time.
At start-up to head home, voltage was 15.0V, then 14.8V for a few seconds then back to a solid 14.5V.
After the engine was switched off the voltage soon dropped to 12.5V and my display showed 12.2V but I had since opened then closed the soft-close door.

Edit: The 12V battery is original and now 5 years old.

Originally Posted by Graeme

At start-up to head home, voltage was 15.0V, then 14.8V for a few seconds then back to a solid 14.5V.
After the engine was switched off the voltage soon dropped to 12.5V and my display showed 12.2V but I had since opened then closed the soft-close door.

Edit: The 12V battery is original and now 5 years old.

Thanks Graeme for the feedback and it is starting to confirm my suspicions that you may be able to charge a Lithium Auxiliary battery directly off one of these vehicle DC/DC units.

This would mean you would not need a DC/DC device and while my existing isolators would work fine, after seeing the video Mahn posted, I have decided to modify the operation of the isolator so that on cold morning starts, the isolator will not connect the auxiliary battery to the Defenders power supply for a short period of time, to allow the Defenders PTC Heater to run and shut down before adding the high current load a low auxiliary battery would apply to the power supply.

This would greatly reduce the chances of over loading the Defenders DC/DC unit.

Please keep sending info about your operating voltages. The info is very much appreciated!