Dual alternator?

You don't need either the extra battery or the extra alternator. If you'd rather save the money, skip them.

The single alternator is 250A. The double is just two of them. You can pull ~150A from the single alternator, it just may not be able to pull it at idle. The dual alternator basically allows it to pull at idle and lowers the load on the single. You'd be fine without it.

Same with the batteries. And you can always charge the single battery from your house battery system if you're concerned.

If you were picking where to spend/save, I'd save on these and spend it on the house electronics - getting better equipment and/or more battery storage.

I obsessed about getting a second alternator, but in the end didn't get one. There are scenarios where it would be great, but if you arrive fully charged, and are set up at a campsite and enjoying the peace and quiet, maybe you don't really want to keep firing up the engine. It's up to your usage scenario of course.

Keep in mind that it's not just getting a second alternator. You need the rest of the gear to turn it into a charging source. And then you have one more item in the engine compartment to maintain. So there are downsides in that direction.

Some of the commercial high-end builders are adding them. But then they aren't paying for the maintenance costs. If you aren't running an air conditioner off your batteries, you can find other ways to get enough power ... like solar, or adding another battery.

It seems like this should be mostly application dependent. How many amp hrs of batteries you have, how much solar panels you have, are you going to be using shore power, or maybe a generator, and finally what are your electric needs. This then implies you know how you are going to build out your van and how you will use it.

I know nothing, I have never had an RV or camper van and therefore have little idea how I will use it. However, I can tell you that the recommended build from my upfitter (Sportsmobile) included the 2nd alternator and battery. This of course is what was suggested for a built out campervan.

Everything in a campervan is trade offs. So if you choose not to get the dual alternator no worries. Just a heads up that this is what was recommended by my builder, who has a better handle on typical needs than I do. Best of luck with the decision.

Dual alternators are not needed for 99.9% of campervan uses.

Dual alternators are primarily useful in industrial applications such as ambulances, mobile welding setups, tradesman vans or refrigerated vans who are frequently and regularly pulling hundreds of amps out of the vehicle’s electrical system.

House batter charging systems never do this. The vast majority of house batter charge controllers are in the 50-60amp range, well within the capabilities of the single stock alternator. Only the most ludicrously over-the-top specialized house electrical system (and we’re talking about something that’s costing over $10,000 with many hundreds of amp-hours of lithium batteries) could charge at higher amps than that, and those systems are put together by people who REALLY understand what they’re doing. (Or who just really enjoy spending money on over-built things)

Seems pretty simple:
If you desire fast charging at idle, dual alternators are valuable. If you don't, then you can likely get by without them. Not everybody cares about this, but I suspect the number is quite a bit greater than 0.1%.

There is also an argument that with duals, you are stressing the system less and they will thus be more durable. I have no data to support or refute this claim.

For me I want to be able to pull as much as I can from the ccp2 for charging house battery and hook up a audio system to ccp1 without any worries in summer when the AC is also cranked on high. This will also allow me to heat a water heater at idle from the charging inverter when i want to. It might also come in handy while parked at ski resorts in winter.

brío said:

Seems pretty simple:
If you desire fast charging at idle, dual alternators are valuable. If you don't, then you can likely get by without them. Not everybody cares about this, but I suspect the number is quite a bit greater than 0.1%.

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I haven't seen many battery charging systems that can draw more than 50-60 amps and the stock single alternator is plenty capable of that at idle.

Princess_Fluffypants said:

I haven't seen many battery charging systems that can draw more than 50-60 amps and the stock single alternator is plenty capable of that at idle.

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The Sterling 120A DC-DC is discussed here a bit - one person has two of them. And I'm not the only person pushing 150A into mine with the DC-AC-DC setup.

I ordered the dual alternators so that I can charge my house batteries at a high amperage (100+) while at idle. When (if) I get the van I'll see how it works out. I've found that there are times when solar just does not keep up with my electric needs. It does depend on how how much electricity one uses. In my case, other than when I need to heat the van, it will be 100% electric while camping.

nealcallan said:

I have a 2020 AWD dual alternator, dual battery. Have a 2/0 wire connected to CCP2 (175Amp) for alternator charging. The hot runs thru a Cyrix-Li-ct relay (see pic - before mounting) that will open when it sees 13.4 volts then to a 200amp breaker. Has been installed over the past year we routinely see >100amp charging when at idle (with auto stop off). Nice to have the high current charge, next is to setup third party high power mode.

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Exactly what I'm planning. I'm going to setup the third party high power mode with the uplifter switches: Upfitter Switches + Third Party High Power Mode +...

mototreks said:

Exactly what I'm planning. I'm going to setup the third party high power mode with the uplifter switches: Upfitter Switches + Third Party High Power Mode +...

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Yeah - I have all the wiring planned just need to take the time to setup. We have been running our system for the past year and typically only stay at a campsite for max 2 nights. So far without third party mode it seems fine but my plan is to use the upfitter switches. Probably do it he same time as installing a winch, so I can minimize the time it takes to disassemble the dash.

nealcallan said:

I have a 2020 AWD dual alternator, dual battery. Have a 2/0 wire connected to CCP2 (175Amp) for alternator charging. The hot runs thru a Cyrix-Li-ct relay (see pic - before mounting) that will open when it sees 13.4 volts then to a 200amp breaker. Has been installed over the past year we routinely see >100amp charging when at idle (with auto stop off). Nice to have the high current charge, next is to setup third party high power mode.
View attachment 166491

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I have thought about using this product.

What are you using to trigger it?

The instructions looks like they use a Victron BMS, but my system won't have that, so I am thinking you could also use the relay feature on the BMV 712 Smart monitor.

Asides from the initial cost of the dual alternator, what are the other downsides, I imagine it puts additional load on the engine reducing MPG? Anything else?

Janus9 said:

I have thought about using this product.

What are you using to trigger it?

The instructions looks like they use a Victron BMS, but my system won't have that, so I am thinking you could also use the relay feature on the BMV 712 Smart monitor.

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Yes I have a Victron BMS and have incorporated the boost feature which lets me start the van using the house battery (have not needed to use this). You can use a a Cyrix-Li-ct relay with a non Victron system such as Battleborn. If you do not want the boost feature I believe you just ground the relay to the shunt and connect the hot to the unit... Best to review the victron literature for the actual wiring diagram, but it can be done.

The trigger is simple the relay opens at 13.4 volts and supplies current to the battery.

Some people just can't imagine any use of an alternator other than charging batteries. I have a 2000 watt inverter powered off CCP 2. Run a water heater, slow cooker, make coffee with no house battery drain while driving. Easily pull 125 amps while at idle. Save the house batteries for quiet times. If I can get by with one less battery in the long run, the second alternator pays for itself.

I'm in the 0.1 percent. Buy what you want, just try not to underestimate your uses. There is no cheaper option for a second alternator down the road.

stevez32 said:

I imagine it puts additional load on the engine reducing MPG?

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Nah. Actually generating more power puts additional load on the engine (no free lunch), but simply having a second alternator does not. Well, there is the friction of spinning an unloaded alternator, but that is trivial.

Spend the thousand bucks on a small Honda generator and you will have a much more versatile dual alternator setup.

If your greatest need is camper van charging, then 1 X 250 amp alternator should be okay. If your electrical system is also going to serve as a whole house emergency backup, the dual alternators might be more appropriate. Also consider resale value.