Date: Mon, 23 Aug 2004 11:09:27 -0400
Reply-To: dhaynes@OPTONLINE.NET
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: [Syncro] dual battery isolator
Content-type: text/plain; charset=us-ascii
Although many folks have had success with conventional isolators, they are overall a bad idea. Yes they can be more reliable than relays since they avoid dirty or welded contacts, but they are inefficient. For starters, after they get warm the actual voltage drop is closer to 1.1 volt. At 90 amps, the isolater is dissapating almost 100 watts. This is why they need heat sinks. You are paying for this power. Now, with this voltage drop, you are getting less than 13 volts to the batteries and accessories. Ok, so now you can modify the regulator to increase the voltage or use a remote sense wire to compensate. At full load the limiting factor of an alternators capacity is its own resistance. Thus at full load, it is only slightly more than 50% efficient. Yes, 1/2 the power produced is given off as heat in the alternator itself. That is why they have a big fan and they still get hot. So, we increase the voltage of the alternator by 1.1 volt so at 90 amps the alternator dissipates an additi
onal 100 watts of heat. Can we say shorter life? So at full load, we are wasting ~200 watts of power due to the use of the isolator. Under ideal conditions, 1 HP = 746 watts. Not that you will notice but we are wasting .26 HP here. The big issue here is the load on the alternator.
Dennis
----- Original Message -----
From: randy charrette <randy_charrette@yahoo.com>
Date: Monday, August 23, 2004 8:25 am
Subject: RE: [Syncro] dual battery isolator
> I'm no electronics expert, so I found a web site (www.vgonman.com)
> and copied his set-up. It has worked great for about 3 years now.
> This is set-up with a isolater.
> Randy
> 87'Syncro TIICO
>
> David Marshall <VANAGON@VOLKSWAGEN.ORG> wrote:
>
> I can't see an issue with a 70A relay load wise as your alternator
> is 90A
> and only on a good day. I use a generic Bosch 40A relay for my 2nd
> batteryin my TriStar and I have never had an issue and I have a
> 120A alternator.
> Charging battery from a dead flat doesn't make the relay nor the
> 2x12ga wire
> running to the battery hot or even warm to the touch. I think the
> relay is
> the simplest and probably the most effective of designs. The diode
> isolators are not good in my opinion as they introduce a 0.7V loss
> in the
> system over both batteries. The computerized isolators that give the
> starting battery and deep cycle the voltage they want to see is
> the best
> bet, but expensive and really I think the deep cycle will charge
> fine on the
> relay with an alternator designed to charge a starting battery.
> 1000s of
> fishermen driving home charging their deep cycles on their F150
> can't be
> that wrong.
>
> David Marshall
>
> Fast Forward Automotive Inc.
> 4356 Quesnel-Hixon Road
> Quesnel BC Canada V2J 6Z3
>
> http://www.fastforward.ca sales@fastforward.ca
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> -----Original Message-----
> From: Westyman [syncrowestytd@mindspring.com]
> Sent: August 22, 2004 10:15 PM
> To: Vanagon list; VWVANFULLTIMERS; Syncro list
> Subject: [Syncro] dual battery isolator
>
>
> Hope this doesn't start a whole new argument on the subject, but I
> seekinput from those who may have done this:
>
> I'm installing a group 29 deep cycle battery as my main camping
> battery in
> my Westy [no, it won't fit under the front seats!] to power my new
> 12-volt
> Norcold DC-0040 fridge. Yes, I finally had enough of dealing with the
> unreliability of the old Dometic! What I'm concerned about is the
> differentcharge rate required between the deep cycle and the main
> battery. The main
> will likely never be drained below 75-percent, but the deep cycle
> may become
> very drained, and often. I currently have a 70-amp relay connected
> as in the
> stock Westfalia method for dual batteries. Will that work 'OK', or
> do I need
> to use some other method or isolator? It seems to me that the
> alternatorwould not charge two batteries of different types and
> levels of drainage
> efficiently. Comments? Thanks.
>
> Karl Mullendore
>
>
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