Safe to pull 30 amps from stock alternator for DC/DC charger?

[goffro]

Hey gang. Guna drop some coin and upgrade to those fancy lithium batteries everybody keeps talking about. Question about how much juice we can pull from the stock alternator.

I plan to wire directly from the + terminal clamp of the starter battery, to a DC-to-DC battery charger that will probably live where the Magnatek power converter is (kinda under the sink). And then, to a coupla Battle Born 100Ah batts in the rear battery box.

In one thread, it was mentioned that "u need to be careful with your charger selection, the stock wiring only supports up to 30A charging" (link). Also in this thread were some doubts as to the usefulness of upgrading to a fancy 200+ amp alternator. We are definitely not planning to upgrade the alternator and I would prefer to keep this component stock anyway because these vans are fickle enough as it is, without going and introducing a completely different charging profile to the ECU.

In another thread (link) it's mentioned that we may have a 120 or 150 amp alternator, but the only way to tell is visual inspection (guna pass on that) or look up the VIN (WV2EB47092H047367).

Putting in a huge, 70-amp DC-to-DC battery charger that will top the batteries off after 2-3 hours of driving is tempting. But I think it will definitely roast the alternator. A more conservative option seems to be the Victron 30 amp DC-to-DC charger (link). Especially since, as noted above, the van's stock charging system is wired stock for a 30 amp draw.

Has anyone had success / failure with this specific charger?

There are a few options to help control the strain this DC-DC charger puts on the alternator -- one option is installing a switch up front, so you can turn the charger on when you're driving nice mellow highway miles, and turn it off when the alternator is at low RPMs during city driving (or crawling up a hill). I understand it's the low-RPM situation, 1500 RPMs or so, where the alternators with heavy draw can melt because they aren't able to cool themselves adequately (since their internal cooling fan is at low RPMs).

Another altnerative is using the Victron settings to tell the charger to shut off if the charge voltage drops below so-and-so many volts, and not to come back on until the voltage goes above so-and-so many volts. This seems like a more coarse way of ensuring alternator health, but it's better than nothing.

And finally we can just hope nothing bad happens with this 30-amp DC/DC charger, and forget about it. Which we'll probably end up doing unless someone here comes up with a compelling argument not to do this!

[mikemtnbike]

Lots of people using the Renogy 30/30, it's also sold by GoWesty recommended for all vans with no recommendation to buy a bigger alternator and I can guarantee that if they could think of a good argument to convince me to spend more money, they'd let me know.
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1991 Vanagon GL 2.1 AT Westfauxlia. "Frankie" Totaled https://www.thesamba.com/vw/forum/viewtopic.php?t=764510&highlight=carnage
1995 Eurovan Camper "Marzivan"
2020 GTI SE manual

[sgirard]

I have the Victron in my 95. I did put a shutoff switch like you mentioned in the dash. I use the switch in the heat of the summer or going up a big hill. Not sure whether the van appreciates it, but it makes me feel better
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95 EVC
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[orbeamike]

The Victron 30A DC/DC charger is an intelligent DC/DC charger with many user selectable parameters that will automatically shut off charging at low engine RPM (low charging voltage). You can independently set the starting charging voltage, shutdown voltage and engine shutdown detection voltage, as well as delay start time and voltage. I installed the 30A unit along with an AO lithium lithium battery in my Eurovan Camper over a year ago using the stock camper wiring and I have not had any issues.

[kourt]

I have the Renogy 50 amp DCDC charger serving my Battleborn 270AH battery. This is in a 2001 EVC with 150 amp alternator.

I replaced all wiring and used a much heavier gauge. So far no problems. I monitor my voltage with a Scangauge 3.

kourt

[goffro]

Great info, thanks! I think I'll stick with the Victron 30A DC-DC charger, running new end-to-end wire for everything, and I'm not going to bother wiring up a switch to control it. I do really like its feature set. I had considered the 30A Renogy which has the bonus built-in solar charge controller for about the same price, but the more I work on systems like these, the more I learn to appreciate having one component do one task ... for upgradability, repairabliity -- basically everything other than affordability unfortunately.

[Magion]

I also went through this.

Mind you I have 95 Westfalia so slightly different.

I installed Renogy 50 amp dcdc with solar controller. And two 100Ah heated Renogy batteries. I left the original westfalia wiring from engine battery to the back in place out of convenience, running new wires would suck. They were 2 parallel 8AWG wires. Good enough. I have also the high output alternator not sure what it was but if you pop the hood open and look down on alternator you will know right away as it says on it in big letters. I cannot remember where but there was a good article about what load is safe to pot on alternator. Something like you should not be exceeding 50% of its capacity for long stretches. So do your math to see where you get. Don't forget to include the running vehicle itself -lights radio etc.
I use the Renogy app for setting the actual amperage, its easy to do. For peace in mind I go with 30amp anyway. When I started the engine for first time and it was set by default to 50amp to engine idle rpms were really low!! so it puts significant load on engine for sure.
Over all I am super happy with my new setup. It allows me to go for weeks without the need for shore power. I also installed Victron 30AMP AC-DC charger for times when I need to top up the batteries when shore power is available.

The photo is before I installed ADDC charger, space was an issue and having integrated DCDC charger with solar controller was big help to me. Might be different situation with Winnebago if that is what you have.

Also make sure you fuse everything properly!

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1975 Westfalia in Brilliant Orange
1995 Westfalia in Caribbean Green

[StokeJC]