That's right, absolutely NAC. Electrical question

Cody Forbes cody at 5000tq.com
Thu May 30 20:54:58 PDT 2013


The line about "24v is 24v" is slightly misleading. 

Two automotive batteries at full charge in series do not add up to 24v. A healthy automotive (and marine, etc) battery is 12.7v. In series you'd be supplying 25.4v which, depending on how sensitive the circuitry is, *could* be enough to let the smoke out. If he accidentally left it plugged in with the engine running the charging system would bring it up over 26-28v. 

The device the customer needs may be relying on a nice clean 24v. Due to other loads on the system, charging system variations, and other variables that "24v" wouldn't be perfect and could potentially cause damage to any sensitive electronics. Diode ripple in the alternator can produce large, very brief (milliseconds), voltage spikes of both DC and AC current. It would still be wise to have a power supply device between the batteries and the load. It wouldn't need to be much more than a very simple voltage regulator. Electronics in the car don't have issues because they have built in power conditioning circuits. A device which has been designed with an external power supply is designed for a very good supply coming in and may not have much, or any, good power conditioning circuitry internal to the main device.

There's another caveat. If he's using it with the engine off (which was specified to me the case) this is obviously going to discharge the batteries by some amount. The voltage will drop as the batteries are depleted. It wouldn't take long before the output is less than 24v in which case a simple regulator can't step it back up to 24v. Again it depends on the requirements of the device; it may work fine at 20v, or it may quit at 23v. Plus you'd likely need a third battery in the morning to have enough juice to fire up the engine.


I've thought lots about solar powering things in a VW camper. My fiancé, my son, and myself lived in my Westfalia for about a year and a half. We also traveled to races in it for a couple years before, during, and after living in it until its demise when a HUGE tree fell and squished it flat. The long and short of it is that to be useful you'd spend a lot of money and add a lot of weight. I added a second battery and a couple small solar panels which made it good enough to run LED interior lighting at night as well as the water pump and the radio over a race weekend. To run much more than that shore power is still the most practical way by far. 

-Cody Forbes (mobile)

On May 30, 2013, at 10:07 PM, "Britt Crowell" <britt at BrittCrowell.com> wrote:

> I agree with Tony, get rid of the 12-110-24, and just use two 12v batts
> in series, deep cycle preferably. Shouldn't any big deal to put in a
> charging system from the regular alt to charge 3 batt when driving.
> And/or a system to charge them when hooked to 120V hookups. 2 trickle
> chargers on the 120 system when at a campsite or charging going down the
> road. Little wiring and a switch or 2. 24V is 24V as long as the batt
> can push the Amps. No reason to convert to AC then back to DC when the
> numbers work out easy. 
> VW Buses are part of the family! I want to put my spare 4.2L 32v V8 in
> one :-)
> Some good Bus pics here, I married the cute one.
> http://www.alisoncrowell.com/brittcrowell.com/2003/2003-09-05_Lake_McCon
> aughy/
> 
> Britt
> -----------------------------------
> Or add a second battery, wired in series to the stock one for the
> purpose you need and pull from the two of them for 24V, and plenty of
> amperage so it won't go dead in short demand. This is exactly how older
> Cummins were wired, 24V starter and alt, 12V everything else.
> 
> HTH,
> Tony
> **********************
> _______________________________________________
> quattro mailing list
> http://www.audifans.com/mailman/listinfo/quattro
> http://www.audifans.com/kb/List_information


More information about the quattro mailing list