TheSamba.com :: View topic - Electric A/C Options

Thu Oct 30, 2025 1:05 pm

While digging through the Type 3 forums researching electric A/C systems, I ran into a question I couldn’t find a clear answer to. I’m pretty inexperienced with electrical stuff—definitely not an engineer or electrician—so apologies if this is a rookie question or totally off-base.

I understand one of the biggest concerns with electric A/C in our vintage VWs is amp draw on the 12V system. It can stress the alternator and battery, generate heat, and require thicker wires and bigger fuses. Especially with the stock “Smallternator” (55–60 amps), that seems like a real limitation.

So here’s my thought experiment:

Let’s say a 12V electric A/C unit is rated at 600 watts, which would draw about 50 amps. Wouldn’t a 24V unit rated at the same 600 watts only draw 25 amps?

If that’s correct, it seems like I might have two possible setups using a second battery:

Option 1: 24V Setup

Passenger side: Original 12V battery

Driver’s side: Second 12V battery

Connection: Wired in series to create 24V

Isolator between systems

Fuse block added for protection

Thought: This keeps the OG 12V system untouched, and powers the A/C with lower amp draw on a dedicated 24V circuit.

Option 2: 12V Setup with Dual Batteries

Passenger side: Original 12V battery

Driver’s side: Second 12V battery

Connection: Wired in parallel to stay at 12V but increase capacity

Isolator between batteries

Fuse block added for protection

Thought: This setup keeps everything at 12V but helps prevent battery drain when running the A/C.

Does either of these sound doable? Am I missing something obvious? I’m not trying to reinvent anything—just trying to understand what’s possible before I start buying parts or frying wires.

Appreciate any thoughts, corrections, or suggestions!

Thu Oct 30, 2025 2:12 pm

Check John Jareson post for Jill's Ghia. He just finished it

Thu Oct 30, 2025 2:17 pm

eyetzr wrote: Check John Jareson post for Jill's Ghia. He just finished it

thank you! That was one of the posts I read and got me thinking of other options. For example, if I didn't want to go bigger than the "smallternator" or do any mods (grinding/cutting) to mount it up.

Thu Oct 30, 2025 2:49 pm

Just thinking out loud... but I think

Option 2 will have the alternator running hot. I suspect that a 600watt electric A/C system will likely be running 100% of the time and not cycling much. If this is the case, then the constant output from the batteries will induce a constant load on the alternator to maintain charge - likely close to the rate that the power is leaving the batteries - leading to high heat. This setup would be better for shorter interval peak loads. Really depends on if the AC is cycling or not.

Option 1 would lower the heat in the alternator for sure, but will require more wiring. Also, I googled 24V alternators and it seems many are 12V style with a different voltage regulator. The risk being that if the regulator fails you will have problems downstream with overcurrent (melting wires).

I believe a typical automotive AC system puts out about 10,000-20,000 btu... which is way more than these 600watt 12V AC systems. So 100% duty cycle seems likely if trying to cool on a hot summer day.