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Date:         Wed, 21 Feb 2007 20:19:10 -0800
Reply-To:     Mark Drillock <mdrillock@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mark Drillock <mdrillock@COX.NET>
Subject:      Re: was fav 12 V acc, now 2nd battery relay system - files posted
Comments: To: Sam Walters <sam.cooks@VERIZON.NET>
In-Reply-To:  <45DC8FAF.4090001@verizon.net>
Content-Type: text/plain; charset=us-ascii; format=flowed

I wouldn't change back your relay wiring just yet. The great old posts you referenced have a glaring omission in their discussions. The typical weakness of the small relay/small wire method of 2nd battery connection is not fully explained in them. There is a good reason that devices like the 1315 exist.

The fact that some people find the charging rate supplied by the small system adequate in no way means every one will. The amount of alternator current that flows to the aux battery terminal often needs to be greater than what the battery itself needs even for slow charging. People who have things connected to the aux battery often need to run those things while the vehicle is running as well as stopped. That current, for things like stereos, 12 volt fridge operation, devices running on the cig lighter socket, inverters and their loads, etc. must also come across that one small wire at the same time the charging current does or the aux battery will drain rather than charge. Running these things may in theory still leave some current left for charging the aux battery but in practice the voltage may have dropped low enough to prevent much charging from taking place at the aux battery.

A volt meter measurement at the aux battery with the engine running and all loads switched on is a good place to start. Compare that measurement with what you see at the main battery when you move the meter leads over without changing anything else.

The low cost battery relay kits I have seen from various vendors are only about half the capacity of the stock dual battery charging systems VW fitted on many 85-91 vanagon models. This makes some sense for the pre-waterboxer VW vans with their 55 amp alternators of yesteryear but waterboxers 90 amp alternators can support a more robust system, as VW fitted. VW used metric wire of slightly greater capacity than #10 awg and a 40 amp relay connected such that the second battery never supplies any starting current. No fuse was used.

Even the VW relay system is too small for some of us. If you need to recharge a deeply discharged aux battery in a hurry you may need a higher capacity relay system and may find the 1315 a very useful device. Most people don't, assuming they or the installer understood the limitations and wired things up taking real loads into account, not just the simple charging of the batteries.

Mark

Sam Walters wrote: > Michael, > > I agree - the basic relay system works just fine. While the Sure power > 1315 is a nice device, it is unnecessary as an alternative to a properly > setup relay system. > > Frank Condelli was right when he said that this issue had been discussed > many times before, but, based on what I have read, not in his > conclusions about the inadequacy and substantial inferiority of the > relay system. It is a perfectly adequate system to handle the auxiliary > battery for a Vanagon. VW used it for the job. > > This supposed inferiorities and inadequacies of the relay system have > been debunked long ago on the list past by engineering types who wrote > lengthy technical essays explaining why the relay system sold by Bus > Depot or its equivalent would work just fine and, in fact is better than > many of the supposedly superior solutions other people advocate. They > explained why all sorts of imagined problems that purportedly could > occur with a relay system just wouldn't happen. I have just posted two > of these explanation to the files section of the Vanagon@yahoogroups > list page. I set up a folder under my last name and under it a > subfolder for 2nd battery installation information. > > They are two files are composted of posts that I found in the list > archives and saved. These files primarily have information from Beckett > Cantrell and Frank Grunthaner. > > In fact, after re-reading these files, I am going to rewire my Syncro's > second battery system going back to the charging wire and fuse capacity > that came with the Bus Depot kit in the first place, removing the larger > wire and heavier fuse that I installed based on other information. > Should have read what I had stored on my computer more carefully. > > I will be creating other subfolders and uploading other information to > the Vanagon@yahoogroups page soon. > > Sam > > -- > Sam Walters > > Baltimore, MD >


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