MHEV DC to DC Converter Failures

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Originally Posted by kenl

On my MY23.5 D300 defender, the DC converter failed last August, it was after a night free camping. I suspect the car battery draw plus the caravan draw plus the Auxilery battery draw (two fridges running) are what broke the camels back. My Aux battery is charged by a Victron 30amp DC|DC charger, I don't know what the Land Rover trailer plug supplies to the Caravan.

In hind sight I have disconnected the carvan power, I may put a switch on it so I can select when it starts to draw power. I will also replace my Victron DC|DC converter with the newer XS model that can be regulated to supply a set current. Beyond that there is not a lot one can do except be mindful of heater usage ect.

For such a expensive car I think we could reasonably expect that the 12v DC power supply would have it's own overload protection. I don't know if anyone has had an out of warrenty claim on this part in Australia, but I suspect consumer law would protect you against any cost?

Very annoying!

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Hi Keni, do you know what was the overnight temperature when your DC/DC converter failed?

I am guessing it would have been about 10 deg, it was a clear winters night in the wheatbelt. I did have two fridges running in the car that tend to keep the cabin temp warmer though.

I did Freecamp again a few weeks later but was much more careful with consumption.

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Originally Posted by kenl

I am guessing it would have been about 10 deg, it was a clear winters night in the wheatbelt. I did have two fridges running in the car that tend to keep the cabin temp warmer though.

I did Freecamp again a few weeks later but was much more careful with consumption.

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So your load in addition to the car was 30A for the aux DCDC plus the trailer plug which has a 15A fuse on the auxiliaries wire. This is not a lot so there must have been something else wrong with the MHEV DCDC. My advice from LR is to limit auxiliaries draw to 50A via the Anderson plug I have for caravan charging.
Going by this thread I'll monitor the current via my GAP tool and turn on caravan charging after giving some time for the car's battery to recharge.
Might have some data during a trip next week.

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Originally Posted by jwb

So your load in addition to the car was 30A for the aux DCDC plus the trailer plug which has a 15A fuse on the auxiliaries wire. This is not a lot so there must have been something else wrong with the MHEV DCDC. My advice from LR is to limit auxiliaries draw to 50A via the Anderson plug I have for caravan charging.
Going by this thread I'll monitor the current via my GAP tool and turn on caravan charging after giving some time for the car's battery to recharge.
Might have some data during a trip next week.

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The 30 DC/DC device's current draw would be more like about 40 amps.

DC/DC devices pull in a lot more than they put out.

Add to this that kenl's Cranking Battery would have been cold, so the total current draw could have been quite high.

Has anybody monitored the voltage levels of their new Defenders while driving?

@ jwb, I completely agree that we have to start monitoring our current draw to save ourselves from being stranded! The GAP live values seems to be my most available tool at the moment, but a warning when exceeding say 120amps would be nice.

Even better would be Land Rover limiting current draw for non essential items to protect its' own charge system. My D4 would shut down the entertainment and touch screen when the battery was low, I also had my alternator fail on me and everything including lights shut down but I got home! The Defender must be more advanced than the Disco 4 ?

They probably can't stop the battery draw but surely they can prevent the heating devices from drawing current when over a certain threshold. Perhaps it's then admitting liability IDK?

If the failure was the same as described in the TSB that I posted then the cause seems to be a connector overheating and/or loosing contact issue which can cause FET failure. Was a wiring harness also replaced?


Edit: My D350 L405's voltage is 14.4V soon after start-up.

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Originally Posted by Graeme

Edit: My D350 L405's voltage is 14.4V soon after start-up.

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Thanks Graeme, do you know how long it stayed at that voltage?

BTW, you can't really compare your L322s alternator operation with these new Defenders 12v supply.

In the video, he achieved 170 amps while the vehicle was idling.

You would be lucky to get 50 amps from your L322 alternator at idle and the same goes for a D4.

I have a MY21.5 D350 MHEV L405 these days.

Edit: Sorry, I misunderstood your comments. However as my L322 had a 220A alternator, I expect that my L405 needs more than 220A to be available, but not stating that it was available at idle.

What is the IIDTool parameter to monitor the DCDC output current on these MHEV vehicles?

Found the parameter..

Idling with a/c on, 185A 14.0V until the 25A DCDC charger connects then 195A 13.9V and 60Ah Lithium 13.5V then 206A 13.8V and Lithium 13.5V with the 2 LED driving lights on.

The car did a 450km run this morning.

From a wiring side. The 12V cable from the DCDC to the starting battery is 35mm2 and protected by a 350A fuse.
I've read of people pulling 70A for their aux battery chargers without issue (so far).
Really getting some good data from this thread.