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Generator + audio system questions
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gilg
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PostPosted: Mon May 10, 2021 8:06 am    Post subject: Generator + audio system questions Reply with quote

Hi guys,

I'm resurrecting a 1972 Super Beetle. It still runs a generator, but I've installed a brand new Wolfsburg West harness and upgraded the fuses to a blade-style block.

I'm now trying to design a decent audio system for it. I'm thinking about a 1200w Blaupunkt 4 channel amp along with a 4-speaker setup and two small subwoofers. I am retaining the old style head unit, and want to conceal most everything else either under the hood or behind the rear seat.

My question: how much power can this generator and harness really support, and what do I need to do to mitigate future problems?

Secondary battery, capacitors, deep cycle battery?
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mukluk
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PostPosted: Mon May 10, 2021 9:52 am    Post subject: Re: Generator + audio system questions Reply with quote

P=IV
Power (in watts) equals Current (in amps) times Voltage.

So we have a stock VW generator which is rated 30A/14V, giving us a maximum possible output of 420 watts. Safe to say this isn't going to support running the car, lights, charge the battery, and come anywhere near to supporting the max output of the stereo you're envisioning. Wink
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gilg
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PostPosted: Mon May 10, 2021 11:18 am    Post subject: Re: Generator + audio system questions Reply with quote

Sure, that makes sense - totally wouldn't be running the amp at max watts. However, I'm wondering how much extra wattage a generator has to work with.

I found threads like this which indicate people are running 100-250w systems on a 30a generator without a problem: https://www.thesamba.com/vw/forum/archive/index.php/o-t--t-165714--.html

How many watts does the car itself draw? If I can work with a few hundred extra watts, I think I could have a 1.0-2.0 farad stiffening capacitor and be safe, however that's the big question for me.
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AirHead1966
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PostPosted: Mon May 10, 2021 1:09 pm    Post subject: Re: Generator + audio system questions Reply with quote

gilg wrote:

How many watts does the car itself draw? If I can work with a few hundred extra watts, I think I could have a 1.0-2.0 farad stiffening capacitor and be safe, however that's the big question for me.


Well, that depends on what you are running. The coil and distributer, plus choke, etc. (all engine compartment stuff) will not draw more than 10 amps, probably 8. The lights etc. will have some draw, you can calculate that by looking at the wattage on your bulbs. Add wipers, 7 amps ball park as it is on an 8 amp fuse.


For estimation, I would say you could draw up to 20 amps with lights on and wipers going, to run the car. Ballpark additional 5 amps would go to keeping the battery charged. That leaves you with about 5 amps to play with on a 30 amp generator. Also note that the generator will not be producing full 30 amps all the time the car is running.

This is all theoretical ballpark estimation. I would go with a bigger alternator.
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EVfun
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PostPosted: Mon May 10, 2021 3:37 pm    Post subject: Re: Generator + audio system questions Reply with quote

I ran a Sony 250 watt 3 channel amp on a '65 Dodge Dart with a stock 36 amp alternator. If I cranked it up I could watch the dash lighting flicker and the amp meter dance to the drums.

I would figure on 20 amps for the car, plus the amps. I would take their stated wattage and divide by 12 to get peak amps then divide by 2 to estimate the addition current you should have available from the alternator or generator.

If it's really a 1200 watt amp go for a 70 amp alternator. Another option is class D (digital) amps, you get more volume for less power because they are more efficient. It might be possible to faintly hear artifacts, but since most of us are playing compressed digital music I bet not.
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jeffrey8164 Premium Member
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PostPosted: Sun May 16, 2021 7:41 am    Post subject: Re: Generator + audio system questions Reply with quote

I don’t have any digital images because it was so long ago but back in the day I have a generator to power the car and I use an AC bracket with a cut up generator stand bolted to it to run an alternator to the power battery for the stereo. Worked well enough except at idle.
In my current version I’m running about 1150 watts with two amps. I have a 90 amp alternator. You don’t need a deep cycle battery that’s for when you want to run it dead and still be able to charge it reliably. You will want a capacitor so your lights don’t dim to the beat.

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