D4 2015 Alternator loading

**Sandy** · 10th July 2022, 04:51 PM

I am about to choose a DC-DC charger for my D4 (build 2015). I was planning on having a 40A or 50A Redarc installed. Can any wise ones advise on what capacity my alternator may have and what typical amperage draw the D$ might have under normal operating conditions. I was told by the autoelec that a 50A unit might be a mistake. Thank you in advance.

**drivesafe** · 10th July 2022, 05:16 PM

Why are you fitting a DC/DC to your D4?

**Sandy** · 11th July 2022, 07:43 AM

Originally Posted by drivesafe

Why are you fitting a DC/DC to your D4?

Hi Tim, earlier this year you and others were very helpful in providing advice on a dual battery system. I decided to go with a lithium battery setup. I don't really want to go back over that. With covid delays I am only just getting around to getting the back of the truck fitted out.

So in trying to work out the size of the charger, I thought it would be good to try and understand what the alternator capacity was.

**kelvo** · 11th July 2022, 08:16 AM

Originally Posted by Sandy

I thought it would be good to try and understand what the alternator capacity was.

180Amp for the Diesel engines (TDV6/SDV6), and 150Amp for the petrol engine (SCV6).

**Sandy** · 11th July 2022, 08:54 AM

Originally Posted by kelvo

180Amp for the Diesel engines (TDV6/SDV6), and 150Amp for the petrol engine (SCV6).

Thanks Kelvo - yes a diesel.

Any thoughts on typical operating load on the alternator?

**drivesafe** · 11th July 2022, 02:31 PM

Originally Posted by Sandy

Thanks Kelvo - yes a diesel.

Any thoughts on typical operating load on the alternator?

As D4 draws up to 40 amps, with a 150 amp alternator, you have up to 110 amp available, depending on your motors RPM.

A 40 amp DC/DC, depending on the brand, will draw up to 60 or more amps.

so you have a huge margin to work with.

**Sandy** · 11th July 2022, 03:31 PM

Originally Posted by drivesafe

As D4 draws up to 40 amps, with a 150 amp alternator, you have up to 110 amp available, depending on your motors RPM.

A 40 amp DC/DC, depending on the brand, will draw up to 60 or more amps.

so you have a huge margin to work with.

If I have the 180 amp alternator - diesel I will have even more. Thank you again Tim.

**drivesafe** · 11th July 2022, 03:41 PM

Originally Posted by Sandy

If I have the 180 amp alternator - diesel I will have even more. Thank you again Tim.

Hi Sandy and you do have a 180 amp alternator. I was just using the 150 as a worst case.

**Tombie** · 11th July 2022, 05:58 PM

Much to Tim’s frustration

I fitted a Dc/Dc a while ago and I’m shifting to Lithium in both camper and Aux in vehicle to make some under bonnet space.

I have a 50a version and no issues at all with it, or the 65a worth of frontal auxiliary lighting I run!

**drivesafe** · 11th July 2022, 07:42 PM

Originally Posted by Tombie

Much to Tim’s frustration

I fitted a Dc/Dc a while ago and I’m shifting to Lithium in both camper and Aux in vehicle to make some under bonnet space.

I have a 50a version and no issues at all with it, or the 65a worth of frontal auxiliary lighting I run!

Hi Tombie, it's not the lithium batteries I dislike, it's the fact that you have to use a DC/DC device in any vehicle fitted with a SMART alternator, to be able to charge the lithuim battery.

This may surprise you but I have beed running a 100Ah lithium battery in my Tiguan for the past 18 months.

I am wrapped with the results of the testing so far, and the biggest plus is how well my cranking battery is being maintained.

My guess is that not only should the Lithium last at least 10 years, but I reckon I will get at least 10 years out of my lead acid cranking battery.

The difference between our systems is that I neither need nor would I ever use a DC/DC device. They are just too slow at recharging.

Because I can and have deactivated the SMRT alternator function, I have adapted one of my isolators to control the setup and charge the lithium direct off the alternator.

The results are brilliant.

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