Date:         Mon, 7 Aug 2017 19:29:30 -0700
Reply-To:     Neil N <musomuso@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Neil N <musomuso@GMAIL.COM>
Subject:      Re: Fuse Size: Aux battery to fuse block
Comments: To: Dennis Haynes <d23haynes57@hotmail.com>
In-Reply-To:  <CY4PR20MB13031DDA51455D462072915BA08A0@CY4PR20MB1303.namprd20.prod.outlook.com>
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Steve: No. No motor or anything like that. Thanks.

Thanks Dennis. Ok, I see what I did wrong. Wire charts I looked at
were for 12 Volts (vs 13.8 or 14). The marine application wire size
calculator I saw could be set to a 10% voltage drop for "non critical"
loads so on the wire size calculator I actually used, (here):

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

I figured 5% was ok. And this was in spite of it having a default 2%
setting. Of course as you point out, at 2%, the minimum wire size is
10 AWG. (and that's for a 6.91' wire) Regarding fusing the #12 fuse
block supply wire with a 40 Amp fuse, I was focused on "fusing the
wire" against a dead short based upon (my incorrect) Amp capacity.

Loads on fuse block: two 55 Watt Fog lights, CB, Stereo + amp, 1 LED
festoon, USB outlets. As mentioned, I'll measure these loads but had
used the manufacturer supplied fuses or specs for each load (15, 2,
15, ? 4.x) to calculate the potential total current.

And, I now see more clearly why VW did what they did regarding unfused
or fused wires.

Back to the drawing board!

Neil.



On 8/7/17, Dennis Haynes <d23haynes57@hotmail.com> wrote:

> This is not the best approach. Overkill for a fuse between the battery and
> fuse distribution block and then undersize wiring for variable loads, some
> that may be continuous.
> While a 5% voltage drop does not sound like much for intermittent loads that
> may be OK. For continuous loads not. Let do the match another way. 5% of 14
> volts is 0.7 volts. 0.7 volts at 50 amps = 35 watts. Do you really want to
> lose 35 watts across a piece of wire? Then there will be the rail voltage
> drop, each of the connections. I love pulling out headlight relays with the
> connector plugs melted.
>
> There is a lot of wiring in the vanagon that is not fused. Most of the fused
> circuits are protecting the wiring from device or appliance failure, and
> there is a level of coordination. There is not protection from the battery
> to harness or from the alternator. Using the correct wire size and
> insulation, you can go from battery to fuse block. If your anticipated max
> load is 40 amps you want a number 8 or minimum 10 here. For each of your
> branch circuits none should be wire sized or fused for less than 80% rated
> load. Things like motors and lights and battery chargers are continuous
> loads that will cause wire heating.  Consider that while using a house
> battery available voltage will often be well below 12 volts. You want as
> little drop as possible. 20 amp 12 gauge. 30 amp 10. 14 gauge for 15 and
> lower just to maintain mechanical strength. Use a good grade of automotive
> or marine primary wire and name brand terminals.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> Neil N
> Sent: Monday, August 7, 2017 7:35 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Fuse Size: Aux battery to fuse block
>
> Hi all.
>
> I've connected my group 41 aux. battery to an ATO type fuse block with a
> fused 7.5' of #12 AWG wire. I anticipate maximum load at fuse block will be
> 40 Amps.
>
> At 13.8 VDC, even at a 5% voltage drop, online calculators suggest that the
> #12 wire is sufficient to handle up to 50 Amps.
>
> Would it be ok to use a 50 Amp fuse on the wire from battery to fuse block?
>
> A 40 Amp fuse be sufficient, even with all loads on. I will measure current
> draw of each load.
>
> Also, FWIW, an orange murret type wire connector threads nicely onto the B+
> stud on this type of fuse block. Image link:
> http://www.techspan.ca/images/pageheaders/fusepanel.jpg
>
> Even though the fuse block is installed in front of the glove box, I wanted
> to reduce the risk of that stud inadvertently connecting to ground.
>
>
>
> Thanks
>
> Neil.
>
> --
> Neil n
>
> Blog: Vanagons, Westfalia, general <http://tubaneil.blogspot.ca>
>
> 1988 Westy Images <https://picasaweb.google.com/musomuso/New1988Westy>
>
> 1981 Westfalia "Jaco" Images, technical <http://tubaneil.googlepages.com/>
>
> Vanagon-Bus VAG Gas Engine Swap Group <http://tinyurl.com/khalbay>
>


--
Neil n

Blog: Vanagons, Westfalia, general <http://tubaneil.blogspot.ca>

1988 Westy Images <https://picasaweb.google.com/musomuso/New1988Westy>

1981 Westfalia "Jaco" Images, technical <http://tubaneil.googlepages.com/>

Vanagon-Bus VAG Gas Engine Swap Group <http://tinyurl.com/khalbay>