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Date:         Thu, 26 Feb 2004 18:42:18 -0800
Reply-To:     mark drillock <drillock@EARTHLINK.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         mark drillock <drillock@EARTHLINK.NET>
Subject:      Re: 2nd battery ??
Comments: To: RAlanen@AOL.COM
Content-Type: text/plain; charset=us-ascii

Frank, the fridge relay power circuit you have is not up to the task of fully charging your second battery, especially while the fridge is also running on 12 volts. There are a couple of ways to go. Here is a simple one. You can run a separate heavier wire straight from the main battery, down under the van and over to the other battery box. Use another relay, controlled by the output lead of the fridge relay. Use a 30 amp fuse at the main battery connection, #10 wire, and a 30 amp relay in the second battery box. By using the fridge relay output to control the second relay you do not add any additional load to the alternator charge indicator circuit and you also insure that the second battery will never be drawn on during starting. This is critical.

If you want faster charging and the capability to use both batteries during starting you will need much heavier wiring and a much heavier relay and fuse. That is how I do it. Here are some links to the relay I use.

Stancor Model 120-901 , from Allied, $15 plus shipping,

It is rated at 100 amp continuous, 400 amp inrush, compact and easy to mount, not FLAPS crap but industrial grade with silver contacts. http://www.alliedelec.com/cart/partlookup.asp?ST=AS&PartNumber=5763007

This next catalog link shows pictures of both the 120 series relays I prefer along with the common 70 series sold by FLAPS and gives the specs for them. Similar ratings but different layouts. The FLAPS one is easy to get, rated for slightly more extreme cold if that matters to you. I'm in SoCal so -20F for my preferred 120-901 model is fine but I suppose some may need the -40F rating of the 70 series.

http://www.alliedelec.com/catalog/pf.asp?FN=773.pdf

That commonly repeated BS about a discharged aux battery instantly draining the main battery must be stopped!

Mark

Frank Condelli wrote: > .... > Mark, this is intriguing. I have the Optima yellow top as second battery > using the fridge relay and 12 gauge wire between the main battery and the relay > to the Optima. The battery never does seem to get charged properly and > looses voltage quickly while sitting for a few days with only the radio's back > lights and LCD clock running. I've been wondering about this situation for a > while now and your suggestion seems like the most plauible reason and way to > solve this problem. What route have you found to be the best to pass the 02 > or 03 battery cable from the main battery to the aux battery ? Under the van > or in the van under the carpet ? Are you using a starter solonoid for the > main relay ? Do you not find that when the aux battery is completely drained > that the main battery will dump half its load to the aux battery immediately > upon starting the vehicle, or will the alternator charge rate be able to keep > this from being a problem ? This is the main reason I chose to use the 12 > gauge wire fom the main battery to the aux battery relay. > Cheers, >


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